Spatial and temporal abundance, substrate partitioning and species co-occurrence in a guild of Neotropical blackflies (Diptera: Simuliidae)

Abstract

Abstract Blackfly larvae were sampled monthly from two small Neotropical mountain streams 500 m apart from each other in northern Venezuela during a 15-month period, and ten habitat variables were measured at two altitudes (800 and 900 m) to determine local spatial and temporal variations in abundance, stream variables, species co-occurrence, and substrate preference within the blackfly guild. The blackfly species composition of each stream was the same, with five species (in order of abundance): SimuliumochraceumWalker s.l., S. payneiVargas, S. metallicum Bellardicytospecies E, Simulium sp., and S. horacioi Okazawa & Onishi. There were clear differences in community structure between streams (not among altitudes), although S. ochraceum s.l. was the most abundant species in both habitats. Principal component and correlation analyses revealed that structural (great depth, width, flow, and discharge) and chemical (low conductivity) factors were the stream variables best associated to the spatial distribution of most blackfly species. Blackfly abundance was greater in the larger stream. Larvae were most abundant on submerged rocks and fallen leaves, although the patterns of substrate use within the guild revealed substrate partitioning among most blackfly species. There was one general annual peak of abundance at the end of the rainy season. We suggest that blackfly community structure in these Neotropical headwaters streams, over the small spatial scale examined here, is largely influenced by interactions among stream size and velocity-related factors (width, streamflow, discharge and substrate availability-stability) and the rainfall regime.