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Ecology, Vol. 48, No.3 90% of the tests performed the results of the first encounter were confirmed in subsequent encounters. APPENDIX IIIn the behavioural repertoire of the male, threat behaviour, chasing, fighting, and aggressive grooming may be regarded as good indicators of aggressive interaction. The question is, which of these acts, or what combination of them, is the most sensitive indicator of aggressiveness in males? This question was partly answered by plotting each act against the sum of all four acts for each bout. Data from the control series in the experiments on seasonal changes in aggressiveness were used. The four resulting scatter diagrams are shown in Figure 5. Threats and chases show a consistent relation to total aggression, while fights and aggressive grooming appear to add only a random factor. Hence the sum of threats and chases was chosen as the most sensitive index of aggressiveness.Abstract. The uses in ecology of the terms richness, diversity, homogeneity, and similarity are considered in the context of recent studies of plant and animal communities. Various uses of diversity are reviewed and an index of diversity derived from the distance measure of similarity is suggested. This index is / .~ n;2 where S equals the number of species and \ / t=l 11 equals the number of individuals in each species. This index is compared with other indices of diversity. The principal problem of measuring diversity is the assessment of the homogeneity or similarity of the samvle or samples being studied. An advantage of the proposed index is that it derives from a measure of similarity of which it is a special case, and it is a more natural and familiar representation of points in a coordinate system. lNTROpUCTION

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The Background of Ecology is a critical and up-to-date review of the origins and development of ecology, with emphasis on the major concepts and theories shared in the ecological traditions of plant and animal ecology, limnology, and oceanography. The work traces developments in each of these somewhat isolated areas and identifies, where possible, parallels or convergences among them. Dr McIntosh describes how ecology emerged as a science in the context of nineteenth-century natural histor