The Princeton Guide to Ecology

Human activities are profoundly altering the biodiversity of the earth. The principal drivers of change thus far have been the transformation of lands for human use, accompanying fragmentation of remaining natural habitats, hunting, and modification of native disturbance regimes. These forces have resulted in the extinction of numerous species and radically altered the abundances of countless others. Empirical and theoretical studies imply that many more of the world’s species will experience the same fate as humanity’s collective impacts on the planet further expand and intensify. Long-lived plants and animals and animal species in which individuals range widely in space appear to be particularly vulnerable because of the strong dependence of their populations on the dwindling number of regions that are free of significant human influence. In numerical terms, the impacts of humans on terrestrial biodiversity are generally larger in the tropics because of the restricted spatial distributions of many tropical species and the high species diversity of many tropical ecosystems compared to their high-latitude counterparts. Two additional, and increasingly important, modifiers of terrestrial ecosystem biodiversity are the introduction of exotic species into ecosystems and human-induced changes in climate. These more recently recognized agents of change may act independently of, or synergistically with, land cover change, habitat fragmentation, hunting, and altered disturbance regimes to yet further modify the composition of the world’s ecosystems over the coming century and beyond.

early successional species. Species that appear in an ecosystem following a disturbance event, such as a fire, landslide, or logging. Early successional species typically possess r-selected traits, such as high dispersal ability, short generation time, and rapid growth, but at the expense of having a short lifespan and poor competitive ability. As a result, their population sizes usually increase immediately after disturbances, and then decline later as conditions become more crowded and they are competitively replaced by late successional species.

endemics. Species that have a relatively narrow geographic range, such as species found only on a particular island, or in a particular habitat or region.

fire return interval. The number of years between two successive fire events at a particular location.

invasive species. Introduced or nonindigenous species that are rapidly expanding outside of their native range.

late successional species. Species found in an ecosystem that has not experienced a disturbance for a long period of time. Late successional species typically have K-selected traits, such as long generation time, slow rates of growth, but long lifespan and strong competitive ability. As a result, late successional species come to dominate an ecosystem when no further disturbances occur.

species-area curve. A graph showing the number of species found in an area as a function of the area’s size.

Human population growth and economic development have led to a radical transformation of the earth’s land surface. As plate 8 illustrates, humanity’s footprint

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