Species Distribution and Biogeography

Biogeography is the study of the distribution of organisms across geographic space, and the processes that shape these distributions. Broadly speaking, the theory of biogeography states that any species present in a specific location either evolved there or moved there from a different location. If the latter is true, when these colonizers arrive at their new location, characteristics of the environment like food availability, and interactions with other species will decide whether they establish a new population or perish.

The theory of Island Biogeography was formulated in 1967, by Edward O. Wilson and Robert MacArthur. It's based on the assumption that the number of species at any given site, is determined by the colonization and extinction rates. The theory is called Island Biogeography, because it was first used to explain the variations in a number of species on oceanic islands. But Island Biogeography theory can also be applied to city species distribution in many other non-continuous habitat types, such as forests fragmented by agriculture.

One major prediction of Island Biogeography theory is that islands closer to the mainland will have a greater colonization rate, than islands that are further away. This makes a lot of sense. If an island is far away from the mainland, it's hard for organisms to physically travel there. Secondly, larger islands will typically be able to support more species than smaller islands. Additionally, with the increasing size of islands the extinction risk of a species would decrease, because larger islands can support larger, more robust populations of any individual species, like this booming colony of bunnies. On the other hand, the extinction rate increases as more and more distinct species coexist on an island, and in terms of statistics, this is simply because there are more opportunities for extinction events to occur. Ecologically speaking, more species inhabiting the same island, also leads to an increased chance of antagonistic interactions, like predator-prey interactions or territory fights. Furthermore, as more species inhabit the island, the colonization rate decreases, because there are fewer resources to go around, and niche space is occupied, so new arrivals are less likely to be able to establish.

Overall the theory of Island Biogeography predicts that there will be a dynamic equilibrium on any given island - meaning that the number of species should remain stable at the point where colonization and extinction rates meet. Note that this also means that the composition of species on the island can still change as some species go extinct, and new immigrants become established. Additionally, the actual values at equilibrium will always be particular to the characteristics of the individual island, such as its size or proximity to the mainland.

In this laboratory, you will test the theory of Island Biogeography through a simulation with artificial islands of different sizes.