Ecotones and gradient as determinants of herpetofaunal community structurein the primary forest of Mount Kupe, Cameroon

The relative effects of the elevational gradient and of environmental disco ntinuities (ecotones) on the structure of a herpetofaunal assemblage in a t ropical upland forest were contrasted by means of canonical correspondence analysis. Qualitative descriptors were used to define the elevational posit ions of the ecotones of interest, namely transitions in forest type and pre sence/absence of water bodies. The elevational gradient was coded in a form that accommodated different types of community response. Analyses were run for four subsets of the entice assemblage: (1) reptiles, (2) amphibians, ( 3) amphibians dependent on streams for reproduction, and (4) amphibians tha t do not use streams for reproduction. All subsets showed a significant rel ationship with the gradient, which suggested that most species respond to t he physical continuum associated with the change in elevation. A response t o ecotones was revealed for the amphibian subset only and associated with t he presence or absence of watercourses. However, this response disappeared within subsets 3 and 4. A variation partitioning analysis was used to asses s the individual and common contributions of gradient and ecotone descripto rs to the elevational variation in the structure of subsets 1 and 2. The gr adient descriptors explained more variation in the reptile subset than did ecotones, while the reverse was found in the amphibian subset. The dependen ce of most amphibians on aquatic breeding sites that were not available at all elevations reduced the relative importance of the gradient on the speci es distributions in subset 2 and accounted for the difference to the reptil es. In all, these findings add to the results of previous null model tests on the same four subsets, where competitive interactions were assigned a mi nor importance in limiting elevational distributions. The response patterns revealed by the present approach, with ecotones and gradient contrasted in a single analysis, emphasised the role of individual responses to the grad ient according to the species' physiological tolerance limits.