Herbivore Dynamics in Savanna Ecosystems

Savanna ecosystems, spanning grasslands punctuated by scattered trees, are shaped fundamentally by the activities of large mammalian herbivores. Through grazing and browsing, these animals regulate primary productivity, fire regimes and vegetation structure, thereby influencing carbon storage, nutrient cycling and biodiversity. Herbivore communities range from megaherbivores such as elephants to smaller meso-herbivores, each exerting distinct pressures on plant assemblages and ecosystem processes. Their distributions and population sizes respond to seasonal rainfall patterns, predation risk and disease outbreaks, as well as to human-driven land-use change and livestock substitution. Fluctuations in herbivore biomass can trigger trophic cascades: for example, reductions in grazing may lead to increased tree cover, altered fire frequency and shifts in soil carbon pools. Understanding these dynamics is critical for conserving savanna biodiversity, managing fire risk and sustaining ecosystem services such as forage provision and climate regulation.

Research from Nature Portfolio

Recent genomic reconstructions reveal that large herbivore populations declined precipitously throughout the Late Pleistocene and Holocene, with human expansion driving a 92–95 percent reduction in total megafauna biomass and energy turnover over the past 50 000 years. This loss has fundamentally restructured savanna ecosystems by diminishing trophic interactions and altering carbon fluxes.

Comparative analyses of historical and contemporary herbivore communities in sub-Saharan Africa demonstrate that replacing native wildlife with livestock has produced divergent outcomes: wetter regions have endured marked biomass losses, while arid zones often show increased grazer densities. These shifts have crossed thresholds that govern fire suppression, leading to expanded woody cover, a doubling of methane emissions and a collapse to below 5 percent of past lateral nutrient-diffusion capacity.

Global simulation models emphasise that the largest terrestrial herbivores are disproportionately important for ecosystem functioning. Continued declines of megabiota are predicted to reduce terrestrial heterotrophic biomass by up to 44 percent, metabolism by 18 percent and soil fertility by 92 percent, underlining the urgency of conserving large species to maintain savanna productivity and resilience.

Herbivore Dynamics in Savanna Ecosystems publication trend

The graph below shows the total number of articles in herbivore dynamics in savanna ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Savanna: A biome characterised by a balance of grasses and scattered trees, maintained by seasonal rainfall, fire and grazing.

Functional composition: The distribution of species or groups within an ecosystem based on their ecological roles, such as grazers, browsers or mixed feeders.

Trophic cascade: Indirect effects that propagate through multiple trophic levels, for example when changes in herbivore numbers alter fire regimes and tree density.

Exclosure experiment: A field study design using fenced plots to prevent access by certain herbivores and thereby assess their ecological impacts.

Biomass turnover: The rate at which living organic matter is produced and consumed within an ecosystem.

References

1. Worldwide Late Pleistocene and Early Holocene population declines in extant megafauna are associated with Homo sapiens expansion rather than climate change. Nature Communications (2023).
2. The consequences of replacing wildlife with livestock in Africa. Scientific Reports (2017).
3. Lateral Diffusion of Nutrients by Mammalian Herbivores in Terrestrial Ecosystems. PLOS ONE (2013).
4. The megabiota are disproportionately important for biosphere functioning. Nature Communications (2020).
5. A Disease-Mediated Trophic Cascade in the Serengeti and its Implications for Ecosystem C. PLOS Biology (2009).
6. Piecewise Disassembly of a Large-Herbivore Community across a Rainfall Gradient: The UHURU Experiment. PLOS ONE (2013).
7. Habitat selection by large herbivores in a southern African savanna: the relative roles of bottom‐up and top‐down forces. Ecosphere (2013).