Species traits in relation to a habitat templet for river systems

SUMMARY This paper focuses on the premise that the habitat provides the templet upon which evolution forges characteristic species traits. Alternative hypotheses are that there are historic and phylogenetic constraints on the match between organism and environment. In our analysis of river systems, as one dimension of the templet we choose temporal heterogeneity and assume some relationship between this and the frequency of disturbance. The second dimension is spatial heterogeneity in the physicochemical environment and we pay particular attention to the way such variation can ameliorate the influence of disturbances through the provision of refugia. We derive predictions about the traits of species, including size, generation time, reproductive tactics, body form, mobility and potential for regeneration, that are likely to occur in particular regions of the two‐dimensional templet. We also present predictions about community‐level characteristics such as number of species per resource category and total species richness. The general predictions are intended to apply to a wide range of plants, micro‐organisms and animals, provided the measurements have been made at a scale appropriate to them. Hypotheses can be tested by comparing traits predicted for particular habitats, whose spatial and temporal heterogeneity have been quantified, with those actually observed. If the fit turns out to be good, we will be able to conclude that the habitat templet approach offers a sound framework within which to pose questions in river ecology.