The average body size of grazing animals in an ecosystem affects the balance of nutrients available to plants, a study finds. Plant productivity in ecosystems reflects the availability of key nutrients such as nitrogen and phosphorus, which must be delivered in specific quantities and ratios. Herbivore feces represent an important source of such nutrients, but the nutrient profile of herbivore waste varies with the size of the animal. Elizabeth le Roux and colleagues suggest that environmental factors influencing herbivore body size alter the nitrogen-to-phosphorus ratios available to plants. Using landcover heterogeneity and rainfall as proxies, the authors found that predation risk and food availability alter the average body size of herbivores in an ecosystem, but the quantity of fecal material that accumulates on grazing lawns remains roughly the same. However, the authors also found that dung from larger-bodied herbivores contains less phosphorus and higher nitrogen-to-phosphorus ratios, compared with dung from smaller herbivores, suggesting that plants growing in areas visited more often by large grazers receive correspondingly different nutrient supplies via defecation. The study suggests that processes that control the size distribution of herbivores across a landscape affect the distribution and composition of plant-available nutrients. According to the authors, the findings may also provide insight into extinction events that preferentially remove large species.
Article #20-03269: "Animal body size distribution influences the ratios of nutrients supplied to plants," by Elizabeth le Roux, Laura S. van Veenhuisen, Graham I. H. Kerley, and Joris P.G.M. Cromsigt.
MEDIA CONTACT: Elizabeth le Roux, Department of Zoology, Nelson Mandela University, Port Elizabeth, SOUTH AFRICA; e-mail: elizabeth.liza.le.roux@gmail.com
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Journal
Proceedings of the National Academy of Sciences