FORAGING FOR SURVIVAL: YEARLING BABOONS IN AFRICA

Stuart A. Altmann, The University of Chicago Press: Chicago and London, 1998, 536 pp. £49.00. Hardcover. ISBN: 0-226-01595-5

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This is an amazing volume for several reasons: (1) it reflects about 35 years of meticulous research at Amboseli in Kenya, (2) it contains the most intensive observations of all aspects of foraging behaviour, and their consequences for survival and reproduction, and (3) it relates statistically actual diets to optimal diets, with detailed analysis of food choice (and quantity consumed of each) and food composition (nutrients and secondary compounds). The key conclusion is that the survival of these yearling baboons, and their reproductive success, could be predicted from what they ate as yearlings.

There are ten chapters and ten appendices. Five specific research questions are posed: (1) what do weanling baboons eat, and what not? (2) what are the nutritional consequences of this selective foraging (in terms of nutrients and toxins)? (3) in view of the foods available, what, optimally, should they eat? (4) is their actual diet optimal? (5) do individuals whose diets come closer to the optimum have higher expected fitness? The meticulous and thorough approach is awesome in its breadth and depth!

Eclectic omnivory is discussed, the methods are described, dietary diversity is quantified, adequate and optima] diets, and then read versus ideal diets, are compared, individual differences and age changes are presented, from food to fitness is investigated, why be choosy is discussed, and, finally, how to be an eclectic omnivore is described. The appendices contain much data and analysis. The grouping of the tables at the end is very irritating; I wanted to see them in the relevant place in the text, along with the figures (I accept that others may find them disruptive of the text if so placed). Some of the complex tables are more difficult to read, because plant species and parts are represented by 4-letter codes. Chapter summaries would have been very helpful, given the complexity of data presentation and arguments.

Altmann uses a single analytical framework to treat the problems (1) meeting requirements of food minima, for energy and nutrients (ecological and physiological), (2) meeting requirements of food maxima, for toxins (botanical), and (3) simultaneously satisfying requirements of cost or profit function (naturalistic).

The intricacy of thinking and thoroughness of analysis is well illustrated by the questions posed concerning an optimal diet: (1) maximising energy and feeding time, (2) limitation of energy and protein in diet, (3) slack values and safety margins (4) marginal values of limiting factors (leverage), (5) marginal value ranges for requirement/tolerance, (6) energy/protein and time leeway, (7) energy/protein time shortfall and extra feeding time, (8) degeneracy and (9) uniqueness.

Altmann's optimal diets embrace the maximisation of energy and protein, the minimisation of feeding time, and the maximisation of energy and protein intake rates, with macro-nutrient constraints. Milk fever tree gum and seeds, and ripe Azuma berries are the key foods that can fulfill the above criteria. With extended constraints' he uses 25 foods to maximise energy at 4.69 MJ/day, 21 to maximise protein at 31 gm/day, 6 to minimise feeding time to 51 min/day, 8 to maximise energy intake rate at 82 min/day and 8 foods to maximise protein intake rate at 157 gm/day. Recurring foods are milk (more than 50% in some cases), gums (high in carbohydrates), acacia seeds (high in energy), grass leaves, corms, fruit and especially flowers (high in protein and energy), and meat (with a long harvesting time).

Nine problems are enumerated in relation to the ten optimal diets described: realisability, seasonal and availability constraints, water sources, mineral constraints and time budget limitations for the first five, and energy rate maximisation, foraging time minimisation and competing demands for the second five. In comparing real with ideal diets (chapter 61, food specific time budgets] unit intake rates and unit masses yield a mean animal diet and mean daily intake of nutrients. Since they do not necessarily feed on the most nutritious foods, actual diets are not optimal. Acacias, grasses and sedges are the main sources of food: apart from milk and water, 31% of the diet by weight are flowers, seeds and fruit, 54% green leaves, 29% fever tree gum, 5.4% corms, rhizomes and petioles, 0.005% wood and bark, and 0.2% animal matter.

Individual differences and age changes (chapter 7) are analysed in great detail for 4 groups of 10-week periods for ages of 30-70 weeks. Fitness (chapter 8) is analysed only in terms of energy intake; lipids or fibre are the usual shortfall. Social play is not a good predictor of female lifetime fitness. Choosiness (chapter 9) relates to avoiding toxins and seeking carbohydrates. The Amboseli baboons are compared with baboons elsewhere in Africa, and with the smaller vervets at Amboseli; vervets avoid phenolic compounds more than baboons, but otherwise eat similar plant foods, although they specialise on fewer at any one time. The baboon diet is much more diverse - they are terrestrial, social, with a very varied high- quality, low-bulk diet (chapter 10). Baboons range more widely, store food in cheek pouches, they are stronger and manipulate foods well and are clever (extractive foraging and cognitive maps). Being larger than yearlings, adult baboons conserve heat better but locomotion costs more. Yearlings have problems getting at some foods, they need milk and carriage and protection, hence their problems of survival.

It saddens me that even the great talk about "oestrous" in haplorhine primates, apparently not understanding the fundamental difference in their reproductive biology from other mammals. Year-round breading capacity, along with frugivory, need to be recognised as central to the success of such primates, and to the emergence of humans. Similarly and more relevant to this volumes is the need to question the meaning of "omnivory", as we hoed into the twenty-first century. Few seem to have questioned its meaning and usefulness. In the old days it was a category for those animals which were not specialised for eating animal matter or foliage; nowadays we recognise that such animals are mostly frugivores (a term that I could not find in this book). It bridges the gap betwean animal matter and foliage, and guts cannot usually cope with significant amounts of foliage and animal matter, hence the so-called omnivores are either frugivores or foli- frugivores or fauni-frugivores.

It disappoints me that the author does not tackle this question. It is not central to his thesis, and it may seem churlish to pursue it, but it is an important back-drop. We have to shift from qualitative definitions to quantitative ones. "Eclectic omnivory" seems to me to be tautologous. The important question that surely merits discussion is whether consuming items from the whole dietary spectrum makes you "omnivorous" and not just eclectic, or whether, as I favour, you need to eat significant quantities of the main food categories (for reasons of digestive functional anatomy), e.g. 20% each of animal matter and foliage, in addition to fruit. Indeed, the yearling baboons spent 24% of their feeding time on milk, with traces of animal matter, 29% on fruit and seeds, 8% on gums and 35% plant material (leaves, petioles, corms] etc.). This, I suppose, is "omnivory" (and would apply to all weanling primates), but adult baboons have to be regarded as foli-frugivores, with 43% fruit and seeds, 7% flowers, 25% corms, 18% leaves, and only 2% animal matter: this, surely is not omnivory but is an eclectic diet.

Thus baboons are shown to be unparalleled among primates in their success in terms of geographic range, large biomass, ability to live in diverse biological communities and to use many local habitats - arboreal and terrestrial - to withstand marked fluctuations in local conditions and to cope well with competitors and predators. Food-getting ability is at the heart of their success. We have known all this for 30 years or so, but this detailed analysis substantiates like never before such descriptions. It is an outstanding volume, for which I hope I have outlined the scope and contents adequately. It can only be properly understood by thorough reading. It will be an essential source for primatologists, behavioural (and plant) ecologists, mammalogists and nutritionists for decades to come. It is depressing to think that the like of it for other primate taxa may never be seen; it takes special dedication, endeavour and intellect to produce such unique research.