Life-history traits predict responses of wild bees to climate variation

Abstract

Life-history traits, which are physical traits or behaviours that affect growth, survivorship and reproduction, could play an important role in how well organisms respond to environmental change. By looking for trait-based responses within groups, we can gain a mechanistic understanding of why environmental change might favour or penalize certain species over others. We monitored the abundance of at least 154 bee species for 8 consecutive years in a subalpine region of the Rocky Mountains to ask whether bees respond differently to changes in abiotic conditions based on their life-history traits. We found that comb-building cavity nesters and larger bodied bees declined in relative abundance with increasing temperatures, while smaller, soil-nesting bees increased. Further, bees with narrower diet breadths increased in relative abundance with decreased rainfall. Finally, reduced snowpack was associated with reduced relative abundance of bees that overwintered as prepupae whereas bees that overwintered as adults increased in relative abundance, suggesting that overwintering conditions might affect body size, lipid content and overwintering survival. Taken together, our results show how climate change may reshape bee pollinator communities, with bees with certain traits increasing in abundance and others declining, potentially leading to novel plant–pollinator interactions and changes in plant reproduction.

Smaller, more diverse and on the way to the top: Rapid community shifts of montane wild bees within an extraordinary hot decade

“…In Berchtesgaden, mean community body size declined in the warmer year, consistent with the predictions derived from theory and the observation that along spatial temperature gradients, body size declines with increasing temperature (Figure 6a). The reduction in community body size over a relatively short time period is in line with a recent study, which studied bee community response to climate variation in eight consecutive years (Pardee et al, 2022). Body size declines can also be observed over longer time scales up to 140 years (Bartomeus et al, 2013; Nooten & Rehan, 2020).…”

“…and the observation that along spatial temperature gradients, body size declines with increasing temperature (Figure 6a). The reduction in community body size over a relatively short time period is in line with a recent study, which studied bee community response to climate variation in eight consecutive years (Pardee et al, 2022).…”

Six years of wild bee monitoring shows changes in biodiversity within and across years and declines in abundance

“…Understanding which adaptations or life history traits are associated with population increases or decreases over time in some cases could be a better approach to explain species' changes in abundance over time (e.g., Stemkovski et al, 2020 ; Williams et al, 2009 ). However, given that a suite of natural history traits was not associated with the species‐level changes we observed (Table A2 ), it may take more investigation into environmental variable to understand what mechanism may be driving species' population changes over time in our system (Hamblin et al, 2018 ; Ogilvie et al, 2017 ; Pardee et al, 2022 ; Stemkovski et al, 2020 ).…”

“…In some studies, natural history traits helped explain changes in bee abundance over time or responses to environmental fluctuations (Bartomeus et al, 2013 ; Hamblin et al, 2018 ). For example, Pardee et al ( 2022 ) found that bee body size and nesting strategy impacted species' responses to changing temperature. We found that 6 commonly studied natural history traits did not predict changes in abundance when controlling for phylogeny.…”

“…We included two traits determined by our data, phenological breadth, seasonality, and 4 other traits gathered from the literature including: body length, social vs. solitary, specialized vs. generalist diet, and below ground versus above ground nesting. These natural history traits have been used in other studies to help explain changes in relative abundance over time (Bartomeus et al, 2013 ) and responses to environmental change (Hamblin et al, 2018 ; Pardee et al, 2022 ). We tested the relationship between these traits and change in abundance over time by fitting phylogenetic generalized linear models for each trait with a Brownian motion model of trait evolution.…”