impacts of exotic species to foodweb structure of hawaiian streams richard a. mackenzie, tara...
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Impacts of exotic species to foodweb structure of Hawaiian streams
Richard A. MacKenzie, Tara Holitzki, Karla McDermid
Research objectivesTo document how poeciliids are affecting Hawaiian streams.
We hypothesized that high densities of omnivorous poeciliids would:H1. shift food resources available for native gobiesH2. shift trophic position of native gobies
Study site
1. Substrate2. Riparian canopy3. Watershed4. Land use5. Elevation6. Stream width
• Collected samples for d13C, d15N, dD
1) Leaf litter2) Algae (epilithon scrapes)3) Invertebrates (surber)4) L. concolor and P. reticulata
(dipnets)
METHODS
13C (‰)
-26 -24 -22 -20 -18 -16 -14
1
5N
(‰
)
2
4
6
8
ChironomidaeC. analisL. concolor
13C (‰)
-26 -24 -22 -20 -18 -16 -14
1
5N
(‰
)
2
4
6
8
ChironomidaeC. analis (Green)C. analis (Brown)
Dugesia sp. Col 25 vs Col 26 L. concolor
Multiple food resources
Chironomid
C. analis (G)
C. analis (B)
Dugesia
Per
cen
t co
ntr
ibu
tio
n
0
20
40
60
80
100Gobies in poeciliid-free streamsGobies in poeciliid-invaded streams
*
A
MacKenzie et al. in review
FCL INV
Chiron
omid
C. ana
lis (G
)
C. ana
lis (B
)
Duges
ia
Per
cen
t co
ntr
ibu
tio
n
0
20
40
60
80
100Exotic poeciliids in poeciliid-invaded streamsNative gobies in poeciliid-invaded streams
B
*
MacKenzie et al. in review
41-44%36-56%
41-44%36-56%
93% 68%32%
???%
Trophic position of L. concolor
Trophic positionconsumer = (d15Nconsumer – d15Nbaseline)/3.4 + 2
Vander Zanden et al. 1999
Poeciliid-free Poeciliid-invaded
Fo
od
Ch
ain
Len
gth
0
1
2
3
4p < 0.05
Conclusions1. Invasion of Hawaiian streams by exotic poeciliids are
altering food web structure of native stream fish by shifting food resources from high (i.e., Chironomidae) to low quality food sources (i.e., Cheumatopsyche analis)
2. Trophic position of L. concolor decreased by 1/2 trophic lengthin poeciliid-invaded streams
3. The introduction of exotic invertebrates to Hawaiian streams (i.e., C. analis) may be altering food web structure by shifting basal food resources (e.g., increased importance of leaf litter)
Impacts of exotic species to foodweb structure of Hawaiian anchialine ponds
Bruce Dudley, Richard A. MacKenzie, Troy Sakihara
kiawe native veg.
open (no fish)
open (fish)
Anchialine pool food web
D (‰)
-220 -200 -180 -160 -140 -120 -100
1
3C
(‰
)
-26
-24
-22
-20
-18
-16
-14
-12
-10
kiawemiloopen (no fish)open (fish)
algae
algae
leaflitter
leaflitter
Chironomidae65%
Diptera15%
JV Atyids12%
Larval Atyids5%
C. analis3%
Lentipes concolor gut content
Hawai‘i
Oahu
D (‰)
-170 -160 -150 -140 -130 -120 -110 -100 -90
15N
(‰
)
3
4
5
6
7
8
9
10 Midge fly (chironomid)
Caddisfly
L. concolor (non-invaded stream)
MacKenzie et al. in review
D (‰)
-170 -160 -150 -140 -130 -120 -110 -100 -90
15N
(‰
)
3
4
5
6
7
8
9
10 Midge fly (chironomid)CaddisflyL. concolor (invaded stream)L. concolor (non-invaded stream)P. reticulata
MacKenzie et al. in review
Trophic positionconsumer = (d15Nconsumer – d15Nbaseline)/3.4 + 2
• Calculated percent contributions to diets using ISOSOURCE (Phillips and Gregg 2003)
• Calculated trophic position (Vander Zanden et al. 1999)
METHODSMETHODS
Invasive taxa in Pearl Harbor
No.
Aquatic insects 49
Crustaceans 5
Mollusks 10
Amphibians 3
Fish 18
Cheumatopsyche analisProcambrus clarkii
Pomacea canaliculata
Englund 2002
Rana catesbeiana
Bufo marinus
Sarotherodon melanochromis
Gambusia affinis
40%
60%
80%20%
Vander Zanden et al. 1999
13C (‰)
-26 -24 -22 -20 -18 -16 -14
1
5N
(‰
)
2
4
6
8
ChironomidaeC. analis
13C (‰)
-26 -24 -22 -20 -18 -16 -14
1
5N
(‰
)
2
4
6
8
ChironomidaeC. analisL. concolor
13C
-26 -24 -22 -20 -18 -16 -14
1
5N
(‰
)
2
4
6
8
ChironomidaeC. analisL. concolor