Plant Community Level Research Articles

Community-level plant–pollinator interactions in a Palaeotropical montane evergreen oak forest ecosystem

ABSTRACT The montane terrain of northern Laos is covered by species-rich subtropical evergreen oak forests, home to endemic tree genera such as Mytilaria (Hamamelidaceae), and characterised by the coexistence of several honeybee and bumblebee species. We explored community-level plant–pollinator interactions of this unique little-known ecosystem. Extensive direct observations on flowering phenology and flower-visitor assemblages of 288 plant species of 82 families were conducted in a montane forest ecosystem in Houaphanh and Xiangkhouang Provinces, Laos, from 2005 until 2016. Based mainly on the extensive flower-visit data, we assessed the pollination system of each plant species. Five sympatric honeybee species (Apis dorsata, A. laboriosa, A. cerana, A. florea and A. andreniformis) were common on various types of flowers, and floral preferences differed among species. Long-tongued bees belonging to Bombini and Anthophorini (Apidae) were species-rich and frequent visitors on various deep flowers, especially Acanthaceae, Balsaminaceae, Lamiaceae, Rubiaceae and Zingiberaceae. Character displacement by tongue length was observed among the bee species, and many relaxed species-specific and species-semispecific interactions were observed between the bees and the deep-flowers. Four plant species, in the genera Mytilaria, Chloranthus, Dioscorea and Cryptocarya, were visited exclusively by thrips. Two plant species, in the genera Lysimachia and Thladiantha, had oil-secreting flowers, which were specifically visited by the oil-collecting bees Macropis and Ctenoplectra, respectively. The dominant pollination system assessed was general insect pollination (31%), followed by long-tongued bee, small bee, honeybee, dipteran, lepidopteran, beetle, wasp, carpenter bee, thrips (e.g. the endemic genus Mytilaria), bird and hemipteran pollination. Our results suggest that the plant–pollinator interactions in the Palaeotropic montane ecosystem are characterised by significant contribution of the five honeybee species and species-rich, morphologically diverse long-tongued bees, both of which have contributed to shaping the remarkable diversity of angiosperms with deep flowers.

Urban green areas retain just a small fraction of tree reproductive diversity of the Atlantic forest

Urban green spaces have gained notoriety in recent years, as they have been argued to play an important role in supporting native biodiversity, ecosystem services and human well-being. However, such a promising perspective is poorly investigated in the tropical context. Here we examine the role played by urban green areas in a major city (Recife-Brazil) as a repository for Atlantic forest biodiversity relative to pollination systems. Plant assemblages were examined across 17 urban green areas and compared to those from ten old-growth forest stands in the largest Atlantic forest remnant in northeastern Brazil (natural areas). Just a small portion of tree species inhabiting urban green areas is native to the northeastern Brazilian Atlantic forest (29.8 %). At plant community-level, squares and parks were impoverished in terms of number of species and individuals with specialized pollination systems (e.g. bats, Sphingids), as compared to forest remnants. Moreover, urban green areas were dominated by generalist-pollinated trees with reproductive traits associated with easily accessible floral resources and an increase of hermaphrodites. Finally, squares and parks had similarly low functional diversity of reproductive traits. Our results suggest that urban green areas support largely distorted and impoverished tree assemblages in terms of floral rewards and pollination, while services are restricted to those offered by generalist small insects. This pattern emerges mainly from the contribution of exotic plants. This largely limits the tropical urban green areas as biodiversity repositories and potential source for specialized pollination services, what calls for a better use of tropical urban areas as conservation tool.

Mowing alters nitrogen effects on the community-level plant stoichiometry through shifting plant functional groups in a semi-arid grassland

Land-use practices such as mowing and nitrogen (N) fertilization can have significant impacts on plant stoichiometry. However, the interactive effects of mowing and N fertilization on the community-level plant stoichiometry and the underlying processes are not well understood. We examined the impacts of mowing (once a year) and N fertilization (12 g N m−2 yr−1) on the community-level plant stoichiometry in a semi-arid grassland on the Loess Plateau. Results obtained showed that mowing alone had no effect on the community-level plant N or phosphorus (P) concentration. N fertilization alone significantly reduced the community-level plant P concentration, but did not affect the community-level plant N concentration, leading to an enhancement of plant N:P ratio. However, mowing altered the effects of N fertilization, leading to a higher plant N (and P) concentration than the fertilization-only plots. Also, mowing significantly reduced soil nitrate (NO3−), but increased soil temperature, photosynthetic active radiation, plant diversity, richness and gross ecosystem productivity. In addition, mowing and N fertilization significantly affected plant community composition through shifting dominant plant functional groups (PFGs) (e.g. asteraceae, forbs and grass). Further, our structural equation modeling analysis showed that shifts in PFGs played an important role in regulating plant stoichiometry under mowing and N fertilization. Together, these results illustrate that effective management of mowing and N fertilization may induce changes in soil limiting nutrients and shifts in plant community composition, potentially altering plant N:P stoichiometry at the community level.

Effects of selenium hyperaccumulators on soil selenium distribution and vegetation properties.

The ecological implications of hyperaccumulation have been investigated at the organismal level, but are poorly understood at the plant community level. Questions addressed here were: Does the presence of selenium (Se) hyperaccumulators affect Se distribution and concentration in their native soil, and do hyperaccumulators affect overall vegetation properties and species composition? Plant survey and soil Se mapping were performed at three seleniferous sites in Colorado. In season one, plots with and without hyperaccumulators were compared for (1) bare ground, canopy cover, and species richness; (2) relative species abundance; (3) soil Se distribution and concentration. In season two, a smaller-scale design was implemented, focusing on areas 3 m in diameter around hyperaccumulators versus nonhyperaccumulators in 44 paired plots on one site. Plots with hyperaccumulators generally showed more bare ground, less canopy cover, higher species richness, and 2-3-fold higher soil Se levels. These patterns were not consistently significant across all sites; the effects of hyperaccumulators may have been diluted by their low abundance and the relatively large area of survey. In the smaller-scale study, highly significant results were obtained, showing more bare ground, less canopy cover, and higher species richness in plots with hyperaccumulators; soil Se concentration was also higher in plots with hyperaccumulators. Hyperaccumulators may significantly affect local soil Se concentration and vegetation over at least a 3 m diameter area, or 4× their canopy. These differences may result from the combined positive and negative allelopathic effects observed earlier at the organismal level.

The Allocation Method of Vegetation Types in the Green Belt of the Bay City Landscape Park

Pan, Z., 2020. The allocation method of vegetation types in the green belt of the bay city landscape park. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 1093–1097. Coconut Creek (Florida), ISSN 0749-0208.In view of the low utilization rate of resources in most of the green belt vegetation allocation methods used in the bay city landscape park, this paper puts forward the research on the allocation methods of green belt vegetation in the bay city landscape park. Analyze the ecological efficiency of the green belt, calculate the value of the direct green service function according to the geographical location of the vegetation filter belt and the river bank buffer belt, establish the regression model, enrich the level of plant community, stabilize the structure of plant community, and realize the allocation of vegetation types in the green belt of the bay city landscape park. The experimental results show that compared with the conventional allocation method, the resource consumption of the proposed method is lower and the resource utilization rate is greatly improved.

Shifts in plant community composition weaken the negative effect of nitrogen addition on community-level arbuscular mycorrhizal fungi colonization.

Nitrogen addition affects plant-arbuscular mycorrhizal fungi (AMF) association greatly. However, although the direct effect of nitrogen addition on AMF colonization has received investigation, its indirect effect through shifts in plant community composition has never been quantified. Based on a 7-year nitrogen addition experiment in an alpine meadow of Qinghai-Tibet Plateau, we investigated the effects of nitrogen addition on plant community, AMF diversity and colonization, and disentangled the direct and indirect effects of nitrogen addition on community AMF colonization. At plant species level, nitrogen addition significantly decreased root colonization rate and altered AMF community composition, but with no significant effect on AMF richness. At plant community level, plant species richness and AMF colonization rate decreased with nitrogen addition. Plant species increasing in abundance after nitrogen addition were those with higher AMF colonization rates in natural conditions, resulting in an increased indirect effect induced by alternation in plant community composition with nitrogen addition, whereas the direct effect was negative and decreased with nitrogen addition. Overall, we illustrate the effect of nitrogen addition and plant species in influencing the AMF diversity, demonstrate how shifts in plant community composition (indirect effect) weaken the negative direct effect of nitrogen addition on community-level AMF colonization rate, and emphasize the importance of plant community-mediated mechanisms in regulating ecosystem functions.

Dominant species' dominant role and spatial stability are enhanced with increasing stocking rate

Stipa breviflora Grisb. (S. breviflora) is a dominant species in the desert steppe of northern China. Its function and role at the plant community level increases with increasing stocking rate. However, the response of spatial stability remains unclear. We selected treatment areas representing no grazing (CK), light grazing (LG), moderate grazing (MG) and heavy grazing (HG) in a long-term grazing experiment (2004–2017) in a S. breviflora desert steppe in Inner Mongolia, northern China. Using a mechanical sampling method, 40 m × 40 m representative sample plots were selected to obtain the height, coverage and density of the S. breviflora population and community, and we computed the standing crop of mechanical sampling quadrats based on a random sample of cutting quadrats. Analysis of standing crop, density of S. breviflora population and its ratio in the plant community showed that the dominant role of S. breviflora population in the plant community increased with increasing grazing intensity, while the spatial stability of S. breviflora population not only had many dimensions, but also many states. The dimension or combination of dimensions of its stability performance and its adaptive state varied under different disturbance intensities and frequencies.

Different responses of leaf and root traits to changes in soil nutrient availability do not converge into a community-level plant economics spectrum

Spatial heterogeneity in soil can influence the distribution of plant communities because plants differ in their ability to acquire resources. In nutrient-poor soils, plants should bear traits that prioritize conservation of resources over growth, whereas the opposite is expected in nutrient-rich soils. A coordinated response to soil fertility, in which leaves and roots converge into the same strategy, would lead to a community-level plant economics spectrum (PEScom). Here, we examine how nutrient availability across different soil types shapes the functional structure of desert shrub communities and how much of this variation is explained by species turnover or intraspecific variability (ITV). We measured leaf and root traits of 16 shrub species in four sites with contrasting soil nutrient availability in the southern edge of the Atacama Desert. In leaves, changes in soil nutrient availability were associated with a leaf economics spectrum, shifting from communities with more acquisitive strategies to communities with more conservative strategies with increasing nutrient limitation. No such pattern of co-variation was observed for roots; thus, the relationship between above and below-ground traits did not fit the PEScom. Variation of leaf traits was mainly determined by species turnover, while for root traits it was determined equally by species turnover and ITV. The lack of a PEScom appears to be related to the co-limitation of multiple resources, which promotes different responses in root traits. We highlight the importance of incorporating leaf and root traits to understand how multiple resource limitation shapes plant ecological strategies.

Myristate and the ecology of AM fungi: significance, opportunities, applications and challenges.

A recent study by Sugiura and coworkers reported the non-symbiotic growth and spore production of an arbuscular mycorrhizal (AM) fungus, Rhizophagus irregularis, when the fungus received an external supply of certain fatty acids, myristates (C:14). This discovery follows the insight that AM fungi receive fatty acids from their hosts when in symbiosis. If this result holds up and can be repeated under nonsterile conditions and with a broader range of fungi, it has numerous consequences for our understanding of AM fungal ecology, from the level of the fungus, at the plant community level, and to functional consequences in ecosystems. In addition, myristate may open up several avenues from a more applied perspective, including improved fungal culture and supplementation of AM fungi or inoculum in the field. We here map these potential opportunities, and additionally offer thoughts on potential risks of this potentially new technology. Lastly, we discuss the specific research challenges that need to be overcome to come to an understanding of the potential role of myristate in AM ecology.

Plant response to N availability in permafrost-affected alpine wetlands in arid and semi-arid climate zones

Nutrient cycling in alpine permafrost-affected wetlands remains insufficiently studied, as it is influenced by a complex network of interrelated climatic and environmental factors, at both regional and local scale. Therefore, we applied mathematical models to examine relationship between environmental factors and plant functional traits reflecting N availability in wetland communities developed under locally variable conditions in a geographic and climatic gradient of high-altitude habitats. Moreover, we assessed impact of local differences in soil chemistry on plant fractionation of N isotopes as a response to N availability. Based on environmental data and chemistry of biomass from 192 study sites from the Pamir Mountains (Tajikistan) and Khangai and Khentei Mountains (Mongolia), a matrix of rank correlations was prepared for regional and local factors and community level plant functional traits. For the traits that were highly correlated either with regional or with local drivers (that is plant N:P ratio and plant δ15N), linear models were built, with a limited set of predictors selected according to the Risk Inflation Criterion and the SOS algorithm. The models were fitted for each of the studied regions. Presented regional models indicated significant influence of soil NH4+ and/or PO43− content on plant N:P ratio, which showed increase with altitude and lowering precipitation. Thus, its values clearly distinguished between the Pamir Mountains (high N:P) and the Mongolian ranges (low N:P). Models for plant δ15N showed its strong positive correlations with soil δ15N and soil salinity. Average values of plant δ15N were comparable for both study areas. The studied plant functional traits showed different response to regional and local drivers. Plant N:P ratio was controlled by regional drivers via their influence on soil NH4+ content. Contrastingly, plant δ15N was significantly affected by local factors, namely soil δ15N and soil salinity expressed as Na:EC.

Enhancement of nutrient resorption efficiency increases plant production and helps maintain soil nutrients under summer grazing in a semi-arid steppe

Grazing regime is the most important factor that alters nutrient cycling in grassland ecosystems. Grazing exclusion has been used for restoration of degraded natural grasslands in Northern China during past two decades, while we propose that 'summer grazing' could be a better management than grazing exclusion for this purpose. Summer grazing allows plants to resorb more nutrients in autumn, thus preventing grazing-induced grassland degradation while keeping grassland in production. However, our understanding of grazing effects on nutrient resorption remains limited. In the present study, we examined plant nitrogen (N) and phosphorous (P) resorption at plant species and community levels in a natural steppe grassland that had experienced contrasting 'summer grazing' versus no-grazing treatments over a 6-year period in central Inner Mongolia. Plant community nutrient resorption efficiency (RE) and resorption fluxes were estimated, along with nutrient return fluxes via animal excreta and litter deposition. We found that (1) Summer grazing at moderate intensity increased plant production, but did not alter soil quality indicators such as soil organic carbon, total nitrogen, and total and plant available phosphorous. (2) Summer grazing increased plant community nutrient RE as the post-grazing plant re-growth with elevated nutrient concentration compensated for the nutrient removal by defoliation. Summer grazing increased nitrogen RE in Leymus chinensis and Cleistogenes squarrosa, but not in Stipa krylovii; and increased phosphorous RE in L. chinensis, but decreased that in S. krylovii and C. squarrosa. (3) Summer grazing accelerated nutrient cycling via animal excreta and litter deposition, but did not reduce plant nutrient resorption fluxes in autumn, which is a major mechanism for plant production enhancement and soil nutrient maintenance under the grazing regime. Our findings provide the key evidence to support moderate-intensity summer grazing as a sustainable grassland management regime to improve plant production while maintaining soil nutrients.

Improving our knowledge of species interaction networks

A recommendation – based on reviews by Nicolas Deguines, Michael Lattorff and three anonymous referees – of the article: Magrach, A., Molina, F. P., and Bartomeus, I. (2020). Niche complementarity among pollinators increases community-level plant reproductive success. bioRxiv, 629931, ver. 7 peer-reviewed and recommended by PCI Ecology. doi: 10.1101/629931. doi: 10.1101/629931

Effects of invasive Cirsium arvense on pollination in a southern Appalachian floral community vary with spatial scale and floral symmetry

Invasive plants can alter pollination dynamics by disrupting pollinator visitation and pollen transfer dynamics. However, a consensus regarding the direction of their overall effects (competitive vs. facilitative) remains elusive. Here, we evaluate the role of floral traits and spatial scale (community vs. floral neighborhood) in mediating invasive Cirsium arvense effects on resident plant species at multiple stages of the pollination process. C. arvense decreased pollinator visitation rate at the community level only for species with radial floral symmetry. At the floral neighborhood scale, pollinator visitation rate to all resident species was lower in the presence of C. arvense regardless of symmetry. C. arvense altered patterns of conspecific pollen receipt at the floral neighborhood scale, but the direction of the effect varied by plant species. We argue that these scale-dependent effects may be mediated by differences in foraging range and behavior of the main pollinators in the community. C. arvense, however, did not affect the overall reproductive success of resident species at either scale, suggesting that plants at our study sites may not be pollen limited. We further show evidence suggesting that C. arvense may alter the structure of community-level plant–plant interactions via heterospecific pollen transfer by subverting the roles of resident pollen donors within the pollen transfer network. Overall, our results suggest that generalized species (with radial flowers) may be more susceptible to invasive species’ effects than specialized ones (bilateral flowers) and highlight the need to consider scale-dependent effects in order to develop a more predictive understanding of invasive species effects in nature.

Responses of peatland vegetation to 15‐year water level drawdown as mediated by fertility level

AbstractQuestionsPeatland ecosystems are a globally important carbon storage that is predicted to turn into a carbon source due to water level drawdown (WLD) associated with climate change. The predictions assume stable plant communities but how realistic is this assumption? If the vegetation is not stable, what are the nature and rate of changes?LocationPeatland complex in Southern Finland.MethodsWe conducted a water level drawdown (WLD of ~10 cm) experiment over 17 years in three peatland types differing in their fertility. On each peatland type, we included an adjacent forestry drained (FD, with water table ca. 40 cm lower than in control) area for comparison.ResultsPeatland type had a clear impact on the response to WLD: at the ecosystem level, the two minerotrophic fens underwent rapid species turnover, while the vegetation in nutrient‐poor bog was more resilient to change. In nutrient‐rich sites, WLD initiated tree canopy development and created understorey conditions that strengthened impact of WLD. In nutrient‐poor site, tree establishment was seen only in the FD area. In addition to high nutrient level, high wetness accelerated change at the plant community level, where we found three types of responses: accelerating change, decelerating change, and stability. Succession resulted in an overall loss of community heterogeneity.ConclusionsInteraction between hydrology, nutrient availability, and biological factors in boreal peatlands is important: the drop in water table required to achieve the shift from open peatland to forested system is inversely proportional to the nutrient level of the system. The results suggest that predictive models of peatland functions under climate change should consider compositional change for fens and their diverse plant communities but are more realistic for bogs. The response of bog vegetation to climate change may, however, be more dependent on changes in rainfall regime and therefore needs to be further addressed.

The influence of bioactive mobile telephony radiation at the level of a plant community – Possible mechanisms and indicators of the effects

Abstract Environmental exposure to radiofrequency electromagnetic fields (RF-EMFs) from mobile telephony has rapidly increased in the last two decades and this trend is expected to continue. The effects of this exposure at plant community level are unknown and difficult to assess in a scientifically appropriate manner. Such an assessment can be scientifically adequate if a studied plant community is completely new and control-impact radiation treatment is used. In this review we aimed to predict ecological effects and identify indicators of the impact of bioactive RF-EMFs at the mobile telephony frequency range on plant communities. We considered the scenario where a plant community was exposed to radiation generated by a base transmitting station antenna mounted on a nearby mast. This plant community can be represented by mesic meadow, ruderal or arable weed community, or other herbaceous, moderately productive vegetation type. We concentrated primarily on radiation effects that can be recorded for a year since the exposure started. To predict them we used physical theories of radiowave propagation in vegetation and the knowledge on plants physiological responses to RF-EMF. Our indicators can be used for the detection of the impact of RF-EMFs on vegetation in a control-impact experiment. The identified indicators can be classified into the following groups: (1) canopy parameters; (2) plant characteristics to be measured in the field or laboratory in a number of individuals that represent the populations of selected species; (3) community weighted means/medians (CWMs) of plant traits and strategies; (4) the abundance of other organisms that interact with plants and can influence their fitness or population size. The group of canopy parameters includes mean height, vertical vegetation structure and dry weight of above-ground standing phytomass. Plant characteristics requiring biometric sampling in the field are plant height, the number of fruits and seeds, as well as seed viability. The group of plant traits that are calculated as CWMs covers seed releasing height, seed dispersal mode, SLA, leaf orientation, month of germination and flowering, Ellenberg’s light indicator value, and the proportion of individuals in the classes of competitors and stress tolerators according to Grime's CSR strategy scheme. The group of “non-plant” indicators includes primarily the frequency of flower visits by beetles, wasps, hoverflies, and bees that have their nests over ground. To detect ecological responses that occur for the first year since a herbaceous community has been exposed to potentially bioactive RF-EMF, the first two indicators groups should be used.

Responses of plant community mycorrhization to anthropogenic influence depend on the habitat and mycorrhizal type

Anthropogenic impact represents a major pressure on ecosystems, yet little is known about how it affects symbiotic relationships, such as mycorrhizal symbiosis, which plays a crucial role in ecosystem functioning. We analyzed the effects of three human impact types – increasing urbanity, introduction of alien plant species (alienness) and modifications in plant species distribution ranges (as a proxy for naturalness) – on plant community overall mycorrhization (including arbuscular, ecto‐, ericoid and orchid mycorrhizal plants) and arbuscular mycorrhization (indicating the degree of forming mycorrhizal symbiosis at plant community level using the relative abundance of mycorrhizal and arbuscular mycorrhizal plants, respectively). The study was carried out in three habitat types, each dominated by a distinct mycorrhizal type – ectomycorrhizal woodlands, ericoid mycorrhizal heathlands and arbuscular mycorrhizal grasslands – at the regional scale in the Netherlands. The response of community mycorrhization and arbuscular mycorrhization to anthropogenic influence showed contrasting patterns, depending on the specific aspect of human impact. Community mycorrhization responded negatively to urbanity and positively to increasing alienness, while arbuscular mycorrhization showed the reverse trend. More natural heathlands were found to be more mycorrhizal and less arbuscular mycorrhizal. The strongest responses were detected in woodlands and heathlands, while mycorrhization in grasslands was relatively insensitive to human impact. Our study highlights the importance of considering mycorrhizal symbiosis in understanding and quantifying the effects of anthropogenic influence on plant communities, especially in woodlands and heathlands.

Soil nutrient levels define herbage yield but not root biomass in a multispecies grass-legume ley

The response of above- and below-ground biomass to soil nutrient availability is crucial for estimating belowground carbon input and predicting changes in soil carbon storage. However, the response is far from clear at plant community level, especially for grassland systems. Using a long-term field experiment initiated 123 years ago with varying soil nutrient levels (deficient, sub-optimal, optimal and over-optimal) established by use of two nutrient sources (animal manure or mineral fertiliser), we examined the effects of soil nutrient level and source on herbage yield and composition, root biomass and root-to-shoot (R/S) ratio of an unfertilised multispecies grass-legume ley. Increased nutrient levels enhanced herbage yield, but did not affect root biomass. The R/S ratio decreased from deficient to sub-optimal level, but remained constant from optimal to over-optimal level. Nutrient source did not influence herbage yield, root biomass or R/S ratio, but the legume proportion increased in soils previously receiving mineral fertiliser. The R/S ratio decreased with herbage yield, but did not vary with herbage composition. We conclude that soil nutrient level and herbage yield rather than nutrient source and herbage composition determine biomass allocation between aboveground and belowground in temperate grassland leys.

Increasing Pollinator Abundance in Undisturbed Mediterranean Montane Habitats over Recent Decades

The widely held notion of “pollinator decline” has mostly arisen from studies undertaken at biologically impoverished, human-managed ecosystems from mid-latitude regions. Long-term studies have been not conducted so far in biologically diverse, well-preserved natural communities. The dynamics of pollinator functional abundance was investigated for 65 plant species sampled over two decades at 29 sites in undisturbed Mediterranean montane habitats of southeastern Spain. At the plant-community level, pollinator abundance increased over the study period, largely because of an increase in solitary bees and, to a lesser extent, beetles. This provides evidence that pollinator declines are not universal beyond anthropogenic ecosystems. Photo credit: Carlos M. Herrera. Photo credit: Carlos M. Herrera. Photo credit: Carlos M. Herrera. Photo credit: Carlos M. Herrera. Photo credit: Carlos M. Herrera. These photographs illustrate the article “Complex long-term dynamics of pollinator abundance in undisturbed Mediterranean montane habitats over two decades” by Carlos M. Herrera published in Ecological Monographs. https://doi.org/10.1002/ecm.1338

Complex long‐term dynamics of pollinator abundance in undisturbed Mediterranean montane habitats over two decades

AbstractCurrent notions of “pollinator decline” and “pollination crisis” mainly arose from studies on pollinators of economic value in anthropogenic ecosystems of mid‐latitude temperate regions. Comprehensive long‐term pollinator data from biologically diverse, undisturbed communities are needed to evaluate the actual extent of the so‐called “global pollination crisis.” This paper analyzes the long‐term dynamics of pollinator abundance in undisturbed Mediterranean montane habitats using pollinator visitation data for 65 plant species collected over two decades. Objectives are (1) to elucidate patterns of long‐term changes in pollinator abundance from the perspectives of individual plant species, major pollinator groups, and the whole plant community and (2) to propose a novel methodological implementation based on combining a planned missing data design with the analytical strength of mixed effects models, which allows one to draw community‐wide inferences on long‐term pollinator trends in species‐rich natural habitats. Probabilistic measurements (“patch visitation probability” and “flower visitation probability” per time unit) were used to assess pollinator functional abundance for each plant species on two separate, randomly chosen years. A total of 13,054 pollinator censuses accounting for a total watching effort of 2,877,039 flower‐min were carried out on 299 different dates. Supra‐annual unstability in pollinator functional abundance was the rule, with visitation probability to flowering patches and/or individual flowers exhibiting significant heterogeneity between years in the majority of plant species (83%). At the plant‐community level, there was a significant linear increase in pollinator functional abundance over the study period. Probability of pollinator visitation to flowering patches and individual flowers increased due to increasing visitation by small solitary bees and, to a lesser extent, small beetles. Visitation to different plant species exhibited contrasting changes, and insect orders and genera differed widely in sign and magnitude of linear abundance trends, thus exemplifying the complex dynamics of community‐wide changes in pollinator functional abundance. Results of this investigation indicate that pollinator declines are not universal beyond anthropogenic ecosystems; stress the need for considering broader ecological scenarios and comprehensive samples of plants and pollinators; and illustrate the crucial importance of combining ambitious sampling designs with powerful analytical schemes to draw reliable inferences on pollinator trends at the plant community level.

Simulation of herbicide impacts on a plant community: comparing model predictions of the plant community model IBC-grass to empirical data

BackgroundSemi-natural plant communities such as field boundaries play an important ecological role in agricultural landscapes, e.g., provision of refuge for plant and other species, food web support or habitat connectivity. To prevent undesired effects of herbicide applications on these communities and their structure, the registration and application are regulated by risk assessment schemes in many industrialized countries. Standardized individual-level greenhouse experiments are conducted on a selection of crop and wild plant species to characterize the effects of herbicide loads potentially reaching off-field areas on non-target plants. Uncertainties regarding the protectiveness of such approaches to risk assessment might be addressed by assessment factors that are often under discussion. As an alternative approach, plant community models can be used to predict potential effects on plant communities of interest based on extrapolation of the individual-level effects measured in the standardized greenhouse experiments. In this study, we analyzed the reliability and adequacy of the plant community model IBC-grass (individual-based plant community model for grasslands) by comparing model predictions with empirically measured effects at the plant community level.ResultsWe showed that the effects predicted by the model IBC-grass were in accordance with the empirical data. Based on the species-specific dose responses (calculated from empirical effects in monocultures measured 4 weeks after application), the model was able to realistically predict short-term herbicide impacts on communities when compared to empirical data.ConclusionThe results presented in this study demonstrate an approach how the current standard greenhouse experiments—measuring herbicide impacts on individual-level—can be coupled with the model IBC-grass to estimate effects on plant community level. In this way, it can be used as a tool in ecological risk assessment.