Local and regional dynamics of fish metacommunities in intermittent, drought prone streams

Background/Question/Methods

Population and community dynamics are driven by factors that operate across multiple scales. Metacommunity perspectives address the role of spatial configuration and connectivity among local habitats and the movement of organisms across community boundaries on local and regional processes and patterns of biodiversity. Temperate headwater streams experience unique spatial and temporal community dynamics as hydrological conditions and connectivity change due to seasonal oscillations between flowing and non-flowing (drought) conditions. Metacommunity models (patch dynamics, species sorting, mass effects, and neutral) predict local communities and regional metacommunities to be variously structured in space and time according to abiotic and biotic conditions, such as, species dispersal opportunities, physical and chemical environment, and species interactions. In an ongoing field study, we surveyed fish assemblages from two intermittent streams in north Texas, USA, across multiple spatial scales to investigate metacommunity dynamics over time. Species richness and abundance were quantified across local and regional scales for comparisons of community structure and alpha, beta, and gamma diversity. Movement of individuals was quantified by mark/recapture using visual implant elastomer. Multivariate techniques were used to identify correlations between community structure, diversity and spatial arrangement and local habitat variables.

Results/Conclusions

We collected more than 5,000 individuals representing 10 families and 27 species. Local scale richness (alpha diversity) varied from 2 to 14 species across all stream locations and sample dates, while total regional richness (gamma diversity) at the stream level ranged from 19 to 24 species in Hickory Creek and Clear Creek, respectively. Analysis of assemblage composition revealed significant differences between local fish assemblages, indicating a high degree of species turnover (beta diversity) within stream segments and through time, as well as, distinct fish communities across the two streams. Preliminary movement data suggests varying levels of dispersal between local habitat patches depending on spatial (distance), macrohabitat conditions, and species traits. Hydrologically-mediated connectivity among communities (i.e. following high flows or during drought) affected patterns of community structure among local communities. Direct gradient ordination identified associations between local environmental factors and fish assemblage structure, but spatial context (longitudinal position) and connectivity was important for interpreting patterns in beta diversity. Variation among species in response to local environment, spatial arrangement of sites, and seasonality was tied partly to species’ life history traits.  These results preliminarily support mass effects and species sorting models of metacommunity dynamics, depending on the timing of hydrologic events.