Spatiotemporal variation in phenology and abundance of floral resources [used by bees and other flower-visiting insects] on shortgrass prairie

Phenology and abundance of the floral resources used by bees and other flower-visiting insects were recorded weekly from permanent quadrats for two years on two shortgrass prairie sites in the Laramie Basin, Wyoming. Each site was composed of three distinct plant communities. Results suggest considerable spatiotemporal variability in floral resources. Specifically, most species at both sites showed the following temporal variation: (1) bloom times between one and two weeks earlier in the second year; (2) differences of approximately 1-2 weeks in bloom span between years; (3) substantial differences in abundance of flowers between years. Species blooming during the last half of the census period were significantly more variable in flower abundance between years than those blooming earlier. Spatial variation was shown both by differences between sites and between plant communities within sites in the direction and magnitude of between-year changes in floral abundance. For example, floral production at Boulder Ridge in 1976 was much lower than in 1975, but at The Dirt Farm between-year differences were less pronounced and depended upon season. Similarity measures and cluster analysis suggest differences in the structure of the bloom season at both sites between years, and a relatively rapid turnover of floral composition within years such that bees face a very different flora over the latter part of their flight seasons relative to that encountered initially. Evidence from other reports support the hypothesis of spatiotemporal unpredictability of floral resources.