Climate extremes are associated with invertebrate taxonomic and functional composition in mountain lakes

Climate change is expected to increase climate variability and the occurrence of extreme climatic events, with potentially devastating effects on aquatic ecosystems. However, little is known about the role of climate extremes in structuring aquatic communities or the interplay between climate and local abiotic and biotic factors. Here, we examine the relative influence of climate and local abiotic and biotic conditions on biodiversity and community structure in lake invertebrates. We sampled aquatic invertebrates and measured environmental variables in 19 lakes throughout California, USA, to test hypotheses of the relationship between climate, local biotic and environmental conditions, and the taxonomic and functional structure of aquatic invertebrate communities. We found that, while local biotic and abiotic factors such as habitat availability and conductivity were the most consistent predictors of alpha diversity, extreme climate conditions such as maximum summer temperature and dry‐season precipitation were most often associated with multivariate taxonomic and functional composition. Specifically, sites with high maximum temperatures and low dry‐season precipitation housed communities containing high abundances of large predatory taxa. Furthermore, both climate dissimilarity and abiotic dissimilarity determined taxonomic turnover among sites (beta diversity). These findings suggest that while local‐scale environmental variables may predict alpha diversity, climatic variability is important to consider when projecting broad‐scale aquatic community responses to the extreme temperature and precipitation events that are expected for much of the world during the next century.     

Using functional trait diversity to evaluate the contribution of multiple ecological processes to community assembly during succession

Successional chronosequences provide a unique opportunity to study the effects of multiple ecological processes on plant community assembly. Using a series of 0.5 × 0.5 m² plots (n = 30) from five successional sub‐alpine meadow plant communities (ages 3, 5, 9, 12, and undisturbed) in the Qinghai‐Tibetan Plateau, we investigated whether community assembly is stochastic or deterministic for species and functional traits. We tested directional change in species composition, functional trait composition, and then functional trait diversity measured by Rao's quadratic entropy for four traits – plant height, leaf dry matter content, specific leaf area, and seed mass – along two comparable successional chronosequences. We then evaluated the importance of species interactions, habitat filtering and stochasticity by comparing with random communities and partitioning the environmental and spatial components of Rao's quadratic entropy. We found no directional change in species composition, but clear directionality in functional trait composition. None of the abiotic environmental variables (except P) showed linear change with successional age, but soil moisture and nitrogen were positively related to functional diversity within meadows. Functional trait diversity increased significantly with the increase in successional age. Comparison with random communities showed a significant shift from trait divergence in early stages of succession (3‐ and 5‐yr) to convergence in the later stages of succession 9‐, 12‐yr and undisturbed). The relative importance of abiotic variables and spatial structure for functional trait diversity changed in a predictable manner with successional age. Stochasticity at the species level may indicate dispersal limitation, but deterministic effects on functional trait distributions show the role of both habitat effects and biotic interactions.     

Trophic interactions and abiotic factors drive functional and phylogenetic structure of vertebrate herbivore communities across the Arctic tundra biome

Communities are assembled from species that evolve or colonise a given geographic region, and persist in the face of abiotic conditions and interactions with other species. The evolutionary and colonisation histories of communities are characterised by phylogenetic diversity, while functional diversity is indicative of abiotic and biotic conditions. The relationship between functional and phylogenetic diversity infers whether species functional traits are divergent (differing between related species) or convergent (similar among distantly related species). Biotic interactions and abiotic conditions are known to influence macroecological patterns in species richness, but how functional and phylogenetic diversity of guilds vary with biotic factors, and the relative importance of biotic drivers in relation to geographic and abiotic drivers is unknown. In this study, we test whether geographic, abiotic or biotic factors drive biome‐scale spatial patterns of functional and phylogenetic diversity and functional convergence in vertebrate herbivores across the Arctic tundra biome. We found that functional and phylogenetic diversity both peaked in the western North American Arctic, and that spatial patterns in both were best predicted by trophic interactions, namely vegetation productivity and predator diversity, as well as climatic severity. Our results show that both bottom–up and top–down trophic interactions, as well as winter temperatures, drive the functional and phylogenetic structure of Arctic vertebrate herbivore assemblages. This has implications for changing Arctic ecosystems; under future warming and northward movement of predators potential increases in phylogenetic and functional diversity in vertebrate herbivores may occur. Our study thus demonstrates that trophic interactions can determine large‐scale functional and phylogenetic diversity just as strongly as abiotic conditions.     

植物——土壤反馈研究进展

该文综述了植物—土壤反馈研究的定义、途经、方法和国内外的研究现状以及存在的问题。植物—土壤反馈是指植物改变根际土壤的生物和非生物特征,同时被改变的也能提高或降低该植物的生长,形成正的或负的反馈,从而影响植物群落组成及植物间相互作用。植物—土壤反馈研究对于理解植物群落演替、生态系统多样性与生产力形成与维持机制,认识生态系统对气候变化和生物入侵等全球生态事件的响应具有重要的理论意义。外来物种快速生长和繁殖及其可能的负反馈可能会导致本地种被竞争排除,未来气候变化可能导致物种组成发生变化及生物多样性丢失,但资源互补和植物—土壤反馈效应则可能使植物群落具有较高的生产力和多样性。因此,未来植物—土壤反馈关系应该加强以下几方面研究:(1)开展不同生态系统植物—土壤反馈关系的比较研究;(2)植物—土壤及土壤—植物等群落水平的反馈研究;(3)特别是要加强分子和基因工具在植物土壤—反馈关系中的应用,揭示植物—土壤反馈关系的分子机理。     

Invader presence disrupts the stabilizing effect of species richness in plant community recovery after drought

Higher biodiversity can stabilize the productivity and functioning of grassland communities when subjected to extreme climatic events. The positive biodiversity–stability relationship emerges via increased resistance and/or recovery to these events. However, invader presence might disrupt this diversity–stability relationship by altering biotic interactions. Investigating such disruptions is important given that invasion by non‐native species and extreme climatic events are expected to increase in the future due to anthropogenic pressure. Here we present one of the first multisite invader × biodiversity × drought manipulation experiment to examine combined effects of biodiversity and invasion on drought resistance and recovery at three semi‐natural grassland sites across Europe. The stability of biomass production to an extreme drought manipulation (100% rainfall reduction; BE: 88 days, BG: 85 days, DE: 76 days) was quantified in field mesocosms with a richness gradient of 1, 3, and 6 species and three invasion treatments (no invader, Lupinus polyphyllus, Senecio inaequidens). Our results suggest that biodiversity stabilized community productivity by increasing the ability of native species to recover from extreme drought events. However, invader presence turned the positive and stabilizing effects of diversity on native species recovery into a neutral relationship. This effect was independent of the two invader's own capacity to recover from an extreme drought event. In summary, we found that invader presence may disrupt how native community interactions lead to stability of ecosystems in response to extreme climatic events. Consequently, the interaction of three global change drivers, climate extremes, diversity decline, and invasive species, may exacerbate their effects on ecosystem functioning.     

Extreme weather events and plant–plant interactions: shifts between competition and facilitation among grassland species in the face of drought and heavy rainfall

Biotic interactions play an important role in ecosystem function and structure in the face of global climate change. We tested how plant–plant interactions, namely competition and facilitation among grassland species, respond to extreme drought and heavy rainfall events. We also examined how the functional composition (grasses, forbs, legumes) of grassland communities influenced the competition intensity for grass species when facing extreme events. We exposed experimental grassland communities of different functional compositions to either an extreme single drought event or to a prolonged heavy rainfall event. Relative neighbour effect, relative crowding and interaction strength were calculated for five widespread European grassland species to quantify competition. Single climatic extremes caused species specific shifts in plant–plant interactions from facilitation to competition or vice versa but the nature of the shifts varied depending on the community composition. Facilitation by neighbouring plants was observed for Arrhenatherum elatius when subjected to drought. Contrarily, the facilitative effect of neighbours on Lotus corniculatus was transformed into competition. Heavy rainfall increased the competitive effect of neighbours on Holcus lanatus and Lotus corniculatus in communities composed of three functional groups. Competitive pressure on Geranium pratense and Plantago lanceolata was not affected by extreme weather events. Neither heavy rainfall nor extreme drought altered the overall productivity of the grassland communities. The complementary responses in competition intensity experienced by grassland species under drought suggest biotic interactions as one stabilizing mechanism for overall community performance. Understanding competitive dynamics under fluctuating resources is important for assessing plant community shifts and degree of stability of ecosystem functions.     

Sensitivity of three grassland communities to simulated extreme temperature and rainfall events

Three grassland communities in New Zealand with differing climates and proportions of C3 and C4 species were subjected to one‐off extreme heating (eight hours at 52.5°C) and rainfall (the equivalent of 100 mm) events. A novel experimental technique using portable computer‐controlled chambers simulated the extreme heating events. The productive, moist C3/C4 community was the most sensitive to the extreme events in terms of short‐term community composition compared with a dry C3/C4 community or an exclusively C3 community. An extreme heating event caused the greatest change to plant community species abundance by favouring the expansion of C4 species relative to C3 species, shifting C4 species abundance from 43% up to 84% at the productive, moist site. This was observed both in the presence and absence of added water. In the absence of C4 species, heating reduced community productivity by over 60%. The short‐term shifts in the abundance of C3 and C4 species in response to the single extreme climatic events did not have persistent effects on community structure or on soil nitrogen one year later. There was no consistent relationship between diversity and stability of biomass production of these plant communities, and species functional identity was the most effective explanation for the observed shifts in biomass production. The presence of C4 species resulted in an increased stability of productivity after extreme climatic events, but resulted in greater overall shifts in community composition. The presence of C4 species may buffer grassland community productivity against an increased frequency of extreme heating events associated with future global climate change.     

Mutualistic rhizobia reduce plant diversity and alter community composition

Mutualistic interactions can be just as important to community dynamics as antagonistic species interactions like competition and predation. Because of their large effects on both abiotic and biotic environmental variables, resource mutualisms, in particular, have the potential to influence plant communities. Moreover, the effects of resource mutualists such as nitrogen-fixing rhizobia on diversity and community composition may be more pronounced in nutrient-limited environments. I experimentally manipulated the presence of rhizobia across a nitrogen gradient in early assembling mesocosm communities with identical starting species composition to test how the classic mutualism between nitrogen-fixing rhizobia and their legume host influence diversity and community composition. After harvest, I assessed changes in α-diversity, community composition, β-diversity, and ecosystem properties such as inorganic nitrogen availability and productivity as a result of rhizobia and nitrogen availability. The presence of rhizobia decreased plant community diversity, increased community convergence (reduced β-diversity), altered plant community composition, and increased total community productivity. These community-level effects resulted from rhizobia increasing the competitive dominance of their legume host Chamaecrista fasciculata. Moreover, different non-leguminous species responded both negatively and positively to the presence of rhizobia, indicating that rhizobia are driving both inhibitory and potentially facilitative effects in communities. These findings expand our understanding of plant communities by incorporating the effects of positive symbiotic interactions on plant diversity and composition. In particular, rhizobia that specialize on dominant plants may serve as keystone mutualists in terrestrial plant communities, reducing diversity by more than 40 %.     

Feedback effects between plant and flower-visiting insect communities along a primary succession gradient

Primary successions of glacier forelands are unique model systems to investigate community dynamics and assembly processes. However, successional changes of plant and insect communities have been mainly analysed separately. Therefore, changes in plant–insect interactions along successional gradients on glacier forelands remain unknown, despite their relevance to ecosystem functioning. This study assessed how successional changes of the vegetation influenced the composition of the flower-visiting insect assemblages of two plant species, Leucanthemopsis alpina (L.) Heyw. and Saxifraga bryoides L., selected as the only two insect-pollinated species occurring along the whole succession. In addition, we investigated the links between reproductive output of these plants and pollinator abundance through experimental exclusion of pollinators. Plant community structure changed along the succession, affecting the distribution and the abundance of insects via idiosyncratic responses of different insect functional groups. L. alpina interacted with ubiquitously distributed pollinators, while S. bryoides pollinators were positively associated with insect-pollinated plant species density and S. bryoides abundance. With succession proceeding, insect assemblages became more functionally diverse, with the abundance of parasitoids, predators and opportunists positively related to an increase in plant cover and diversity. The reproductive output of both plant species varied among successional stages. Contrary to our expectation, the obligate insect-pollinated L. alpina showed a reproductive output rather independent from pollinator abundance, while the reproductive output of the self-fertile S. bryoides seemed linked to pollinator abundance. Observing ecological interactions and using functional traits, we provided a mechanistic understanding of community assembly processes along a successional gradient. Plant community diversity and cover likely influenced insect community assembly through bottom-up effects. In turn, pollinators regulate plant reproductive output through top-down control. We emphasise that dynamics of alpine plant and insect communities may be structured by biotic interactions and feedback processes, rather than only be influenced by harsh abiotic conditions and stochastic events.     

Community diversity outweighs effect of warming on plant colonization

Abiotic environmental change, local species extinctions and colonization of new species often co‐occur. Whether species colonization is driven by changes in abiotic conditions or reduced biotic resistance will affect community functional composition and ecosystem management. We use a grassland experiment to disentangle effects of climate warming and community diversity on plant species colonization. Community diversity had dramatic impacts on the biomass, richness and traits of plant colonists. Three times as many species colonized the monocultures than the high diversity 17 species communities (~30 vs. 10 species), and colonists collectively produced 10 times as much biomass in the monocultures than the high diversity communities (~30 vs. 3 g/m²). Colonists with resource‐acquisitive strategies (high specific leaf area, light seeds, short heights) accrued more biomass in low diversity communities, whereas species with conservative strategies accrued most biomass in high diversity communities. Communities with higher biomass of resident C4 grasses were more resistant to colonization by legume, nonlegume forb and C3 grass colonists, but not by C4 grass colonists. Compared with effects of diversity, 6 years of 3°C‐above‐ambient temperatures had little impact on plant colonization. Warmed subplots had ~3 fewer colonist species than ambient subplots and selected for heavier seeded colonists. They also showed diversity‐dependent changes in biomass of C3 grass colonists, which decreased under low diversity and increased under high diversity. Our findings suggest that species colonization is more strongly affected by biotic resistance from residents than 3°C of climate warming. If these results were extended to invasive species management, preserving community diversity should help limit plant invasion, even under climate warming.     

Biotic and abiotic variables show little redundancy in explaining tree species distributions

Abiotic factors such as climate and soil determine the species fundamental niche, which is further constrained by biotic interactions such as interspecific competition. To parameterize this realized niche, species distribution models (SDMs) most often relate species occurrence data to abiotic variables, but few SDM studies include biotic predictors to help explain species distributions. Therefore, most predictions of species distributions under future climates assume implicitly that biotic interactions remain constant or exert only minor influence on large‐scale spatial distributions, which is also largely expected for species with high competitive ability. We examined the extent to which variance explained by SDMs can be attributed to abiotic or biotic predictors and how this depends on species traits. We fit generalized linear models for 11 common tree species in Switzerland using three different sets of predictor variables: biotic, abiotic, and the combination of both sets. We used variance partitioning to estimate the proportion of the variance explained by biotic and abiotic predictors, jointly and independently. Inclusion of biotic predictors improved the SDMs substantially. The joint contribution of biotic and abiotic predictors to explained deviance was relatively small (~9%) compared to the contribution of each predictor set individually (~20% each), indicating that the additional information on the realized niche brought by adding other species as predictors was largely independent of the abiotic (topo‐climatic) predictors. The influence of biotic predictors was relatively high for species preferably growing under low disturbance and low abiotic stress, species with long seed dispersal distances, species with high shade tolerance as juveniles and adults, and species that occur frequently and are dominant across the landscape. The influence of biotic variables on SDM performance indicates that community composition and other local biotic factors or abiotic processes not included in the abiotic predictors strongly influence prediction of species distributions. Improved prediction of species' potential distributions in future climates and communities may assist strategies for sustainable forest management.     

Climatic and biotic extreme events moderate long‐term responses of above‐ and belowground sub‐Arctic heathland communities to climate change

Climate change impacts are not uniform across the Arctic region because interacting factors causes large variations in local ecosystem change. Extreme climatic events and population cycles of herbivores occur simultaneously against a background of gradual climate warming trends and can redirect ecosystem change along routes that are difficult to predict. Here, we present the results from sub‐Arctic heath vegetation and its belowground micro‐arthropod community in response to the two main drivers of vegetation damage in this region: extreme winter warming events and subsequent outbreaks of the defoliating autumnal moth caterpillar (Epirrita autumnata). Evergreen dwarf shrub biomass decreased (30%) following extreme winter warming events and again by moth caterpillar grazing. Deciduous shrubs that were previously exposed to an extreme winter warming event were not affected by the moth caterpillar grazing, while those that were not exposed to warming events (control plots) showed reduced (23%) biomass from grazing. Cryptogam cover increased irrespective of grazing or winter warming events. Micro‐arthropods declined (46%) following winter warming but did not respond to changes in plant community. Extreme winter warming and caterpillar grazing suppressed the CO₂ fluxes of the ecosystem. Evergreen dwarf shrubs are disadvantaged in a future sub‐Arctic with more stochastic climatic and biotic events. Given that summer warming may further benefit deciduous over evergreen shrubs, event and trend climate change may both act against evergreen shrubs and the ecosystem functions they provide. This is of particular concern given that Arctic heath vegetation is typically dominated by evergreen shrubs. Other components of the vegetation showed variable responses to abiotic and biotic events, and their interaction indicates that sub‐Arctic vegetation response to multiple pressures is not easy to predict from single‐factor responses. Therefore, while biotic and climatic events may have clear impacts, more work is needed to understand their net effect on Arctic ecosystems.     

The relative role of dispersal and local interactions for alpine plant community diversity under simulated climate warming

Most studies on factors determining diversity are conducted in temperate or warm regions, whereas studies in climatically harsh and low productivity areas, such as alpine regions, are rare. We examined the relative roles of seed availability and different biotic and abiotic factors for the diversity of an alpine plant community in southern Norway. Furthermore, because climate warming is predicted to be an important driver of alpine species diversity, we assessed how the relative impacts of dispersal and local interactions on diversity might change under experimental warming (open top chambers, OTCs).
Addition of seeds from 27 regional species increased community diversity. The establishment of the species was negatively related both to the diversity of the existing system and the cover of the abundant dwarf shrub Dryas octopetala . These results show that both species dispersal limitation and local biotic interactions are important factors for alpine plant community diversity. Despite relatively harsh environmental conditions and low productivity, competition from the resident vegetation appeared to have a greater role for species establishment and diversity than facilitation and experimental warming. Higher temperature appeared to increase the negative relationship between resident species diversity and species establishment. This may suggest that climate warming can increase the role of interspecific competition for alpine plant community structure, and thus alter the long-term effects of biotic interactions on diversity.     

Biotic interactions drive species occurrence and richness in dynamic beach environments

Biotic interactions are predicted to have the strongest influence on species assemblages in extreme environments. We therefore test the hypothesis that in abiotically-severe beaches plant–plant interactions, specifically facilitation, are important relative to abiotic conditions. This hypothesis is tested by assessing the influence of dominant vascular plant species on the fine-scale occurrence and richness of vascular and cryptogam species using a unique dataset of boreal beaches along the Finnish Baltic Sea, characterized by strong post-glacial land uplift and large environmental gradients. We studied three different levels of vegetation patterns across a broad geographical scale; individual species, functional groups and the entire community. Results showed that dominant vascular species strongly drive species occurrence and richness in dynamic beach environments, with some species having an influence similar to that of key abiotic variables. In contrast to expectations, facilitative effects did not dominate in these harsh environments. Instead, the outcomes of biotic interactions were species-specific, and also differed between vascular and cryptogam species, with the former group most strongly influenced by a pioneer species and the latter by a late succession generalist. Our study highlights the importance of incorporating biotic interaction effects into models of multiple vegetation properties and cautions against overly simplistic generalizations to describe relatively idiosyncratic interaction effects.     

Community maturity, species saturation and the variant diversity-productivity relationships in grasslands

Detailed knowledge of the relationship between plant diversity and productivity is critical for advancing our understanding of ecosystem functioning and for achieving success in habitat restoration efforts. However, effects and interactions of diversity, succession and biotic invasions on productivity remain elusive. We studied newly established communities in relation to preexisting homogeneous vegetation invaded by exotic plants in the northern Great Plains, USA, at four study sites for 3 years. We observed variant diversity–productivity relationships for the seeded communities (generally positive monotonic at three sites and non-monotonic at the other site) but no relationships for the resident community or the seeded and resident communities combined at all sites and all years. Community richness was enhanced by seeding additional species but productivity was not. The optimal diversity (as indicated by maximum productivity) changed among sites and as the community developed. The findings shed new light on ecosystem functioning of biodiversity under different conditions and have important implications for restoration.     

Biotic context and soil properties modulate native plant responses to enhanced rainfall

Background and Aims The environmental and biotic context within which plants grow have a great potential to modify responses to climatic changes, yet few studies have addressed both the direct effects of climate and the modulating roles played by variation in the biotic (e.g. competitors) and abiotic (e.g. soils) environment.Methods In a grassland with highly heterogeneous soils and community composition, small seedlings of two native plants, Lasthenia californica and Calycadenia pauciflora, were transplanted into factorially watered and fertilized plots. Measurements were made to test how the effect of climatic variability (mimicked by the watering treatment) on the survival, growth and seed production of these species was modulated by above-ground competition and by edaphic variables.Key Results Increased competition outweighed the direct positive impacts of enhanced rainfall on most fitness measures for both species, resulting in no net effect of enhanced rainfall. Both species benefitted from enhanced rainfall when the absence of competitors was accompanied by high soil water retention capacity. Fertilization did not amplify the watering effects; rather, plants benefitted from enhanced rainfall or competitor removal only in ambient nutrient conditions with high soil water retention capacity.Conclusions The findings show that the direct effects of climatic variability on plant fitness may be reversed or neutralized by competition and, in addition, may be strongly modulated by soil variation. Specifically, coarse soil texture was identified as a factor that may limit plant responsiveness to altered water availability. These results highlight the importance of considering the abiotic as well as biotic context when making future climate change forecasts.     

Influence of microclimate and species interactions on the composition of plant and invertebrate communities in alpine northern Norway

We assessed the effects of both biotic processes and abiotic factors on the community composition of vascular plant species and invertebrates at a site in northern Norway. Plant species were assigned to functional (woody versus herbaceous) and biogeographic (boreal versus alpine) groups. Invertebrate species were classified as either herbivore or predator. When species interactions and effects of the abiotic environment were partitioned, boreal species appeared to influence the distribution of alpine species and woody species the distribution of herbaceous species. Analysis of partial correlations indicated that facilitation was the dominant mode of interaction between the two pairs of plant groups. Among abiotic factors, the thermal environment probably influenced all components of the plant and invertebrate communities, except for predatory invertebrates, and wind appeared important in determining the composition of woody and alpine components of the plant community but not the herbaceous component. The composition of the boreal component of the plant community apparently influenced the composition of all invertebrate communities, except for predatory invertebrates. The composition of the woody component of the plant community influenced the composition of both herbivore and predator communities. The alpine plant-community composition influenced predatory invertebrate community composition. Woody plant community composition influenced the composition of both herbivore and predator communities. Our analytic approach, based on two kinds of structural equation models (d-separation and path analysis), provides a useful method for identifying the biotic as well as abiotic factors that influence community structure.     

Interactive effects of elevation,species richness and extreme climatic events on plant–pollinator networks

Plant–pollinator interactions are essential for the functioning of terrestrial ecosystems, but are increasingly affected by global change. The risks to such mutualistic interactions from increasing temperature and more frequent extreme climatic events such as drought or advanced snow melt are assumed to depend on network specialization, species richness, local climate and associated parameters such as the amplitude of extreme events. Even though elevational gradients provide valuable model systems for climate change and are accompanied by changes in species richness, responses of plant–pollinator networks to climatic extreme events under different environmental and biotic conditions are currently unknown. Here, we show that elevational climatic gradients, species richness and experimentally simulated extreme events interactively change the structure of mutualistic networks in alpine grasslands. We found that the degree of specialization in plant–pollinator networks (H2′) decreased with elevation. Nonetheless, network specialization increased after advanced snow melt at high elevations, whereas changes in network specialization after drought were most pronounced at sites with low species richness. Thus, changes in network specialization after extreme climatic events depended on climatic context and were buffered by high species richness. In our experiment, only generalized plant–pollinator networks changed in their degree of specialization after climatic extreme events. This indicates that contrary to our assumptions, network generalization may not always foster stability of mutualistic interaction networks.     

Disentangling how climate change can affect an aquatic food web by combining multiple experimental approaches

Predicting the biological effects of climate change presents major challenges due to the interplay of potential biotic and abiotic mechanisms. Climate change can create unexpected outcomes by altering species interactions, and uncertainty over the ability of species to develop in situ tolerance or track environmental change further hampers meaningful predictions. As multiple climatic variables shift in concert, their potential interactions further complicate ecosystem responses. Despite awareness of these complexities, we still lack controlled experiments that manipulate multiple climatic stressors, species interactions, and prior exposure of species to future climatic conditions. Particularly studies that address how changes in water availability interact with other climatic stressors to affect aquatic ecosystems are still rare. Using aquatic insect communities of Neotropical tank bromeliads, we combined controlled manipulations of drought length and species interactions with a space‐for‐time transplant (lower elevations represent future climate) and a common garden approach. Manipulating drought length and experiment elevation revealed that adverse effects of drought were amplified at the warmer location, highlighting the potential of climatic stressors to synergistically affect communities. Manipulating the presence of omnivorous tipulid larvae showed that negative interactions from tipulids, presumably from predation, arose under drought, and were stronger at the warmer location, stressing the importance of species interactions in mediating community responses to climate change. The common garden treatments revealed that prior community exposure to potential future climatic conditions did not affect the outcome. In this powerful experiment, we demonstrated how complexities arise from the interplay of biotic and abiotic mechanisms of climate change. We stress that single species can steer ecological outcomes, and suggest that focusing on such disproportionately influential species may improve attempts at making meaningful predictions of climate change impacts on food webs.     

Experimental assessment of biotic and abiotic filters driving community composition

Species occurrence in a site can be limited by both the abiotic environment and biotic interactions. These two factors operate in concert, but their relative importance is often unclear. By experimentally introducing seeds or plants into competition‐free gaps or into the intact vegetation, we can disentangle the biotic and abiotic effects on plant establishment. We established a seed‐sowing/transplant experiment in three different meadows. Species were introduced, as seeds and pregrown transplants, into competition‐free gaps and the intact vegetation. They included 12 resident plants from the locality and 18 species typical for different habitats. Last two years, gaps were overgrown with vegetation from surrounding plants and we observed the competitive exclusion of our focal plants. We compared plant survival with the expected occurrence in target locality (Beals index). Many of the species with habitat preferences different from our localities were able to successfully establish from seeds and grow in the focal habitat if competition was removed. They included species typical for much drier conditions. These species were thus not limited by the abiotic conditions, but by competition. Pregrown transplants were less sensitive to competition, when compared to seedlings germinated from seeds. Beals index significantly predicted both species success in gaps and the ability to withstand competition. Survival in a community is dependent on the adaptation to both the abiotic environment and biotic interactions. Statistically significant correlation coefficients of the ratio of seedling survival in vegetation and gaps with Beals index suggest the importance of biotic interactions as a determinant of plant community composition. To disentangle the importance of abiotic and biotic effect on plant establishment, it is important to distinguish between species pool as a set of species typically found in given community type (determined by Beals index) and a set of species for which the abiotic conditions are suitable.