Predation, parasitism, and competition
For many bee lineages, sociality may have arisen as a strategy for
mitigating the effects of inter- and intraspecific interactions,
especially parasitism, predation, and intraspecific competition (Lin and
Michener, 1972; Wcislo and Fewell, 2017). Climate change will impact the
distribution and abundances of diverse communities of bees’ competitors
and natural enemies, with variable consequences for bee social behavior.
In populations under strong selective pressure from parasitism or
predation, sociality can enable bees to forage without leaving their
nests unattended. Active defensive behavior by guard bees, or even
simply the presence of a bee in the nest, can successfully deter natural
enemies (Kukuk et al., 1998; Mikát et al., 2016; Zammit et al., 2008).
Abrams and Eickwort observed cleptoparasitic bees (Nomada ,
Apidae) entering solitary nests of the sweat bee Agapostemon
virescens Fabricius, 1775 (Halictidae), but never communal nests, which
were continuously guarded (1981). Similarly, solitary Ceratina
australensis nests were more severely parasitized by chalcid wasps
(Eurytoma sp.) than social nests of the same species (Rehan et
al., 2011). Importantly, social nesting can also provide insurance
against nest failure in the event of foundress mortality (Gadagkar,
1990; Queller, 1994). In one study of the facultatively eusocial sweat
bee Megalopta genalis Meade-Waldo, 1916, adults in the nest
successfully defended brood against raiding ants, but orphaned brood all
succumbed to ant predation (Smith et al., 2003).
Similarly, in environments characterized by strong intraspecific
competition, sociality can provide strategies for securing and
safeguarding limiting resources, especially food and nesting substrate.
Social nests of the facultatively social carpenter bee, Xylocopa
pubescens Spinola, 1838, contain a non-reproductive guarding female and
a reproductive forager (Gerling et al., 1981). In one study, the
presence of a guard in the nest prevented pollen robbing by conspecifics
and also allowed the dominant reproductive to complete longer foraging
trips (Hogendoorn and Velthuis, 1993). Importantly, the relative costs
and benefits of tolerating a guard (i.e., a reproductive rival) in the
nest depended on local resource availability and therefore the intensity
of pollen robbing (Hogendoorn and Velthuis, 1993). Competition over
nests is also a driver of social evolution in some bees, especially when
nest substrate is limited or costly to exploit. Shifts in nest substrate
availability may even drive social evolutionary transitions, as for one
stem-nesting allodapine bee, Braunsapis puangensis Cockerell,
1929. The recent introduction of B. puangensis to Fiji
accompanied by a shift to communal nesting from the ancestral strategy
of reproductive queueing (da Silva et al., 2016). Because Fiji has no
native stem-nesting bees, low competition for nesting substrate in their
introduced environment may have expanded opportunities for egalitarian
sociality (2016). Finally, nests may be limiting not due to a shortage
of substrate, but due to costs of exploiting that substrate. For large
carpenter bees (Xylocopa ), the high metabolic costs of wood nest
excavation may favor sociality via nest inheritance strategies (Ostwald
et al., 2021). Indeed, for one population of Xylocopa virginicaLinnaeus, 1771, high-density conditions led to an increase in social
nesting due to saturation of available nests (Vickruck and Richards,
2021). Under climate change, as species are redistributed in time and
space (phenological and geographic shifts), we expect social
evolutionary consequences of these changes in selective pressures
related to parasitism, predation, and intraspecific competition.