This paper focuses on the environmental factors that influence the distribution, composition, relative abundance and persistence of benthic insect assemblages in 13 sampling sites belonging to three ecosystem types (ponds, rivers and springs) that drain in the new Zimapán dam. Hydrological period under study was from July 2000 to June 2001. 20,854 individuals were collected and separated into 12 entomological orders (approximately 30 families). Because many environmental factors are intercorrelated and are surrogates for both regional and local events, and because their effects are all interrelated and probably inseparable statistically, we used analytical process studies to go beyond correlations. Diptera (26.9%), Ephemeroptera (19.5%) and Hemiptera (18.7%) are the groups that dominate the benthic insect assemblage. No significant differences were detected in the composition of the assemblage among ecological seasons in the area (beginning of flooding and of desiccation periods; and beginning and ending of hydrological stability periods). However, the major groups and some minor groups, such as Plecoptera and Lepidoptera, significantly increased their relative numbers in populations following the different water regimes from flooding to desiccation. Highest number of taxonomic orders was recorded after the rain season, when most of the ecosystems studied are hydrologically stables (September). And though the highest number of individuals from all the orders was recorded at the beginning of the rain season, when the aquatic systems are flooding (April), major groups reached their highest relative density during the rainy season (July). The principal environmental factors influencing benthic insect assemblages are at regional scale: ecosystem type (spring, stream or river), habitat (pool-riffle system) and substrate types. And at local scale: succession of annual herbs and refuge availability. Our data support the thesis that explain that biotic and abiotic processes produce patterns of benthic insect assemblages, and both, patterns and processes depend of the scale of study.
Keywords: ecology, habitat selection
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