Species sorting and spatial effects in hyporheic invertebrate functional groups

Abstract Invertebrate communities in the hyporheic zone are structured by metacommunity processes including environmental filtering and spatial effects (e.g., dispersal). We investigated how these processes differentially influence two functional groups: groundwater-obligate invertebrates (stygobionts) and benthic insects. We predicted that environmental filtering would dominate for insects, while spatial effects would prevail for stygobionts. We collected 76 samples from 28 hyporheic sites along 109 km of the Rio Grande, Texas, USA, enumerating 54,508 individuals across 80 taxa. Concordance analysis and RDA revealed two communities: one dominated by insects, and another by crustaceans and soft-bodied organisms, including all stygobionts. In linear models, insect richness and abundance were influenced by temperature, alkalinity, oxygen, and pH. Stygobionts were associated with higher nitrate, higher temperature, and lower specific conductance (indicating groundwater discharge in the study area). Stygobiont presence, richness, and abundance increased near springs. Stygobiont communities exhibited spatial autocorrelation while insect communities did not. Insect responses to environmental variables suggest species sorting effects, which prevail for taxa with sufficient dispersal ability. Stygobiont responses to spatial variables suggest limited dispersal from source populations in adjacent aquifers. Dispersal ability may limit stygobionts’ ability to recolonize habitats after hydrologic disturbances, especially when connection with adjacent aquifers is lost.