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 ...