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Heavy impact on seedlings by the impala suggests a central role in woodland dynamics

Published online by Cambridge University Press:  12 April 2012

Christopher A. J. O'Kane ,
Kevin J. Duffy ,
Bruce R. Page  and
David W. Macdonald
Christopher A. J. O'Kane*
Affiliation:
Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, The Recanati-Kaplan Centre, Tubney House, Abingdon Road, Tubney, Oxon OX13 5QL, UK Institute of Systems Science, Durban University of Technology, P.O. Box 1334, Durban 4000, South Africa School of Biological and Conservation Sciences, Westville Campus, University of KwaZulu Natal, Private Bag X 54001, Durban 4000, South Africa
Kevin J. Duffy
Affiliation:
Institute of Systems Science, Durban University of Technology, P.O. Box 1334, Durban 4000, South Africa
Bruce R. Page
Affiliation:
School of Biological and Conservation Sciences, Westville Campus, University of KwaZulu Natal, Private Bag X 54001, Durban 4000, South Africa
David W. Macdonald
Affiliation:
Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, The Recanati-Kaplan Centre, Tubney House, Abingdon Road, Tubney, Oxon OX13 5QL, UK
*
1Corresponding author. Email: christopher.okane@zoo.ox.ac.uk
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Abstract:

Research has increasingly established that mesoherbivores influence the regeneration of woody plants. However the relationship between mesoherbivore density and degree of impact, and the spatial component of this impact, has not been well established. Using a novel sampling design, we assessed in iMfolozi Park, South Africa, the impact of impala (Aepyceros melampus) across the full complement of woody species within the home range, evaluating its spatial component and relationship to impala density. We used four GPS collars, in separate breeding herds, and a GIS to detect zones of different density of impala in the landscape, thus defining a fine-grain browsing gradient. We assessed impact on woody recruits (≤ 0.5 m height) across this gradient by means of 1600 random 1 × 1-m quadrats. Densities of woody seedlings, and mean percentage of remaining canopy, were significantly less in areas of high impala density versus low-density areas. There was a significant correlation between increasing impala density and decreasing density of favoured woody recruits. We propose a hypothesis of impala-induced patch dynamics. It seems likely that the ubiquitous impala may create and sustain a shifting mosaic of patches, and thus function as a key determinant of landscape heterogeneity.

Keywords

Aepyceros melampusbrowserelephantguildskeystonepatch dynamicssavannaseedlingsSouth Africa
Type
Research Article
Information
Journal of Tropical Ecology , Volume 28 , Issue 3 , May 2012 , pp. 291 - 297
Copyright
Copyright © Cambridge University Press 2012

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References

LITERATURE CITED

AUGUSTINE, D. J. & MCNAUGHTON, S. J. 1998. Ungulate effects on the functional species composition of plant communities: herbivore selectivity and plant tolerance. Journal of Wildlife Management 62:1165–1183.CrossRefGoogle Scholar
AUGUSTINE, D. J. & MCNAUGHTON, S. J. 2004. Regulation of shrub dynamics by native browsing ungulates on East African rangeland. Journal of Applied Ecology 41:45–58.CrossRefGoogle Scholar
BALFOUR, D. A. & HOWISON, O. E. 2001. Spatial and temporal variation in a mesic savanna fire regime: responses to variation in annual rainfall. African Journal of Range and Forage Science 19:45–53.CrossRefGoogle Scholar
BARNES, M. E. 2001. Effects of large herbivores and fire on the regeneration of Acacia erioloba woodlands in Chobe National Park, Botswana. African Journal of Ecology 39:340–350.CrossRefGoogle Scholar
BELSKY, A. J. 1984. Role of small browsing mammals in preventing woodland regeneration in the Serengeti National Park, Tanzania. African Journal of Ecology 22:271–279.CrossRefGoogle Scholar
BEN-SHAHAR, R. 1996. Do elephants over-utilize mopane woodlands in northern Botswana? Journal of Tropical Ecology 12:505–515.CrossRefGoogle Scholar
BERGSTRÖM, R. & EDENIUS, L. 2003. From twigs to landscapes – methods for studying ecological effects of forest ungulates. Journal for Nature Conservation 10:203–211.CrossRefGoogle Scholar
BIRKETT, A. & STEVENS-WOOD, B. 2005. Effect of low rainfall and browsing by large herbivores on an enclosed savannah habitat in Kenya. African Journal of Ecology 43:123–130.CrossRefGoogle Scholar
BOUNDJA, R. P. & MIDGLEY, J. J. 2010. Patterns of elephant impact on woody plants in the Hluhluwe-Imfolozi park, Kwazulu-Natal, South Africa. African Journal of Ecology 48:206–214.CrossRefGoogle Scholar
BRAAK, L. E. O. 1995. Seasonal activity of savanna termites during and after severe drought. Koedoe 38:73–82.Google Scholar
CRAWLEY, M. J. 2005. Statistics: an introduction using R. John Wiley, Chichester. 327 pp.CrossRefGoogle Scholar
CROZE, H. 1974. The Seronera bull problem. l. The elephants. East African Wildlife Journal 12:1–27.CrossRefGoogle Scholar
DU TOIT, J. D. 1990. Feeding-height stratification among African browsing ruminants. African Journal of Ecology 28:55–61.CrossRefGoogle Scholar
DUBLIN, H. T., SINCLAIR, A. R. E. & MCGLADE, J. 1990. Elephants and fire as causes of multiple stable states in the Serengeti–Mara woodlands. Journal of Animal Ecology 59:1147–1164.CrossRefGoogle Scholar
EMSLIE, R. H. 1999. The feeding ecology of the black rhinoceros (Diceros bicornis minor) in Hluhluwe–Umfolozi Park, with special reference to the probable causes of the Hluhluwe population crash. Ph.D. dissertation. University of Stellenbosch, Stellenbosch, South Africa. 644 pp.Google Scholar
FARNSWORTH, K. D., FOCARDI, S. & BEECHAM, J. A. 2002. Grassland–herbivore interactions: How do grazers coexist? American Naturalist 159:24–39.CrossRefGoogle ScholarPubMed
GANDAR, M. V. 1982. Trophic ecology and plant/herbivore energetics. Pp. 514–534 in Huntley, B. J. & Walker, B. H. (eds.). Ecology of tropical savannas. Springer, Berlin.CrossRefGoogle Scholar
GILLSON, L. 2004. Evidence of hierarchical patch dynamics in an east African savanna? Landscape Ecology 19:883–894.CrossRefGoogle Scholar
GOHEEN, J. R., KEESING, F., ALLAN, B. F., OGADA, D. L. & OSTFELD, R. S. 2004. Net effects of large mammals on Acacia seedling survival in an African savanna. Ecology 85:1555–1561.CrossRefGoogle Scholar
GULDEMOND, R. & VAN AARDE, R. 2009. The influence of tree canopies and elephants on sub-canopy vegetation in a savannah. African Journal of Ecology 48:180–189.CrossRefGoogle Scholar
HAGENAH, N., MUNKERT, H., GERHARDT, K. & OLFF, H. 2009. Interacting effects of grass height and herbivores on the establishment of an encroaching savanna shrub. Plant Ecology 201:553–566.CrossRefGoogle Scholar
HOBBS, N. T. 1996. Modification of ecosystems by ungulates. Journal of Wildlife Management 60:695–713.CrossRefGoogle Scholar
JARMAN, M. V. 1970. Attachment to home area in impala. East African Wildlife Journal 8:198–200.CrossRefGoogle Scholar
KEESING, F. 1998. Impacts of ungulates on the demography and diversity of small mammals in central Kenya. Oecologia 116:381–389.CrossRefGoogle ScholarPubMed
LEVICK, S. & ROGERS, K. 2008. Patch and species specific responses of savanna woody vegetation to browser exclusion. Biological Conservation 141:489–498.CrossRefGoogle Scholar
MACARTHUR, R. H. & PIANKA, E. R. 1966. On optimal use of a patchy environment. American Naturalist 100:603–609.CrossRefGoogle Scholar
MAKHABU, S. W. 2005. Resource partitioning within a browsing guild in a key habitat, the Chobe Riverfront, Botswana. Journal of Tropical Ecology 21:641–649.CrossRefGoogle Scholar
MOE, S. R., RUTINA, L. P., HYTTEBORN, H. & DU TOIT, J. T. 2009. What controls woodland regeneration after elephants have killed the big trees? Journal of Applied Ecology 46:223–230.CrossRefGoogle Scholar
MOURIK, A. A., VAN LANGEVELDE, F., VAN TELLINGEN, E., HEITKONIG, I. M. A. & GAIGHER, I. 2007. Stability of wooded patches in a South African nutrient-poor grassland: do nutrients, fire or herbivores limit their expansion? Journal of Tropical Ecology 23:529–537.CrossRefGoogle Scholar
MOUSTAKAS, A., SAKKOS, K., WIEGAND, K., WARD, D., MEYER, K. M. & EISINGER, D. 2009. Are savannas patch-dynamic systems? A landscape model. Ecological Modelling 220:3576–3588.CrossRefGoogle Scholar
MUCINA, L. & RUTHERFORD, M. C. 2006. The vegetation of South Africa, Lesotho and Swaziland. South African National Biodiversity Institute, Pretoria. 807 pp.Google Scholar
MURRAY, M. G. 1982. Home range, dispersal and the clan system of impala. African Journal of Ecology 20:253–269.CrossRefGoogle Scholar
NOSS, R. F. 1990. Indicators for monitoring biodiversity: a hierarchical approach. Conservation Biology 4:355–364.CrossRefGoogle Scholar
O'KANE, C. A. J., DUFFY, K. J., PAGE, B. R. & MACDONALD, D. W. 2011. Overlap and seasonal shifts in use of woody plant species amongst a guild of savanna browsers. Journal of Tropical Ecology 27:249–258.CrossRefGoogle Scholar
POOLEY, E. S. 2003. The complete field guide to trees of Natal, Zululand & Transkei. Natal Flora Publications Trust, Durban. 512 pp.Google Scholar
PRINS, H. T. & VAN DER JEUGD, H. P. 1993. Herbivore population crashes and woodland structure in East Africa. Journal of Ecology 81:305–314.CrossRefGoogle Scholar
RIGINOS, C. & YOUNG, T. P. 2007. Positive and negative effects of grass, cattle, and wild herbivores on Acacia saplings in an East African savanna. Oecologia 153:985–995.CrossRefGoogle Scholar
ROSELL, F., BOZSER, O., COLLEN, P. & PARKER, H. 2005. Ecological impact of beavers Castor fiber and Castor canadensis and their ability to modify ecosystems. Mammal Review 35:248–276.CrossRefGoogle Scholar
RUSSELL, F. L. & FOWLER, N. L. 2004. Effects of white-tailed deer on the population dynamics of acorns, seedlings and small saplings of Quercus buckleyi. Plant Ecology 173:59–72.CrossRefGoogle Scholar
SEYMOUR, C. L. 2008. Grass, rainfall and herbivores as determinants of Acacia erioloba (Meyer) recruitment in an African savanna. Plant Ecology 197:131–138.CrossRefGoogle Scholar
SHARAM, G., SINCLAIR, A. R. E. & TURKINGTON, R. 2006. Establishment of broad-leaved thickets in Serengeti, Tanzania: the influence of fire, browsers, grass competition, and elephants. Biotropica 38:599–605.CrossRefGoogle Scholar
SHAW, M. T., KEESING, F. & OSTFELD, R. S. 2002. Herbivory on Acacia seedlings in an East African savanna. Oikos 98:385–392.CrossRefGoogle Scholar
SMITHERS, R. H. N. 1983. The mammals of the Southern African subregion. University of Pretoria, Pretoria. 736 pp.Google Scholar
STEPHENS, D. W. & KREBS, J. R. 1986. Foraging theory. Princeton University Press, Princeton. 262 pp.Google Scholar
STOKKE, S. & DU TOIT, J. T. 2000. Sex and size related differences in the dry season feeding patterns of elephants in Chobe National Park, Botswana. Ecography 23:70–80.CrossRefGoogle Scholar
VERWEIJ, R. J. T., VERRELST, J., LOTH, P. E., HEITKÖNIG, I. M. A. & BRUNSTING, A. M. H. 2006. Grazing lawns contribute to the subsistence of mesoherbivores on dystrophic savannas. Oikos 114:108–116.CrossRefGoogle Scholar
WARD, A. I., WHITE, P. C. L., WALKER, N. J. & CRITCHLEY, C. H. 2008. Conifer leader browsing by roe deer in English upland forests: effects of deer density and understorey vegetation. Forest Ecology and Management 256:1333–1338.CrossRefGoogle Scholar
WHATELEY, A. & PORTER, R. N. 1983. The woody vegetation communities of the Hluhluwe-Corridor–Umfolozi Game Reserve Complex. Bothalia 14:745–758.CrossRefGoogle Scholar