|SCOTT, V. - University Of Colorado|
Submitted to: Proceedings of the Entomological Society of Washington
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2015
Publication Date: 7/15/2015
Citation: Goldstein, P.Z., Scott, V.L. 2015. Taxonomic and behavioral components of faunal comparisons over time: The bees of Boulder County past and present (Colorado, USA) (Hymenoptera: Anthophila). Proceedings of the Entomological Society of Washington. 117(3):290-346.
Interpretive Summary: Bees are the most economically important pollinators of wild and cultivated plants alike, and as threats to managed bees become increasingly apparent, it is important to evaluate options for relying on native bees as either surrogates for them or buffers against their loss. Few, if any, historical collections lend themselves to rigorous statistical comparisons with recent data, but qualitative assessments may help understand limitations and refine our interpretations of existing data as well as mitigate shortcomings of commonly employed protocols. In comparing historical and recent collections from Boulder County, Colorado, a diverse and topographically complex area, we identify several pitfalls in using faunal sampling data as the basis for assessing faunal change. Primary among these is the potential for raw species numbers to mask shifts in behavioral composition, specifically differential changes among generalist versus specialist pollinators, across trophic levels (e.g. social versus parasitic bees), etc. We suggest that those behavioral cohorts potentially most vulnerable to impacts are also most vulnerable to sampling artifact. This biostatistical coincidence potentially confounds our ability to differentiate actual faunal change from sampling artifact, and suggests that rapid assessments of pollinator faunas be interpreted with caution. Anyone conducting bee sampling, interpreting sampling data, or assessing faunal change will benefit from comparisons with the data presented here.
Technical Abstract: 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 and change over time. A compilation of bee records from Boulder Co., CO (USA) (Scott et al., 2011) is used as a basis for re-examining the comparison of an historical data set (Cockerell, 1907) with a current one (Kearns & Oliveras, 2009a,b). Despite numerical comparability reported by Kearns and Oliveras, the taxonomic and behavioral composition of these data sets differ markedly from each other and, in different ways, from that of the subset of bee species common to both and the total fauna documented from Boulder County. The rank order of species richness across bee families and across cohorts of bees with different social behaviors, and feeding preferences, 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 with different taxonomic affiliations, social behaviors, and degrees of host plant specificity lend themselves to being sampled, and possibly to their appearing to undergo faunal turnover. When these behaviors are taken into account, these comparisons imply either (1) impacts, in descending order of severity, on parasitic bees, oligolectic solitary bees, and polylectic solitary bees or, alternatively (2) the relative ineffectiveness with which these classes of bees are sampled with general pan- or bowl-trapping techniques and sampling regimes. Seasonally-limited summer sampling protocols may favor polylectic social bees, as reflected in halictids’ being disproportionately well-sampled relative to andrenids, which account for a majority of early season oligolectic solitary bees—ironically those of potentially greatest interest when evaluating the stability of pollinator faunas. By virtue of their abundance and protracted flight seasons, in contrast, eusocial bees appear to be among the most readily sampled, though potentially less relevant to the purposes of evaluating the integrity of animal-pollinated plant communities.