An inventory of epigeal ants of the western Soutpansberg Mountain Range, South Africa

Abstract

The distribution, abundance and sensitivity of invertebrates to habitat change are largely unknown. Long-term monitoring of ecological gradients with standardised and comparable protocols can form the basis of a better understanding. Altitudinal gradients are particularly relevant within this context. Here we provide a check list and baseline data for ant species collected over a 5-year period across the Soutpansberg Mountain Range, South Africa. Standardised pitfall surveys across 11 sites yielded a total of 133 species in 38 genera and 6 subfamilies. Sample coverage of epigeal ants was 0.98 for the transect as a whole. Of these species, 21% were restricted to the southern slope of the mountain and 14% to the northern slope. Extrapolated richness estimates reached an asymptote for all, except for three sites. These were the only sites impacted by bush encroachment. Observed richness was the highest at a low-altitude mesic site that is exposed to considerable disturbance by megaherbivores and mechanical clearing of woody vegetation. Structural classification of vegetation was predictive of a broad-scale ant assemblage structure. On a smaller scale, however, structure was a function of elevation, space and temperature.Conservation implications: Future monitoring should target indicator taxa associated with bush encroachment, particularly with reference to their impacts on grasslands. Bush encroachment could endanger several ant species associated with mesic grasslands and woodlands on the mountain, as well as ant diversity, as these were the habitats with the highest ant diversity.