Taxonomic and behavioral components of faunal comparisons over time: The bees (Hymenoptera: Anthophila) of Boulder County past and present (Colorado, USA)

Historical and recent studies of Boulder County, Colorado (USA) bees (Hymenoptera:  Anthophila) illustrate the potential and the pitfalls of using comparative collection data to evaluate faunal composition over time. A recent compilation of bee records from Boulder Co., CO (USA) (Scott et al., 2011) is used to examine and compare an historical data set (Cockerell, 1907) and a recent data set (Kearns & Oliveras, 2009). Despite numerical comparability, the taxonomic and behavioral composition of these data sets differed markedly from each other and, in different ways, from that of the total “background” fauna documented from Boulder County in Scott et al. The rank order of species richness across bee families, social versus solitary and parasitic bees, and oligolectic versus polylectic pollen-collecting bees, likewise do not co-vary among data sets:  taxonomically, colletids, andrenids and megachilids are relatively under-represented in the more recent data set, in which halictids are better represented than any other family. Behaviorally, parasitic bees are under-represented in both datasets, and oligolectic solitary bees, primarily Andrena spp., especially so in the more recent, which is dominated by polylectic social bees. Ensemble comparisons of raw species richness may mask differences in the readiness with which bees of different taxonomic affinities, social behaviors, and degrees of host plant specificity lend themselves to being sampled, which may in turn hide faunal turnover relevant to concerns of pollinator decline.