D3222: Functional traits in bee ecology: A review

Functional traits are measurable morphological, behavioral, phenological, and physiological features related to an organism’s fitness and its function within the ecosystem. Bees are among the most important pollinators and the application of functional traits to understand their ecological function, as well as their responses to changes in landscape and climate, is increasingly common in ecological studies. However, information on the types of traits, definitions, quantification, and functional significance remains scattered in the literature. Based on a literature survey, we reviewed the functional traits used in bee studies during the last decade. We screened each publication and retrieved the number, type (morphological, physiological, etc.), and definition of traits, number of bee species analyzed, and research location. Among the 30 publications evaluated, we found that 27 functional traits have been scored from more than 2000 bee species, most of them from North America and Europe. Each study, on average, analyzed five functional traits from an assemblage of 122 bee species. Body size, sociality, nesting location, and level of pollen specialization were common traits to all studies. Physiological or phenological traits are few or non-existent. Trait definition and characterization varied among studies. For example, body size has been assessed as either a continuous (intertegular distance or body length) or discrete (small, medium, and large) variable; parasitism, a reproductive strategy, has been treated as either a level of sociality, nesting, or feeding strategy. These results highlight the need for robust definitions of functional traits in bees, as well as the exploration of others.