title: Herbivore effects on productivity vary by guild: cattle increase mean productivity while wildlife reduce variability.
abstract: Wild herbivores and livestock share the majority of rangelands worldwide, yet few controlled experiments have addressed their individual, additive, and interactive impacts on ecosystem function. While ungulate herbivores generally reduce standing biomass, their effects on aboveground net primary production (ANPP) can vary by spatial and temporal context, intensity of herbivory, and herbivore identity and species richness. Some evidence indicates that moderate levels of herbivory can stimulate aboveground productivity, but few studies have explicitly tested the relationships among herbivore identity, grazing intensity, and ANPP. We used a long-term exclosure experiment to examine the effects of three groups of wild and domestic ungulate herbivores (megaherbivores, mesoherbivore wildlife, and cattle) on herbaceous productivity in an African savanna. Using both field measurements (productivity cages) and satellite imagery, we measured the effects of different herbivore guilds, separately and in different combinations, on herbaceous productivity across both space and time. Results from both productivity cage measurements and satellite normalized difference vegetation index (NDVI) demonstrated a positive relationship between mean productivity and total ungulate herbivore pressure, driven in particular by the presence of cattle. In contrast, we found that variation in herbaceous productivity across space and time was driven by the presence of wild herbivores (primarily mesoherbivore wildlife), which significantly reduced heterogeneity in ANPP and NDVI across both space and time. Our results indicate that replacing wildlife with cattle (at moderate densities) could lead to similarly productive but more heterogeneous herbaceous plant communities in rangelands.
authors.affiliation: Department of Plant Sciences, University of California, Davis, California, 95616, USA.|Mpala Research Centre, PO Box 555, Nanyuki, 10400, Kenya.
authors.forename: Grace K
authors.initials: GK
authors.lastname: Charles
authors.affiliation: Mpala Research Centre, PO Box 555, Nanyuki, 10400, Kenya.|Rangeland Resources Research Unit, USDA-ARS, 1701 Centre Avenue, Fort Collins, Colorado, 80526, USA.
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Porensky
authors.affiliation: Mpala Research Centre, PO Box 555, Nanyuki, 10400, Kenya.|Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, 82071, USA.
authors.forename: Corinna
authors.initials: C
authors.lastname: Riginos
authors.affiliation: Mpala Research Centre, PO Box 555, Nanyuki, 10400, Kenya.|Department of Wildland Resources and Ecology Center, Utah State University, Logan, Utah, 84322, USA.
authors.forename: Kari E
authors.initials: KE
authors.lastname: Veblen
authors.affiliation: Department of Plant Sciences, University of California, Davis, California, 95616, USA.|Mpala Research Centre, PO Box 555, Nanyuki, 10400, Kenya.
authors.forename: Truman P
authors.initials: TP
authors.lastname: Young
mesh_terms: D000818:Animals; D001188:Artiodactyla / Q000502:physiology*; D018533:Biomass; D002417:Cattle; D004606:Elephants / Q000502:physiology*; D018397:Equidae / Q000502:physiology*; D065948:Grassland; D060434:Herbivory; D007630:Kenya; D018521:Plant Physiological Phenomena
keywords: KLEE; Kenya Long-term Exclosure Experiment; aboveground net primary productivity; defaunation; ecosystem function; livestock