Responses of Weed Populations to Human Manipulations of the Natural Environment

The occurrence, abundance, and nature of weed communities were reviewed in relation to man's manipulation of the natural environment. Manipulations of the environment necessary for agricultural production have favored secondary successional species. That many of these seral species have opportunistic genotypes has led to the development of weeds. Weeds conform to the concepts of ecologic succession, but agricultural ecosystems are very dynamic with sudden and recurrent changes. The acceleration of successional patterns has provided environments conducive to the selection of competitive genotypes among numerous weeds. Specialized breeding systems provide rapid responses to changing conditions. Weeds increase the diversity of agricultural ecosystems by utilizing environmental potential concentrated for crop production. Weeds have been the shadow of history in that they have mirrored man's activities. The introduction of weed species to new environments may be one of the greatest manipulations of the natural environment, the total consequences of which will be determined in the future.