INVERTEBRATE RESISTANCE AND RESILIENCE TO INTERMITTENCY IN A DESERT STREAM

Invertebrate responses to water loss were investigated during drying, dry and rewetting phases in Sycamore Creek, an intermittent Sonoran Desert stream. Some taxa were resistant to drying because they could tolerate rapidly changing water quality and/or move upstream to avoid stranding. Community shifts occurred at one site when it became isolated from up- and downstream reaches; taxa such as beetles, hemipterans, and the snail Physella virgata became dominant. No community changes were detected at a second site which remained connected with upstream reaches by surface flow. Mortality after water loss was severe as few individuals survived longer than 10 days. Low resistance during the dry phase was associated with rapid moisture loss from sediments. Invertebrate persistence in intermittent reaches was due to recolonization after rewetting; however, density increases after floods which reestablished flow at dry sites were lower than reported values for perennial sites in Sycamore Creek. Slower rates of recovery may reflect the composition, reduced size and remoteness of macroinvertebrate colonist pools. Nonetheless, invertebrate persistence in desert streams where both flooding and drying are frequent is due largely to their ability to rapidly recolonize disturbed sites.