Data from: Does primary productivity modulate the indirect effects of large herbivores? A global meta-analysis

1. Indirect effects of large mammalian herbivores (LMH), while much less
studied than those of apex predators, are increasingly recognized to exert
powerful influences on communities and ecosystems. The strength of these
effects is spatiotemporally variable, and several sets of authors have
suggested that they are governed in part by primary productivity. However,
prior theoretical and field studies have generated conflicting results and
predictions, underscoring the need for a synthetic global analysis. 2. We
conducted a meta-analysis of the direction and magnitude of large
mammalian herbivore-initiated indirect interactions using 67 published
studies comprising 456 individual responses. We georeferenced 41 of these
studies (comprising 253 responses from 33 locations on 5 continents) to a
satellite-derived map of primary productivity. Because predator
assemblages might also influence the impact of large herbivores, we
conducted a similar analysis using a global map of large-carnivore species
richness. 3. In general, LMH reduced the abundance of other consumer
species and also tended to reduce consumer richness, although the latter
effect was only marginally significant. 4. There was a pronounced
reduction in the strength of negative (i.e., suppressive, due e.g. to
competition) indirect effects of LMH on consumer abundance in more
productive ecosystems. In contrast, positive (facilitative) indirect
effects were not significantly correlated with productivity, likely
because these comprised a more heterogeneous array of mechanisms. We found
no effect of carnivore species richness on herbivore-initiated indirect
effect strength. 5. Our findings help to resolve the fundamental problem
of ecological contingency as it pertains to the strength of an
under-studied class of multi-trophic interactions. Moreover, these results
will aid in predicting the indirect effects of anthropogenic wildlife
declines and irruptions, and how these effects might be mediated by
climatically driven shifts in resource availability. To the extent that
intact ungulate guilds help to suppress populations of small animals that
act as agricultural pests and disease reservoirs, the negative impacts of
large-mammal declines on human well-being may be relatively stronger in
low-productivity areas.