the wallace line - university of wisconsin–madisonflora going south to refugias — extinction of...

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The Wallace LineAlfred Wallace, one of the premier zoobiogeographers, wrote the definitivetreatise “Distributions of Animals” in 1876 where he summarized the knowndistributions and causes of their biogeographical patterns

Alfred Wallace’s main interest was in the vertebrate fauna of the Indo-MalayArchipelago from Asia to Australia where he clearly saw a sharp faunistic break

Wallace’s trips

Sclater’s & Wallace’sfaunistic regions

Probably his mostimportant trip he evermade was a 6 km ferryride from Bali to Lombok

The Wallace Line

“In the archipelago . . . there are two distinct faunas rigidly circumscribed,which differ as much as those of South America and Africa, and more than thoseof Europe and North America” [Letter to Henry Bates in London (1858)]

Sclater’s & Wallace’sfaunistic regions

Wallace’s trips

The Wallace Line

“The boundary line often passes between islands closer than others in the samegroup. I believe the western part to be a separated portion of continental Asia,the eastern the fragmentary prolongation of a former Pacific continent”

Looking east from Bali across 6 km Lombok Straits

“In the archipelago . . . there are two distinct faunas rigidly circumscribed,which differ as much as those of South America and Africa, and more than thoseof Europe and North America” [Letter to Henry Bates in London (1858)]

The Wallace Line

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Cover plate from Distributions of Animals

Wallace graphically depicts what has since been termed the “Wallace Line”in his book by showing birds and mammals that are found in the Oriental(Borneo, left) and Australian (New Guinea, right) sides

tarsier tree kangaroo

tree shrew

tapir

lory

raquet-tailedkingfisher

Oriental Fauna Australian Fauna

The Wallace Line

• Wallace Line — the imaginary lineseparating the Oriental andAustralian biotas — extends betweenBali and Lombok and betweenBorneo/Philippines and Sulawesi

• Several other lines have beenproposed in the region based onparticular groups of animals orplants.

• Main issue with most lines is whatdo with Sulawesi (Celebes)

The Wallace Line

Crested blackmacaque

Bear cuscus(marsupial)

Backboneof Sulawesi

Sulawesi, with its mixture of Oriental and Australian fauna, was so perplexing toWallace, that he vacillated back and forth on where to place the island

The Wallace Line

Now know that the two regions are different continental plates that have been movingindependently — the Asian and Australian plates

The IndoMalay - New GuineaArchipelago area includes islandgroups mostly confined to either oftwo continental shelves:

Sunda shelf — Asian

Sahul shelf — Australian

The Wallace Line

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Stewartia sinensis

Stewartia malacodendronTheaceae - tea family

Stewartia pseudocamellia

Eastern North America andEastern Asia is the“classic” north temperatedisjunction pattern

Eastern North America - Eastern Asia

This disjunct pattern, also seen in animals, was one of the original repeatedpatterns that led Rosen, Nelson, and Platnick to formulate cladisticbiogeography

They interpreted such a repeated pattern as due to vicariance (erection ofbarrier in once continual biota)


Floristic connection between the two areas is strong at the generic level

Impression of a biological connection has been strengthened by similarities inclimate and ecology or ecological biogeography


First disjunction recognized by botanical biogeographers and thus played an

important role in Darwin’s evidence for evolution

Pattern also involves fossil taxa from the Tertiary (back to about 40 mya), and thushas been termed the Arcto-Tertiary Flora


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Credit for the recognition of the floristic similarities often given to Asa Gray

(Harvard University), but the first published reference was in a thesis by Linnaeus’student Jona Halenius (1750)

Pattern first noticed by a Jesuit priest, Father Joseph Lafitau, who found Americanginseng (1716) near Montreal after reading description of the Chinese ginseng


Caulophyllum robustum

Caulophyllum thalictroidesBlue cohosh - Berberidaceae

Four quick points (reviewed in Jun Wen’s 1999 paper in Ann Rev Ecol Syst)

1. Pattern originally thought to include “identical species” (Gray listed 134) butnow believed to be largely congeneric not conspecific. By 1992 the list includedonly 8 conspecific examples, and by 1999 only 1.




Mitchella repensPartridge-berry, Rubiaceae

Mitchella undulata




Symplocarpus renifolius

Symplocarpus foetidusSkunk cabbage, Araceae


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Phryma leptostachya var. asiatica

Phryma leptostachya var. leptostachyaLopseed, Verbenaceae



2. Up to 120 genera of plants have been cited as exhibiting this pattern. Ifremove genera (like blue beech) with western North American or westernEuropean distributions as well, then 65 genera in 42 different families involved

Carpinus carolinianaAmerican hornbeam, blue beech

Betulaceae

Carpinus betulusEurope


Liriodendron tulipferaTulip tree, Magnoliaceae

Liriodendron chinense


2. . . . and included in the 65 genera are trees

1 sp. E. Asia vs. 1 sp. E. North America


Hamamelis virginianaWitch hazel, Hamamelidaceae

Hamamelis mollis


2. . . . and included in the 65 genera are trees

2 spp. E. Asia vs. 2 spp. E. North America


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Parthenocissus quinquefoliaVirgnia creeper, woodbine, Vitaceae


Parthenocissus heneryana

2. . . . and included in the 65 genera are vines

9 spp. E. Asia vs. 3 spp. E. North America


Campsis radicansTrumpet creeper, Bignoniaceae

Campsis sp.


2. . . . and included in the 65 genera are vines



Jeffersonia diphyllaTwinleaf, Berberidaceae

Jeffersonia dubia


2. . . . and included in the 65 genera are herbs



Podophyllum peltatumMayapple, BerberidaceaePodophyllum hexandra





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Nelumbo luteaLotus lily, Nelumbonaceae

Nelumbo nucifera





Sanguinaria canadensisBloodroot, Papaveraceae

Eomecon chionantha


3. In few cases, the disjunction involves different but closely related genera


Diervilla splendensBush honeysuckle, Caprifoliaceae

Weigela florida

3. In few cases, the disjunction involves different but closely related genera



4. The disjunction typically involves E. North America and E. Asia . . .



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4. . . . but can involve western North America . . .


Clintonia, bead lily


4. . . . and central Asia/Europe


The European plane tree is a hybrid betweenthe eastern North American and centralAsian sycamores - Platanus x hybrida - andis more tolerant to urbanization


Ginkgo, now confined to east-central China, had a wide Holarctic distribution from thePaleocene into the Neogene as indicated by fossil localities ()

Fossil evidence indicates widespread Arcto-Tertiary Flora existed with subsequentextinction in many portions of this range:


Pseudotsuga (Douglas fir) is widespread today in western North America but has only relictualstands (+) in eastern Asia. Fossil localities () indicate its wider distribution in the past.



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Sequoia, now confined to coastal California and adjacent Oregon, had a Holarctic Tertiarydistribution as indicated by some of its fossil sites ().


Eastern North America - Eastern AsiaSummary: Tertiary, as well as present day distributions, indicate that a widespreadArcto-Tertiary or Holarctic Flora existed, especially during 25-3 mya, throughoutthe entire North Temperate region, and facilitated by Bering and North Atlantic landbridges. Why not present today?

1. Climate deterioration during endof Tertiary and into the Pleistocene

2. Mountain building in w. NorthAmerica, grassland formation, andextinction of forest species

3. Glaciation effects most severe inwestern Europe where E-Wmountain chains prevented forestflora going south to refugias —extinction of forest species

Ginkgo - Tertiary

Stewartia - today


General interpretation is that the Arcto-Tertiary Flora (and Fauna) was awidespread biota that got fragmented by various events — vicariance

Summary: Tertiary, as well as present day distributions, indicate that a widespreadArcto-Tertiary or Holarctic Flora existed, especially during 25-3 mya, throughoutthe entire North Temperate region, and facilitated by Bering and North Atlantic landbridges. Why not present today?


Aralia spinosaDevil’s walking stick, Araliaceae

New Twists - Molecular Systematics

Phylogenetic analyses of 11 putative pairs of vicariad species - are they sister species?

Aralia — NO


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Hamamelis — NO


HamamelisWitch hazel, Hamamelidaceae



Gledistsia — NO


GleditsiaHoney locust, Fabaceae



Panax — NO


Panax quinquefoliusAmerican ginseng, Araliaceae


Nyssa sylvatica - sour gum,black gum,black tupelo


Nyssa — +/-



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Symplocarpus — YES


Symplocarpus renifolius

Symplocarpus foetidus, skunk cabbage


Molecular clocks - when did the species diverge and at same time?


1. Liriodendron - tulip trees

13 mya

2. Magnolia - magnolias

2 mya

3. Campsis - trumpet creepers

25 mya



from reading!

Recent analysis of 100 examples of disjunctions (33 with absolute timedivergences) among these four areas provides some new insights on theHolarctic Flora

Eastern North America - Eastern AsiaNew Twists - Molecular Systematics

animalsplants

% of examples showing various disjunct patterns

1. Plants show considerably higher proportion of Eastern Asia - Eastern NorthAmerica disjunct pattern than do animals


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animalsplants

% of examples showing various disjunct patterns

2. Plants show considerably lower proportion of Western North America -Eastern North America disjunct pattern than do animals

1. Plants show considerably higher proportion of Eastern Asia - Eastern NorthAmerica disjunct pattern than do animals

Eastern North America - Eastern AsiaNew Twists - Molecular Systematics

Arrows indicate inferreddirections of dispersal

3. Eastern Asia is source of 20 of the disjuncts, andEastern North America only 1. These dispersalevents occurred over the last 30 my and withBeringia the likely route.


Summary: Tertiary, as well as present day distributions, indicate that a widespreadArcto-Tertiary or Holarctic Flora existed, especially during 25-3 mya, throughoutthe entire North Temperate region, and facilitated by Bering and North Atlantic landbridges. Is vicariance a mechanism for the repeated pattern?

• Vicariad species recognized on morphological similarity are not necessarilysister species using phylogenetics.

• The large range in estimated time splits for vicariad species indicates thatvicariance alone is not an adequate explanation.

• Dispersal and speciation did not all occur at the same time in all groups.


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