Co‐occurrence modelling highlights conservation implications for two competing spiral‐horned antelope

Abstract

AbstractWe assessed the potential competitive exclusion of southern bushbuck (hereafter bushbuck,Tragelaphus scriptus) by nyala (Tragelaphusangasii), the larger of the two spiral‐horned browsing antelopes (members of the Tragelaphine family). It has been suggested that high concentrations of nyala, capable of browsing a greater breadth of food items, negatively influence bushbuck. Using camera trap data, we explored factors influencing spatio‐temporal activity patterns and co‐occurrence of both species within three Protected Areas (PAs) of the Maputaland Conservation Unit, South Africa. Bushbuck have gone locally extinct within one of our survey areas, likely because of competitive pressures and cascading effects. Our results indicated a segregation of activities; bushbuck was more nocturnal, particularly in areas with higher nyala occupancy. Nyala occupancy overall was higher than bushbuck. When comparing occupancies at the management level, bushbuck occupancy was higher than nyala within two survey areas: where nyala were modelled as present but populations were managed through culling, and where leopard (Panthera pardus) populations were highest. Co‐occurrence was most likely in these two survey areas, indicating a threshold of nyala occupancy up to which bushbuck were tolerant. Where nyala were present in conjunction with high leopard density, bushbuck occupancy was higher. Conversely, where leopard density was low, the cascading effect was of high nyala occupancy, with subsequent competitive exclusion of bushbuck. Our results have critical management implications for PAs, including the management of carrying capacities, the preservation of native species assemblages and habitat management. We provide evidence that a larger‐bodied sympatric species can outcompete subordinate sympatric browsers when not effectively managed, particularly where the predation effects that influence population dynamics are limited.