Some Relationships between Systematics and Trophic Ecology in Nearctic Aquatic Insects, with Special Reference to Trichoptera

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Abstract
Based on the general premise that the genus represents an ecological, as well as a morphological type, a number of generalizations are developed concerning the use of food resources in fresh waters by Trichoptera and some other aquatic orders of the Nearctic fauna. There are more genera of the Nearctic order Trichoptera (144) than in the orders Ephemeroptera (59), Odonata (84), or Plecoptera (88). Trichoptera have a wide range of habitats and a broader range of trophic categories than any of these other wholly aquatic orders. This relatively high ecological diversity is attributed to the many uses of silk by trichopteran larvae. Genera of 3 families of filter—feeding Trichoptera show differences in distribution which are correlated with the type of food particle. Most of these genera are found in the eastern deciduous forest biome and all sizes of organic particles are filtered. In the western montane forest biome, generalist filter feeders are absent or underrepresented; predacious genera or those filtering very fine particles have been more successful. Possibly there are differences in the quality and quantity of fine particulate detritus between eastern and western forest which account for the above distributions. In the trichopteran family Limnephilidae, genera of the detritivorous shredders have exploited lotic, lentic, and even terrestrial habitats; grazer genera are mostly confined to cool lotic habitat. Grazers in other families of Trichoptera are also more diverse in upstream areas, and grazer genera are particularly well—represented in the western montane forest biome. In streams of the eastern deciduous forest biome, the relative proportions of feeding categories shown by trichopteran genera appear to agree with a general trophic model of benthic invertebrate communities in that dominance of shredder—collector genera in upstream sections gives way to grazer—collector dominance downstream. In western montane streams, trichopteran generic distributions conform to the model downstream, but show relatively more grazers than the model would predict for upstream areas. Periphyton growth, and thus food for grazers, may be more abundant in the western coniferous forest than in the shaded streams of the eastern deciduous forest. In general, an ecological analysis of Nearctic Trichoptera at the generic level appears to provide a reasonable indication of the energy resources available in aquatic habitats.