POLLINATION ECOLOGY OF HAWAIIAN COASTAL PLANTS

A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE

UNIVERSITY OF HAWAI‘I AT MĀNOA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

IN

BOTANY

(ECOLOGY, EVOLUTION AND CONSERVATION BIOLOGY)

AUGUST 2014

By

Kimberly R. Shay

Thesis Committee:

Donald R. Drake, Chairperson

Kasey E. Barton

Andrew D. Taylor

Keywords: pollination network, coastal pollinators, coastal plants, Jacquemontia sandwicensis,

Hylaeus

ii

ACKNOWLEDGEMENTS

I would like to thank and acknowledge the following people for all of their help and

support throughout this research and my thesis. In particular, I would like to thank my advisor

Don Drake for truly being a great mentor. I am tremendously grateful to my committee

members, Kasey Barton and Andy Taylor, Heather Sahli for sharing this research with me, the

Botany Department faculty and staff, my family and friends for their continued support, and

especially my husband, Chris.

Chapter 1: I would like to thank Patrick Aldrich, Melody Euaparadorn, Michelle Elmore, Doug

Powless, Jennifer Imamura, Paul Krushelnycky, Stephanie Joe, Will Haines, Jennifer Bufford,

Jesse Eiben, Tad Fukami, and Christian Torres-Santana for collecting the data, Luc Leblanc for

identifying and managing all of the collected insects, and the State of Hawaiʽi Department of

Land and Natural Resources Division of Forestry and Wildlife and Charmian Dang for

overseeing the permits to complete this work.

Chapter 2: I would like to thank Kobey Togikawa for all of his hard work, Amelia Harvey for

assisting with observations, Christopher Shay, Joshua Boothby, and Hiroshi Park for collecting

cuttings, Sheldon Plentovich, Paul Krushelnycky, and Karl Magnacca for identifying insects, and

State of Hawaiʽi Department of Land and Natural Resources Division of Forestry and Wildlife

and Cynthia King for overseeing the permits to collect the insects. Funding was generously

provided by the Hawai‘i Audubon Society, the Charles H. Lamoureux Fellowship from the

Botany Department, and the Torrey-Degener-Rock Scholarship from the Botany Department.

iii

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ................................................................................................ ii

LIST OF TABLES ...............................................................................................................v

LIST OF FIGURES ........................................................................................................... vi

CHAPTER 1. ALIEN INSECTS DOMINATE THE PLANT-POLLINATOR NETWORK OF A

HAWAIIAN COASTAL ECOSYSTEM ............................................................................1

Abstract ....................................................................................................................1

Introduction ..............................................................................................................1

Methods....................................................................................................................4

Results ....................................................................................................................11

Discussion ..............................................................................................................22

Conclusion .............................................................................................................29

CHAPTER 2. CHAPTER II. THE POLLINATION BIOLOGY OF Jacquemontia sandwicensis

(CONVOLVULACEAE) ...................................................................................................31

Abstract ..................................................................................................................31

Introduction ............................................................................................................31

Methods..................................................................................................................34

Results ....................................................................................................................41

Discussion ..............................................................................................................47

Conclusion .............................................................................................................53

iv

APPENDIX A. NETWORK AND GROUP INDICES OF KAʽENA POINT ..................55

APPENDIX B. 2009 QUANTITATIVE MATRIX OF KAʽENA POINT .......................59

LITERATURE CITED ......................................................................................................60

v

LIST OF TABLES

Table 1.1. Plant species in the networks at Ka‘ena Point, O‘ahu, Hawai‘i .........................7

Table 1.2. Pollinator taxa in the networks at Ka‘ena Point, O‘ahu, Hawai‘i .......................9

Table 1.3. Network Metrics of the binary and quantitative networks of Ka‘ena Point, O‘ahu,

Hawai‘i ...............................................................................................................................14

Table 1.4. Network Indices for the binary and quantitative datasets of Ka‘ena Point, O‘ahu,

Hawai‘i ...............................................................................................................................15

Table 1.5. Insect orders represented in networks of Ka‘ena Point, O‘ahu, Hawai‘i .........17

Table 1.6. Plant species’ proportions of visits from Hylaeus spp. from the quantitative network of

Ka‘ena Point, O‘ahu, Hawai‘i ............................................................................................19

Table 2.1. Floral morphology of Jacquemontia sandwicensis ..........................................36

Table 2.2. Treatments in the breeding experiment of Jacquemontia sandwicensis ...........39

Table 2.3. Pollinators at field sites and their proportions of visits to Jacquemontia sandwicensis

............................................................................................................................................46

Table 2.4. Summary of flowering species at sites .............................................................48

vi

LIST OF FIGURES

Figure 1.1. Ka‘ena Point, O‘ahu, Hawai‘i ..........................................................................5

Figure 1.2. 2008-2009 Binary plant-pollinator network of Ka‘ena Point, O‘ahu, Hawai‘i ...

............................................................................................................................................12

Figure 1.3. 2009 Quantitative plant-pollinator network of Ka‘ena Point, O‘ahu, Hawai‘i ...

............................................................................................................................................13

Figure 1.4. The distribution of visits of generalized pollinators to plant species from the

quantitative network of Ka‘ena Point, O‘ahu, Hawai‘i .....................................................20

Figure 1.5. The proportion of visits by pollinator taxa out of the total visits in the quantitative

network of Ka‘ena Point, O‘ahu, Hawai‘i .........................................................................21

Figure 1.6. The proportion of visits by plant species out of the total visits of the quantitative

network of Ka‘ena Point, O‘ahu, Hawai‘i .........................................................................23

Figure 1.7. Categories of plant species or pollinator taxa d’ values from the quantitative network

of Ka‘ena Point, O‘ahu, Hawai‘i .......................................................................................24

Figure 2.1. Map of Study sites ...........................................................................................35

Figure 2.2. Flower of Jacquemontia sandwicensis ...........................................................37

Figure 2.3. Lab breeding experiment .................................................................................43

Figure 2.4. Field breeding experiment ...............................................................................44

Figure 2.5. Control treatment (no manipulation, open to natural pollinators) at 3 sites and results

............................................................................................................................................45

1

CHAPTER 1. ALIEN INSECTS DOMINATE THE PLANT-POLLINATOR NETWORK OF A

HAWAIIAN COASTAL ECOSYSTEM

ABSTRACT

Little is known regarding pollination webs involving island coastal plants and pollinators,

and the roles that non-native flower visitors may play in these interaction networks. Plant-

pollinator observations collected in March 2008 and 2009 were used to describe the pollination

network for Kaʽena Point, one of Hawaii’s best-conserved coastal communities. The network

includes 15 native plant species, 2 native insect species, and 27 non-native insect taxa, forming

119 interactions. Network connectance is 29.4% and weighted nestedness is 18.3, which is

similar to other dry habitat, island networks. The network’s structure has a compartment of

generalized pollinators followed by more specialized pollinators. Nearly all plant species interact

with two or more generalist pollinators and a variable number of specialists. Small, non-native

bees (Lassioglossum, Ceratina), wasps (Proconura), and flies (Tachinidae) were responsible for

71.6% of the flower visits and visit five plant species not visited by native bees. The two native

visitors, Hylaeus anthracinus and H. longiceps, (both proposed as threatened/endangered) belong

to a radiation of > 60 endemic species in Hawaii’s only genus of native bees. Hylaeus spp.

(especially females) provided 20.6% of the flower visits, foraging on many species and at high

frequencies, including the endangered Scaevola coriacea and Sesbania tomentosa. In Hawaii’s

coastal habitat, non-native insects form novel interactions with native species, and can maintain

an ecosystem’s function after losing most of the original native species. However, the two

remaining native Hylaeus species are still important pollinators to many native plants on which

they rely for nectar and pollen resources.

INTRODUCTION

Species interaction networks have been referred to as “the architecture of biodiversity”

because of their importance for community composition and dynamics (Jordano et al 2006,

Bascompte and Jordano 2007). Network analyses are increasingly being used to understand how

communities are changing as a result of species invasions or extinctions (Memmott et al 2004,

2

Bjerknes et al 2007, Kaiser-Bunbury et al 2010a). Plant-pollinator networks are especially

important, because 87.5% of the world’s flowering plant species are pollinated by animals,

particularly insects (Ollerton 2011), and networks are a way to assess a community’s pollination

activity, importance for community composition, and dynamics. A pollination network can be

represented either as a matrix or as a two-mode data set with species as nodes and the

interactions between species as links (Jordano 1987, Jordano et al 2006). Networks may be

described qualitatively, depicting simply the presence or absence of interactions, or

quantitatively, based on the frequency of visits within an interaction. The interactions and visits

can be used to calculate network indices that are then used to interpret patterns and processes in

the community (Dormann et al 2009). For example, networks can be analyzed to identify

keystone species (Christianou and Ebenman 2005), monitor biodiversity (Forup et al 2008), and

determine the functional roles of non-native species (Kaiser-Bunbury et al 2010b, Tylianakis et

al 2010).

Plant-pollinator networks on islands are of interest for a variety of reasons. Owing to

their isolation, island biotas are often naturally disharmonic and relatively species-poor

(MacArthur and Wilson 1967, Whittaker and Fernandez-Palacios 2007). As a result, their plant-

pollinator networks commonly have generalized mutualisms (most species interact with many

mutualists; Olesen 2002, Dupont 2003) and taxonomic disharmony in the pollinators (Kaiser-

Bunbury et al 2010b). This often translates into small network sizes, high connectance (= a high

proportion of potential plant-pollinator interactions being realized), and a super-generalist

species which dominates interactions (Olesen 2002, Dupont et al 2003, Trojelsgaard and Olesen

2012). Additionally, many island systems involve native species that have become rare (or gone

extinct), and one or more non-native species dominating interactions or visits (Dupont et al 2003,

Kaiser-Bunbury et al 2010b, Traveset et al 2013). Non-native species typically enter a network

by interacting with generalized native species. This has been documented with non-native plant

invasions (Bjerkens et al 2007, Bartomeus et al 2008, Traveset and Richardson 2006) and the

honey bee, Apis mellifera (Dupont et al 2003, Kaiser-Bunbury 2011). Once in the network, non-

native species have a large impact by interacting with many partners (Bartomeus et al 2008,

3

Padron et al 2009) and affecting other species’ interactions (Aizen et al 2008, Kaiser-Bunbury et

al 2011, Traveset et al 2013).

In Hawai‘i, few studies have assessed relationships between plants and their insect

pollinators (Howarth 1985, Medeiros et al 2013). Hawai‘i’s native insect fauna is disharmonic

because many of the taxa of pollinators common in other ecosystems are underrepresented or

absent here. For example, social insects (Wilson 1990) and butterflies (Hawai‘i has only 2

endemic butterflies; Zimmerman 1958). Hawai‘i’s only bees are a radiation of >60 species of

Hylaeus, (Colletidae, yellow-faced bees) (Magnacca 2007). They have been found visiting

flowers of native plants throughout Hawai‘i (Magnacca 2007, Wilson et al 2010, Koch and Sahli

2013, Krushelnycky 2014). Unfortunately, lowland native insect communities have been

devastated by a variety of factors, including interactions with non-native insects (Howarth 1985,

Cole et al 1992), novel predators (i.e. Kraus et al 2012), and habitat loss (Asquith and Messing

1993). As a result of these disruptions, many insect pollinators, including many Hylaeus spp.,

are rare or extinct (Howarth 1985, Cox 2000, Magnacca and King 2013).

Little is known about the coastal strand ecosystem of Hawaiʽi beyond general

descriptions of vegetation and the physical environment (Richmond and Mueller-Dombois 1972,

Gagne and Cuddihy 1990, Warshauer et al 2009), and the observation that these ecosystems have

been severely impacted by development, recreation, and non-native species (Richmond and

Mueller-Dombois 1972, Cuddihy and Stone 1990, Warshauer et al 2009). Three coastal plant

species require a pollinator for outcrossing or for transfer of self-pollen to the stigma for seed set

(Hopper 2002, Yorkston and Daehler 2006, Shay Chapter 2). Observations of flower-visitors of

five other coastal plant species have recorded 2 native and at least 19 non-native insect taxa,

mostly bees, ranging from likely pollinators to nectar thieves (Hopper 2002, Elmore 2008,

Pleasants and Wendel 2010, Shay Chapter 2). These studies’ authors frequently postulate the

importance of native Hylaeus species as likely pollinators and in some cases, dominant visitors.

Threats such as habitat loss, fragmentation, and non-native species disrupt plant-

pollinator interactions on islands around the world (Traveset and Richardson 2006, Kiers et al

4

2010, Potts et al 2010). The startling numbers of non-native insects (>2500 species) and plants

(>900 species) established in Hawai‘i (Pimental et al 2005) and recent observations of non-

native flower visitors on native coastal plants (cited above), suggest that native plant-pollinator

interactions there may be affected by non-native species (Traveset and Richardson 2006, Kaiser-

Bunbury et al 2010b). The alteration or loss of plant-pollinator interactions may impact the

fitness of the corresponding partner (Kiers et al 2010, Potts et al 2010, Colwell 2012). Based on

the lack of information on native plant-pollinator interactions, the presence of endangered and

rare native species in the coastal community, and the high numbers of invasive species there,

coastal pollination webs warrant further investigation.

The objectives of this research are to 1) describe a plant-pollinator network qualitatively

and quantitatively, in a native community of coastal plants, and 2) determine the relative

diversity and potential importance of native and alien insects in the network. I predict that 1) the

network will include both native and non-native pollinators, and 2) non-native pollinators will

interact with many partners and contribute a large proportion of visits. I expect our network to

have similar parameters and results to other small networks of islands, which typically have

fewer species with higher proportion of partners compared to continental networks (Trojelsgaard

et al 2013).

METHODS

Study site - The study was carried out in late March of 2008 and 2009 at Ka‘ena Point Natural

Area Reserve on the northwest coast of O‘ahu (Figure 1). Ka‘ena Point has a low annual rainfall

of approximately 650 mm / year, concentrated mainly in the winter with drought in the summer

(Richmond and Mueller-Dombois 1972, Gagne and Cuddihy 1990, Giambelluca et al 2013), and

mean annual temperature 22.2°C to 25.5°C (Richmond and Mueller-Dombois 1972, Giambelluca

et al 2014). This site area also experiences solar radiation, constant and strong winds, and effects

of salt spray (Richmond and Mueller-Dombois, 1972, Gagne and Cuddihy 1990, Giambelluca et

al 2014). The study area contains protected native coastal strand and dune vegetation dominated

by shrubs and low growing plants.

5

Figure 1. Ka‘ena Point, O‘ahu, Hawai‘i. (A) Approximate transect through coastal habitat at Ka‘ena Point (red dashed line). (B) Example of dune vegetation, including Sesbania tomentosa

and Scaevola taccada. (C) Example of coastal strand vegetation. (D) Map of O‘ahu, Hawai‘i

with Ka‘ena Point marked in the northwest point of the island (yellow arrow).

A

B C D

6

Observations – Observations were collected previous to this thesis in 2008 and 2009. Ten

observation points were placed 20-50 m in from the shoreline, at approximately 100 m intervals

from east to west along the north edge of the Natural Area Reserve (Figure 1). Alternate

observation points were observed on every other day for 7 days in 2008 and 4 days in 2009.

Fifteen native plant species and no non-native species (other than grasses) flowered

regularly during observations (Table 1). At each observation point, a representative of each

plant species within 10 m of the observation point was randomly selected and observed for 15

min, if possible. For a plant species not occurring within 10 m of the observation point, the

closest flowering individual within 30 m was observed or in some cases at a different

observation point to obtain similar amounts of observation times for each species. Observations

occurred from 9:30 a.m. to 5:00 p.m., and totaled 72 hr and 30 min in 2008 and 56 hr in 2009.

Observers recorded: observation point, plant species, number of flowers observed, flower visitor,

number of flowers visited by the visitor, duration of visit, if reproductive structures of the flower

were touched by the visitor, and if the visitor foraged for nectar, pollen, or both. The flower

visitors were identified in the field when possible; when insects could not be identified in the

field they were collected, when possible, for later. Collected insects were deposited, identified

and resolved to the lowest possible taxonomic level by Dr. Luc Leblanc of University of Hawai‘i

at Mānoa’s Insect Museum.

In 2009, flower abundance (no./m2) was determined in a 20 x 20 m plot centered on each

observation point. For species having few or large flowers, all flowers in the plot were counted.

For species having small or numerous flowers, flowers were counted in five, parallel 0.5 x 20 m

transects spaced 5 m apart. For plant species having small flowers borne in specialized

inflorescences (Boerhavia, Melanthera), each inflorescence was counted as a single flower.

Network analysis – As part of my master’s thesis, I am analyzing the observations from 2008

and 2009. The observations were combined to build a bipartite, binary network. A bipartite

network consists of two trophic levels, in this case plants and pollinators. A binary network

7

Table 1. Plant species in the networks at Ka‘ena Point, O‘ahu, Hawai‘i.

Family Species Statusa

Present in 2009

Quantitative web

Asteraceae Melanthera integrifolia e yes

Boraginaceae Heliotropium anomalum ind yes

Convolvulaceae Cuscuta sandwichiana e yes

Jacquemontia sandwicensis e yes

Euphorbiaceae Euphorbia degeneri e no

Fabaceae Sesbania tomentosa e, * yes

Goodeniaceae Scaevola coriacea e, * yes

Scaevola taccada ind yes

Lamiaceae Vitex rotundifolia ind yes

Malvaceae Sida fallax ind yes

Waltheria indica ind yes

Nyctaginaceae Boerhavia repens ind yes

Santalaceae Santalum ellipticum e no

Scrophulariaceae Myoporum sandwicense ind yes

Zygophyllaceae Tribulus cistoides ind no a Status of plant species: e=endemic, ind=indigenous, *=endangered.

8

records only the presence or absence of species-pair interactions. Combining years creates a

more comprehensive estimate of interactions for a community (Nielson and Bascompte 2007,

Hegland et al 2010).

Pollinator species were removed from the network if they were recorded visiting flowers

only once (singletons). Removing singletons has little effect on most network indices (Dormann

et al 2009). Flower visitors including ants or visitors that never were observed contacting

reproductive structures were removed from the network. Though ants were frequent visitors

(945 of the 1,962 observed flower visits), they were removed from the analysis (see Discussion).

While we only have data on flower visitation, not pollination, we will follow other studies in

referring to the network as a plant-pollinator network (Jordano 1987), based on our criteria that

flower visitors must visit more than once and must touch the reproductive structures on at least

one of the visits (Dupont et al 2003). Similarly, we will refer to the flower visitors as (potential)

pollinators based on the same criteria (Table 2).

A quantitative network was created for 2009, in which the interactions were weighted based on

how often a pollinator visited a plant species. Henceforth, I will use the term “interaction” to

indicate the presence of an interaction between two species, and the term “visits” to refer to the

flower visitation rate, i.e., how often the pollinator was observed visiting a flower of that plant

species. For each observation session the total number of visits to flowers was summed over all

visitors of the given pollinator taxon and then divided by the number of flowers observed and the

observation time, to give a rate of visits per flower per hour. Note that in this usage a ‘visit’ is to

a flower, not the plant; a single visitor might visit several flowers on the plant, and might even

make more than one visit to the same flower. These rates, for a given plant-pollinator pair, were

then averaged over all observation sessions at a given observation point. Because observations

were stratified by plant species, and were not proportional to flower abundance, the average

visitation rate for a plant-pollinator pair at an observation point was multiplied by the number of

flowers of that plant species at that point (i.e. in the 20x20m plot) to give an estimate of the

frequency of that interaction (as visits to flowers) for the entire plot. This measure is similar to

weight M5 of Castro-Urgal et al. (2013), in that it takes into account observation time, the

9

Table 2. Pollinator taxa in the networks at Ka‘ena Point, O‘ahu, Hawai‘i.

Order Family Species Present in 2009

Quantitative web

Coleoptera Bruchidae Stator sp. no

Chrysomelidae Chrysomelidae sp. yes

Coccinellidae Coccinellidae sp. larvae yes

Scolytidae Scolytidae sp. yes

Diptera Syrphidae Toxomerus marginatus yes

Tachinidae Archytas cirphis yes

Chaetogaedia monticola yes

Eucelatoria armigera no

Tachinidae sp. yes

Unknown Diptera sp. 1 yes

Unknown Diptera sp. 2 yes

Unknown Diptera sp. 3 yes

Unknown Diptera sp. 4 no

Hemiptera Cicadellidae Cicadellidae sp. no

Lygaeidae Nysius sp. yes

Hymenoptera Apidae Ceratina arizonensis yes

Ceratina smaragdula yes

Braconidae Braconidae spp. no

Chalcididae Proconura migratoria MS

Yoshimoto (Leblanc pers

comm)

yes

Colletidae Hylaeus anthracinus yes

Hylaeus longiceps yes

Crabronidae Tachysphex sp. no

Eulophidae Eulophidae sp. yes

Halictidae Lasioglossum imbrex yes

Megachilidae Megachile sp. yes

Vespidae Delta campaniforme

esuriens

no

Polistes aurifer yes

Lepidoptera Lycaenidae Lampides boeticus yes

10

number of flowers observed, and the abundance of the flowers. These rates were then averaged

across the 10 observation points to give a measure of the community-wide frequency of visits by

a given pollinator to flowers of a given plant species.

Network Indices – The bipartite package (version 2.04, Dormann et al 2009) in R 3.0.2 (R Core

Team 2013) was used to calculate qualitative and quantitative network indices at the network

level, trophic level, and at the species level to describe plant-pollinator interactions of this

community.

We will use the terms generalist/generalized and specialist/specialized with respect to the

number of interactions in which a species is involved. Connectance is the realized proportions of

links in the matrix (Dunne et al 2002). In interaction networks, a nested pattern is present when

each species interacts with a subset of those species interacting with the more generalist species

(Bascompte et al 2003). The nested pattern will be measured with 2 indices, temperature and

weighted nestedness. Temperature (T) is a nestedness measure based on the departure from a

perfectly nested interaction matrix, where T°=0 is maximum nestedness (Bascompte and Jordano

2013). The isocline of a perfectly nested matrix is calculated based on the number of plants and

pollinators. Unexpected absences of interactions before the isocline and unexpected presences of

interactions after the isocline are recorded. The unexpected absences’ and presences’ distance

from the isocline is calculated and averaged into the metric temperature (Atmar and Patterson).

A maximally-nested network has species arranged by decreasing number of interactions (T=0°),

and a non-nested network has a checkerboard pattern (T=100°). Weighted nestedness (WNODF)

is a quantitative nested measure that is more robust to different patterns of species interactions

than other measures of nestedness are, and is based on overlap and decreasing number of

interactions (Almeida-Neto et al 2011). Values range from 0 (not nested) to 100 (highly nested).

Compartments include species that interact more among themselves than with the rest of the

network (Dormann et al 2009). Interaction evenness, based on Shannon evenness, describes the

distribution and uniformity of interactions between species in a community (Tylianakis et al

2007, Kaiser-Bunbury et al 2011). The values range from 0 (uneven) to 1 (uniform). Degree is

the number of links, or interactions of a species (Dormann et al 2009). Generality is calculated

11

for both trophic levels and is the weighted mean number of partners per species across a trophic

level, using the Shannon diversity for frequency of interactions by species (Bersier et al 2002).

Network selectivity H2’, based on Shannon entropy, measures the level of selectiveness of the

network (Bluthgen et al 2006). Values range from 0 (highly opportunistic) to 1 (highly

selective). Species selectiveness index d’ is low when a species’ interactions are proportionate to

the abundance of its partners, reflecting opportunistic interactions, and is high when a species’

interactions are not proportional to the abundances of potential partners (selective; Bluthgen et al

2006). Values range from 0 (highly opportunistic) to 1 (highly selective).

Other indices calculated in ‘networklevel’ and ‘grouplevel’ of bipartite which are not

reported in results are included in Appendix A.

Data Analysis - The observed patterns for temperature in the 2008-2009 binary dataset used a t-

test against 1000 null models using the Patefield algorithm in bipartite (Dormann et al 2009).

The result of the t-test was signficiant if p < 0.05.

RESULTS

The binary plant-pollinator network of 2008 and 2009 (Figure 2) includes 15 native plant

species (Table 1), 2 native insect species, and 26 non-native insect taxa (Table 2), and has 119

interactions. The quantitative network of 2009 (Figure 3) includes 12 plant species (Table 1), 2

native insect species, and 19 non-native insect taxa (Table 2), with 51 interactions. Because the

females of the two native Hylaeus species are indistinguishable in the field, Hylaeus were

grouped together as one taxon in both networks (i.e. Forup et al 2008), yielding 27 pollinators in

the 2008-2009 binary dataset and 20 in the quantitative dataset. A full report of indices

calculated in the bipartite package using the functions ‘networklevel’ and ‘grouplevel’ is

included in Appendix A.

Binary Network – The 2008-2009 binary dataset had a connectance of 29.4% (Table 3). The

temperature index (Table 4), is significantly lower than the mean temperature of the randomized

12

Figure 2. 2008-2009 Binary plant-pollinator network of Ka‘ena Point, O‘ahu, Hawai‘i. Pollinators are represented in the columns, and plants are represented in the rows. Each shaded

cell represents an interaction between two species. Matrix rows and columns are sorted

according to the “binmatnest” algorithm in bipartite. Species names are abbreviated. The

specific epithet or most resolved name for species and taxa are in Table 1 and Table 2 for plants

and pollinators respectively.

13

Figure 3. 2009 Quantitative plant-pollinator network of Ka‘ena Point, O‘ahu, Hawai‘i. Each cell

is shaded from white (no interaction and no visits) to black (interaction present and visits very

frequent) indicating the strength of the interaction between the plant and pollinator. Pollinators

are represented in the columns, and plants are represented in the rows. Matrix rows and columns

are sorted according to the weighted interaction version of the “NODF” algorithm in bipartite.

The specific epithet or most resolved name for species and taxa are in Table 1 and Table 2 for

plants and pollinators respectively. The legend displays the color and corresponding number of

visits in the interaction.

14

Table 3. Network Metrics of the binary and quantitative networks of Ka‘ena Point, O‘ahu,

Hawai‘i.

Network Parameter 2008-2009 Binary Dataset 2009 Quantitative Dataset

Number of plant species (P)a

15 12

Number of pollinator taxa (A)b

27 20

Total Interactionsc

119 51

Number of Visitsd

975 138

A/Pe

1.8 1.7

Network Sizef

405 240

Connectanceg

29.4% 21.3%

a The number of plant species is represented as P.

b The number of pollinator taxa is represented as A.

c Total interactions is the sum of all interactions in the network.

d Number of visits is the total observations of pollinators visiting flowers.

e A/P is the ratio of number of pollinator taxa to the number of plant species.

f Network size is the number of pollinator taxa times the number of plant species (A*P).

g Connectance is the realized proportions of links in the matrix (Dunne et al 2002).

15

Table 4. Network Indices for the binary and quantitative datasets of Ka‘ena Point, O‘ahu,

Hawai‘i. Standard error of the means are reported for temperature, degree, and d’.

Network Index 2008-2009 Binary Dataset 2009 Quantitative Dataset

Temperaturea

31.6 25.2

Mean Null Model Temperature 38.1±0.12 15.1±0.12

WNODFb

--- 18.3

Mean Degree Ac

4.4±0.73 2.6±0.59

Mean Degree P

7.9±0.85 4.3±0.58

Max Degree Ad

13 9

Max Degree P

14 8

Generality Ae

--- 2.4

Generality P --- 2.9

Interaction Evennessf

--- 0.52

H2g

--- 0.72

Mean d’Ah

--- 0.57±0.04

Mean d’P --- 0.58±0.06

a Temperature measures the departure from a perfectly nested interaction matrix, where T°=0 is

maximum nestedness (Bascompte and Jordano 2013). b WNODF is weighted nestedness, a quantitative nested measure that is based on overlap and

decreasing number of interactions (Almeida-Neto et al 2011). c Mean Degree is the mean number of links, or interactions of a species (Dormann et al 2009).

d Max Degree is the species with the maximum number of links.

e Generality is the mean number of partners per species from a trophic level weighted by their

marginal totals (Bersier et al 2002). f Interaction evenness, based on Shannon evenness, describes the distribution and uniformity of

interactions between species in a community (Tylianakis et al 2007). g H2 is the specialization of the network which is based on Shannon entropy (Bluthgen et al

2006). h d’ measures the level of specialization of a species (Bluthgen et al 2006), based on Shannon

entropy (Bluthgen et al 2006).

16

networks, indicating a nested pattern relative to null models. This network lacks compartments

(Appendix A), but does have a core block of generalists where majority of the interactions occur

(Figure 2).

Quantitative Network – The quantitative network’s connectance is 21.3% (Table 3).

Nestedness temperature of the observed network was (Table 4) significantly higher than the

mean nestedness temperature of the randomized networks, suggesting that the observed network

was less nested than the null model. WNODF was 18.3, where a value of 0 means no nested

pattern and 100 indicates a perfectly nested pattern. This network lacks compartments

(Appendix A), but has a core block of generalists (Figure 3). Interaction evenness (IE) of the

quantitative network is 0.52. The H2 value of 0.72, indicates a selective network.

Pollinators and Plants – In both datasets, native bees (Hylaeus), and non-native small bees

(Lassioglossum, Ceratina), wasps (Proconura), and flies (Tachinidae) were the most frequent

flower visitors both for interactions and visits (Table 5). Hymenoptera made up the largest

proportion of taxa involved in the networks. Hymenoptera were involved in the most

interactions and visits compared to other insect orders. After Hymenoptera, Diptera was second

for most taxa, interactions, and visits. Coleoptera, Hemiptera, and Lepidoptera made up minor

proportions of the taxa, interactions, and visits.

In both years, non-native insects visited 5 plant species not visited by native Hylaeus

bees, and in 2009 they provided 79.45% of visits in the quantitative network. The number of

partners ranged from 1 to 13 out of 15 possible plant species with a mean degree of 4.4 ± 0.73

(S.E.M.) in the 2008-2009 binary dataset. In the 2009 quantitative dataset, non-native insects

visited from 1 to 9 out of 12 possible plant species and had a mean degree of 2.6 ± 0.59. This

difference is due to the subset of data used for the 2009 quantitative analysis. Overall animal

generality, weighted mean number of partners, was 2.4 in the 2009 quantitative dataset.

The two native visitors, Hylaeus anthracinus and H. longiceps, provided 20.55% of the

flower visits in 2009, and foraged at high frequencies and on many species, including the

17

Table 5. Insect orders represented in networks of Ka‘ena Point, O‘ahu, Hawai‘i. The number of

pollinator taxa or the proportion of that insect order involved in different degrees in the network

are presented for the 2008-2009 binary dataset (B) and 2009 quantitative dataset (Q). The full

list of pollinator taxa and insect orders are in Table 2.

No. taxaa Taxa %

b Interaction %

c Visit %

d

Insect Order B Q B Q B Q Q

Hymenoptera 11 8 40.7 40 62.2 72.5 58.0

Diptera 9 7 33.3 35 22.7 15.7 34.18

Coleoptera 4 3 14.8 15 8.4 5.9 6.07

Hemiptera 2 1 7.4 5 5.0 2.0 0.11

Lepidoptera 1 1 3.7 5 1.7 3.9 1.64

a No. taxa is the number of pollinator taxa observed for the network that fall into that insect

order. b Taxa % is the proportion of pollinator taxa of an insect order out of the total number of taxa

observed. c Int. % is the proportion of interactions an insect order was involved in out of the total

interactions observed in the network. d Visit % is the proportion of visits an insect order was involved in out of the total visits in the

network.

18

endangered Scaevola coriacea and Sesbania tomentosa. Hylaeus spp. provided high proportions

of visits to 4 plant species (Table 6), including 50.38% for Scaevola coriacea, 43.22% for

Sesbania tomentosa, and 32.99% of visits for Scaevola taccada. Hylaeus spp. visited most often

Myoporum sandwicense, Sesbania tomentosa, and Scaevola taccada (69.47%, 14.43%, and

12.52% of Hylaeus visits, respectively).

Generalized non-native pollinators (Lasioglossum imbrex, Ceratina smaragdula, and

Proconura migratoria) interacted with many plant species (Figure 2, 3). These 3 pollinators

visited ≥ 80% of the 15 species in the 2008-2009 binary dataset and ≥ 58% of the 12 species in

the 2009 quantitative dataset. This difference is due to the subset of data used in the 2009

quantitative analysis. These three pollinators visited the plants frequently, making up 23.6% of

the visits in the quantitative network (Figure 4). Two specialized pollinators, Diptera sp. 2 and

Eulophidae sp., visited Myoporum sandwicense and C. sandwichiana, respectively, and

accounted for 28.2% and 9.4% of the visits in the quantitative network, respectively. In the 2008-

2009 binary dataset, Myoporum sandwicense had 12 partners, but in the 2009 quantitative

dataset, it had 3. Out of these 3 pollinators, Diptera sp. 2 provided 63.3% visits to Myoporum

sandwicense. This interaction was the strongest (accounting for 28.2% of visits in the network)

due to the high abundance of Myoporum sandwicense flowers in a plot (5,648 flowers). C.

sandwichiana had 2 visitor species in the 2008-2009 binary dataset and 1 in the 2009

quantitative dataset. Eulophidae sp. provided 100% of the 2009 visits to C. sandwichiana. In

2009, the remaining 14 out of the 20 pollinators (flies, wasps, beetles, true bugs, and a butterfly)

interacted with relatively few plant species, ≤ 2 out of the 12, and did so relatively infrequently,

accounting for 18.3% of the visits in the network (Figure 5).

The native coastal plant species include both common (J. sandwicensis, Sida fallax, and

Scaevola taccada) and endangered species (Scaevola coriacea and Sesbania tomentosa). In both

datasets, most plant species interacted with several pollinators, appearing to be generalists (mean

19

Table 6. Plant species’ proportions of visits from Hylaeus spp. from the quantitative network of

Ka‘ena Point, O‘ahu, Hawai‘i.

Plant % visits from Hylaeus spp

(plant view)

% Hylaeus spp. visits

(Hylaeus view)

Scaevola coriacea 50.38 0.62

Sesbania tomentosa 43.22 14.43

Scaevola taccada 32.99 12.52

Myoporum sandwicense 32.38 69.47

Jacquemontia sandwicensis 8.27 2.36

Sida fallax 1.20 0.48

Melanthera integrifolia 0.29 0.12

Vitex rotundifolia 0.00 0.00

Waltheria indica 0.00 0.00

Heliotropium anomalum 0.00 0.00

Boerhavia repens 0.00 0.00

Cuscuta sandwichiana 0.00 0.00

20

Figure 4. The distribution of visits (y axis) of generalized pollinators to plant species (x axis) from the quantitative network of Ka‘ena Point, O‘ahu, Hawai‘i. The specific epithet or most

resolved name for species and taxa are in Table 1 and Table 2 for plants and pollinators

respectively.

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Jac

san

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int

Sca

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Sid

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Sca

cor

Cu

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No

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ts

Generalized pollinator visits

Pro mig

Cer sma

Hyl spp

Las imb

21

Figure 5. The proportion of visits (y axis) by pollinator taxa (x axis) out of the total visits in the quantitative network of Ka‘ena Point, O‘ahu, Hawai‘i. The specific epithet or most resolved

name for taxa are in Table 2 for pollinators.

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

Dip

t 2

Hyl

sp

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Eulo

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a

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Co

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mar

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a m

on

Lam

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e

Cer

ari

Tach

sp

Meg

a sp

Arc

cir

Ch

ry s

p

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% Pollinators' visits out of total visits

22

plant degree 7.9 ± 0.85 in the 2008-2009 binary dataset and 4.3 ± 0.58 in the 2009 quantitative

dataset). Plant generality, weighted mean of partners, for the 2009 quantitative dataset was 3.0.

In the 2009 quantitative dataset, the plants with the most visits of the network included

Myoporum sandwicense (44.1% visits), Melanthera integrifolia (8.7% visits), and Sida fallax

(8.2% visits; Figure 6). Results that involve Scaevola coriacea should be interpreted cautiously

because only one individual grows at Ka‘ena Point.

Species selectiveness – To assess species’ selectivity, the d’ index, was evaluated in the

quantitative network. Most plants and pollinators (42% and 50%, respectively) were categorized

as selective (Figure 7; using the same 4 categories from Castro-Urgal and Traveset 2013).

DISCUSSION

In a Hawaiian coastal flowering-plant community consisting entirely of native plants, the

pollinator community is dominated by introduced insect species. This is an extreme example of

the preponderance of novel interactions between natives and non-natives within a community.

The non-native pollinators comprise 95% (19/20 in the 2009 quantitative dataset) to 96% of the

taxa (26/27 from the 2008-2009 binary dataset) and are involved in 79.45% of flower visits in

the quantitative dataset for 2009. There are no collections of coastal pollinators in Hawaiʽi to

compare this work to and the species composition of the original native pollinator community in

the coastal habitat is unknown (Howarth 1985, Leblanc pers comm). Several studies have

documented incorporation of non-native plants (Bjerkens et al 2007, Bartomeus et al 2008,

Traveset and Richardson 2006) and/or pollinators into a plant-pollinator network (Kaiser-

Bunbury and Muller 2009), but none have reported such an extreme case of a native plant

community interacting primarily with non-native pollinators. A large shift in the pollinator

assembly from natives to non-natives has been reported on the Ogasawara (Bonin) Islands,

Mauritius, and the Galapagos Islands (Abe et al 2006, Kaiser-Bunbury and Muller 2009,

Traveset et al 2013). Many native and endemic small bee taxa of the Ogasawara Islands have

decreased due to predation by introduced anoles (Abe et al 2006, 2007). Non-native taxa made

23

Figure 6. The proportion of visits (y axis) by plant species (x axis) out of the total visits of the quantitative network of Ka‘ena Point, O‘ahu, Hawai‘i. The specific epithet or most resolved

name for species Table 1 for plants.

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%

40.00%

45.00%

50.00%

Myo

san

Mel

int

Sid

fal

Cu

s sa

n

Sca

tac

Ses

tom

Jac

san

Vit

ro

t

Bo

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p

Wal

ind

Hel

an

o

Sca

corSp

ecie

s %

vis

its

ou

t o

f to

tal v

isit

s % Plants' visits out of total visits

24

Figure 7. Categories of plant species or pollinator taxa d’ values from the quantitative network of

Ka‘ena Point, O‘ahu, Hawai‘i. Species selectivity d’ measures the level of selectivity of a

species (Bluthgen et al 2006). The index decreases when a species’ interactions are

proportionate to abundant partners, which is considered opportunistic, and the index increases

when a species’ interactions are disproportionately higher with a rare species which is considered

selective. d’ categories (Castro-Urgal and Traveset 2014) are: 0 ≤ d ≤ 0.25 (Highly

opportunistic), 0.25 < d ≤ 0.50 (Opportunistic) , 0.50 < d ≤ 0.75 (Selective) , 0.75 < d ≤ 1.00

(Highly selective).

25

up at least 35 out of 161 observed pollinator taxa (22%) and made 63% of the flower visits in

heath vegetation in Mauritius (Kaiser-Bunbury and Muller 2009). In the Galapagos Islands dry

zone habitat, alien pollinators make up 21% of the pollinator taxa and provide 38% of

interactions (links). Other studies have documented interactions involving individual non-native

pollinators. Pollination of native plants by non-native pollinators may be either less efficient or

more efficient than pollination by native pollinators (Ings et al 2005, Kenta et al 2007,

Chamberlain and Schlising 2008).

Similar to our findings, non-native species have been found to dominate various other

arthropod assemblages in Hawai‘i, including lowland insects (Asquith and Messing 1993),

aquatic arthropods (Englund 2002), and parasitoids of native moths feeding on native plants on

Kaua‘i (Henneman and Memmott 2001). Additionally, other systems in Hawai‘i and on other

islands include novel interactions between native and non-native species, which in some cases

appear to maintain ecosystem functions. In New Zealand, non-native rats (Rattus rattus) and the

recent colonist silvereye (Zosterops lateralis) pollinate some native forest plants (Pattemore and

Wilcove 2012). On Hawai‘i Island, native and non-native pollinators shared three native plants

(Clermontia parviflora, C. montis-loa, and C. hawaiiensis), but the visits were dominated by the

non-native Japanese white-eye (Zosterops japonicus) (Aslan et al 2014). Z. japonicus was

unable to pollinate C. hawaiiensis effectively due to a morphological mismatch, but pollinated C.

parviflora and C. montis-loa. On Maui, in dry forest dominated by native plants but lacking

native birds, the avian seed disperser community consists entirely of non-native species which

disperse the seeds of most of the fleshy-fruited native and non-native plants (Chimera and Drake

2010). Non-native species have the potential to provide mutualistic services in the absence of

native animals, though the quality and quantity of the services may not be exactly the same as

those provided by the natives (Aslan et al 2012).

In some plant-pollinator communities, native generalist species could provide a way for

non-native species to enter the community (Bjerkens et al 2007, Lopezaraiza-Mikel et al 2007).

Many insects can easily visit the flowers of many coastal plants of Hawai‘i, including most of

those present at Kaʽena Point, because the flowers are open and thus easily accessible, and are

26

available throughout much of the year. The results from our study support this idea that most

plants interact with several partners (high mean plant degree, Table 4). Once involved in the

network, non-native species could replace native species (Olesen et al 2002, Bartomeus et al

2008, Padron et al 2009), by usurping and disrupting the current interactions and visits in the

network (Aizen et al 2008, Traveset et al 2013). Alien plants have been reported to increase the

visits received by other plants by attracting more pollinators to them (Lopezaraiza-Mikel et al

2007) and, conversely, by dominating the interactions with pollinators and thus reducing visits to

other plants (Bartomeus et al 2008). Overall, integration of a non-native species into a network

appears to depend on the species involved and the circumstances (Vila et al 2009).

Network metrics – Both the binary and quantitative network parameters are similar to those of

other small networks on islands (Olesen et al 2002, Padron et al 2009, Trojelsgaard and Olesen

2013). Compared to the average island network (Trojelsgaard and Olesen 2013), our networks

have fewer species and higher connectance, which could be due to removing singletons. When

compared to other island networks with relatively small sizes and in dry ecosystems, however,

the total number of taxa, connectance, ratio of animals to plants, and average degree of

pollinators and of plants, are broadly similar (Dupont et al 2003, Philipp et al 2006, Bartomeus et

al 2008, Padron et al 2009).

Nested patterns – The Ka‘ena Point 2008-2009 binary dataset was nested based on the

temperature index and Patefield null model. The 2009 quantitative dataset has a similar

WNODF value as other networks on islands (WNODF ranges from 9.21 through 21.73; Traveset

et al 2013, Castro-Urgal and Traveset 2014), where number of plant species ranges from 18 to 25

and number of pollinator species ranges from 60 to 93. WNODF was not tested against null

models because current quantitative null models are based on discrete number of visits and are

inappropriate for our flower visitation rate (Ulrich et al 2009, Gotelli and Ulrich 2011). Other

studies have found mixed results when using different nestedness measures (Kratochwil et al

2009, Ulrich et al 2009), but most plant-pollinator networks are nested (Bascompte et al 2003).

Our networks have a core block of generalized plants interacting with generalized pollinators

(Bascompte et al 2003). Some studies report that the presence of non-natives increases

27

nestedness (Bartomeus et al 2008, Traveset et al 2013), but this likely depends on the specific

system.

An unusual case in our network is the interaction between native C. sandwichiana and a

non-native wasp, Eulophidae sp. C. sandwichiana does not have any other partners, and

Eulophidae sp. interacts with C. sandwichiana, J. sandwicensis, and W. indica. This appears to

be a native specialist interacting with a non-native specialist. However, C. sandwichiana may

have other pollinators at other seasons, and other species of Cuscuta have a variety of pollinators

(Wright et al 2012).

Quantified Indices – The interaction evenness (IE) of the quantitative network was

lower than that of other island networks (Kaiser-Bunbury et al 2009, Traveset et al 2013, Castro-

Urgal and Traveset 2014). IE declined in more heavily invaded sites in Mauritius (Kaiser-

Bunbury et al 2011). Our network has mostly non-native pollinators, and the IE is similar to that

of those invaded sites.

Few plant-pollinator network studies report H2 and d’ values, but the values I observed in

this network fall in the upper range of values for other island pollinator networks for which these

indices have been calculated (Traveset et al 2013, Castro-Urgal and Traveset 2014). The

observed values indicate a selective network (Bluthgen et al 2006).

Species Interactions – Non-native, flower-visiting taxa in this study were mostly bees, wasps,

and flies, and they also provided most of the flower visits. The most generalized pollinators

(Ceratina smaragdula, Lasioglossum imbrex, and Proconura migratoria) interacted with the

same plants, had similar degree, and provided many visits overall in the network, as did the

native Hylaeus spp. However, the three non-native species distributed their visits among plant

species differently than Hylaeus spp. These 4 pollinators may dominate in visits and share plant

species as partners, but different plant species received varying number of visits from these

frequent pollinators

28

The only native pollinator taxon was Hylaeus spp. The two native Hylaeus species are

important pollinators because of the high frequency of their visits to flowers. The Hylaeus taxon

represented 1/27th

of the pollinator taxa in the 2008-2009 binary dataset and 1/20th

of the

pollinator taxa in the 2009 quantitative dataset, but interacted with many partners (10 out of 15

species in the binary network and 7 out of 12 plant species in the quantitative network) and made

many visits (20.55% of the total visit frequency in the 2009 quantitative dataset). Hylaeus are

recognized across the Hawaiian Islands as potentially important pollinators for native plants

(Hopper 2002, Magnacca 2007, Koch and Sahli 2013, Krushelnycky 2014). Since this study was

conducted in 2008 and 2009, Hylaeus populations appear to have declined throughout Hawai‘i

(Magnacca and King 2013). Hylaeus bees have rarely been observed at Ka‘ena Point since 2012

(Magnacca and King 2013, Magnacca pers comm, Shay pers obs).

Another interesting change since 2008-2009 is the presence of Apis mellifera, which was

not observed in 2008 or 2009 probably because of the varroa mite (Taylor pers comm). A.

mellifera was quite noticeable in previous years (Taylor per obs) and visiting many flowers in

spring 2014 (Shay pers obs). Studies show A. mellifera integrates into other island and native

networks and dominates partners and visits (Butz Huryn 1997). A. mellifera dominated the

pollinator abundance and performed 43.8% of the visits in Mauritius (Kaiser-Bunbury 2011),

including 95% of the visits to an endemic shrub Bertiera zaluzania (Kaiser-Bunbury and Muller

2009). Honey bees visited 50% of the plant species in Canary Islands (Dupont et al 2003). With

the apparent decline in the remaining native pollinators and return of A. mellifera, Ka‘ena Point

may be approaching a completely native plant community interacting with a completely non-

native pollinator community.

Some of the most active non-native flower-visiting insects in Hawai‘i’s coastal

ecosystem are ants, Lasioglossum imbrex, Ceratina smaragdula, and A. mellifera (Hopper 2002,

Elmore 2008, Shay Chapter 2, Shay per obs). In several other studies in this habitat, these

insects have been observed as frequent flower visitors and, except for ants, as potential

pollinators to Scaevola taccada, Scaevola coriacea, (Elmore 2008), Sesbania tomentosa,

29

(Hopper 2002), Sida fallax, and J. sandwicensis (unpublished data, Shay Chapter 2) These

results are consistent with those of the present study at Kaʽena Points.

Not all flower visitors are effective pollinators (Popic et al 2013). One in particular that I

believe was rarely legitimate pollinator to Sesbania tomentosa was Lampides boeticus.

Lampides boeticus visited both V. rotundifolia and Sesbamia tomentosa, but contacted

reproductive structures of only V. rotundifolia. I suspect it oviposits on Sesbania tomentosa, as

suggested by previous authors (Hopper 2002, Pratt et al 2011).

Ants are an important component of this community, but one whose effects I was unable

to determine. Ants visited all plant species and were recorded 945 times out of the original total

of 1,962 observations of flower visitors across both years. Ants were removed from the analysis

because they are only rarely pollinators (Beattie et al 1984). However, other insect interactions

in the community could be affected by ants. Ants could be removing floral resources or

physically interfering with pollinators on flowers (Lach 2008, Junker et al 2011, LeVan et al

2014), and could decrease pollinator populations in the habitat (Cole et al 1992, Krushelnycky

and Gillespie 2008, Junker et al 2011).

CONCLUSION

I described and analyzed plant-pollinator networks to develop a basic understanding of

coastal plant-pollinator interactions of Hawai‘i and of the dominating presence of non-native

pollinators. I expected the network parameters and indices to be similar to those of other insular

ecosystems, and in spite of the dominating presence of non-native pollinators, the network was

still similar to other insular ecosystems. Most network parameters and binary indices were quite

similar to values observed in other island networks (Traveset et al 2013, Trojelsgaard and Olesen

2013, Castro-Urgal and Traveset 2014).

This description of plant-pollinator interactions can assist efforts to restore and conserve

the native coastal ecosystem of Hawai‘i (Medeiros et al 2013, Young et al 2013). Restoration

plans should consider assessing the status of remaining native pollinators, such as Hylaeus spp.,

30

and non-native pollinators, because both are involved in many interactions and visits in the

community (Magnacca et al 2007, Medeiros et al 2013). This study and other examples (Aslan

et al 2012) describe how non-native species form novel interactions with native species, and can

maintain an ecosystem’s function after losing most of the original native species.

31

CHAPTER II. THE POLLINATION BIOLOGY OF Jacquemontia sandwicensis

(CONVOLVULACEAE)

ABSTRACT

Native plants of Hawaiʽi have received little attention regarding their basic ecology and

pollination biology. As human impacts on island systems increase, so, too does the importance

of understanding native species’ life histories and population dynamics for plant conservation.

The breeding system and pollinator observations were assessed for the native coastal vine

Jacquemontia sandwicensis (Convolvulaceae), a common plant in the coastal strand habitat. To

evaluate the breeding system of this plant, field and lab experiments involving natural and hand

pollination treatments were performed, as well as pollinator observations in 3 coastal sites of the

southeast coast of Oʽahu. J. sandwicensis is a hermaphroditic species with a flexible, mixed

mating system. High fruit set, seed set, and germinating seeds depend on pollen being deposited

on the stigma by an active pollinator rather than a passive vector (wind or autogamy). However,

this species still produces some seeds even in the absence of manipulation, suggesting it can

reproduce when pollinators are absent or in low abundances. In the observed sites, this plant was

visited by a variety of mostly non-native Hymenoptera (A. mellifera and Lasioglossum spp.).

Native Hylaeus anthracinus visited J. sandwicensis, but at much lower frequency than the non-

native pollinators. Non-native pollinators appear to be effective pollinators for J. sandwicensis

and could provide pollination services in the face of absent or declining native pollinators.

INTRODUCTION

Native plants on islands are threatened by habitat fragmentation and loss, decline and

extinction of mutualists, and invasion by non-native species (Cuddihy and Stone 1990, Whittaker

and Fernandez-Palacios 2007, Kaiser-Bunbury et al 2010b), among other factors. As human

impacts on island systems increase, so, too does the importance of understanding native species’

life histories and population dynamics for plant conservation (Anderson et al 2001, McMullen

2009, Caujape-Castells et al 2010). Unfortunately, basic ecological studies do not exist for many

island species, common or rare (Baker 1967, Anderson et al 2001, Caujape-Castells et al 2010).

Relative to continental floras, island floras have higher proportions of plants that are

dioecious, or self-compatible (Baker 1955, Carlquist 1974, Sakai et al 1995, Barrett 1996,

32

Anderson et al 2001, Schlessman et al 2014), and tend to have generalized pollinator interactions

(Kaiser-Bunbury et al 2010b). Dioecious plants bear male or female flowers, forcing individuals

to outcross for reproduction (Bawa 1980). Self-compatible plants are able to use their own

pollen to fertilize ovules (Willmer 2011) and may or may not rely on pollinators for reproduction

(Baker 1955). Dioecy and self-compatibility are contrasting strategies for colonizing an island

and adapting to conditions of an island (Baker 1955, Carlquist 1974, Barrett 1996, Cheptou

2012), but both are observed in islands, including Hawaiʽi and others (McMullen 1987, Sakai et

al 1995, Anderson 2001, Bernardello et al 2001, Schlessman 2014). If a plant that relies on

pollinators colonizes an island, then it must find effective pollinators on the island (Kaiser-

Bunbury et al 2010b). The pollinators on the island are likely a different assemblage than the

plant’s origins (MacArthur and Wilson 1967). Island plants typically interact with many

partners, and are considered generalists; some are even supergeneralists, having wide pollination

niches and interacting with a disproportionately large fraction of the pollinator community

(Olesen 2002).

Native insect pollinators and their interactions are not well known in Hawaiʽi. The

pollinator community is almost certainly naturally depauperate and disharmonic compared to

continental ecosystems (MacArthur and Wilson 1967, Whittaker and Fernandez-Palacios 2007).

In Hawaiʽi, native pollinators could include 955 moth species (Ziegler 2002), 63 Hylaeus bees

(Magnacca and King 2013), 94 Nesodynerus or potter wasps (Carpenter 2008), and 2 species of

butterflies (Zimmerman 1958). The yellow-faced bees of Hawaiʽi, Hylaeus, have radiated from

one colonist to over 60 species (Magnacca and Danforth 2006). Hylaeus have been observed

visiting flowers of native Hawaiian plants in many habitats across the islands (Wilson et al 2010,

Koch and Sahli 2013, Krushelnycky 2014), and are potential and sometimes dominant

pollinators for native coastal plants, including J. sandwicensis (Hopper 2002, Chapter 1).

Hylaeus and other lowland insects have been devastated by many factors (Medeiros et al 2013),

including non-native insects disturbing native insects in various ways (Howarth 1985, Cole et al

1992), novel predators (i.e. Kraus et al 2012), and land use (Asquith and Messing 1993).

Consequently, insects, such as Hylaeus, are declining in abundance and becoming endangered or

extinct (Magnacca and King 2013). The loss of one species in a plant-pollinator relationship

may reduce the fitness of its partner (Kiers et al 2010, Potts et al 2010).

33

In contrast, non-native insects are quite prevalent in lowland ecosystems. Over 2,500

species of non-native insects have established in Hawaiʽi (Pimental et al 2005). The non-native

flower visitors range from likely pollinators to nectar thieves (Hopper 2002, Elmore 2008,

Pleasants and Wendel 2010, Shay unpub). Non-native insects may increase or decrease the

pollination activities of other insects in the community (Ings et al 2005, Kenta et al 2007,

Bartomeus et al 2008).

Few studies have investigated Hawaiʽi’s coastal plants’ breeding systems and pollinators

thoroughly. Some of Hawaiʽi’s coastal plants are self-compatible (Hopper 2002, Yorkston and

Daehler 2006, Pleasants and Wendel 2010), hermaphroditic (Wagner et al 1990), and interact

with multiple pollinators (Hopper 2002, Elmore 2008, Chapter 1).

Jacquemontia sandwicensis (pāʻūʻohiʻiaka, Convolvulaceae), is an endemic coastal

morning glory found on all of the main Hawaiian islands and is the only species in its genus

native to Hawaiʽi (Robertson 1974, Namoff et al 2010). J. sandwicensis is recognized as a main

component and sometimes a dominant plant that defines the coastal vegetation (Richmond and

Mueller-Dombois 1972, Gagne and Cuddihy 1990). In the coastal habitat, it can be found

growing as a vine close to the ground, often with Sida fallax (pers obs). Despite its apparent

ecological importance, little is known about its ecology or reproductive biology. Other studies

that investigated Hawaiian plants mating systems have suggested J. sandwicensis is a

hermaphroditic self-compatible plant based on herbarium and field samples (Carlquist 1966) and

the Manual of the Flowering Plants of Hawaiʽi (Wagner et al 1990, Sakai et al 1995). However,

these studies did not test the breeding systems experimentally, did not observe pollinators, and

did not link the role of pollinators with J. sandwicensis’ breeding system.

In the native-dominated vegetation at Kaʽena Point in 2008 and 2009, Jacquemontia

sandwicensis was observed as an important generalized plant species in terms of plant-pollinator

interactions, interacting with Hylaeus spp. and 10 non-native taxa. In 2009, it received 5.9% of

the community’s pollinator visits and 8.3% of those visits involved Hylaeus (Chapter 1). The

objectives of this study were to 1) investigate the pollinators elsewhere on Oʽahu, in more

disturbed communities, to see if its pollinators differed and 2) investigate the breeding system of

J. sandwicensis to determine its reliance on pollinators for reproduction. I predicted that

Hymenoptera species, including Hylaeus, if present, visit J. sandwicensis (Chapter 1).

34

Jacquemontia sandwicensis is expected to have a mixed mating system, which means a

hermaphroditic plant reproduces by self and cross fertilization (Goodwillie 2005), similar to J.

reclinata, a related coastal species in Florida (Pinto-Torres and Koptur 2009).

METHODS

Study sites – This study involved 4 sites along a 3.5 km stretch of coastline on the southeast of

Oʽahu (Figure 1). The sites were near the Halona Blowhole (21°16’50” N, 157°40’44” W; 23.8

m elevation; BH), the Kaʽiwi Scenic Shoreline (21°17’50” N, 157°39’20” W; 3 m elevation; KI),

a cliff near the Makapuʽu Lighthouse Trail (21°17’59” N, 157°39’06” W, 66 m elevation; MC),

and Wawamalu Beach Park (21°17’13.98”N, 157°40’08.23”W; 2 m elevation; WP). These low

elevation, low rainfall (670 mm/yr; Giambelluca et al 2013) sites experience harsh

environmental conditions such as high temperature and intense solar radiation and support dry

coastal plant communities with a mix of native and non-native species (Richmond and Mueller-

Dombois 1972, Gagne and Cuddihy 1990).

Floral description - The inflorescence of J. sandwicensis ranges from 1 to a few flowers in a

cyme in the leaf axil (Wagner et al 1999). Flower traits were measured in 22 flowers, selected

from 22 different individuals from the cultivated plants used in the breeding experiment (Table

1). Basic flower morphology was measured using calipers (Raimundez-Urrutia et al 2008). The

flowers vary in color from white to pale blue (Figure 2). The corolla is sympetalous and broadly

campanulate, and can have 2 tall stamens and 3 short stamens. The tall stamens are of similar

length to the style. Pollen-ovule ratio was based on pollen counts from a single anther, from

flowers of 7 individuals, made under a dissecting microscope (Cruden 1977), and the number of

ovules is always 4 (Wagner et al 1999). Mean pollen grains per anther was 587±33.25 (n = 7),

and the pollen-ovule ratio was 733.8.

Breeding experiments - Cuttings of J. sandwicensis were collected at the 4 study sites (20 to 25

individuals per site) in May 2013. The cuttings were trimmed to 10 cm to 15 cm with 3 to 5

nodes, and leaves under the 3rd

or 4th

node from the apex were removed to reduce water loss

35

Figure 1. Map of Study sites. The upper left inset is a map of the island Oʽahu with the area

highlighted with the yellow rectangle expanded into the central image. The central image has the

4 study sites, Halona Blowhole, Wawamalu Beach Park, Kaʽiwi Shoreline, and the Lighthouse

Trail at Makapuʽu marked.

36

Table 1. Floral morphology of Jacquemontia sandwicensis. All traits were measured on a single

flower from 22 individuals, reported in (mean in mm ± standard error). Corolla length is the

length of the corolla from base to top. Corolla diameter is the diameter of the corolla at the top

of the flower. Corolla base is the diameter of the corolla at the base of the flower. Style length

is the length of the style. Short anther is the length of one of the 3 shorter anthers. Long anther

is the length of one of 2 longer anthers.

Corolla

Length

Corolla

Diameter

Corolla

Base

Style

Length

Short

Anther

Long

Anther

13.8±0.35 13.1±0.38 5.0±0.10 8.0±0.17 4.7±0.19 7.2±0.22

37

Figure 2. Flower of Jacquemontia sandwicensis. (A) Both male and female reproductive

structures are white. The solid black arrow points to the bilobed stigma and the dashed black

arrows point to the two taller stamens. (B) A male Hylaeus anthracinus visiting J. sandwicensis

(Photo: Kobey Togikawa), (C) J. sandwicensis in coastal habitat at Kaʽiwi Shoreline, Oʽahu.

A

C

B

38

from transpiration. The cuttings were planted in 15.2 cm diameter and 12.7 cm height pots with

a mix of 3 parts perlite to 1 part vermiculite, and kept well watered (Hawaiian Native Plant

Propagation 2001). Once the plants grew and developed, they were transplanted into 25.4 cm

diameter and 25.4 cm height pots with a mix of 4 parts commercial potting soil to 3 parts perlite

to 1 part vermiculite. The plants were grown outdoors in full sunlight, where they were allowed

to mature and flower. The breeding pollination treatments were conducted from 1/6/2014

through 2/11/2014.

A total of 51 plants received each of the following treatments: control (C), autogamy (A),

self (S), within population (I), and between populations (O) (Table 2; Dafni et al 1992, Ushimaru

and Kikuzawa 1999, Pinto-Torres and Koptur 2009). The C treatment was not bagged and the

sexual structures received no manipulation; this tested for the effect of bagging (insect visitors

were uncommon on the roof of the building where the plants were grown). The A treatment was

bagged and the sexual structures received no manipulation. This tested if the flower facilitates

self-pollination in the absence of pollinators (autogamy). In the S treatment the flower was hand-

pollinated with pollen from a different flower on the same plant (geitonogamy), to test for self-

incompatibility. In the I and O treatments the flower was pollinated with pollen either from a

different individual from within the same site (I) or from another site (O) by hand (xenogamy or

outcrossing); this assesses effects of inbreeding vs outcrossing and maximum potential seed set

among populations (Dafni et al 1992, Schoen and Lloyd 1992, Pinto-Torres and Koptur 2009).

All treatments except the C used a bag made of organza fabric to isolate the flower from

pollinators and pollen sources (Dafni et al 1992, Kearns and Inouye 1993). Because it is difficult

to isolate individual flowers in a bag, other flowers and buds in the same axil as the treated

flower were removed. Pollination was effected by using forceps to apply an open anther to a

stigma (Dafni et al 1992). After treatment, flowers were bagged again, to exclude other possible

pollen donors. Because flowers of J. sandwicensis last only one 1 day, the bag was removed the

day following the treatment to avoid any effects of the bag on fruit development. Treated

flowers were checked every other day. The developing fruit was collected when it was ripe and

easily to detached. All fruit was collected by 3/14/14.

The breeding experiment was performed in the field as well on 31 plants at MC in May

2013; they received 4 treatments: C, A, F (a modified A treatment where the flower was hand

39

Table 2. Treatments in the breeding experiment of J. sandwicensis. Each treatment includes a

description of the application performed, the implications of that treatment for the plant’s

breeding system, and the setting where this was performed in the lab or field experiments.

Treatment Application Description Tests for Lab Field

Control (C) No bag. Flower accessible to

natural pollinators.

Pollen limitation Yes Yes

Auto (A) Bagged. No hand pollination.

Flower self-pollinates without an

external agent

Autogamy – self-

pollination

Yes Yes

Facilitated

Selfing (F)

Bagged. Pollen from the flower

that also receives pollen by hand

pollination.

Self-incompatibility No Yes

Self (S) Bagged. Pollen from a different

flower of the same individual by

hand pollination.

Self-incompatibility Yes No

In (I) Bagged. Pollen from a different

individual from the same site by

hand pollination.

Seed set within a population

and inbreeding depression

Yes Yes

Out (O) Bagged. Pollen from a different

individual from a different site by

hand pollination.

Maximum potential seed set

and xenogamy or

outcrossing

Yes No

40

pollinated with its own anthers testing for self-compatibility and facilitated selfing), and I.

Individuals were selected haphazardly in the site. The I treatment involved crosses with

individuals that were approximately 5 m away, to reduce the likelhood of selfing between

different ramets of a clone. Fruit was collected by 6/2/2014.

The C treatment was also performed in the field at 3 sites (KI, MC, and BH) on June 14,

2013, testing for pollen limitation. At each site, individuals and flowers were selected at random

points. One flower on each of 40 plants at each site was tagged and left open to pollinators.

Fruits were checked every other day for 25 days. They were collected when they were ripe and

about to detach from the individual, or on the 25th

day.

The collected fruits from the lab breeding experiment, field breeding experiment, and the

control treatment at the 3 sites were stored at 20º C in wax paper envelopes in a dry environment

(Pinto-Torres and Koptur 2009). Fruit and seed set were recorded for each treatment. Fruit from

the field breeding experiment at MC was collected too early and was not tested for seed

germination. Seeds were carefully removed from the fruit capsule and scarified with a razor

blade. Each fruit’s seeds were placed on a wet paper towel in a petri dish, and placed under

continuous fluorescent light (irradiance = 85-120 µmol m-2

sec-1

) at 20º C. Every other day

seeds were moistened and dishes rearranged to avoid positional effects. After 2 weeks, seeds

with an emerged radicle or cotyledon(s) were counted as germinated (Pinto-Torres and Koptur

2009).

Pollinator Observations - I observed flower visitors to Jacquemontia sandwicensis in May and

June of 2013 at 3 of the 4 study sites, BH, KI, and MC, for a total of 30 hours of observations.

Ten individuals were observed per day of observations. The individuals were picked

haphazardly and observed for 15 minutes each. All sites and time of day (8:00 am – 5:00 pm)

were equally sampled.

When a flower visitor made contact with a flower, I recorded the species of flower

visitor, the number of flowers observed, the number of flowers visited by the flower visitor, the

duration of the visit, if the reproductive structures of the flower were touched by the visitor, and

if the visitor foraged for nectar or pollen or both. Unknown flower visitors were caught when

field identification was not possible. These were later identified by Paul Krushelnycky, Sheldon

Plentovich, and Karl Magnacca (pers comm). Each visitor approaching the observed flowers on

41

an individual was considered a new individual and a separate visit. The frequency of visits (FV)

were calculated as:

FV = (V / O) / T

The number of flowers visited (V) by a flower visitor is divided by the number of flowers

observed during an observation period (O), which is divided by the total number of hours

observed in the field (T). T was 30 hours for calculating the FV for all 3 sites, and T was 10

hours for calculating the FV for each site. The FV is the proportion of flowers visited by flower

visitors per hour (Castro-Urgal et al 2012). FVs were summed by flower visitor.

Flower abundance counts were performed at KI and MC on May 24, 2013 and BH on

May 27, 2013 to help interpret overall flower visitation rates. A transect line was placed

haphazardly through the middle of Jacquemontia habitat. Plots (2 m x 2 m) were laid out every

2 m on alternating sides of the transect and placed a random distance of 0 to 5 m off of the

transect. Each site 30 plots were laid out and the numbers of open flowers of all flowering

species were counted and recorded.

Statistics – In our study, fruit set, seeds per fruit, and germinated seeds per flower are measures

of reproductive success (note that seeds germinated per flower was not tested for field breeding

experiment due to collecting the fruit before it was ripe). To test for fruit set in the lab

experiment, I performed the Cochran-Mantel-Haenszel test. Controlling for plant individual, the

relationship between fruit production and the treatment is examined using a Cochran-Mantel-

Haenszel analysis. The median number of seeds per fruit in the lab experiment and the control

treatment at the 3 sites were tested using the Kruskal-Wallis one way analysis of variance on

ranks. Post hoc analyses were conducted using Dunn’s Method. The median number of seeds

germinated per flower was tested using the Friedman repeated measures analysis of variance on

ranks. Post hoc analyses were conducted using Tukey’s procedure. In the field breeding

experiment, seeds per flower were tested using one way repeated measures analysis of variance.

All tests were significant if p < 0.05.

RESULTS

Breeding experiments – In the lab breeding experiment, hand-pollinated plants (S, I, and O)

were about twice as likely to set fruit as unmanipulated plants, (C and A) regardless of pollen

42

source (Figure 3a). Controlling for the plant individual, a significant difference was found

between fruit production and the treatment, (χ2

1, N = 255 = 50.1818, p < 0.0001).

The seed set per fruit of hand-pollinated plants (S, I, and O) was higher than the

treatments without hand pollination in the lab breeding experiment (C and A; Figure 3b). A

statistical difference was found between median seed set per fruit and treatment (χ2

4 = 12.016, p

< 0.017), but post hoc tests did not reveal differences in pairwise multiple comparison.

Flowers from hand pollinated treatments produced about twice as many germinating

seeds as the treatments without hand pollination in the lab breeding experiment (Figure 3c).

Median seeds germinated per flower differed between treatments (χ2

4, N = 255 = 46.435, p < 0.001)

(Figure 3c). Tukey tests revealed that the C and A treatments’ seeds germinated did not differ,

the A and I treatments did not differ, and the hand pollinated treatments (S, I, and O) did not

differ. Hand pollinated treatments differed statistically from the treatments without hand

pollination.

In the field breeding experiment at MC, fruit set (Figure 4a) was higher in treatments

with vectors manipulating pollen (C, F, and I) than the treatment with no manipulation available

(A). However, mean seeds per flower in the field breeding experiment did not differ between

treatments (F 3, 30 = 1.124, p = 0.344; Figure 4b).

The C treatments’ fruit set ranged from 54% at MC to 88% at BH (Figure 5a). The

median seeds per fruit did not differ between the 3 sites (χ2

2=1.684, p=0.431; Figure 5b). Seeds

germinated per flower were similar at BH and KI, but at MC, very few seeds germinated (Figure

5c; see Discussion).

Pollinator observations - Flower visitors to J. sandwicensis were mostly bees (96%) and wasps

(4%) (Table 3). Overall, non-native pollinators, A. mellifera and Lasioglossum spp., provided

most of the flower visits (37.8% and 45.6% respectively) to J. sandwicensis. Three species of

Lasioglossum were present in and near the sites, L. imbrex, L. microlepoides, and L. impavidum

(Magnacca, pers comm). Not all Lasioglossum individuals could be distinguished in the field,

and were not collected. Other non-native pollinators included Tachysphex sp. which is the only

wasp observed, and C. smaragdula. Native pollinator Hylaeus anthracinus, was present at KI

and MC, and provided 4.2% of the total visits. Males of Hylaeus species can be identified

43

Figure 3. Lab breeding experiment (N = 51 plants). Treatments are: C=Control, no pollen

applied, open to pollinators; A=Autogamy, no pollen applied, pollinators excluded; S=Self,

pollen applied from a different flower of the same individual, pollinators excluded; I=In, pollen

applied from a different individual’s flower that was from the same site, pollinators excluded;

O=Out, pollen applied from a different individual’s flower that was from a different site,

pollinators excluded. Treatments with the same letter do not differ significantly from each other

(P, 0.05). From top to bottom, (A) Fruit set per flower, (B) Mean seed set per fruit, and (C)

Mean germinated seeds per flower and standard error. Treatments sharing the same letter (C) did

not differ statistically in median seeds germinated per flower.

0

0.2

0.4

0.6

0.8

1

fru

it p

er f

low

er

A

0

1

2

3

4

seed

s p

er f

ruit

B

0

0.5

1

1.5

2

2.5

C A S I O

germ

inat

ed s

eed

s p

er f

low

er

C

a

ab

bc

c c

44

Figure 4. Field breeding experiment (N = 31 plants). Treatments are: C=Control, no pollen

applied, open to pollinators; A=Autogamy, no pollen applied, pollinators excluded; F=Facilitated

selfing, pollen applied from within the flower to the same flower, pollinators excluded; I=In,

pollen applied from a different individual’s flower that was from the same site, pollinators

excluded. From top to bottom, (A) Fruit set per flower and (B) Mean seeds per flower and

standard error.

0

0.2

0.4

0.6

0.8

1

fru

it p

er f

low

er

A

0

0.5

1

1.5

2

2.5

C A F I

seed

s p

er f

low

er

B

45

Figure 5. Control treatment (no manipulation, open to natural pollinators) at 3 sites and results.

From an initial treatment of 40 flowers, I retrieved 39 fruits at Makapuʽu Cliff (MC), 36 at

Kaʽiwi Shore (KI), and 40 at Halona Blowhole (BH). From top to bottom, (A) Fruit set per

flower, (B) Mean seed set per fruit, and (C) Mean germinated seeds per flower and standard

error.

0

0.2

0.4

0.6

0.8

1

fru

it p

er f

low

er

A

0

1

2

3

4

seed

s p

er f

ruit

B

-0.5

0

0.5

1

1.5

MC KI BH

germ

inat

ed s

eed

s p

er f

low

er

C

46

Table 3. Pollinators at field sites and their proportions of visits to J. sandwicensis. The % of

visits for all 3 sites (V), Kaʽiwi Shore (KI), Halona Blowhole (BH), and Makapuʽu Cliff (MC).

The % of observations out of total number of observations when a flower visitor contacted the

reproductive structures (RS), collected nectar (N), or collected pollen (P). Some flower visitors

collected both pollen and nectar in a visit. The duration of the visit (V Dur) is mean seconds /

observation.

Pollinator Family V KI BH MC RS N P V Dur

Apis mellifera Apidae 37.8 53.3 0.0 67.4 13/15 14/15 0 8.9

Ceratina smaragdula Apidae 8.3 0.0 18.9 6.6 2/3 1/3 2/3 92.3

Hylaeus anthracinus Colletidae 1.0 0.0 0.0 4.1 1/1 0 1/1 60.0

Hylaeus Female Colletidae 3.2 4.0 0.0 6.6 2/3 1/3 1/3 26.7

Lassioglossum spp. Halictidae 45.6 37.6 81.1 7.0 21/27 19/27 15/27 41.3

Tachysphex sp. Crabronidae 4.0 5.1 0.0 8.3 2/3 3/3 0 12.8

47

because of facial markings, but females are indistinguishable in the field. Ants also visited J.

sandwicensis 28 times, but were removed from further analysis because they are unlikely

pollinators.

Sites varied in pollinator assemblages and in the frequencies of their visits (Table 3). The

most striking pollinator community was at the BH site because two pollinators, Lasioglossum

spp. and C. smaragdula visited J. sandwicensis, with Lasioglossum spp. providing 81.1% of the

visits. At KI, 4 species were present, but A. mellifera provided 53.3% of the visits.

Lasioglossum spp. also provided many visits, 37.6% at KI. A. mellifera provided the most visits,

67.4%, at MC.

All flower visitors were considered potential pollinators because they contacted

reproductive structures often (>67%) during observations (Table 3). Lasioglossum spp., H.

anthracinus, Hylaeus female sp., and C. smaragdula were all observed collecting pollen and

nectar, whereas A. mellifera and Tachysphex sp. were observed collecting only nectar.

Lasioglossum spp. were often covered in white pollen (assumed to be J. sandwicensis). They

often crawled over anthers and contacted the stigma. They searched the base of the flower,

presumably for nectar, and groomed in J. sandwicensis flowers. A. mellifera foraged at the base

of the flower (for nectar presumably) and accidentally contacted anthers or the stigma.

Lasioglossum spp. spent more time on a flower (mean 41.3 s/obs) than A. mellifera (mean 8.9

s/obs). Activity was throughout the day, approximately 8 AM through 4 PM

Flower abundance of J. sandwicensis and other species varied by site (Table 4). The

abundance of Jacquemontia flowers per meter squared was higher at KI and MC (2.13 and 2.32

respectively) than at BH (0.46). KI had the highest species richness (6 native species, 6 non-

native species), followed by BH (4 native species, 6 non-native species), and MC (4 native

species, 4 non-native species).

DISCUSSION

Breeding system – The breeding experiments demonstrated that J. sandwicensis has a mixed

mating system, reproducing equally well through both selfing and outcrossing. High levels of

fruit set, seed set per fruit, and seeds germinating per flower depended on pollen getting

deposited on the stigma by a pollinator. In the absence of a pollen vector, fewer fruits and seeds

48

Table 4. Summary of flowering species at sites. This describes the mean flowers available per

meter squared and flowering plant species richness per site. MC = Makapuʽu Cliff Lighthouse

Trail, KI = Kaʽiwi Shoreline, BH = Halona Blowhole, N=native, and A=alien.

Plant species Origins MC KI BH

Boerhavia repens N 1.28 4.57 0.00

Jacquemontia sandwicensis N 2.32 2.13 0.46

Myoporum sanwicense N 0.00 1.86 0.00

Scaevola taccada N 0.00 0.50 0.00

Sida fallax N 2.05 1.76 0.24

Waltheria indica N 0.18 0.12 0.18

Asystasia gangetica A 0.00 0.00 0.10

Emilia spp. A 0.00 0.34 0.15

Euphorbia hirta A 0.28 0.25 0.02

Fabaceae sp. A 0.00 0.08 0.00

Lantana camara A 0.00 0.00 0.02

Leucaena leucocephala A 0.02 0.06 0.00

Sonchus oleraceus A 0.00 0.91 0.61

Stapelia gigantea A 0.03 0.00 0.00

Tridax procumbens A 0.18 0.00 0.04

Species richness 6N, 9A 4N, 4A 6N, 6A 4N, 6A

49

were produced, indicating that while they can self, the frequency of this in the field is probably

low without pollinators. Reproductive success was independent of pollen source, suggesting that

facilitated selfing, geitonogamy, and xenogamy are all successful modes of reproduction (Lloyd

1992). High levels of fruit, seeds, and seeds germinating from S and F treatments in the lab and

field, respectively, demonstrate this species is self-compatible (Dafni et al 1992, Lloyd and

Schoen 1992). High levels of germination from within-population pollen donors suggest that

inbreeding is not limiting production of viable seeds, but a better evaluation would be growing

the progeny past germination (Charlesworth and Charlesworth 1987, Goodwillie 2005). In the

wild, J. sandwicensis needs a pollinator to handle and manipulate pollen onto a stigma,

regardless of the pollen source, for high reproductive output.

Mixed mating systems are the most prevalent in animal-pollinated plants and considered

the “best of both worlds” because they are able to outcross and self-pollinate (Lloyd 1992,

Goodwillie 2005). Autogamy could provide reproductive assurance when mates or pollinators

are scarce (Kalisz and Vogler 2003, Brys and Jacquemyn 2011), but could have costs due to

gamete and pollen discounting (Lloyd 1992) and inbreeding depression (Charlesworth and

Charlesworth 1987). Other modes of selfing that rely on pollinators, facilitated selfing and

geitonogamy, do not provide reproductive assurance (Kalisz and Vogler 2003) and may be

unavoidable by-products of selection for outcrossing success if multiple flowers are required to

attract a pollinator (Barrett 2003, Goodwillie 2005).

Although autogamy is possible in J. sandwicensis, it is certainly not as effective as pollen

getting deposited on the stigma by a pollinator (Lloyd 1992). Placement of sexual organs in a

flower can affect the mating systems in a plant, and J. sandwicensis typically has 2 different

length anthers in every flower. Similar length anthers and style could allow a pollinator to

precisely place the pollen on the stigma, but could easily lead to facilitated selfing, where

different length anther filament from the style in a flower could help prevent facilitated selfing,

but would also result in less precise pollen placement (Barrett 2002; Figure 2). J. sandwicensis

flowers typically have 3 short anthers and 2 long anthers, which could allow for outcrossing and

selfing. I did not emasculate any flowers and did not test for all types of autogamy (Schoen and

Lloyd 1992), but I suspect that wind is a possible mechanism which causes the anthers to brush

against the stigma lobes, transferring pollen in the process. The breeding experiment showed the

50

A treatment does not produce fruits as readily, as many seeds, or as many seeds that will

germinate compared to treatments with pollen being transferred by hand. The breeding system

of J. sandwicensis favors pollinators depositing pollen, but some seed set is possible without

pollinators in the community.

The field breeding experiment and C from MC, BH, and KI show that pollen limitation

did not drastically impact fruit set, seed set, or germinating seeds. The 3 sites produced fruit,

seeds, and germinating seeds. The number of germinating seeds at BH and KI and at MC from

the field breeding experiment fell within the range of germinating seeds from the treatments of

breeding experiment. This could suggest there is some pollen limitation in the wild and could

select selfing mechanisms for reproductive assurance (Goodwillie 2005). However, pollen

limitation is reported widely (Burd 1994). Hand pollination and C treatments in the field

produced higher seed set compared to the C and A treatments in the lab and A treatments in the

field breeding experiments, which were not exposed to pollinators or hand pollination. While

MC had lower fruit set and seed set per fruit than the other sites, it had extremely low seeds

germinated per flower. There were fewer pollinator visits overall in this site, but this is still

lower than lab and field treatments that received no pollen manipulation. Even if there were no

pollinators in this site, it should have produced a similar number of seeds germinated per flower

as the C and A lab and A field treatments. I suspect an environmental factor (i.e. heat or

drought) interfered with reproduction at this site (Finkelstein et al 2002, Liu et al 2004, Su et al

2013).

The breeding system of J. sandwicensis contrasts with that of the related, endangered

species from the Florida coast, J. reclinata (Pinto-Torres and Koptur 2009). In J. reclinata,

nearby individuals were assumed to be more closely related than individuals further away

(Maschinski et al 2006). In J. reclinata, reproductive success, defined as fruit set per flower,

seed set per flower, and seed set per fruit, generally increased as the degree of outcrossing

(distance from pollen donor) increased (Pinto-Torres and Koptur 2009). However, J. reclinata is

capable of producing some seeds via autogamy and geitonogamy. For J. sandwicensis,

deposition of pollen by an active vector seems to be the most important factor, and plant

relatedness has negligible effect on production of a first generation of viable seeds. The breeding

system has been evaluated for many species of Convolvulaceae. Species of Calystegia

51

(Ushimaru and Kikuzawa 1999), Convolvulus (Suarez et al 2004), Ipomoea (Devall and Thein

1992), and Merremia (Raimundez-Urrutia et al 2008) vary in self-compatibility, autogamy, and

outcrossing.

Flower visit observations - J. sandwicensis blooms throughout the year (Wagner et al 1999),

and its flowers start to open in the morning around 7 a.m. and close in early-to-late afternoon,

with most closed around 5 p.m. (pers obs). Across the 3 sites, I observed 5 potential pollinator

genera (4 bee and 1 wasp) active throughout the day (approximately 8 a.m. through 4 p.m.).

These potential pollinators all frequently contacted reproductive structures. The majority of

visits (83.4%) involved non-native bees, A. mellifera and Lasioglossum spp. One native bee, H.

anthracinus and presumably females of H. anthracinus, are potential pollinators, but had very

few visits in this study.

Although the three field sites were separated by < 3.5 km, pollinator abundance and

activity differed. At KI, I observed 4 flower visitors (A. mellifera and Lasioglossum spp.

providing many visits), frequent visits, and high numbers of flowers in the site. At MC, J.

sandwicensis had high numbers of flowers through the site, and 6 flower visitors were observed

(A. mellifera provided the most visits). Altogether these 6 flower visitors provided about half the

visitation observed at KI or BH. Only 2 flower visitors were observed frequently visiting

flowers at BH (Lasioglossum spp. dominating the visits). However, there were far fewer flowers

in this site than the others. This site also contained more non-native plants than the other two

sites.

Non-native species are potentially providing most pollination services for J. sandwicensis

at these 3 sites because of their dominating visitation rates. Hylaeus species across Hawaiʽi are

declining in abundance (Magnacca and King 2013), and they were uncommon visitors in this

study. However, they were frequent and potential pollinators to another native coastal plant,

Sida fallax, in these same sites and time period (Shay unpub). Potentially, Lasioglossum spp.

and A. mellifera could become important substitute pollinators for J. sandwicensis owing to their

frequent visits during which they contact reproductive structures. Additionally, these non-

natives were the dominant visitors at BH and KI. The C treatment from BH and KI both had

higher fruit set, seeds per flower, and seeds germinated per flower than the C and A lab

52

treatments. Assuming that most of the reproductive success is due to the dominant visitors,

Lasioglossum spp. and A. mellifera, they appear to be satisfactory pollinators for J. sandwicensis.

Carpenter bees, Xylocopa sonorina, were not recorded visiting J. sandwicensis flowers,

but were occasionally observed visiting other individuals of J. sandwicensis at KI. X. sonorina

was the only pollinator in the community that appeared to experience difficulty visiting J.

sandwicensis due to its large size preventing it from reaching the base of the flower for nectar.

Jacquemontia sandwicensis flower could not support the carpenter bees visiting and would bend

over if they visited.

The native yellow-faced bees, Hylaeus anthracinus and H. longiceps, and a variety of

non-native bees, wasps, and flies were observed visiting Jacquemontia sandwicensis at Kaʽena

Point, Oʽahu in 2008 and 2009 (Chapter 1). Lasioglossum imbrex, Ceratina smaragdula,and

Hylaeus anthracinus were the most frequent visitors. A variety of native and non-native

pollinators can visit J. sandwicensis, but most visitors are bees and wasps. J. sandwicensis’

ability to interact with a variety of pollinators, both native and non-native, agrees with Baker’s

Law (Baker 1955, Baker 1967) and plant-pollinator interactions of islands (Kaiser-Bunbury

2010b).

Jacquemontia sandwicensis population could be sustained by its ability to form

interactions with many pollinators and through occasional autogamy when mates or pollinators

are scarce (Lloyd and Schoen 1992, Goodwillie 2005). Jacquemontia sandwicensis is thought to

have colonized Hawaiʽi by fruits or seeds drifting in the ocean through the Central American

Seaway (Namoff et al 2010), before the Isthmus of Panama fully closed around 3 to 4 million

years ago (Coates and Stallard 2013). The known native pollinators, Hylaeus spp., are estimated

to have colonized Hawaiʽi 500,000-700,000 years ago (Magnacca and Danforth 2006). Prior to

the arrival of Hylaeus, J. sandwicensis would have required other pollinators or had to rely on

autogamy for reproduction by seed. The same conditions exist for the coastal Gossypium

tomentosum (Pleasants and Wendel 2010), suggesting that at least these two coastal plant species

are able to adapt to changing pollinator assemblage or can rely on their mixed mating systems to

survive.

53

Other species of Jacquemontia elsewhere are visited mostly by small to medium sized

bees. In Florida, J. reclinata was visited by 18 taxa of Hymenoptera (15 taxa of bees) (Pinto-

Torres and Koptur 2009). In Brazil, J. montana, J. nodiflora, and J. multiflora are visited by

predominantly small to medium sized bees (Silva et al 2010, Kiill and Simao-Bianchini 2011,

Kiill and Ranga 2000). Other species of Convolvulaceae also report high visitation from mostly

bees and the bee syndrome, melittophily, (Galetto and Bernardello 2004, Maimoni-Rodella and

Yanagizawa 2007, Pick and Schlindwein 2011).

Body size in bees correlates to their foraging range (Greenleaf et al 2007), which could

affect pollen flow between individuals and populations of J. sandwicensis. The observed bees in

this study were both small (Lasioglossum spp., Hylaeus females) and medium-sized bees (A.

mellifera). The small bees are predicted to move pollen within a population due to their smaller

foraging range of 150-600 m, whereas A. mellifera could move over >1 km depending on

resources in the landscape (Gathmann and Tscharntke 2002, Greenleaf et al 2007). The sites I

observed are approximately 3.5 km (BH to MC), 2.9 km (BH to KI), or 586 m (KI to MC) apart,

but the vegetation is semi-continuous through these sites and could allow for bee foraging across

sites.

Often, ants were observed visiting J. sandwicensis flowers (28/80 observed visits). Ants

were excluded from the analysis because they are unlikely pollinators (Beattie et al 1984,

McMullen 2009). Ants have been observed removing floral resources preferentially at native

Hawaiian plants due to lack of barriers or defenses against ants (Junker et al 2011). Pollinators

could also be impacted by ants due to physical interference on the flowers (Lach 2008) and by

predation and competition in the habitat (Cole et al 1992, Krushelnycky and Gillespie 2008).

CONCLUSION

J. sandwicensis, a common plant in the coastal strand habitat, has a flexible, mixed

mating system. High fruit set, seed set, and germinating seeds depend on pollen being deposited

on the stigma by an active pollinator rather than a passive vector (wind or autogamy). However,

this species still produces some seeds even in the absence of manipulation, suggesting it can

reproduce when pollinators are absent or in low abundances. In the observed sites, this plant was

visited by a variety of mostly non-native Hymenoptera (A. mellifera and Lasioglossum spp.).

54

Non-native pollinators appear to be effective pollinators for J. sandwicensis and could provide

pollination services in the face of absent or declining native pollinators.

55

APPENDIX A. NETWORK AND GROUP INDICES OF KAʽENA POINT

Network and group indices of pollinators (A) and plants (P) calculated using the bipartite 2.04

package (Dormann et al 2009) for the binary and quantitative datasets of Kaʽena Point not

reported in Chapter 1.

Index Definition (Dormann et al 2009) Binary Quantitative

Web Asymmetry Balance between numbers in the two levels:

positive values indicate more A species, negative

more P species

0.29 0.25

Links per species Mean number of links per species (qualitative):

sum of links divided by number of species.

2.8 1.6

Number of

compartments

Compartments are sub-sets which are not

connected to another compartment.

Mathematically, they are Jordan blocks.

1 1

Cluster coefficient The cluster coefficient is the average cluster

coefficients of its members, i.e. the number of

realized links divided by the number of possible

links.

0.20 0.08

Weighted

nestedness (WINE)

A nestedness version that considers interaction

frequencies. It ranges between 1 (nested) and 0

(chaotic).

0.26 0.20

Interaction strength

asymmetry

(dependence)

Dependence asymmetry is a measure of

specialization, across both trophic levels.

Positive values indicate higher dependence in the

A trophic level.

0 0.16

Specialization

asymmetry

Asymmetry (A vs. P) of specialization (based on

d’) is insensitive to the dimensions of the web.

Can be weighted by abundance or d' values log

transformed. Positive values indicate a higher

specialization of the A trophic level.

-0.33 -0.12

56

Appendix A. (continued) Network and group indices of Kaʽena Point.

Linkage density Marginal totals-weighted diversity of

interactions per species (quantitative), equivalent

to the average of generality of A and P.

8.4 2.6

Weighted

connectance

Linkage density divided by A + P. This will

respond to whether non-interacting species are

included or not.

0.20 0.08

Shannon diversity Shannon’s diversity of interactions. 4.8 2.9

Alatalo interaction

evenness

A different measure for web entry evenness. 1 0.52

Mean no. shared

partners A

Mean number of partners shared among A. 1.4 0.6

Mean no. shared

partners P

Mean number of partners shared among P. 3.7 1.6

Cluster coefficient

A

Cluster coefficient for A. 0.50 0.36

Cluster coefficient

P

Cluster coefficient for P. 0.34 0.20

Weighted cluster

coefficient A

Weighted version uses interactions as weights

unless the data are binary.

0.96 0.63

Weighted cluster

coefficient P

Weighted version uses interactions as weights

unless the data are binary.

0.75 0.34

Niche overlap A Mean similarity in interaction pattern between

pollinators, calculated as Horn’s index. Values

near 0 indicate no common use of niches, 1

indicates perfect niche overlap.

0.24 0.11

Niche overlap P Mean similarity in interaction pattern between

plants, calculated as Horn’s index. Values near 0

indicate no common use of niches, 1 indicates

perfect niche overlap.

0.44 0.24

57

Appendix A (continued) Network and group indices of Kaʽena Point.

Togetherness A Mean number of co-occupancies across all

species-combinations; the whole matrix is

scanned for submatrices of the form (0, 0, 1, 1),

representing perfect matches of co-presences and

co-absences.

0.11 0.07

Togetherness P Mean number of co-occupancies across all

species-combinations; the whole matrix is

scanned for submatrices of the form (0, 0, 1, 1),

representing perfect matches of co-presences and

co-absences.

0.28 0.21

C score A Mean number of checkerboard combinations

across pollinators. Values close to 1 indicate that

there is evidence for disaggregation. Values

close to 0 indicate aggregation of pollinators.

0.52 0.64

C score P Mean number of checkerboard combinations

across plants. Values close to 1 indicate that

there is evidence for disaggregation. Values

close to 0 indicate aggregation of plants.

0.28 0.39

V ratio A Variance-ratio of species numbers to interaction

numbers within A. Values larger than 1 indicate

positive aggregation, values between 0 and 1

indicate disaggregation of pollinators.

4.72 3.45

V ratio P Variance-ratio of species numbers to interaction

numbers within P. Values larger than 1 indicate

positive aggregation, values between 0 and 1

indicate disaggregation of plants.

2.54 1.51

58

Appendix A (continued) Network and group indices of Kaʽena Point.

Discrepancy A Nestedness measure that first sorts the matrix by

marginal totals. Then, A interactions are

maximally compacted, yielding P. Discrepancy

is the number of disagreements of A.

38 20

Discrepancy P Nestedness measure that first sorts the matrix by

marginal totals. Then, A interactions are

maximally compacted, yielding P. Discrepancy

is the number of disagreements of P.

40 25

Extinction slope A Slope of the secondary extinction sequence in A,

following extermination of species in P.

3.27 1.58

Extinction slope P Slope of the secondary extinction sequence in P,

following extermination of species in A.

7.32 3.67

Robustness A Calculates the area below the secondary

extinction curve.

0.76 0.61

Robustness P Calculates the area below the secondary

extinction curve.

0.87 0.78

Functional

complementarity A

Functional complementarity measures of niche

complementarity as the total branch length of a

“functional dendrogram” based on qualitative

differences of interactions of one level with the

other.

47.4 25108

Functional

complementarity P

Functional complementarity measures of niche

complementarity as the total branch length of a

“functional dendrogram” based on qualitative

differences of interactions of one level with the

other.

39.4 26280

Partner diversity A (Weighted) mean Shannon diversity of the

number of interactions for the species of A.

1.8 0.66

Partner diversity P (Weighted) mean Shannon diversity of the

number of interactions for the species of P.

2.2 0.97

59

APPENDIX B. 2009 QUANTITATIVE MATRIX OF KAʽENA POINT

Las

im

b

Hyl

spp

Cer

sm

a

Pro

mig

Eulo

sp

Dip

t 2

Pol

aur

Lam

boe

Coc

lar

Tox m

ar

Cha

mon

Cer

ari

Tac

h s

p

Meg

a sp

Arc

cir

Chry

sp

Sco

l sp

Dip

t 1

Dip

t 3

Nysi

sp

Jac

san

414.4

130.6

7

521.6

104.6

1

281.6

67.2

0

0

0

0

0

0

0

0

0

0

0

0

30.4

30.4

Mel

int

816.6

7

6.8

0

560

0

0

0

0

0

579.6

0

0

278

0

0

100.6

7

0

0

0

0

Sca

tac

170.1

8

694.0

6

944

53.3

3

0

0

0

0

0

0

0

0

0

188.8

0

0

53.3

3

0

0

0

Sid

fal

47.2

26.6

7

0

113

0

0

0

0

1482.6

7

0

554.6

7

0

0

0

0

0

0

0

0

0

Vit

rot

336

0

171.9

5

179.2

0

0

0

144.5

2

0

0

0

385.7

8

0

0

0

0

0

0

0

0

Wal

ind

100

0

96.4

3

0

42.8

6

0

150

0

0

0

0

0

0

0

128.5

7

0

0

0

0

0

Ses

tom

0

800

272.4

4

0

0

0

480

298.6

7

0

0

0

0

0

0

0

0

0

0

0

0

Hel

ano

49.3

3

0

16.7

3

29.6

6

0

0

0

0

0

0

0

0

0

0

0

0

0

52

0

0

Myo s

an

0

3850.6

7

512

0

0

7530.6

7

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Boe

rep

264

0

0

552.8

9

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Sca

cor

33.5

8

34.1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Cus

san

0

0

0

0

2214

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

60

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