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.