Does Interspecific Competition or Predation Shape the African Ungulate Community?

(1) Although interspecific competition has been the suggested process producing resource partitioning and coexistence of African ungulates, recent evidence has pointed to intraspecific competition, predation, and facilitation as alternative hypotheses. (2) The ungulate community in the Serengeti-Mara region of Tanzania and Kenya was examined in the light of these hypotheses between 1980 and 1983. The wildebeest migration provided a natural experiment to alter the intensity of interspecific competition among eight other species of grazing ungulates. (3) Data on vegetation choice, habitat overlap with wildebeest, and herd spacing between species were obtained from vehicle transects in the presence and absence of wildebeest. These data were used to test the predictions derived from six hypothetical processes: (i) interspecific competition, (ii) intraspecific competition, (iii) autecological factors, (iv) predation, (v) facilitation, and (vi) random processes. (4) There was a high similarity in vegetation choice between species, and a large overlap with the competing wildebeest. (5) Most species were found closer to wildebeest than an expected random distribution would suggest. (6) Comparing these results with the predictions, they suggest that Thomson's and Grant's gazelles are strongly influenced by predation. (7) Zebra, topi, impala, waterbuck and warthog are influenced by both predation and interspecific competition and these species may be showing a mixed evolutionarily stable strategy to cope with two opposing pressures. Zebra, in particular, are using the wildebeest to obtain protection from predators. (8) In general predation appears to play as much a role as interspecific competition in structuring this community.