The potential for phenological mismatch between Lathyrus littoralis and Habropoda miserabilis with climate warming

Premise of research. Climate change may alter the timing of flowering and pollinator activity to differing degrees, resulting in phenological mismatches between mutualist partners. Assessing the potential for such mismatches requires an understanding of the environmental factors that cue flowering and pollinator activity. Methodology. I characterized the current phenological overlap of the silky beach pea (Lathyrus littoralis [Fabaceae]) and one of its main pollinators, the solitary ground-nesting silver bee (Habropoda miserabilis [Apidae]), in coastal northwestern California. I then examined associations of abiotic variables in the environment with the spatial variation observed in the phenology of the two species. Based on the relationship of phenology dates with temperature accumulation, I projected changes in phenological overlap with climate warming. Bagging experiments and field observations were used to examine the mutual dependence of the beach pea and silver bee at my study sites. To my knowledge, this study presents the first attempt to characterize the phenology cuing of a solitary ground-nesting bee under field conditions. Pivotal results. Degree-days above freezing best predicted flowering and bee activity, although an interaction of temperature with moisture influenced the onset of flowering as well. Projections based on climate warming predictions suggest that bee emergence will advance more rapidly than flowering with temperature increases, resulting in a decrease in phenological overlap. However, start and peak dates are expected to shift differently in both species. Peak flowering and nesting were separated by an average of 2 days in 2013, but this value varied from 1 to 9 days, depending on study site. The highest projected increase in global temperatures by the end of the century (5.8˚C) would increase the average asynchrony of peak phenology to 7 days. Start dates were more variable across sites, and the onset of bee activity and flowering were separated by an average of 6 days in 2013. Start date asynchrony is projected to increase to an average of 17 days with an increase of 5.8˚C. Conclusions. The potential impacts of an increasing phenological mismatch between the beach pea and silver bee are difficult to assess, but the consequences to these species are likely to be modest. Overlap in flowering and bee activity is likely to remain high in spite of shifts in the timing of activity. Furthermore, both species are generalists and are able to use resources from other members of the local community. Concern about the mismatch of these species should be focused on the beginning of the season, as start date asynchrony is likely to increase the most by climate warming. Pattern of shift in these species gives us insight into how pollination mutualisms in the coastal dune systems may be affected in the future. In addition, as many solitary ground nesting bee species are difficult to study at the nest site, this study may give insight into the factors that cue phenology for other similar species.