COLONIZATION BY LOTIC MACROINVERTEBRATES - A REVIEW OF PROCESSES AND PATTERNS

Ways in which invertebrates colonize lotic habitats are reviewed, tracing patterns in behaviour, trophic ecology, and life history that could lead to predictions concerning resilience of stream communities after disturbance. Patterns are described for small-scale experimental studies using introduced or natural substrates, for large-scale observations of new or rewatered channels, for rivers recovering from pollution, and for unstable rivers with fluctuating discharge. Colonization depends on invertebrate mobility (drift, swimming, crawling, and flight), substrate texture and associated food supplies, competition, and predation. Epilithon-browsers and filter feeders can use the resources of smooth stones; gatherers colonize as fine detritus accumulates; grazers increase as periphyton becomes established; shredders and predators tend to be late arrivals. Propagules for colonization are made more available by asynchronous and aseasonal life cycles, long oviposition periods, and refuges in the streambed or neighbouring waterbodies. Species in frequently disturbed streams benefit from these characteristics. Although disturbance may be due to stochastic factors, recovery is not due to chance. Recurring ecological patterns among early colonizers suggest that knowledge of the hydrologic regime, food resources, and dominant taxa can be used to predict the overall resilience of a stream community.