Island Biogeography

10/15

• How different aspects of an island can affect the number and types of species who live there

• The Theory of Island Biogeography

Characteristics that determine # of species island can support

• NPP and latitude (certain amount of energy)

• Size

• Distance from mainland

• Big and close most equilibrium

Rate of immigration and extinction. Distance from the mainland (rate of immigration). This graph shows the combined effects of island size and distance from the mainland on the number of species it can support. Being closer to the mainland means it is easier for species to get there, so it will happen more and more often. Island size plays a role in the rate of extinctions, mostly due to resource availability, and how natural disruptions scale in isolated habitats. Where the rate of immigration and rate of extinction intersect provides a good general estimate of the number of species that are or can be present on an island. This number is an estimate for number of species an island is able to support. The actual number will probably be higher or lower, but will usually come to that equilibrium point. The species composition is also likely to change through time due to random extinctions and arrivals.

What happens to organism competition strategies over time as they compete for the limited number of resources in a fairly isolated, yet relatively unoccupied environment?

• Start to specialize

• Resource partitioning to fill up all the available niches

• Galapagos Finches and Tortoises

African cichlid fishes are another remarkable case of "explosive speciation" (the Hawaiian Drosophila of the fish world). Geology and geography again plays an important role. African rift lakes: great fresh-water lakes in east Africa. Formed recently: < 1 million years old. Lake Victoria colonized by one (??) founder 200,000 years ago(??) now has ~ 200 species of fish!. Recent study used mitochondrial DNA to show that the species in the lake are indeed monophyletic and that there is very little sequence divergence between species: confirms short time span. But there has been remarkable evolution of morphological, ecological and behavioral variation in these fish: algae grazers, snail crushers, plankton feeders, paedophages (clamp onto the mouth of a fish brooding her young in her mouth and force her to spit out here young into the mouth of the attacker), one fish (in Lake Malawi) plucks the eyes out of other fish as food. All this diversity in 200,000 years with very little genetic differentiation. This results in the extremely unique biodiversity that we see today on islands. Even though they make up a relatively small portion of the Earth’s land area (1/6th) they account for a third of the terrestrial biodiversity hotspots, as well as half of marine tropical diversity. The Horizontal competition (competing for same resources, vs vertical competition (predation)), has also led to a large number of specialist species, as exampled by the different traits of the african cichlids or darwin’s finches that allow them to occupy different niches.

How does island biogeography explain the kinds of species you’d expect to find on an island?

• not enough resources to support large predators

• in absence of large predators, top-down control, dodo & galapagos giant tortoises

• island gigantism & dwarfism, bottom-up pressure on islands

  • grazers like deer get smaller to not use as much energy

• animals get really giant because they don’t have to hide

• unique biodiversity on islands

• result in mass scale extinctions

No!!! It also helps explain the types of species and the relationships between them. Obviously, crazy large or immobile organisms won’t be able to make it to an island (on their own at least, lol at the Catalina Island Bison (dropped in the 1920’s and have been ballin since)). Ok, well what about the avid swimmers and apex predators like jaguars? Since there are smaller populations & less primary productivity available, would they be able to sustain a population? So we see a lot more bottom-up pressure on ecosystems and species here, with most non-producers only being primary or secondary consumers, and pretty much only having small predators. This actually causes some really funny stuff to happen, namely island gigantism and dwarfism. Essentially, larger organisms such as deer (isla pedro gonzalez deer, As a result of this small space, limited available food supplies, and a lack of any large predators, these deer rapidly shrank down into a dwarfed form to survive. By 6000 years ago they were the size of a small dog, just 35-40cm tall at the shoulder (1’2″-1’4″) and weighing less than 10kg (22lbs). Unfortunately extinct due to human hunting thousands of year ago), or larger predators need to adapt to become much smaller to make up for the lack of resources. However, normally small species, which are no longer subject to predation pressures, are able to get huge (either for territoriality, ability to control,use,or store resources, or just cuz), such as the flores giant rat of indonesia Also, the bison are hurting endemic species on catalina island because their shaggy fur can carry imported species all over the island, which can outcompete the endemic plants Also helps explain the uniqueness due to isolation & potential openness of resources/ability to speciate

Habitat conservation and SLOSS

• single large good for higher trophic level, apex predators, to have more land to hunt keeps population stable

• small terrestrial islands have more resistance towards large disasters and invasive species, since it’s contained within the small islands

• Austin has small islands in caves in parts of the aquifer, using several small islands

• golden-cheeked warbler is good for single large habitat, since its biggest op is brown-headed cowbird (lays eggs in warblers’ nests), which thrives in edge habitats

Connect the habitats!!!!! Stop the islands For protecting a large number of species, a large reserve is more beneficial than many small reserves, as it can support more and different kinds of species. It does get funky, though, depending on what you’re going for. Many small reserves can be better able to protect a species from a quick demise due to some kind of disruption, as they are in different places. They can also allow for many different kinds of habitats or areas to be chosen, and protected specifically.