ASSOCIATIONS BETWEEN PATCH AREA AND VITAL RATES: CONSEQUENCES FOR LOCAL AND REGIONAL POPULATIONS

Abstract

The negative association between patch area and extinction risk is one of the most ubiquitous observations in ecology. This association is often attributed to the disproportionate effects of stochastic fluctuations on small populations, but it also may be explained by deterministic relationships between patch area and vital rates (i.e., fecundity and survival). We explored the consequences of including deterministic relationships between patch area and vital rates in metapopulation models. Field studies have revealed that fecundity and monthly survivorship were positively associated with patch size for the Florida scrub lizard (Sceloporus woodi). Using simulation techniques, we compared metapopulation models of artificial landscapes that included vital rates for this species (scaled for patch area) to models that used averaged estimates of vital rates for all patches. These two types of metapopulation models produced dramatically different results with respect to the proportion of occupied patches and the extinction probability of the regional population. Including deterministic relationships between patch area and vital rates often resulted in either all patches being occupied or all patches going extinct, depending on the size of the local patches. Few artificial landscapes resulted in a dynamic colonization–extinction equilibrium characteristic of a “classic metapopulation.” In contrast, model simulations with demographic parameters equal for all patch sizes produced a more linear decline in extinction probability with patch size. Our results highlight considerations for application of metapopulation theory in conservation.