Are cattle surrogate wildlife? Savannah plant community composition explained by total herbivory, not herbivore identity

Authors: VEBLEN, KARI - Utah State University; Porensky, Lauren; REGINOS, CORINNA - University Of Wyoming; YOUNT, TRUMAN - University Of California

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2016
Publication Date: 9/3/2016
Citation: Veblen, K.E., Porensky, L.M., Reginos, C., Yount, T.P. 2016. Are cattle surrogate wildlife? Savannah plant community composition explained by total herbivory, not herbivore identity. Ecological Applications. 26(6):1610-1623.

Interpretive Summary: Wild ungulate herbivores are being replaced by domestic livestock in African savannas, and this replacement involves two interrelated phenomena: 1) loss or reduction in numbers of individual wildlife species or guilds, and 2) addition of livestock to the system. Each has important implications for plant community dynamics, forage quality, and forage quantity. Yet very few studies have addressed the individual, combined, and potentially interactive effects wild versus domestic herbivore species on herbaceous plant communities within a single system. Since 1995, the Kenya Long-term Exclosure Experiment (KLEE) has manipulated access by different replicated combinations of mega-herbivores, meso-herbivore ungulate wildlife, and cattle in a wooded savanna ecosystem. Herbaceous vegetation was sampled 25 times between 1999 and 2013 in each of the eighteen 4 ha KLEE plots. We assessed effects of herbivore treatments on overall plant community composition. We found evidence for additive effects of the resident community of wild ungulates (which included grazers, browsers and mixed feeders) and cattle (mostly grazers). This suggests that overall herbivory pressure, rather than complex interactions among different types of herbivores, drove plant community dynamics. Plant species that responded negatively to cattle also tended to respond negatively to wild herbivores, and species responding positively to cattle also tended to respond positively to wild herbivores. Differences between cattle and wild ungulate impacts on the herbaceous layer of this savanna ecosystem may be most closely related to the higher density of cattle, compared to wildlife. Our results suggest considerable functional similarity between a suite of native wild herbivores (spanning different feeding guilds) and domestic livestock with respect to understory plant community composition. However, responses of individual plant species demonstrate that at a finer scale, impacts of a single livestock species are not identical to those of a diverse group of native herbivores.

Technical Abstract: The 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 has important implications for plant community dynamics. Yet very few studies have addressed the individual, combined, and potentially interactive effects of the presence and absence of wild versus domestic herbivore species on herbaceous plant communities within a single system. Additionally, there is little experimental evidence addressing the question of 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 (KLEE) has since 1995 manipulated access by different replicated combinations of mega-herbivores, meso-herbivore ungulate wildlife, and cattle in a wooded savanna ecosystem. Herbaceous vegetation was sampled 25 times between 1999 and 2013 in each of the eighteen 4 ha KLEE plots. We used partial redundancy analysis (RDA) to assess effects of herbivore treatments on overall plant community composition. We found evidence for additive effects of the resident community of wild ungulates (which included grazers, browsers and mixed feeders) and cattle (mostly grazers) on herbaceous community composition. Responses to herbivory varied among plant species, but those that responded negatively to cattle also tended to respond negatively to wild herbivores, and species responding positively to cattle also tended to respond positively to wild herbivores. This suggests that overall herbivory pressure, rather than complex interactions among different types of herbivores, drove plant community dynamics. Differences between cattle and wild ungulate impacts on the herbaceous layer of this savanna ecosystem may be related more to the higher density of cattle than to differences related to species-specific, per-animal impacts. Although our results suggest considerable functional similarity between a suite of native wild herbivores (spanning different feeding guilds) and domestic livestock 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.