Introduction: The Interaction Between Wildlife and Agroecosystems Effects of Agroecosystems on Wildlife Positive Effects of Agriculture on Wildlife Negative Effects of Agriculture on Wildlife Case Studies: The Use of Agroecosystems by Wildlife Wildlife and Rice Cultivation
Migratory Birds, Agroecosystems, and Agricultural Chemicals Agricultural Practices in Coffee Agroecosystems Trees as Row Crops: Plantation Forestry and Wildlife Conclusions — Net Effects of Agroecosystems Loss of Biodiversity Change in Community Structure Recommendations for the Mitigation of Impacts References
INTRODUCTION: THE INTERACTION BETWEEN WILDLIFE AND AGROECOSYSTEMS
Agriculture is among the most important of all human enterprises. A small number of species of crops, domesticated by a variety of early civilizations, now provides the basis of most of our food consumption. Fifteen species of plants, primarily grains, provide over 90% of all human energy needs, and over 98% of all human food is produced in terrestrial habitats (Paoletti et al., 1992). Agriculture, forestry, and human settlements occupy 95% of all terrestrial environments, whereas nondeveloped areas such as national parks account for only 3.2% worldwide (Pimental et al., 1992). The balance between protected areas and modified landscapes has shifted strongly toward the latter, and there is little doubt that agricultural diversification and expansion has decreased biodiversity over the past two centuries (Dahlberg, 1992). Thus, concerns over the effects of agriculture on wildlife have increased in recent years.
The major impacts on wildlife are caused by habitat conversion and habitat fragmentation. The U.S. provides a good example of this process in a developed country. About 70% of the U.S. (excluding Alaska) is held in private ownership by millions of individuals, although 50% of the land is in the hands of only 2% of the population. About 50% of the country is either cropland, pasture land, or rangeland, owned by approximately 4.7 million individuals (U.S. Department of Agriculture, 1996). Over 200 different species of crops are produced on this land; however, 80% of this total production is accounted for by four species: hay, wheat, corn, and soybeans (U.S. Department of Agriculture, 1996). When forests or grasslands are converted to an agroecosystem, virtually all native species of plants and many of the animals are lost. There is often some degree of utilization of the agricultural fields by vertebrates and invertebrates, but when these species cause losses of crops, they are controlled, usually by chemical means. This often results in the elimination of nontarget organisms as well. Some natural ecosystems, for example, wetlands, have been particularly severely impacted by agricultural expansion. Up until the 1950s, approximately 87% of all wetland conversion was attributable to agriculture, though recent legislation has reduced that percentage. In fact, between 1982 and 1992, 57% of wetland losses were due to urban expansion, and only 20% to agriculture (U.S. Department of Agriculture, 1996).
Economic incentives frequently contribute to habitat conversion. Increased economic pressures and new technological innovations can cause losses of biological diversity in the early stages of development (Howitt, 1995). This is especially a problem in the tropics. Developed country policies often determine the agricultural practices of developing countries; developing countries generally function as "price takers" and are largely exporters of primary products to the developed world (McNeely and Norgaard, 1992). Agricultural development projects financed through international aid agencies have neglected environmental issues in the past. The impact on wildlife in developing tropical nations has been substantial; however, there are several innovative proposals to link economic and ecological systems in agricultural development (McNeely and Norgaard, 1992).
We present a summary of the effects of agriculture on wildlife, both positive and negative. For each individual scenario, there are both benefits and costs. We present four different case studies that attempt to capture the complexity of issues and effects. Finally, we close with some recommendations.
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