Conceptualizing and measuring ecological spillover effects from protected areas

Protected areas influence their surroundings in a variety of ways. These “spillover effects” can change an area's conservation value and affect its social license. Advanced statistical tools for quantifying protected area spillovers are well established, but underlying assumptions about spillover geography and measurement often lack clarity. Although spillover effects should decline with increasing distance from a protected area, there are no published guidelines for determining the rate, magnitude, or scale of decline and there is no conceptual framework to guide tests of alternative hypotheses. Current practices heavily increase the risk of Type II errors (detecting spillover where none exists), particularly at distances far from protected areas. I propose an approach that recognizes alternative forms for ecological and biophysical spillovers and background variance as competing hypotheses. In particular, careful consideration must be given to the question of how many measurements are needed to rigorously distinguish spillovers from background variance in study environments .