The natural regulation of buffalo populations in East Africa: The food supply as a regulating factor, and competition*

Abstract

Summary Evidence is presented to show that both the quality and quantity of food available to a buffalo population falls below the minimum maintenance requirements of that population at certain times of the year. In the Serengeti grasslands there was a shortage of the only good quality component, grass leaf, in the dry season, with the result that the animals consumed an increasing proportion of poor quality food such as grass stem. By the end of the dry season the diet had dropped in quality below the minimum maintenance level. In areas such as Mt. Meru where there was a more continuous growing season, the high density of animals kept the standing crop of leaf at a low level. During the cooler dry season the growth of leaf became insufficient in quantity for the maintenance requirements of the population. These two quite different situations suggested that food shortage was a more general phenomenon in eastern Africa. Various measurements of feeding behaviour were made. Total grazing time per 24 h did not differ between seasons but ruminating time may have increased as the season became drier and could have been a response to the more fibrous food. Analysis for cycles of activity showed that there was more temporal organization during the dry season. These changes in activity cycles appeared to be related to the increase in energy expenditure produced by heat stress and sweating. Old animals with poor teeth did not compensate for the poor food supply by changing their feeding behaviour. There was a positive relationship between annual rainfall and mean crude density in different areas of eastern Africa, indicating that regulation was taking place. Since rainfall determined the amount of available food, it could have operated through the food supply. On a finer scale it was found that the extent of the preferred riverine habitats was also related to density. Thus rainfall, the extent of riverine habitat and perhaps soil moisture were three limiting factors that determined mean density and all could have taken effect through the food supply. As a result of initial selective grazing the amount of available leaf declined as the dry season progressed to the extent that by the end of the season the proportion of this component in the diet fell to a very low level. The impact of the population on its limited food supply indicated that intra‐specific competition was acting as the cause of regulation. Measurements of wildebeest eating the same food in the same habitats as buffalo showed that inter‐specific competition was also taking place. A small proportion (7“) of the wildebeest population could have reduced the buffalo population by approximately 18o,‘, from its potential population size. The buffalo population in the Serengeti was regulated by adult mortality which was caused by undernutrition as a result of food shortage. This food shortage was caused by intra‐ and inter‐specific competition. The effect of predation and disease was to hasten the response of the population to changes in the food supply. The limiting...

Population regulation of African buffalo in the Mara–Serengeti ecosystem

“…The effects of drought are most strongly felt when animal populations experience extreme food limitation and either engage in limited movements or occupy habitats that experience droughtrelated food limitation at some stage on their migration -like the Mara-Serengeti wildebeest. Our finding that the Mara-Serengeti buffalo population is limited by food supply not only supports the food limitation hypothesis (H 1 ) but is also supported by several previous studies in the region (Sinclair 1973b(Sinclair , 1974b(Sinclair , 1977(Sinclair , 1983(Sinclair , 1985Dublin et al 1990a). Indeed, following his long-term study on the African buffalo in the Serengeti, Sinclair (1977), argued that the importance of food limitation to buffalo has led to the evolution of specific behavioural strategies and physiological mechanisms to detect and avoid food shortages.…”

“…Thus, the conclusion that competition alone was of overriding importance in the regulation of the buffalo (Sinclair 1974b(Sinclair , 1977Dublin et al 1990a) seems insufficient to explain dramatic changes in the buffalo population in the Mara-Serengeti between 1984 and 2010.…”

What limits the Serengeti zebra population?

“…In the Serengeti ecosystem long-term studies on buffalo (Sinclair 1974(Sinclair , 1977 and wildebeest demonstrated that predation did not have a major impact on these populations which were mainly regulated by food supply, especially during dry years.…”

The maximum attainable body size of herbivorous mammals: morphophysiological constraints on foregut, and adaptations of hindgut fermenters

“…In their study, the buffalo had the lowest value for colonic water absorption of all species investigated. Accordingly, African buffalo depend on the availability of drinking water (Sinclair 1974;Field 1976). Bartocci et al (1997), Clauss et al (1998) and Behrend (2000).…”