Sodium constraints on megaherbivore communities in Africa

Authors: ABRAHAM, A - Northern Arizona University; HEMPSON, G - University Of Witwatersrand; LE ROUX, E - Aarhus University; MARE, C - Aarhus University; TAYLOR, LL - University Of Sheffield; WEBSTER, A - University Of Pretoria; DUVALL, E - Cornell University; PRYS-JONES, TOMOS - Northern Arizona University; COPPOCK, JOHN - Collaborator; RIDENOUR, CHASE - Northern Arizona University; DE JAGER, PIETER - University Of Pretoria; Augustine, David; CHAPMAN, COLIN - Vancouver Island University; FASHING, PETER - California State University; HARFOOT, MICHAEL - Vizzuality; HOLDO, RICARDO - University Of Georgia; HOPCRAFT, J - University Of Glasgow; JOHNSON, CALEY - Fordham University; VAN LANGEVELDE, FRANK - Wageningen University And Research Center; MALHI, YADVINDER - University Of Oxford; MOREL, ALEXANDRA - University Of Dundee; NGUYEN, NGA - California State University; OWEN-SMITH, NORMAN - University Of Witwatersrand; POTTER, ARJUN - Wake Forest University; PRINS, HERBERT - Wageningen University And Research Center; ROTHMAN, JESSICA - Hunter College; SWEDELL, LARISSA - Queens College; SVENNING, JENS-CHRISTIAN - Aarhus University; THOMSON, ELEANOR - University Of Oxford; VAN DER PLAS, FONS - Wageningen University; VELDHUIS, MICHIEL - Leiden University; PRINGLE, ROBERT - Princeton University; CLAUSS, MARCUS - University Of Zurich; DOUGHTY, CHRISTOPHER - Northern Arizona University

Submitted to: Nature Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2025
Publication Date: 12/9/2025
Citation: Abraham, A.J., Hempson, G., le Roux, E., Maré, C., Taylor, L., Webster, A.B., Duvall, E., Prys-Jones, T., Coppock, J., Ridenour, C., de Jager, P., Augustine, D.J., Chapman, C.A., Fashing, P.J., Harfoot, M.B.J., Holdo, R.M., Hopcraft, J.G.C., Johnson, C., van Langevelde, F., Malhi, Y., Morel, A., Nguyen, N., Owen-Smith, N., Potter, A.B., Prins, H.H.T., Rothman, J.M., Swedell, L., Svenning, J., Thomson, E.R., van der Plas, F., Veldhuis, M.P., Pringle, R.M., Clauss, M., Doughty, C.E. 2025. Sodium constraints on megaherbivore communities in Africa. Nature Ecology and Evolution. 0. https://doi.org/10.1038/s41559-025-02917-y.
DOI: https://doi.org/10.1038/s41559-025-02917-y

Interpretive Summary: Sodium is an essential nutrient required by all mammals, but it is not an essential nutrient for plant growth. As a result, mammalian herbivores are often challenged to acquire enough sodium in their diet to meet growth and maintenance requirements. African savannas are characterized by a diverse and often abundant community of large mammalian herbivores which do not receive any mineral supplements. We analyzed the variation in distribution of sodium in vegetation across the African continent, and use these maps to examine where and when sodium constrains affect herbivore abundance. We examine this constraint imposed by sodium in relation to sea-salt deposition, hydrology, and soil chemistry.

Technical Abstract: Sodium (Na) is an essential nutrient for animals, but not for most plants. Consequently, herbivores may confront a mismatch between the concentration of Na in plant tissues and the quantities required for growth and reproduction. Recent work further suggests that large-bodied mammals should be particularly vulnerable to Na deficits, yet there is little evidence that Na availability constrains the density or distribution of large herbivores at broad scales. Here, we show that plant Na availability varies >1,000-fold across sub-Saharan Africa—the last refuge of diverse large-mammal communities—and helps to explain continent-scale patterns of herbivore abundance. We combined field data with machine learning approaches to generate high-resolution maps of plant Na, which reveal multi-scale gradients arising from sea-salt deposition, hydrology, soil chemistry, and plant traits (e.g., higher among C4 grasses than C3 eudicots). Faecal Na was highly correlated with modelled dietary Na, and higher in grazers, corroborating the prediction that geographic gradients in plant Na availability, together with diet, regulate herbivore Na intake. Incorporating forage-Na availability with body mass improved model predictions of herbivore density. Browsing megaherbivores (>1000 kg) were less abundant in Na-deficient regions and peaked at intermediate concentrations (100–300 mg kg-1); mesoherbivores (<500 kg) showed the opposite pattern, indicating a lack of Na limitation. Our study offers an explanation for the scarcity of megaherbivores in parts of West Africa and more generally provides evidence that Na constrains herbivore community structure in Africa, which has conventionally been explained with reference to climate, floristics, and plant macronutrients. This constraint has major ecological ramifications given large herbivores’ influence on many ecosystem functions, and human activities that redistribute Na may profoundly alter patterns of animal behaviour and human-wildlife conflict.