Inferring Interspecific Interactions Among African Savannah Herbivores Using (…)

ABSTRACT

Competition and facilitation are fundamental concepts in ecology, but evidence for the strength and direction of interspecific interactions within trophic levels is difficult to obtain, particularly in large assemblages of free-ranging animals. We investigated abundance patterns and interspecific associations among 10 African savannah herbivores by implementing a multispecies hierarchical distance-sampling model with a variance–covariance matrix that accounted for (i) imperfect detection; (ii) habitat preferences; and (iii) ‘indirect’ associations (i.e., shared/contrasting associations between two species mediated by any third species). Animal groups were more likely to go undetected at sampling locations with more woody vegetation. Herds of all species were less numerous on sandier soils and far from water, while associations with NDVI and woody vegetation were mixed. Positive associations dominated the correlations among species (before accounting for ‘indirect’ associations), and ‘direct’ pairwise associations after accounting for habitat preferences were generally weaker (correlation for all species pairs <|0.55|); the strongest positive correlation was between white rhino and warthog (0.47, posterior probability = 95%). The lack of strong negative associations among species is consistent with coexistence theory's premise that intraspecific competition outweighs interspecific competition. The directions of the weaker ‘direct’ pairwise interactions were largely consistent with biological mechanisms proposed or identified in previous work.