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With the retreat and extinction of glaciers worldwide, new areas are exposed for colonization by diverse plants and associated insects. Yet, glacier retreat is also followed by the loss of plants and insects from local communities, causing changes in species diversity, species composition and plant–insect interactions. However, the impact of glacier retreat and extinction on pollination networks remains poorly understood. An integrative understanding of pollination network dynamics following glacier retreat is therefore of major importance to biodiversity maintenance and ecosystem functioning and services. Here, we addressed how glacier retreat affects directly and indirectly through biodiversity the frequency, complexity, and diversity of plant–insect interactions. After reconstructing the geochronology of glaciers (Mont Miné glacier, Swiss Alps), we surveyed plant–insect interactions and analyzed network dynamics. We observed sharp changes in the diversity of both plant and insect communities. We found an increase in the frequency of their interactions following glacier retreat, but an ultimate decrease with glacier extinction. Yet, after controlling for the effects of flower diversity, interaction frequency showed a regular, ‘universal’ pattern. Accordingly, the complexity of pollination networks and interaction diversity tended to change at constant rates with glacier retreat. Our results indicate that, in the long-term, glacier retreat decreases biodiversity and influence the stability of ecological networks. The good news is that increasing flower diversity would counteract these impacts by increasing interaction diversity and complexity. Supporting plant and flower diversity may therefore be a key strategy for halting the erosion of ecological networks while increasing ecosystem functioning.

Biodiversity is crucial for supporting ecosystem functioning, yet some species play a disproportionate role in maintaining complex ecological processes. Ecosystem engineers are species that directly influence ecosystems by modifying biophysical environments, creating novel habitats, altering biogeochemical cycles, increasing biodiversity and/or modulating ecological processes. Although these species may substantially influence ecosystem functioning, their role is often overlooked and difficult to quantify. Understanding the status, dynamics and trends of ecosystem engineers is essential for mitigating biodiversity loss and maintaining healthy ecosystems. This review reveals the common but underappreciated roles that ecosystem engineers play in ecosystem functioning across many different taxa, biomes and ecological processes. We first synthesise how knowledge of ecosystem engineering improves our understanding of species interactions and the ecological processes underlying both ecosystem functioning and BEF relationships. We provide a conceptual model for addressing the effects of ecosystem engineers in BEF research and ecological dynamics. We provide a ‘how to’ analytical framework for monitoring and quantifying changes in ecosystem engineers and their effects on ecosystem functioning. This framework includes (i) what variables to measure, how and at which scale; (ii) experiments involving species exclusion or removal, introduction and comparative designs when experimental manipulation is not feasible and (iii) statistical, data-driven and theory-driven models. We discuss how to leverage ecosystem engineering in the context of current global change and ecosystem restoration efforts. Including ecosystem engineers in conservation and restoration programs, when implemented in the appropriate context and supported by an understanding of ecological mechanisms and processes, may be crucial for sustaining biological diversity and functional ecosystems.

Intensively managed agricultural landscapes often lack suitable habitats to support diverse wildlife, particularly harming pollinator communities. Besides mass flowering crops, remnant patches of natural and semi-natural vegetation may play a key role in maintaining and conserving biodiversity. Yet, the effects of different natural habitats, including forests and grasslands, on different pollinator communities are poorly understood at the landscape scale. We examined the abundance, richness, and diversity of wild bees and hoverflies, two key pollinator groups, across a land-use gradient spanning forest edges, grassland, wildflower strips, and sunflower monoculture. We also examined the distribution of hoverfly larvae trophic guilds and wild bee nesting traits across the above-mentioned land-use gradient. Finally, we evaluated the impact of landscape structure (forest, grassland, and water cover in the surrounding landscape) on pollinator community composition. Our results indicate that forest and grassland habitats supported a higher abundance and greater richness of pollinators than wildflower strips and sunflower monocultures. Furthermore, hoverflies were more sensitive to habitat and floristic homogenization than wild bees. Sunflower and wildflower habitats also hosted a lower diversity of larvae trophic guilds and wild bee nesting guilds as compared to forests and grasslands. Our study suggests that conserving and restoring forest and grassland habitats within agricultural mosaics may serve as the main ‘refuge’ for wild pollinators.

Plant recruitment interactions (i.e., what recruits under what) shape the composition, diversity, and structure of plant communities. Despite the huge body of knowledge on the mechanisms underlying recruitment interactions among species, we still know little about the structure of the recruitment networks emerging in ecological communities. Modeling and analyzing the community-level structure of plant recruitment interactions as a complex network can provide relevant information on ecological and evolutionary processes acting both at the species and ecosystem levels. We report a data set containing 143 plant recruitment networks in 23 countries across five continents, including temperate and tropical ecosystems. Each network identifies the species under which another species recruits. All networks report the number of recruits (i.e., individuals) per species. The data set includes >850,000 recruiting individuals involved in 118,411 paired interactions among 3318 vascular plant species across the globe. The cover of canopy species and open ground is also provided. Three sampling protocols were used: (1) The Recruitment Network (RN) protocol (106 networks) focuses on interactions among established plants (“canopy species”) and plants in their early stages of recruitment (“recruit species”). A series of plots was delimited within a locality, and all the individuals recruiting and their canopy species were identified; (2) The paired Canopy-Open (pCO) protocol (26 networks) consists in locating a potential canopy plant and identifying recruiting individuals under the canopy and in a nearby open space of the same area; (3) The Georeferenced plot (GP) protocol (11 networks) consists in using information from georeferenced individual plants in large plots to infer canopy-recruit interactions. Some networks incorporate data for both herbs and woody species, whereas others focus exclusively on woody species. The location of each study site, geographical coordinates, country, locality, responsible author, sampling dates, sampling method, and life habits of both canopy and recruit species are provided. This database will allow researchers to test ecological, biogeographical, and evolutionary hypotheses related to plant recruitment interactions. There are no copyright restrictions on the data set; please cite this data paper when using these data in publications., Fondo Europeo de Desarrollo Regional, Grant/Award Number, ICTS-2017-08-CSIC-4; SUMHAL, Grant/Award Numbers: 418RT0555, 501100011033, LIFEWATCH-2019-09-CSIC-13, MCIN/ AEI/10.13039, PGC2018-100966-B-100, PID2020-113157GB-I00, POPE 2014-2020

Despite increasing evidence indicating that invasive species are harming biodiversity, ecological systems and processes, impacts of multiple species invasion and their links with changes in plant and soil communities are inadequately documented and remain poorly understood. Addressing multiple invaders would help to ward against community-wide, synergistic effects, aiding in designing more effective control strategies. In this work, correlative relationships are examined for potential impacts of three co-occurring invasive plant species, Amorpha fruticosa, Fraxinus pennsylvanica, and Acer negundo, on soil conditions and native plant diversity. The research was conducted in riparian ecosystems and included the following treatments: (1) co-occurrence of the three invasive plant species, (2) occurrence of a single invasive species, and (3) control, i.e., absence of invasive species. Co-occurrence of three invasive plant species caused higher direct impact on soil properties, soil functioning, and native plant diversity. Soil in mixed plots (those populated with all three invaders) contained higher levels of nitrifying bacteria, organic matter, nitrogen, and carbon as well as lower carbon to nitrogen ratio as compared to single species invaded plots and control plots. Furthermore, native plant diversity decreased with invasive plants co-occurrence. Differences in soil conditions and lower native plant diversity revealed the interactive potential of multiple invasive species in depleting biodiversity and eroding soil functionality, ultimately affecting ecological and biogeochemical processes both below and above ground. Our results highlight the need to prevent the impact of multispecies invasion, suggesting that riparian ecosystems affected by co-occurring invaders should be prioritized for invasion monitoring and ecological restoration.

AimsHarsh environmental conditions in alpine ecosystems shape vegetation structure into patches, where many different plant species cluster and grow together. Yet, which factors are important for the structure and dynamics of such plant–patch networks remains poorly understood. We aim to assess which and how environmental and biotic factors predict the assembly of plant–patch networks along a mountain range.MethodsWe examined the distribution of plant species in more than 5500 vegetation patches in 37 Mediterranean alpine grasslands distributed along a 500 m altitudinal gradient (National Park of Sierra Guadarrama, Spain). We established a plant–patch network for each grassland community and analyzed how nestedness and modularity vary with environmental (altitude, insolation and soil conditions) and biotic factors (number of species per plot, mean patch area and total pasture area).Important FindingsPlant–patch networks showed consistent, non-random patterns characterized by a nested, but not modular, structure, which suggests that positive associations among co-occurring specialists promote their growth within patches as subsets of a pool with more generalist species. Both nestedness and modularity of plant–patch networks varied among grasslands. Specifically, nestedness decreased with increasing species per plot and increased with mean patch area, while it was independent of environmental variables; modularity increased with increasing pasture area and species per plot. The negative relationship between species per plot and nested patterns may be linked to the restricted number of species that can coexist within the same patch at a given size. Moreover, the positive relationship between patch size and nestedness indicates that the growth of rare plant species within vegetation patches occupied by more abundant species is facilitated in bigger rather than smaller patches. Furthermore, these results indicate that the nested assembly of vegetation patches may be independent of abiotic conditions. These findings suggest that large and unfragmented vegetation patches are fundamental for the maintenance of plant diversity in alpine grasslands. Looking at species distribution at fine spatial scales may shed new light on the biotic processes underlying plant network assembly and provide novel ways for conserving biodiversity.

Plants acting as ecosystem engineers create habitats and facilitate biodiversity maintenance within plant communities. Furthermore, biodiversity research has demonstrated that plant diversity enhances the productivity and functioning of ecosystems. However, these two fields of research developed in parallel and independent from one another, with the consequence that little is known about the role of ecosystem engineers in the relationship between biodiversity and ecosystem functioning across trophic levels. Here, we present an experimental framework to study this relationship. We combine facilitation by plants acting as ecosystem engineers with plant–insect interaction analysis and variance partitioning of biodiversity effects. We present a case‐study experiment in which facilitation by a cushion‐plant species and a dwarf‐shrub species as ecosystem engineers increases positive effects of plant functional diversity (ecosystem engineers and associated plants) on ecosystem functioning (flower visitation rate). The experiment, conducted in the field during a single alpine flowering season, included the following treatments: (1) removal of plant species associated with ecosystem engineers, (2) exclusion (covering) of ecosystem engineer flowers, and (3) control, i.e., natural patches of ecosystem engineers and associated plant species. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases, patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity–ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver. A potential mechanism is that synergy and complementarity between engineers and associated plants increase attractiveness for shared visitors and widen pollination niches. In synthesis, facilitation among plants can scale up to a full network, supporting ecosystem functioning both directly via microhabitat amelioration and indirectly via diversity effects. ISSN:0012-9658 ISSN:1939-9170

AimsEcosystem engineers substantially modify the environment via their impact on abiotic conditions and the biota, resulting in facilitation of associated species that would not otherwise grow. Yet, reciprocal effects are poorly understood as studies of plant–plant interactions usually estimate only benefits for associated species, while how another trophic level may mediate direct and indirect feedback effects for ecosystem engineers is hardly considered.MethodsWe ran a field experiment with two ecosystem engineers (Arenaria tetraquetra and Hormathophylla spinosa) blooming either alone or with associated plants to decompose net effects and to test the hypothesis that pollinator-mediated interactions provide benefits that balance costs of facilitation by ecosystem engineers.Important FindingsWe found that net costs of facilitation are accompanied by pollinator-mediated benefits. Despite ecosystem engineers producing fewer flowers per plant, they were visited by more and more diverse pollinators per flower when blooming with associated plants than when blooming alone. Although seed production per plant was higher when ecosystem engineers bloomed alone, fruit set and seed set varied between species. In one case (A. tetraquetra), fruit and seed sets were negatively affected by the presence of associated plants, whereas, in another case (H. spinosa), fruit set and seed set were higher and unaffected when ecosystem engineers bloomed with associated plants, respectively. Our findings suggest that besides experiencing direct costs, ecosystem engineers can also benefit from facilitating other species via increasing their own visibility to pollinators. Thus, we highlight that pollination interactions can compensate for costs of facilitation depending on ecosystem engineer species. This study illuminates how the outcome of direct plant–plant interactions might be mediated by indirect interactions including third players.

[Background] Plant communities are usually characterised by species composition and abundance, but also underlie a multitude of complex interactions that we have only recently started unveiling. Yet, we are still far from understanding ecological and evolutionary processes shaping the network-level organisation of plant diversity, and to what extent these processes are specific to certain spatial scales or environments. [Aims] Understanding the systemic mechanisms of plant–plant network assembly and their consequences for diversity patterns. [Methods] We review recent methods and results of plant–plant networks. [Results] We synthetize how plant–plant networks can help us to: (a) assess how competition and facilitation may balance each other through the network; (b) analyse the role of plant–plant interactions beyond pairwise competition in structuring plant communities, and (c) forecast the ecological implications of complex species dependencies. We discuss pros and cons, assumptions and limitations of different approaches used for inferring plant–plant networks. [Conclusions] We propose novel opportunities for advancing plant ecology by using ecological networks that encompass different ecological levels and spatio-temporal scales, and incorporate more biological information. Embracing networks of interactions among plants can shed new light on mechanisms driving evolution and ecosystem functioning, helping us to mitigate diversity loss, GL is supported by the Swiss National Science Foundation (IZSEZ0_180195) and by the ETH Biocommunication group. AMN is supported by a Juan de la Cierva-Incorporación fellowship from the Spanish Ministry of Economy and Competitiveness (IJCI-2015-23498). H.S. is supported by the European Research Council (ERC Grant agreement 647038 [BIODESERT]) and by a Juan de la Cierva-Formación fellowship from the Spanish Ministry of Economy and Competitiveness (FJCI-2015-26782)

Species distributions are driven by abiotic conditions that filter species with specific traits and physiological tolerances and match them with their suitable environment. Plant–plant interactions can constrict (through competition) or loosen (through facilitation) the strength of these environmental filters, which in turn inhibit or enhance establishment and recruitment of plant species at a finer spatial scale. Although competition is often the focus of community assembly processes that further impede the entry of plant species into a site, facilitation is also important for potentially loosening environmental filters (especially climatic filters such as temperature and precipitation), ultimately enhancing species occurrence beyond their physiological optimum. We used multiple data sets from the arid site of Rambla del Saltador Valley to test the hypothesis that facilitation by a nurse-plant promotes the presence of herbaceous, beneficiary species beyond their environmental optimum relative to open sites. Furthermore, we propose that the median elevation and community composition of herbaceous species expands with the age of the nurse-plant, and we tested this hypothesis by examining 105 beneficiary species under 50 nurse-plant shrubs varying in age from 6 to 48 years old. We found nurse-plants both facilitate herbaceous species occurrence beyond their median elevation and support more diverse and a distinctly different composition of species in contrast to open sites. Specifically, herbaceous species that originate from a median elevation more than 600 to 700 m above the site only existed beneath nurse-plants, and below this median elevation, half the species only occurred below the nurse-plant. Moreover, the richness and elevation provenance of the herbaceous species increased with increasing nurse-plant age. Our results highlight the importance of facilitation for alleviating physiological strain (in support of the strain hypothesis) and mediating regional species distributions, which has implications for understanding species movements and community assembly at larger-scales under hotter and drier climates., This work was funded by the Spanish Research Agency (AEI) (CGL2017-84515-R). MOB was supported by the Swiss National Science Foundation through an Advanced Postdoc Mobility Fellowship (P300PA_167758). This work contributes to the University of Zurich Research Priority Program on Global Change and Biodiversity (URPP-GCB).