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Ecological interactions link species in networks. Loss of species from or introduction of new species into an existing network may have substantial effects for interaction patterns. Predicting changes in interaction frequency while allowing for rewiring of existing interactions-and hence estimating the consequences of community compositional changes-is thus a central challenge for network ecology. Interactions between species groups, such as pollinators and flowers or parasitoids and hosts, are moderated by matching morphological traits or sensory clues, most of which are unknown to us. If these traits are phylogenetically conserved, however, we can use phylogenetic distances to construct latent, surrogate traits and try to match those across groups, in addition to observed traits. Understanding how important traits and trait matching are, relative to abundances and chance, is crucial to estimating the fundamental predictability of network interactions. Here, we present a statistically sound approach ("tapnet") to fitting abundances, traits, and phylogeny to observed network data to predict interaction frequencies. We thereby expand existing approaches to quantitative bipartite networks, which so far have failed to correctly represent the nonindependence of network interactions. Furthermore, we use simulations and cross validation on independent data to evaluate the predictive power of the fit. Our results show that tapnet is on a par with abundance-only, matching centrality, and machine learning approaches. This approach also allows us to evaluate how well current concepts of trait matching work. On the basis of our results, we expect that interactions in well-sampled networks can be well predicted if traits and abundances are the main driver of interaction frequency.

1. Switching plant species visited by pollinators (partner flexibility) has been proposed as a behavioural mechanism able to attenuate the negative impacts of shifts in plant communities on pollination. However, it is unclear whether the magnitude of such response is generalizable or depends on the environmental context. Moreover, the ability of pollinators to exploit plants with dissimilar traits (trait flexibility) has been overlooked, even though it can affect the spectrum of new partners available. 2. To shed some light on this problem, we quantified partner and trait flexibility in five communities from four different environments, from Alpine to semi-arid. We evaluated whether the rate at which pollinators incorporated new plant species throughout the flowering season was similar across communities or context dependent. Then, we assessed whether pollinators changed the type of flowers visited and if such trait flexibility was related to their capacity to visit new plant species. Finally, we developed an agent-based model to explore whether diet flexibility can protect pollination when the plant community changes. To this end, we used scenarios of phenological decoupling. 3. In general, pollinators switched interaction partners to cope with the temporal replacement of plant species. Yet, the magnitude of such behaviour varied across communities, probably in response to differences in the number of floral resources available. Also, pollinators were able to visit plant species with dissimilar traits, though both components of diet flexibility (partner identity and traits) did not necessarily covary. Thus, to have a full picture of pollinators' diet flexibility, we need to consider the floral traits of partners. Finally, our theoretical model shows that diet flexibility can protect pollination after shifts in plant communities, but that such positive effects are limited by trait-matching between co-occurring species. 4. Synthesis. Overall, our study highlights the importance of incorporating plant traits when evaluating the ability of pollinators to find new interaction partners. Besides, our simulation results suggest that diet flexibility may not unequivocally protect pollination against changes in plant communities, especially if they entail shifts in the characteristics of the floral assemblage, and hence, the ability of pollinators to find new interaction partners can be compromised., We are thankful to Marcelo Aizen and Carolina Morales for their constructive comments in the initial ideas of this work. Field work from the Monte desert community was funded by CONICET (PIP 6564and 2781) and FONCYT (PICT 20805, 1471, 2010-2779 and 2014-3168). Work at Mediterranean alpine communities was supported by the project LIMITES (CGL2009-07229), MOUNTAINS (CGL2012-38427) and PHENOTYPES (PGC2018-099115-B-100) of the Spanish Ministry of Ministry of Economy and Competitiveness (MINECO). The study on Temperate montane communities was part of the research cooperation ‘Climatic Impacts on Ecosystems and Climatic Adaptation Strategies’ (FORKAST) funded by the Bavarian Ministry of Sciences, Research and the Arts, Germany. CLR was supported by a Juan de la Cierva Incorporación post-doctoral fellowship (Spanish Ministry of Science: IJC2019-041342-I).T.M.-L. was supported by CONICET (PICT-2018-01566). This work did not need field permits as we used databases already available.

The study of mutualistic interaction networks has led to valuable insights into ecological and evolutionary processes. However, our understanding of network structure may depend upon the temporal scale at which we sample and analyze network data. To date, we lack a comprehensive assessment of the temporal scale-dependence of network structure across a wide range of temporal scales and geographic locations. If network structure is temporally scale-dependent, networks constructed over different temporal scales may provide very different perspectives on the structure and composition of species interactions. Furthermore, it remains unclear how various factors – including species richness, species turnover, link rewiring and sampling effort – act in concert to shape network structure across different temporal scales. To address these issues, we used a large database of temporally-resolved plant–pollinator networks to investigate how temporal aggregation from the scale of one day to multiple years influences network structure. In addition, we used structural equation modeling to explore the direct and indirect effects of temporal scale, species richness, species turnover, link rewiring and sampling effort on network structural properties. We find that plant–pollinator network structure is strongly temporally-scale dependent. This general pattern arises because the temporal scale determines the degree to which temporal dynamics (i.e. phenological turnover of species and links) are included in the network, in addition to how much sampling effort is put into constructing the network. Ultimately, the temporal scale-dependence of our plant–pollinator networks appears to be mostly driven by species richness, which increases with sampling effort, and species turnover, which increases with temporal extent. In other words, after accounting for variation in species richness, network structure is increasingly shaped by its underlying temporal dynamics. Our results suggest that considering multiple temporal scales may be necessary to fully appreciate the causes and consequences of interaction network structure. Fil: Schwarz, Benjamin. Albert Ludwigs University of Freiburg; Alemania Fil: Vazquez, Diego P.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina Fil: Cara Donna, Paul J.. Chicago Botanic Garden; Estados Unidos Fil: Knight, Tiffany M.. German Centre for Integrative Biodiversity Research; Alemania Fil: Benadi, Gita. Albert Ludwigs University of Freiburg; Alemania Fil: Dormann, Carsten F.. Albert Ludwigs University of Freiburg; Alemania Fil: Gauzens, Benoit. German Centre for Integrative Biodiversity Research; Alemania Fil: Motivans, Elena. German Centre for Integrative Biodiversity Research; Alemania Fil: Resasco, Julian. University of Colorado; Estados Unidos Fil: Blüthgen, Nico. Universitat Technische Darmstadt; Alemania Fil: Burkle, Laura A.. Montana State University; Alemania Fil: Fang, Qiang. Henan University of Science and Technology; China Fil: Kaiser Bunbury, Christopher N.. University of Exeter; Reino Unido Fil: Alarcón, Ruben. California State University; Estados Unidos Fil: Bain, Justin A.. Chicago Botanic Garden; Estados Unidos Fil: Chacoff, Natacha Paola. Universidad Nacional de Tucumán. Instituto de Ecología Regional. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Ecología Regional; Argentina Fil: Huang, Shuang Quan. Central China Normal University; China Fil: LeBuhn, Gretchen. San Francisco State University; Estados Unidos Fil: MacLeod, Molly. Rutgers University; Estados Unidos Fil: Petanidou, Theodora. Univversity of the Aegean; Estados Unidos Fil: Rasmussen, Claus. University Aarhus; Dinamarca Fil: Simanonok, Michael P.. Montana State University; Estados Unidos Fil: Thompson, Amibeth H.. German Centre for Integrative Biodiversity Research; Alemania Fil: Fründ, Jochen. Albert Ludwigs University of Freiburg; Alemania

Many pollinating animals visit a variety of flowering plant species. Rare plant species pollinated by such generalists may experience a low quality or quantity of pollination, depending on the pollinators' foraging behaviour. How plants cope with this rarity disadvantage is not well understood. One possibility would be to offer a higher floral reward, for example a higher nectar sugar concentration. However, since nectar production is costly, rare plants may only be able to increase their nectar concentration for a limited time and offer little reward afterwards. In this study we performed a laboratory experiment with bumblebees (Bombus terrestris) foraging on artificial flowers of two colours to investigate whether the bees' foraging behaviour produces a rarity disadvantage and if so, whether the rare flower type could improve its pollination success through temporal variation of its nectar sugar concentration, i.e. a temporary increase of nectar sugar followed by a period with low concentration. We found that when both flower colours offered equal rewards, the rare colour received only slightly fewer visits per flower, but had a considerably lower expected pollination success based on the bumblebees' visitation sequences. Temporal variation of the rare colour's sugar concentration increased both the quantity and quality of visits it received. This positive effect was reduced when there were fewer rare flowers or when two bumblebees foraged simultaneously. Our results suggest that temporal variation of floral rewards can alleviate, but not completely eliminate the rarity disadvantage.

Collapsing lemming cycles have been observed across the Arctic, presumably due to global warming creating less favorable winter conditions. The quality of wintering habitats, such as depth of snow cover, plays a key role in sustaining population dynamics of arctic lemmings. However, few studies so far investigated habitat use during the arctic winter. Here, we used a unique long-term time series to test whether lemmings are associated with topographical and vegetational habitat features for their winter refugi. We examined yearly numbers and distribution of 22,769 winter nests of the collared lemming Dicrostonyx groenlandicus from an ongoing long-term research on Traill Island, Northeast Greenland, collected between 1989 and 2019, and correlated this information with data on dominant vegetation types, elevation and slope. We specifically asked if lemming nests were more frequent at sites with preferred food plants such as Dryas octopetala x integrifolia and at sites with increased snow cover. We found that the number of lemming nests was highest in areas with a high proportion of Dryas heath, but also correlated with other vegetation types which suggest some flexibility in resource use of wintering lemmings. Conversely, they showed a distinct preference for sloped terrain, probably as it enhances the formation of deep snow drifts which increases the insulative characteristics of the snowpack and protection from predators. With global warming, prime lemming winter habitats may become scarce through alteration of snow physical properties, potentially resulting in negative consequence for the whole community of terrestrial vertebrates.

Most studies of plant-animal mutualistic networks have come from a temporally static perspective. This approach has revealed general patterns in network structure, but limits our ability to understand the ecological and evolutionary processes that shape these networks and to predict the consequences of natural and human-driven disturbance on species interactions. We review the growing literature on temporal dynamics of plant-animal mutualistic networks including pollination, seed dispersal and ant defence mutualisms. We then discuss potential mechanisms underlying such variation in interactions, ranging from behavioural and physiological processes at the finest temporal scales to ecological and evolutionary processes at the broadest. We find that at the finest temporal scales (days, weeks, months) mutualistic interactions are highly dynamic, with considerable variation in network structure. At intermediate scales (years, decades), networks still exhibit high levels of temporal variation, but such variation appears to influence network properties only weakly. At the broadest temporal scales (many decades, centuries and beyond), continued shifts in interactions appear to reshape network structure, leading to dramatic community changes, including loss of species and function. Our review highlights the importance of considering the temporal dimension for understanding the ecology and evolution of complex webs of mutualistic interactions.

Species phenology plays a key role in determining mutualistic interactions, such as those between plants and pollinators. Notably, temporal synchrony shapes the patterns of interactions by influencing the probability of encounters between interacting partners; thus, species phenology greatly contributes to structuring ecological communities. In these communities, specialized species are expected to show a high level of synchrony with their partners; however, the relationship between species phenology and specialization remains largely unexplored. In three localities in the tropical mountains of Costa Rica, we quantified the level of phenological synchrony in plant-pollinator networks and tested whether phenological synchrony is associated with the degree of pollinator specialization on plant partners. We also tested the relationship between pollinator specialization and the length of the flowering phase of the visited plants. Across all three studied networks, our results show a strong asynchrony between interacting plant and pollinator species. We also found that more specialized pollinators were more asynchronous with their plant partners and, moreover, that specialized pollinators preferably visited plant species with shorter flowering phases compared to generalized pollinators. These patterns suggest that specialized pollinators may be more vulnerable to mutualistic disruptions because they depend primarily on short-lived resources and have a high risk of phenological mismatch. This discovery has important consequences for specialized species' potential to survive and adapt to changes in the phenology of their interacting partners, which is highly relevant in a time characterized by changing climates and associated shifts in species phenology.

Most pollinators have the foraging flexibility to visit a wide variety of plant species. Yet few studies of pollinator-mediated processes in plants have considered the effects of variation in individual foraging patterns on plant reproductive success. In this study, we use an individual-based model of pollinator foraging economics to predict how visitation rates and pollination success of two coflowering plant species change with their frequency (relative abundance). Whereas previous studies suggested that adaptive foraging of pollinators always favors pollination of abundant plant species (positive frequency dependence), here we show that under certain conditions the per capita pollination success of a rare plant species can exceed that of a more abundant species. Specifically, when the overall flower density is sufficiently high and pollinators' perception ranges are sufficiently large, animals with limited memory of previously encountered rewards forage in a way that favors pollination of the rarer plant species. Moreover, even with perfectly informed foragers, a rare plant species benefits more from offering a higher floral reward than a more abundant species. Our results show that adaptive foraging of individual pollinators can have important implications for plant community dynamics and the persistence of rare plant species.

Recent studies have shown that the diversity of flowering plants can enhance pollinator richness and visitation frequency and thereby increase the resilience of pollination. It is assumed that flower traits explain these effects, but it is still unclear which flower traits are responsible, and knowing that, if pollinator richness and visitation frequency are more driven by mass-ratio effects (mean trait values) or by trait diversity. Here, we analyse a three-year data set of pollinator observations collected in a European grassland plant diversity experiment (The Jena experiment). The data entail comprehensive flower trait measurements, including reward traits (nectar and pollen amount), morphological traits (height, symmetry, area, colour spectra) and chemical traits (nectar-amino acid and nectar-sugar concentration). We test if pollinator species richness and visitation frequency of flower communities depend on overall functional diversity combining all flower traits within a community, single trait diversities (within trait variation) and community-weighted means of the single traits, using Bayesian inference. Overall functional diversity did not affect pollinator species richness, but reduced visitation frequency. When looking at individual flower traits separately, we found that single trait diversity of flower reflectance and flower morphology were important predictors of pollinator visitation frequency. Moreover, independent of total flower abundance, community-weighted means of flower height, area, reflectance, nectar-sugar concentration and nectar-amino acid concentration strongly affected both pollinator species richness and visitation frequency. Our results, challenge the idea that functional diversity always positively affects ecosystem functions. Nonetheless, we demonstrate that both single trait diversity and mass-ratio effects of flower traits play an important role for diverse and frequent flower visits, which underlines the functionality of flower traits for pollination services.

In the light of rapid losses of biodiversity worldwide, it has become more important than ever to study the factors that ensure the continued existence of diverse ecological communities. Whereas the diversity-enhancing effects of antagonistic interactions are relatively well understood, much less is known about the contribution of mutualistic interactions to biodiversity maintenance. This study assesses the influence of mutualistic interactions with pollinators on the diversity of plant communities with alternative means of reproduction besides animal pollination. In contrast to a recent more general model of plant-animal mutualisms, the results of our simulations suggest that interactions with pollinators do not generally promote plant diversity, irrespective of the structure of the interaction network. Despite a potential for increased plant species richness through the positive effect of pollinators on plant birth rates, species richness was mostly negatively affected by the presence of pollinators because existing abundance asymmetries were amplified by animal pollination. Our results imply that for plant communities with alternative means of reproduction, the loss of pollinators will usually not lead to decreased diversity. However, whereas the immediate effects of pollinator loss on plant community composition may be negligible, the long-term population genetic consequences are likely to be severe.

Specialization has often been suggested as one of the main factors influencing the stability of ecological systems at the population and community level. Generally, highly specialized systems are believed to be the most sensitive toward disturbances, as the dependence of specialized species on the availability of particular resources or partner species is greatest. The flip side of specialization is, however, that it reduces the intensity of interspecific competition and thus the risk of extinction through competitive exclusion. Moreover, since ecological stability is a highly ambiguous concept, general statements about the relationship between specialization and stability cannot be made based on a single stability criterion. In this study, we examine the relationship between specialization and stability in plant–animal mutualistic systems using a population dynamic model with two species in each group. We compare results for four different stability criteria, both for a general type of plant–animal mutualism and specifically for a plant–pollinator system. Contrary to previous studies which concluded that specialization increases system vulnerability to disturbances, we find that positive, negative and unimodal relationships are possible depending on the stability criterion applied and the characteristics of species interactions. Our results call for further investigations of the consequences of ecological specialization, and emphasize the special properties of pollination mutualisms.

Impacts of climate change on individual species are increasingly well documented, but we lack understanding of how these effects propagate through ecological communities. Here we combine species distribution models with ecological network analyses to test potential impacts of climate change on >700 plant and animal species in pollination and seed-dispersal networks from central Europe. We discover that animal species that interact with a low diversity of plant species have narrow climatic niches and are most vulnerable to climate change. In contrast, biotic specialization of plants is not related to climatic niche breadth and vulnerability. A simulation model incorporating different scenarios of species coextinction and capacities for partner switches shows that projected plant extinctions under climate change are more likely to trigger animal coextinctions than vice versa. This result demonstrates that impacts of climate change on biodiversity can be amplified via extinction cascades from plants to animals in ecological networks., In addition to affecting individual species, climate change can modify species interactions. Coupling simulation models with networks between plants and animal pollinators and seed dispersers, Schleuning et al. show that animal persistence under climate change depends more strongly on plant persistence than vice versa.

Relationships between neighboring groups feature prominently in socioecological theory, but few empirical studies have focused on the effects of neighbors on the behavior of primates. Interactions between neighboring groups are most conspicuous during intergroup encounters, but the likelihood of encounters with neighbors can also affect ranging and activity patterns indirectly, and, as a result, behavioral patterns in areas of exclusive use may differ from those in overlap areas of adjacent home ranges. The aim of this study was to examine intergroup relations and spatial variation in home range use in Verreaux's sifaka (Propithecus verreauxi) during the annual mating season. Based on 230 hr of focal animal data collected from ten members of five adjacent groups, we found that behavioral patterns and patterns of resource utilization were not markedly different between areas of exclusive use and overlap areas of adjacent home ranges. Group cohesion tended to be higher in overlap than in core areas, but the proportion of time spent resting and foraging did not differ between these two areas. However, dominant males exhibited a higher scent-marking rate in overlap areas. Observations during intergroup encounters revealed that chases between males occurred frequently, whereas fights involving physical contact were not observed. We also found that the intergroup dominance hierarchy depended on the relative group size or the number of males in each group, with groups of lower dominance rank exhibiting a tendency to sleep proportionally more often in their core areas. The results of this study suggest that in primate species with a moderate level of intergroup aggression, such as Verreaux's sifaka, the possibility of encountering neighbors in areas of home range overlap does not exert strong influence on their behavior and resource utilization.

Co-flowering plant species commonly share flower visitors, and thus have the potential to influence each other's pollination. In this study we analysed 750 quantitative plant–pollinator networks from 28 studies representing diverse biomes worldwide. We show that the potential for one plant species to influence another indirectly via shared pollinators was greater for plants whose resources were more abundant (higher floral unit number and nectar sugar content) and more accessible. The potential indirect influence was also stronger between phylogenetically closer plant species and was independent of plant geographic origin (native vs. non-native). The positive effect of nectar sugar content and phylogenetic proximity was much more accentuated for bees than for other groups. Consequently, the impact of these factors depends on the pollination mode of plants, e.g. bee or fly pollinated. Our findings may help predict which plant species have the greatest importance in the functioning of plant–pollination networks

One of the most noticeable effects of anthropogenic climate change is the shift in timing of seasonal events towards earlier occurrence. The high degree of variation in species' phenological shifts has raised concerns about the temporal decoupling of interspecific interactions, but the extent and implications of this effect are largely unknown. In the case of plant-pollinator systems, more specialized species are predicted to be particularly threatened by phenological decoupling, since they are assumed to be less flexible in the choice of interaction partners, but until now this hypothesis has not been tested. In this paper, we studied phenology and interactions of plant and pollinator communities along an altitudinal gradient in the Alps as a model for the possible effects of climate change in time. Our results show that even relatively specialized pollinators were much more flexible in their use of plant species as floral resources than their local flower visitation suggested. We found no relationship between local specialization of pollinators and the consistency of their visitation patterns across sites, and also no relationship between specialization and phenological synchrony of pollinators with particular plants. Thus, in contrast to the conclusions of a recent simulation study, our results suggest that most pollinator species included in this study are not threatened by phenological decoupling from specific flowering plants. However, the flexibility of many rarely observed pollinator species remains unknown. Moreover, our results suggest that specialized flower visitors select plant species based on certain floral traits such as the length of the nectar holder tube. If that is the case, the observed flexibility of plant-pollinator interactions likely depends on a high degree of functional redundancy in the plant community, which may not exist in less diverse systems.

Plant-pollinator networks are systems of outstanding ecological and economic importance. A particularly intriguing aspect of these systems is their high diversity. However, earlier studies have concluded that the specific mechanisms of plant-pollinator interactions are destabilizing and should lead to a loss of diversity. Here we present a mechanistic model of plant and pollinator population dynamics with the ability to represent a broad spectrum of interaction structures. Using this model, we examined the influence of pollinators on the stability of a plant community and the relationship between pollinator specialization and stability. In accordance with earlier work, our results show that plant-pollinator interactions may severely destabilize plant coexistence, regardless of the degree of pollinator specialization. However, if plant niche differentiation, a classical stabilizing mechanism, is sufficiently strong to overcome the minority disadvantage with respect to pollination, interactions with pollinators may even increase the stability of a plant community. In addition to plant niche differentiation, the relationship between specialization and stability depends on a number of parameters that affect pollinator growth rates. Our results highlight the complex effects of this particular type of mutualism on community stability and call for further investigations of the mechanisms of diversity maintenance in plant-pollinator systems.

Plant–pollinator interactions are often thought to have been a decisive factor in the diversification of flowering plants, but to be of little or no importance for the maintenance of existing plant diversity. In a recent opinion paper, Pauw (2013 Trends Ecol. Evol . 28, 30–37. ( doi:10.1016/j.tree.2012.07.019 )) challenged this view by proposing a mechanism of diversity maintenance based on pollination niche partitioning. In this article, I investigate under which conditions the mechanism suggested by Pauw can promote plant coexistence, using a mathematical model of plant and pollinator population dynamics. Numerical simulations show that this mechanism is most effective when the costs of searching for flowers are low, pollinator populations are strongly limited by resources other than pollen and nectar, and plant–pollinator interactions are sufficiently specialized. I review the empirical literature on these three requirements, discuss additional factors that may be important for diversity maintenance through pollination niche partitioning, and provide recommendations on how to detect this coexistence mechanism in natural plant communities.