Geographical ecology of Nigerian mammals

1. The vegetation zones of Nigeria replace each other with increasing latitude. Rainforest and swamp forest in the south are succeeded by derived savanna, Guinea savanna, Sudan savanna and finally Sahel savanna in the extreme north. Climatic characteristics such as mean annual rainfall, mean number of rainy days each year and mean monthly minimum temperatures decrease from south to north, whereas number o fmonths with less than 25 mm of rain, mean monthly maximum temperatures and range of mean annual temperature increase from south to north. Associated with this clinal pattern is increased seasonality, decreased productivity and lower mean vegetation height from south to north.2. Nigeria has a diverse mammalian fauna of 42 families, 133 genera and 241 species. The general distribution of each species according to vegetation zones is tabulated. The proportional representation of each order is about the same as found in other African countries, although Chiroptera and Primates are especially well represented. The number of mammalian species is close to the predicted number in relation to the surface area of the country. The greatest numbers are found in the rainforest (116 spp) despite the small area of this vegetation zone; numbers decline in each successive zone to the north. The numbers of species of Chiroptera, Primates and Rodentia decline in each successive vegetation zone from south to north, but the Carnivora and Artiodactyla attain their highest species numbers in Guinea and Sudan savannas. The species composition of the rainforest zone is essentially different to that of any other zone; in contrast, there is considerable similarity between the faunas of the savanna zones. The rainforest fauna has the highest number of endemic species whereas Sudan and Sahel savannas contain very few endemic species. Correlation between climatic factors and species numbers in rodents show that annual range of temperature and annual rainfall are the best predictors of species numbers; in contrast no significant correlations are apparent for all species of mammals probably because of the different responses of the major orders to changes within the vegetation zones.3. The mammals of Nigeria are typical of West Africa. The affinities of the fauna show that the majority of mammals are those of ’savanna’, ’rainforest’ and ’widespread’ origin. Other species are of ’Saharan’, ’montane’, ’western rainforest’, and ’eastern rainforest’ origins; and one species is endemic. Thus all except one species occur in other West African countries.4. The mammals of the rainforest zone may be considered as two groups, divided by the Niger river; of the endemic rainforest species 60 occurwest of the river and 69 occur east of the river. The Niger river appears to act as a dispersal barrier to 27 species (i.e., 35% of endemic rainforest species). The Jos plateau, forest relics in the savanna, and savanna-like habitats in the rainforest zone have influenced the distribution of some species.5. Analysis of the distribution and proportional abundance of small terrestrial rodents shows that species diversity indices are highest in the derived savanna and lowest in the rainforest. Many of these species occur in only one vegetation zone and have small habitat breadths; only three species have wide habitat breadths.6. Trophic levels and diversity are examined in relation to bats. Nigerian bats show the same pattern of diversity as those of Botswana and Zimbabwe. The majority are insectivorous and a small but significant proportion are fruit/nectar feeders.7. Eight ’faunal regions’ are recognized for the purposes of conservation of Nigerian mammal communities. Most faunal regions are, or will be, adequately conserved in proposed or gazetted reserved areas except for ’rainforest’ and the ’Jos plateau and relic forest’ communities; additional conservation areas are required in these two faunal regions.8. Geographical ecology of the mammals of Nigeria (as well as for many other African countries) is hampered by inadequate information on distribution patterns and an absence of quantitative and synecological studies. A community approach is necessary in order to understand many of the fascinating aspects of the geographical ecology of African mammals.