Structure of Plant-Arthropod Associations: Impact of Herbivores on Community Composition and Host Performance

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9527536 Root The conditions created by a long-term experiment involving the removal of insects from abandoned agricultural fields provide an exceptional opportunity to examine key assumptions in models of plant succession. In a previous experiment, the suppression of plant-feeding insects released the controls on goldenrod populations. Under these circumstances, goldenrods became strong competitive dominants that suppressed many plant species that are prominent in normal plant succession. This study will measure the changes that follow the withdrawal of insecticide treatments to reveal how herbivores can account for vegetational change in communities that are dominated by plants with strong inhibitory influences. The results of this experiment will also demonstrate whether the removal of insects, a major component in most terrestrial ecosystems, merely sets back the normal sequence of successional changes or if it causes the community to develop along an entirely new trajectory that produces a persistent and previously unknown plant association. In another set of experiments, the attributes that are responsible for the dominance of goldenrods will be examined. Previous work has shown that goldenrods respond to herbivore damage by reducing their fecundity, but not the quality of their seeds. As is the case with our understanding of the population biology of most plants, little is known about the fate of the seeds after they leave the parent. The availability of germination sites, loss of viability in aging seeds, size of the seed bank, and dispersal of seeds will be addressed in field experiments in isolated gardens where the density and age of seeds are controlled. This investigation will further our understanding of management strategies for fields in long-term fallow. The studies on seed dispersal and the dynamics of seed banks will provide better insight into the processes involved in the establishment of weed populations.