Grown in a transplant garden that provides field conditions but prevents predation by pocket gophers, plants of Erythronium grandiflorum (Liliaceae) have been exhumed annually (as dormant corms), photographed, and weighed over 33 years. From seed, plants grow to flowering size in about 5-6 years. They subsequently regulate their size by occasional vegetative splitting and by flowering and fruiting; producing one fruit costs a plant about 8% of the weight it would have gained if it had not flowered. Death is rare: a few plants have gradually lost weight and died in a way consistent with classical senescence, but others have died suddenly from fungal infection after previously growing robustly. Additional years of observation will be needed to clarify the issue of senescence. The data are archived and future collaborators are sought.

Heterostylous plants are defined by the reciprocal positioning of stigmas and anthers in floral morphs—a trait proposed by Darwin to enhance the efficiency of disassortative (intermorph) pollen transfer. This floral polymorphism may also reduce gamete wastage by minimizing sexual interference between male and female reproductive organs. In distylous species, two floral morphs occur: a long‐styled morph with stigmas positioned above the anthers and a short‐styled morph with stigmas below the anthers. A related floral polymorphism, known as stigma‐height dimorphism, involves variation in stigma height but not anther placement. To test how floral architecture influences pollen transfer and reproductive interference, we used 3D‐printed artificial flowers based on Petunia grandiflora , incorporating real styles and anthers from glasshouse‐grown plants. These artificial flowers simulated distyly and two forms of stigma‐height dimorphism. In flight cage experiments, captive bumblebees ( Bombus impatiens ) from commercial colonies facilitated pollen transfer within and between flowers. We measured pollen grain deposition on stigmas and styles, as well as residual pollen in donor anthers. Our results provided partial support for Darwin's hypothesis: in distylous arrays, reciprocal sex‐organ placement enhanced intermorph pollen deposition, especially in the short‐styled morph. Bumblebee foraging time influenced pollen load, with longer visits to long‐styled flowers resulting in increased pollen deposition. Patterns of self‐pollen deposition—a form of reproductive interference—varied with the degree of spatial separation between sexual organs. As expected, stigma‐height dimorphic arrays exhibited higher self‐pollen transfer than distylous arrays. While not conclusive, our findings emphasize the role of floral morphology in shaping pollination dispersal, self‐interference and pollinator behaviour. The use of three‐dimensional printed flowers demonstrates a promising experimental approach for future studies on plant–pollinator interactions and the functional significance of floral design. Read the free Plain Language Summary for this article on the Journal blog.

1. Worldwide, riparian zones of many intermittent rivers and ephemeral streams (IRES) have been severely degraded. However, compared with perennially flowing waters, there have been few restoration efforts (e.g., revegetation, livestock removal) to halt or reverse this degradation. Even rarer are assessments of whether desired responses occurred and, if so, their underlying mechanisms, especially where flow extremes such as drying and flooding in IRES might alter or delay ecological responses to restoration. 2. In order to assess how aquatic invertebrate communities responded to riparian replanting and livestock removal in three degraded lowland IRES in southeastern Australia, we conducted an eight-year experiment (2004-2013), sampling paired control (unrestored) and treatment (restored, between 2005 and 2007 across creeks) sites twice yearly before and after restoration. To evaluate likely mechanisms underlying invertebrate responses to riparian restoration, we used a range of structural (e.g., richness) and functional (e.g., trait-based) metrics. We also monitored environmental variables predicted to be likely drivers of aquatic invertebrate responses such as macrophyte and canopy cover, water quality, in-stream organic matter and instream wood. The study coincided with the last few years of a decade-long drought that broke with severe floods (in 2010-2012), so we opportunistically examined how these hydrological extremes affected invertebrate responses to riparian restoration. 3. At all three sites, macrophyte and canopy cover, water quality, organic matter and instream wood were comparable at treatment and control sites throughout the eight-year experiment. There were also no significant differences in structural or functional metrics to indicate aquatic invertebrate responses to restoration after 6-8 years. This lack of predicted invertebrate responses apparently reflected how severely the drought impeded the riparian restoration, delaying even short-term responses. Pervasive effects of catchment-scale degradation may have further diminished the predicted benefits of the reach-scale restoration efforts. 4. By contrast, invertebrate metrics responded strongly to flow extremes, especially the brief floods that occurred as drought broke. These responses were evident for functional groups and individual families (especially rheophilic ones), but were not detected by a commonly used integrative measure of stream condition. This highlights the importance of selecting appropriate indicators in restoration monitoring programs and recognising their variability in responsiveness to restoration versus flow extremes. 5. IRES are abundant and, in many parts of the world, increasingly common. Understanding how their inherent hydrological extremes may delay, modify and even overwhelm predicted responses to riparian restoration is crucial to setting realistic goals for IRES in the Anthropocene. Furthermore, assessing the success of riparian restoration in IRES requires a long-term view given the extended time frames over which responses may occur, especially when expectations are often based on results of riparian restoration of perennial streams and rivers.

Assessing the relative contributions of different pollinator taxa to pollination services is a central task in both basic eco-evolutionary research and applied conservation and agriculture. To that end, many studies have quantified single-visit pollen deposition and visitation frequency, which together determine a pollinator species' rate of conspecific pollen delivery. However, for plant species that require or benefit from outcrossing, pollination service quality further depends upon the ratio of outcross to self-pollen deposited, which is determined by two additional pollinator traits: pollen carryover and movement patterns among genetically compatible plant individuals. Here, we compare the pollination capacities of managed honey bees, native bumble bees, and native mining bees in apple-a varietally self-incompatible commercial crop-when pollen carryover and pollinator movement patterns are considered. We constructed simulation models of outcross pollen deposition parameterized using empirically measured single-visit pollen deposition, visitation frequency, and probabilities of intertree movement exhibited by each pollinator type, as well as pollen carryover patterns simulated based on parameters reported in the literature. In these models, we also explicitly specified the spatial relationships among cross-compatible trees based on field-realistic orchard layout schemes. We found that estimated pollination service delivery was considerably reduced for all pollinator types when pollen carryover and pollinator movement patterns were considered, as compared to when only single-visit pollen deposition and visitation frequency were considered. We also found that the performance of different pollinator types varied greatly across simulated orchard layout schemes and pollen carryover scenarios, including one instance where bumble and mining bees reversed their relative rankings. In all simulations, native bumble and mining bees outperformed managed honey bees in terms of both outcross pollen delivery per unit time and per flower visited, with disparities being greatest under scenarios of low pollen carryover. We demonstrate the degree to which pollination studies may reach inaccurate conclusions regarding pollination service delivery when pollen carryover and pollinator movement patterns are ignored. Our finding of the strong context dependence of pollination efficiency, even within a single plant-pollinator taxon pair, cautions that future studies in both basic and applied pollination biology should explicitly consider the ecological context in which pollination interactions take place.

An occupational hazard for editors is the powerful temptation to editorialize. In pondering a possible contribution to the SCAPE Special Issue, I decided to indulge that temptation by expanding part of with my plenary address to SCAPE 2018 at Abisko into a personal comment expressing scepticism about the practice of constructing pollination networks. At that time, and on various occasions since, some colleagues suggested that publishing my perspective might help foster a useful conversation.

You have probably realised that the Journal of Pollination Ecology changed its look, coming with an updated submission system, provided by OJS of PKP. Further changes in the near future. Find out more!

Explanations of floral adaptation to diverse pollinator faunas have often invoked visitor-mediated trade-offs in which no intermediate, generalized floral phenotype is optimal for pollination success, i.e. fitness valleys are created. In such cases, plant species are expected to specialize on particular groups of flower visitors. Contrary to this expectation, it is commonly observed that flowers interact with various groups of visitors, while at the same time maintaining distinct phenotypes among ecotypes, subspecies, or congeners. This apparent paradox may be due to a gap in our understanding of how visitor-mediated trade-offs could affect floral adaptation. Here we provide a conceptual framework for analysing visitor-mediated trade-offs with the hope of stimulating empirical and theoretical studies to fill this gap. We propose two types of visitor-mediated trade-offs to address negative correlations among fitness contributions of different visitors: visitor-mediated phenotypic trade-offs (phenotypic trade-offs) and visitor-mediated opportunity trade-offs (opportunity trade-offs). Phenotypic trade-offs occur when different groups of visitors impose conflicting selection pressures on a floral trait. By contrast, opportunity trade-offs emerge only when some visitors' actions (e.g. pollen collection) remove opportunities for fitness contribution by more beneficial visitors. Previous studies have observed disruptive selection due to phenotypic trade-offs less often than expected. In addition to existing explanations, we propose that some flowers have achieved 'adaptive generalization' by evolving features to avoid or eliminate the fitness valleys that phenotypic trade-offs tend to produce. The literature suggests a variety of pathways to such 'trade-off mitigation'. Trade-off mitigation may also evolve as an adaptation to opportunity trade-offs. We argue that active exclusion, or floral specialization, can be viewed as a trade-off mitigation, occurring only when flowers cannot otherwise avoid strong opportunity trade-offs. These considerations suggest that an evolutionary strategy for trade-off mitigation is achieved often by acquiring novel combinations of traits. Thus, phenotypic diversification of flowers through convergent evolution of certain trait combinations may have been enhanced not only through adaptive specialization for particular visitors, but also through adaptive generalization for particular visitor communities. Explorations of how visitor-mediated trade-offs explain the recurrent patterns of floral phenotypes may help reconcile the long-lasting controversy on the validity of pollination syndromes.

Widespread reports of declining populations of pollinators have raised concerns that plant populations may be incurring increasing shortfalls in pollination, but few studies have measured pollination deficits over enough seasons to detect such changes. I have conducted pollen-supplementation experiments in a wild population of the glacier lily (Erythronium grandiflorum, Liliaceae) from 1993 to 2018. Pollination deficits were estimated by comparing the fruit set of hand-pollinated, single-flowered plants to that of open-pollinated controls. For a subset of years, seed set data were also available. A previous publication reported a significant deterioration of pollination in this population from 1993 to 2009, and suggested phenological dislocation as a possible cause. That deterioration is no longer evident in the longer-term data set. Very long time series may be necessary to detect temporal trends in pollination service. This population consistently experiences stronger pollination deficits before its flowering peak than after. This heterogeneity suggests caution in characterizing a population as pollination-limited or not, even within a single season.

Background and Aims If two plant species share pollinators, it has been proposed that the interaction between them may range from competitive to facilitative, depending on the way in which they intermingle. In particular, the presence of a rewarding plant species may increase the rate of pollinator visitation to a less rewarding species in its vicinity, but the beneficial increase in visitation may be counteracted by a detrimental increase in heterospecific pollen transfer. We assessed this trade-off using bumble-bees foraging over a gradual spatial transition between two plant species in an indoor cage experiment. Methods We used two 'species' of artificial flowers - one more rewarding than the other - in arrays that varied in the degree of species intermingling. The flowers dispensed and received powdered food dyes serving as pollen analogues. Captive bumble-bees visited to collect sucrose solution. We quantified dye delivery to the adhesive-tape 'stigmas' in flowers by spectrophotometry. Key Results Across the spatial transition between species, the less attractive species received more dye (more bee visits) when in proximity to the more attractive species than it did when alone, but the larger dye loads were less pure (more heterospecific pollen transfer). The decline in purity cancelled out the gain in acquisition, so conspecific pollen receipt by the less attractive species was neutrally affected. The more attractive species received fewer visits when surrounded by the less attractive species, so the interaction between the two species was amensalism when considering conspecific pollen reception. Conclusions Pollinator-mediated interactions between plant species depend on pollination quantity and purity, both of which can depend on spatial intermingling.

Geographical variation in pollinators visiting a plant can produce plant populations adapted to local pollinator environments. We documented two markedly different pollinator climates for the spring ephemeral wildflower Claytonia virginica: in more northern populations, the pollen-specialist bee Andrena erigeniae dominated, but in more southern populations, A. erigeniae visited rarely and the bee-fly Bombylius major dominated. Plants in the northern populations experienced faster pollen depletion than plants in southern populations. We also measured divergent pollen-related plant traits; plants in northern populations produced relatively more pollen per flower and anther dehiscence was more staggered than plants in southern populations. These plant traits might function to increase pollen dispersal via the different pollen vectors.

It is widely recognized that plants are visited by a diverse community of pollinators that are highly variable in space and time, but biologists are often unable to investigate the pollinator climate across species’ entire ranges. To study the community of pollinators visiting the spring ephemerals Claytonia virginica and Claytonia caroliniana, we assembled a team of citizen scientists to monitor pollinator visitation to plants throughout the species’ ranges. Citizen scientists documented some interesting differences in pollinator communities; specifically, that western C. virginica and C. caroliniana populations are visited more often by the pollen specialist bee Andrena erigeniae and southern populations are visited more often by the bombyliid fly Bombylius major. Differences in pollinator communities throughout the plants’ range will have implications for the ecology and evolution of a plant species, including that differences may affect the male fitness of individual plants or the reproductive success of plant populations, or both.

Across angiosperm species, the longevity of individual flowers can range from fixed to highly plastic. The orchid family is noteworthy for frequent reports of species in which flower lifespans are greatly prolonged if flowers are not pollinated. Less dramatic cases of pollination-induced senescence of anthesis have been reported for various species in other families, but such reports are scattered. Frequently, such findings are peripheral components of more general pollination studies. Because pollination-dependent plasticity can ameliorate phenological dislocations between plants and pollinators, it is worthwhile to conduct systematic surveys of its magnitude and taxonomic distribution. As a start, we report a set of experiments comparing the active lifespans of pollinated flowers to those of unpollinated controls in a set of nine species from a local subalpine flora. In all species, unpollinated flowers had longer mean times of receptiveness than pollinated ones, although the differences in means were often small. Three species exhibited significantly extended floral longevity in the absence of pollination.

Shifts in the timing of life history events have become an important source of information about how organisms are responding to climate change. Phenological data have generally been treated as purely temporal, with scant attention to the inherent spatial aspects of such data. However, phenological data are tied to a specific location, and considerations of sampling design, both over space and through time, can critically affect the patterns that emerge. Focusing on flowering phenology, we describe how purely spatial shifts, such as adding new study plots, or the colonization of a study plot by a new species, can masquerade as temporal shifts. Such shifts can look like responses to climate change but are not. Furthermore, the same aggregate phenological curves can be composed of individuals with either very different or very similar phenologies. We conclude with a set of recommendations to avoid ambiguities arising from the spatiotemporal duality of phenological data.

The study of ecological communities through time can reveal fundamental ecological processes and is key to understanding how natural and human pressures will affect biodiversity. Most studies of ecological communities through time consider only one or a few summary measures (e.g. species richness, total abundance), which might neglect important aspects of community structure or function. We studied temporal variation in several measures of species diversity, size diversity, and species composition in an intensively sampled bird community to determine whether different biodiversity measures change synchronously. We used a novel function regression model, which supports the study of diversity measures that are distributions (e.g. species abundance distributions) alongside measures that are scalar values (e.g. species richness). Most diversity measures changed predictably within years, but inter-annual changes in size diversity and species composition were not reflected in species diversity. Within and among years, there was considerable variation in distributional measures that was not captured in scalar measures. Predictable variation within years probably was related to seasonal variation in weather patterns or food availability, but variation in size diversity among years probably resulted from stochastic changes in species composition. These results suggest that species and size diversity may be decoupled, and that inferences on scalar diversity measures might not reflect fundamental changes to community structure or function. Our method supports the inclusion of size-based measures and distributional measures in ecological analyses, and broader uptake of our approach is likely to provide new insight into the processes structuring ecological communities, and inform the links between structure and function in ecological communities.

Exploratory behavior—an individual’s response to novel environments, resources, or objects—should vary with the associated benefits, including new sources of food and reduced levels of competition, and the costs, such as predation pressure. Using guppies from multiple streams and rivers in Trinidad, we compared guppies from high- and low-predation populations. We found that wild-caught male and female guppies from low-predation populations were more exploratory than high-predation fish when tested in the field and in controlled laboratory conditions. We did not detect significant evidence for a genetic basis for differences in the behavior of high- and low-predation fish using a common-garden approach, but further study is required before conclusions can be made about the relative contribution of genes to population differences in exploratory behavior of guppies. Theory has assumed that predation risk is a cost that will select against high levels of exploratory behavior; this study is one of the few that has tested this assumption, and we show that exploratory behavior is indeed suppressed in guppies from high-predation localities.

AbstractPollinators that collect pollen – and specifically, pollen‐specialist bees – are often considered to be the best pollinators of a (host) plant. Although pollen collectors and pollen specialists often benefit host plants, especially in the pollen that they deliver (their pollination “effectiveness”), they can also exact substantial costs because they are motivated to collect as much pollen as possible, reducing the proportion of pollen removed that is subsequently delivered to stigmas (their pollination “efficiency”). From the plant perspective, pollen grains that do not pollinate conspecific stigmas are “wasted”, and potentially costly. We measured costs and benefits of nectar‐collecting, pollen‐collecting, and pollen‐specialist pollinator visitation to the spring ephemeral Claytonia virginica. Visits by the pollen‐specialist bee Andrena erigeniae depleted pollen quickly and thoroughly. Although all pollinators delivered roughly the same number of grains, the pollen specialist contributed most to C. virginica pollen delivery because of high visitation rates. However, the pollen specialist also removed a large number of grains; this removal may be especially costly because it resulted in the depletion of pollen grains in C. virginica populations. While C. virginica appears to rely on pollen transfer by the pollen specialist in these populations, nectar‐collecting visitors could provide the same benefit at a lower cost if their visitation rates increased. Pollen depletion affects a pollinator's value to plants, but is frequently overlooked. If they lower the effectiveness of future floral visitors, visits by A. erigeniae females to C. virginica may be more detrimental than beneficial compared to other pollinators and may, in some circumstances, reduce plant fitness rather than increase it. Therefore, A. erigeniae and C. virginica may vary in their degree of mutualism depending on the ecological context.

Miller-Struttmann et al. (2015) suggest that, in a North American alpine ecosystem, reduced flower abundance due to climate change has driven the evolution of shorter tongues in two bumble bee species. We accept the evidence that tongue length has decreased, but are unconvinced by the adaptive explanation offered. It posits foraging responses and competitive relationships not seen in other studies and interprets phenotypic change as evidence of evolutionary adaptation. By oversimplifying a complex phenomenon, it may exaggerate the potential for bees to quickly adapt to environmental changes.

Plant species can influence the pollination and reproductive success of coflowering neighbors that share pollinators. Because some individual pollinators habitually forage in particular areas, it is also possible that plant species could influence the pollination of neighbors that bloom later. When flowers of a preferred forage plant decline in an area, site-fidelity may cause individual flower feeders to stay in an area and switch plant species rather than search for preferred plants in a new location. A newly blooming plant species may quickly inherit a set of visitors from a prior plant species, and therefore experience higher pollination success than it would in an area where the first species never bloomed. To test this, we manipulated the placement and timing of two plant species, Delphinium barbeyi and later-blooming Gentiana parryi. We recorded the responses of individually marked bumble bee pollinators. About 63% of marked individuals returned repeatedly to the same areas to forage on Delphinium. When Delphinium was experimentally taken out of bloom, most of those site-faithful individuals (78%) stayed and switched to Gentiana. Consequently, Gentiana flowers received more visits in areas where Delphinium had previously flowered, compared to areas where Delphinium was still flowering or never occurred. Gentiana stigmas received more pollen in areas where Delphinium disappeared than where it never bloomed, indicating that Delphinium increases the pollination of Gentiana when they are separated in time. Overall, we show that individual bumble bees are often site-faithful, causing one plant species to increase the pollination of another even when separated in time, which is a novel mechanism of pollination facilitation.

Abstract The interaction between floral traits and reproductive isolation is crucial to explaining the extraordinary diversity of angiosperms. Heterostyly, a complex floral polymorphism that optimizes outcrossing, evolved repeatedly and has been shown to accelerate diversification in primroses, yet its potential influence on isolating mechanisms remains unexplored. Furthermore, the relative contribution of pre‐ versus postmating barriers to reproductive isolation is still debated. No experimental study has yet evaluated the possible effects of heterostyly on pre‐ and postmating reproductive mechanisms. We quantify multiple reproductive barriers between the heterostylous Primula elatior (oxlip) and P. vulgaris (primrose), which readily hybridize when co‐occurring, and test whether traits of heterostyly contribute to reproductive barriers in unique ways. We find that premating isolation is key for both species, while postmating isolation is considerable only for P. vulgaris; ecogeographic isolation is crucial for both species, while phenological, seed developmental, and hybrid sterility barriers are also important in P. vulgaris, implicating sympatrically higher gene flow into P. elatior. We document for the first time that, in addition to the aforementioned species‐dependent asymmetries, morph‐dependent asymmetries affect reproductive barriers between heterostylous species. Indeed, the interspecific decrease of reciprocity between high sexual organs of complementary floral morphs limits interspecific pollen transfer from anthers of short‐styled flowers to stigmas of long‐styled flowers, while higher reciprocity between low sexual organs favors introgression over isolation from anthers of long‐styled flowers to stigmas of short‐styled flowers. Finally, intramorph incompatibility persists across species boundaries, but is weakened in long‐styled flowers of P. elatior, opening a possible backdoor to gene flow through intramorph pollen transfer between species. Therefore, patterns of gene flow across species boundaries are likely affected by floral morph composition of adjacent populations. To summarize, our study highlights the general importance of premating isolation and newly illustrates that both morph‐ and species‐dependent asymmetries shape boundaries between heterostylous species.

Estimated changes in habitat availability for each specie under revegetation schedules derived from Zonation cell ranks.