Abstract
The distribution, abundance and sensitivity 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.
Highlights
Invertebrates comprise the bulk of diversity in an ecosystem, they are often excluded from conservation initiatives. Cardoso et al (2011) identified seven reasons for this
One other study of ants along an altitude exists for the Savanna Biome in South Africa, where Schoeman & Foord (2012) found 104 species in 29 genera along a 1000 m elevational range in the Marakele National Park
With a higher generic plant diversity than the Cape Floristic Kingdom (Hahn 2006) and 90% of all spider families found in the Savanna Biome (Foord et al 2011), the Soutpansberg is characterised by rich, higher taxon diversity. doi:10.4102/koedoe.v57i1.1244
Summary
Invertebrates comprise the bulk of diversity in an ecosystem, they are often excluded from conservation initiatives. Cardoso et al (2011) identified seven reasons for this. Three of the shortfalls had to do with: (1) the distribution of invertebrate species is unknown (Wallacean), (2) invertebrate abundance and their changes in space and time are unknown (Prestonian) and (3) invertebrates’ way of life and sensitivity to habitat types are largely unknown (Hutchinsonian). These three shortfalls are relevant to how ecologists practise their science, as the distribution, abundance in time and space, and sensitivities to habitat change are largely unknown for most species These constraints can be resolved through inventories that follow standardised and comparable protocols (Cardoso et al 2011). In addition to being diverse, abundant and a dominant component of animal biomass in terrestrial ecosystems (Hölldobler & Wilson 1990), they perform important functions in ecosystems, including pollination, myrmechory and nutrient cycling, among others (Wielgoss et al 2014)
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