The roles of abiotic factors, dispersal, and species interactions in structuring stream assemblages of black flies (Diptera: Simuliidae)

ABSTRACT: BACKGROUND: The patterns and drivers of species assemblages represent the core of community ecology.We focus on the assemblages of a single family of ubiquitous lotic insects, the Simuliidae(black flies), of which the larvae play a critical role in resource turnover in steams. We useMantel tests and null models to tease out the potential influence of abiotic stream conditions,species interactions, and dispersal on the assemblage patterns of larval black flies over twospatial scales (within and across ecoregions) and two seasons (spring and summer). RESULTS: When stream sites were considered across ecoregions in the spring, stream conditions anddispersal were correlated significantly with species similarity; however, within ecoregions inthe spring, dispersal was important only in the Piedmont and Sandhills and abiotic factorsonly in the Mountains. In contrast, results of the summer analyses within and acrossecoregions were congruent; assemblage similarity was significantly correlated with streamconditions both across and within ecoregions. Null models suggested that patterns of speciessegregation in the spring were consistent with a community structured by competition,whereas patterns in the summer were consistent with species assemblages influenced byabiotic factors. CONCLUSIONS: Species composition of black flies at streams sites is correlated with dispersal factors andstream conditions, but results vary over spatial and temporal scales. Communities of blackflies can be viewed within a metacommunity context; local assemblages are consistent withspecies sorting and mass effects. Given that black flies have a terrestrial stage, with femalesdeciding where to place the eggs, a full understanding of the processes that determine local aquatic assemblages will require integration of the dynamics of the aquatic immature stagesand the terrestrial adults.