ASSESSING THE IMPACT OF COMPETITION ON COMMUNITY ASSEMBLY - A CASE-STUDY USING SMALL MAMMALS

Competition has been shown to be an important factor in natural system s. Yet, its effect on community structure remains poorly understood an d is often disputed. Null models have been employed by researchers in recent years, but these generally suffer from a lack of power estimati on and unclear distinction between statistical significance and biolog ical importance, Models that employ an appropriate alternative hypothe sis allow for power estimates and for quantitative evaluation of the e ffects of competition. We have developed methodologies to (1) allow fo r testing the significance of competition in natural communities, (2) determine the power of these estimates, and (3) produce maximum likeli hood estimates of interaction parameters for these communities. Using these methodologies we show that small mammal communities at the inter face 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 compe tition, interference competition, and apparent competition. Secondaril y, we show that the geographic origin of the component species (Valdiv ian vs. Patagonian) is relatively more important than their habitat af finities in structuring these communities.