Physiological thermal limits predict differential responses of bees to urban heat-island effects

Abstract

Changes in community composition are an important, but hard to predict, effect of climate change. Here, we use a wild-bee study system to test the ability of critical thermal maxima (CT, a measure of heat tolerance) to predict community responses to urban heat-island effects in Raleigh, NC, USA. Among 15 focal species, CT ranged from 44.6 to 51.3°C, and was strongly predictive of population responses to urban warming across 18 study sites ( = 0.44). Species with low CT declined the most. After phylogenetic correction, solitary species and cavity-nesting species (bumblebees) had the lowest CT, suggesting that these groups may be most sensitive to climate change. Community responses to urban and global warming will likely retain strong physiological signal, even after decades of warming during which time lags and interspecific interactions could modulate direct effects of temperature.

Ecological filtering in scrub fragments restructures the taxonomic and functional composition of native bee assemblages

“…, Hamblin et al. ) may all influence how bee species respond to novel ecological filters. Results of our range size analyses suggest that bee assemblages in fragments, on average, tend to be composed of species that are capable of surviving in a wider array of ecological contexts than are bees in reserves, consistent with the view that ecological filters present in fragments exclude species that are more narrowly adapted to their distinct local ecosystem.…”

“…Range size is not a functional trait per se, but it does serve as a proxy for an important ecological function that remains difficult to quantify: overall niche breadth (Brown 1984, Slatyer et al 2013. Lecty seems likely to be a key axis of niche breadth (Bommarco et al 2010, Williams et al 2010; however, selectivity of nesting substrates (Westrich 1996, Cane et al 2007, phenological flexibility (Rafferty et al 2015), and physiological tolerance to abiotic conditions (Classen et al 2015, Hamblin et al 2017) may all influence how bee species respond to novel ecological filters. Results of our range size analyses suggest that bee assemblages in fragments, on average, tend to be composed of species that are capable of surviving in a wider array of ecological contexts than are bees in reserves, consistent with the view that ecological filters present in fragments exclude species that are more narrowly adapted to their distinct local ecosystem.…”

“…Ecological filters can be abiotic factors, such as temperature (Hamblin et al. ) or moisture (Myers and Harms ), or biotic factors, such as the availability of food resources (Gámez‐Virués et al. ) or the presence of natural enemies (Skelton et al.…”

“…Novel selection pressures in altered habitats can create ecological filters (Mayfield et al 2005): processes that determine whether or not species can establish and persist at a given site (Keddy 1992(Keddy , D ıaz et al 1998). Ecological filters can be abiotic factors, such as temperature (Hamblin et al 2017) or moisture (Myers and Harms 2011), or biotic factors, such as the availability of food resources (G amez-Viru es et al 2015) or the presence of natural enemies (Skelton et al 2017). The strength and specificity of ecological filters depend on the form of disturbance, the natural history of the organisms in question, and the action of additional forces that shape community assembly including dispersal, population dynamics, and biotic interactions (Orrock andWatling 2010, Myers andHarms 2011).…”

Estimates of accessible food resources for pollinators in urban landscapes should take landscape friction into account

“…Most species are central-place foragers that have rather restricted foraging ranges around their nests (Steffan-Dewenter et al 2001, Gathmann and. This may explain why pollinator richness and abundance, and pollination success often decrease with increasing urbanization (Ahrn e et al 2009, Pellissier et al 2012, Fortel et al 2014, even if an alternative explanation for this pattern in warm areas also can be urban heat-island effects (e.g., Hamblin et al 2017). This may explain why pollinator richness and abundance, and pollination success often decrease with increasing urbanization (Ahrn e et al 2009, Pellissier et al 2012, Fortel et al 2014, even if an alternative explanation for this pattern in warm areas also can be urban heat-island effects (e.g., Hamblin et al 2017).…”