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Many nature‐based solutions (NBS), including urban greenspaces, urban agriculture and agroforestry, depend upon animal‐pollinated plants to sequester carbon or to provide other ecosystem services. Thus, long‐term success of these solutions also depends upon resilient pollinator communities. Despite their importance to functioning communities, a literature search revealed that 0%–3% of papers on NBS and related topics considered pollinators or pollination. Pollinators were more likely to be considered in the subgroup of papers on NBS related to agricultural production, where 12.5% considered pollination. Conservation of species interactions is essential to conservation of biodiversity and the sustained benefits of NBS. By applying our understanding of the ecology of plant‐pollinator mutualisms to the implementation of NBS, we can promote their functioning under future climatic conditions. In particular, we point to the need to identify keystone plants and pollinators, those species that contribute most to biodiversity maintenance, community stability and ecosystem function, and to leverage these species and their interactions in NBS and conservation efforts. We further advocate for the use of phylogenetic trait‐based analyses to understand the characteristics associated with keystoneness. Synthesis: Resilience of pollination services rests upon the responses of keystone species and their partners, and the likelihood that they continue to express traits that confer mutual benefit under future climates. By understanding the traits of species of outsized importance to their communities, we gain insight into the mechanisms underlying the resilience of pollination services and the NBS that rely on those services in a changing world. [ABSTRACT FROM AUTHOR]

Climate change is affecting species and their mutualists and can lead to the weakening or loss of important interspecific interactions. Through independent shifts in partner phenology and distribution, climatic stress can separate mutualists temporally or spatially, leading to alterations in partner functional traits and fitness. Here, we explored the effects of the loss of microbial mutualists on legume germination success and phenology. In particular, we assessed the effects of mutualism loss via soil sterilization, increased drought, and introduction to novel soils found beyond the current distributions of two focal legume species in subalpine environments. Through common garden experiments in controlled environments, we found evidence that soil sterilization (and consequent microbial absence) and dry soils caused species‐specific phenological delays of 2–5 weeks in germination, likely as a result of interaction loss between legumes and specialized germination‐promoting soil microbes, such as mutualistic rhizobia. Delays in germination caused by a mismatch between legumes and beneficial microbes could negatively affect legume fitness through increased plant–plant competition later in the season. Additionally, we found evidence of the presence of beneficial microbes beyond the current elevational range of one of our focal legumes, which may allow for expansion of the leading edge, although harsh abiotic factors in the alpine may hinder this. Alterations in the strength of soil microbe‐legume mutualisms may lead to reduced fitness and altered demography for both soil microbes and legumes. [ABSTRACT FROM AUTHOR]

Climate change is affecting interactions among species, including host-parasite interactions. The effects of warming are of particular interest for interactions in which parasite and host physiology are intertwined, such as those between parasitic plants and their hosts. However, little is known about how warming will affect plant parasitic interactions, hindering our ability to predict how host and parasite species will respond to climate change. Here, we test how warming affects aboveground and belowground biomass of a hemiparasitic species (Castilleja sulphurea) and its host (Bouteloua gracilis), asking whether the effects of warming depend on the interaction between these species. We also measured how warming affected the number of haustorial connections between parasite and host. We grew each species alone and together under ambient and warmed conditions. Hosts produced more belowground biomass under warming. However, host biomass was reduced when plants were grown with a hemiparasite. Thus, parasitism negated the benefit of warming on belowground growth of the host. Host resource allocation to roots versus shoots also changed in response to both interaction with the parasite and warming, with hosts producing more root biomass relative to shoot biomass when grown with a parasite and when warmed. As expected, hemiparasite biomass was greater when grown with a host. Warmed parasites had lower root:shoot ratios but only when grown with a host. Under elevated temperatures, hemiparasite aboveground biomass was marginally greater, and plants produced significantly more haustoria. These findings indicate that warming can influence biomass production, both by modifying the interaction between host plants and hemiparasites and by affecting the growth of each species directly. To predict how species will be affected, it is important to understand not only the direct effects of warming but also the indirect effects that are mediated by species interactions. Ultimately, understanding how climate change will affect species interactions is key to understanding how it will affect individual species. [ABSTRACT FROM AUTHOR]

Shifts in the timing of flowering are a conspicuous biological signal of climate change. These shifts have been documented across the globe for diverse communities. Although many species are flowering earlier, others have exhibited no shifts or delays in flowering., How species respond phenologically will shape interactions both with other community members and with the abiotic environment, altering fitness, abundance and ultimately persistence., To understand if variability in phenological response is influenced by evolutionary history, we tested for phylogenetic signal in shifts in flowering onset for 13 communities representing 116 families across the Northern Hemisphere. We compared the fit of models of neutral evolution (Brownian Motion) with models that incorporate selection (Ornstein-Uhlenbeck)., We found significant signal in whether species had shifted and the magnitude of response, with both traits conforming to an Ornstein-Uhlenbeck model of trait evolution., Synthesis. These results show there is global phylogenetic signal in the direction and magnitude of shifts in flowering onset and indicate selection has shaped flowering time responses of related species under climate change; thus, environmentally determined optima may constrain whether and to what degree species respond phenologically to climate change. Our findings further demonstrate the value of testing for phylogenetic signal across multiple communities and comparing multiple models of trait evolution. [ABSTRACT FROM AUTHOR]

Climate change may disrupt plant–pollinator mutualisms by generating phenological asynchronies and by altering traits that shape interaction costs and benefits. Our knowledge is limited to studies that manipulate only one partner or focus on either phenological or trait‐based mismatches. We assembled communities of three annual plants and a solitary bee prior to flowering and emergence to test how springtime warming affects phenologies, traits, interactions and reproductive output. Warming advanced community‐level flowering onset, peak and end but did not alter bee emergence. Warmed plant communities produced fewer and smaller flowers with less, more‐concentrated nectar, reducing attractiveness, and warmed bees were more generalized in their foraging, reducing their effectiveness. Plant–bee interactions were less frequent, shorter and peaked earlier under warming. As a result, warmed plants produced fewer, lighter seeds, indicating pollinator‐mediated fitness costs. Climate change will perturb plant–pollinator mutualisms, causing wide‐ranging effects on partner species and diminishing the ecosystem service they provide. [ABSTRACT FROM AUTHOR]

Ecological networks of two interacting guilds of species, such as flowering plants and pollinators, are common in nature, and studying their structure can yield insights into their resilience to environmental disturbances. Here we develop analytical methods for exploring the strengths of interactions within bipartite networks consisting of two guilds of phylogenetically related species. We then apply these methods to investigate the resilience of a plant-pollinator community to anticipated climate change. The methods allow the statistical assessment of, for example, whether closely related pollinators are more likely to visit plants with similar relative frequencies, and whether closely related pollinators tend to visit closely related plants. The methods can also incorporate trait information, allowing us to identify which plant traits are likely responsible for attracting different pollinators. These questions are important for our study of 14 prairie plants and their 22 insect pollinators. Over the last 70 years, six of the plants have advanced their flowering, while eight have not. When we experimentally forced earlier flowering times, five of the six advanced-flowering species experienced higher pollinator visitation rates, whereas only one of the eight other species had more visits; this network thus appears resilient to climate change, because those species with advanced flowering have ample pollinators earlier in the season. Using the methods developed here, we show that advanced-flowering plants did not have a distinct pollinator community from the other eight species. Furthermore, pollinator phylogeny did not explain pollinator community composition; closely related pollinators were not more likely to visit the same plant species. However, differences among pollinator communities visiting different plants were explained by plant height, floral color, and symmetry. As a result, closely related plants attracted similar numbers of pollinators. By parsing out characteristics that explain why plants share pollinators, we can identify plant species that likely share a common fate in a changing climate. [ABSTRACT FROM AUTHOR]

Growing concern about the influence of climate change on flowering plants, pollinators, and the mutualistic interactions between them has led to a recent surge in research. Much of this research has addressed the consequences of warming for phenological and distributional shifts. In contrast, relatively little is known about the physiological responses of plants and insect pollinators to climate warming and, in particular, how these responses might affect plant-pollinator interactions. Here, we summarize the direct physiological effects of temperature on flowering plants and pollinating insects to highlight ways in which plant and pollinator responses could affect floral resources for pollinators, and pollination success for plants, respectively. We also consider the overall effects of these responses on plant-pollinator interaction networks. Plant responses to warming, which include altered flower, nectar, and pollen production, could modify floral resource availability and reproductive output of pollinating insects. Similarly, pollinator responses, such as altered foraging activity, body size, and life span, could affect patterns of pollen flow and pollination success of flowering plants. As a result, network structure could be altered as interactions are gained and lost, weakened and strengthened, even without the gain or loss of species or temporal overlap. Future research that addresses not only how plant and pollinator physiology are affected by warming but also how responses scale up to affect interactions and networks should allow us to better understand and predict the effects of climate change on this important ecosystem service. [ABSTRACT FROM AUTHOR]

The earlier flowering times exhibited by many plant species are a conspicuous sign of climate change. Altered phenologies have caused concern that species could suffer population declines if they flower at times when effective pollinators are unavailable. For two perennial wildflowers, Tradescantia ohiensis and Asclepias incarnata, we used an experimental approach to explore how changing phenology affects the taxonomic composition of the pollinator assemblage and the effectiveness of individual pollinator taxa. After finding in the previous year that fruit set varied with flowering time, we manipulated flowering onset in greenhouses, placed plants in the field over the span of five weeks, and measured pollinator effectiveness as the number of seeds produced after a single visit to a flower. The average effectiveness of pollinators and the expected rates of pollination success were lower for plants of both species flowering earlier than for plants flowering at historical times, suggesting there could be reproductive costs to earlier flowering. Whereas for A. incarnata, differences in average seed set among weeks were due primarily to changes in the composition of the pollinator assemblage, the differences for T. ohiensis were driven by the combined effects of compositional changes and increases over time in the effectiveness of some pollinator taxa. Both species face the possibility of temporal mismatch between the availability of the most effective pollinators and the onset of flowering, and changes in the effectiveness of individual pollinator taxa through time may add an unexpected element to the reproductive consequences of such mismatches. [ABSTRACT FROM AUTHOR]

Climate change is known to affect regional weather patterns and phenology; however, we lack understanding of how climate drives phenological change across local spatial gradients. This spatial variation is critical for determining whether subpopulations and metacommunities are changing in unison or diverging in phenology. Divergent responses could reduce synchrony both within species (disrupting gene flow among subpopulations) and among species (disrupting interspecific interactions in communities). We also lack understanding of phenological change in environments where life history events are frequently aseasonal, such as the tropical, arid, and semi-arid ecosystems that cover vast areas. Using a 33-year-long dataset spanning a 1,267-m semi-arid elevational gradient in the southwestern United States, we test whether flowering phenology diverged among subpopulations within species and among five communities comprising 590 species. Applying circular statistics to test for changes in year-round flowering, we show flowering has become earlier for all communities except at the highest elevations. However, flowering times shifted at different rates across elevations likely because of elevation-specific changes in temperature and precipitation, indicating diverging phenologies of neighboring communities. Subpopulations of individual species also diverged at mid-elevation but converged in phenology at high elevation. These changes in flowering phenology among communities and subpopulations are undetectable when data are pooled across the gradient. Furthermore, we show that nonlinear changes in flowering times over the 33-year record are obscured by traditional calculations of long-term trends. These findings reveal greater spatiotemporal complexity in phenological responses than previously recognized and indicate climate is driving phenological reshuffling across local spatial gradients. • Flowering time is diverging among communities across an elevational gradient • Divergence reflects nonlinear shifts in flowering phenology over three decades • Climatic variables have also changed differently across space and over time • Changing climate is driving phenological reshuffling across local spatial gradients Using 33 years of data, Rafferty et al. test whether flowering times have diverged for neighboring communities comprising 590 species across an elevational gradient. Divergent and nonlinear shifts in flowering time are related to elevation-specific changes in temperature and precipitation and will likely alter species interactions and gene flow. [ABSTRACT FROM AUTHOR]

Species interactions, such as those between plants and pollinators, are known to be shaped by both evolutionary history and ecological factors. However, little is known about how multiple factors (e.g. phylogeny, phenology, abundance and functional traits) interactively affect interaction patterns.Using a plant–bumblebee network comprising 2,428 interactions between 29 plant species and 12 bumblebee species in the Himalaya–Hengduan Mountains, we tested for phylogenetic signal and whether phylogenetic pattern was explained by abundance, phenology and 13 plant and bumblebee functional traits. We also tested whether trait matching in two pairs of plant–bumblebee traits explained interaction frequencies at both species and individual levels.The network showed significant phylogenetic signal; closely related bumblebees tended to visit similar sets of plants, but not vice versa. Among all the measured factors, nectar volume and sugar concentration, rather than other phylogenetically constrained factors, were most important for explaining phylogenetic pattern (64% and 54% respectively). Although long–tongued bumblebee species tended to interact with long–tubed flowers, trait matching did not predict short–tongued bee interaction frequencies. Despite this, trait matching was apparent at the level of individual bees, reflecting intraspecific variation in tongue length and body size. Different selection pressures may exist within this bumblebee community, resulting in specialized, co–evolved traits in long–tongued species and adaptive generalization in short–tongued species to gain access to a variety of flowers.Together, these findings contribute to our understanding of phylogenetic trait–based structure in species interaction networks. In particular, this study provides new evidence for the importance of nectar rewards in structuring interaction patterns in pollination mutualisms. The results also demonstrate that trait matching may occur at the individual level, despite not being detectable at the species level, and underline the necessity of taking intraspecific trait variation into account in studies of community structure. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Synchrony defines an organism's overlap with potential resources and mates, essential for survival and reproduction. Flowering synchrony influences gene flow within species and patterns of interaction among plants and with other trophic levels, including pollinators. Climate‐change driven shifts in plant phenology may disrupt plant–plant and plant–pollinator interactions, resulting in reshuffling of communities and altered ecosystem processes. We present a unique long‐term metacommunity‐wide study relating changes in flowering synchrony within and among species along an elevational gradient to changes in local climatic conditions. We apply a circular statistical method that estimates flowering phenology overlap between entire flowering distributions, overcoming limitations and biases of single indicators such as first and last flowering dates. We analyzed more than 300 000 flowering overlap estimates between 217 species in five plant communities across a 1267 m gradient over four decades (1984–2019) in the southwestern USA. We show that co‐flowering synchrony significantly decreased in all plant communities, with a maximum of 28.1% of synchrony lost at the lowest elevations. Decreased synchrony was significantly negatively correlated with increasing temperatures recorded across the gradient. Reduced precipitation had locally‐dependent effects and, in combination with warmer temperatures, accelerated the decrease in synchrony, especially at the lowest elevations. Flowering synchrony within plant species occurring in multiple communities increased between most community pairs, with a maximum increase of 30.5%, and at accelerated rates in recent years. The exception, likely associated with differences in topography, was a 5.6% decrease in synchrony between the two highest‐elevation communities. Overall, increased synchrony within species occurring at multiple elevations indicates homogenization of flowering phenology across the gradient. These results show significant reshaping of flowering synchrony within and between plant communities in response to changing climate. Because plant phenology influences many ecological processes, such fundamental changes may have far‐reaching and negative effects on ecosystem stability. [ABSTRACT FROM AUTHOR]

Climate change has the potential to desynchronize the phenologies of interdependent species, with potentially catastrophic effects on mutualist populations. Phenologies can evolve, but the role of evolution in the response of mutualisms to climate change is poorly understood. We developed a model that explicitly considers both the evolution and the population dynamics of a plant-pollinator mutualism under climate change. How the populations evolve, and thus whether the populations and the mutualism persist, depends not only on the rate of climate change but also on the densities and phenologies of other species in the community. Abundant alternative mutualist partners with broad temporal distributions can make a mutualism more robust to climate change, while abundant alternative partners with narrow temporal distributions can make a mutualism less robust. How community composition and the rate of climate change affect the persistence of mutualisms is mediated by two-species Allee thresholds. Understanding these thresholds will help researchers to identify those mutualisms at highest risk owing to climate change. [ABSTRACT FROM AUTHOR]