POPULATION-SIZE DEPENDENCE, COMPETITIVE COEXISTENCE AND HABITAT DESTRUCTION

1. Spatial dynamics can lead to coexistence of competing species even with strong asymmetric competition under the assumption that the infer ior competitor is a better colonizer given equal rates of extinction. Patterns of habitat fragmentation may alter competitive coexistence un der this assumption. 2. Numerical models were developed to test for th e previously ignored effect of population size on competitive exclusio n and on extinction rates for coexistence of competing species. These models neglect spatial arrangement. 3. Cellular automata were develope d to test the effect of population size on competitive coexistence of two species, given that the inferior competitor is a better colonizer. The cellular automata in the present study were stochastic in that th ey were based upon colonization and extinction probabilities rather th an deterministic rules. 4. The effect of population size on competitiv e exclusion at the local scale was found to have little consequence fo r the coexistence of competitors at the metapopulation (or landscape) scale. In contrast, population size effects on extinction at the local scale led to much reduced landscape scale coexistence compared to sim ulations not including localized population size effects on extinction , especially in the cellular automata models. Spatially explicit dynam ics of the cellular automata vs, deterministic rates of the numerical model resulted in decreased survival of both species. One important fi nding is that superior competitors that are widespread can become exti nct before less common inferior competitors because of limited coloniz ation. 5. These results suggest that population size-extinction relati onships may play a large role in competitive coexistence. These result s and differences are used in a model structure to help reconcile prev ious spatially explicit studies which provided apparently different re sults concerning coexistence of competing species.