I. The Physical Template
B. Environmental Variation
II. Surviving Variable Abiotic Conditions
B. Water Balance
C. Air and Water Chemistry
D. Other Abiotic Factors
III. Factors Affecting Dispersal Behavior
A. Life History Strategy
C. Nutritional Status
D. Habitat and Resource Conditions
E. Mechanism of Dispersal
IV. Responses to Anthropogenic Changes
INSECTS ARE A DOMINANT GROUP OF ORGANISMS IN VIRTUALLY ALL terrestrial, freshwater, and near-coastal marine habitats, including many of the harshest ecosystems on the globe (e.g., deserts, hot springs, and tundra). However, particular species have restricted ranges of occurrence dictated by their tolerances to a variety of environmental factors.
One of the earliest (and still important) objectives of ecologists was explanation of the spatial patterns of species distributions (e.g., Andrewartha and Birch 1954, A. Wallace 1876). The geographic ranges of insect species generally are determined by their tolerances, or the tolerances of their food resources and predators, to variation in abiotic conditions. Insect morphological, physiological, and behavioral adaptations reflect the characteristic physical conditions of the habitats in which they occur. However, variation in physical conditions requires some flexibility in physiological and behavioral traits. All ecosystems experience climatic fluctuation and periodic disturbances that affect the survival of organisms in the community. Furthermore, anthropogenic changes in habitat conditions increase the range of conditions to which organisms must respond.
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