From ecological disturbances to geological changes, there are many biogeographic factors shaping the distribution of organisms and biodiversity in an ecosystem.
Scientists often study biogeography, which is an area of study that focuses on the distribution of plants and animals in space or time. It focuses on how geography changes or affects biodiversity in a community. Biodiversity is the number and variety of species in a given area; all living organisms within species, between species, and of ecosystems. It includes differences among living things in a community. Biogeography is not only focused on the observed patterns of distribution in a community, such as the dispersal of dandelion seeds by wind, but also with identifying the factors responsible for changes in distribution. In addition, biogeography provides evidence in support of evolutionary processes. There are several biogeographical factors that affect geographical distributions.
One example of a factor is the theory of continental drift, the movement of Earth's continents over time. The essence of continental drift is that the surface of the earth has plates that shift and move, creating and destroying landmasses. Pangaea was a "supercontinent" that existed 335 to 175 million years ago, which later broke into the continents. After Pangaea broke apart, the continents slowly drifted apart and into their current positions. The movement of continents, a biogeographical factor, changed the distribution of species on Earth over time. A habitat is the physical area where an organism lives.
A large spatial region where ecosystems—all organisms living in one geographic region and all the environmental factors that affect those organisms—share a broadly similar biological evolutionary history is called a biogeographic realm. There are six biogeographic realms, which are roughly equivalent to the continents. Each realm is based on the relationships between plants and animals because of their evolution, caused by continental drift and other factors.
A second biogeographic factor is island size, also known as the island effect. Island biogeography explains why there is an uneven distribution of species on different islands. This theory is based on the idea of a proportionate relationship between island size and biodiversity. A larger island supports a greater range of habitats. This larger island size also affects the rate at which new species populate. That is, a large island size can withstand a larger population volume of organisms living there.
The distribution of marsupials, animals that carry their young in pouches, such as kangaroos, over time is an example of biogeography. Based on fossil evidence, it is thought that marsupials evolved in the northern hemisphere, probably in what is now China. Over time this distribution changed as marsupials began to spread out to other regions, specifically North and South America, Antarctica, and Australia, all of which were close to each other in Pangaea. As Australia drifted apart from the other continents, marsupials became geographically isolated, causing their populations to grow and adapt within this specific region. Marsupials, however, did not last long in Antarctica. Because of the cold weather, they became extinct there. While some marsupial populations remained in South America, they also became extinct in North America.