Fine-scale invertebrate community partitioning in an arid headwater stream suggests unique habitat requirements for predators

Authors: Kate S. Boersma, Michael T. Bogan

Year: 2010 (xlii)

Abstract

Predators are considered more susceptible to rapid changes in environmental variables than other trophic levels because of their high resource requirements. Predator losses destabilize community structure and can lead to irreversible changes to aquatic ecosystem functioning. Therefore, examining the existing relationship between predator distributions and abiotic variables is an important first step in order to predict aquatic community responses to climate change in streams. We sampled invertebrate communities in fragmented pools within a single arid headwater stream in southeastern Arizona in order to relate fine-scale differences in abiotic characteristics with 1) top predator presence/absence, and 2) the diversity and abundance of generalist predators. Multivariate ordination revealed that warm, deep pools with little canopy cover (WDPs) and cool, shallow pools with extensive canopy cover (CSPs) contained distinct invertebrate communities, and presence of top predators was associated with WDPs. Additionally, generalist predator diversity and abundance were significantly higher in WDPs than in CSPs. Indicator species analysis demonstrated that this WDP predator community was dominated by obligate aquatic beetles and bugs, unlike the CSPs, which were characterized by prey species with aquatic larvae and terrestrial adults. Under regional climate projections of longer, more frequent, and more intense droughts, both CSPs and WDPs are threatened by stream drying. Importantly, the loss of the WDP predatory taxa may significantly alter community structure due to cascading trophic effects. As a result, conservation efforts focused on WDPs may be required in order to maintain intact communities in arid headwater streams.