Surface-Water Constraints on Herbivore Foraging in the Kruger National Park, South Africa

Abstract

Abstract. 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 distributions. 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 dryseason, landscape-scale distribution patterns of eight herbivore species. Hypotheses regarding 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 surfacewater 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.

The Utilization of Water Points by Wildlife Species in Nyae Nyae Conservancy, Namibia

“…Buffalos are grazers which are known to be relatively water dependent in order to supplement the low water content in grass with frequent drinking (Redfern et al, 2003). A study done by Smit and Grant (2009) showed that buffalo occurred 1.5km from surface water sources while other grazer species occurred approximately 2km from surface water sources.…”

Identifying the water sources consumed by bison: implications for large mammalian grazers worldwide

“…At the landscape-scale, the often patchy distribution of resource availability over time drives distribution patterns of large herbivores (Fryxell 1991, Bailey et al 1996, Wilmshurst et al 1999, Allred et al 2011, Smit 2011). Forage quality for large herbivores can be constrained by access to reliable water sources (Bailey et al 1996, Redfern et al 2003. As such, access to water imposes a limitation on herd distributions across the landscape and regulates an animal's ability to access both high quality and quantities of forage (Redfern et al 2003).…”

“…Forage quality for large herbivores can be constrained by access to reliable water sources (Bailey et al 1996, Redfern et al 2003. As such, access to water imposes a limitation on herd distributions across the landscape and regulates an animal's ability to access both high quality and quantities of forage (Redfern et al 2003). Limitations on grazing distances from water sources vary among ungulate species according to digestive throughput rate, fecal moisture content, urine volume and osmolality and other physiological and morphological characteristics associated with the grazer's ability to maintain an optimal temperature and water balance (Cain et al 2012).…”

“…Limitations on grazing distances from water sources vary among ungulate species according to digestive throughput rate, fecal moisture content, urine volume and osmolality and other physiological and morphological characteristics associated with the grazer's ability to maintain an optimal temperature and water balance (Cain et al 2012). Some ruminants (e.g., African buffalo, Syncerus caffer) may be especially sensitive to the foraging constraints set by access to surface water availability, because trade-offs between forage quality and water availability are manifest during periods when forage quantity is low (Redfern et al 2003, Smit et al 2007, Smit 2011 and when the moisture content of grasses decreases following senescence (Western 1975).…”

“…For example, presumed drinking water sources have been reported using visual observations of herd habitat selection (Coppock et al 1983, Bergstrom and Skarpe 1999, de Leeuw et al 2001, camera traps (Whiting et al 2010), aerial census (Western 1975, Redfern et al 2003, and distances to water calculated using GPS collars (Fortin et al 2003, Allred et al 2011, Dancose et al 2011, Cain et al 2012. These techniques provide a template for presumed water-use by grazers based on the assumption that the water consumed comes from either the most abundant or most proximal water source to the animal's location.…”