Does Increasing Food-Web Stability Mediate the Effects of Cattle Grazing in Aquatic Desert Ecosystems?

Authors: Hannah Moore, Howard Whiteman

Year: 2018

Abstract

Anthropogenic activities have led to habitat degradation in streams throughout much of Western North America. In particular, cattle grazing has caused a loss of riparian vegetation resulting in higher water temperatures and an increase in nutrient runoff. The effects of habitat degradation on food quality and quantity for aquatic consumers could have large implications for stream communities. Since omnivores feed at multiple trophic levels, they increase community complexity and may be resilient to altered food webs. Theoretically, this would allow them to stabilize communities in degraded habitats where resources have been reduced. To test the hypothesis that omnivores positively impact community stability in degraded habitats, I established artificial mesocosms using 1000L cattle tanks with varying levels of two disturbance factors: shade (loss of shade mimicking a degraded riparian zone) and nutrients (increased nutrients representing agricultural fertilizer inputs), and the presence or absence of the omnivorous speckled dace (Rhinichthys osculus). I compared the rate of change of community structure and ecosystem function by analyzing invertebrate biodiversity and biomass, algal biomass, and water chemistry in order to determine if dace play a stabilizing role in degraded streams. By understanding the role omnivory plays in degraded aquatic systems, we can gain insight into both the management and restoration of these ubiquitous habitats.