Herpetology - An Introductory Biology of Amphibians and Reptiles by Laurie J. Vitt Janalee P. Caldwell

Author:Laurie J. Vitt, Janalee P. Caldwell [Caldwell, Laurie J. Vitt, Janalee P.]
Language: eng
Format: epub, pdf
Tags: gnv64
Published: 2011-03-22T16:30:04+00:00

Chapter | 13 Biogeography and Phylogeography

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Tectonics

Australia

Gaffney

Seddon et al.

Georges et al.

FIGURE 13.8 Comparison of phylogenetic relationships of chelid turtles and their distributions to the tectonics of southern continents. Unfortunately, the most recent cladogram (far right) fails to falsify either of the earlier hypotheses because Chelodina, South American chelids, and remaining Australian chelids form an unresolved polytomy. Cladograms adapted from Gaffney, 1977; Seddon et al., 1997; and Georges et al., 1998.

The Seychelles and chelid examples highlight the neces-

been presented to account for this high diversity. One,

sity of a pluralist approach to biogeographic analysis and of

the Vanishing Refuge Theory (often referred to as the

the need to provide explanations (hypotheses) that can be

Climatic Disturbance Hypothesis), which was originally

tested. Multiple levels of interpretations are likely required

applied to birds and lizards, has received considerable

for the patterns of most herpetofaunas and their component

attention. This hypothesis basically posits that environ-

species. We now examine a subset of the recent analyses that

mental fluctuations during the Pleistocene (2 million to

address questions of historical biogeography of amphibians

10 thousand years before present) resulted in repeated

and reptiles. Each of these provides new insights into old

expansions and contractions of rain forest, resulting in

questions, and each raises additional questions.

repeated isolation of faunas and resultant speciation. Pol-

len profiles from Pleistocene deposits indicate that the rain

forest was both more and less extensive in the past. Other

Recovering History: Phylogenetic

hypotheses include (1) the Riverine Barrier Hypothesis,

Approaches to Biogeography

which suggests that the large rivers in the Amazon basin

were distribution barriers for species living in terra firma

Prior to the use of dated phylogenies, biogeographic scenar-

forest, thus restricting gene flow resulting in divergence

ios were, for the most part, storytelling. The fossils existed,

across rivers; (2) the Ecological Gradients Hypothesis,

present-day distributions existed, and information on his-

which suggests that habitat gradients (e.g., temperature,

toric distribution of continents existed. What was missing

moisture) can serve as sufficient barriers to restrict gene

was the ability to independently date divergence patterns

flow; (3) the Historic Mountain Ridge Hypothesis, in

in taxonomic groups of interest. To put it another way, dis-

which mountain ranges (the Andes in particular) were

tributional histories were simply fitted to the movement of

barriers; and (4) the Marine Incursion Hypothesis, in which

continents. Dated phylogenies have changed that line of

influx of saltwater produced barriers. The lizard example

thinking dramatically, and as previously indicated, histori-

forming the basis for the Vanishing Refuge Theory

cal biogeography has transformed into phylogeography

was the Anolis nitens (formerly chrysolepis) complex. At

with the ability to explicitly test hypotheses. Rather than

the time that this was proposed by Paulo Vanzolini and

summarizing everything that is known about biogeography

Ernest Williams, four subspecies of A. nitens were recogn-

of amphibians and reptiles, we have selected a set of studies

ized, and for the most part, these rain forest lizards had

that make specific points about the process of distributional

nonoverlapping distributions. One subspecies, A. n. brasi-

histories and diversification. We refer the interested reader

liensis, was known from only a few isolated patches of dry

to other sources for detailed and more complete summaries

forest south of the Amazon Basin, and these patches were

of the biogeography of amphibians and reptiles.

believed to be remnants of a once much more wide-

spread Amazon rain forest.

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