Body size and measurement of species diversity in large grazing mammals Boniface O. Oindo NationalEnvironmentalManagementAuthority,P.O.Box47146,Nairobi,Kenya Abstract Species are by de¢nition di¡erent from each other. This fact favours ranking rather than additive indices. How- ever, ecologists have measured species diversity in terms ofspeciesrichness,orbycombiningspeciesrichnesswith the relative abundance of species within an area. Both methods raise problems: species richness treats all spe- cies equally, while relative abundance is not a ¢xed prop- erty of species but varies widely temporally and spatially, and requires a massive sampling e¡ort. The functional aspect of species diversity measurement may be strengthened by incorporating di¡erences between species such as body size as a component of diversity. An index of diversity derived from a measure of variation in body size among species is proposed for large grazing mammals.Theproposeddiversity index relatedpositively to species abundance, indicating that the use of body size as a surrogate for diversity is adequate. Because the pro- posed index is based on presence or absence data, the expensive and time consuming counting of individuals per species in each sampling unit is not necessary. Key words: biodiversity index, body size, grazers, mam- mals Re¤sume¤ Par de¤ ¢nition, les espe' ces di¡e' rent les unes des autres. Ce fait favorisepluto“ t laclassi¢cation que des indices supple¤ - mentaires. Pourtant, des e¤ cologistes ont mesure¤ la diver- site¤ des espe' ces en termes de richesse des espe' ces ou en combinant la richesse des espe' ces avec l’abondance relativedesespe' cedansunendroitdonne¤ .Lesdeuxme¤ th- odes engendrent des proble' mes: la richesse des espe' ces traite toutes les espe'ces de la me“me fac ¸on tandis que l’abondance relative n’est pas une proprie¤te¤ ¢xe d’une espe' cemaisvarieconside¤ rablementdansletempsetdans l’espace, et exige des e¡orts d’e¤ chantillonnage impor- tants. On peut renforcer l’aspect fonctionnel de la mesure de la diversite¤ des espe'ces en inte¤grant des di¡e¤rences entre les espe'ces telles que la taille corporelle comme e¤ tant des composantes de la diversite¤ . On propose pour les grands mammife' res herbivores un index de diversite¤ de¤ rive¤ d’une mesure de lavariation de la taille corporelle parmi les espe'ces. L’index de diversite¤ propose¤ e¤tait lie¤ positivement a' l’abondance des espe'ces, ce qui montre que l’utilisation de la taille corporelle en remplacement de la diversite¤ est opportune. Comme l’index propose¤ se base sur des donne¤es de pre¤sence ou d’absence, il n’est pas ne¤ cessaire de proce¤ der dans chaque unite¤ au compt- age des individus de chaque espe' ce, si cou“ teux et si long. Introduction To prioritize conservation e¡orts, di¡erences in biodiver- sity across an area often need to be assessed (Groom- bridge, 1992). There has been controversy over the meaningof biologicaldiversity, over methodsformeasur- ingand assessing diversityas wellas the ecological inter- pretation of di¡erent levels of diversity. In the ensuing confusion, Hurlbert (1971) despaired, declaring diversity to be a nonconcept. However, his despair proved prema- ture, and when carefully de¢ned according to an appro- priate notation, diversity can be as unequivocal as any other ecological parameter (Hill,1973). The controversy was largely the result of an unreasonable expectation that a single statistic should contain all the information about the assembly of objects that it represents (Huston, # 2002 East AfricanWild Life Society, Afr. J. Ecol., 40, 267^275 267 Correspondence: Tel: þ31 (0)53 4874 438; fax:þ31 (0)53 4874 388; e-mail: booluoch@yahoo.com