Module 9S1 Ecological Interactions

4.9.3S1 page 4

Lesson Summary

Communities change over time in the process of succession. Ecological disturbances (both human-caused and natural) can destroy communities and return them to rock or to soil. Primary succession begins from bare rock, where little life exists, and may be the result of avalanche or glacial melting. Secondary succession begins from soil, where life still exists as roots, seeds, and other organisms in the soil, and occurs after fire has destroyed a community, or when human settlements or agricultural fields are abandoned. In either case, a predictable pattern of invasion and replacement of species will occur, ending in a stable climax community. The first species to invade is the pioneer species, and the last species is the climax species, by which the community is known. Animal species undergo succession as well. As producer species change with the succession, so does the basis for new consumer food chains and food webs.