Experimental evidence that effects of megaherbivores on mesoherbivore
space use are influenced by species' traitsHarry B. M. Wells, Ramiro D.
Crego & Øystein H. Opedal, et al.Journal of Animal EcologyJune 30,
2021Abstract
The extinction of 80% of megaherbivore (>1,000 kg) species towards the
end of the Pleistocene altered vegetation structure, fire dynamics and
nutrient cycling world-wide. Ecologists have proposed (re)introducing
megaherbivores or their ecological analogues to restore lost ecosystem
functions and reinforce extant but declining megaherbivore populations.
However, the effects of megaherbivores on smaller herbivores are poorly
understood.
We used long-term exclusion experiments and multispecies hierarchical
models fitted to dung counts to test (a) the effect of megaherbivores
(elephant and giraffe) on the occurrence (dung presence) and use intensity
(dung pile density) of mesoherbivores (2–1,000 kg), and (b) the extent to
which the responses of each mesoherbivore species was predictable based on
their traits (diet and shoulder height) and phylogenetic relatedness.
Megaherbivores increased the predicted occurrence and use intensity of
zebras but reduced the occurrence and use intensity of several other
mesoherbivore species. The negative effect of megaherbivores on
mesoherbivore occurrence was stronger for shorter species, regardless of
diet or relatedness.
Megaherbivores substantially reduced the expected total use intensity
(i.e. cumulative dung density of all species) of mesoherbivores, but only
minimally reduced the expected species richness (i.e. cumulative predicted
occurrence probabilities of all species) of mesoherbivores (by <1 species).
Simulated extirpation of megaherbivores altered use intensity by
mesoherbivores, which should be considered during (re)introductions of
megaherbivores or their ecological proxies. Species' traits (in this case
shoulder height) may be more reliable predictors of mesoherbivores'
responses to megaherbivores than phylogenetic relatedness, and may be
useful for predicting responses of data-limited species.
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