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Functional traits offer a potential avenue to generalize and forecast the impacts of changing competition on plant communities, including changing outcomes of competition among species that currently interact (current competition) or that will interact in the future following range shifts (novel competition). However, it remains unclear how well traits explain variation in the outcomes of current and novel competition as well as the underlying processes determining coexistence or competitive exclusion, under changing climate. Here, we interacted pairs of high and low‐elevation species in three sites across an elevation gradient in the Swiss Alps. For each species pair, we quantified the population‐level outcomes of competition (invasion growth rates), relative fitness differences, and niche overlap and related these to 15 functional traits that were measured in each site. Most traits were significantly associated with invasion growth rates at the low elevation, where species had greater relative fitness differences, but these associations were much weaker towards higher elevations. This appears to be because traits, particularly those associated with light competition, captured species' relative fitness differences at lower elevations, but not at the high elevation site, highlighting that the predictive ability of traits can depend on environmental context. The amplified relative fitness differences towards lower elevations suggest that climate warming may increase the likelihood of competitive exclusion. In addition, novel competitors tended to show greater niche overlap than current competitors, leading to stronger overall competitive effects. However, in general, trait differences predicted competitive outcomes of novel and current competitors similarly well, suggesting that traits can predict interactions between species that do not yet interact. Our study reinforces the importance of considering changing interactions for predicting species responses to climate change and provides experimental evidence supporting the usefulness of functional trait differences in forecasting the impacts of future plant interactions under changing climate. [ABSTRACT FROM AUTHOR]

Major theories regarding microbe‐mediated plant community dynamics assume that plant species cultivate distinct microbial communities. However, few studies empirically assess the role of species‐associated microbial community dissimilarity in plant competitive dynamics.In this study, we paired a competition experiment between eight annual forbs with characterisation of species‐associated fungal communities to assess whether mycobiome dissimilarity is associated with pairwise competitive dynamics.Using a quantitative approach informed by modern coexistence theory, we found that fungal dissimilarity was correlated with both increased stabilising niche differences and fitness inequalities. Additionally, we found that the probability of coexistence increased with mycobiome dissimilarity.When subsetting the community into different fungal functional groups (pathotrophs, saprotrophs, symbiotrophs), overall relationships between dissimilarity and competitive dynamics were independent of these functional groups.Synthesis. These results suggest that fungal community divergence may play an important role in mediating plant competitive dynamics. Although fungal community dissimilarity is associated with both niche and fitness differences, complex biotic and/or abiotic interactions below‐ground may result in an observed correlation between fungal community dissimilarity and plant coexistence. Ultimately, this study suggests a novel approach to better understanding how microbiome dissimilarity may impact host community dynamics. [ABSTRACT FROM AUTHOR]

Plant–soil feedback (PSF), the reciprocal interaction between plants and their soil environment, is a fundamental ecological process that can influence coexistence and functional structure in plant communities. Current theory establishes that PSF may enhance diversity or lead to exclusion depending on whether soil conditioning disproportionately benefits heterospecific or conspecific individuals. However, a more complete picture of the impact of PSF requires understanding how PSF interacts with competition. To that end, here we propose an integrated mathematical model combining trait‐based competition and soil‐explicit PSF. Contrary to the current paradigm, we find that soil conditioning that disproportionately favours conspecific individuals can promote coexistence. Additionally, we show that priority effects are common when soil‐conditioning species differ in their edaphic preferences. These effects can allow species with large differences in competitive ability to coexist under certain soil conditions. Our results provide testable predictions tying community‐level functional patterns in plant communities to PSF and competition. [ABSTRACT FROM AUTHOR]

Just as plants attack heterospecific competitors with allelopathic phytotoxins, they also attack conspecifics with phytotoxins to inhibit seedling germination and growth (autotoxicity). As a result, for many plant species, autotoxicity limits offspring germination and growth proximate to parental plants—consequently reducing deleterious density dependent effects. Autotoxicity appears to vary across species, but it also may vary within species. We tested autotoxicity and variability in six ecotypes of the model plant, Arabidopsis thaliana, using allelopathy bioassays. We found that autotoxic impacts varied across the Eurasian and African ecotypes, and the negative effects on conspecific root growth were greater from above-than belowground exudate. In half the ecotypes, root growth decreased 71% in seedlings treated with exudate from the same ecotype than when treated with exudate from other ecotypes. That the ecotypes limited themselves more than they did other ecotypes is consistent with coexistence theory, which assumes species limit themselves more than others. Moreover, it is consistent with negative density dependent theories that suggest seedling mortality is highest near conspecific adults. Finally, the variation in autotoxicity across ecotypes suggests that intraspecific genetic variability and/or local habitat influence autotoxic intensity. It is well recognized that phytotoxic effect (allelopathy and autotoxicity) varies interspecifically but ecotype-level effects suggests that plants may exhibit greater intraspecific variation in autotoxicity than currently recognized. [ABSTRACT FROM AUTHOR]

Interspecific competition is widely considered a powerful process underlying species coexistence and ecological community structure. Although coexistence theory predicts stronger competition between more ecologically similar species, empirical support has largely relied on inferring competition from patterns of species co-occurrence. Coexistence theory also posits that species can only coexist when individuals compete more with conspecifics than with other species, however, few field studies—particularly in reptiles—have simultaneously estimated the strength of both intra- and interspecific competition among co-occurring species. Using an array of 12 experimental plots, we manipulated species presence and population size by plot of three native Anolis lizard species to empirically estimate the strength of competition on one anole species driven by two other species of varying ecological similarity. We observed that the strength of competition—as determined by relative growth rates and gravidity—was highly predictable and correlated to ecological similarity. Interspecific competition was strongest among species of highest ecological similarity, and intraspecific competition—induced by the addition or removal of conspecifics—was consistently the most intense. By employing direct experimental manipulations, our study provides an empirical investigation of the strength of competition as it relates to ecological similarity. [ABSTRACT FROM AUTHOR]

The competition-colonization (CC) trade-off is a well-studied coexistence mechanism for metacommunities. In this setting, it is believed that the coexistence of all species requires their traits to satisfy restrictive conditions limiting their similarity. To investigate whether diverse metacommunities can assemble in a CC trade-off model, we study their assembly from a probabilistic perspective. From a pool of species with parameters (corresponding to traits) sampled at random, we compute the probability that any number of species coexist and characterize the set of species that emerges through assembly. Remarkably, almost exactly half of the species in a large pool typically coexist, with no saturation as the size of the pool grows, and with little dependence on the underlying distribution of traits. Through a mix of analytical results and simulations, we show that this unlimited niche packing emerges as assembly actively moves communities toward overdispersed configurations in niche space. Our findings also apply to a realistic assembly scenario where species invade one at a time from a fixed regional pool. When diversity arises de novo in the metacommunity, richness still grows without bound, but more slowly. Together, our results suggest that the CC trade-off can support the robust emergence of diverse communities, even when coexistence of the full species pool is exceedingly unlikely. [ABSTRACT FROM AUTHOR]

Work on the Lake Victoria cichlids Pundamilia nyererei (red dorsum males, deeper water), Pundamilia pundamilia (blue males, shallower water) and related species pairs has provided insights into processes of speciation. Here, we investigate the female mating behaviour of 5 Pundamilia species and 4 of their F1 hybrids through mate choice trials and paternity testing. Complete assortative mating was observed among all sympatric species. Parapatric species with similar depth habitat distributions interbred whereas other parapatric and allopatric species showed complete assortative mating. F1 hybrids mated exclusively with species accepted by females of the parental species. The existence of complete assortative mating among some currently allopatric species suggests that pre-existing mating barriers could be sufficient to explain current patterns of co-existence, although, of course, many other factors may be involved. Regardless of the mechanism, mating preferences may influence species distribution in potentially hybridizing taxa, such as in the adaptive radiation of cichlid fish. We suggest that this at least partly explains why some species fail to establish breeding populations in locations where they are occasionally recorded. Our results support the notion that the mating preferences of potentially cross-breeding species ought to be included in coexistence theory. [ABSTRACT FROM AUTHOR]

Intraspecific trait variation is ubiquitous and is likely to influence species coexistence. Despite theoretical progress, empirical work on the effects of intraspecific variation on the dynamics of competing species is rare. This is because of the formidable empirical requirements necessary to link intraspecific variation in species' functional traits with intraspecific variation in the demographic and competitive rates that mediate coexistence. Here we partially overcome these challenges to determine how intraspecific variation in reproductive phenology in a native Californian annual plant species Lasthenia californica affects its ability to coexist with two non‐native species Bromus madritensis and Lactuca serriola that display contrasting phenological patterns. Using data from a field experiment, we empirically parameterize a model of competitive population dynamics, accounting for the effects of intraspecific phenological trait variation on the native species' response to both intra‐ and interspecific competition. We find that intraspecific variation in phenology drives differences in the native species' response to competition. Moreover, simulations of the parameterized model show that this variation improves the competitive performance of the native species. This occurs because of the effects of nonlinear averaging mediated by a nonlinear, concave‐up competition function that is a general feature of competition across a wide range of taxa. While intraspecific variation improves competitive performance, we also find that the magnitude of the benefit is predicted to be insufficient to prevent competitive exclusion against the non‐native species with early phenogy Bromus. Against the second non‐native species with later phenology Lactuca, intraspecific variation is predicted to result in coexistence where competitive exclusion would otherwise occur, but we could not rule out alternative qualitative outcomes for this interaction. [ABSTRACT FROM AUTHOR]

Explaining the maintenance of diverse species assemblages is a central goal of ecology and conservation. Recent coexistence mechanisms highlight the role of dispersal as a source of the differences that allow similar species to coexist. Here, we propose a new mechanism for species coexistence that is based on dispersal differences, and on the geometry of the habitat patch. In a finite habitat patch with complex boundaries, species with different dispersal abilities will arrange themselves in stable, concentric patterns of dominance. Species with superior competitive and dispersal abilities will dominate the interior of the patch, with inferior species at the periphery. We demonstrate and explain the mechanism on a simple one-dimensional domain, and then on two-dimensional habitat patches with realistic geometries. Finally, we use metrics from landscape ecology to demonstrate that habitat patches with more complex geometries can more easily support coexistence. The factors that underpin this new coexistence mechanism—different dispersal abilities and habitat patches with complex geometries—are common to many marine and terrestrial ecosystems, and it is therefore possible that the mechanism is a common factor supporting diverse species assemblages. [ABSTRACT FROM AUTHOR]

The ability of native communities to maintain invasion resistance in the face of environmental changes is crucial for biodiversity conservation. However, previous studies have primarily focused on the inhibitive effects experienced by invaders, providing limited insights into the ultimate outcome of resistance.In this study, we integrated modern coexistence theory into biotic resistance research to investigate the impact of nutrient enrichment on the resistance of Phragmites australis marshes to Spartina alterniflora invasion in the Yangtze estuary saltmarshes of China.Our results demonstrated that under non‐enriched conditions, successful invasion resistance was facilitated by stable coexistence between native and invasive species in the field. This prediction of invasion resistance aligned with the distribution dynamics of the two species in the Yangtze estuary saltmarshes over the past two decades. However, nutrient enrichment was likely to lead to a fundamental shift in their coexistence and ultimately, the failure of resistance.Synthesis and applications. Integrating modern coexistence theory into biotic resistance studies advances the assessment of invasion resistance by shifting from quantifying relative strength to predicting explicit resistance outcomes. Ecosystem managers can draw explicit conclusions about the potential establishment and impact of invaders by analysing observational or experimental data within the framework of modern coexistence theory. This information aids in identifying the most efficient strategies for addressing invasive species. [ABSTRACT FROM AUTHOR]

Ecological differences between coexisting species within plant communities can be assessed by considering functional and phylogenetic dissimilarities either separately or in a complementary way. Here, we studied (a) the potential overlap between functional (FD) and phylogenetic diversities (PD) and (b) their combined and unique roles in explaining community assembly patterns across different temperate vegetation types and across functional traits representing multiple dimensions of plant strategy (plant size, leaf, floral and reproductive, clonal and bud bank traits).We tested the strength of the PD–FD relationship within and across vegetation types and functional traits (Pearson correlations) and tested whether it depended on the strength of the phylogenetic signal (Pagel's lambda and Blomberg's K). We tested deviations from random expectations in FD and 'decoupled FD' (i.e. functional dissimilarity after accounting for the effect of phylogenetic distances between species) to reveal the importance of ecological differences for community assembly.PD–FD correlations were predominantly significant but rarely strong, and largely depended on the studied functional trait and vegetation type. Phylogenetic signals were partially but inconsistently related to the overlap between FD and PD.Community assembly patterns tended to shift from under‐dispersion (FD lower than random expectations) towards over‐dispersion (FD higher than random expectations) when functional distances were decoupled from phylogenetic distances indicating that species within the same clade were dissimilar to each other regarding their traits. However, we found the opposite pattern as well, mainly for floral and below‐ground traits, which indicated functional differentiation across clades.Synthesis. Decoupling functional and phylogenetic differences between species might provide further information on plant community assembly: showing cases where the strongest ecological differentiation between coexisting species occurs between phylogenetically related species rather than between phylogenetically unrelated ones. [ABSTRACT FROM AUTHOR]

Phosphorus, Iron and Aluminum are the key elements in solar cell materials and typically difficult to remove during MG-Si refining process. The evaluations of their thermodynamic properties in Si dilute solutions are crucial for the possibility and efficiency of impurities elimination process. In the present study, the activities and self-interaction parameters of P、Fe and Al in molten Si at 1723-1873 K were investigated by applying the models of mass action concentrations for Si-P、Si-Fe and Si-Al Binary Solution. The activities of Fe, Al with a mass concentration range of 1–2000 ppmw and P with a mass concentration range of 1–100 ppmw in dilute Si-based solutions are calculated by the model. The effects of temperature and impurity concentration on the thermodynamic properties of Si-based binary solutions were also determined by the models. [ABSTRACT FROM AUTHOR]

Research in community ecology has tended to focus on trophic interactions (e.g., predation, resource competition) as driving forces of community dynamics, and sexual interactions have often been overlooked. Here we discuss how sexual interactions can affect community dynamics, especially focusing on frequency‐dependent dynamics of horizontal communities (i.e., communities of competing species in a single ecological guild). By combining mechanistic and phenomenological models of competition, we place sexual reproduction into the framework of modern coexistence theory. First, we review how population dynamics of two species competing for two resources can be represented by the Lotka–Volterra competition model as well as frequency dynamics, and how niche differentiation and overlap produce negative and positive frequency‐dependence (i.e., stable coexistence and priority effect), respectively. Then, we explore two situations where sexual interactions change the frequency‐dependence in community dynamics: (1) reproductive interference, that is, negative interspecific interactions due to incomplete species recognition in mating trials, can promote positive frequency‐dependence and (2) density‐dependent intraspecific adaptation load, that is, reduced population growth rates due to adaptation to intraspecific sexual (or social) interactions, produces negative frequency‐dependence. We show how reproductive interference and density‐dependent intraspecific adaptation load can decrease and increase niche differences in the framework of modern coexistence theory, respectively. Finally, we discuss future empirical and theoretical approaches for studying how sexual interactions and related phenomena (e.g., reproductive interference, intraspecific adaptation load, and sexual dimorphism) driven by sexual selection and conflict can affect community dynamics. [ABSTRACT FROM AUTHOR]

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Classic ecological theory explains species coexistence in variable environments. While spatial variation is often treated as an intrinsic feature of a landscape, it may be shaped and even generated by the resident community. All species modify their local environment to some extent, driving changes that can feed back to affect the composition and coexistence of the community, potentially over timescales very different from population dynamics. We introduce a simple nested modeling framework for community dynamics in heterogeneous environments, including the possible evolution of heterogeneity over time due to community-environment feedbacks. We use this model to derive analytical conditions for species coexistence in environments where heterogeneity is either fixed or shaped by feedbacks. Among other results, our approach reveals how dispersal and environmental specialization interact to shape realized patterns of habitat association and demonstrates that environmental feedbacks can tune landscape conditions to allow the stable coexistence of any number of species. Our flexible modeling framework helps explain feedback dynamics that arise in a wide range of ecosystems and offers a generic platform for exploring the interplay between species and landscape diversity. [ABSTRACT FROM AUTHOR]

Plant–arbuscular mycorrhizal fungal (AMF) associations can mediate soil resources among competing plants to influence plant resource capture and fitness, making AMF a potential agent of plant coexistence. We assessed plant coexistence, via niche and fitness differences, using six plant species varying in their mycorrhizal status. We grew the species in 15 competitive pairs with or without AMF. Effects of AMF on coexistence were determined by parametrizing pair-wise Lotka–Volterra plant competition models. Responses of the six plant species to AMF were determined by comparing the shoot biomass of single plants grown in the absence of any competition with AMF to the shoot biomass without AMF. The inoculation with AMF reduced the fitness differences between competitors, but the degree of AMF-mediated coexistence depended on the identity of the competing plant species. A greater AMF response difference between competing plant species reduced niche overlap and increased coexistence. These results show that while AMF generally reduce fitness differences, the equalizing effect of AMF is not always strong enough to overcome a competitive imbalance due to niche overlap and thus does not always lead to coexistence. Instead, it is the intrinsic growth response of different plant species to AMF, which can predict reduced niche overlap that in turn leads to coexistence. This implies that mycorrhizal dependence is a plant strategy to reduce niche overlap with competitors, thus allowing for greater coexistence. [ABSTRACT FROM AUTHOR]

Understanding the effects of evolution on emergent population properties such as intrinsic growth rates, species abundances or resilience is not only a key theoretical question, but has major empirical implications, for instance in conservation, agroecology and invasion ecology. Evolution can also lead to polymorphism based on niche differentiation among different phenotypes. The present article has three aims. First, we clarify the evolutionary scenarios allowing for optimization of population growth rate and abundance. Second, we relate the eco‐evolutionary emergence of polymorphism to the niche‐overlap and fitness‐ratio sensu coexistence theory. Third, we discuss whether properties of polymorphic populations can be optimized due to niche‐displacement among phenotypes. We revisit previous theoretical results on eco‐evolutionary optimization and link them with our Lotka–Volterra framework. Depending on how the traits under selection affect species intrinsic growth rates or ecological interactions, we uncover three scenarios, ranging from the optimization of all three properties to no optimization and link evolutionary dynamics to coexistence theory. Optimization is, in general, incompatible with niche differentiation sensu coexistence theory and, therefore, with the emergence of polymorphism. Niche displacement between resident and mutant phenotypes, and potentially polymorphism, only arise when we do not expect optimality to hold. Finally, we show how our approach can be generalized to coevolutionary scenarios. In the discussion, we propose biological scenarios and traits that may fall into our three scenarios. Although it is possible to find traits for which optimality is expected, for the majority of the cases optimization arguments do not hold. We also provide practical applications of our results in conservation, agroecology, harvesting and invasion ecology. [ABSTRACT FROM AUTHOR]

Competition is among the most important factors regulating plant population and community dynamics, but we know little about how different vital rates respond to competition and jointly determine population growth and species coexistence. We conducted a field experiment and parameterised integral projection models to model the population growth of 14 herbaceous plant species in the absence and presence of neighbours across an elevation gradient (284 interspecific pairs). We found that suppressed individual growth and seedling establishment contributed the most to competition‐induced declines in population growth, although vital rate contributions varied greatly between species and with elevation. In contrast, size‐specific survival and flowering probability and seed production were frequently enhanced under competition. These compensatory vital rate responses were nearly ubiquitous (occurred in 92% of species pairs) and significantly reduced niche overlap and stabilised coexistence. Our study highlights the importance of demographic processes for regulating population and community dynamics, which has often been neglected by classic coexistence theories. [ABSTRACT FROM AUTHOR]

For millennia, societies have tried to find ways to sustain people's livelihoods by setting rules to equitably and sustainably access, harvest and manage common pools of resources (CPR) that are productive and rich in species. But what are the elements that explain historical successes and failures? Elinor Ostrom suggested that it depends on at least eight axiomatic principles of good governance, whereas empirical results suggest that these principles are not sufficient to describe them, especially when applied to CPRs that possess great social and ecological diversity. The aim of this article is to explore the behavior of a mathematical model of multi-species forest dynamics that respects the foundations of ecology and Ostrom's governance theory, in order to detect possible constraints inherent to the functioning of these complex systems. The model reveals that fundamental structural laws of compatibilities between species life-history traits are indeed constraining the level of co-existence (average and variance) between a diversity of co-vulnerable timber resource users (RU) and of competing tree species. These structural constraints can also lead to unexpected outcomes. For instance in wetter forest commons, opening up the access to as many diverse RUs as there are competing tree species, produces a diversity of independently-controlled disturbances on species, collectively improving the chances of coexistence between species with different life-history traits. Similar benefits are observed on forest carbon and on profits from timber harvesting. However in drier forest commons, the same benefits cannot be observed, as predicted on the basis of the constraining laws. The results show that the successes and failures of certain management strategies can be reasonably explained by simple mechanistic theories from ecology and the social-ecological sciences, which are themselves constrained by fundamental ecological invariants. If corroborated, the results could be used, in conjunction with Ostrom's CPR theory, to understand and solve various human-nature coexistence dilemmas in complex social-ecological systems. [ABSTRACT FROM AUTHOR]

For millennia, societies have tried to find ways to sustain people’s livelihoods by setting rules to equitably and sustainably access, harvest and manage common pools of resources (CPR) that are productive and rich in species. But what are the elements that explain historical successes and failures? Elinor Ostrom suggested that it depends on at least eight axiomatic principles of good governance, whereas empirical results suggest that these principles are not sufficient to describe them, especially when applied to CPRs that possess great social and ecological diversity. The aim of this article is to explore the behavior of a mathematical model of multi-species forest dynamics that respects the foundations of ecology and Ostrom’s governance theory, in order to detect possible constraints inherent to the functioning of these complex systems. The model reveals that fundamental structural laws of compatibilities between species life-history traits are indeed constraining the level of co-existence (average and variance) between a diversity of co-vulnerable timber resource users (RU) and of competing tree species. These structural constraints can also lead to unexpected outcomes. For instance in wetter forest commons, opening up the access to as many diverse RUs as there are competing tree species, produces a diversity of independently-controlled disturbances on species, collectively improving the chances of coexistence between species with different life-history traits. Similar benefits are observed on forest carbon and on profits from timber harvesting. However in drier forest commons, the same benefits cannot be observed, as predicted on the basis of the constraining laws. The results show that the successes and failures of certain management strategies can be reasonably explained by simple mechanistic theories from ecology and the social-ecological sciences, which are themselves constrained by fundamental ecological invariants. If corroborated, the results could be used, in conjunction with Ostrom’s CPR theory, to understand and solve various human-nature coexistence dilemmas in complex social-ecological systems.

Pathogen coexistence depends on ecological processes operating at both within and between‐host scales, making it difficult to quantify which processes may promote or prevent coexistence. Here, we propose that adapting modern coexistence theory—traditionally applied in plant communities—to pathogen systems provides an exciting approach for examining mechanisms of coexistence operating across different spatial scales. We first overview modern coexistence theory and its mechanistic decomposition; we subsequently adapt the framework to quantify how spatial variation in pathogen density, host resources and immunity, and their interaction may promote pathogen coexistence. We apply this derivation to an example two pathogen, multiscale model comparing two scenarios with generalist and strain‐specific immunity: one with demographic equivalency among pathogens and one with demographic trade‐offs among pathogens. We then show how host–pathogen feedbacks generate spatial heterogeneity that promote pathogen coexistence and decompose those mechanisms to quantify how each spatial heterogeneity contributes to that coexistence. Specifically, coexistence of demographically equivalent pathogens occurs due to spatial variation in host resources, immune responses, and pathogen aggregation. With a competition–colonization trade‐off, the superior colonizer requires spatial heterogeneity to coexist, whereas the superior competitor does not. Finally, we suggest ways forward for linking theory and empirical tests of coexistence in disease systems. [ABSTRACT FROM AUTHOR]

Resource competition theory predicts coexistence and exclusion patterns based on species' R *s, the minimum resource values required for a species to persist. A central assumption of the theory is that all species have equal access to resources. However, many systems are characterized by preemption exploitation, where some species deplete resources before their competitors can access them (e.g., asymmetric light competition, contest competition among animals). We hypothesized that coexistence under preemption requires an R *-preemption trade-off—that is, the species with the priority access should have a higher R * (lower "efficiency"). Thus, we developed an extension of resource competition theory to investigate partial and total preemption (in the latter, the preemptor is unaffected by species with lower preemption rank). We found that an R *-preemption trade-off is a necessary condition for coexistence in all models. Moreover, under total preemption, the trade-off alone is sufficient for coexistence. In contrast, under partial preemption, more conditions are needed, which restricts the parameter space of coexistence. Finally, we discuss the implications of our finding for seemingly distinct trade-offs, which we view as special cases of the R *-preemption trade-off. These trade-offs include the digger-grazer trade-off, the competition-colonization trade-off, and trade-offs related to light competition between trees and understories. [ABSTRACT FROM AUTHOR]

Janzen–Connell effects (JCEs), specialised predation of seeds and seedlings near conspecific trees, are hypothesised to maintain species richness. While previous studies show JCEs can maintain high richness relative to neutral communities, recent theoretical work indicates JCEs may weakly inhibit competitive exclusion when species exhibit interspecific fitness variation. However, recent models make somewhat restrictive assumptions about the functional form of specialised predation—that JCEs occur at a fixed rate when offspring are within a fixed distance of a conspecific tree. Using a theoretical model, I show that the functional form of JCEs largely impacts their ability to maintain coexistence. If predation pressure increases additively with adult tree density and decays exponentially with distance, JCEs maintain considerably higher species richness than predicted by recent models. Loosely parameterising the model with data from a Panamanian tree community, I elucidate the conditions under which JCEs are capable of maintaining high species richness. [ABSTRACT FROM AUTHOR]

Recent developments in understanding and predicting species responses to climate change have emphasised the importance of both environmental variability and consideration of the wider biotic community. However, to date, the interaction between the two has received less attention. Both theoretical and empirical results suggest that the combined effect of environmental variability and interspecific interactions can have strong impacts on existing range limits. Here we explore how competitive interactions and temporal variability can interact with the potential to strongly influence range shift dynamics. We highlight the need to understand these between‐process interactions in order to predict how species will respond to global change. In particular, future research will need to move from evaluating possibilities to quantifying their impact. We emphasise the value and utility of empirically parameterised models to determine the direction and relative importance of these forces in natural systems. [ABSTRACT FROM AUTHOR]

The massive release of captive-bred native species ("intentional release") is a pervasive method to enhance wild populations of commercial and recreational species. However, such external inputs may disrupt the sensitive species interactions that allow competing species to coexist, potentially compromising long-term community stability. Here, we use theory and long-term data of stream fish communities to show that intentional release destabilizes community dynamics with limited demographic benefit to the enhanced species. Our theory predicted that intentional release intensifies interspecific competition, facilitating the competitive exclusion of unenhanced species that otherwise stably coexist. In parallel, the excessive input of captive-bred individuals suppressed the natural recruitment of the enhanced species via intensified within-species competition. Consequently, the ecological community with the intentional release is predicted to show reduced community density with unstable temporal dynamics. Consistent with this prediction, stream fish communities showed greater temporal fluctuations and fewer taxonomic richness in rivers with the intensive release of hatchery salmon-a major fishery resource worldwide. Our findings alarm that the current overreliance on intentional release may accelerate global biodiversity loss with undesired consequences for the provisioning of ecosystem services.