The importance of nutrient hot-spots in the conservation and management of large wild mammalian herbivores in semi-arid savannas.

摘要

Extensive studies in the Serengeti showed a strong link between patchy herbivory and forage quality, and the factors that determine forage patch selection at different scales have been evaluated in various models. The purpose of this study was to examine to what extent favoured forage patches in the Lowveld of South Africa are determined by forage quality and how important these are as forage resources. Understanding the factors that determine herbivore distribution will provide insights into how the utilization of forage by herbivores affects and is influenced by the ecosystem and thereby improve our abilities to conserve and manage these systems. The Kruger National Park is a large wildlife conservation area, with stratified rainfall and soil nutrient patterns. Tuft utilization and number of faecal deposits were used to determine favoured forage patches within these stratifications. On the low-nutrient granites, the use of grass tufts on the crests of hillslopes was about a quarter that on sodic sites, and a third of that of termite mounds. On the high-nutrient basalts, utilization of crests was about a third of that of termite mounds and about a quarter of the utilization of sodic sites in the wet and growth season, but towards the end of the dry season all patches were utilized to a similar extent. On sodic sites, shorter grass grazers accounted for almost ten times more faecal deposits than other species, although there was evidence of all the other large herbivore groups also utilizing these sites. The foliar nitrogen and phosphorus concentrations from termite mounds and sodic patches were up to twice that found on the crests in the wet season, especially on the granites, indicating that forage quality may indeed play an important role in determining favoured forage patches. Furthermore, only the patches on the sodic sites and termite mounds produced foliage of sufficient quality to support reproduction and maintenance of body condition. These patches thus form key resource areas that determine animal condition and hence dry season survival. These findings have important management consequences: firstly in predicting the number of animals that may be supported by an area; secondly, because these nutrient hot-spots are so intensely utilized by herbivores, they will be the first to show degradation, and monitoring programs should thus include these areas. Appropriate monitoring designs will detect degradation in these areas in time to take appropriate management actions that would avoid irreversible system changes..