Scale Dependence and Scale Independence in Habitat Associations of Small Mammals in Southern Temperate Rainforest

Abstract

Although field biologists commonly employ methodologies that either are time-tested or are believed (usually for very good reason) to be suitable to the conditions that are encountered, it is rare that results generated using differing methods can be compared on a single fauna. We reanalyze data from three studies conducted on the small mammal fauna of Valdivian temperate rainforests in southern Chile. By restricting our analyses to a relatively homogeneous habitat type we avoid many problems associated with studies over large spatial scales, such as increased species richness via beta diversity. The studies involve a temporal transect, an elevational transect, and a latitudinal transect, and comprise a spatially nested series. Because these studies differed in their initial objectives, they employed different methodologies, both in the field and during subsequent data analysis. At all scales of analysis there is notable overlap in habitat use by all species. Although we observed some seasonal differences in habitat use by species, these were not substantial and involved a small subset of the species. At a local scale, numerically dominant species selected non-random microhabitats but co-occurred with other species more frequently than expected by chance. At a larger spatial scale species appeared to select large subsets of the macrohabitat (i.e., mesohabitat), providing patterns suggestive of apparent competition among species. At an even larger spatial scale, that of temperate southern South America, we predict that species assemblages will again exhibit positive associations. Thus, views on the importance of competition and other biological processes depend critically on the spatial and temporal scales over which observations are made.