Insects have a considerable capacity to escape adverse conditions and to find optimal conditions within temperature, moisture, and chemical gradients across landscapes or watersheds. Dispersal is the movement of individuals away from their source. This is an important adaptive behavior that minimizes the risk that the entire population will be destroyed by disturbance or resource depletion, maximizes the chance that some individuals will find and exploit new resources, and maximizes genetic heterogeneity (D. Johnson 2004, Schowalter 1985, Wellington 1980; see Chapter 5).
Nevertheless, dispersal entails considerable risk and requires considerable energy expenditure (Rankin and Burchsted 1992). Torres (1988) documented cases of exotic insects being introduced into Puerto Rico by hurricane winds, including a swarm of desert locusts blown across the Atlantic Ocean from Africa. Many insects (and other organisms) fail to find or reach suitable habitats.
Flight capacity contributes enormously to insect ability to disperse. Adult aquatic insects can disperse from an intermittent pond or stream before the water disappears and search for other bodies of water. Dispersal may be particularly important for distributing populations and minimizing risk in ecosystems characterized by frequent disturbances. A number of factors affect the probability of successful dispersal (i.e., arrival at suitable habitats), including life history strategy, crowding, nutritional status, habitat and resource conditions, and the mechanism of dispersal.
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