Information about Zoogeography
Zoogeography is the branch of the science of biogeography that is concerned with the geographic distribution of animal species and their attributes. That makes Zoogeography the study of patterns of biodiversity regarding time and space.
Green turtles live in tropical oceans worldwide. Ascension Island's rookery is located on the mid-Atlantic ridge between Brazil and Liberia near west Africa. Their feeding grounds are around the coastal areas of South America, and their females lay eggs on South American beaches.
With a distance of around 2000km (1242mi) from the main body of the range, how did the turtles establish a colony on Ascension Island that is so isolated?
Dispersal hypothesis: these animals make very long distance migrations of up to 5,000 km (3,106mi) between feeding and nesting areas and dispersed from South America to Ascension Island.
Vicariance hypothesis: aka the "Carr-Coleman" hypothesis after two long term investigators of turtle biology. Hypothesis suggests that ancestors of Ascension Island turtles nested on beaches of islands adjacent to S.A. coast throughout the late Cretaceous (135-65 mya).
Over the last 70 my, these islands have been displaced by "sea-floor spreading" (2 cm/year). This, coupled with the natal homing ability of turtles, resulted in the present colony on Ascension Island.
Q: How can zoogeographic investigation provide a test to distinguish these hypothesis? Dispersal and vicariance hypotheses are part of an age-old divide in zoogeographic inference (more on that later!). What predictions do the two hypotheses make that can be used to distinguish between them by collecting data?
A: One approach was taken by Bowen et al. (1992) who used molecular assays (mitochondrial DNA) to address this problem. They reasoned that the "vicariant hypothesis" implies that the Ascension and S.A. rookeries have been largely isolated over 70 million years and that such long term isolation should result in major genetic differences between the rookeries.
By contrast, the dispersal hypothesis predicts very recent contact between the S.A. and Ascension Island rookeries (perhaps even to the present day) and hence little long term evolutionary isolation and consequently there should be little genetic divergence between the rookeries.
What was the result? In a nutshell, sequence divergence estimates between Ascension Island and S.A. rookeries were VERY low (about 0.2% sequence divergence). Most "haplotypes" were identical (i.e. shared) between the two rookery areas which suggested that the rookeries had only been isolated for only a very short time (less than 1 million years) and that this isolation was incomplete (there was current dispersal between Brazil and Ascension Island rookeries).
The shallow genetic divergence (contrasted with a major split at about 0.7% divergence between Atlantic and Pacific groups of C. mydas) was inconsistent with long term isolation predicted by the vicariance hypothesis. These results, coupled with ecological knowledge of the dispersal capabilities of green turtles strongly suggest that the dispersal hypothesis for the origin of the Ascension Island rookery is correct.
2. Avise, J.C. 1994. Molecular markers, natural history and evolution. Chapman and Hall. Pp. 224-226.
3. Bowen, B.W. et al. 1992. Global population structure and natural history of the green turtle (Chelonia mydas) in terms of matriarchial phylogeny. Evolution 46: 865-881.
Overview
Zoogeography is the study of the patterns of the past, present, and future distribution of animals (and their attributes) in nature and the processes that regulate these distributions, and it’s the scientific analysis of the patterns of biodiversity regarding time and space. Zoogeography integrates information on the historical and current ecology, genetics, and physiology of organisms and their interaction with environmental processes (continental drift, climate) in regulating geographic distributions of animals. Scientists use descriptive and analytical approaches useful in hypothesis testing in zoogeography and which illustrates the applied aspects of zoogeography (e.g. refuge design in conservation).Branches of Zoogeography
Zoogeography is often divided into two main branches: Ecological Zoogeography and Historical Zoogeography. The former investigates the role of current day biotic and abiotic interactions in influencing animal distributions; the latter are concerned with historical reconstruction of the origin, dispersal, and extinction of taxa.Branches of Biology relevant to Zoogeography
It’s part of a more general science known as biogeography. Phytogeographers are concerned with patterns and process in plant distribution. Most of the major questions and kinds of approaches taken to answer such questions are held in common between phyto- and zoogeographers.Case Study
Green sea turtles (Chelonia mydas) on Ascension Island – dispersal or vicariance?)
A Hawaiian Green Sea Turtle
Green turtles live in tropical oceans worldwide. Ascension Island's rookery is located on the mid-Atlantic ridge between Brazil and Liberia near west Africa. Their feeding grounds are around the coastal areas of South America, and their females lay eggs on South American beaches.
With a distance of around 2000km (1242mi) from the main body of the range, how did the turtles establish a colony on Ascension Island that is so isolated?
Dispersal hypothesis: these animals make very long distance migrations of up to 5,000 km (3,106mi) between feeding and nesting areas and dispersed from South America to Ascension Island.
Vicariance hypothesis: aka the "Carr-Coleman" hypothesis after two long term investigators of turtle biology. Hypothesis suggests that ancestors of Ascension Island turtles nested on beaches of islands adjacent to S.A. coast throughout the late Cretaceous (135-65 mya).
Over the last 70 my, these islands have been displaced by "sea-floor spreading" (2 cm/year). This, coupled with the natal homing ability of turtles, resulted in the present colony on Ascension Island.
Q: How can zoogeographic investigation provide a test to distinguish these hypothesis? Dispersal and vicariance hypotheses are part of an age-old divide in zoogeographic inference (more on that later!). What predictions do the two hypotheses make that can be used to distinguish between them by collecting data?
A: One approach was taken by Bowen et al. (1992) who used molecular assays (mitochondrial DNA) to address this problem. They reasoned that the "vicariant hypothesis" implies that the Ascension and S.A. rookeries have been largely isolated over 70 million years and that such long term isolation should result in major genetic differences between the rookeries.
By contrast, the dispersal hypothesis predicts very recent contact between the S.A. and Ascension Island rookeries (perhaps even to the present day) and hence little long term evolutionary isolation and consequently there should be little genetic divergence between the rookeries.
What was the result? In a nutshell, sequence divergence estimates between Ascension Island and S.A. rookeries were VERY low (about 0.2% sequence divergence). Most "haplotypes" were identical (i.e. shared) between the two rookery areas which suggested that the rookeries had only been isolated for only a very short time (less than 1 million years) and that this isolation was incomplete (there was current dispersal between Brazil and Ascension Island rookeries).
The shallow genetic divergence (contrasted with a major split at about 0.7% divergence between Atlantic and Pacific groups of C. mydas) was inconsistent with long term isolation predicted by the vicariance hypothesis. These results, coupled with ecological knowledge of the dispersal capabilities of green turtles strongly suggest that the dispersal hypothesis for the origin of the Ascension Island rookery is correct.
See also
References
1. Brown, J.H. & Lomolino, M.V. 1998. Biogeography. 2nd edition. Chapter 1.2. Avise, J.C. 1994. Molecular markers, natural history and evolution. Chapman and Hall. Pp. 224-226.
3. Bowen, B.W. et al. 1992. Global population structure and natural history of the green turtle (Chelonia mydas) in terms of matriarchial phylogeny. Evolution 46: 865-881.
- Introduction to Zoogeography by Dr. Eric B. (Rick) Taylor, Department of Zoology, University of British Columbia
External links
Resources for students of Zoogeography
- Biology 413: A course outline and collection of Web resources by Dr. Taylor, UBC
Biogeography is the study of the distribution of biodiversity over space and time. It aims to reveal where organisms live, at what abundance, and why.[1]
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species is one of the basic units of biological classification. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring.
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Chelonia
Latreille in Sonnini & Latreille, 1802
Species: C. mydas
Binomial name
Chelonia mydas
(Linnaeus, 1758)
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Latreille in Sonnini & Latreille, 1802
Species: C. mydas
Binomial name
Chelonia mydas
(Linnaeus, 1758)
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Phytogeography is the branch of biogeography that is concerned with the geographic distribution of plant species, or more generally, plants. Phytogeography is concerned with all aspects of plant distribution, from the controls on the distribution of individual species ranges to the
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Biogeography is the study of the distribution of biodiversity over space and time. It aims to reveal where organisms live, at what abundance, and why.[1]
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Zoology (from Greek: ζῴον, zoion, "animal"; and λόγος, logos, "knowledge") is the biological discipline which involves the study of animals.
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