Island Biogeography Lab

Introduction

Island biogeography is one of the most important concepts in ecology and evolution. It describes how different habitats vary in population number and diversity.

Scientists E.O. Wilson and Robert MacArthur first developed the theory of island biogeography in the 1960s. The basic theory says that on larger islands there is a larger number of species, while smaller islands have less species diversity.

Island biogeography doesn't just involve islands. In the theory, an "island" can be any ecosystem that is different from the ecosystems around it, such as an oasis in the desert; a small rainforest surrounded by farmland, or one of the Sky Island Mountains in southern Arizona.

According to this theory, every island has equilibrium for the optimum number of species it can support. Species diversity on an island mainly depends on three things.

1. Extinction—how many species die out over time
2. Immigration—how many new species move to the island from neighboring islands or landmasses
3. Emigration—how many species leave the island to settle elsewhere

Other things that affect species diversity include time, isolation, and climate. The distance of an island or other isolated habitat from other habitats is an important contributor to the levels of immigration and emigration and also can lead to adaptive radiation and specialization.

An island close to a large mainland will have more animals arriving from the mainland to colonize the island than an isolated island many miles from other land will.

The Implications of Island Biogeography

Modern science uses island biogeography theory to understand evolution and species today and to help endangered species.

Charles Darwin proposed that species present on islands may have diverged genetically from their continental relatives and yet have similar ecological roles. To demonstrate that organisms like iguanas, tortoises, and finches came from mainland South America, Darwin performed experiments in which he placed organisms on logs and rafts of vegetation to observe how far they could travel in the sea. He also soaked seeds in seawater to see how long they could remain viable under these conditions. They would have to travel 600 miles to the closest Galapagos island!

The theory of island biogeography is important to conservation biology because it helps scientists predict how many species should thrive in a given area and gives them information on how to develop protective reserves or develop habitat corridors, strips of habitats connecting similar areas that would otherwise be isolated as islands in the middle of development or farmland. Habitat corridors might increase the effective size of the two habitats, allowing them to act as one island and therefore increase the number and genetic diversity of species the area can support.

Watch this video https://www.youtube.com/watch?v=-P7pFYdhXPc and refer to the information above.

1.       The theory of Island Biogeography distills what determine biodiversity on islands into what two factors?

 It shows it in two main points.  The first being the size of the island.  The second one is the distance to the island.

2.       The ecologist who developed this theory knew that other factors contributed to island biodiversity. Why did he not include them in his model?

A lot of the other factors that could relate to his theory were unpredictable and these two factors he chose seemed to be the major factors playing a role in biogeography diversity.  Even if other factors came into to play there were not significant enough to make a difference in his theory.

3.       List three biotic and three abiotic factors determining success of colonization on islands. Remember, the term “island” has broad connotations.

Three biotic factors would be the vegetation of the island (what is there to survive off of), the health of the animals colonizing that particular island and the ability for the animals to reproduce in order to colonize the island.  Three abiotic factors would include that of natural water to drink, the terrain (suitable hiding spots, safe places for animals to rest) and size of the island(if an animal’s s trying to colonize and can’t do so because the animal already has as many species as it can handle.)

4.       How can the theory of island biogeography help scientists understand the role of fragmentation in species extinction and to develop ways to prevent such extinction? 

Fragmentation limits species by disrupting their natural habitat.  Because of human expansion and the elimination of their habitats more and more animals are being thrown into island scenarios where they have to adapt or slowly become extinct.  Animals are cut off from natural food sources and migration routes due to new cities, roads, etc...  Scientist can use the theory of islands to help species by either helping move them to more suitable area for populations size or providing what they need in the area they are currently in.  Island biogeography relates to how well a population size can live on the ecosystem it is currently living in.  Certain population control methods could be necessary to help them survive.

5.       Ecologically speaking, what is an island? Identify an island within about ten miles from your home. Explain why it is an island. Is it a natural island, or did humans have a role in its development. Always been an island and give a thoughtful explanation of how species might be inhibited in terms of reproduction or dispersal. 

                An island is ecosystem that has developed through time separate from other ecosystems near it creating unique adaptations from other forms of life.  There is an island ecosystem not even a mile from where I live.  It is called the duck pond and is home to many different ducks and fish.  It is a man made ecosystem.  Having been made by man it has created a unique ecosystem in the desert where there usually wouldn’t be ducks and these types of fish.  These animals have started reproducing and living on their own creating a unique and diverse ecosystem island right here in the desert.  The population of fish and ducks continue to grow which creates an issue because if there are too many fish and ducks they eventually will not be able to survive our will have to adapt to survive.