Community structure and food web dynamics in endangered, ephemeral wetlands of the high plains

Background/Question/Methods

Understanding factors controlling food webs is challenging, especially in natural settings because diversity and food web interactions can fluctuate widely through space and time. The problem is aggravated when the focus is on relatively permanent ecosystems with diverse habitats and high species diversity as well as confounding factors within large watersheds. In contrast, playa lakes, ephemeral wetlands in arid to semi-arid regions, have low species diversity and relatively homogenous habitat, which eliminates many of these difficulties. These systems offer opportunities to reveal factors controlling food webs.

Our study focuses on factors controlling biodiversity and food web dynamics in playas in the U.S. high plains, specifically: the ecological importance of ecosystem size habitat diversity, hydrologic cycles, and anthropogenic disturbances.

Results/Conclusions

During summer 2011, we collected macroinvertebrates and amphibians from 45 playas and food web data from 25 of those playas from grassland areas of eastern Colorado. Sampled playas varied in many environmental features including size, depth, turbidity, plant structure, and anthropogenic impacts (roads, crops, grazing, etc.). Food web complexity was evaluated using stable isotope analyses and Layman’s stable isotope metrics. Many more playas are being sampled in 2012 from Wyoming and other northern Great Plains states, and experiments in artificial playas are beginning simultaneously.

Biodiversity and food web complexity rose as habitat complexity increased. Aquatic insects (water beetles, water boatmen, backswimmers, and many dipterans) and amphibians (tadpoles and salamanders) were more abundant in larger and deeper playas. However, most playa communities in Colorado were dominated by large branchiopods (fairy, tadpole, and clam shrimps) and various planktonic crustaceans regardless of ecosystem size and habitat complexity. Species richness was generally higher in larger, deeper, less turbid playas and in natural vs. artificial pools. Disturbance type (grazing, row crops, distance from roads, etc.) did not significantly affect community metrics, possibly because organisms were not sufficiently affected by the degree and type of disturbance or the organisms found within the playas are simply opportunists and the response to the disturbance is overwhelmed by the presence of water.

Additional biodiversity and food web studies are critically needed in playas because these ecosystems are vital aquatic systems in the Great Plains, they have rarely been studied, and they are mostly unprotected by environmental laws.