Community Patterns and Competition in Folivorous Insects

Abstract

Patterns in assemblages of phytophagous insects are interestingly similar to those displayed in many other groups of species. Specifically, we review eight such patterns. (1) Large areas support more species than small areas. (2) Complex habitats support more species than simple habitats. (3) Persistent habitats have more species, with narrower feeding niches, than ephemeral habitats. (4) Significant ecological (Hutchinsonian) distances exist between body sizes of successive instars. (5) Communities "saturate" with species in ecological time. (6) Density compensation occurs in depauperate guilds. (7) Species compete most strongly with close relatives. (8) Within habitats species show niche separation. In many other groups, such as vertebrates, these patterns are widely attributed to the effects of interspecific competition, either in whole or in part. For folivorous insects, in contrast, we argue that classical, interspecific competition for food is weak and infrequent, and that it cannot fill the major ecological and evolutionary role favored for it by many workers on other organisms. Instead, we favor the view that most community patterns can be explained without invoking interspecific competition. For insects on plants, we posit that autecological factors of a harsh and changing climate, host plant phenology, seasonal sequences of chemical and physical changes in host tissue, and patchiness of food plant resources are obviously of great importance to phytophages. Natural enemies in the form of parasitoids and predators frequently combine with autecological factors to lend what regulation of numbers we do see among insects on host plants. Only much less frequently can competition for food or coevolution be shown to have an influence on communities of folivorous insects.