Integrating species traits with extrinsic threats: closing the gap between predicting and preventing species declines

In studies of extinction risk, it is often insufficient to conclude that species with narrow ranges or small clutch sizes require prioritized protection. To improve conservation outcomes, we also need to know which threats interact with these traits to endanger some species but not others. In this study, we integrated the spatial patterns of key threats to Australian amphibians with species' ecological/life-history traits to both predict declining species and identify their likely threats. In addition to confirming the importance of previously identified traits (e.g. narrow range size), we find that extrinsic threats (primarily the disease chytridiomycosis and invasive mosquitofish) are equally important and interact with intrinsic traits (primarily ecological group) to create guild-specific pathways to decline in our model system. Integrating the spatial patterns of extrinsic threats in extinction risk analyses will improve our ability to detect and manage endangered species in the future, particularly where data deficiency is a problem.     

Spreading messages about invasives

Although control of invasive species remains a common part of ecological restoration efforts, there is a growing dialogue within scientific and conservation communities regarding positive influences of invaders and potential negative consequences of their removal. As one example, a recent Diversity & Distributions article cautions that removal of exotic and invasive honeysuckle (Lonicera spp.) may negatively affect populations of frugivorous birds and, therefore, may have undesirable ecological outcomes. In response, I share several insights from research in my lab on bird‐honeysuckle interactions that show how honeysuckle disproportionately impacts birds of conservation concern and acts as an ecological trap even for generalist species. Although there is a real need to fully consider both positive and negative consequences of invasive species, if such research is not placed within the proper ecological context, we risk sending distorted or mixed messages to managers.     

When does invasive species removal lead to ecological recovery? Implications for management success

The primary goal of invasive species management is to eliminate or reduce populations of invasive species. Although management efforts are often motivated by broader goals such as to reduce the negative impacts of invasive species on ecosystems and society, there has been little assessment of the consistency between population-based (e.g., removing invaders) and broader goals (e.g., recovery of ecological systems) for invasive species management. To address this, we conducted a comprehensive review of studies (N = 151) that removed invasive species and assessed ecological recovery over time. We found positive or mixed outcomes in most cases, but 31% of the time ecological recovery did not occur or there were negative ecological outcomes, such as increases in non-target invasive species. Ecological recovery was more likely in areas with relatively little anthropogenic disturbance and few other invaders, and for the recovery of animal populations and communities compared to plant communities and ecosystem processes. Elements of management protocols, such as whether invaders were eradicated (completely removed) versus aggressively suppressed (≥90% removed), did not affect the likelihood of ecological recovery. Our findings highlight the importance of considering broader goals and unintended outcomes when designing and implementing invasive species management programs.     

中国农业生态系统外来种入侵及其管理现状

农业生态系统极易遭受外来生物入侵。作者根据文献资料和多年工作观察统计出入侵我国农业生态系统的外来生物共计92科175属239种, 其中植物155种, 动物55种, 微生物29种, 植物多为有意引入后逸生, 而动物和微生物则主要是无意引入。外来入侵种发生数量呈现从南到北、从东到西逐渐减少的趋势。这些入侵种中, 来源于美洲的最多(占45.04%), 其次是欧洲(22.90%); 菜地(包括温室大棚)和果园入侵种最多, 分别达64.85%和66.53%, 而半年期的秋熟旱地和夏熟旱地分别占34.31%和23.85%。其中17种外来杂草、10种害虫、7种病原菌为恶性有害生物, 应作为防除的重点目标。目前农业生态系统外来入侵物种的控制以化学防治为主, 但由于长期施用化学农药, 在侵入我国农田的入侵种中, 已有51种在世界不同地区演化出抗药性生物型, 因而需重视生物防治、农业和生态防治以及检疫等的综合应用。今后外来种对农业生态系统的入侵格局、机制和趋势, 入侵途径以及生物入侵和抗药性生物型对农业生态系统中有害生物群落演替的影响、转基因作物导致的生物入侵等问题值得关注。     

Interactions between frequency and size of disturbance affect competitive outcomes

Disturbance has many effects on ecological communities, and it is often suggested that disturbance can affect species diversity by altering competitive outcomes. However, disturbance regimes have many distinct aspects that may act, and interact, to influence species diversity. While there are many theoretical models of disturbance-prone communities, few have specifically documented how interactions between different aspects of a disturbance regime change competitive outcomes. Here, we present a model of two plant species subject to disturbance which we then use to examine species coexistence over varying levels of two aspects of disturbance: frequency, and spatial extent (i.e., area disturbed). We show that the competitive outcome is affected differently by changes in each aspect and that the effect of disturbance frequency on species coexistence depends strongly on the spatial extent of the disturbance, and vice versa. We classify the nature of these interactions between disturbance frequency and extent on the basis of the shape of the resulting coexistence regions in a frequency?Cextent parameter plane. Our results illustrate that different types of interaction can result from differences in life-history traits that control species-specific sensitivity to frequency and extent of disturbance. Thus, our analysis shows that the various aspects of disturbance must be carefully considered in concert with the life-history traits of the community members in order to assess the consequences of disturbance.     

京津冀外来入侵植物的种类调查与分析

【目的】近年来,外来入侵植物对京津冀地区的生态安全和经济贸易发展构成了严重威胁。了解京津冀地区入侵植物种类组成,分析其分布特点,能够为京津冀地区外来入侵植物扩散的防控、生物多样性保护与生态安全提供理论依据。【方法】对京津冀外来入侵植物的种类、原产地、生活型、危害程度、引入途径等进行调查和分析。【结果】京津冀目前有99种外来入侵植物,其中恶性杂草11种。菊科和禾本科为优势科,所含种数分别为24和12种。京津冀外来入侵植物以一、二年草本植物为主;美洲是京津冀入侵植物的最大起源地,其中,北美地区23种,美洲热带和中、南美洲共32种;人为有意引进共56种,占外来入侵植物总种数的56.57%。【结论】当前京津冀地区外来植物入侵状况比较严重,且该地区入侵植物的入侵与其社会经济学因子和生物地理学因子密切有关,有意引入是京津冀地区外来植物入侵的主要途径。     

Why close relatives make bad neighbours: phylogenetic conservatism in niche preferences and dispersal disproves Darwin's naturalization hypothesis in the thistle tribe

The number of exotic plant species that have been introduced into the United States far exceeds that of other groups of organisms, and many of these have become invasive. As in many regions of the globe, invasive members of the thistle tribe, Cardueae, are highly problematic in the California Floristic Province, an established biodiversity hotspot. While Darwin's naturalization hypothesis posits that plant invaders closely related to native species would be at a disadvantage, evidence has been found that introduced thistles more closely related to native species are more likely to become invasive. To elucidate the mechanisms behind this pattern, we modelled the ecological niches of thistle species present in the province and compared niche similarity between taxa and their evolutionary relatedness, using fossil‐calibrated molecular phylogenies of the tribe. The predicted niches of invasive species were found to have higher degrees of overlap with native species than noninvasive introduced species do, and pairwise niche distance was significantly correlated with phylogenetic distance, suggesting phylogenetic niche conservatism. Invasive thistles also displayed superior dispersal capabilities compared to noninvasive introduced species, and these capabilities exhibited a phylogenetic signal. By analysing the modelled ecological niches and dispersal capabilities of over a hundred thistle species, we demonstrate that exapted preferences to the invaded environment may explain why close exotic relatives may make bad neighbours in the thistle tribe.     

Ecological and genetic assessment of spatial structure among replicate contact zones between two topminnow species

The spatial structure of contact zones is often described as disjunct, diffuse or mosaic and presumed to be related to underlying ecological gradients. However, the ecology of contact zones, how they are structured, and if that structure is predictable based on the strength and nature of ecological gradients is unknown. Large spatial scales and the unreplicated nature of many of the best studied contact zones has made it difficult to codify broader ecological patterns. Freshwater stream fish contact zones have the advantage of being potentially replicated with well defined boundaries and predictable linear gradients (river continuum concept). We sampled four replicate topminnow (Fundulus olivaceus and F. notatus) contact zones in Gulf of Mexico drainages. In each, we quantified contact zone spatial structure and the strength of ecological gradients (habitat, physicochemical variables and fish community functional traits). All three types of contact zone structure were represented. Systems with weaker gradients had diffuse contact zones, low species richness and were numerically dominated by generalist species. Rates of hybridization were also variable among systems. There was no hybridization detected in the mosaic zone while hybrids were found at most of the co-occurrence sites in the diffuse and disjunct zones. Overall, local ecology clearly influences contact zone structure and the two species interact in fundamentally different ways in these four systems.     

Testing Darwin's naturalization hypothesis in the Azores

Invasive species are a threat for ecosystems worldwide, especially oceanic islands. Predicting the invasive potential of introduced species remains difficult, and only a few studies have found traits correlated to invasiveness. We produced a molecular phylogenetic dataset and an ecological trait database for the entire Azorean flora and find that the phylogenetic nearest neighbour distance (PNND), a measure of evolutionary relatedness, is significantly correlated with invasiveness. We show that introduced plant species are more likely to become invasive in the absence of closely related species in the native flora of the Azores, verifying Darwin's 'naturalization hypothesis'. In addition, we find that some ecological traits (especially life form and seed size) also have predictive power on invasive success in the Azores. Therefore, we suggest a combination of PNND with ecological trait values as a universal predictor of invasiveness that takes into account characteristics of both introduced species and receiving ecosystem.     

外来入侵杂草的生物防治及生防因子对本地非目标种的影响

随着生物入侵所引起的生态及经济问题日益严重,对有害入侵生物的防治问题也备受人们关注。生物防治因具有持续、高效、安全等优点,已成为防治有害入侵生物的重要方法。传统生防是防治有害入侵杂草的一种重要方法。在简单介绍生物防治的基础上,重点阐述了传统生物防治的理论基础——天敌逃逸假说,生防因子对外来人侵种的影响及其对本地非目标种的直接和间接效应,并针对这些问题,对我国开展生物防治工作提出几点建议。     

Invasive Species and Evolution

Invasive species are a major threat to modern ecosystems and cause billions of dollars in economic damage annually. The long-term impacts of species invasions are difficult to assess on ecological timescales available to biologists, but the fossil record provides analogues that allow investigation of the long-term impacts of species invasions. Two case studies of ancient invasions, the Late Devonian Biodiversity Crisis (~375?million years ago) and the Late Ordovician Richmondian Invasion (~446?million years ago), provide insight into the effect of invasive species on extinction, speciation, and ecosystem structuring. During both intervals, invasive species are characterized by broad ecological tolerances, broad geographic ranges, and higher-than-average survival potential through the crisis interval. Among the native species, narrowly adapted ecological specialists are more likely to become extinct, while broadly-adapted generalist species persisted through the invasion interval by modifying aspects of their ecological niche through niche evolution. In addition, formation of new species practically stopped during the invasion intervals due to reduced opportunities for geographic isolation and speciation. The results of these impacts produced post-invasion biotas with less diversity, greater biotic homogenization between regions, and a lack of new species forming. Conservation efforts to eradicate invasive species may help mitigate these outcomes in the current biodiversity crisis.     

Assessment of ecological risks in weed biocontrol: Input from retrospective ecological analyses

Prediction of the outcomes of natural enemy introductions remains the most fundamental challenge in biological control. Quantitative retrospective analyses of ongoing biocontrol projects provide a systematic strategy to evaluate and further develop ecological risk assessment. In this review, we highlight a crucial assumption underlying a continued reliance on the host specificity paradigm as a quantitative prediction of ecological risk, summarize the status of our retrospective analyses of nontarget effects of two weevils used against exotic thistles in North America, and discuss our prospective assessment of risk to a federally listed, threatened species (Cirsium pitcheri) based on those studies. Our analyses quantify the fact that host range and preference from host specificity tests are not sufficient to predict ecological impact if the introduced natural enemy is not strictly monophagous. The implicit assumption when such use is made of the host specificity data in risk assessment is that population impacts are proportional to relative preference and performance, the key components of host specificity. However, in concert with shifting awareness in the field, our studies demonstrate that the environment influences and can alter host use and population growth, leading to higher than expected direct impacts on the less preferred native host species at several spatial scales. Further, we have found that straightforward, easily anticipated indirect effects, on intraguild foragers as well as on the less preferred native host plant species, can be both widespread and significant. We conclude that intensive retrospective ecological studies provide some guidance for the quantitative prospective studies needed to assess candidate biological control agent dynamics and impacts and, so, contribute to improved rigor in the evaluation of total ecological risk to native species.     

Environmental data sets matter in ecological niche modelling: an example with Solenopsis invicta and Solenopsis richteri

Aim  In response to a recent paper suggesting the failure of ecological niche models to predict between native and introduced distributional areas of fire ants ( Solenopsis invicta ), we sought to assess methodological causes of this failure.
Location  Ecological niche models were developed on the species' native distributional area in South America, and projected globally.
Methods  We developed ecological niche models based on six different environmental data sets, and compared their respective abilities to anticipate the North American invasive distributional area of the species.
Results  We show that models based on the 'bioclimatic variables' of the WorldClim data set indeed fail to predict the full invasive potential of the species, but that models based on four other data sets could predict this potential correctly.
Main conclusions  The difference in predictive abilities appears to centre on the complexity of the environmental variables involved. These results emphasize important influences of environmental data sets on the generality and ability of ecological niche models to anticipate novel phenomena, and offer a simpler explanation for the lack of predictive ability among native and invaded distributional areas than that of niche shifts.     

Scale, environment, and trophic status: the context dependency of community saturation in rocky intertidal communities

Our understanding of the relative influence of different ecological drivers on the number of species in a place remains limited. Assessing the relative influence of local ecological interactions versus regional species pools on local species richness should help bridge this conceptual gap. Plots of local species richness versus regional species pools have been used to address this question, yet after an active quarter-century of research on the relative influence of local interactions versus regional species pools, consensus remains elusive. We propose a conceptual framework that incorporates spatial scale and ecological interaction strength to reconcile current disparities. We then test this framework using a survey of marine rocky intertidal algal and invertebrate communities from the northeast Pacific. We reach two main conclusions. First, these data show that the power of regional species pools to predict local richness disintegrates at small spatial scales coincident with the scale of biological interactions, when studying ecologically interactive groups of species, and in generally more abiotically stressful habitats (e.g., the high intertidal). Second, conclusions of past studies asserting that the regional species pool is the primary driver of local species richness may be artifacts of large spatial scales or ecologically noninteractive groups of species.     

A dominance‐based approach to map risks of ecological invasions in the presence of severe uncertainty

Aim Uncertainty has been widely recognized as one of the most critical issues in predicting the expansion of ecological invasions. The uncertainty associated with the introduction and spread of invasive organisms influences how pest management decision makers respond to expanding incursions. We present a model‐based approach to map risk of ecological invasions that combines two potentially conflicting goals: (1) estimating the likelihood of a new organism being established at a given locale and (2) quantifying the uncertainty of that prediction. Location Eastern and central Canada. Methods Our methodology focuses on the potential for long‐distance, human‐assisted spread of invasive organisms. First, we used a spatial simulation model to generate distributions of plausible invasion outcomes over a target geographical region. We then used second‐degree stochastic dominance (SSD) criteria to rank all geographical locations in the target region based on these distributions. We applied the approach to analyze pathways of human‐assisted spread (i.e., with commercially transported goods) of the emerald ash borer (EAB) (Agrilus planipennis Fairmaire), a major pest of ash trees in North America. Results The projected potential of the pest to establish at remote locations is significantly shaped by the amount of epistemic uncertainty in the model‐based forecasts. The estimates based on the SSD ranking identified major ‘crossroads’ through which the movement of the EAB with commercial transport is most likely to occur. The system of major expressways in Ontario and Quebec was confirmed as the primary gateway of the pest’s expansion throughout the Canadian landscape. Main conclusions Overall, the new approach generates more realistic predictions of long‐distance introductions than models that do not account for severe uncertainties and thus can help design more effective pest surveillance programmes. The modelling technique is generic and can be applied to assess other environmental phenomena when the level of epistemic uncertainty is high.     

Using prior information to build probabilistic invasive species risk assessments

Understanding why some introduced species become naturalized and invasive whereas others do not is a major focus of invasion ecology. Invasive species risk assessments address this same question, but are not typically based on the results from recent ecological studies. Applying results from the ecological literature to risk assessment is difficult, in part because there are no general explanations of invasion likelihood across taxa. Most ecological studies are also specific to a particular region and it is unclear whether outcomes in one region will necessarily apply to another. Here we show how a hierarchical Bayesian statistical framework can make better use of ecological studies for applied risk assessments. We focus on three key opportunities afforded by these models: (1) the ability to leverage information from one region to form prior expectations for other regions about which little is known, (2) the ability to quantify uncertainty of predictions, and (3) flexibility to incorporate within-group heterogeneities in probabilities of naturalization. We illustrate these principles using a case study where we predict the probability of plant taxa naturalizing in New Zealand and Australia, showing how prior information can be particularly valuable when data are limited. As more studies document invasion patterns around the world, a framework that can formally incorporate prior information will help link the accumulating data on species introductions to risk assessments.     

Complex interactions between spatial pattern of resident species and invasiveness of newly arriving species affect invasibility

Understanding the factors that affect establishment success of new species in established communities requires the study of both the ability of new species to establish and community resistance. Spatial pattern of species within a community can affect plant performance by changing the outcome of inter-specific competition, and consequently community invasibility. We studied the effects of spatial pattern of resident plant communities on fitness of genotypes from the native and introduced ranges of two worldwide invasive species, Centaurea stoebe and Senecio inaequidens, during their establishment stage. We experimentally established artificial plant mixtures with 4 or 8 resident species in intra-specifically aggregated or random spatial patterns, and added seedlings of genotypes from the native and introduced ranges of the two target species. Early growth of both S. inaequidens and C. stoebe was higher in aggregated than randomly assembled mixtures. However, a species-specific interaction between invasiveness and invasibility highlighted more complex patterns. Genotypes from native and introduced ranges of S. inaequidens showed the same responses to spatial pattern. By contrast, genotypes from the introduced range of C. stoebe did not respond to spatial pattern whereas native ones did. Based on phenotypic plasticity, we argue that the two target species adopted different strategies to deal with the spatial pattern of the resident plant community. We show that effects of spatial pattern of the resident community on the fitness of establishing species may depend on the diversity of the recipient community. Our results highlight the need to consider the interaction between invasiveness and invasibility in order to increase our understanding of invasion success.     

Molecular genetic approaches to elucidate the ecological and evolutionary issues associated with biological invasions

Biological invasions may cause serious damage to the native environments and threaten the native biodiversity. Molecular genetic approaches have been found to be powerful tools for investigating the ecological and evolutionary aspects of biological invasions because the genetic structure and level of genetic variation of an invasive species are changed following its invasion. The present article reviews the use of molecular markers in addressing various aspects of invasive species. The application of these techniques has shown that many invasive species are actually "cryptic" species – species whose uniqueness is only recognizable at the genetic level. An estimation of the actual number of invasive species is essential when evaluating its ecological and economic impacts. Molecular genetic approaches have also enabled the source populations of invasive species to be identified. Reconstructions of invasion histories are crucial to preventing future invasions and conserving the native biodiversity, while comparisons of genetic variations between the native and introduced populations provide valuable opportunities to elucidate the mechanisms of rapid adaptation demonstrated by many invasive species.     

Assessment of ecological risks in weed biocontrol: Input from retrospective ecological analyses

Prediction of the outcomes of natural enemy introductions remains the most fundamental challenge in biological control. Quantitative retrospective analyses of ongoing biocontrol projects provide a systematic strategy to evaluate and further develop ecological risk assessment. In this review, we highlight a crucial assumption underlying a continued reliance on the host specificity paradigm as a quantitative prediction of ecological risk, summarize the status of our retrospective analyses of nontarget effects of two weevils used against exotic thistles in North America, and discuss our prospective assessment of risk to a federally listed, threatened species (Cirsium pitcheri) based on those studies. Our analyses quantify the fact that host range and preference from host specificity tests are not sufficient to predict ecological impact if the introduced natural enemy is not strictly monophagous. The implicit assumption when such use is made of the host specificity data in risk assessment is that population impacts are proportional to relative preference and performance, the key components of host specificity. However, in concert with shifting awareness in the field, our studies demonstrate that the environment influences and can alter host use and population growth, leading to higher than expected direct impacts on the less preferred native host species at several spatial scales. Further, we have found that straightforward, easily anticipated indirect effects, on intraguild foragers as well as on the less preferred native host plant species, can be both widespread and significant. We conclude that intensive retrospective ecological studies provide some guidance for the quantitative prospective studies needed to assess candidate biological control agent dynamics and impacts and, so, contribute to improved rigor in the evaluation of total ecological risk to native species.     

Ecological correlates of the non-indigenous parasitoid assemblage associated with a Hawaiian endemic moth

Understanding what ecological factors might predispose indigenous habitats to invasion by invasive species is an important aspect of conservation and invasive species management, particularly when biological control is considered for suppression of the invasive species. This study seeks to identify ecological factors that might play a role in determining the structure of the parasitoid assemblage associated with caterpillars of the endemic Hawaiian moth Udea stellata (Crambidae). Parasitoids were reared from field-collected U. stellata larvae at 18 locations. Fourteen environmental variables were measured at each site. Two multivariate analyses, principal component analysis (PCA) and partial redundancy analysis (RDA), were used to analyze the parasitoid assemblage across a range of habitats varying in environmental characteristics. The PCA analysis showed that the occurrence of some species were highly correlated, and associated with less disturbed sites, whereas other species were associated with sites of medium and high levels of disturbance. The RDA analysis showed that only three of the measured environmental variables (U. stellata density, elevation, and level of habitat disturbance) significantly explained variability in the parasitoid assemblage among sites. There was greater parasitoid species richness associated with U. stellata larvae at higher elevation sites with a lower degree of habitat disturbance by exotic vegetation. The purposely introduced parasitoid species were associated with the non-target moth at sites located at higher elevations with low levels of disturbance. Multivariate analysis has the potential to provide valuable insights into the identification of important environmental factors that mediate parasitoid assemblage structure and level of parasitism on a particular target or non-target species, and therefore facilitate identification of suitable target habitats or susceptible non-target habitats.