Species traits in relation to temporal and spatial heterogeneity in streams: A test of habitat templet theory

Abstract

1. The habitat templet approach depends on defining templet axes appropriate to the organism(s) of interest, predicting the traits of species associated with different parts of the templet, and testing these predictions in a range of habitats whose positions in the templet have been determined. 2. In this study of thirty-five benthic insect taxa at fifty-four tributary sites of the Taieri River on the South Island of New Zealand, we chose as the temporal axis the intensity/frequency of disturbance, defined in terms of bed movement during high discharge events. As the spatial axis, we postulated that three features would provide refugia and therefore ameliorate disturbance-percentage of the bed with low shear stress, percentage of the bed made up of large substratum particles and availability of interstitial space in the bed-from which we derived a combined multivariate refugium axis. 3. More disturbed communities contained a significantly higher percentage of individuals possessing the following traits: small size, high adult mobility, habitat generalist (each predicted to confer resilience in response to disturbance), clinger, streamlined/flattened and with two or more life stages outside the stream (each predicted to confer resistance in the face of disturbance). When analyses were performed on the percentage of taxa having particular traits, the predicted positive relationships with average bed movement were found for high adult mobility and habitat generalist traits. 4. The percentage of variance in trait scores explained by intensity of disturbance was generally higher in sites with less refugia available and lower in sites further from the headwaters. The percentage of variance explained was higher in sites recently subject to a major high discharge disturbance, suggesting that disturbances tend to strengthen the pattern of preponderance of resilience/resistance traits. 5. We mapped insect taxa onto the two-dimensional templet, following Grime et al.'s triangular terrestrial plant classification. The full variety of resistance and resilience traits were represented in insect species throughout the templet, but taxa associated with more disturbed conditions generally displayed a larger number of resilience and resistance traits, combined, than taxa associated with more stable stream beds.