Assessing the Impact of Competition on Community Assembly: A Case Study using Small Mammals

Abstract

Competition has been shown to be an important factor in natural systems. Yet, its effect on community structure remains poorly understood and is often disputed. Null models have been employed by researchers in recent years, but these generally suffer from a lack of power estimation and unclear distinction between statistical significance and biological importance. Models that employ an appropriate alternative hypothesis allow for powers estimates and for quantitative evaluation of the effects of competition. We have developed methodologies to (1) allow for testing the significance of competition in natural communities, (2) determine the power of these estimates, and (3) produce maximum likelihood estimates of interaction parameters or these communities. Using these methologies we show that small mammal communities at the interface between Valdivian temperate rain forest and Patagonian steppe in southern South America appear significantly and importantly structured by competition, although we cannot distinguish between resource competition, interference competition, and apparent competition. Secondarily, we show that the geographic origin of the component species (Valdivian vs. Patagonian) is relatively more important than their habitat affinities in structuring these communities.