We used live-trapping and foraging from experimental food patches to test for habitat preference, interspecific competition, and predation risk of small mammals and birds at Lajuma Research Center, South Africa. These approaches were used in unison across taxa including: Rhabdomys pumilio, Mus minutoides, Dendromus mystacalis, Micaelamys namaquensis, Aethomys ineptus, Elephantulus myurus, and Francolinus natalensis. To accomplish this we established grids that straddled adjacent macro-habitats (woodland, rocky hillside, and grassland with wooded patches). We used trapping to measure habitat use and feeding opportunities and giving-up densities (GUDs) to measure habitat-specific foraging costs. The species with the lowest GUD under a specific habitat, microhabitat, activity time, or food was considered the most efficient and presumed to have a competitive advantage under these conditions.
Results/Conclusions
R. pumilio exhibited a distinct-preference for the interior of grassland and consumed relatively high proportions of alfalfa pellets and seeds. D. melanotis exhibited a significant a vertical pattern in the wooded patches which provided a distinct preference axis for its coexistence with the ground-foraging R. pumilio and M. minutoides. A. ineptus and M. namaquensis were the only small mammal inhabitants of the woodland with higher abundance and activity by the smaller M. namaquensis. A. ineptus preferred the herbaceous cover of the woodland and woody patches within the grassland whereas, M. namaquensis showed greater preference for rocky outcrops than woodland. The two species had similar diet preferences, being highest on alfalfa and seeds. The rock-dwelling community comprised of F. natalensis, M. namaquensis, and the insectivorous E. myurus. F. natalensis had its highest activity in the rocky areas and under the cover of the wooded patches in the grassland, and had a dietary advantage over the rodents by consuming mealworms and seeds of different sizes. Habitat edges appeared to be of lower quality than interior for all species (high GUDs), suggesting increased risk of predation.
This uniform distribution across habitats suggests that feeding opportunities are fairly available in all habitats; however, the distinct patterns of habitat preferences are shaped by competition and species-specific foraging costs. These communities showed a stable co-existence driven mainly by “the ghost of competition past” that forces species to occupy different habitats. The combination of trapping and GUDs provided an unbiased and controlled measure of both habitat use and foraging costs when equal opportunities are simultaneously provided in the different habitats. This approach is widely applicable in understanding the coexistence of across-taxa communities and to effectively quantify edge effects.
