Experimental warming in the field delays phenology and reduces body mass, fat content and survival: Implications for the persistence of a pollinator under climate change

Abstract

Climate change is rapidly altering thermal environments across the globe. The effects of increased temperatures in already warm environments may be particularly strong because organisms are likely to be near their thermal safety margins, with limited tolerance to additional heat stress. We conduct an in situ field experiment over 2 years to investigate the direct effects of temperature change on an early‐season solitary bee in a warm, arid region of the Southwestern USA. Our field experiment manipulates the thermal environment of Osmia ribifloris (Megachilidae) from larval development through adult emergence, simulating both previous cooler (c. 1950; nest boxes painted white) and future warmer (2040–2099; nest boxes painted black) climate conditions. In each year, we measure adult emergence phenology, linear body size, body mass, fat content and survival. Bees in the warming treatment exhibit delayed emergence phenology and a substantial increase in phenological variance. Increases in temperature also lead to reductions in body mass and fat content. Whereas bees in the cooling and control treatments experience negligible amounts of mortality, bees in the warming treatment experience 30%–75% mortality. Our findings indicate that temperature changes that have occurred since c. 1950 have likely had relatively weak and non‐negative effects, but predicted warmer temperatures create a high stress thermal environment for O. ribifloris. Later and more variable emergence dates under warming likely compromise phenological synchrony with floral resources and the ability of individuals to find mates. The consequences of phenological asynchrony, combined with reductions in body mass and fat content, will likely impose fitness reductions for surviving bees. Combined with high rates of mortality, our results suggest that O. ribifloris may face local extinction in the warmer parts of its range within the century under climate change. Temperature increases in already warm ecosystems can have substantial consequences for key components of life history, physiology and survival. Our study provides an important example of how the responses of ectothermic insects to temperature increases in already warm environments may be insufficient to mitigate the negative consequences of future climate change. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13151/suppinfo is available for this article.

Solitary Bee Life History Traits and Sex Mediate Responses to Manipulated Seasonal Temperatures and Season Length

“…Understanding how solitary bee species are responding to climate change is difficult in part because, unlike plants, there is little long-term data on phenology and species abundances to link with changes in climate (Ogilvie and Forrest, 2017). While studies incorporating temperature manipulations in the field impart realism (e.g., Forrest and Thomson, 2011;CaraDonna et al, 2018), controlled laboratory studies are better equipped to elucidate response mechanisms. However, solitary bee responses to temperature have only been investigated in a limited number of managed species (e.g., Kemp, 2003, 2004;Sgolastra et al, 2010Sgolastra et al, , 2011O'Neill et al, 2014;Schenk et al, 2018a), and have primarily isolated responses to a single component of climate change (e.g., extended fall duration, winter temperature, or spring temperature, Kemp, 2000, 2003;Sgolastra et al, 2011;Fründ et al, 2013;O'Neill et al, 2014;Schenk et al, 2018a; but see Bosch and Kemp, 2004).…”

Early spring warming may hasten leaf emergence in Erythronium americanum

“…One result of this general warming trend is changes in the timing of the onset of seasons, including the arrival of spring (Groffman et al., ; Wilson, ). In response to this warming, some species have adjusted the timing of life history events including egg hatching, migrations, flowering, and fruiting (Badeck et al., ; Forrest et al., ; Wipf, ; Hänninen and Tanino, ; Wilson, ; Hansson et al., ; Bertin, ; Jacques et al., ; CaraDonna et al., ; Groner et al., ; McDonough MacKenzie et al., ; Rice et al., ; Daru et al., ).…”

American Foulbrood and the Risk in the Use of Antibiotics as a Treatment

“…The combination of harsh temperatures and shortened flowering periods, as associated with insufficient water, can result in reductions to fat reserves and overall body mass in bees. This status can translate into fewer pollinating and honey-producing activities [7], as well as an increased incidence of specific diseases affecting honey bees weakened by nutritional deficits [8,9].…”