Sociality
Sociality is another predictor of ecological patterns in bees, both because of its role in shaping fitness outcomes and environmental interactions, and because of the sheer diversity of social forms in bees (Michener, 1974; Wcislo and Fewell, 2017). Social bees may be more resilient than solitary bees to some forms of environmental change, due to advantages of communication strategies, resource sharing, and social behavioral thermoregulation (Ostwald et al., 2023). Defining the lexicon to describe bee sociality has been ongoing and contentious endeavor (Costa and Fitzgerald, 1996; Dew et al., 2016; Richards, 2019; Wcislo, 2005, 1997). This complexity was reflected in the diversity of methods for classifying social forms in the functional trait studies assessed here (Supplementary Table 3). A common classification method was to divide bees into “social” and “solitary” species, but studies differed in whether “social” referred to all non-solitary bees, or only to eusocial bees. Fewer studies explicitly distinguished eusocial bees from non-eusocial bees that are not solitary, and these differed widely in their classifications. Further, certain inconsistencies in terminology suggested misunderstanding of these lesser studied, “intermediate” forms of sociality, i.e., bees that are neither obligately solitary nor obligately eusocial. Examples of problematic classifications of these bees include categorizing all intermediate forms as “semisocial,” or classifying nest aggregations of solitary bees as “communal/semisocial.” Importantly, many bee species exhibit intraspecific variation in social organization (Michener, 1974; Shell and Rehan, 2017). Indeed, Michener (1974) and others have argued that social labels are often not applicable at the species level because they obscure this intraspecific variation, which tends to be underestimated (Wcislo, 2005, 1997). This issue presents a problem for functional trait studies examining sociality, which are generally comparative at the species level and for which it would be prohibitively challenging to assess social organization at the individual or colony level, due to the observation-intensive nature of this work. Several studies in our analysis addressed this through the use of unique terms for species known to exhibit social polymorphism (e.g., “multiple,” “variable,” “facultatively social”; Bartomeus et al., 2013, 2018; Davis & Comai, 2022; Graham et al., 2021; Jacquemin et al., 2020; Moretti et al., 2009; Ricotta & Moretti, 2011).
These considerations emphasize the need to clearly define social terminology, particularly because social categorizations may differ according to the question of interest (Wcislo, 2005, 1997). Nevertheless, only a quarter of the studies that measured sociality as a functional trait defined the social terms they used (16 of 61 studies; 26.2%). Several authors have argued that inconsistency in bee social terminology has presented an obstacle to synthesis in phylogenetics (Dew et al., 2016; Kocher and Paxton, 2014; Richards, 2019); the same is likely to be true in comparative bee functional ecology in the absence of clearly and consistently defined social terminology.