1. Historical Distribution and Evolution:
* Continental Drift: Over millions of years, the Earth's continents have drifted apart. This means that animals that were once together on a single landmass were eventually separated. For example, the presence of marsupials in Australia and South America is due to their common ancestor living on a single supercontinent millions of years ago.
* Evolutionary Adaptation: Once separated, animals adapted to their new environments. This leads to unique species evolving on different continents. For example, penguins evolved in the Southern Hemisphere while similar birds like auks evolved in the Northern Hemisphere.
2. Migration:
* Seasonal Migrations: Many animal species migrate long distances, often following food sources or favorable breeding conditions. Birds like the Arctic tern migrate thousands of miles between the Arctic and Antarctica.
* Historical Migrations: Some animals may have migrated to new regions in the past due to climate changes or other environmental pressures.
3. Human Introduction:
* Intentional Introduction: Humans have intentionally introduced animals to new regions for various reasons, such as agriculture, pest control, or pets. Examples include rabbits in Australia and the zebra mussel in the Great Lakes.
* Accidental Introduction: Animals can be accidentally introduced through shipping, tourism, or other human activities. The brown tree snake in Guam is a prime example of an accidental introduction with devastating consequences.
4. Climate and Geography:
* Climatic Zones: Different parts of the world have different climates, and animals are adapted to specific climates. For example, polar bears live in the Arctic due to their adaptations for cold environments.
* Geographic Barriers: Mountains, oceans, and deserts can act as barriers to animal dispersal, resulting in different species being found in different regions.
5. Biogeography:
* Biogeographic Regions: The Earth is divided into biogeographic regions based on shared evolutionary histories and environmental factors. Each region has a unique set of species, reflecting the influences of historical events and adaptations.
It's important to note that the distribution of animals is a complex and dynamic process influenced by a combination of these factors. Understanding these factors helps us appreciate the diversity of life on Earth and the interconnectedness of different ecosystems.