I. Classes of Interactions
II. Factors Affecting Interactions
A. Abiotic Conditions
B. Resource Availability and Distribution
C. Indirect Effects of Other Species
III. Consequences of Interactions
A. Population Regulation
B. Community Regulation
JUST AS INDIVIDUALS INTERACT IN WAYS THAT AFFECT POPULATION structure and dynamics, species populations in a community interact in ways that affect community structure and dynamics. Species interactions vary considerably in their form, strength, and effect and often are quite complex. One species can influence the behavior or abundance of another species directly (e.g., a predator feeding on its prey) or indirectly through effects on other associated species (e.g., an herbivore inducing production of plant chemicals that attract predators or deter feeding by herbivores arriving later). The web of interactions, direct and indirect and with positive or negative feedbacks, determines the structure and dynamics of the community (see Chapters 9 and 10) and controls rates of energy and matter fluxes through ecosystems (see Chapter 11).
Insects have provided rich fodder for studies of species interactions. Insects are involved in all types of interactions, as competitors, prey, predators, parasites, commensals, mutualists, and hosts. The complex and elaborate interactions between insect herbivores and host plants and between pollinators and their hosts have been among the most widely studied. Our understanding of plant-herbivore, predator-prey, animal-fungus, and various symbiotic interactions is derived largely from models involving insects. This chapter describes the major classes of interactions, factors that affect these interactions, and consequences of interactions for community organization.
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