Biogeography: Definition, Theory, Evidence & Examples

Living organisms evolve traits over time that are ideally suited for their particular climate zone, and the other organisms that come with it. Biogeography is the study of the geographical patterns of distribution of species living today or in the Earth’s past, based on how species adapt to their environments.

Biogeographers are interested in the regions the organisms inhabit or inhabited on Earth, and why they are, or were, present in those particular environments, but not others.

TL;DR (Too Long; Didn't Read)

Biogeography is a branch of geography that studies the landmasses of Earth and the distribution of organisms across the planet, and why the organisms are distributed that way.

Biogeographers can study extinct species to learn how landmasses shifted due to continental drift, and they can use changes in measures of organisms in specific regions to monitor climate change and for other conservation efforts.

Biogeography Definition and Theory

Biogeographers study organism distribution patterns across landmasses in the past to learn about biological and geological history, and they study present day organism distribution to learn about ongoing ecological changes.

Biogeographers consider questions like the following:

  • Why is this organism present in this region but not that one?
  • Why is this organism more populous in some regions at certain times of year?
  • Why are some regions more species rich than others?

An area's species richness is the count of how many distinct species exist there. In other words, it is one way to measure the location's species diversity.

Regardless of whether there are billions of a certain species of bacteria and only one individual tree of a certain species, each of those species gets counted once.

Factors That Affect the Distribution of Species

The distribution area of each species is called its species range. Biogeography examines the factors that change an organism’s range.

Many factors can cause a change in a species’ range. Some of these are biotic, which means that they have to do with other living things. Other factors are abiotic, which means that they have to do with non-living things.

Some examples of biotic factors that influence range are:

  • Over-hunting by humans
  • Decrease in predators
  • Invasive species causing a food shortage

Some examples of abiotic factors are:

  • Smoke and debris from a forest fire causing light and air pollution
  • Climate change causing animals to migrate away from the rising temperatures near the equator
  • Changes in the weather patterns and air currents spreading seeds and spores farther or in new directions

Biogeographical Evidence in the Galápagos Islands

Charles Darwin’s 19th century theory of evolution and natural selection was developed during his famous Pacific journey that led him through the Galápagos archipelago. Darwin was a geologist and, until the end of his trip, a creationist.

As he sailed on the HMS Beagle, he observed that many of the Galápagos islands were relatively close to each other. Upon stopping to investigate several of them, he saw that they were geologically young. They were home to plants and animals that were similar to the ones on the other islands, but never the same; there were inevitably some traits that set the species apart in some way from island to island.

His conclusion was that these islands had drifted apart from each other relatively recently in Earth’s history. The particular biome of each island and its environmental challenges pushed what had once been unified species to evolve differently on each island until they branched off into different sets of species, isolated from their plant and animal cousins by relatively small distances of water.

Darwin's scientific explorations in the Galápagos archipelago, which led to the publication of his book "On the Origin of Species," were a form of island biogeography.

The Founder of Biogeography

Darwin kept his theory of evolution to himself for 20 years. When he met a fellow scientist named Alfred Russel Wallace who had conceived of similar ideas, Wallace convinced him to publish it.

Wallace made many contributions of his own. He was responsible for giving the field of biogeography its start. He traveled extensively to Southeast Asia, where he studied phenomena such as the distribution patterns of species on the landmasses to either side of an imaginary line that ran through the ocean in the area of the Malay archipelago.

Wallace theorized that historically, the land had risen up from the seabed, creating distant landmasses with different flora and fauna on them. That line has become known as the Wallace line.

Biogeography Examples and Uses

Biogeography is useful for understanding what extinct species were like, based on knowledge of where their fossils were found and what that area was like at the time. It is also useful for understanding ancient Earth.

For example, an animal’s fossils found in two continents suggest that a land bridge might have connected the two regions in the past. This is called historical biogeography.

Ecological biogeography, which focuses on current environments for given species, is useful for conservation efforts. Organizations work to restore habitats to the way they were before man-made climate change wrought harm on many ecosystems. The understanding of how things were before and why helps conservationists in their efforts.

References

About the Author

Rebecca E. received a degree in human development before attending graduate school in writing. She has an extensive background in cognition and behavior research, particularly the neurological bases for personality traits and psychological illness. As a freelance writer, her specialty is science and medical writing. She's written for Autostraddle, The Griffith Review and The Sycamore Review. More information about Rebecca can be found at www.rebeccathewriter.com.