Are cattle surrogate wildlife? Savanna plant community composition explained by total herbivory more than herbivore type

Abstract

The widespread replacement of wild ungulate herbivores by domestic livestock in African savannas is composed of two interrelated phenomena: (1) loss or reduction in numbers of individual wildlife species or guilds and (2) addition of livestock to the system. Each can have important implications for plant community dynamics. Yet very few studies have experimentally addressed the individual, combined, and potentially interactive effects of wild vs. domestic herbivore species on herbaceous plant communities within a single system. Additionally, there is little information about whether, and in which contexts, livestock might functionally replace native herbivore wildlife or, alternatively, have fundamentally different effects on plant species composition. The Kenya Long-term Exclosure Experiment, which has been running since 1995, is composed of six treatment combinations of mega-herbivores, meso-herbivore ungulate wildlife, and cattle. We sampled herbaceous vegetation 25 times between 1999 and 2013. We used partial redundancy analysis and linear mixed models to assess effects of herbivore treatments on overall plant community composition and key plant species. Plant communities in the six different herbivore treatments shifted directionally over time and diverged from each other substantially by 2013. Plant community composition was strongly related (R = 0.92) to residual plant biomass, a measure of herbivore utilization. Addition of any single herbivore type (cattle, wildlife, or mega-herbivores) caused a shift in plant community composition that was proportional to its removal of plant biomass. These results suggest that overall herbivory pressure, rather than herbivore type or complex interactions among different herbivore types, was the main driver of changes in plant community composition. Individual plant species, however, did respond most strongly to either wild ungulates or cattle. Although these results suggest considerable functional similarity between a suite of native wild herbivores (which included grazers, browsers, and mixed feeders) and cattle (mostly grazers) with respect to understory plant community composition, responses of individual plant species demonstrate that at the plant-population-level impacts of a single livestock species are not functionally identical to those of a diverse group of native herbivores.

Interacting effects of land use and climate on rodent-borne pathogens in central Kenya

“…In general, pastoral land use also does not seem to cause such strong and systematic changes in plant or small-mammal abundance as does experimental wildlife removal [17,43], likely because (at least at low-to-moderate densities) domestic herbivores often closely mimic and at least partially compensate for many effects of native large herbivores [87,88]. In this case, domestic herbivores may substitute for native large herbivores as food sources for vectors.…”

“…In this case, domestic herbivores may substitute for native large herbivores as food sources for vectors. The compositional changes of small mammals in response to pastoral use are also less dramatic [44,87]. Pastoral landscapes also do not tend to have the highly seasonal compositional dynamics that cropland does in the region; thus, the compositional changes in small mammals that do occur in pastoral systems may not favour the very fast-living, commensal rodents that are most likely to be hyper-reservoirs of infection [27].…”

Herbivory and drought generate short‐term stochasticity and long‐term stability in a savanna understory community

“…Details of the sampling are given in our companion paper, Veblen et al (2016), which made use of the same data set. Here, we use aerial plant cover data collected by counting the number of pins hit by each species of grass or forb over a 10-point pin frame at gridded sampling stations spread over the innermost hectare of each plot.…”

“…We excluded plant species that occurred in <5% of all samples (all plots over all sample periods), resulting in a data set of 55 taxa (46 species and 9 multi-species groups) accounting for >99.8% of total plant cover (see Veblen et al [2016] for more details). Relative cover provides an index of the contribution of each species to the herbaceous community while controlling for differences in total biomass due to herbivore treatments and rainfall variability.…”

“…Many rangelands have a long evolutionary history of grazing by wild ungulates; however, contemporary livestock grazing practices may not mimic historical grazing patterns for a variety of reasons. Thus, depending on the circumstances, livestock grazing may either fill some of the functional role of historic grazing in community and ecosystem dynamics (Veblen et al 2016) or represent a novel disturbance for which there is no historical analog (Eldridge et al 2016). Thus, depending on the circumstances, livestock grazing may either fill some of the functional role of historic grazing in community and ecosystem dynamics (Veblen et al 2016) or represent a novel disturbance for which there is no historical analog (Eldridge et al 2016).…”