Geographical Distribution Of Animal's,

Geographical Distribution Of Animal's,
patterns that characterize where animals are found around the globe. When scientists study the distribution of animals, they investigate why reindeer, for instance, are found only in certain parts of the arctic tundra, or why malaria-bearing mosquitoes proliferate in damp subtropical areas. Scientists study animal distribution to understand the spread of animal-borne diseases, to acquire knowledge about the preservation of rare species that may have special needs, and to become informed about the changing geography of the world, and our place in its history and its future. To understand these issues, scientists need to identify the specific climates, foods, and geographic features different animals require, and what areas best provide them. The study of animal distribution is called zoogeography.


Animals vary widely in their tolerance of environmental conditions. Some can survive in a variety of habitats, whereas others perish when removed from their natural surroundings. No animals other than humans can create sufficient artificial changes to enable them to exist in a totally strange environment without evolving through many generations of adaptation. The specific interactions of animals with their environments are the subject matter of ecology. The factors affecting animal distribution range from global geological events to local weather conditions.

Global Conditions,

Present distribution patterns of plants and animals are largely a result of shifting landmasses (see Paleoclimatology). About 225 million years ago, all the continents were connected into one supercontinent called Pangaea. Over the course of about 50 million years, Pangaea split into two huge chunks of land that drifted farther and farther apart. About 65 million years ago, these large landmasses split into the continents we recognize today, and began inching toward their present positions (see Plate Tectonics). When the continents separated 65 million years ago, populations of animals that could not fly or swim were unable to move to other continents. They evolved, isolated from their relatives on other continents, in response to their own unique environments.

The regions that were to become South America, Africa, and Australia, for example, were once joined in a chunk of land that separated from Pangaea, called Gondwanaland. Flightless birds evolved in Gondwanaland, and over the centuries, became widely dispersed over the landmass. When Gondwanaland broke up, a flock of flightless birds, along with plants and other animals, was carried away on each floating continent. Separated by the ocean and unable to fly, the isolated birds could not breed with their family members on the other continents. As a result, four distinct species of flightless birds evolved, each adapted to its own region: the cassowary and emu in Australia, the rhea in South America, and the ostrich in Africa. Fossil evidence and comparisons of deoxyribonucleic acid (DNA), the distinct genetic material found in all cells, confirm that these flightless birds are related; all are descendents of the original Gondwanaland flightless bird family.

As continents drifted over the course of millions of years, their distances from the Earth’s poles and equator changed, altering the amount of sunlight they received. This produced drastic changes in long-term meteorological conditions such as temperature, rain, and wind, collectively known as climate, which in turn produced changes in the types of organisms that could live in one region. Dramatic temperature cycles of global warming and cooling have also punctuated the Earth’s history, resulting in extensive changes in plant and animal distribution. About seven million years ago, for example, a period of extreme cooling caused glaciers to spread over much of North America, Europe, and Asia, changing the northernmost regions from warm, temperate habitats into vast sheets of ice (see Ice Ages). The animals that lived in these areas migrated south to warmer climates, and animals that thrived in freezing temperatures took over their territory. When the Earth slowly warmed again, the ice sheets melted, and the migrations reversed. The Earth has experienced at least four major cycles of cooling and warming; the most recent Ice Age ended about 10,000 years ago. Evidence of these changes is seen in the fossils of animals adapted for extreme cold, such as mastodons, that are found in temperate, or mild, regions of Europe and North America. Fossils of tropical animals such as jaguars found beneath arctic ice are also testimony to major climate fluctuations of the past.

In some instances, factors other than the movement of continents cause animals to move from one landmass to another. For example, iguanas have been found to travel from one Caribbean island to another by riding on trees that had been uprooted and hurled into the ocean by hurricanes. Some scientists believe that other animals have also traveled on floating logs; in particular, rodents are thought to have rafted to Australia from other landmasses between five million to six million years ago.