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Seasonal Colonization Dynamics of Macroinvertebrates in an Idaho Stream

Field experiments were conducted to examine effects of macroinvertebrate removal frequency on community development on bricks with similar food resource levels (chlorophyll a levels and diatom composition). The experiments were conducted during summer and fall to examine effects of seasonal differences in animal abundances. For each experiment macroinvertebrates were removed from groups of bricks at intervals of 3, 9, or 27 days or were not removed for 54 days. Insect removal frequency had no significant effect on macroinvertebrate abundance in summer when overall animal abundance and richness were low. During fall, when overall abundance was 3× greater, there were significantly fewer animals on bricks with a 3-day removal interval. Baetis tricaudatus represented 65% of all invertebrates in summer, but declined in relative abundance to about 25% in fall. In contrast, the Chironomidae increased from 6% of the assemblage in summer to comprise over 30% in fall, suggesting that differences in the composition of dispersal modes influenced the patterns of colonization observed. We suggest that an algal resource is important in the colonization dynamics of macroinvertebrates by acting as a food source and/or habitat templet. Our experiments illustrate that macroinvertebrate colonization and community development on rocks is influenced by seasonal changes in animal density and composition.