Bowling for bees: optimal sample number for “bee bowl” sampling transects

Abstract

The use of bowl traps to sample bee diversity has become common in recent years. To provide guidance in optimizing bee bowl sampling effort, we used several independent datasets from North America (Pacific Northwest golf courses, suburban Maryland, and Chihuahuan Desert) to estimate the number of bowls in a sampling event at which additional bowls added little to estimates of species richness or to cumulative species lists. We examined changes in the value of a nonparametric richness estimator (Chao2) as a function of bowl number by randomly resampling (without replacement) the data for each sampled transect. We also carried out rarefaction (interpolation of expected species richness for all numbers of bowls up to the actual number). Using as our criterion of ''optimal'' number of bowl samples per transect the number of samples at which five additional bowls added \1 additional species to the Chao2 estimate, we find that 30-bowl transects would have met this standard for nearly three quarters or more of the sampling events in any of our three datasets (for the suburban Maryland and Chihuahuan Desert data sets, at least three quarters of sampling events met this criterion with just 20 and 25 bowls, respectively). Results from rarefaction analysis for all sampling events indicate that 30-bowl transects would have met our ''five additional bowls'' standard for more than 80 % of our suburban Maryland and Chihuahuan Desert sampling events, but for only about 61 % of our Pacific Northwest sampling events. For the Pacific Northwest sampling events, there was notable among-site heterogeneity in required sampling intensity. Thus, although 30-bowl transects appear to be adequate for assessing local bee species richness in most instances, investigators may wish to increase (or decrease) this number based on their particular goals and specific knowledge about local bee diversity.

The challenge of accurately documenting bee species richness in agroecosystems: bee diversity in eastern apple orchards

“…The results of this study do agree with the heterogeneity required in sampling intensity in other systems, suggesting that sampling intensity should be considered in experimental design when the study taxa are diverse or dynamic (e.g., Shapiro et al. ). Temporal variation may drive some of the differences in the sampling required to fully describe the bee diversity in each orchard, although four of the six sites where the year‐to‐year variation was lower than the regional variation were undersampled.…”

“…Neither orchard size nor percent agriculture in the surrounding landscape bears a relationship to the proportion of expected species richness in our apple orchards, so the mechanism driving the need for some orchards to be more heavily sampled is still unclear. The results of this study do agree with the heterogeneity required in sampling intensity in other systems, suggesting that sampling intensity should be considered in experimental design when the study taxa are diverse or dynamic (e.g., Shapiro et al 2014). Temporal variation may drive some of the differences in the sampling required to fully describe the bee diversity in each orchard, although four of the six sites where the year-to-year variation was lower than the regional variation were un-dersampled.…”

“…We targeted bee species that were actively foraging within apple orchards, which allowed us to focus on potential pollinators. Pan trapping may find a still greater bee species richness, as it could attract bees moving through the orchards but not actively foraging on apple (Shapiro et al 2014). In other words, our study may represent a subset of the total background bee community.…”

“…Pan trapping may find a still greater bee species richness, as it could attract bees moving through the orchards but not actively foraging on apple (Shapiro et al. ). In other words, our study may represent a subset of the total background bee community.…”

Different sampling intervals for bowl trapping survey of Aculeata (Hymenoptera) in a semidecidual seasonal forest fragment

“…Shapiro et al (2014) suggested that the optimal sample number for bee bowl sampling transects is 30 bowls but the effect of sample number has not been tested in the neotropics, then our results can be considered not reliable in terms of sample number alone. But even considering that a high number of samples can retrieve a larger proportion of aculeate community, the sampling interval remains crucial to deal with phenology because the insect communities are strongly affected by seasonal and interannual fluctuations (OERTLI et al, 2005).…”