Capturing pests and releasing ecosystem engineers: translocation of common but diminished species to re-establish ecological roles

Abstract

Translocation of abundant but declining ecologically important species for re-establishing more sustainable ecosystem function is a neglected but promising form of conservation intervention. Here, we developed a translocation program in which we capture pests and release ecosystem engineers, by relocating California ground squirrels Otospermophilus beecheyi from areas where they are unwanted to conserved lands where they can perform ecosystem services such as burrowing and vegetation alteration. We accomplished this using an experimental approach in which some factors were measured or experimentally manipulated, while others were held constant. We translocated 707 squirrels and examined survival and movement patterns as a function of several translocation tactics and ecological factors. We released squirrels at 9 different plots with varying ecological contexts and at each plot experimentally manipulated post-release habitat using mowing, mowing plus the use of augers to establish starter burrows, and controls that remained unmanipulated. The most influential variables affecting short-term survival, dispersal, and long-term persistence were factors relating to soils and vegetation structure. Translocated squirrels had higher initial survival on plots where dense exotic grasses were experimentally altered, greater dispersal when released at sites with less friable clay soils, and improved long-term persistence at sites characterized by more friable soils associated with metavolcanic than alluvial geological layers. Squirrel persistence was also improved when translocations supplemented previous translocation sites than during initial translocations to sites containing no resident squirrels. Our results demonstrate how California ground squirrels can be successfully translocated as part of a larger objective to favorably alter ecological function in novel grassland ecosystems dominated by non-native vegetation. In broader context, our study highlights the importance of testing release strategies, and examining habitat variables and restoration techniques more closely when selecting release sites to improve translocation outcomes.