Niche differentiation, a shift in the environmental requirements of a population, can alleviate interspecific competition. Two hyrax species (Heterohyrax brucei and Procavia johnstoni) co-occur on rock outcroppings (kopjes) in Tanzania. These two species interact, share space, and are thought to have variably overlapping diets. To determine if competition between hyrax species leads to niche differentiation, I examined the feeding patterns of nine populations at five study sites. I observed population sizes, food choices and feeding locations. At the four sites where the two species co-occurred, Heterohyrax browsed significantly more and tended to feed from more peripheral locations than Procavia. Procavia mostly grazed, but still browsed frequently. As predicted by competition theory, Heterohyrax became increasingly specialized in browsing with increased interspecific competition. Procavia, rather than becoming more specialized in grazing, browsed more with increased interspecific competition. These niche shifts suggest that interspecific competition influences feeding patterns in hyraxes, though the results for Procavia are puzzling. Further observations including data on each species in allopatry may help us understand the responses of hyraxes to interspecific competition.
Alissa Zimman, ’01 Green Bay, WI
Sponsor: Andrew McCollum