Group Name:
Solitary Bees (Halictidae)
Minimum Criteria for an Occurrence:
Evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals in appropriate habitat where the species is presumed to be established and breeding.
For large species that are similar in size to bumble bees (> 15mm in TL), consider using a Separation Distance of 10 km.
Mapping Guidance:
EOs can be based on an observation of any bee. When using photographs to document an occurrence, identification should be confirmed by an expert.
Separation Barriers:
None.
Separation Distance for Unsuitable Habitat:
3 kilometers
Separation Distance for Suitable Habitat:
5 kilometers
Separation Justification:
Dispersal distance is poorly known in most solitary bees. It appears to be a function of size since body size is negatively correlated with population genetic structure (Lopez-Uribe et al. 2019) and is positively correlated with foraging distance (van Niewstadt and Iraheta 1996, Gathmann and Tscharntke 2002, Greenleaf et al. 2007). The colonization of Hawaii by solitary bees in the genus Hylaeus indicates that these small insects can (on occasion) disperse over great distances (Daly and Magnacca 2003); however, most dispersal events probably occur over much smaller distances. A population of cellophane bee (Colletes inaequalis) within a local (14 km2) area showed genetic differentiation among nest aggregations despite the ability of these bees to fly longer distances. Average kinship fell below that expected with random mating at distances greater than 3.5 km, although this was not statistically significant (Uribe et al. 2015).
Most solitary bees have rather small foraging ranges, although they would be expected to disperse significantly farther than they forage. Gathmann and Tscharntke (2002) studied 16 species of solitary bees and found maximum foraging distances of 150-600 m.
It seems reasonable to suggest, then, that most solitary bees disperse less than 5 km, and therefore the element occurrence separation distance across suitable habitat is set at that distance.
Unsuitable habitat: In theory, solitary bees could fly through unsuitable habitat but there is evidence that unsuitable habitat can act as a deterrent to dispersal. In specialist bees, for example, the population genetic structure seems to be dependent on the availability of floral hosts and nesting habitats (Exeler et al. 2008). The separation distance across unsuitable habitat is therefore reduced to 3 km.