SURFACE‐WATER CONSTRAINTS ON HERBIVORE FORAGING IN THE KRUGER NATIONAL PARK, SOUTH AFRICA

At a landscape scale, the combined influence of biotic and abiotic factors may determine the distribution patterns of large herbivores in African savanna ecosystems. Herbivores foraging in these ecosystems may become nutritionally stressed during an annual dry season when both forage quality and quantity are reduced. Additionally, the locations of water sources may impose a landscape-scale constraint on dry-season herbivore distri- butions. We used logistic regression to analyze 13 years of aerial census data collected in the Kruger National Park (KNP), South Africa, and evaluated hypotheses regarding the relative influences that surface water, forage quality, and forage quantity exert on the dry- season, landscape-scale distribution patterns of eight herbivore species. Hypotheses re- garding the degree of correlation between species' distributions and distance to water were developed using previous observations of species' relative water dependence. We also developed hypotheses regarding species' responses to the trade-off that may occur between surface-water constraints and nutritional requirements when either forage quality or quantity is reduced. In general, we expect an increase in species' mean distance to water as a result of individuals mitigating limitations in nutritional requirements (i.e., intake quality or quantity) by foraging farther from water. Our analyses suggest that the trade-off between nutritional requirements and surface-water constraints that species face varies according to the species' water dependence, size, and gut morphology. Of the four grazers considered in our analyses, waterbuck distributions appear to be constrained primarily by surface- water availability. Distributions of buffalo, a large ruminant grazer, suggest that individuals face a trade-off between nutritional requirements and surface-water constraints when forage quantity is reduced. Alternatively, distributions of wildebeest, a smaller ruminant grazer, suggest that individuals face this trade-off when access to high-quality forage is limited. In comparison to buffalo and wildebeest, the strength of this trade-off is moderate for zebra, a nonruminant similar in size to wildebeest, when either forage quality or quantity is reduced. Distribution patterns for browsers are characterized by a weak relationship with distance to water, as expected for these relatively water-independent species. Population densities relative to forage quality confound exploration of this trade-off for mixed feeders.

[1]  R. Scholes,et al.  TO CULL OR NOT TO CULL: LESSONS FROM A SOUTHERN AFRICAN DROUGHT , 1987 .

[2]  D. Western.  Water availability and its influence on the structure and dynamics of a savannah large mammal community , 1975 .

[3]  R. Gray,et al.  Can ecological theory predict the distribution of foraging animals? A critical analysis of experiments on the ideal free distribution , 1993 .

[4]  R. Owen-Smith,et al.  Megaherbivores: The Influence of Very Large Body Size on Ecology , 1990 .

[5]  Robert J. Scholes,et al.  The influence of soil fertility on the ecology of southern African dry savannas , 1990 .

[6]  F. Venter.  Soil Patterns Associated with the Major Geological Units of the Kruger National Park , 1986 .

[7]  B. Walker,et al.  Aspects of the Stability and Resilience of Savanna Ecosystems , 1982 .

[8]  Michael H. Kutner.  Applied Linear Statistical Models , 1974 .

[9]  N. Owen‐Smith.  Ecological guidelines for waterpoints in extensive protected areas , 1996 .

[10]  W. Gertenbach.  Rainfall patterns in the Kruger National Park. , 1980 .

[11]  D. Collett.  Modelling Binary Data , 1991 .

[12]  M. Coe,et al.  Biomass and production of large African herbivores in relation to rainfall and primary production , 1976, Oecologia.

[13]  B. P. Farm,et al.  Spatial distribution of Serengeti wildebeest in relation to resources , 1999 .

[14]  J. Derry,et al.  The nature and modelling of piospheres: a review , 1999 .

[15]  A. Pusey.  The behavior guide to African mammals: by Richard Despard Estes, University of California Press, 1991. $75.00 hbk (xxii + 611 pages) ISBN 0 520 05831 3 , 1992 .

[16]  N. Zambatis,et al.  Rainfall and temperatures during the 1991/92 drought in the Kruger National Park , 1995 .

[17]  N. Owen‐Smith.  Factors Influencing the Consumption of Plant Products by Large Herbivores , 1982 .

[18]  M. C. Rutherford.  Annual plant production-precipitation relations in arid and semi-arid regions , 1965 .

[19]  W. Getz,et al.  Biases in estimating population size from an aerial census: a case study in the Kruger National Park, South Africa , 2002 .

[20]  S. Fretwell,et al.  On territorial behavior and other factors influencing habitat distribution in birds , 1969 .

[21]  P. Jarman,et al.  The Social Organisation of Antelope in Relation To Their Ecology , 1974 .

[22]  John M. Fryxell,et al.  Forage Quality and Aggregation by Large Herbivores , 1991, The American Naturalist.

[23]  M H Andrew,et al.  Grazing impact in relation to livestock watering points. , 1988, Trends in ecology & evolution.

[24]  Derek W. Bailey,et al.  Large Herbivore Foraging and Ecological HierarchiesLandscape ecology can enhance traditional foraging theory , 1987 .

[25]  S. Fretwell.  Populations in a seasonal environment. , 1973, Monographs in population biology.

[26]  H Breman,et al.  Rangeland Productivity and Exploitation in the Sahel , 1983, Science.

[27]  J. Wilmshurst,et al.  The allometry of patch selection in ruminants , 2000, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[28]  E. Laca,et al.  Mechanisms that result in large herbivore grazing distribution patterns. , 1996 .

[29]  William W. Hargrove,et al.  Predicting spatial distribution of foragers over large resource landscapes : a modeling analysis of the Ideal Free Distribution , 1997 .

[30]  H. Prins,et al.  Ecology and Behaviour of the African Buffalo , 1996, Chapman & Hall Wildlife Ecology and Behaviour Series.

[31]  R. L. Senft.  Hierarchical foraging models: Effects of stocking and landscape composition on simulated resource use by cattle , 1989 .

[32]  G. L. Smuts.  Interrelations Between Predators, Prey, and Their Environment , 1978 .

[33]  Montague W. Demment,et al.  A Nutritional Explanation for Body-Size Patterns of Ruminant and Nonruminant Herbivores , 1985, The American Naturalist.

[34]  J. Redfern.  Manipulating Surface Water Availability to Manage Herbivore Distributions in the Kruger National Park, South Africa , 2002 .

[35]  R. Bell.  The Effect of Soil Nutrient Availability on Community Structure in African Ecosystems , 1982 .