What are the gaps in our understanding of bee functional ecology?
Our analysis revealed critical knowledge gaps in the field of comparative bee functional ecology. While a subset of morphological and behavioral traits was well represented, phenological traits were more rare and physiological trait data was nearly absent. Despite a wealth of physiological research on honey bees and bumble bees, physiological trait data for other bee species has lagged. In other insect taxa, comparative physiological trait data (e.g., thermal tolerance and desiccation resistance) has been usefully leveraged to understand and predict performance under climate change (Baudier et al., 2015; Bujan et al., 2020, 2016; Roeder et al., 2021). Interest in quantifying these traits in non-Apis bees is increasing (Burdine and Mccluney, 2019; Gonzalez, 2020; da Silva et al., 2021), yet they are still rare in comparative functional trait studies (Hamblin et al., 2017), due perhaps to the labor-intensive nature of quantifying these traits, especially relative to better-studied traits that can be sourced from the literature. Prioritizing physiological trait data collection and data sharing will vastly expand opportunities to predict performance under future climate scenarios. Phenological traits, especially flight seasonality, also merit increased attention in future functional trait studies. Despite known links between bee seasonality and vulnerability to environmental change, this trait was poorly represented in the studies we analyzed. While we emphasize the need to fill these trait gaps, we equally stress that trait selection should generally be hypothesis driven.
Urgently, future work should also expand the topical and geographic breadth of functional trait studies. The vast majority of functional trait studies were conducted in Europe and North America (80.4% of studies), mirroring a larger bias in ecological research (Archer et al., 2014; Martin et al., 2012; Pyšek et al., 2008). The geographic bias in bee functional trait research is even more extreme than the one reported by Winfree et al. (2011) for studies of native pollinators in human-altered landscapes (52% of studies conducted in Europe and North America). Preserving global crop pollination is a top priority for sustaining food security, yet relevant data is concentrated in wealthy regions that are lowest priority for this aim. Over-reliance on geographically-restricted data will undercut our ability to predict bee responses to environmental change globally. Finally, these studies were dominated by research on agroecosystems and agricultural/land use questions. This contrasts with a broader pattern in terrestrial ecology, where natural systems tend to be overrepresented in ecological studies (Martin et al., 2012). Climate change questions, in particular, were poorly represented in the studies analyzed here. Increasing attention to these topical gaps will help balance the body of functional trait literature better in line with conservation priorities.