Invasion of a dominant floral resource: effects on the floral community and pollination of native plants

Seed dormancy types and germination response of 15 plant species in temperate montane peatlands

Despite their crucial role in determining the fate of seeds, the type and breaking mode of seed dormancy in peatland plants in temperate Asia with a continental monsoon climate are rarely known. Fifteen common peatland plant species were used to test their seed germination response to various dormancy-breaking treatments, including dry storage (D), gibberellin acid soaking (GA), cold stratification (CS), warm followed cold stratification (WCS), GA soaking + cold stratification (GA + CS) and GA soaking + warm followed cold stratification (GA + WCS). Germination experiment, viability and imbibition test, and morphological observation of embryos were conducted. Of the 15 species, nine showed physiological dormancy (PD), with non-deep PD being the dominant type. Four species, Angelica pubescens, Cicuta virosa, Iris laevigata, and Iris setosa exhibited morphophysiological dormancy. Two species, Lycopus uniflorus and Spiraea salicifolia, demonstrated nondormancy. Overall, the effect hierarchy of dormancy-breaking is: CS > GA > WCS > GA + CS > D > GA + WCS. Principal component analysis demonstrated that seed traits, including embryo length: seed length ratio, seed size, and monocot/eudicot divergence, are more likely to influence seed dormancy than environmental factors. Our study suggests that nearly 90% of the tested peatland plant species in the Changbai Mountains demonstrated seed dormancy, and seed traits (e.g. embryo-to-seed ratio and seed size) and abiotic environmental factors (e.g. pH and temperature seasonality) are related to germination behavior, suggesting seed dormancy being a common adaptation strategy for the peatland plants in the temperate montane environment.

Color-advertising strategies of invasive plants through the bee eye

Invasive plants represent a significant global challenge as they compete with native plants for limited resources such as space, nutrients and pollinators. Here, we focused on four invasive species that are widely spread in the French Pyrenees, Buddleja davidii, Reynoutria japonica, Spiraea japonica and Impatiens glandulifera, and analyzed their visual advertisement signals with respect to those displayed by their surrounding native species using a perceptual approach based on the neural mechanisms of bee vision given that bees are regular pollinators of these plants. We collected 543 spectral reflections from the 4 invasive species, and 66 native species and estimated achromatic and chromatic similarities to the bee eye. R. japonica, S. japonica and B. davidii were inconspicuous against the foliage background and could be hardly discriminated in terms of color from their surrounding native plants. These characteristics promote generalization, potentially attracting pollinators foraging on similar native species. Two morphs of I. glandulifera were both highly salient in chromatic and achromatic terms and different from their surrounding native species. This distinctive identity facilitates detection and learning in association with rich nectar. While visual signals are not the only sensory cue accounting for invasive-plant success, our study reveals new elements for understanding biological invasion processes from the perspective of pollinator perceptual processes.

The Patterns of Intraspecific Variations in Mass of Nectar Sugar along a Phylogeny Distinguish Native from Non-Native Plants in Urban Greenspaces in Southern England

To serve human needs, non-native species are selected based on an array of functional traits, which generally confer competitive advantages to these species in their recipient environments. Identifying non-obvious functional traits that indirectly inform human selection of non-natives to introduce into urban greenspaces is not yet part of common discussions in invasion biology. We tested whether functional traits integrated within a phylogenetic framework, may reveal those subtle criteria underlying the introduction of non-native plants into urban greenspaces. We found no differences in terms of functional traits between natives and non-natives. We also found no evidence that functional traits predict nectar production, irrespective of how nectar production was measured. Finally, we found that the mean sugar concentration of nectar per flower is evolutionarily shared both within closely related non-native plants as well as within close native plants. However, phylogenetically close species share similar intraspecific variation in mass of nectar sugar per flower, but this is true only for non-native plants, thus revealing a non-obvious selection criteria of non-native plants for urban greenspaces. Our results indicate that the phylogenetic patterns of intraspecific variation in mass of nectar sugar per flower is the major criterion distinguishing non-natives from native plants in urban greenspaces in Southern England.

Specific alien plant species predominantly deliver nectar sugar and pollen but are not preferentially visited by wild pollinating insects in suburban riparian ecosystems

The invasion of alien plants has been rapidly proceeding worldwide due to urbanisation. This might be beneficial to wild pollinating insects, since some alien plant species have large flowers and/or long flowering periods, which can increase nectar sugar and pollen availability. To determine the relative contribution of alien plants to floral resource supply and whether resource-rich alien plants, if any, serve as an important food source of pollinating insects, we performed year-round field observations in suburban riverbanks. We quantified the per-unit-area availability of nectar sugar and pollen delivered by alien and native flowering species and counted wild flower visitors (bees and wasps, hoverflies and butterflies) per plant species. The available nectar sugar and pollen per area were predominantly delivered by a few specific alien species, and the relative contribution of other species to floral resource provision was low throughout the period that wild flower visitors were observed. Nonetheless, the resource-rich alien plants were not visited by as many insects as expected based on their contribution to resource provision. Rather, on a yearly basis, these plants received equal or even fewer visits than other flowering species, including resource-poor natives. We show that despite their great contribution to the gross floral resource supply, resource-rich alien plants do not serve as a principal food source for wild pollinating insects, and other plants, especially natives, are still needed to satisfy insect demand. For the conservation of pollinating insects in suburban ecosystems, maintaining floral resource diversity would be more beneficial than having an increase in gross floral resources by allowing the dominance of specific alien plants.

Distribución de plantas nativas y exóticas a lo largo de gradientes de elevación en senderos de montaña en los Andes de Mendoza, Argentina

Introducción y objetivos: El cambio climático, el ganado y el creciente uso turístico favorecen la dispersión de plantas exóticas, amenazando la conservación de los ecosistemas altoandinos. Estudiamos los patrones de distribución de plantas nativas y exóticas en senderos recreativos de montaña. M&M: Implementamos el protocolo MIREN en seis senderos (2400-3600 m s.n.m.) en dos áreas protegidas de los Andes centrales de Mendoza en las Cordilleras Frontal y Principal. Resultados: Encontramos 180 especies nativas y 41 exóticas. La riqueza de especies nativas fue máxima a elevaciones intermedias, mientras que la riqueza de exóticas disminuyó con la elevación. La riqueza regional de nativas fue mayor en la Cordillera Frontal que en la Principal (114 versus 71 nativas, respectivamente) mientras que la riqueza regional de exóticas fue menor en la Frontal que en la Principal (20 versus 28 exóticas, respectivamente). La riqueza de exóticas por parcela fue mayor en la Cordillera Frontal que en la Principal. El rango de distribución altitudinal de exóticas fue mayor en la Cordillera Frontal. Dos exóticas abundantes, Taraxacum officinale y Cerastium arvense, estuvieron a lo largo de todo el gradiente en la Cordillera Frontal, alcanzando los 3600 m s.n.m. Encontramos siete exóticas no citadas anteriormente. Conclusiones: Los nuevos registros amplían los rangos de distribución conocidos para algunas especies exóticas. A pesar de que el número de especies exóticas fue similar cerca y lejos de los senderos, cinco especies sólo estuvieron en los bordes de los mismos, lo que sugiere que los senderos favorecen los procesos de invasión.

Effect of Landscape Composition and Invasive Plants on Pollination Networks of Smallholder Orchards in Northeastern Thailand

Destruction of natural habitat, land-use changes and biological invasion are some of the major threats to biodiversity. Both habitat alteration and biological invasions can have impacts on pollinator communities and pollination network structures. This study aims to examine the effect of an invasive plant, praxelis (Praxelis clematidea; Asteraceae), and land-use types on pollinator communities and the structure of pollination networks. We conducted the study in smallholder orchards which are either invaded or non-invaded by P. clematidea. We estimated the pollinator richness, visitation rates, and pollinator diversity and evaluated the network structures from 18 smallholder orchards in Northeastern Thailand. The effect of landscape structure in the vicinity of the orchards was investigated, with the proportion of agricultural, forest, and urban landscape within a 3 km radius analyzed. The invasive species and land-use disturbance influence the pollinator communities and pollination network structure at species level was affected by the presence of P. clematidea. Bees were the most important pollinator group for pollinator communities and pollination networks of both invaded or non-invaded plots, as bees are a generalist species, they provide the coherence of both the network and its own module. The urban landscape had a strong negative influence on pollinator richness, while the proportions of agriculture and forest landscape positively affected the pollinator community.

Low Pollinator Sharing Between Coexisting Native and Non-native Plant Pairs: The Effect of Corolla Length and Flower Abundance

Understanding the mechanisms by which non-native plants can attract pollinators in their new geographical zones is important because such species infiltrate native communities and can disrupt native ecological interactions. Despite the large number of studies assessing how invasive plants impact plant–pollinator interactions, the specific comparison of pollination interactions between native and non-native plant pairs has received much less attention. Here we focused on four coexisting co-flowering pairs of common native and non-native species, both with abundant flowers but different floral traits, and asked: (1) to what extent native and non-native plants share pollinator species, and whether the non-native plants attract a different set of pollinators, (2) whether the most shared pollinators are the most frequent floral visitors and the most generalized in their interactions, and (3) how much of the variation in the diversity and frequency of pollinator species between native and non-native plant species can be explained by floral trait dissimilarity and flower abundance. Direct pollinator observations revealed that the plant pairs shared a low fraction (0–33%) of insect species, i.e., non-native plants tended to acquire a different set of pollinators than their native counterparts. The most shared pollinators in each plant pair were the most common but not the most generalized species, and non-native species attracted both generalized and specialized pollinators. Corolla length at opening and flower abundance showed to be important in determining the differences in flower visitation rate between natives and non-natives. Our findings support the general pattern that non-native species have no barriers at the pollination stage to integrate into native communities and that they may attract a different assemblage of pollinators relative to those that visit native plants with which they coexist.

Impacts of plant invasions in native plant-pollinator networks

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.

Heated rivalries: Phenological variation modifies competition for pollinators among arctic plants

When plant species compete for pollinators, climate warming may cause directional change in flowering overlap, thereby shifting the strength of pollinator-mediated plant-plant interactions. Such shifts are likely accentuated in the rapidly warming Arctic. Targeting a plant community in Northeast Greenland, we asked (a) whether the relative phenology of plants is shifting with spatial variation in temperature, (b) whether local plants compete for pollination, and (c) whether shifts in climatic conditions are likely to affect this competition. We first searched for climatic imprints on relative species phenology along an elevational gradient. We then tested for signs of competition with increasing flower densities: reduced pollinator visits, reduced representation of plant species in pollen loads, and reduced seed production. Finally, we evaluated how climate change may affect this competition. Compared to a dominant species, Dryas integrifolia × octopetala, the relative timing of other species shifted along the environmental gradient, with Silene acaulis and Papaver radicatum flowering earlier toward higher elevation. This shift resulted in larger niche overlap, allowing for an increased potential for competition for pollination. Meanwhile, Dryas emerged as a superior competitor by attracting 97.2% of flower visits. Higher Dryas density resulted in reduced insect visits and less pollen of S. acaulis being carried by pollinators, causing reduced seed set by S. acaulis. Our results show that current variation in climate shifts the timing and flowering overlap between dominant and less-competitive plant species. With climate warming, such shifts in phenology within trophic levels may ultimately affect interactions between them, changing the strength of competition among plants.

A review of the challenges and opportunities for restoring animal-mediated pollination of native plants

Ecological restoration is increasingly implemented to reverse habitat loss and concomitant declines in biological diversity. Typically, restoration success is evaluated by measuring the abundance and/or diversity of a single taxon. However, for a restoration to be successful and persistent, critical ecosystem functions such as animal-mediated pollination must be maintained. In this review, we focus on three aspects of pollination within ecological restorations. First, we address the need to measure pollination directly in restored habitats. Proxies such as pollinator abundance and richness do not always accurately assess pollination function. Pollen supplementation experiments, pollen deposition studies, and pollen transport networks are more robust methods for assessing pollination function within restorations. Second, we highlight how local-scale management and landscape-level factors may influence pollination within restorations. Local-scale management actions such as prescribed fire and removal of non-native species can have large impacts on pollinator communities and ultimately on pollination services. In addition, landscape context including proximity and connectivity to natural habitats may be an important factor for land managers and conservation practitioners to consider to maximize restoration success. Third, as climate change is predicted to be a primary driver of future loss in biodiversity, we discuss the potential effects climate change may have on animal-mediated pollination within restorations. An increased mechanistic understanding of how climate change affects pollination and incorporation of climate change predictions will help practitioners design stable, functioning restorations into the future.

Mathematical modeling of self-contained CRISPR gene drive reversal systems

There is a critical need for further research into methods to control biological populations. Numerous challenges to agriculture, ecological systems, and human health could be mitigated by the targeted reduction and management of key species (e.g. pests, parasites, and vectors for pathogens). The discovery and adaptation of the CRISPR/Cas editing platform co-opted from bacteria has provided a mechanism for a means to alter an entire population. A CRISPR-based gene drive system can allow for the forced propagation of a genetic element that bypasses Mendelian inheritance which can be used to bias sex determination, install exogenous information, or remove endogenous DNA within an entire species. Laboratory studies have demonstrated the potency by which gene drives can operate within insects and other organisms. However, continued research and eventual application face serious opposition regarding issues of policy, biosafety, effectiveness, and reversal. Previous mathematical work has suggested the use of modified gene drive designs that are limited in spread such as daisy chain or underdominance drives. However, no system has yet been proposed that allows for an inducible reversal mechanism without requiring the introduction of additional individuals. Here, we study gene drive effectiveness, fitness, and inducible drive systems that could respond to external stimuli expanding from a previous frequency-based population model. We find that programmed modification during gene drive propagation could serve as a potent safeguard to either slow or completely reverse drive systems and allow for a return to the original wild-type population.

Urbanisation modulates plant-pollinator interactions in invasive vs. native plant species

Pollination is a key ecological process, and invasive alien plant species have been shown to significantly affect plant-pollinator interactions. Yet, the role of the environmental context in modulating such processes is understudied. As urbanisation is a major component of global change, being associated with a range of stressors (e.g. heat, pollution, habitat isolation), we tested whether the attractiveness of a common invasive alien plant (Robinia pseudoacacia, black locust) vs. a common native plant (Cytisus scoparius, common broom) for pollinators changes with increasing urbanisation. We exposed blossoms of both species along an urbanisation gradient and quantified different types of pollinator interaction with the flowers. Both species attracted a broad range of pollinators, with significantly more visits for R. pseudoacacia, but without significant differences in numbers of insects that immediately accessed the flowers. However, compared to native Cytisus, more pollinators only hovered in front of flowers of invasive Robinia without visiting those subsequently. The decision rate to enter flowers of the invasive species decreased with increasing urbanisation. This suggests that while invasive Robinia still attracts many pollinators in urban settings attractiveness may decrease with increasing urban stressors. Results indicated future directions to deconstruct the role of different stressors in modulating plant-pollinator interactions, and they have implications for urban development since Robinia can be still considered as a "pollinator-friendly" tree for certain urban settings.

No consistent pollinator-mediated impacts of alien plants on natives

The introduction of an alien plant is widely assumed to have negative consequences for the pollinator-mediated fitness of nearby natives. Indeed, a number of studies, including a highly cited meta-analysis, have concluded that the trend for such interactions is competitive. Here we provide evidence that publication bias and study design have obscured our ability to assess the pollinator-mediated impacts of alien plants. In a meta-analysis of 76 studies, we demonstrate that alien/native status does not predict the outcome of pollinator-mediated interactions among plants. Moreover, we found no evidence that similarity in floral traits or phylogenetic distance between species pairs influences the outcome of pollinator-mediated interactions. Instead, we report that aspects of study design, such as distance between the control and nearest neighbour, and/or the arrangement of study plants better predict the impact of a neighbour than does alien/native status. Our study sheds new light on the role that publication bias and experimental design play in the evaluation of key patterns in ecology. We conclude that, due to the absence of clear, generalisable pollinator-mediated impacts of alien species, management schemes should base decisions on community-wide assessments of the impacts of individual alien plant species, and not solely on alien/native status itself.