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PLOS ONE  2013 

Piecewise Disassembly of a Large-Herbivore Community across a Rainfall Gradient: The UHURU Experiment

DOI: 10.1371/journal.pone.0055192

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Abstract:

Large mammalian herbivores (LMH) strongly influence plant communities, and these effects can propagate indirectly throughout food webs. Most existing large-scale manipulations of LMH presence/absence consist of a single exclusion treatment, and few are replicated across environmental gradients. Thus, important questions remain about the functional roles of different LMH, and how these roles depend on abiotic context. In September 2008, we constructed a series of 1-ha herbivore-exclusion plots across a 20-km rainfall gradient in central Kenya. Dubbed "UHURU" (Ungulate Herbivory Under Rainfall Uncertainty), this experiment aims to illuminate the ecological effects of three size classes of LMH, and how rainfall regimes shape the direction and magnitude of these effects. UHURU consists of four treatments: total-exclusion (all ungulate herbivores), mesoherbivore-exclusion (LMH >120-cm tall), megaherbivore-exclusion (elephants and giraffes), and unfenced open plots. Each treatment is replicated three times at three locations (“sites”) along the rainfall gradient: low (440 mm/year), intermediate (580 mm/year), and high (640 mm/year). There was limited variation across sites in soil attributes and LMH activity levels. Understory-plant cover was greater in plots without mesoherbivores, but did not respond strongly to the exclusion of megaherbivores, or to the additional exclusion of dik-dik and warthog. Eleven of the thirteen understory plant species that responded significantly to exclusion treatment were more common in exclusion plots than open ones. Significant interactions between site and treatment on plant communities, although uncommon, suggested that differences between treatments may be greater at sites with lower rainfall. Browsers reduced densities of several common overstory species, along with growth rates of the three dominant Acacia species. Small-mammal densities were 2–3 times greater in total-exclusion than in open plots at all sites. Although we expect patterns to become clearer with time, results from 2008–2012 show that the effects of excluding successively smaller-bodied subsets of the LMH community are generally non-additive for a given response variable, and inconsistent across response variables, indicating that the different LMH size classes are not functionally redundant. Several response variables showed significant treatment-by-site interactions, suggesting that the nature of plant-herbivore interactions can vary across restricted spatial scales.

References

[1]  Barnosky AD, Matzke N, Tomiya S, Wogan GOU, Swartz B, et al. (2011) Has the Earth’s sixth mass extinction already arrived? Nature 471: 51–57.
[2]  Ceballos G, Ehrlich PR (2002) Mammal population losses and the extinction crisis. Science 296: 904–907.
[3]  Hughes JB, Daily GC, Ehrlich PR (1997) Population diversity: its extent and extinction. Science 278: 689–692.
[4]  Agrawal AA, Ackerly DD, Adler F, Arnold AE, Caceres C, et al. (2007) Filling key gaps in population and community ecology. Front Ecol Environ 5: 145–152.
[5]  Belyea LR, Lancaster J (1999) Assembly rules within a contingent ecology. Oikos 86: 402–416.
[6]  Burkepile DE, Hay ME (2006) Herbivore vs. nutrient control of marine primary producers: Context-dependent effects. Ecology 87: 3128–3139.
[7]  Johnson NC, Graham JH, Smith FA (1997) Functioning of mycorrhizal associations along the mutualism-parasitism continuum. New Phytol 135: 575–586.
[8]  Lawton JH (1999) Are there general laws in ecology? Oikos 84: 177–192.
[9]  McNaughton SJ (1983) Serengeti grassland ecology: the role of composite environmental factors and contingency in community organization. Ecol Monogr 53: 291–320.
[10]  Schmitz OJ (2010) Resolving Ecosystem Complexity. New Jersey: Princeton University Press.
[11]  Vaughn KJ, Young TP (2010) Contingent conclusions: year of initiation influences ecological field experiments, but temporal replication is rare. Restor Ecol 18: 59–64.
[12]  Kareiva P, Andersen M (1988) Spatial aspects of species interactions: the wedding of models and experiments. In: Hastings A, editor. Community Ecology: Lecture Notes in Biomathematics 77. Berlin: Springer-Verlag. 35–50.
[13]  Wiens JA (1989) Spatial scaling in ecology. Funct Ecol 3: 385–397.
[14]  Knapp AK, Beier C, Briske DD, Classen AT, Luo Y, et al. (2008) Consequences of more extreme precipitation regimes for terrestrial ecosystems. BioScience 58: 811–821.
[15]  Austin AT, Vivanco L (2006) Plant litter decomposition in a semi-arid ecosystem controlled by photodegradation. Nature 442: 555–558.
[16]  Fay PA, Kaufman DM, Nippert JB, Carlisle JD, Harper CW (2008) Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to climate change. Glob Change Biol 14: 1600–1608.
[17]  Ernest SKM, Brown JH, Parmenter RR (2000) Rodents, plants, and precipitation: spatial and temporal dynamics of consumers and resources. Oikos 88: 470–482.
[18]  Previtali M, Lima M, Meserve PL, Kelt DA, Gutierrez JR (2009) Population dynamics of two sympatric rodents in a variable environment: rainfall, resource availability, and predation. Ecology 90: 1996–2006.
[19]  Ogutu JO, Owen-Smith N (2003) ENSO, rainfall and temperature influences on extreme population declines among African savanna ungulates. Ecol Lett 6: 412–419.
[20]  Sankaran M, Hanan NP, Scholes RJ, Ratnam J, Augustine DJ, et al. (2005) Determinants of woody cover in African savannas. Nature 438: 846–849.
[21]  Sankaran M, Ratnam J, Hanan N (2008) Woody cover in African savannas: the role of resources, fire, and herbivory. Glob Ecol Biogeog 17: 236–245.
[22]  Staver AC, Archibald S, Levin S (2011) Tree cover in sub-Saharan Africa: rainfall and fire constrain forest and savanna as alternative stable states. Ecology 92: 1063–1072.
[23]  Staver AC, Archibald S, Levin SA (2011) The global extent and determinants of savanna and forest as alternative biome states. Science 334: 230–232.
[24]  Cardillo M, Mace GM, Jones KE, Bielby J, Bininda-Emonds ORP, et al. (2005) Multiple causes of high extinction risk in large mammal species. Science 309: 1239–1241.
[25]  Davidson AD, Hamilton MJ, Boyer AG, Brown JH, Ceballos G (2009) Multiple pathways to extinction in mammals. Proc Natl Acad Sci USA 106: 10702–10705.
[26]  Brook BW, Bowman DMJS (2005) One equation fits overkill: why allometry underpins both prehistoric and modern body size-biased extinctions. Popul Ecol 47: 137–141.
[27]  Augustine DJ, McNaughton SJ (1998) Ungulate effects on the functional species composition of plant communities: Herbivore selectivity and plant tolerance. J Wildlife Manag 62: 1165–1183.
[28]  Coughenour MB (1991) Spatial components of plant-herbivore interactions in pastoral, ranching, and native-ungulate ecosystems. J Range Manag 44: 530–542.
[29]  C?té SD, Rooney TP, Tremblay JP, Dussault C, Waller DM (2004) Ecological impacts of deer overabundance. Ann Rev Ecol Evol Syst 113–147.
[30]  Diaz S, Lavorel S, McIntyre S, Falczuk V, Casanoves F, et al. (2007) Plant trait responses to grazing - a global synthesis. Glob Change Biol 13: 313–341.
[31]  Hobbs NT (1996) Modification of ecosystems by ungulates. J Wildlife Manag 60: 695–713.
[32]  Milchunas DG, Lauenroth WK (1993) Quantitative effects of grazing on vegetation and soils over a global range of environments. Ecol Monogr 63: 327–366.
[33]  Augustine DJ, Veblen KE, Goheen JR, Riginos C, Young TP (2011) Pathways for positive cattle–wildlife interactions in semiarid rangelands. In: Georgiadis NJ, editor. Conserving Wildlife in African Landscapes: Kenya’s Ewaso Ecosystem. Washington, D.C.: Smithsonian Institution Scholarly Press. 55–71.
[34]  Pringle RM, Palmer TM, Goheen JR, McCauley DJ, Keesing F (2011) Ecological importance of large herbivores in the Ewaso Ecosystem. In: Georgiadis NJ, editor. Conserving Wildlife in African Landscapes: Kenya’s Ewaso Ecosystem. Washington, D.C.: Smithsonian Institution Scholarly Press. 55–71.
[35]  Hagenah N, Prins HHT, Olff H (2009) Effects of large herbivores on murid rodents in a South African savanna. J Trop Ecol 25: 483–492.
[36]  Ims RA, Yoccoz NG, Brathen KA, Fauchald P, Tveraa T, et al. (2007) Can reindeer overabundance cause a trophic cascade? Ecosystems 10: 607–622.
[37]  Keesing F (1998) Impacts of ungulates on the demography and diversity of small mammals in central Kenya. Oecologia 116: 381–389.
[38]  McCauley DJ, Keesing F, Young TP, Allan BF, Pringle RM (2006) Indirect effects of large herbivores on snakes in an African savanna. Ecology 87: 2657–2663.
[39]  Palmer TM, Stanton ML, Young TP, Goheen JR, Pringle RM, et al. (2008) Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna. Science 319: 192–195.
[40]  Pringle RM, Young TP, Rubenstein DI, McCauley DJ (2007) Herbivore-initiated interaction cascades and their modulation by productivity in an African savanna. Proc Natl Acad Sci USA 104: 193–197.
[41]  Pringle RM (2008) Elephants as agents of habitat creation for small vertebrates at the patch scale. Ecology 89: 26–33.
[42]  Smit R, Bokdam J, den Ouden J, Olff H, Schot-Opschoor H, et al. (2001) Effects of introduction and exclusion of large herbivores on small rodent communities. Plant Ecol 155: 119–127.
[43]  Goheen JR, Palmer TM, Keesing F, Riginos C, Young TP (2010) Large herbivores facilitate savanna tree establishment via diverse and indirect pathways. J Anim Ecol 79: 372–382.
[44]  Maclean JE, Goheen JR, Doak DF, Palmer TM, Young TP (2011) Cryptic herbivores mediate the strength and form of ungulate impacts on a long-lived savanna tree. Ecology 92: 1626–1636.
[45]  Lagendijk G, Page BR, Slotow R (2012) Short-term effects of single species browsing release by different-sized herbivores on sand forest vegetation community, South Africa. Biotropica 44: 63–72.
[46]  Young TP, Palmer TM, Gadd ME (2005) Competition and compensation among cattle, zebras, and elephants in a semi-arid savanna in Laikipia, Kenya. Biol Conserv 122: 351–359.
[47]  Riginos C, Porensky LM, Veblen KE, Odadi WE, Sensenig RL, et al. (in press) Lessons on the relationship between pastoralism and biodiversity from the Kenya Long-term Exclosure Experiment (KLEE). Pastoralism: Research, Policy and Practice.
[48]  Anderson TM, Ritchie ME, McNaughton SJ (2007) Rainfall and soils modify plant community response to grazing in Serengeti National Park. Ecology 88: 1191–1201.
[49]  Frank DA, Depriest T, McLauchlan K, Risch AC (2011) Topographic and ungulate regulation of soil C turnover in a temperate grassland ecosystem. Global Change Biol 17: 495–504.
[50]  Osem Y, Perevolotsky A, Kigel J (2004) Site productivity and plant size explain the response of annual species to grazing exclusion in a Mediterranean semi-arid rangeland. J Ecol 92: 297–309.
[51]  Bakker ES, Ritchie ME, Olff H, Milchunas DG, Knops JMH (2006) Herbivore impact on grassland plant diversity depends on habitat productivity and herbivore size. Ecol Lett 9: 780–788.
[52]  Chase JM, Leibold MA, Downing AL, Shurin JB (2000) The effects of productivity, herbivory, and plant species turnover in grassland food webs. Ecology 81: 2485–2497.
[53]  Olff H, Ritchie ME (1998) Effects of herbivores on grassland plant diversity. Trends Ecol Evol 13: 261–265.
[54]  Lortie CJ, Callaway RM (2006) Re-analysis of meta-analysis: support for the stress-gradient hypothesis. J Ecol 94: 7–16.
[55]  Whittaker RJ (2010) Meta-analyses and mega-mistakes: calling time on meta-analysis of the species richness-productivity relationship. Ecology 91: 2522–2533.
[56]  Gruner DS, Smith JE, Seabloom EW, Sandin SA, Ngai JT, et al. (2008) A cross-system synthesis of consumer and nutrient resource control on producer biomass. Ecol Lett 11: 740–755.
[57]  Ahn PM, Geiger LC (1987) Soils of Laikipia District. Nairobi: Ministry of Agriculture, National Agricultural Laboratories.
[58]  Soil Survey Staff (1999) Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. Lincoln, NE: United States Department of Agriculture, Natural Resources Conservation Service.
[59]  Augustine DJ (2003) Spatial heterogeneity in the herbaceous layer of a semi-arid savanna ecosystem. Plant Ecol 167: 319–332.
[60]  Augustine DJ, Mcnaughton SJ (2004) Regulation of shrub dynamics by native browsing ungulates on East African rangeland. J Appl Ecol 41: 45–58.
[61]  Heady HF (1960) Range Management in East Africa. Nairobi: Government Printer.
[62]  Pringle RM (2012) How to be manipulative. American Scientist 100: 30–37.
[63]  Augustine DJ (2010) Response of native ungulates to drought in semi-arid Kenyan rangeland. Afr J Ecol 48: 1009–1020.
[64]  Nagy KA, Girard IA, Brown TK (1999) Energetics of free-ranging mammals, reptiles, and birds. Ann Rev Nutr 19: 247–277.
[65]  Stuart C, Stuart T (2000) A field guide to the tracks and signs of Southern and East African Wildlife. Cape Town: Struik Publishers.
[66]  Grossman RB, Reinsch TG (2002) The solid phase. In: Dane JH and Topp C, editors. Methods of Soil Analysis, Part 4: Physical Methods. Madison, WI: Soil Society of America. 201–293.
[67]  Gee GW, Orr D (2002) Particle size analysis. In: Dane JH and Topp C, editors. Methods of Soil Analysis, Part 4: Physical Methods. Madison, WI: Soil Society of America. 255–293.
[68]  Hendershot WH, Lalande H, Duquette M (2008) Ion exchange and exchangeable cations. In: Carter MR and Gregorich E, editors. Soil Sampling and Methods of Analysis. Boca Raton, FL: Canadian Society of Soil Science and CRC Press. 173–178.
[69]  V?gen T, Winowiecki L, Desta LT, Tondoh JE (2010) The land degradation surveillance framework field guide. Nairobi: World Agroforestry Centre (ICRAF).
[70]  McNaughton SJ, Milchunas DG, Frank DA (1996) How can net primary productivity be measured in grazing ecosystems? Ecology 77: 974–977.
[71]  Augustine DJ (2002) Large herbivores and process dynamics in a managed savanna ecosystem. Ph.D. Dissertation: Syracuse University, New York.
[72]  McLaren JR, Turkington R (2010) Ecosystem properties determined by plant functional group identity. J Ecol 98: 459–469.
[73]  Blundell M (1982) The Wild Flowers of Kenya. London: Collins.
[74]  Bogdan AV (1976) A Revised List of Kenya Grasses (with keys for identification). Nairobi: Government Printer.
[75]  van Oudtshoorn F (2009) Guide to Grasses of Southern Africa. Pretoria: Briza Publications.
[76]  Dharani N (2006) Field Guide to Acacias of East Africa. Cape Town: Struik Publishers.
[77]  Gillett JB, McDonald PG (1970) A Numbered Check-list of Trees, Shrubs and Noteworthy Lianes Indigenous to Kenya. Nairobi: Government Printer.
[78]  Glass GV, Peckham PD, Sanders JR (1972) Consequences of failure to meet assumptions underlying fixed effects analyses of variance and covariance. Rev Ed Res 42: 237–288.
[79]  Schmider E, Ziegler M, Danay E, Beyer L, Buehner M (2010) Is it really robust? Reinvestigating the robustness of ANOVA against violations of the normal distribution assumption. Methodology 6: 147–151.
[80]  McNaughton SJ (1985) Ecology of a grazing ecosystem: the Serengeti. Ecol Monogr 55: 259–294.
[81]  Soil Survey Division Staff (1993) Soil survey manual. US Department of Agriculture Handbook 18.
[82]  Haynes RJ, Mokolobate MS (2001) Amelioration of Al toxicity and P deficiency in acid soils by additions of organic residues: a critical review of the phenomenon and the mechanisms involved. Nutr Cycl Agroecosys 59: 47–63.
[83]  Brady NC, Weil RR (1999) The Nature and Properties of Soils. Upper Saddle River, New Jersey: Simon & Schuster.
[84]  du Toit JT (1990) Feeding-height stratification among African browsing ruminants. Afr J Ecol 28: 55–61.
[85]  Gagnon M, Chew AE (2000) Dietary preferences in extant African Bovidae. J Mammal 81: 490–511.
[86]  Rodgers WA (1976) Seasonal diet preferences of impala from South East Tanzania. E Afr Wildl J 14: 331–333.
[87]  Stewart DRM (1971) Food preferences of an impala herd. J Wildlife Manage 35: 86–93.
[88]  Augustine DJ, McNaughton SJ (2004) Regulation of shrub dynamics by native browsing ungulates on East African rangeland. J Appl Ecol 41: 45–58.
[89]  Bond WJ (2008) What Limits Trees in C4 Grasslands and Savannas? Annu Rev Ecol Evol Syst 39: 641–659.

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