plant and animal species and communities to distinctive landscape patterns. Geographic information systems (GIS) and remote sensing technologies—new tools in this area of study—are leading to rapid advances in understanding how temporal and spatial variation affect survival of endangered species, pest populations, and beneficial organisms.

One technique of landscape ecology used by weed scientists involves manipulating spatial access to water and nutrients in order to suppress weed populations and increase crop yield. Thus, techniques and tools developed by landscape ecology scientists and traditional techniques in life-system ecology can be used to identify subtle changes in some agricultural landscapes that could improve the competitive advantage of beneficial organisms while negatively impacting pests. The effects of specific changes in the agricultural landscape on the overall durability of any local cropping system can only be adequately addressed by interdisciplinary teams including weed scientists, plant pathologists, entomologists, biochemists, economists, sociologists, crop scientists, etc.

Biological Characteristics that Enable Organisms to Adapt to Changes in Physical, Chemical, and Biotic Conditions

It is known that repeated use of pesticides conditions many targeted pests to naturally select for resistant biotypes. Currently, the arthropod class contains the largest number of species to have developed resistance to pesticides. However, weeds developing resistance to herbicides is a growing problem in crop production; in fact, researchers have discovered plant pathogens that can overcome resistant cultivars within just a few growing seasons. Although the mechanisms and dynamics of pesticide resistance have received increased attention over the past 40 years, more research is needed to understand how both detrimental and beneficial agricultural organisms adapt to their environment. The little information that does exist on this topic indicates that organisms in agricultural and forest systems readily adapt to the many abiotic and biotic changes in their habitats.

Classical tools of ecological genetics and population genetics, and new tools of molecular biology, are being used by researchers in attempts to slow the rate at which pests adapt to chemical and physical stresses and, at the same time, increase the rate at which beneficial predators adapt to these stresses and to the defenses of their target prey. For example, Lewis and Martin (1990) found that preconditioned parasitoids are more effective than nonconditioned parasitoids when released into the environment.

Better Ways to Understand How Multispecies and Multitrophic-Level Interactions Contribute to Pest Population Dynamics

Plant pests are components of ecological systems. Their presence is made possible by many ecological factors, and their effects result in multiple ecological



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