Resolving Indirect Effects of Large Herbivores on Terrestrial Ecosystem Functioning

G. Adam Meyer, Shawn J. Leroux

The world’s large herbivores play outsized roles in shaping ecosystem processes like primary production, decomposition, and mineralization. Contemporary management of these animals is therefore poised to be a powerful tool for holistic ecosystem management. Yet we currently lack (i) adequate understanding of indirect interactions underlying herbivore control of ecosystem processes, especially belowground, and consequently (ii) an ability to predict how ecosystems will respond to ongoing changes to large herbivore populations such as (re)introductions, range shifts, and population collapse. In this contribution, we synthesize current approaches to meet these challenges and provide a framework to better resolve indirect effects of large herbivores on terrestrial ecosystem functioning. Specifically, we synthesize empirical evidence from across the globe and demonstrate that the consumptive and non-consumptive effects of large herbivores frequently disrupt and restructure the primary biotic and abiotic controls on ecosystem functioning. Next, we derive an analytical framework and illustrate how empiricists can use this framework to resolve key relationships among large herbivores, biotic/abiotic controls, ecosystem processes, and environmental context. Our framework can uncover emergent patterns that are not revealed with existing approaches. We conclude with a roadmap to operationalizing our framework using existing research infrastructure (e.g., large exclosures and distributed networks).