Using total abundance as a proxy for wild bee species richness: A practical tool for non-experts

As there is growing interest among non-specialists in participating in pollinator conservation initiatives, developing proxies for wild bee species richness that could be potentially used by non-experts can aid conservation, decision support systems for managers and policymakers, and create entry points for future taxonomists. We used data from 63 independent studies in which wild bees were sampled, covering all main European habitats and climates. We tested two proxies for wild bee species richness: abundance of all wild bees (excluding the honeybee) and abundance of bumblebees. These proxies require basic taxonomic training and have the potential for routine implementation by non-experts. Within-region, the abundance of wild bees was a strong predictor of wild bee species richness at the local scale, with an average correlation exceeding 0.80. Bumblebee abundance was a poorer proxy for total wild bee species richness (correlation coefficient of ~0.55) and was unsuitable for warm-temperate and Mediterranean climates. Observed abundance-richness correlations were consistent across climates, habitats and sampling methods, suggesting that, after a simple training, counting all bee individuals in transect walks provides a non-lethal, robust estimate of wild bee species richness. We observed a weak negative relationship between sample coverage and the strength of the abundance-richness correlation. Synthesis and applications. The use of a simple but effective proxy could be an important starting point for the expansion of wild bee monitoring initiatives at the regional scale, particularly given the growing involvement of non-specialists. We provided here a simple implementation framework to use this proxy in rapid biodiversity assessments, such as the evaluation of payment-by-result schemes by farmers and measuring the efficacy of conservation actions in urban green areas or protected areas by citizens and site managers, respectively. It is important to stress that we are not advocating for the replacement of the urgently needed long-term monitoring of pollinator status and trends. Instead, we propose that employing an effective proxy for non-experts could enhance the evaluation of many local and regional conservation initiatives that currently lack any basic assessment schemes.