The influence of hydrology on aquatic invertebrate diversity and food web structure

Background/Question/Methods

Temporary woodland ponds in temperate forests and intermittent streams in deserts exhibit strong community responses to variation in hydrological properties. Climatic changes in temperature and precipitation events can alter the natural flow regime rendering these habitats unsuitable for the invertebrates that rely on them. Invertebrates play key roles in nutrient cycling, primary productivity, ecosystem functioning and their loss can have dramatic consequences for ecosystem sustainability. We used aquatic invertebrate community data sets from woodland ponds in SE Ontario, Canada and arid-land streams in SE Arizona, USA to address the influence of hydrology on diversity (taxonomic and trait) and community and food web structure. We used quantile regression to determine upper and lower limits of biotic responses to flow permanence and used carbon and nitrogen stable isotopes to calculate the realized food chain length and trophic diversity in ponds. 

Results/Conclusions

Both ecosystem types showed increased species richness with increases in hydroperiod. Ponds with longer hydroperiod had higher invertebrate richness, higher trophic diversity, and had the longest food chains. Similarly, perennial streams had higher invertebrate richness, functional richness and functional evenness and perhaps, indicating longer food chains. We found that the duration of stream drying events and flow permanence place limiting constraints on the responses of functional and taxonomic richness. Together these results demonstrate that community composition and hydrology substantially influenced the functional richness and trophic diversity of ponds and streams. We hope this work stimulates discussion and helps facilitate synthesis of work on understanding the connection between biodiversity and food web structure across different types of aquatic habitats.