In this book we have explored the physiological responses of insects to a range of environmental variables, but mostly to variation in food quality, temperature, and water availability. The extent to which insects have to alter their physiology to cope with a changing environment depends, in large measure, on the extent of their behavioural flexibility, the microhabitats they select, and variation in the characteristics of these habitats. However, the physiological capabilities of insects also directly affect their behaviour. These capabilities determine under what conditions insects can survive, and therefore be active, and what habitats they can potentially occupy, so ultimately affecting not only their broad-scale distributions, but also community structure and coexistence at a local level. Because physiological tolerances play a large role in determining habitat selection, which in turn has an influence on survival, understanding the interactions between tolerances and alterations in habitat structure may also aid in understanding the effects of habitat alteration on the conservation of threatened species. There are many striking examples of these interdependencies, including interactions between thermal tolerance, overwintering, and deforestation threat (Anderson and Brower 1996), ant assemblage structure and the tolerances of the species comprising those communities (Cerda et al. 1997, 1998; Bestelmeyer 2000; Cerda and Retana 2000), and the ways in which tolerance might lead to assemblage nestedness (Worthen et al. 1998; Worthen and Haney 1999). Of course, physiological limits will not always be directly involved in determining variations in the population dynamics of species and consequently their abundances and distributions (Klok et al. 2003). Therefore, just as ecologists must pause to consider the physiological plausibility of the mechanisms they are proposing, so too must physiologists consider the ecological and evolutionary relevance of the mechanisms they are studying. An integrated physiological ecology has the advantage of promoting and integrating both perspectives. In consequence, it has much to offer biology.
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