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Pollinators are thought to be the main drivers of floral evolution. Flowers are also colonized by abundant communities of microbes that can affect the interaction between plants and their pollinators. Very little is known, however, about how flower-colonizing microbes influence floral evolution. Here we performed a 6-generation experimental evolution study using fast-cycling Brassica rapa, in which we factorially manipulated the presence of pollinators and flower microbes to determine how pollinators and microbes interact in driving floral evolution. We measured the evolution of 6 morphological traits, as well as the plant mating system and flower attractiveness. Only one of the 6 traits (flower number) evolved in response to pollinators, while microbes did not drive the evolution of any trait, nor did they interact with pollinators in driving the evolution of morphological traits. Moreover, we did not find evidence that pollinators or microbes affected the evolution of flower attractiveness to pollinators. However, we found an interactive effect of pollinators and microbes on the evolution of autonomous selfing, a trait that is expected to evolve in response to pollinator limitations. Overall, we found only weak evidence that microbes mediate floral evolution. However, our ability to detect an interactive effect of pollinators and microbes might have been limited by weak pollinator-mediated selection in our experimental setting. Our results contrast with previous (similar) experimental evolution studies, highlighting the susceptibility of such experiments to drift and to experimental artefacts. [ABSTRACT FROM AUTHOR]

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Species exhibit a range of specialisation in diet and other niche axes, with specialists typically thought to be more efficient in resource use but more vulnerable to extinction than generalists. Among herbivorous insects, dietary specialists seem more likely to lack acceptable host plants during the insect's feeding stage, owing to fluctuations in host‐plant abundance or phenology. Like other herbivores, bee species vary in host breadth from pollen specialisation (oligolecty) to generalisation (polylecty).Several studies have shown greater interannual variation in flowering phenology for earlier‐flowering plants than later‐flowering plants, suggesting that early‐season bees may experience substantial year‐to‐year variation in the floral taxa available to them.It was therefore reasoned that, among bees, early phenology could be a more viable strategy for generalists, which can use resources from multiple floral taxa, than for specialists. Consequently, it was expected that the median dates of collection of adult specimens to be earlier for generalist species than for specialists. To test this, phenology data and pollen diet information on 67 North American species of the bee genus Osmia was obtained.Controlling for latitude and phylogeny, it was found that dietary generalisation is associated with significantly earlier phenology, with generalists active, on average, 11–14 days earlier than specialists.This result is consistent with the generalist strategy being more viable than the specialist strategy for species active in early spring, suggesting that dietary specialisation may constrain the evolution of bee phenology—or vice versa. [ABSTRACT FROM AUTHOR]

The phenologies of co‐occurring trees and spring‐blooming understory herbs in northeastern North American hardwood forests appear to be regulated by different environmental drivers – air temperature and soil temperature/snowpack, respectively. Accordingly, it has been hypothesized that climate change–driven asymmetry in the advancement of canopy leaf‐out relative to the timing of understory growth could reduce photosynthetic rates and reproductive success of understory herbs through greater early‐season shading.To determine whether trees and spring‐flowering forest herbs are advancing their phenologies at different rates with respect to increasing global temperatures, we examined the phenological responses to warming of 10 species of trees and 11 species of spring‐flowering forest herbs (8045 observations from 965 sites) in northeastern North America using 13 years of data collected by citizen scientists under the auspices of the USA‐National Phenology Network.Contrary to expectation, the degree of advancement of leaf‐out as a function of temperature was greater in spring‐flowering forest herbs than in trees, with a mean response rate of −4.9 days/°C (95% BCI [−5.2, −4.6]) for spring‐flowering forest herbs vs. −3.3 days/°C (95% BCI [−3.5, −3.1]) for trees. However, the response to temperature was not consistent across the latitudinal range, with spring‐flowering forest herbs responding more strongly to warming than trees at middle (40–44°N) and higher (45–48°N) latitudes but not at lower latitudes (35–39°N).Synthesis. In contrast to previous suggestions, our study shows spring‐flowering forest herbs advancing their phenology at a higher rate than trees with respect to warming through most of the latitudinal range investigated, which could translate into a longer growing season and increased carbon uptake for spring‐flowering forest herbs as spring temperatures rise. [ABSTRACT FROM AUTHOR]

Land use change threatens global biodiversity and compromises ecosystem functions, including pollination and food production. Reduced taxonomic α-diversity is often reported under land use change, yet the impacts could be different at larger spatial scales (i.e., γ-diversity), either due to reduced β-diversity amplifying diversity loss or increased β-diversity dampening diversity loss. Additionally, studies often focus on taxonomic diversity, while other important biodiversity components, including phylogenetic diversity, can exhibit differential responses. Here, we evaluated how agricultural and urban land use alters the taxonomic and phylogenetic α-, β-, and γ-diversity of an important pollinator taxon-bees. Using a multicontinental dataset of 3117 bee assemblages from 157 studies, we found that taxonomic α-diversity was reduced by 16%-18% in both agricultural and urban habitats relative to natural habitats. Phylogenetic α-diversity was decreased by 11%-12% in agricultural and urban habitats. Compared with natural habitats, taxonomic and phylogenetic β-diversity increased by 11% and 6% in urban habitats, respectively, but exhibited no systematic change in agricultural habitats. We detected a 22% decline in taxonomic γ-diversity and a 17% decline in phylogenetic γ-diversity in agricultural habitats, but γ-diversity of urban habitats was not significantly different from natural habitats. These findings highlight the threat of agricultural expansions to large-scale bee diversity due to systematic γ-diversity decline. In addition, while both urbanization and agriculture lead to consistent declines in α-diversity, their impacts on β- or γ-diversity vary, highlighting the need to study the effects of land use change at multiple scales., (© 2025 John Wiley & Sons Ltd.)