Host diversity can strongly influence disease prevalence, but whether it dilutes or amplifies disease remains debated. We applied community assembly theory to examine whether conditionality from abiotic and biotic filtering could explain variation in rodent diversity and Sin Nombre hantavirus (SNV) prevalence across 24 locations in the southwestern United States. Overall, community composition, not diversity per se, drove diversity-disease relationships. Environmental factors determined community composition, which regulated primary host abundance and SNV infection via resource competition. Across roughly half the communities, dilution effects emerged because added species increased dietary overlap, reducing focal host abundance and SNV infection. In other communities, environmental and biotic structuring favoured competitors, suppressing host abundance and SNV infection across diversity levels. Our results highlight how environmental structuring and substitutive assembly processes interact to influence diversity-disease patterns. Community assembly theory provides a framework for integrating abiotic and biotic processes to inform landscape-scale disease patterns.

Recruitment is the most sensitive plant life stage to environmental filters. Yet, most research linking functional traits to environmental filters has focused on adult plants with little known about early plant traits, their interactions with environmental filters, or their relation to species abundance. Likewise, how such relationships might vary between native and exotic species or influence plant invasion outcomes is unclear. We quantified regeneration traits for 12 native and 12 exotic (naturalized and invasive) forbs and evaluated trait relationships and their associations with species abundance across an environmental gradient in semi-arid grasslands. Species differentiated along two orthogonal trait axes suggestive of two distinct trait syndromes. The first trait syndrome, likely associated with competitive ability, was correlated with seed mass and growth-related seedling traits. Conversely, the second trait syndrome revealed a tradeoff between traits related to development and growth and traits related to resource management. This syndrome may reflect different approaches for seedling stress tolerance and avoidance. Neither trait syndromes nor mean trait values differed between native and exotic species, whether exotics were invasive or naturalized. Two traits and one trait syndrome were significantly associated with adult species abundance on the landscape. First, species with faster seedling maturation were generally more abundant. Naturalized exotic species with lower specific leaf area were also more abundant, suggesting a possible link between lower specific leaf area and greater drought survival. Abundance of native and invasive exotic species was greater for taxa with faster development and growth and thin, carbon-rich leaves, traits associated with stress avoidance. Importantly, the greater abundance of invasive exotics over other taxa was not accounted for by differences in regeneration traits. Evidence of regeneration trait syndromes and tradeoffs points to important selective forces shaping early plant life-history strategies. Linkages between some of these traits and adult plant abundance also suggest a significant role in recruitment success. Better elucidating these traits and their connections to species abundance-particularly across life stages-can help improve our understanding of plant community assembly.

Plant functional ecology research has primarily focused on juvenile and adult plants even though regeneration from seed can be the most consequential life-history bottleneck with cascading influence on later stages of growth and reproduction. Understandings of relationships among phenology, morphology and growth-related functional traits have improved our knowledge of plant life-history strategies and adaptive responses to changing climate. However, whether relationships among phenological and morpho-physiological traits exist during plant regeneration is unknown. We also lack understanding of the relative importance of these relationships compared with those of regeneration phenology with other factors like plant phylogeny, geographic location and whether a species is native or non-native to the location. To better understand these gaps in knowledge, we evaluated three phenological traits (days to germination, first and third true leaves) and six morpho-physiological traits (seed mass, relative growth rate, root elongation rate, root: shoot ratio, specific leaf area and seedling C:N) associated with regeneration for 131 forb species from six globally distributed grasslands. Morpho-physiological traits showed several significant correlations with phenological traits. Boosted regression trees revealed that their relative importance in predicting phenological traits varied among the three phenological stages (34%-51%). Interestingly, the relative importance of morpho-physiological traits on the phenological stages was comparable to that of phylogeny (36%-46%). In general, species with faster phenologies produced seedlings that grew faster. The influence of geographic location on phenological traits was strongest at germination (29%) and decreased (8%-15%) at later phenological stages. Native versus non-native origin had little to no impact (0%-2%) on regeneration phenology. Strong relationships between days to germination and geographic location indicate signatures of local adaptation in the earliest life stages. Similar morpho-physiological trait values between native and non-native forbs imply that trait matching may be essential for non-native establishment. While associations between phenological and morpho-physiological traits during regeneration have not been previously recognized, our results suggest that these are complex and variable across plant regeneration. Better understanding of these associations and their variation across plant life stages may help capture species shifts with ongoing climate change and be used to develop novel approaches to seed-based restoration.Read the free Plain Language Summary for this article on the Journal blog.

Anthropogenic nitrogen (N) deposition presents a global threat to ecosystem functions. In terrestrial ecosystems, N-deposition is predicted to increase plant productivity but reduce diversity by bolstering dominant plants that suppress subordinate species. However, herbivores are predicted to offset these effects by consuming excess biomass produced by N-deposition. Here, we use a multifactorial field experiment in a grassland ecosystem to investigate the effects of N-addition on top-down control by herbivores and plant diversity. We show that at ambient N, grasshoppers suppress total plant biomass and community dominance sufficiently to increase plant Shannon diversity, indicating top-down control. Without grasshoppers, N-addition increases total plant biomass by promoting the community dominant and suppressing some subordinates as predicted, but it does not affect plant Shannon diversity relative to ambient-N levels. However, with grasshoppers, N-addition eliminates herbivore controls while simultaneously increasing total plant biomass and community dominance, triggering a 21% plant Shannon diversity loss compared to ambient-N conditions. Mechanistically, we find that N-addition disrupts top-down control by reducing herbivore abundance via effects on (1) plant chemistry, which diminishes food quality, and (2) plant architecture, which elevates predatory spider abundance and lethality. Therefore, we show that N-deposition can toggle system controls from top-down to bottom-up, to the detriment of plant diversity.

Developing tools for rapidly predicting which introduced species will become invasive is essential for effective management. It’s also notoriously difficult. Quantitative models exist but often require extensive data, precluding timely application. A qualitative modeling approach, Fuzzy Interaction Webs (FIW), offers a practical alternative. FIWs hold the potential to predict impacts, guide early responses, and identify research needs using the limited data commonly available on an invasion front. As a case study, we applied FIWs to predict effects of introduced European praying mantis (Mantis religiosa) populations in grassland communities of western Montana, USA. Using available field data, published data, and expert opinion, we modeled mantid impacts on this community. We also explored how abiotic conditions (winter severity) and natural enemies (parasitoids) might independently and interactively influence mantid abundance. Our model predicted that current mantid densities, which are comparatively low, produce negligible impacts. At increased mantid densities, our model predicted declines across invertebrate guilds, with the greatest impacts at highest densities, especially on invertebrate predators, herbivores, and pollinators. Mantids were also predicted to reduce songbird abundance via indirect effects. However, if wild parasitoids establish, our model predicted they would maintain mantids below these impact levels, even under mild winter conditions. The potential adverse effect of parasitoids on native mantids is unknown, warranting additional study. We recommend monitoring M. religiosa populations within the study area and suggest that our predictions may help guide management decisions. More broadly, our case study demonstrates the potential usefulness of FIWs for evaluating invasion fronts.

Anthropogenic impacts like climate change, pollution, and habitat loss represent ominous environmental threats that can seem insurmountable to concerned citizens. Habitat loss through urbanization presents a particularly acute threat to insect pollinators, which are essential to human agricultural systems and human well-being. Herein, we introduce a user-friendly online modeling tool, The Urban Pollinator Matrix, that predicts how actions initiated by citizens and municipalities can benefit pollinators in backyards and across local communities. The Urban Pollinator Matrix applies a fuzzy interaction web approach to qualitatively model how backyard and community-scale actions can increase pollinator populations. We demonstrate an application of this tool by contrasting how cultivating native flowering plants vs. discontinuing traditional lawn care (i.e., lawn mowing and broadleaf herbicide use) in Missoula, MT, USA, might affect urban pollinators. Our model predicts that reducing traditional lawn care by 50% would increase pollinators modestly, with generalists like honeybees (Apis mellifera) benefiting most. In contrast, increasing native landscaping to levels comparable with ornamental landscaping (60% of the community), with no constraints on lawn care, was predicted to generate substantial increases in pollinator abundance, particularly for sensitive groups like bumblebees (Bombus spp.) and other native bees. These predictions suggest that cultivating native plants can achieve far greater benefits for important pollinator groups than less socially acceptable actions like discontinuation of traditional lawn care. The Urban Pollinator Matrix provides a modeling template for citizens and municipalities around the globe to incorporate pollinator conservation into urban planning for the betterment of the planet.

Biological invasions arise when humans intentionally or unintentionally transport biological organisms to new regions of the world where many establish and become serious pest species. Globally, biological invasions represent a leading cause of anthropogenic change by reducing biological diversity, altering ecosystem functions, and disrupting ecosystem services to humans. This article outlines the causes, consequences, and management of biological invasions and overviews the current state of the science of invasion biology.

Understanding how some introduced plants achieve invasive status while most simply become naturalized is a fundamental question in invasion ecology. Traditional approaches comparing native and introduced plants have linked ruderal traits such as annual life history, high fecundity, and rapid growth rates to invasiveness. However, they do not explain why other introduced species bearing similar traits fail to become invasive, possibly because generic comparisons ignore local processes that drive community assembly. Herein, we contrasted native and introduced annuals in the context of local successional processes to elucidate how introduced annual bromes like cheatgrass (Bromus tectorum) overtake perennial grasslands in the intermountain western United States. We created disturbed plots and seeded them first with annuals representing natives, naturalized species, or invasive bromes. We then seeded plots with native perennial community dominants to examine how the different annuals influenced succession. Native annuals established transient populations that facilitated perennial establishment compared to unseeded controls, enabling the shift to perennial dominance. Naturalized annuals mirrored the natives, but invasive annuals maintained robust populations at high biomass that inhibited perennial establishment and impeded succession. Mechanistically, invasive annuals reduced soil moisture and elevated plant biomass, litter, and soil N. However, only litter abundance correlated with perennial seedling recruitment across treatments. Overall, litter showed a unimodal relationship wherein lower litter abundance associated with native and naturalized annuals appeared to facilitate perennial seedling establishment while higher litter levels generated by invasives appeared to suppress perennial establishment and inhibit succession. Additional experiments provided little support for the roles of pathogen spill-over or plant-soil feedbacks favoring the introduced bromes. The domination of perennial grasslands by annual bromes may be driven by litter buildup that allows these introduced plants to break local succession rules by acting as both early seral and climax species. Traits like litter accumulation may strongly influence invasion outcomes but are indistinguishable using trait comparisons lacking community context.

Most terrestrial plants disperse by seeds, yet the relationship between seed mass, seed dispersal traits, and plant dispersion is poorly understood. We quantified seed traits for 48 species of native and introduced plants from the grasslands of western Montana, USA, to investigate the relationships between seed traits and plant dispersion patterns. Additionally, because the linkage between dispersal traits and dispersion patterns might be stronger for actively dispersing species, we compared these patterns between native and introduced plants. Finally, we evaluated the efficacy of trait databases versus locally collected data for examining these questions. We found that seed mass correlated positively with the presence of dispersal adaptations such as pappi and awns, but only for introduced plants, for which larger-seeded species were four times as likely to exhibit dispersal adaptations as smaller-seeded species. This finding suggests that introduced plants with larger seeds may require dispersal adaptations to overcome seed mass limitations and invasion barriers. Notably, larger-seeded exotics also tended to be more widely distributed than their smaller-seeded counterparts, again a pattern that was not apparent for native taxa. These results suggest that the effects of seed traits on plant distribution patterns for expanding populations may be obscured for long-established species by other ecological filters (e.g., competition). Finally, seed masses from databases differed from locally collected data for 77% of the study species. Yet, database seed masses correlated with local estimates and generated similar results. Nonetheless, average seed masses differed up to 500-fold between data sources, suggesting that local data provides more valid results for community-level questions.

The past 100 years of empirical research in ecology have generated tremendous knowledge about the component interactions that structure ecological communities. Yet, we still lack the ability to reassemble these puzzle pieces to predict community responses to perturbations, a challenge that grows increasingly urgent given rapid global change. We summarize key advances in community ecology that have set the stage for modeling ecological systems and briefly review the evolution of ecological modeling efforts to identify critical hurdles to progress. We find that while Robert May demonstrated that quantitative models could theoretically predict community interactions nearly 50 years ago, in practice, we still lack the ability to predict ecological outcomes with reasonable accuracy for three reasons: (1) quantitative models require precise data for parameterization (often unavailable) and have restrictive assumptions that are rarely met; (2) estimating interaction strengths for all network components is extremely challenging; and (3) determining which species are essential to include in models is difficult (model structure uncertainty). We propose that fuzzy interaction webs (FIW), borrowed from the social sciences, hold the potential to overcome these modeling shortfalls by integrating quantitative and qualitative data (e.g., categorical data, natural history information, expert opinion) for generating reasonably accurate qualitative predictions sufficient for addressing many ecological questions. We outline recent advances developed for addressing model structure uncertainty, and we present a case study to illustrate how FIWs can be applied for estimating community interaction strengths and predicting complex ecological outcomes in a multitrophic (plants, herbivores, predators), multi-interaction-type (competition, predation, facilitation, omnivory) grassland ecosystem. We argue that incorporating FIWs into ecological modeling could significantly advance empirical and theoretical ecology.

Disturbance is a primary driver of exotic plant invasions, but why disturbance commonly favours exotics over natives is unresolved. To address this question, we conducted the first biogeographic study of disturbance across multiple plant species. We experimentally disturbed grasslands and added seeds of 34 plant species to plots in their native range and in two introduced ranges that differed in invasibility (susceptibility to invasion) to evaluate recruitment while examining potential influences of resource availability, native community recovery from disturbance (resilience) and life‐history traits in local species pools. Species pools in the native (donor) range were more strongly skewed towards ruderal taxa than species pools in the introduced ranges. This bias in the donor pool was exacerbated by introduction filters that further selected for ruderal traits, strongly skewing exotic species pools in the introduced ranges towards ruderals. Sown species, which reflected these trait patterns, benefited from disturbance universally, but their disturbance response was 10‐fold greater in the more invasible introduced range. This result was not explained by nutrient availability, which responded similar to disturbance across ranges. Nor was it driven by background propagule pressure, which was minimal. Rather, the exaggerated disturbance effect in the more invasible introduced range appeared to be driven by weak recovery of the native plant community that allowed ruderal‐biased exotics to proliferate. Overall, disturbance appeared to favoured exotics because they were much more likely than natives to be ruderal. However, this trait bias only corresponded with an invader advantage in the more invasible range where weak community resilience was linked to slow‐growing, stress‐tolerant natives that failed to rapidly recover space and resources. In contrast, in the less invasible introduced range, highly competitive native perennials quickly filled the disturbance gap, demonstrating high community resilience that appeared to limit invader recruitment. Synthesis : Biogeographic influences on local species pools can facilitate invader success following disturbance, but final invasion outcomes are conditioned by native community resilience.

Placing traits into novel evolutionary contexts may profoundly alter their functional roles. Here, we investigated whether the elaiosome, a lipid‐rich appendage located on seeds, retained its role as a seed dispersal trait promoting mutualisms with insectivorous ants following human‐mediated introduction of the elaiosome‐bearing Carduus nutans into the Argentinean Caldenal. This system is located within the Neotropical region, an alleged myrmecochory cold spot. Specifically, we first tested the assumption that the elaiosome mediates the interaction between C. nutans and the native ant Pheidole bergi . Then, we explored the hypothesis that, instead of a mutualism, the elaiosome promotes an antagonism between these species because P. bergi predates on both insects and seeds. Finally, we assessed the possibility that the elaiosome is rare in our system, as predicted from its location within the Neotropics. By manipulating the presence/absence of C. nutans ' elaiosomes, we demonstrated that P. bergi strongly prefers to collect seeds with versus without C. nutans ' elaiosomes, indicating that the elaiosome indeed mediates the interaction between these species. While we detected no direct signs of predation on nor alteration of viability in seeds recovered from P. bergi 's refuse dumps, 80% of offered C. nutans seeds remained inside P. bergi colonies, where they are likely consumed by ants, buried too deep for emergence or destroyed by pathogens. Importantly, by quantifying the outcome of the C. nutans – P. bergi interaction, we showed that this relationship is strongly antagonistic. Finally, by sampling taxa most likely to have elaiosomes, we identified eight native species with that trait, preliminary confirming that elaiosome‐bearing species are uncommon in the Caldenal. Taken together, our findings suggest that the elaiosome promotes an antagonism that deters invasion in a cold spot of myrmecochore diversity. The functions of phenotypic traits can thus vary according to the ecological and evolutionary contexts in which they operate.

Parasites can catalyze or inhibit interactions between their hosts and other species, but the ecosystem-level effects of such interaction modifications are poorly understood. We conducted a large-scale field experiment in temperate grasslands of China to understand how foliar fungal pathogens influenced top-down effects of cattle on plant diversity and productivity. When foliar pathogens were suppressed, cattle grazing strongly reduced biomass of the dominant grass, Leymus chinensis, generating competitive release that significantly increased community-level species richness and evenness. In the absence of grazing, pathogen attack on L. chinensis had no measurable effect on host biomass. However, pathogens disrupted top-down effects of herbivory by inhibiting grazing effects on plant biomass and species richness. Mechanistically, fungal pathogens were linked to increased alkaloid and reduced nitrogen levels in leaf tissue, which appeared to deter cattle grazing on L. chinensis. In conclusion, foliar pathogens can suppress top-down effects of large herbivores on grassland community composition and ecosystem function by modifying the strength of their host's interactions with dominant consumers. Parasites may act as modulators of ecosystem function when their direct effects on host abundance are overshadowed by powerful influences on host traits that modify their interactions with competitors, herbivores, or predators.

Land managers rely heavily on herbicides to mitigate exotic plant invasions but the nontarget effects of herbicides on treated plant, animal, and soil communities are often overlooked. Biological soil crusts (biocrusts) are important components of ecosystems yet the effects of different herbicides on biocrusts are rarely considered. We tested the impact of three widely used herbicides, indaziflam, imazapic, aminocyclopyrachlor, and chlorsulfuron, two of which were applied with or without a surfactant, on biocrusts dominated by mosses or lichens in intermountain grasslands. We found that neither the herbicides nor surfactant impacted biocrust moss or lichen cover within 2 years of their application.

Biological organisms are increasingly being introduced and eradicated in an effort to maintain biodiversity and ecosystem function in the face of anthropogenic threats. However, these conservation actions can have unintended consequences to non-target species. Careful vetting of these actions using ecological modelling tools could help predict and avoid unintended consequences. Qualitative modelling tools, such as fuzzy interaction webs (FIWs), allow for qualitative rankings of community properties (e.g. interaction strength = high, medium, low) in combination with quantitative information to predict management outcomes. These tools have lower data requirements than strictly quantitative models, facilitating their use for communities lacking comprehensive parameterization. However, no studies have evaluated the efficacy of FIWs for predicting unintended consequences against empirically documented outcomes. Moreover, there is no process for systematically identifying which species to incorporate in community-level conservation assessments to overcome model structure uncertainty. Finally, there is a need to make qualitative modelling tools more accessible for conservation practitioners. We applied FIWs to the case study of lake trout introduction into Yellowstone Lake, Yellowstone National Park, to assess its ability to predict documented community-level outcomes from an intentional species introduction. Next, we used the case study of the intentional red squirrel introduction to Newfoundland to show how a community assessment framework can help define the community interaction web needed for applying a FIW. Lastly, we introduced a user-friendly web interface () for applying FIWs to conservation questions. We found that the FIW predicted previously documented directional changes in the abundance of community components relatively well in the Yellowstone Lake case study, even with minimal knowledge of the system. The community assessment framework provided a formal process for identifying community components for the Newfoundland case study, and the resulting FIW predicted documented unintended consequences. The user interface predicts realistic outcomes in our study system and allows managers to build and apply FIWs for conservation planning. Synthesis and applications. Our community assessment framework and user interface can be used to apply FIWs to identify and avert potential unintended outcomes of species introductions and eradications for improved conservation management.

Plant invasions can alter food resources and habitat conditions that structure animal communities. These effects are negative for many native animals, but neutral or even positive for others. Understanding why we see this variation in responses is critical for mitigating invasion outcomes, yet we lack a synthetic framework to explain and potentially predict effects of invasive plants on native animals. We propose a trait-based framework for understanding how invasive plants affect native fauna, which draws on community assembly, niche, and trait theories to define the mechanisms by which invasive plants alter ecological conditions relevant to native animals. This approach moves beyond prior frameworks by explicitly accounting for the context dependency that defines most ecological interactions and invasion outcomes. Namely, by characterizing the plant community in terms of functional effect traits (e.g., seed size) relevant to consumers and quantifying those traits along a consumer resource axis, we can map the functional relationship between plant resources and animals. We can then delineate how plant invaders alter the plant community and associated resource axes to restructure consumer communities. We apply this framework to case studies of rodents, spiders, and birds to demonstrate the process and explore its utility. For example, we show that by focusing on how a nonnative grass altered seed sizes (relative to the native plant community), we can better understand declines in abundance of granivorous rodents and increases in opportunists. This approach can elucidate which native animals will be most likely affected by plant invasion, as well as how and why they might respond. Moreover, these mechanistic explanations provide working hypotheses for how invasive plants impact native animals more generally, with potential for predicting impacts of future invaders.

Understanding the causes of plant invasions requires that parallel field studies are conducted in the native and introduced ranges to elucidate how biogeographical shifts alter the individual performance, population success and community‐level impacts of invading plants. Three primary methods deployed in in situ biogeographical studies are directed surveys, where researchers seek out populations of target species, randomized surveys and field experiments. Despite the importance of these approaches for advancing biogeographical research, their relative merits have not been evaluated. We concurrently deployed directed surveys, randomized surveys and in situ field experiments for studying six grassland plant species in the native and introduced ranges. Metrics included plant size, fecundity, recruitment, abundance and invader impact, as well as soil properties and root associations with putative fungal mutualists and pathogens. Consistent with key invasion hypotheses, Bromus tectorum experienced increased size and fecundity in the introduced range linked to population increases and significant invader impacts, along with altered fungal associations. However, performance differences did not predict population increases and invader impacts across species. A notable finding was that disturbance facilitated greater recruitment in the introduced range for most species, thereby playing a crucial, though underappreciated, role in driving invader success. Directed surveys consistently generated information on plant performance and fungal associations. However, soil sampling suggested that directed surveys may have been biased towards disturbed conditions for half the species. Randomized surveys generated robust data for population comparisons and impact, but generally failed to produce performance metrics for species that were uncommon or flowered outside the peak sampling window. Field experiments controlled for bias and confounding factors and provided rare information on recruitment and disturbance effects, but poor recruitment in the native range and ethical constraints on growing invaders in the introduced range hindered comparisons of performance and plant–fungal interactions. Synthesis. Each method had strengths and weaknesses. However, when combined they provided complementary information to paint the most complete biogeographical picture to date for several introduced plants. We propose a hybrid approach to optimize biogeographical studies.

Ecological restoration commonly emphasizes reestablishing native plant communities. Implicit in this approach is the assumption that actively restoring plant communities can passively restore structure and function of other community components like wildlife. However, this assumption is rarely tested. We evaluated how plant restoration in grasslands of the northwestern United States affected the structure (composition and relative abundance) of native small mammal communities and the important functional role they play as seed predators. We quantified vegetation, small mammal community structure, small mammal seed predation, and effects of seed predation on native plant recruitment in comparable grasslands that were either native‐dominated, planted with introduced forage grasses, or had undergone restoration treatments to suppress introduced grasses and increase native plants with and without supplemental watering. Native plant cover averaged ≥5 times higher at restoration sites relative to introduced grass sites. Small mammals, primarily deer mice ( Peromyscus maniculatus ), were least abundant in introduced grass sites and most abundant in water‐supplemented restoration treatments, with intermediate levels in native and unwatered restoration sites. Seed offerings and seed sowing experiments indicated that seed predation and its effects on plant recruitment correlated with small mammal abundance, with effects generally weakest in introduced grass and strongest in restoration sites. Our results suggest that active plant restoration can passively restore the structure and function of native small mammal communities. While small mammal seed predation is a desired long‐term function, it can also inhibit restoration efforts. We discuss emerging strategies for mitigating seed predation during restoration seeding.