ABSTRACT
Many ecosystems are dominated directly by humanity, and no ecosystem on earth’s surface is free of pervasive human influence. This chapter provides an overview of human effects on earth’s ecosystems. The use of land to yield goods and services represents the most substantial human alteration of the earth system. Human use of land alters the structure and functioning of ecosystems, and it alters how ecosystems interact with the atmosphere, with aquatic systems, and with surrounding land. Human alterations of marine ecosystems are more difficult to quantify than those of terrestrial ecosystems, but several kinds of information suggest that they are substantial. Many of the fisheries that capture marine productivity are focused on top predators, whose removal can alter marine ecosystems out of proportion to their abundance. The supply of this fixed N controls (at least in part) the productivity, carbon storage, and species composition of many ecosystems.
