Early arrivals may the appearance of later species by changing the environment. facilitate For example, early herbaceous species may increase soil fertility. species may establishment of later species. inhibit Early species may later species but neither hinder nor help their colonization. tolerate Concept 53.4 Biogeographic factors affect community biodiversity Two key factors correlated with a community’s (species diversity) are its geographic biodiversity • 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 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 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. Over the course of evolutionary time, species diversity may increase in a community as more • speciation events ° Tropical communities are generally older than temperate or polar communities. ° The growing season in the tropics is five times longer than that in a tundra community. Biological time thus runs five times faster in the tropics. ° Repeated glaciation events have eliminated many temperate and polar communities. Climate is likely the primary cause of latitudinal gradients in biodiversity. • ° Solar energy input and water availability can be combined as a measure of evapotranspiration, the evaporation of water from soil plus the transpiration of water from plans. determined by the amount of radiation, temperature, and water Actual evapotranspiration, availability, is much higher in hot areas with abundant rainfall than in areas with low temperatures or precipitation. a measure of energy availability, is determined by the amount of Potential evapotranspiration, solar radiation and temperature. The species richness of plants and animals correlates with both measures of evapotranspiration. Species richness is related to a community’s geographic size. The species-area curve quantifies what may seem obvious: the larger the geographic area of a • community, the greater the number of species. Larger areas offer a greater diversity of habitats and microhabitats than smaller areas.
Early arrivals may facilitate the appearance of later species by changing the environment. For example, early herbaceous species may increase soil fertility. species may inhibit establishment of later species. Early species may tolerate later species but neither hinder nor help their colonization. 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 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 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. • Over the course of evolutionary time, species diversity may increase in a community as more speciation events ° Tropical communities are generally older than temperate or polar communities. ° The growing season in the tropics is five times longer than that in a tundra community. Biological time thus runs five times faster in the tropics. ° Repeated glaciation events have eliminated many temperate and polar communities. • Climate is likely the primary cause of latitudinal gradients in biodiversity. ° Solar energy input and water availability can be combined as a measure of evapotranspiration, the evaporation of water from soil plus the transpiration of water from plans. Actual evapotranspiration, determined by the amount of radiation, temperature, and water availability, is much higher in hot areas with abundant rainfall than in areas with low temperatures or precipitation. Potential evapotranspiration, a measure of energy availability, is determined by the amount of solar radiation and temperature. The species richness of plants and animals correlates with both measures of evapotranspiration. Species richness is related to a community’s geographic size. • The species-area curve quantifies what may seem obvious: the larger the geographic area of a community, the greater the number of species. Larger areas offer a greater diversity of habitats and microhabitats than smaller areas.
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