Redundant or complementary? Evaluation of different metrics as surrogates of macrophyte biodiversity patterns in Mediterranean ponds

Abstract

Ecological metrics constitute one of the mainstream tools in modern ecology to assess varying information about processes and patterns of regional biodiversity. However, the performance of different metrics on Mediterranean pond macrophyte assemblages is still largely unknown, thus hampering the selection of suitable indices for biomonitoring purposes. In an attempt to fill this gap of knowledge, we compared the response of six ecological metrics (i.e. species richness, Shannon diversity, beta diversity, functional diversity, and average and variation in taxonomic distinctness) to determine which ones are redundant and constructed Generalized Additive Models (GAM) to assess their utility for macrophyte biodiversity evaluation. The study was performed at assemblage level in a vast area of approximately 94,000 km2 in northwestern Spain. Several environmental filters related to habitat conditions revealed themselves to have considerable impact on biodiversity measures. Physical factors exhibited the highest drop in deviance values for species richness, Shannon diversity and functional diversity, whereas beta diversity and taxonomic distinctness metrics were more sensitive to water chemistry changes. Our results, based on correlations among indices and partial response curves to primary environmental drivers, showed complementarity in at least three different biodiversity measures (i.e. functional diversity, beta diversity and taxonomic distinctness). Ultimately, the use of a combination of these three metrics should provide a complete picture of macrophyte biodiversity patterns and their response to major environmental forces, including the variation in the identities of species among communities and the functional and phylogenetic status of species. These findings underline the importance of considering different biodiversity measures for conservation planning at regional scale and should assist in the selection of suitable indices for future pond management initiatives in Mediterranean landscapes.