Study ID 362

Plant and small-mammal responses to large-herbivore exclusion in an African savanna

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Realm: Terrestrial
Climate: Tropical
Biome: Tropical and subtropical grasslands, savannas and shrublands
Central latitude: 0.389236
Central longitude: 36.891566
Duration: 4 years, from 2009 to 2012

30969 records

18 distinct species

Across the time series Mus sp is the most frequently occurring species

Citation(s):

Goheen, J.R., Palmer, T.M., Charles, G.K., Helgen, K.M., Kinyua, S.N., Maclean, J.E., Turner, B.L., Young, H.S. & Pringle, R.M. (2013) Piecewise disassembly of a large-herbivore community across a rainfall gradient: the UHURU experiment. PLoS One, 8, e55192.Kartzinel, T.R., Goheen, J.R., Charles, G.K., DeFranco, E., Maclean, J.E., Otieno, T.O., Palmer, T.M. & Pringle, R.M. (2014) Plant and small?mammal responses to large?herbivore exclusion in an African savanna: five years of the UHURU experiment. Ecology, 95, 787-787.

Methods

Beginning in 2008 a series of three herbivory treatments and a control were randomly assigned to contiguous 1-ha plots replicated three times at each of three sites along a rainfall gradient (36 total plots). Any field experiment entails a trade-off between plot size and replication. Plot sizes of 1 ha are larger than those in many prior large-herbivore-exclusion studies and enabled us to include nine replicates of each plot type which was necessary both to sample multiple sites along the rainfall gradient and to achieve adequate statistical power. And although 1 ha is not large enough to detect all ecological effects of LMH (e.g. seed dispersal numerical responses of smaller LMH to the exclusion of larger LMH) it is adequate to document strong and consistent effects in many individual- population- and community-level responses of plants and small mammals (Goheen et al. 2013) as well as behavioral (as opposed to numerical) responses of smaller LMH to the exclusion of larger LMH (e.g. Young et al. 2005). Total exclosures exclude all large mammalian herbivores (LMH) larger than ~5 kg and ~50-cm tall but are accessible to hares and other small mammals; these exclosures use 2.4-m high fences consisting of 14 strands of wire electrically charged by solar powered batteries with a 1-m tall barrier consisting of 10-cm chain link. Mesoherbivore exclosures consist of 11 wires beginning 30-cm above the ground allowing access to only the smallest LMH (dik-dik Madoqua cavendishi and warthog Phacochoerus africanus) and excluding larger species. Megaherbivore exclosures consist of two wires 2-m above ground level and exclude only megaherbivores (elephants Loxodonta africana and giraffes Giraffa camelopardalis). Open? plots are unfenced and demarcated by a series of 1-m tall wooden posts at 10-m intervals; these plots allow access to all LMH species. On all fences a series of 1-m long wires at 2-m height extend horizontally outward from plots to deter animals that approach the barriers. In January 2009 vertical connecting wires were added to total- and mesoherbivore exclusion fences to increase security and stability. Exclosure plots are regularly inspected and maintained by project personnel. Rapid repairs are made whenever damage to the fencing is discovered. For the eight most common LMH species exclosure effectiveness ranged from 92% (for elephants) to 99% (for warthog and dik-dik; mean effectiveness for all LMH = 96%) during the first 3 years of the experiment (Goheen et al. 2013). Herdsmen for Mpala?s cattle-ranching operation are asked to keep cattle out of the plots. Within each plot a 0.36-ha grid (60 ? 60 m) marked by 49 rebar stakes at 10 m intervals provides a spatial template for much of the experimental monitoring. Small mammals were live trapped at two-month intervals in total-exclusion and open plots using Sherman live-traps (Goheen et al. 2013). In each trapping session and for four consecutive days a single trap was set at each of the 49 grid stakes in the center of each plot opened in the late afternoon and checked and closed in the early morning. All species of small mammals were fit with two fingerling ear tags with the exceptions of individuals in the genera Acomys Crocidura and Mus. These genera are too small or too fragile (Seifert et al. 2012) for ear tags; we instead marked individuals in these genera with black marker for subsequent identification within trapping sessions. Abundance data was obtained for bird species within a specific region through mapping line transects and occasionally nest counting. This data was then converted to a density index and displayed. Unit of abundance = IndCountInt, Unit of biomass = NA