Summary of Chapter Concepts

Landscape ecology examines ecological patterns and processes at large spatial scales. Habitat heterogeneity exists across the landscape as a result of both natural processes and human activities, both in the past and in modern times. This heterogeneity allows more species to exist at the landscape scale than at local scales. Species diversity can change with spatial scale; we quantify alpha diversity at the local scale, gamma diversity at the regional scale, and beta diversity across habitats. The process of species sorting determines which species from the regional species pool are found in a local community.

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The number of species increases with area. The number of species found in areas of different sizes can be described by the species–area curve. As the area sampled grows, we see an increase in species richness because we begin to sample new habitats that contain different species. Habitat fragmentation divides a large habitat into several small habitats and thereby increases the amount of habitat edge. These effects cause the decline in the abundance of many species, but favor those species that prefer habitat edges.

The equilibrium theory of island biogeography incorporates both area and isolation. Species diversity is highest on large islands that are close to a source of colonizing species because these islands have a low rate of species extinction and a high rate of colonization by new species. In contrast, species diversity is lowest on small islands that are far from a source of colonizing species because these islands have a high rate of species extinction and a low rate of colonization by new species.

On a global scale, biodiversity is highest near the equator and declines toward the poles. Species diversity can also vary within a given latitude belt as a result of habitat heterogeneity, temperature, and precipitation. In terrestrial ecosystems, the best predictor of species diversity is potential evapotranspiration. The energy–diversity hypothesis states that sites with higher amounts of energy are able to support more species. In marine ecosystems, the best predictor of species diversity is the temperature at the surface of the sea.

The distribution of species around the world is affected by Earth’s history. Continental drift is a major factor in determining the distribution of species. As continents have come together and separated, they have experienced unique evolutionary lineages that today are recognized as distinct biogeographic regions. The drift of the continents has also affected historic climate changes including widespread changes in the distribution of tropical, temperate, and polar regions around the world.