Prdation and Parasitism
Evidence suggests that in some systems, prédation and parasitism are important drivers of population dynamics (Dempster 1983, Hassell 1985). (Competition among insect herbivores, in contrast, is thought to be infrequent [Strong et al. 1984, but see Denno et al. 1995, Ohgushi 1997].) Direct effects of climate change on the development rates and activity of insect predators can affect butterfly predation (Porter 1983, Courtney 1986). For example, under local cooling, the food requirements of endothermic predators increase, leading to the consumption of more prey (Gilbert and Singer 1975). Weather and climate also can alter the exposure of butterflies to predators by influencing butterfly activity or total time of susceptibility (Lederhouse 1983, Shreeve 1986). For example, low temperatures make both larvae and adults relatively immobile, but some predators (e.g., birds and some small parasitoids) can successfully attack at low air temperatures (see Dennis 1993 and references therein). Similarly, at high temperatures, adult butterflies may be vulnerable to predation while standing in heat avoidance posture (Kingsolver and Watt 1983). Weather-driven declines in habitat quality also can increase the visibility of larvae as they search for food (Sato 1979, Dennis 1993).
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