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Abstract Climate models predict increases in the frequency and intensity of extreme‐weather events. The impacts of these events may be modulated by biotic agents in unpredictable ways, yet few experiments cover sufficient spatiotemporal scales to measure the interactive effects of multiple extreme events.We used 15 years of a 28‐year experiment spanning several significant droughts to investigate how rainfall, large herbivores, and soil‐engineering termites affect understorey vegetation in a semi‐arid savanna.Herbivory was the dominant influence on community structure—decreasing cover, increasing species richness, and favouring occurrence of annuals relative to perennials—but these effects were contingent on rainfall and termitaria in non‐additive (hence unpredictable) ways.A separate experiment showed that resource enrichment, mimicking the effects of termitaria, does not straightforwardly compensate for top‐down effects of herbivory.Synthesis. Our study highlights the potency of top‐down forcing in African savannas. It suggests impressive robustness to drought and underscores the value of multi‐decadal experiments for studying interactions among multiple drivers of ecosystem dynamics. 

Abstract Diet composition is among the most important yet least understood dimensions of animal ecology. Inspired by the study of species abundance distributions (SADs), we tested for generalities in the structure of vertebrate diets by characterising them as dietary abundance distributions (DADs). We compiled data on 1167 population‐level diets, representing >500 species from six vertebrate classes, spanning all continents and oceans. DADs near‐universally (92.5%) followed a hollow‐curve shape, with scant support for other plausible rank‐abundance‐distribution shapes. This strong generality is inherently related to, yet incompletely explained by, the SADs of available food taxa. By quantifying dietary generalisation as the half‐saturation point of the cumulative distribution of dietary abundance (sp50, minimum number of foods required to account for 50% of diet), we found that vertebrate populations are surprisingly specialised: in most populations, fewer than three foods accounted for at least half the diet. Variation insp50was strongly associated with consumer type, with carnivores being more specialised than herbivores or omnivores. Other methodological (sampling method and effort, taxonomic resolution), biological (body mass, frugivory) and biogeographic (latitude) factors influencedsp50to varying degrees. Future challenges include identifying the mechanisms underpinning the hollow‐curve DAD, its generality beyond vertebrates, and the biological determinants of dietary generalisation. 

Abstract The composition of mammalian gut microbiomes is highly conserved within species, yet the mechanisms by which microbiome composition is transmitted and maintained within lineages of wild animals remain unclear. Mutually compatible hypotheses exist, including that microbiome fidelity results from inherited dietary habits, shared environmental exposure, morphophysiological filtering and/or maternal effects. Interspecific hybrids are a promising system in which to interrogate the determinants of microbiome composition because hybrids can decouple traits and processes that are otherwise co‐inherited in their parent species. We used a population of free‐living hybrid zebras (Equus quagga×grevyi) in Kenya to evaluate the roles of these four mechanisms in regulating microbiome composition. We analysed faecal DNA for both thetrnL‐P6 and the 16S rRNA V4 region to characterize the diets and microbiomes of the hybrid zebra and of their parent species, plains zebra (E. quagga) and Grevy's zebra (E. grevyi). We found that both diet and microbiome composition clustered by species, and that hybrid diets and microbiomes were largely nested within those of the maternal species, plains zebra. Hybrid microbiomes were less variable than those of either parent species where they co‐occurred. Diet and microbiome composition were strongly correlated, although the strength of this correlation varied between species. These patterns are most consistent with the maternal‐effects hypothesis, somewhat consistent with the diet hypothesis, and largely inconsistent with the environmental‐sourcing and morphophysiological‐filtering hypotheses. Maternal transmittance likely operates in conjunction with inherited feeding habits to conserve microbiome composition within species. 

Abstract Fire and herbivory interact to alter ecosystems and carbon cycling. In savannas, herbivores can reduce fire activity by removing grass biomass, but the size of these effects and what regulates them remain uncertain. To examine grazing effects on fuels and fire regimes across African savannas, we combined data from herbivore exclosure experiments with remotely sensed data on fire activity and herbivore density. We show that, broadly across African savannas, grazing herbivores substantially reduce both herbaceous biomass and fire activity. The size of these effects was strongly associated with grazing herbivore densities, and surprisingly, was mostly consistent across different environments. A one‐zebra increase in herbivore biomass density (~100 kg/km²of metabolic biomass) resulted in a ~53 kg/ha reduction in standing herbaceous biomass and a ~0.43 percentage point reduction in burned area. Our results indicate that fire models can be improved by incorporating grazing effects on grass biomass. 

Abstract Crop raiding by wildlife poses major threats to both wildlife conservation and human well‐being in agroecosystems worldwide. These threats are particularly acute in many parts of Africa, where crop raiders include globally threatened megafauna such as elephants, and where smallholder agriculture is a primary source of human livelihood. One framework for understanding herbivore feeding behaviour, the forage‐maturation hypothesis, predicts that herbivores should align their movements with intermediate forage biomass (i.e., peak green‐up); this phenomenon is known as “surfing the green wave.” Crop‐raiding elephants, however, often consume not just foliage, but also fruits and tubers (e.g., maize and potatoes), which generally mature after seasonal peaks in photosynthetic activity. Thus, although elephants have been reported to surf the green wave in natural habitats, they may utilize a different strategy in cultivated landscapes by selecting crops that are “browning down.”We sought to understand the factors that underpin movement of elephants into agricultural landscapes.In Mozambique's Gorongosa National Park, we used movement data from GPS‐collared elephants, together with precipitation records, remotely sensed estimates of landscape greenness (NDVI), DNA‐based diet analysis, measurements of plant nutritional quality and survey‐based metrics of crop availability to understand spatiotemporal variation in elephant crop‐raiding behaviour.Elephants tracked peak NDVI while foraging inside the Park. During the dry season, however, when NDVI within the Park declined and availability of mature crops was high, crop raiding increased dramatically, and elephants consistently selected crop plants that were browning down while foraging in cultivated landscapes. Crops contained significantly higher digestible energy than wild food plants, but comparable (and sometimes lower) levels of digestible protein, suggesting that this foraging strategy maximized energy rather than protein intake.Our study is the first to combine GPS tracking data with high‐resolution diet analysis and community‐based reporting of crop availability to reveal fine‐scale plasticity in foraging behaviour of elephants at the human–wildlife interface. Our results extend the forage‐maturation hypothesis by showing that elephants surf waves of plant brown‐down in cultivated landscapes. These findings can aid efforts to reduce human–elephant conflict by enabling wildlife managers to prioritize mitigation actions in time and space with limited resources.