As an introduction Shorrocks surveys savannahs worldwide, describes the climatic patterns of the African savannahs, driven by seasonal shifts in the Intertropical Convergence Zone, and details the different vegetation complexes of "grass and shrub savannah", "tree and shrub savannah", "woodland savannah", and "forest-savannah mosaic".

This is followed by a chapter on vegetation, which considers the relationship between precipitation and biomass or tree cover, offers a typology of the different kinds of savannah plants, and then describes some of the individual grasses and trees. Only the more important species are covered here, but with some sketches of plants and seeds this could serve as a brief field guide. There is also a detailed study of the Serengeti-Mara, looking at local variation in soils and rainfall and the resulting patterns in biomass production and fires.

A chapter on animals passes over insects and birds quickly and focuses on the mammalian megafauna, in something of the manner of a field guide, with descriptions of species accompanied by distribution maps and small black and white photos. Shorrocks also offers some broader biology, however, looking for example at ungulate foot structure and dentition, and at the differences between hindgut fermentation and rumination.

Turning to single species populations, Shorrocks describes some of the methods for estimating species numbers: capture-recapture, identification from neck patterns or ear clipping, transects, aerial photography, etc. Studies of buffalo and wildebeest and modelling of wildebeest and zebra numbers in the Serengeti-Mara, and studies from elsewhere, sugggest that ungulate numbers are limited by rainfall.

Three kinds of species interactions are treated. "Predator-prey" relationships include herbivore-plant, carnivore-herbivore, and parasite-host interactions. Different herbivores are taken by different sized predators; rather than Lotka-Volterra cycles, rainfall appears to be the dominant forcing; and parasites may have the greatest effect on malnourished animals. Competitive interactions include grasses versus trees, herbivore competition and niche differentiation, and kleptoparasitism (kill stealing) between carnivores. And mutualistic interactions include grazing succession, ant-acacias (where Shorrocks provides a guide to identifying the four species of ant that live on whistling thorn acacias) and vulture-mammal scavenging "collaboration".

A final chapter on the savannah community touches on energy flows and food webs, assembly rules (patterns in the species which make up communities), biogeography, and conservation issues (hunting and poaching, habitat destruction, and human-wildlife competition). It's notable that the vast bulk of vegetation is consumed by decomposers such as termites or fires, and that insects (caterpillars and grasshoppers) take about as much as vertebrate herbivores.

All this makes for something of a grab-bag of material: bits and pieces of ecological theory, some mathematical models, field methods, miscellaneous biology, and local detail. The introduction says it is aimed at "senior undergraduate and graduate students" studying savannah or tropical ecology, but it seems a bit unfocused to make a good textbook. There is a clear regional focus, with most of the studies based on work done in East Africa and in particular the Serengeti-Mara.

One obvious audience will be scientists doing fieldwork in the region. Shorrocks includes a good assortment of clearly presented diagrams, however, and doesn't use any statistical tools more sophisticated than regression. So another audience will be travellers on safari who have an interest in ecology and want to go beyond ticking species off checklists and watching animal behaviour — The Biology of African Savannahs is a lot more interesting than the standard wildlife field guides.

Note: The Biology of African Savannahs contains a disconcerting density of "wrong word" spelling errors.

March 2011

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- books about Africa + African history
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