Climate-associated phenological advances in bee pollinators and bee-pollinated plants

Abstract

The phenology of many ecological processes is modulated by temperature, making them potentially sensitive to climate change. Mutualistic interactions may be especially vulnerable because of the potential for phenological mismatching if the species involved do not respond similarly to changes in temperature. Here we present an analysis of climate-associated shifts in the phenology of wild bees, the most important pollinators worldwide, and compare these shifts to published studies of bee-pollinated plants over the same time period. We report that over the past 130 y, the phenology of 10 bee species from northeastern North America has advanced by a mean of 10.4 ± 1.3 d. Most of this advance has taken place since 1970, paralleling global temperature increases. When the best available data are used to estimate analogous rates of advance for plants, these rates are not distinguishable from those of bees, suggesting that bee emergence is keeping pace with shifts in host-plant flowering, at least among the generalist species that we investigated.

Fig. 1.

Rates of change in bee phenology and temperature over time. Each point represents a bee specimen used in the analysis. Raw data are shown without correcting for covariates (see text for details). The collection day for each bee specimen, where January first is day 1 (A), and the mean temperature during the month of April (in °C) at the location where the specimen was collected (B). The overall trend (black lines) and the trend from 1970 to 2010 (red lines) are shown. (C) The correlation between collection day and temperature. The overall trend is shown (black line). (D–G) Representative species for the genera in our analysis: A. miserabilis, C. inaequalis, O. lignaria, and B. impatiens queen. (Photos by J.S.A.)

Fig. 2.

Comparison of bee and plant studies. Mean and 95% confidence interval (CI) for the rate of phenological advance for all bee species in combination (filled circles), compared with the mean and 95% CI for plants (hollow circles). The values for bees differ among comparisons because we used only the bee data from the same period over which plants were studied in each comparison. A dotted line is drawn between the bee and plant mean for purposes of visual comparison. From left to right, the plant studies are refs. –.