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Abstract Pollen protein content has been demonstrated to be an essential nutritional component for bees and thus important in mediating plant–pollinator interactions. However, little is known on the drivers and consequences of among‐species variation in pollen protein content and how this can impact male and female reproductive success across plant species. Among‐species variation in resources allocated to pollen nutrition could further be constrained by life‐history strategies (e.g. survival‐reproduction trade‐offs) or evolutionary history.Here, we surveyed pollen protein content for 29 species within a diverse co‐flowering community and evaluated the effect of pollen protein on male and female reproductive success. We also tested the role of life history (annuals vs. perennials) and phylogeny in mediating differences in resource allocation to pollen nutrition.We found that pollen protein content influences components of male (bee visitor abundance and pollen dispersal) but not female (conspecific pollen deposition and pollen tube growth) reproductive success, suggesting this trait affects plants only via male function. This sex‐specific effect further suggests the potential for sexual conflicts driven by differential investment on this trait. We found no phylogenetic signal on pollen protein content. However, pollen protein content was higher in annual compared to perennial species suggesting survival versus reproduction trade‐offs also contribute to variation in pollen protein at the community level.Our study underscores the importance of understanding the ecological and evolutionary drivers of pollen protein content across plant species. Our results further suggest the existence of sexual conflicts and ecological trade‐offs mediated by differential investment in pollen nutritional quality, with important implications for community assembly and the structure of plant–pollinator interactions. Read the freePlain Language Summaryfor this article on the Journal blog. 

ABSTRACT Flowering plants can be visited by a wide diversity of pollinating insects; however, the structure of plant–insect interactions for non‐bee pollinators is not well‐known, even though non‐bee insects can play a central role in the pollination of many plant species. Pollination by non‐syrphid flies, such as bee flies (Bombylius majorL., Bombyliidae, Diptera), has often been underappreciated. Bee flies represent a diverse group of long‐tongue nectar‐feeding insects that are often reported as generalists who visit flowers indiscriminately. Here, we used individual‐based pollen transport networks to assess patterns of individual foraging in bee flies over two flowering seasons in a diverse co‐flowering community. Using this approach, we uncover the structure (e.g., modular vs. nested) of bee fly individual foraging and the degree of individual specialisation. We further evaluate the role of resource availability (floral abundance) and intraspecific trait variation (proboscis length and body size) in shaping individual specialisation. Overall, bee flies visited 20 different plant species. However, network analysis shows that individuals are more specialised and tend to partition the floral resource as reflected by the high degree of network modularity. Most bee fly individuals concentrate their foraging on only a few floral resources (two to four plant species) suggesting strong niche partitioning in this group of pollinators. This modular foraging pattern was not explained by differences in resource availability over the season. Proboscis length, however, was negatively related to the level of individual specialisation. Individuals with larger proboscis had larger foraging niches (less specialisation) perhaps due to easier access to a wide range of plant species with different floral tube sizes. Overall, our study reveals high individual specialisation and niche partitioning in bee‐fly interactions, mediated by differences in proboscis length, and with important implications for pollen transfer dynamics, plant–plant competition and plant reproductive success in diverse co‐flowering communities. 

Abstract The patterns and drivers of pollen transport on insect bodies can have important consequences for plant reproductive success and floral evolution; however, they remain little studied. Recently, pollinator bodies have been further described as pollen competitive arenas, where pollen grains can compete for space, with implications for the evolution of pollen dispersal strategies and plant community assembly. However, the identity, strength, and diversity of pollen competitive interactions and how they vary across pollinator functional groups is not known. Evaluating patterns and drivers of the pollen co‐transport landscape and how these vary across different pollinator groups is central to further our understanding of floral evolution and co‐flowering community assembly.Here, we integrate information on the number and identity of pollen grains on individual insect pollen loads with network analyses to uncover novel pollen co‐transport networks and how these vary across pollinator functional groups (bees and bee flies). We further evaluate differences in pollen load size, species composition, diversity and phylogenetic diversity among insect groups and how these relate to body size and gender.Pollen co‐transport networks were diverse and highly modular in bees, with groups of pollen species interacting more often with each other on insect bodies. However, the number, identity and frequency of competitors that pollen grains encounter on insect bodies vary between some pollinator functional groups. Other aspects of pollen loads such as their size, richness and phylogenetical diversity were shaped by bee size or gender, with females carrying larger but less phylogenetically diverse pollen loads than males.Synthesis. Our results show that the number, identity and phylogenetic relatedness of pollen competitors changes as pollen grains travel on the body of different pollinators. As a result, pollinator groups impose vastly different interaction landscapes during pollen transport, with so far unknown consequences for plant reproductive success, floral evolution and community assembly. 

Abstract BackgroundStudies that aim to understand the processes that generate and organize plant diversity in nature have a long history in ecology. Among these, the study of plant–plant interactions that take place indirectly via pollinator choice and floral visitation has been paramount. Current evidence, however, indicates that plants can interact more directly via heterospecific pollen (HP) transfer and that these interactions are ubiquitous and can have strong fitness effects. The intensity of HP interactions can also vary spatially, with important implications for floral evolution and community assembly. ScopeInterest in understanding the role of heterospecific pollen transfer in the diversification and organization of plant communities is rapidly rising. The existence of spatial variation in the intensity of species interactions and their role in shaping patterns of diversity is also well recognized. However, after 40 years of research, the importance of spatial variation in HP transfer intensity and effects remains poorly known, and thus we have ignored its potential in shaping patterns of diversity at local and global scales. Here, I develop a conceptual framework and summarize existing evidence for the ecological and evolutionary consequences of spatial variation in HP transfer interactions and outline future directions in this field. ConclusionsThe drivers of variation in HP transfer discussed here illustrate the high potential for geographic variation in HP intensity and its effects, as well as in the evolutionary responses to HP receipt. So far, the study of pollinator-mediated plant–plant interactions has been almost entirely dominated by studies of pre-pollination interactions even though their outcomes can be influenced by plant–plant interactions that take place on the stigma. It is hence critical that we fully evaluate the consequences and context-dependency of HP transfer interactions in order to gain a more complete understanding of the role that plant–pollinator interactions play in generating and organizing plant biodiversity. 

Summary The disruption of mutualisms by invasive species has consequences for biodiversity loss and ecosystem function. Although invasive plant effects on the pollination of individual native species has been the subject of much study, their impacts on entire plant–pollinator communities are less understood. Community‐level studies on plant invasion have mainly focused on two fronts: understanding the mechanisms that mediate their integration; and their effects on plant–pollinator network structure. Here we briefly review current knowledge and propose a more unified framework for evaluating invasive species integration and their effects on plant–pollinator communities. We further outline gaps in our understanding and propose ways to advance knowledge in this field. Specifically, modeling approaches have so far yielded important predictions regarding the outcome and drivers of invasive species effects on plant communities. However, experimental studies that test these predictions in the field are lacking. We further emphasize the need to understand the link between invasive plant effects on pollination network structure and their consequences for native plant population dynamics (population growth). Integrating demographic studies with those on pollination networks is thus key in order to achieve a more predictive understanding of pollinator‐mediated effects of invasive species on the persistence of native plant biodiversity. 

Abstract The ecological dynamics of co‐flowering communities are largely mediated by pollinators. However, current understanding of pollinator‐mediated interactions primarily relies on how co‐flowering plants influence attraction of shared pollinators, and much less is known about plant–plant interactions that occur via heterospecific pollen (HP) transfer. Invaded communities in particular can be highly affected by the transfer of alien pollen, but the strength, drivers and fitness consequences of these interactions at a community scale are not well understood.Here we analyse HP transfer networks in nine coastal communities in the Yucatan Mexico that vary in the relative abundance of invasive flowers to evaluate how HP donation and receipt varies between native and alien plants. We further evaluate whether HP donation and receipt are mediated by floral traits (e.g. display, flower size) or pollinator visitation rate. Finally, we evaluated whether post‐pollination success (proportion of pollen tubes produced) was affected by alien HP receipt and whether the effect varied between native and alien recipients.HP transfer networks exhibit relatively high connectance (c. 15%), suggesting high HP transfer within the studied communities. Significant network nestedness further suggests the existence of species that predominantly act as HP donors or recipients in the community. Species‐level analyses showed that natives receive 80% more HP compared to alien species, and that alien plants donate 40% more HP than natives. HP receipt and donation were mediated by different floral traits and such effects were independent of plant origin (native or alien). The proportion of alien HP received significantly affected conspecific pollen tube success in natives, but not that of alien species.Synthesis. Our results suggest that HP transfer in invaded communities is widespread, and that native and alien species play different roles within HP transfer networks, which are mediated by a different suite of floral traits. Alien species, in particular, play a central role as HP donors and are more tolerant to HP receipt than natives—a finding that points to two overlooked mechanisms facilitating alien plant invasion and success within native co‐flowering communities. 

Abstract Pollinator-mediated competition and facilitation are two important mechanisms mediating co-flowering community assembly. Experimental studies, however, have mostly focused on evaluating outcomes for a single interacting partner at a single location. Studies that evaluate spatial variation in the bidirectional effects between co-flowering species are necessary if we aim to advance our understanding of the processes that mediate species coexistence in diverse co-flowering communities. Here, we examine geographic variation (i.e. at landscape level) in bidirectional pollinator-mediated effects between co-flowering Mimulus guttatus and Delphinium uliginosum. We evaluated effects on pollen transfer dynamics (conspecific and heterospecific pollen deposition) and plant reproductive success. We found evidence of asymmetrical effects (one species is disrupted and the other one is facilitated) but the effects were highly dependent on geographical location. Furthermore, effects on pollen transfer dynamics did not always translate to effects on overall plant reproductive success (i.e. pollen tube growth) highlighting the importance of evaluating effects at multiple stages of the pollination process. Overall, our results provide evidence of a spatial mosaic of pollinator-mediated interactions between co-flowering species and suggest that community assembly processes could result from competition and facilitation acting simultaneously. Our study highlights the importance of experimental studies that evaluate the prevalence of competitive and facilitative interactions in the field, and that expand across a wide geographical context, in order to more fully understand the mechanisms that shape plant communities in nature.