Occupancy and environmental responses of habitat specialists and generalists depend on dispersal traits

Ecologists have been interested in understanding communities through the lens of specialists and generalists to predict species diversity and distribution patterns and to ameliorate worldwide declines in specialist species. Dispersaltraits are assumed to be associated with specialization (specialists are weaker dispersersthan generalists), but dispersalmodes can be variable within groups. Niche-based predictions of occupancy and environmental responses were assessed using invertebrates from California vernal poolsthat were categorized by specialization (endemic or widespread taxa) and dispersalmode (passive or active dispersal). Data from a latitudinal gradient resulted in widespread taxa with greater percent occupancy than endemic taxa as predicted, but passive dispersershad greater occupancy than active dispersersin contrast to predictions. Endemic species and widespread-active dispersersexhibited similar levels of specialization measured as coefficient of variation among treatments in a mesocosmexperiment. This suggested that habitat choice was important, and these differences in specialization were scale dependent (generalists across habitat types and specialists within a habitat type). A negative correlation between latitudinal occupancy and level of specialization demonstrated how local-scale responses and landscape patterns were related and depend on both specialization and dispersaltraits. This study underscores how habitat heterogeneity and species traits, including specialization and dispersal, can interact to affect community patterns at different spatial scales.