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.