Testing for consistency in ecosystem engineering : do cushion plants always turn up the heat?

Abstract

Ecosystem engineers influence community structure and functioning by altering habitat and resource availability. However, few studies have assessed how consistent ecosystem engineers' impacts are on abiotic habitat conditions and/or community characteristics, either across species or between habitats. Here we test for the consistency of ecosystem engineering across, and within, cushion-forming plant species, a group of ecosystem engineers that are dominant in polar and alpine environments, by reviewing studies that document their effects on temperature. We find inconsistent effects, with cushion plants having contrasting impacts on temperatures in different studies. Even after limiting analyses to a single cushion plant morphology type or to just a single species, impacts on temperature were still inconsistent between studies. Therefore, while cushion plants have relatively consistent impacts on plant communities (e.g. increasing local species richness), their impact on temperature may not be the overarching abiotic mechanism driving this ecological effect. These results, therefore, highlight the need to explicitly test if ecosystem engineers’ biotic and abiotic impacts are consistent through space and time, and emphasize the importance of understanding context-dependence in the outcome of biotic interactions.