Impacts of plant invasions in native plant-pollinator networks.

Simple SummaryComparisons of plant and insect pollinator networks along elevational gradients can help predict future impacts of changing climate on pollinator distribution on local scales. We compare the pollination network structure along the altitudinal gradient of the San Francisco Peaks in Arizona. We evaluate shifts in network connectance, nestedness, modularity, and overall generalization with increased elevation. We conclude that plant–pollinator networks become more nested and generalized with elevation and identify the insect pollinator species most critical for network stability at the higher elevation pollination community. The variation in plant–pollinator network structure at different elevation zones of the San Francisco Peaks helps unveil which local communities currently support the most stable systems in the face of climate change.The structural patterns comprising bimodal pollination networks can help characterize plant–pollinator systems and the interactions that influence species distribution and diversity over time and space. We compare network organization of three plant–pollinator communities along the altitudinal gradient of the San Francisco Peaks in northern Arizona. We found that pollination networks become more nested, as well as exhibit lower overall network specialization, with increasing elevation. Greater weight of generalist pollinators at higher elevations of the San Francisco Peaks may result in plant–pollinator communities less vulnerable to future species loss due to changing climate or shifts in species distribution. We uncover the critical, more generalized pollinator species likely responsible for higher nestedness and stability at the higher elevation environment. The generalist species most important for network stability may be of the greatest interest for conservation efforts; preservation of the most important links in plant–pollinator networks may help secure the more specialized pollinators and maintain species redundancy in the face of ecological change, such as changing climate.

Urban areas often host exotic plant species, whether managed or spontaneous. These plants are suspected of affecting pollinator diversity and the structure of pollination networks. However, in dense cityscapes, exotic plants also provide additional flower resources during periods of scarcity, and the consequences for the seasonal dynamics of networks still need to be investigated. For two consecutive years, we monitored monthly plant–pollinator networks in 12 green spaces in Paris, France. We focused on seasonal variations in the availability and attractiveness of flower resources, comparing native and exotic plants at both the species and community levels. We also considered their respective contributions to network properties over time (specialization and nestedness). Exotic plants provided more abundant and diverse flower resources than native plants, especially from late summer on. However, native plants received more visits and attracted more pollinator species at the community level; and during certain times of the year at the species level as well. Exotic plants were involved in more generalist interactions, increasingly so over the seasons. In addition, they contributed more to network nestedness than native plants. These results show that exotic plants are major components of plant–pollinator interactions in a dense urban landscape, even though they are less attractive than natives. They constitute a core of generalist interactions that increase nestedness and can participate in the overall stability of the network. However, most exotic species were seldom visited by insects. Pollinator communities may benefit from including more native species when managing urban green spaces.

The structural organization of mutualism networks, typified by interspecific positive interactions, is important to maintain community diversity. However, there is little information available about the effect of introduced species on the structure of such networks. We compared uninvaded and invaded ecological communities, to examine how two species of invasive plants with large and showy flowers (Carpobrotus affine acinaciformis and Opuntia stricta) affect the structure of Mediterranean plant-pollinator networks. To attribute differences in pollination to the direct presence of the invasive species, areas were surveyed that contained similar native plant species cover, diversity and floral composition, with or without the invaders. Both invasive plant species received significantly more pollinator visits than any native species and invaders interacted strongly with pollinators. Overall, the pollinator community richness was similar in invaded and uninvaded plots, and only a few generalist pollinators visited invasive species exclusively. Invasive plants acted as pollination super generalists. The two species studied were visited by 43% and 31% of the total insect taxa in the community, respectively, suggesting they play a central role in the plant-pollinator networks. Carpobrotus and Opuntia had contrasting effects on pollinator visitation rates to native plants: Carpobrotus facilitated the visit of pollinators to native species, whereas Opuntia competed for pollinators with native species, increasing the nestedness of the plant-pollinator network. These results indicate that the introduction of a new species to a community can have important consequences for the structure of the plant-pollinator network.

Human influence on the environment is so extensive that virtually all ecosystems on the planet are now affected by biological invasions. And, often, ecosystems are invaded by multiple co‐occurring non‐native species. Hence, it is important to understand the impacts these invasions are producing on biodiversity and ecosystem processes.Here, we present results of a 2‐year long field experiment where we tested the effects of co‐occurring invasive C4African grasses in a Cerrado area in central Brazil. We compared plant and arthropod communities, plant biomass, and soil nitrogen dynamics and soil chemical characteristics across five experimental treatments:Urochloa decumbensremoval;Melinis minutifloraremoval; bothU.decumbensandM.minutifloraremoval;U.decumbensandM.minutiflorainvaded plots; and uninvaded Cerrado. We hypothesized that selective removal of invasive grasses would have distinct effects on the native ecosystem structure and functioning. We expected that each invasive grass would produce a different type of impact on the native ecosystem and that their impacts would be synergistic when co‐occurring.Removal ofM.minutifloradoubled native plant diversity and biomass when compared to invaded plots, whereas removal ofU.decumbensdid not alter these parameters. Cerrado plots had four times more plant species than plots cleared of invasives. Removal of invasive grasses did not affect the species richness or community composition of soil epigeal fauna. Cerrado soils had lower fertility, organic matter content and pH than invaded soils. The effects were generally higher when both invasive grasses were removed, suggesting impacts were synergistic, butM.minutiflorahad greater effects on plants and soils thanU.decumbens. Both invasive species produced negative impacts, but a single species was the main driver. We also detected persistent effects of the invasive grass species on the ecosystem after 2 years of removal.We conclude that invasive species of the same functional group have similar types of effects in native ecosystems, but the magnitude of impact was largely dependent on invasive species biomass and cover. Where multiple invasive species are present, research and management of invaded ecosystems should tackle the interacting effects of co‐occurring invaders.

Introduction Invasive alien species are a major concern in the management and conservation of habitats and species worldwide (Crooks 2002; Bax et al. 2003; Levine et al. 2003; Vila et al. 2010). The direct effects of these species may further cascade in the ecosystem and affect inter- and intraspecific ecological interactions. The introduction of alien plants and animals can have severe consequences, not only for individual native plant and pollinator species, but also for their ecological interactions through plant–pollinator networks (Morales and Traveset 2009; Dohzono and Yokoyama 2010; Schweiger et al. 2010). Integration of alien plant and pollinator species into pollination networks inevitably creates new interactions and may also affect the strength and quality of existing ones. These changes are open niches for novel evolutionary adaptations of both alien and native species (Mooney and Cleland 2001). However, research in this topic is very limited, and has focused mostly on adaptations of alien plant species to pollinator-independent reproduction modes (Barrett et al. 2008). We know of no study investigating adaptations of native plant and pollinator species to invaders, and the ecological and possibly evolutionary consequences of these adaptations in the context of plant–pollinator networks. Such adaptations might have far-reaching ecological and evolutionary implications, as has been shown in plant–herbivore and predator–prey interactions (Cox 2004). Here we outline the main effects of species invasions on plant–pollinator interactions, and deduce the main adaptive mechanisms that native plant species can exhibit in response to changes in their pollination regime. Finally, we explore the characteristics of plant populations that are likely to affect their probability of exhibiting such adaptations and their conservation implications. Effects of alien plant and animal species on native plant pollination Several groups of alien organisms have been shown to affect native plant pollination. Most research has focused on alien plants (Morales and Traveset 2009) and flower visitors (Lach 2003; Dohzono and Yokoyama 2010); however, other groups, such as alien herbivores and predators, can also be influential (Traveset and Richardson 2006). In the following, we explore the possible effects of different groups of alien organisms on pollination of native plants.

Globally, grasslands represent a critical but shrinking habitat for native plants and pollinators, with declines driven by alterations to landscape-scale habitat cover and local-scale disturbance regimes, among other factors. Specifically, as cities expand in size, an increasing proportion of regional pasture and grassland habitat is being replaced by urban development, and fewer periodic grazing and burning regimes are being supported locally, despite evidence that such regimes promote plant species richness and facilitate their interaction with native pollinators. The quantification of these plant-pollinator networks—through indices such as network connectance, specialization, nestedness, and robustness—can provide a unique opportunity to characterize key structural properties of species interactions and their response to human management and seasonal phenology. While urbanization and local disturbance regimes likely influence plant and pollinator communities and their interactions, past research in this area has primarily been conducted at limited spatial and temporal scales and has not typically quantified the impacts of both local and landscape forces on network properties. In this study, we investigate the effects of contemporary (past 10 years) and historic (prior 90 years) disturbance regimes on plant-pollinator community composition and network structure across more than 200 km of grassland in Central Texas. Our analyses indicate that for plant and pollinator communities, both contemporary and historic land management practices have led to significantly dissimilar community composition. Plant and pollinator richness and network nestedness are negatively correlated with phenological period, while pollinator richness is positively correlated with landscape-scale (2 km) urbanized land cover and is higher in historically grazed land, likely due to greater food and nesting resource availability. In contrast, we show that network connectance is positively correlated with phenological period and negatively correlated with landscape-scale urban cover. Finally, we show that pollinator robustness, a measure of resilience to plant species loss, is positively correlated with landscape-scale urbanization, likely due to greater redundancy provided by common weedy plant species. Overall, our results demonstrate that historic grazing regimes, current urbanization levels, and distinct phenological periods can simultaneously drive plant-pollinator community composition and network dynamics in shrinking but critical grassland ecosystems.

Invasive species pose a critical threat to ecosystems, with far-reaching consequences. Invasive plants can directly interact with native pollinators, while wind-pollinated grasses indirectly alter plant-pollinator networks by reshaping the composition of plant and animal communities, diminishing ecosystem functioning. Here, we investigated the effect of invasive grass on pollinator richness, native plant visits, and the structure of plant-pollinator networks. Additionally, we explored the influence of non-native honeybees on these same variables in the Caatinga. Invasive grass negatively affected native pollinators and reduced visitation to native plants. The dominance of invasive grass leads to an increased niche overlap among native pollinators. Surprisingly, this did not affect the number of visits by non-native honeybees. However, the increased honeybee visitation negatively impacted native pollinator richness, causing a 60% decline. Our results underscore the compounded negative effects of invasive grass and non-native honeybees on native plant-pollinator dynamics. Invasive grasses indirectly decrease pollinator visits by altering plant communities. Meanwhile, honeybees, unaffected by invasive grass, decrease native pollinator species' richness and visitation rates. These findings emphasize the significant impact of biological invasions on ecosystem health, shedding light on the complex interplay between invasive species and plant-pollinator interactions in arid, abandoned landscapes.

Agricultural landscapes feature marked seasonal changes in the quality and quantity of habitats and floral resources supporting pollinating insects. Seasonal dynamics can affect the structure of plant–pollinator interactions, yet the relative importance of both landscape elements with spatio‐temporal dynamics and those elements that are more static in space and time remains largely unknown. Such an understanding is needed to identify resource‐mediated modifications of plant–pollinator network structures and their functional and management implications. To understand the spatio‐temporal effects of landscape heterogeneity on the structure of plant–pollinator networks, we sampled plant–pollinator (Apiformes—except Apis mellifera ; Syrphidae) communities over three seasonal periods in 12 landscapes in central Germany. The landscapes comprised spatial gradients in the proportion of semi‐natural habitat cover and edge density. To assess temporal changes, we evaluated the cover of mass‐flowering crops in bloom, floral diversity and honey bee density at each plant–pollinator sampling event. Spatio‐temporally dynamic characteristics, particularly the cover of mass‐flowering crops, were more important than static characteristics in explaining variation in plant–pollinator network structure across the three seasonal periods. The richness of plants and pollinators was generally lower when the proportion of mass‐flowering crops was high. Under such conditions, networks were more connected, with greater niche overlap among pollinators, and decreased network specialization (H2′). Richness was higher in landscapes with high edge density, with an increasing effect on network connectance up to a certain threshold. The proportion of semi‐natural habitat cover and floral diversity had differential effects on the richness of plants and pollinators, with strong effects on the dietary niche overlap of the pollinators, potentially indicating a decrease in competition when semi‐natural habitat cover and flower diversity are high. Synthesis and application. To better support plant–pollinator communities in agricultural‐dominated landscapes, we suggest incentivizing the planting of complementary floral resources and preserving or restoring semi‐natural habitat areas. Especially in intensively used agroecosystems, the negative effects of mass‐flowering crops can be mitigated by maintaining flower‐rich edge habitats and relatively small field sizes, which help support plant and pollinator communities, avoid potential negative effects of exploitative competition, and ensure the sustainability of pollination services via increased functional redundancy.

Summary 1. Habitat loss, land use intensification and biological invasions are all threatening pollinator communities, but the combined effects of these factors on pollinator diversity and pollination services have not been studied yet. 2. Here, we tested the hypotheses that (i) the invasive plant Impatiens glandulifera outcompetes native plant communities for pollinators, and (ii) pollinator abundances depend on landscape structure, but are modulated by this mass‐flowering invader. 3. We selected 14 study sites in riparian habitats along a landscape gradient with decreasing proportion of natural land cover. Within each site paired invaded or non‐invaded plots were studied. We performed standardized surveys of pollinators and established experimental plots by adding the native plant Raphanus sativus to assess the impact of I. glandulifera on visitation rates and seed set. 4. Impatiens glandulifera was well integrated in the plant–pollinator network, being visited by several native pollinators, mainly bumblebees. The invader received higher visitation rates than simultaneously flowering native riparian plants and the experimentally added native R. sativus. However, visitation rates to the native plant community showed no significant differences between invaded and non‐invaded plots, with the exception of honeybees, which slightly increased their visits in invaded plots. With regard to the experimental setting, the presence of I. glandulifera reduced bumblebee visitation to R. sativus pots, but had no significant effects on seed set. 5. We found enhanced visitation rates of bumblebees in intensively used agricultural landscapes. However, in the presence of I. glandulifera this landscape effect was masked by bumblebees being highly attracted to I. glandulifera stands independent of the structure of the surrounding landscape. Surprisingly, wild bees and hoverflies were not affected by landscape structure, but, as also the case with bumblebees, they were principally affected by the immediate community flower abundance. 6. Synthesis. Our data provide no evidence that I. glandulifera outcompetes native plants for pollinators. However, social bees were very attracted to this late‐seasonal floral resource. We conclude that both, plant invasions and landscape structure have important effects on the plant–pollinator community studied, but that they operate at different stages of the flowering season.

Ecological communities are dynamic entities subjected to extinction/colonization events. Because species are connected through complex interaction networks, the arrival of a new species is likely to affect various species across the community, as observed in plant biological invasions. However, plant invasions usually represent extreme scenarios in which the community is strongly dominated by the alien species, confounding the effects of a change in species composition with a massive increase in floral resource availability. Our study addresses changes in plant community composition involving native species, a common phenomenon under the current climate change scenario in which plants are modifying their distribution ranges. We experimentally manipulated patches of a natural scrubland community by introducing a native plant (henceforth colonizing plant). To avoid introducing a disproportionate amount of floral resources we adjusted the number of flowers of the colonizing plant to the amount of floral resources locally available in each patch. We had two objectives: (1) to analyse the effects of the arrival of a new plant on the pollinator community, the rearrangement of plant-pollinator interactions and the structure of the plant-pollinator network; (2) to evaluate potential consequences for pollination and the reproductive success of resident plant species. The colonizing plant acted as a magnet species, attracting bumble bees and facilitating interactions to other plants through spill-over. The introduction of the colonizing plant also affected the structure of plant-pollinator networks (colonized networks were more generalized and more nested than control networks) and modified the arrangement of plant and pollinator species into modules. Ultimately, these changes resulted in higher heterospecific (but not conspecific) pollen deposition and had contrasting effects on the reproductive success of two resident plant species (higher fruit set and lower seed set, respectively). Our study shows that relationships between plants and pollinators are rapidly rearranged in response to novel situations (even when the new plant is not overly dominant), with important functional consequences on pollination and plant reproductive success. Our study establishes a link between network structure and pollination and plant reproductive success, which may be mediated by differences among pollinator species in foraging behavior.

Native plant communities are often invaded by multiple alien species. It is still unclear how increasing diversity of alien invasive species suppresses the growth of native species and thus contributes to invasion success. In the subtropical monsoon region of southeast China, we experimentally created a native plant community with 18 herbaceous species. One week later, we let it be invaded by either zero (controls without invasion), one, two, four or eight alien plant species, with either high or low species evenness. After a four‐month growth period we harvested the aboveground biomass of each species. We found that increasing invasive species richness significantly increased invasive plant biomass, the biomass of all invasive and native plant species within the community, and invasion success (the ratio of invasive plant biomass to the biomass of all native and invasive plants), but it did not significantly reduce native plant biomass. Experimentally manipulating invasive species evenness did not influence invasion success and did not show any differential suppression effects on native plants. One invasive species, Sesbania cannabina , became dominant in terms of plant biomass, irrespective of its proportion in the alien plant mixtures. Throughout this experiment, effects of invasive species richness on invasion success were mainly due to such selection effects among the invasive species. On the other hand, the unchanged biomass of native species under increasing invasive plant richness suggests the presence of at least partly complementary resource niches between invasive and native species.

Analyzing plant phenology and plant–animal interaction networks can provide sensitive mechanistic indicators to understand the response of alpine plant communities to climate change. However, monitoring data to analyze these processes is scarce in alpine ecosystems, particularly in the highland tropics. The Andean páramos constitute the coldest biodiversity hotspot on Earth, and their species and ecosystems are among the most exposed and vulnerable to the effects of climate change. Here, we analyze for the first time baseline data for monitoring plant phenological dynamics and plant–pollinator networks along an elevation gradient between 4,200 and 4,600 m asl in three mountain summits of the Venezuelan Andes, which are part of the GLORIA monitoring network. We estimated the presence and density of plants with flowers in all the summits and in permanent plots, every month for 1 year. Additionally, we identified pollinators. We calculated a phenological overlap index between species. We summarized the plant–pollinator interactions as a bipartite matrix and represented a quantitative plant–pollinator network, calculating structural properties (grade, connectance, nestedness, and specialization). We also evaluated whether the overall network structure was influenced by differences in sampling effort, changes in species composition between summits, and phenology of the plant species. Finally, we characterized the pollination syndrome of all species. Flowering showed a marked seasonality, with a peak toward the end of the wet season. The overall phenological overlap index was low (0.32), suggesting little synchrony in flowering among species. Species richness of both plants and pollinators decreased along the elevation gradient. Flies, bumblebees, and hummingbirds were the most frequent pollinators in the network, while entomophily and anemophily were the prevailing pollination syndromes. The interaction network in all summits showed high connectance values, significant specialization (H2), and low nestedness. We did not find a significant effect of sampling effort, summit plant species composition, or plant phenology on network structure. Our results indicate that these high tropical alpine plant communities and their plant-pollination networks could be particularly vulnerable to the loss of species in climate change scenarios, given their low species richness and functional redundancy coupled with a high degree of specialization and endemism.

The vulnerability of plant-pollinator communities to honeybee decline: A comparative network analysis in different habitat types

PDF HTML阅读 XML下载 导出引用 引用提醒 全球气候变暖影响植物-传粉者网络的研究进展 DOI: 10.5846/stxb201309102245 作者: 作者单位: 江西省吉安市青原区学苑路井冈山大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(31060069, 31360099); 教育部新世纪优秀人才支持计划(NCET-07-0385); 江西省自然科学基金项目(2010GZN0129); 江西省高水平学科(生物学) New advances in effects of global warming on plant-pollinator networks Author: Affiliation: College of Life Sciences, Jinggangshan University，Jiangxi Province Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:植物与传粉者间相互作用,构成了复杂的传粉网络。目前,以气候变化为主要特征的全球变暖对植物-传粉者网络的影响备受关注,概述了近年来这方面研究的几个主要热点问题及其进展,和相关研究方法。并在此基础上,提出了气温持续上升背景下,植物-传粉者网络未来的研究趋势。当前研究的主要热点问题有:(1)气候变暖使植物、传粉者的物候发生变化,并通过影响植物的开花时间和传粉者活动时间,导致两者在物候时间上的不同步。(2)气候变暖导致植物、传粉者的群落结构变化,促使其地理分布向更高纬度和更高海拔扩散,这可能潜在的导致两者空间分布的不匹配。(3)植物和传粉者通过增加或减少其丰富度来响应气候变暖,可能导致传粉网络结构特征发生变化。(4)面对气候变暖导致植物和传粉者间物候和地理分布错配所引发的互作改变、甚至解体,传粉网络可通过自身网络结构及快速进化来缓冲和适应。在今后研究中,以下几个问题值得探讨:1)气候变暖对植物-传粉者网络影响的大时空尺度变异模式。2)多因素协同作用对植物-传粉者网络的影响特征。3)全球气候变暖对植物、传粉者物候匹配性影响的机理。 Abstract:The interactions between plants and pollinators result in complex pollination networks. The effects of global climate warming on plant-pollinator networks have attracted extensive attention at present. In this paper, we attempt to introduce several major advances and some new interests in this area. Furthermore, we discussed the future research trends of plant-pollinator networks based on continuously rising temperature. (1) Climate warming makes phenology shift of plants and pollinators by affecting flowering time of plants and activity time of pollinators, which leads to a temporal decoupling of plants and pollinators. (2) Climate warming may cause changes in community structure of plants and pollinators and thus make them distribute to areas in higher latitude and altitude. These changes may result in spatial mismatch of plants and pollinators. (3) Plants and pollinators response to climate warming by increase or decrease its abundance, which may cause changes in structure of pollination networks. (4) The structure and rapid evolution of pollination networks can adapt to the changes or even collapse of interaction between plants and pollinators that result from the phenological and geographical distribution mismatch caused by climate warming. The following contents should be studied in the further research: (1) The effects of climate warming on plant-pollinator networks at large spatiotemporal scales; (2) The effects of multi-factorial synergy on plant-pollinator networks; (3) The mechanism of phenological matching caused by global warming. 参考文献 相似文献 引证文献

Globally, numerous ecosystems have been co-invaded by multiple exotic plant species that can have competitive or facilitative interactions with each other and with native plants. Invaded ecosystems often exhibit spatial heterogeneity in soil moisture and nutrient levels, with some habitats having more nutrient-rich and moist soils than others. The stress-gradient hypothesis predicts that plants are likely to engage in facilitative interactions when growing in stressful environments, such as nutrient-deficient or water-deficient soils. In contrast, when resources are abundant, competitive interactions between plants should prevail. The invasional meltdown hypothesis proposes that facilitative interactions between invasive species can enhance their establishment and amplify their ecological impact. Considering both hypotheses can offer insights into the complex interactions among invasive and native plants across environmental gradients. However, experimental tests of the effects of soil moisture and nutrient co-limitation on interactions between invasive and native plants at both interspecific and intraspecific levels in light of these hypotheses are lacking. We performed a greenhouse pot experiment in which we cultivated individual focal plants from five congeneric pairs of invasive and native species. Each focal plant was subjected to one of three levels of plant-plant interactions: (1) intraspecific, in which the focal plant was grown with another individual of the same species; (2) interspecific, involving a native and an invasive plant; and (3) interspecific, involving two native or invasive individuals. These plant-plant interaction treatments were fully crossed with two levels of water availability (drought vs. well-watered) and two levels of nutrient supply (low vs. high). Consistent with the stress-gradient and invasional meltdown hypotheses, our findings show that under low-nutrient conditions, the biomass production of invasive focal plants was facilitated by invasive interspecific neighbors. However, under high-nutrient conditions, the biomass production of invasive focal plants was suppressed by invasive interspecific neighbors. When competing with native interspecific neighbors, high-nutrient conditions similarly enhanced the biomass production of both invasive and native focal plants. Invasive and native focal plants were neither competitively suppressed nor facilitated by conspecific neighbors. Taken together, these results suggest that co-occurring invasive exotic plant species may facilitate each other in low-nutrient habitats but compete in high-nutrient habitats.