Professor Yale School of the Environment New Haven, Connecticut, United States
The functioning of species and ecosystems depends on the cycling of at least 25 chemical elements. Yet ecological science still has a very incomplete mechanistic understanding of the biogeochemical processes controlling elemental cycling, particularly controls by animals. This stems from an enduring classic paradigm of elemental cycling steering research, which in the face of mounting evidence needs updating. The classic paradigm is founded on four tenets: (1) species belong to broad trophic groups within ecosystems (e.g., plants, herbivores, carnivores and microbes) where herbivore and carnivore trophic groups are treated as homogenous compartments; (2) animal-resource (trophic) interactions lead to direct upward fluxes of elements to higher trophic groups (i.e., bottom-up forcing); (3) transfer up the trophic chain is inefficient producing trophic pyramids of biomass; with the consequence that (4) the low biomass representation of animals in ecosystems results in small contributions to elemental cycling, via small amounts (relative to plants) of dead organic matter or wastes deposited to the detrital pool, or recycling small amounts of inorganic nutrients. These tenets effectively presume that animals are merely “passengers” rather than “drivers” of elemental cycling.
This presentation will show why the classic paradigm needs updating by tracing the evolution of the study of animal controls over elemental cycling—a research field becoming known as zoogeochemistry. It will deconstruct the core tenets, to provide a significantly updated conceptual framework for understanding the place and role of animals in ecosystems. This re-conception starts by seeing animals as organisms with diverse functional traits with varying and flexible stoichiometric elemental demands, rather than merely as members of homogeneous trophic groups. The re-conception fosters an expanded view of animal impacts on ecosystems through myriad trophic (consumptive), non-trophic (non-consumptive), and feedback (top-down forcing) effects via their movement and interactions across landscapes. These myriad effect pathways enable animals to exert control by directly and indirectly modulating the transfer efficiencies and spatial distributions of elements within ecosystems. Consequently, animals can have outsized control over the chemical elemental content and quality of their living resources and the detrital pool to reinforce or countervail bottom–up forcing, thereby shaping spatial variation in biogeochemistry and plant and microbial abundance, diversity and functioning from the top down. The presentation will end with guidance for new ecological research that provides a more holistic understanding of the interplay among animals, plants and microbes and feedbacks that together shape landscapes and ecosystems and the elements cycled within them.
