Differences in habitat use and dispersal responses among competing species are mechanisms that may influence patterns of coexistence. Predaceous diving beetles (Coleoptera: Dytiscidae) are a model group for testing these potential coexistence mechanisms because they are abundant, interact in finite habitats, and are mobile among habitats. We focused on two morphologically similar species, Laccophilus fasciatus rufus (Aubé) and Laccophilus proximus (Say), to determine if mechanisms exist that help to explain patterns of their coexistence. Behavioral observations and feeding trials in the laboratory, a field experiment, and a mesocosm experiment were used to determine if habitat use, prey consumption, or dispersal rates of these two species were inherently different or changed when in the presence of intra- or interspecific competitors. We found no difference between habitat use or prey consumption between species in constant depth aquaria, and no effect of intra- or interspecifics on their behaviors. In variable depth aquaria, L. proximus occupied significantly shallower habitat when compared with L. ƒ. rufus; in the former this difference only occurred between conspecific treatments. Field collections confirmed that L. proximus occupied shallower habitats than L. f. rufus. In field mesocosms, L. proximus displayed higher dispersal rates than L. ƒ. rufus. These species also do not appear food limited in the field, suggesting that adult competition for food is unlikely. L.f. rufus and L. proximus exhibit different habitat use and dispersal responses, but this does not seem to be in response to intra- or interspecific competitive interactions.
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