Climates are now changing rapidly toward warmer temperatures, and in nearly half the EarthвЂ™s terrestrial surface, this is expected to lead to less water availability in the growing season ( 4). Understanding the basis of the climateвЂ“diversity relationship takes on particular urgency in light of contemporary climate change. Globally, regions with climates that are both warm and wet support more species than regions where the climate is either cold or arid, and this broadscale climatic influence outweighs that of any other predictor of diversity ( 1вЂ“ 3). This control of diversity by climate is clearest when considering taxonomic diversity (species richness) over broad spatial scales. Plant diversity is shaped more strongly in space and time by climate than by any other factor. These results support the tolerance and climatic niche conservatism hypotheses for climateвЂ“diversity relationships, and suggest there is some predictability to future changes in diversity in water-limited climates. Across spatial scales and organizational levels, plant diversity is maximized in more productive (wetter) climates, and these consistent spatial relationships are mirrored in losses of taxonomic, functional, and phylogenetic diversity over time during a recent climatic drying trend. Here, studies of Californian plants are reviewed and new analyses are conducted to synthesize climateвЂ“diversity relationships in space and time. Unresolved aspects of this relationship include what causes it, whether it permeates to community diversity at smaller spatial scales, whether it is accompanied by patterns in functional and phylogenetic diversity as some hypotheses predict, and whether it is paralleled by climate-driven changes in diversity over time. 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 gradient according to the species' physiological tolerance limits.Climate strongly shapes plant diversity over large spatial scales, with relatively warm and wet (benign, productive) regions supporting greater numbers of species. In all, these findings add to the results of previous null model tests on the same four subsets, where competitive interactions were assigned a minor importance in limiting elevational distributions. The dependence of most amphibians on aquatic breeding sites that were not available at all elevations reduced the relative importance of the gradient on the species distributions in subset 2 and accounted for the difference to the reptiles. The gradient descriptors explained more variation in the reptile subset than did ecotones, while the reverse was found in the amphibian subset. A variation partitioning analysis was used to assess the individual and common contributions of gradient and ecotone descriptors to the elevational variation in the structure of subsets 1 and 2. However, this response disappeared within subsets 3 and 4. A response to ecotones was revealed for the amphibian subset only and associated with the presence or absence of watercourses.

All subsets showed a significant relationship with the gradient, which suggested that most species respond to the physical continuum associated with the change in elevation. Analyses were run for four subsets of the entire assemblage: (1) reptiles, (2) amphibians, (3) amphibians dependent on streams for reproduction, and (4) amphibians that do not use streams for reproduction. The elevational gradient was coded in a form that accommodated different types of community response. Qualitative descriptors were used to define the elevational positions of the ecotones of interest, namely transitions in forest type and presence/absence of water bodies. Summary The relative effects of the elevational gradient and of environmental discontinuities (ecotones) on the structure of a herpetofaunal assemblage in a tropical upland forest were contrasted by means of canonical correspondence analysis. AmphibiaВ CameroonВ canonical correspondence analysisВ gradient distributionВ ReptiliaВ species groupsВ tropical forestВ variance partitioning.DГ©partement de sciences biologiques, UniversitГ© de MontrГ©al, Succursale вЂњCentre-Ville,вЂќ MontrГ©al, QuГ©bec, Canada Institut de Biologie, UniversitГ© de NeuchГўtel, Switzerland

Department of Vertebrates, Natural History Museum, Berne, Switzerland

Ecotones and gradient as determinants of herpetofaunal community structure in the primary forest of Mount Kupe, Cameroon.

Ecotone vs continuum