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Lab 10 Island Biogeography

Lab 10 Island Biogeography - ISLAND BIOGEOGRAPHY Lab 10...

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ISLAND BIOGEOGRAPHY Lab 10 10-1 Reminders! Bring memory stick or floppy disc I. BIOGEOGRAPHY Biogeography is the study of the spatial and geographical distribution of organisms. The central question of biogeography is, “Why do we find these organisms at this location?” The answer to this question includes both large scale answers (the community of species found at a given location is a function of the species pool from the larger surrounding region) and small scale answers (local competition and habitat conditions determine community composition), as well as, both historical (the community composition is a function of species and conditions that were there previously) and modern answers (the community composition is strictly a function of recent processes). When discussing the composition of a community, we can analyze it at many taxonomic levels ( e.g. genus, family, etc.), not just at the species level. Biogeography also deals with functional questions of why certain areas tend to have similar or different communities. For instance, Figure 1 shows desert habitats from very distant locations in Asia and North America. Despite very different geographical locations, they support very similar communities of organisms. Similarly, the organisms within those communities may be very distantly related, but show convergent evolution toward a similar ecological role. For example, the recently extinct Tasmanian wolf (Figure 2) was a predatory animal very similar to North American and Eurasian wolves. However, it is a marsupial and is more closely related to kangaroos than wolves (yep, it’s got a pouch and everything). Figure 1. Desert grasslands from the Gobi Desert in Asia and the Chihuahuan desert in New Mexico. Can you tell which one is which? Figure 2. The Tasmanian wolf is more closely related to a kangaroo than a wolf.
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Laboratory 10 Island Biogeography 10-2 II. ISLAND BIOGEOGRAPHY The theory of island biogeography was developed by Robert MacArthur and Edward O. Wilson in 1967. Many early naturalists, including from Captain Cook’s voyage, noticed a relationship between the size of an island and the number of species it supports ( species richness ), with larger islands supporting more species. In the Galapagos Islands, MacArthur and Wilson documented a similar pattern (Figure 3). This trend is true not just for plants in the Galapagos, but also for bird species in Hawaii, bat species in the Caribbean, amphibians and reptiles in the West Indies, and others. Figure 3. The relationship between island size and the number of plant species. (Image from Campbell and Reece 2005). In MacArthur and Wilson’s view, the number of species on an island is a dynamic equilibrium between immigration and extinction rates. The balance between the number of new species arriving and the number of species going extinct on the island will determine the equilibrium number of species on the island. This is called a dynamic equilibrium because the composition of species on the island might change over time, but
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