Can macrophytes be a surrogate for amphibians and physico-chemical features in pond classifications?

Abstract

Our primary goal was to test how consistently macrophytes, physico-chemical features and amphibians classify pond sites, by applying a measure of classification strength based on a set of cross-tests performed with randomisation protocols. Finally, we used ordination methods to identify the major environmental factors correlated with each biotic group. Significant results of concordance and higher values of relative classification strength were obtained at two (or more) cut levels, when the plant classification was performed on amphibians and on physico-chemical characteristics. Significant results and higher values of relative classification strength were also obtained at a cut level when the amphibian classification was performed on physico-chemical features. The ordination analyses revealed that plants and amphibians were affected by the same pond features, mainly conductivity, size and depth. Ponds with high conductivity were dominated by tall emergent plants of the genus Typha and were the preferential sites for Bufo bufo. Smaller shallow ponds with small emergent plants seemed instead to favour Rana dalmatina. Deep ponds with low conductivity were mostly occupied by floating and submerged plants, such as Potamogeton natans and Chara hispida, and hosted newts (Triturus carnifex and T. vulgaris), probably because the latter depend on well structured vegetation with submerged plants for egg deposition. These results suggest that pond ecosystems have “two levels of influence”, and that plants are the “middle level” between environmental features and amphibian assemblages, since they are directly influenced by the former and directly influence the latter. It is probably by virtue of this intermediate position that the classification of ponds based on plant assemblages can be used as a surrogate for predicting environmental features and the presence of amphibian species of conservation interest, in order to preserve their habitat through preliminary and cost-effective assessments. Given the ongoing threats to ponds, these findings are important for their protection, and better understanding of the ecological preferences of various plant and amphibian species is useful for planning management and conservation strategies.