Low cross-taxon congruence among aquatic organisms in artificial tropical ponds: implications for biomonitoring

The use of biodiversity surrogates is often suggested to increase the cost-effectiveness of biomonitoring programs, as this demands less time and taxonomic expertise. In addition, the detection of multi-taxon associations is a first step toward a better understanding of how organisms interact with each other. Such a multi-taxon association is termed a congruence, and can be detected through measuring the similarity in the distributional patterns shown by different biological groups. To assess the ability of different taxa to serve as surrogates for others, we carried out a Procrustes analysis on the beta diversity patterns of seven biological groups (aquatic birds, Amphibians, Macrophytes, Coleoptera, Odonata, Heteroptera and phytoplankton) in 35 ponds of the Cerrado biome. We found that: (i) the values of congruence in the studied ponds were weak; (ii) among all the biological groups compared, the highest congruence was found between amphibians and macrophytes; (iii) amphibians were congruent with the Coleoptera, Heteroptera, and macrophytes; (iv) the different taxa studied had different responses to environmental conditions; and (v) although they showed relatively weak congruence with the other taxa in each pond environment, amphibian communities were the most strongly influenced by environment variables. Almost all the communities observed in these systems showed unique pattern and thus should be studied and monitored in their entirety.We intended to choose an indicator group to better represent the biodiversity in man-made tropical ponds. For these propose we tested the congruence pattern among several aquatic communities. Two explanations have been previously proposed for the congruence among different taxa: (i) that different taxa have the same responses to environmental gradients (Padial et al., 2012a); or (ii) that congruence occurs because of ecological interactions among different groups, for instance, the relationships between predators and prey (Larsen et al., 2012). We hypothesized that the communities that depend directly on both water and land are likely more congruent with each other (e.g., amphibians, Odonata (in part), and macrophytes) than those that live in only one of these habitats (e.g., phytoplankton, aquatic insects, and birds). Although the congruency found for them was weak, amphibians were able to partially represent patterns in the abundance of Coleoptera, Heteroptera, and macrophytes. In terms of richness, macrophytes were able to partially represent patterns in Odonata, Coleoptera and birds. In this way, at least for abundance, our results partially supported the hypothesis that the biotic communities that depend directly on both water and land (e.g., amphibians and macrophytes) are more congruent with each other than those living only in one of these environments.Ultimately, we do not recommend the use of a single surrogate taxon to measure biodiversity: weak overall congruence between taxa; limited biological knowledge about tropical artificial ponds; and numerous taxa whose diversity patterns could not be represented by any surrogate group (phytoplankton, Heteroptera, and birds) illustrate the unsuitability of this approach