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Environmental heterogeneity produced by termitaria in Western Uganda with special reference to mound usage by vertebrates Melton, Derek Arthur


Much ecological work has dealt with the ways extrinsic factors (weather, food, other animals, a place in which to live) affect a species' distribution and abundance. In this study I chose to examine a very conspicuous habitat feature of African savanna, in order to ask two questions related to such environmental factors. First, in what ways do termitaria change the environment for vertebrate species? Second, what termitaria features are utilized by vertebrates and are any species affected in their local distribution by them? The distribution and density of epigeal termite structures was described for one area, Ruwenzori National Park (R.N.P.) Western Uganda, using ground and aerial methods. Environmental changes caused by termitaria were investigated in four areas: the effects of termite mounds on land relief; the interiors of mounds; the soil of mounds; and the effects of mounds on vegetation. The following conclusions were drawn as to the potential importance of changes found to vertebrates. The high percentage of ground surface covered by mounds suggests that any plant or soil changes occurring at mounds are likely to be of significance to herbivores. Mounds were identified as being directly or indirectly involved in wallow formation. Both live and dead mounds can offer areas of complex subdivided space available to small and medium-sized vertebrates. Mounds are often concentrated sources of minerals directly available to animals via geophagy, or indirectly via mound vegetation. The majority of mounds in R.N.P. were in fact vegetated, and it was found that mounds increased the range of nutritive value of grasses available to animals by selective grazing. Vertebrate usage of mounds was studied using both direct and indirect methods. The following conclusions were drawn. Mounds were used by many vertebrate species as raised platforms. Species using mounds as territorial markers may be affected in their distribution by them. Mound interiors were usually occupied by a number of vertebrate species when accessible. During floods and fires termitaria affect the local distribution of certain small mammal species in R.N.P. Little geophagia occurred at mounds or elsewhere in R.N.P. Preferential grazing of mound grasses was demonstrated in R.N.P. This may complete the nutrient requirement of animals throughout the year, or be mainly important as a dry season forage. Orycteropus afer was the only vertebrate regularly digging into mounds for insect food in R.N.P. Although this animal did not preferentially forageat mounds, the mound building M.subhyalinus was the main species eaten. Mounds may influence the distribution of O.afer. The importance to vertebrates of the mound processes described was also discussed for other areas than R.N.P. Emphasis was laid on the variation found to occur between the mounds of different termite species, and between areas. It was concluded that it was possible that termites are increasing the carrying capacity of many areas of Africa, through the diverse mound processes described.

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