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How Biogeography Affects Biodiversity
Alfred Russel Wallace, Father of Biogeography
Figure 1: Alfred Russel Wallace, Father of Biogeography
Some places contain more species than others. For example, Antarctica has fewer species than a temperate deciduous forest, which in turn has fewer species a tropical rainforest. For over 150 years, researchers have sought to make sense of the gross and fine scale spatial patterns in biodiversity, and to elucidate both the proximate and ultimate causes for these patterns.
This article describes some of the major geographic patterns in species richness, and the processes and theories that are thought to account for these patterns. Much of this knowledge has emerged from the tremendous body of work from one scientist, Alfred Russel Wallace (Figure 1), widely regarded as the “Father of Biogeography.” Aside from co-originating the process of Natural Selection with Charles Darwin, Wallace spent extended periods studying the distribution and diversity of plants and animals in Amazonia and Southeast Asia in the mid 1800s. Many of the patterns and processes featured in this article were initially described by Wallace, and careful study of his work indicates that his ideas presaged many of the discoveries made by his numerous successors.
Many of the spatial patterns in biodiversity are overt, others are subtle and yet additional patterns remain undetected. While the existence of these patterns may be obvious — and changes in the environment that are paired with these patterns may also be obvious — the mechanisms that cause the differences in biodiversity along environmental gradients are under still the subject of scientific debate. Because large-scale patterns are the emergent result of complex interactions at many spatial and temporal scales, no single answer is likely to ever emerge, but with continued research our understanding of the processes shaping these patterns increases.
Historical Processes Affecting Biogeography
Darwin's finches of the Galapagos Islands are a classic example of adaptive radiation.
Figure 2: Darwin's finches of the Galapagos Islands are a classic example of adaptive radiation.
All species occurring in at a given place and time either arrived from another place or originated in that location from ancestral species. This fact applies to extinct species that were ancestors of all extant species. Species richness in a given location is the result of three factors — the rate of speciation, the rate of extinction, and the dispersal of species from other locations. In principle, if biogeographers could understand how the current and past environment has shaped these three factors, we would then obtain a comprehensive understanding of what generates all biogeographic patterns of species richness. However, numerous environmental and organismal parameters can drive these historical factors, in both complex and interacting fashions.