SummaryThe Amboseli ecosystem is in a semi‐arid savannah environment in which water availability is highly seasonal, a feature which has an important bearing on the structure and efficiency of the large mammal community.Data are presented to show that the seasonal movements, a wet season dispersal and dry season concentration of water‐dependent species (obligate drinkers) can be related to the seasonality of rainfall and water availability, but that similar patterns do not prevail in the water‐independent species.Evidence suggests that water availability is a crucial parameter in calculating the carrying capacity of a range, and that the duration of ephemeral supplies, which reflect rainfall seasonality, evapotranspiration, and soil water storage capacity, is equally important. A simplified model is presented which calculates the carrying capacity of water‐bound communities–taking into account these two limiting factors.There appears to be a physiological barrier to a heavy utilization of the low water content grasses beyond reach of the water‐dependent species, since most water‐independent species select high water content browse in order to maintain a positive water balance. Significantly, while the water‐independent community is almost exclusively composed of browsers, most water‐dependent species are grazers. The biomass density of large mammals beyond 15 km from water, a radius which encloses 99‐5% of the biomass of water‐dependent species, is extremely low compared to areas within 10 km of water.As a consequence of the physiological barrier to a heavy utilization of low water content forage in water‐deficient areas, the food chain efficiencies are appreciably lower than those with permanent water sources. Livestock development programmes have long appreciated this constraint and employed water development schemes to increase range‐carrying capacity.Seasonality in the movement patterns of Amboseli is compared to other large mammal communities and management implications are discussed.
We compile over 270 wildlife counts of Kenya's wildlife populations conducted over the last 30 years to compare trends in national parks and reserves with adjacent ecosystems and country-wide trends. The study shows the importance of discriminating human-induced changes from natural population oscillations related to rainfall and ecological factors. National park and reserve populations have declined sharply over the last 30 years, at a rate similar to non-protected areas and country-wide trends. The protected area losses reflect in part their poor coverage of seasonal ungulate migrations. The losses vary among parks. The largest parks, Tsavo East, Tsavo West and Meru, account for a disproportionate share of the losses due to habitat change and the difficulty of protecting large remote parks. The losses in Kenya's parks add to growing evidence for wildlife declines inside as well as outside African parks. The losses point to the need to quantify the performance of conservation policies and promote integrated landscape practices that combine parks with private and community-based measures.
Summary Allometric laws which scale numerous biomechanical and physiological processes to size in mammals have long been recognized and widely used in biology. There is now sufficient evidence to suggest that those life history parameters such as growth and maximum rates of reproduction, which depend in part on metabolic rate, are also scaled to size. Data are presented which, coupled with a literature review, show that gestation time, growth rates, age at first reproduction, lifespan, the intrinsic rate of natural increase, birth rate, net reproductive rate and litter weight are allometrically scaled to size and are, in consequence, inter‐related. The exponents of the scaling functions are similar in all mammalian orders but in some taxa such as the primates, the species grow slower, live longer and reproduce at a lower rate. For these taxa the differences in life history parameters can be explained by differences in brain size and an existing hypothesis that the maximum rate of neural tissue growth constrains the maximum rate of growth and development of the entire organism. It is then argued that because size scales the main life history parameters of mammals it should also be a central theme in ecology from the individual to the community level of organisation. Examples are presented to show that size is ubiquitous in ecology and accounts for most of the variation in life history parameters between species. Size scaling offers a method of reducing species of varying size to similar dimensions of time, space and rates of action. It is therefore fundamental in distinguishing those life history parameters which arise as a consequence of size, the first order strategies, from those that vary between populations and according to environmental circumstances, the second order strategies. From this approach should develop a broader biological synthesis in which genetic and physiological determinants will inevitably feature more centrally than they do in ecological and behavioural theory. Résumé Les lois allométriques unissant les processus biomécaniques et physiologiques avec la taille chez les mammifères ont été reconnues depuis longtemps et largement utilisées en biologic Il y a maintenant assez de certitude pour suggérer que les paramètres biologiques tels que croissance et taux maximal de reproduction, qui dépendent partiellement du rendement métabolique, sont aussi fonctions de la taille. Les données présentées ici, couplées avec une revue de la littérature, montrent que la durée de gestation, le taux de croissance, l'âge à la première reproduction, la durée de vie, le taux intrinsèque d'accroissement naturel, le taux de natalité, le taux de reproduction net et le poids de la portée sont en relation allométrique avec la taille et, par conséquent, sont en interrelation.
Woodland loss is a major cause of biodiversity decline in African savanna parks. Decisions about whether remedial steps are possible and warranted depend on the cause. Climate, fire, elephants and human impact, often in combination, have been cited as major causes. The almost complete extinction of woodland in Amboseli National Park since 1950 has been at the centre of such debate. A 20-year study based on an experimental design to test overgrazing, pathogen, climate and elephant browsing theories of woodland loss was established in 1981. The experiment showed that elephants alone are preventing regeneration. Based on the outcome of the experiment, a woodland refuge was restored in the centre of the park to maintain biodiversity and demonstrate the management prospects for habitat restoration. A strong interaction of elephants and pastoralists, played out across the ecosystem over many decades, probably accounts for the habitat mosaic and high biological diversity of the ecosystem prior to the establishment of the national park. The restoration of biodiversity in the park will therefore depend on mimicking the shifting mosaic of habitats created by their interaction. RésuméLa perte de zones boisées est une des causes majeures du déclin de la biodiversité dans les parcs de savane africains. Savoir s'il est possible de prendre des mesures pour y remédier et si elles seraient garanties dépend des causes impliquées. Le climat, les feux, les éléphants et l'impact humain, combinés le plus souvent, ont été cités comme des causes principales. La disparition quasi complète des zones boisées du Parc National d'Amboseli depuis 1950 est au centre d'un tel débat. Une étude de plus de vingt ans a été lancée en 1981, basée sur un projet expérimental destiné à tester les théories impliquant le surpâturage, les agents pathogènes, le climat et les prélèvements par les éléphants dans la perte de la forêt. L'expérience a montré que ce sont les éléphants seuls qui empêchent la régénération. Suite aux résultats de l'étude, un refuge forestier a èté restauré au centre du parc pour maintenir la biodiversité et montrer quelles pourraient être les perspectives de restauration de l'habitat en cas de gestion adéquate. La forte interaction entre les éléphants et les pasteurs qui a duré de nombreuses décennies à travers tout l'écosystème explique probablement la mosaïque de l'habitat et la grande biodiversité de l'écosystème avant la crèation du parc national. La restauration de la biodiversité dans le parc dépendra donc de la façon dont on pourra reproduire la mosaïque changeante des habitats créée par leur interaction.
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