Assessing the conservation value of farmland ponds: Use of predictive techniques to identify surrogate groups

Background/Question/Methods Ponds are among the most diverse and yet threatened components of freshwater biodiversity. The conservation of ponds would greatly benefit from the identification of surrogate taxa in preliminary assessments aimed at detecting ponds of potentially high biodiversity value. Vascular plants and water beetles have often been used in pond conservation assessments. To evaluate whether wetland plants are a suitable surrogate group to evaluate pond biodiversity, we used plant, beetle, and environmental data collected from 54 ponds located in two farmed regions in Ireland. Specifically, we aimed at assessing cross-taxon congruence between water beetles and plants; quantifying and comparing the capacity of vegetation data and environmental variables to predict beetle species composition; assessing and comparing the response of plant and beetle communities to environmental conditions. The predictive strength of vegetation data was evaluated at the levels of species and community type composition, and species diversity. To identify the best predictor data-set for beetle species composition, we used predictive co-correspondence analysis (Co-CA) and predictive canonical correspondence analysis (CCA-PLS). Congruence in species richness was calculated using simple regression analysis, while a generalized linear model was developed to quantify the effect of environmental variables on patterns of beetle and plant diversity.
Results/Conclusions The study ponds supported over 30% of the Irish water beetle fauna (76 species), with five species having some form of IUCN Red List Status in Ireland, and 67 wetland plant species, including a nationally rare one. Co-CA showed that plant species composition had a positive predictive accuracy, which was significantly higher compared to that of data at the plant community type level. Although environmental variables showed a higher predictive capacity compared to that of plant species composition, the difference was not significant. Explanatory CCA analyses showed that plants and beetles both responded to the same subset of environmental conditions, explaining ca.18% of the variation in both plant and beetle species composition. Regional differences, permanency, substratum, and grazing intensity affected the composition of both plant and beetle assemblages. The relationship between plant and beetle diversity was rather weak, reflecting the contribution of few plant species in supporting diverse beetle assemblages. These findings have important implications in conservation planning. First, the composition of wetland plants can be effectively used as a surrogate taxon in the identification of conservation-priority ponds. Second, conservation strategies aimed at maintaining and enhancing pond biodiversity should be based on considerations on the vegetation.