Consistent effects of predator removal on detritivores across a range of biotic and abiotic conditions

Authors: Kate S. Boersma, Michael T. Bogan, David A. Lytle

Year: 2012 (xliv)

Abstract

Predator extinction is a significant mechanism by which a warming and drying climate may affect food web structure in aquatic communities. In arid-land aquatic habitats, fish and large-bodied invertebrate predators are especially vulnerable to climatic changes and stream drying, and several local extinctions of the predatory giant water bug Abedus herberti have been recorded across the southwestern United States. Here we report findings from two predator-removal experiments conducted during the dry seasons of 2010 and 2011. We seeded tanks with stream invertebrates and removed A. herberti as a treatment in both experiments, however several important correlates such as canopy cover and annual rainfall differed dramatically between years. Possibly as a result of these strong interannual abiotic differences, tanks from 2011 contained fewer species than tanks from 2010, regardless of treatment (mean tank richness: 11.55 and 19.75 respectively), and the effects of top predator removal on overall community structure were apparent in the diverse 2010 communities but not in the depauperate 2011 communities. Despite these differences, one consistent pattern emerged. In both years, top predator removal caused significant reductions in the abundance of the dominant detritivore, the sycamore caddisfly, Phylloicus mexicanus. Our study suggests that A. herberti plays a fundamental role in food web processes despite differences in year type and community composition, and its disappearance could slow the processing of organic material in arid-land streams across the region.