Maximum growth rate, size and commonness in a community of bactivorous ciliates

Adaptions which confer competitive ability or resistance to predation are thought to be evolved with a resultant loss in intrinsic rate of increase (r _m). Therefore species which are opportunistic should retain high values of r _m, whereas competitively superior species which employ a strategy of persistance will have low values of r _m. Whether a ciliate species is slow or fast-growing can be judged by comparison with the empirically derived equation relating growth rate and size given by Fenchel (1968). This hypothesis was tested on a group of eleven species of bactivorous ciliates inhabiting a small pond. Species' measured and predicted r _m'S \((r/\hat r)\) were compared with their commonness in the field. The prediction that species with high values of \(r/\hat r\) would be less common, as measured by the number of samples in which they are found, was satisfied by the data. The implications of the data for the ciliate community studied and the potential of \(r/\hat r\) as a predictor of ecological characteristics of species are discussed.