CONICET | Buscador de Institutos y Recursos Humanos

1. Herbivores influence litter quality, soil properties and decomposer communities, with cascading effects on litter decomposition. Vertebrate and invertebrate herbivores can affect decomposition through the same two pathways (litter quality-and soil-mediated) but are expected to do so via different underlying mechanisms and/or with contrasting magnitudes of effect. However, no quantitative synthesis has explicitly compared these groups across ecological contexts.2. We conducted a global meta-analysis of 115 paired observations from 46 articles examining how vertebrate and invertebrate herbivores affect litter decomposition. 3. Neither vertebrates nor invertebrates showed a consistent net effect on litter decomposition. However, vertebrate herbivores accelerated litter decomposition through both litter quality-and soil-mediated pathways, but only in fertileecosystems. They also accelerated the decomposition of non-woody plant litter while slowing the decomposition of woody plant litter via soil-mediated effects. In contrast, invertebrate herbivores altered the chemistry of green leaves but did not have a general effect on litter decomposition across contexts.4. Our findings suggest strong context-dependency and potential functional complementarity between herbivore groups, with each being more influential under different ecological conditions or via diverse plant traits. Our analysis also reveals important biases and gaps, including the scarcity of studies directly comparing vertebrates and invertebrates across the two pathways, and the limited number assessing the mechanisms underlying each pathway. Addressing these gaps with integrative and standardized experiments will be essential to predict how herbivores shape nutrient cycling under global change.

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