The Earth’s surface is home to an array of life, with different regions boasting unique collections of plants and animals. This uneven distribution of biodiversity is not random; it is organized into what scientists call biogeographic realms. These realms offer a framework for understanding why specific species thrive in certain parts of the world and are absent from others. Exploring these large-scale biological divisions helps understand life on our planet.
Defining Biogeographic Realms
Biogeographic realms represent vast geographical areas, either land or ocean, characterized by distinct groups of species that share similar evolutionary histories and distribution patterns. Unlike biomes, which are defined by similar climate and vegetation types, realms are based on the predominant evolutionary lineages found within them. These distinctions arise from long periods organisms have spent evolving in relative isolation within these regions. Their boundaries are defined by the distributions of endemic species—those found exclusively in a particular area—and higher taxonomic groups.
How Realms Are Shaped
The formation and distinctness of biogeographic realms are influenced by geological and environmental factors. Continental drift, driven by plate tectonics, has shaped these patterns by slowly moving landmasses across the globe. As continents separated, populations became isolated, leading to divergent evolution and the formation of new species unique to those areas. For instance, the separation of South America from Africa around 100 million years ago led to distinct evolutionary paths for species on each continent.
Major geographical barriers also play a role in preventing species migration and promoting isolation. Oceans, mountain ranges like the Himalayas, and deserts act as natural impediments to dispersal, fostering unique biotas within enclosed regions. Long-term climate patterns and past glaciations have further influenced species distributions, forcing populations to adapt, migrate, or face extinction, shaping these realms.
The World’s Major Biogeographic Realms
Eight major terrestrial biogeographic realms are recognized, each with characteristic biodiversity. The Palearctic realm, the largest, encompasses most of Europe, Asia north of the Himalayas, and North Africa, featuring diverse environments from boreal forests to steppes. The Nearctic realm covers most of North America, including Canada, Greenland, and highland regions of Mexico, supporting ecosystems like tundra, temperate forests, and grasslands.
The Neotropic realm includes all of South America, Central America, and the Caribbean, known for its biodiversity and high proportion of endemic species, such as the jaguar in the Pantanal wetlands. The Afrotropic realm spans Trans-Saharan Africa and Arabia, characterized by savannas, tropical rainforests, and the flora and fauna of Madagascar. The Indomalaya realm extends from the Indian subcontinent to Southeast Asia, home to species like the Asiatic lion and orangutans.
The Australasia realm includes Australia, New Guinea, and nearby islands, separated from Indomalaya by the Wallace Line, and known for its marsupial mammals. The Oceanian realm encompasses the islands of Polynesia, Micronesia, and Fiji, showcasing biodiversity shaped by island isolation. Finally, the Antarctic realm, covering Antarctica and its surrounding islands, supports highly specialized life adapted to extreme cold.
Significance of Biogeographic Realms
Understanding biogeographic realms provides a framework for understanding the global distribution of life and is relevant to biodiversity conservation. Recognizing these distinct areas helps prioritize conservation efforts by identifying regions with high levels of endemism and evolutionary histories. This knowledge is used to assess biodiversity at a broad scale, considering that different realms face varying drivers of change and require tailored conservation strategies.
Biogeographic realms also offer a lens for studying evolutionary history and large-scale ecological processes. They provide insights into how species have evolved in response to geological and climatic changes. By examining the evolutionary legacies within each realm, scientists can predict how species and ecosystems might respond to current and future environmental shifts, including climate change and habitat loss.