Environmental context shapes the relationship between grass consumption and body size in African herbivore communities
Authors:
Joel O Abraham, John Rowan, Kaedan O'Brien, Kathryn G Sokolowski, J Tyler Faith
Abstract:
Though herbivore grass dependence has been shown to increase with body size across
herbivore species, it is unclear whether this relationship holds at the community
level. Here we evaluate whether grass consumption scales positively with body size
within African large mammalian herbivore communities and how this relationship varies
with environmental context. We used stable carbon isotope and community occurrence
data to investigate how grass dependence scales with body size within 23 savanna herbivore
communities throughout eastern and central Africa. We found that dietary grass fraction
increased with body size for the majority of herbivore communities considered, especially
when complete community data were available. However, the slope of this relationship
varied, and rainfall seasonality and elephant presence were key drivers of the variation—grass
dependence increased less strongly with body size where rainfall was more seasonal
and where elephants were present. We found also that the dependence of the herbivore
community as a whole on grass peaked at intermediate woody cover. Intraspecific diet
variation contributed to these community-level patterns: common hippopotamus (Hippopotamus amphibius) and giraffe (Giraffa camelopardalis) ate less grass where rainfall was more seasonal, whereas Cape buffalo (Syncerus caffer) and savanna elephant (Loxodonta africana) grass consumption were parabolically related to woody cover. Our results indicate
that general rules appear to govern herbivore community assembly, though some aspects
of herbivore foraging behavior depend upon local environmental context.
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