What is biogeography and how does it explain species distribution?

Biogeography is the study of organism distribution across geographic space and the processes shaping these patterns. The theory states that species in any location either evolved there or immigrated from elsewhere. Environmental characteristics like food availability and interactions with other species determine whether colonizers establish new populations or perish in their new habitat.

How do island size and mainland proximity affect species colonization rates?

Islands closer to the mainland experience greater colonization rates because organisms can more easily disperse shorter distances. Larger islands support more species than smaller ones due to greater resources, niches, and larger population sizes that reduce extinction risk. These factors combine to determine the total number of species an island can sustain.

What is dynamic equilibrium in island biogeography?

Dynamic equilibrium occurs when colonization and extinction rates balance, stabilizing the total number of species on an island. Although species composition changes as new immigrants arrive and residents go extinct, the overall species count remains relatively constant. This equilibrium point is unique to each island based on its size, resources, and proximity to the mainland.

Why does extinction rate increase as more species inhabit an island?

As species diversity increases, extinction risk rises due to increased antagonistic interactions like predation and competition. More species also means fewer available resources and niche space for new arrivals. Statistically, more species simply create more opportunities for extinction events to occur among the coexisting populations.

How has island biogeography theory been applied beyond oceanic islands?

Island biogeography principles apply to isolated habitats like sky islands, inland lakes, and forests fragmented by agriculture. These non-continuous habitats function similarly to oceanic islands, with species experiencing isolation and limited dispersal. Understanding these dynamics helps conservation biologists design habitat corridors and reserves to maintain species diversity and prevent extinction.

What factors determine whether colonizing species establish populations in new locations?

When colonizers arrive at a new location, environmental characteristics including food availability and interactions with existing species determine establishment success. Species must overcome biological limitations to disperse, such as limited flight range for birds or seed drift constraints. Birth and immigration rates must equal or exceed death and emigration rates for populations to persist.

Why are endemic species in isolated habitats at greater extinction risk?

Endemic species found only in isolated locations face higher extinction risk due to smaller population sizes and limited habitat areas. These species evolved under specific local environmental pressures and lack genetic diversity from outside populations. Understanding biogeography principles helps conservation efforts protect these vulnerable species through habitat management and artificial corridors connecting fragmented areas.

Species Distribution and Biogeography

Concepts Instructor Prep Student Protocol

10.4K views04:04 min

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.