Introduction
Inferring generalizable patterns in species dynamics, distributions, and
functional variation are central aims of ecology and evolutionary
biology (MacArthur, 1972). Trait-based approaches, which quantify
phenotypic characteristics that impact organisms’ fitness and/or
functional role, provide a tractable comparative framework for
understanding communities, ecosystems, and evolutionary processes
(Mcgill et al., 2006; Violle et al., 2007). Functional trait studies
have proliferated over the past two decades, addressing foundational
questions in community ecology (Cadotte et al., 2015; Mcgill et al.,
2006; Violle and Jiang, 2009), biogeography (Violle et al., 2014), and
conservation biology (Cadotte et al., 2011; Wellnitz and Poff, 2001)
across taxonomic groups. These works emphasize the promise of
trait-based research for generating novel insights into central
ecological concepts and theories.
Increasingly, bee researchers are recognizing the utility of trait-based
approaches for a wide variety of applications in ecological research.
Bees (Hymenoptera: Apoidea: Anthophila) represent more than 20,000
species worldwide and display dramatic interspecific variation in
morphology and behavior (Figure 1), including traits that mediate
pollination services and responses to global environmental change
(Supplementary Table 1). Exploration of functional traits has long been
a cornerstone of bee research, yet only recently have these traits been
systematically applied in bee ecological studies as a comparative
framework for understanding community-level processes. Given their major
functional role as the primary animal pollinators of terrestrial
ecosystems (Ollerton et al., 2011), the bees represent a group ripe for
exploration through a functional ecological lens.
Here, we review an emerging body of literature that quantifies
functional traits across bee communities to address questions in bee
ecology. In doing so, we address the following questions: How have
functional traits been used to study bee ecology? What have been the
major outcomes and limitations in bee functional trait research? How
might this framework be leveraged to address urgent questions in the
study of global bee declines? We review the variety of methods used to
quantify bee trait variation, highlight common methodological problems
and inconsistencies, and recommend best practices. Additionally, we
describe geographic, taxonomic, and trait biases across the body of bee
functional trait work, and highlight research areas that merit
particular attention in future studies. Finally, we emphasize the value
of open trait data sharing, and propose a roadmap toward a global bee
functional trait database, including an initial aggregated dataset of
3369 morphological measurements from 1209 bee species.