Habitat, Life History, and Behavioral Adaptations of Aquatic Insects

The observed patterns of distribution and abundance of aquatic insects indicate successful adaptations to a wide variety of habitats. To demonstrate how organisms adapt to particular niches of the freshwater community, examples of species using certain environments are presented in this chapter and the life cycle is used as a framework for describing diverse modes of coping with environmental characteristics. Factors that influence utilization of a particular habitat can be grouped into four broad categories: (I) physiological constraints (e.g., oxygen acquisition, temperature effects, osmoregulation; (2) trophic considerations (e.g., food acquisition); (3) physical constraints (e.g., coping with habitat); and (4) biotic interactions (e.g., predation, competition). However, these categories are so interrelated that detailed analysis of each factor is not appropriate. Aquatic insect respiration is covered in detail in chapter 4, but it is considered here because activities related to oxygen acquisition are central to behavioral and morphological features associated with most other activities. The traditional division of freshwater systems into standing (lentic) and running (lotic) waters is useful for indicating physical and biological differences. Most insects are adapted to either a lentic or a lotic habitat, but overlaps are common. For example, insects inhabiting pools in streams have "lentic" respiratory adaptations, whereas those on wavewashed shores of lakes are similar to stream riffle inhabitants in both oxygen requirements and clinging adaptations. Despite their success in exploiting most types of aquatic environments, insects are only incompletely or secondarily adapted for aquatic life. With very few exceptions, aquatic insects are directly dependent on the terrestrial environment for part of the life cycle. Even Hemiptera and Coleoptera with aquatic adults may require access to surface air for respiration. This dependence on the terrestrial environment probably contributes to the prevalence of insects in shallow ponds and streams as compared with deep rivers or lakes and to their virtual absence from the open sea. ADAPTATION TO HABITAT