The effects of intra- and inter-specific competition on the population dynamics of black rhinos (Diceros bicornis)

Both intra- and inter-specific competition can influence population dynamics of endangered species. At the population level, intra-specific competition generally manifests as density-dependence wherein population size or density influences population growth parameters. Managers of density-dependent endangered species can leverage this trait to facilitate population growth, but if populations are too small, they could go extinct. Simultaneously, endangered species can face pressure from inter-specific competition where an increase in one species can lead to decrease in another. Managers may intervene with other species to support an endangered population. We evaluated the relative influences of intra- and inter-specific competition on population growth and related parameters (i.e., birth, conception, mortality, sex allocation, age at first conception, inter-calving interval) in black rhino ( Diceros bicornis ). Thirteen reserves that had black rhinos for 6–23 years provided population data as well as game counts of mixed feeders and browsers (i.e., potential competitors). We found that population growth was zero or positive in 159 of 170 site-years. Black rhino density influenced all parameters except conception, but potential competitors only influenced birth occurrence and mortality rate. However, no variables affected population growth, which may reflect these reserves' strategy of establishing small populations to avoid negative density-dependence. The robustness of population growth indicates that, thus far, managers have avoided some pitfalls of small populations, but we caution that meta-population management approaches may be necessary in the future, especially to preserve genetic diversity. Overall, our findings support density-focused management of black rhino and similarly density-dependent endangered species.