Competitive reversals inside ecological reserves: the role of external habitat degradation

Habitat degradation is the slow - and often subtle - deterioration in habit at quality that accompanies human activities through increases in road dens ity, pesticide use, hunting pressure, etc. Such degradation is of particula r concern in fragmented habitats where economic or jurisdictional boundarie s rather than ecological ones determine the level of exploitation adjoining habitat patches endure. To examine the consequences habitat degradation mi ght have on species interactions, we posited a patch of pristine habitat su rrounded by "matrix" habitat whose degradation level was variable. Using a coupled pair of diffusive Lotka-Volterra competition equations with Robin ( mixed) boundary conditions, we modeled the dynamics of two competing specie s inhabiting the pristine patch and incorporated matrix degradation through a tunable "hostility" parameter representing species' mortality rates in t he matrix. We found that the numerical range of competition coefficients ov er which one species is the competitive dominant and the other inferior may grow or shrink as matrix quality deteriorates. In some cases, degradation of the exterior habitat would bring about a complete competitive reversal i nside the preserve. This result, wherein a formerly inferior species suppla nts a formerly dominant one - even inside the "protected" remnant patch its elf - has policy implications for both nature reserve design and management of human activities outside park boundaries.