Biogeography

Introduction

Biogeography is concerned with biodiversity (the various types and numbers of creatures that are present in a particular environment). Biogeography can be descriptive, studying a list of species present in a given environment. Alternatively, historical biogeography involves the study of biodiversity with the passage of time in the particular environment.

The goals of biogeography are to gain a better understanding of the types of environments various organisms live in, their populations, and why some environments support populations of certain organisms but not others.

The time frame for biogeographical studies can be on the order of millions of years, involving factors like the advance and retreat of glaciers during ice ages, changes in the course of rivers due to erosion and surface movement, and species extinction. Biogeography can also involve shorter time frames. For example, the effect of global warming—the warming of Earth’s atmosphere due to human activites—on biodiversity has only been evident for about 100 years, as this atmospheric warming did not begin until the mid-nineteenth century.

Biogeography is important in helping determine how an area can be treated to sustain the life that is present, and in revealing the effects of environmental change on a scale that ranges from local to global.

Historical Background and Scientific Foundations

Biogeography as a scientific theory was developed during the nineteenth century by evolutionary scientists who were studying the distribution of flowers and creatures in various natural environments, including the English naturalist Alfred Russel Wallace (1823–1913).

These early studies tended to describe the observations made in a given environment, with no extension of the observations to consider the consequences of a change in an environment on biodiversity. This merely descriptive view of biogeography expanded with the 1967 publication of The Theory of Island Biogeography by American biologists Robert MacArthur (1930–1972) and Edward O. Wilson (1929–). By studying the biodiversity on islands, the authors demonstrated that the types and abundance of life in an isolated environment could be influenced by factors such as geographical area, the rate at which new species entered the environment, and the removal or extinction of species.

This approach to biogeography, which considers the changes that can occur over time, is known as historical biogeography.

There are several major biogeographical zones (or ecozones) over Earth’s surface. These are Nearctic (which comprises North America and Greenland), Palearctic (which comprises Europe, Russia, northern Asia, and northern Africa), Neotropical (which comprises South America), Ethiopian, Oriental, Australian, and Oceanic (which comprises the Pacific Ocean).

The discovery of the structure of deoxyribonucleic acid (DNA) in the mid-1950s and the increasing sophistication in determining the sequence of the components of DNA in a variety of species in the following decades has increased the power of modern biogeography. In addition to visual observations of species, the relatedness of species can be probed by comparing their DNA sequences. Two species that are closely related such as human and chimpanzees, for example, have DNA that is nearly identical. In contrast, species that diverged from one another long ago will have more differences in their DNA.

Molecular studies of biogeography can also be used to trace the geographical expansion of a single species, since the adaptation of the species to new territories can be reflected in genetic changes.

These studies are part of a branch of biogeography known as paleobiogeography, which combines the study of fossils and changes that have taken place on Earth over billions of years with molecular techniques to chart how the distribution of life has changed over long periods of time. As one example, paloebiogeography research has demonstrated that passerine (perching) birds, which are the largest group of birds, originated in present-day Australia and Antarctica and spread outward across the globe over millions of years. The rate of the spread has been useful in clarifying timing and rate of the separation of the continents from one another.

Impacts and Issues

Biogeography is important in determining the distribution of species in a given area and also the distribution of various habitats. This descriptive type of biogeography is still crucial in decisions concerning land use and in deciding on conservation strategies.

Historical biogeography is also important in revealing changes that are occurring in a region and providing clues as to the reasons for the change. For example, studies of the Amazon rain forest have linked over-logging to declining biodiversity.

On a global scale, the changing patterns of species distribution and abundance is reinforcing the view that the accelerating warming of the atmosphere is affecting life on Earth, and biogeography is helping spur efforts to curb atmospheric warming that is occurring due to the release of gases generated by human activity.

WORDS TO KNOW

ECOZONE: A broad section of Earth’s surface that features distinct climate patterns, ocean conditions, types of landscapes, and species of plants and animals.

FOSSIL: A remnant of a past geological age that was embedded and has been preserved in Earth’s crust.

HABITAT: The natural location of an organism or a population.

See Also Ecosystem Diversity; Genetic Diversity; Reef Ecosystems

BIBLIOGRAPHY

Books

Lomolino, Mark, and Lawrence Heaney. Frontiers of Biogeography. Sunderland, MA: Sinauer Associates, 2004.

Lomolino, Mark, Brett Riddle, and James Brown. Biogeography. 3rd ed. Sunderland, MA: Sinauer Associates, 2005.

Sax, Dov, John Stachowicz, and Steven Gaines. Species Invasions: Insights into Ecology, Evolution, and Biogeography. Sunderland, MA: Sinauer Associates, 2005.

Web Sites

GeoCommunity.http://www.geocomm.com/ (accessed April 10, 2008).