OOS 3-3 - Drivers of sodium deficiency, supplementation, and dispersal by large herbivores

Sodium (Na) plays a critical role in the functioning of terrestrial ecosystems. In Na-poor environments, such as inland tropical regions, plant consumers (herbivores) may experience Na deficiency and adapt by seeking supplementary Na resources. This can markedly impact animal behavior, space-use, and co-existence, with concomitant impacts on ecosystems. Many studies have noted that Na-seeking behaviors, such as soil consumption from mineral licks, are predominately observed for larger-bodied herbivores. However, the mechanisms that drive interspecific variation in Na deficiency and mineral lick use remain poorly understood, and may influence large herbivore roles in nutrient cycling and dispersal (zoogeochemistry). Here, we examine whether allometric scaling of Na requirements can explain variation in mineral lick use by herbivorous and omnivorous mammals. We (1) collated data from published literature to derive an allometric scaling of Na requirements in mammals, (2) compared predicted Na requirements to estimated Na intake of mammal communities in three globally distant sites: the Peruvian Amazon, Kalahari Desert, and Malaysian Borneo, and (3) examined the relationship between predicted Na deficiency and mineral lick use utilizing camera-trap and mammal abundance data at each site. We found that minimum daily Na maintenance requirements in mammals scaled allometrically at a higher factor (BM0.91) than that of food and water Na intake (BM0.71 – 0.79), indicating that larger species may be more susceptible to Na limitation. This aligned with a positive association between mineral lick use and body mass by species at all sites, as well as increased artificial salt and mineral lick consumption by larger-bodied mammals in the Kalahari. Our results suggest that larger herbivores may be more sensitive to anthropogenic impacts on Na availability, which may alter their zoogeochemical roles in Na-poor regions. Further research is needed to explore the consequences of changing Na availability on animals and ecosystems, as well as advance our understanding of Na physiology in mammals.