The effects of climate-warming on solitary bees and their interactions with plants

Abstract

The ecological consequences of anthropogenic climate-warming remain poorly understood for pollinators. In order to better understand these consequences, and thus the consequences of climate-warming for pollination services, we must determine how pollinator life histories mediate responses to climate-warming. To help address these research needs, we conducted three studies. First, we used field-collected solitary bee species (i.e., Osmia spp. and Megachile spp.) to investigate how overwintering life stage (i.e., adult versus prepupae), body size, and sex influenced solitary bee survival, weight loss prior to emerging, and timing of emergence in response to manipulated seasonal temperature and the durations of seasons. Second, we manipulated the amount of asynchrony (days) between female solitary bee emergence and flowering periods. We used a mesocosm-based experimental design to investigate the effects of phenological asynchrony on the female lifespan, female interaction rates with flowers, and reproductive success. In a third study, we manipulated the amount of phenological difference between conspecific male and female solitary bees (i.e., the degree of protandry; males emerging prior to females), and investigated the influence of sex-specific phenological responses to temperature on male-female interactions and reproductive success. Our main findings and subsequent conclusions were that i) compared to bees that overwinter as prepupae, patterns in weight loss prior to emergence, adult longevity, and timing of emergence suggested that post-emergence fitness in adult-wintering bees may decrease under climate-warming as a result of increased energy depletion at the time of emergence, increasing asynchrony with flowering periods, and sex-specific phenological responses, ii) asynchrony between a spring-active female solitary bee species (i.e., Osmia cornifrons) and flowering periods caused reductions in offspring body size and reduced interaction rates between females and flowers, which could have consequences for both bee and plant reproductive success, and iii) when the degree of protandry was either reduced or increased from an intermediate level, the probability of female offspring production tended to decrease. This suggests that changes in the degree of protandry may influence the fitness tradeoffs associated with protandry, resulting in consequences for current and future solitary bee reproductive success.