Concept 53.4 Biogeographic factors affect community biodiversity Two key factors correlated with a community’s biodiversity (species diversity) are its geographic location and its size. In the 1850s, both Charles Darwin and Alfred Wallace pointed out that plant and animal life were more abundant and varied in the tropics. They also noted that small or remote islands have fewer species than large islands or those near continents. Such observations suggest that biogeographic patterns in biodiversity conform to a set of basic principles. Species richness generally declines along an equatorial-polar gradient. Tropical habitats support much larger numbers of species of organisms than do temperate and polar regions. What causes these gradients? The two key factors are probably evolutionary history and climate.
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