基于现代物种共存理论的入侵生态学概念框架

在入侵生态学60多年的发展历程中, 生态学家提出了多种多样的假说来解释生物入侵的机制。这些纷繁复杂的假说在丰富我们对生物入侵认知的同时, 也给入侵生态学概念的整合带来了困难。其中, 外来种和土著种是否存在生态学差异, 以及这种差异如何影响生物入侵, 是入侵生态学研究和争论的焦点问题。现代物种共存理论通过将外来种和土著种的生态学差异划分为生态位差异和适合度差异, 为入侵生态学概念的整合提供了新的视角。依据该理论, 外来种可以通过两种策略实现成功入侵: 一是扩大与土著种的生态位差异, 二是提高自身相较于土著种的适合度优势。因此, 外来种-土著种的生态位差异和适合度差异共同决定了入侵的成败与危害程度。通过对经典入侵假说进行梳理, 我们发现大部分假说都可以在该理论框架下进行解读, 不同假说的主要差别在于强调不同生态学过程对生态位和适合度差异的影响。同时, 这一理论框架很好地解释了为什么外来种-土著种的亲缘关系和性状差异会对生物入侵产生复杂的影响, 为达尔文归化谜团的和解以及外来种-土著种功能性状的比较研究提供了新的思路。目前, 现代物种共存理论还处于快速发展的阶段, 依旧存在很多不足, 但将其运用到生物入侵的实证研究中将是入侵生态学今后一个重要的发展方向。     

Drivers of Solidago species invasion in Central Europe—Case study in the landscape of the Carpathian Mountains and their foreground

AimThe invasion process is a complex, context‐dependent phenomenon; nevertheless, it can be described using the PAB framework. This framework encompasses the joint effect of propagule pressure (P), abiotic characteristics of the environment (A), and biotic characteristics of both the invader and recipient vegetation (B). We analyzed the effectiveness of proxies of PAB factors to explain the spatial pattern of Solidago canadensis and S. gigantea invasion using invasive species distribution models.LocationCarpathian Mountains and their foreground, Central Europe.MethodsThe data on species presence or absence were from an atlas of neophyte distribution based on a 2 × 2 km grid, covering approximately 31,200 km² (7,752 grid cells). Proxies of PAB factors, along with data on historical distribution of invaders, were used as explanatory variables in Boosted Regression Trees models to explain the distribution of invasive Solidago. The areas with potentially lower sampling effort were excluded from analysis based on a target species approach.ResultsProxies of the PAB factors helped to explain the distribution of both S. canadensis and S. gigantea. Distributions of both species were limited climatically because a mountain climate is not conducive to their growth; however, the S. canadensis distribution pattern was correlated with proxies of human pressure, whereas S. gigantea distribution was connected with environmental characteristics. The varied responses of species with regard to distance from their historical distribution sites indicated differences in their invasion drivers.Main conclusionsProxies of PAB are helpful in the choice of explanatory variables as well as the ecological interpretation of species distribution models. The results underline that human activity can cause variation in the invasion of ecologically similar species.     

The enemy release hypothesis as a hierarchy of hypotheses

In ecology, a hypothesis is usually not discarded if a few studies reject it, as long as there are other studies supporting it. How to assess the usefulness of ecological hypotheses is therefore not straightforward. Using the enemy release hypothesis as an example, we show how creating a hierarchy of hypotheses (HoH) can help reviewing and evaluating evidence for and against an ecological hypothesis. In a HoH, a broad, overarching hypothesis branches into more specific and better testable sub‐hypotheses. The enemy release hypothesis is a major hypothesis in invasion ecology and posits that the absence of enemies in the exotic range of an alien species is a cause of its invasion success. Based on a systematic review of empirical tests of this hypothesis, we divided it into sub‐hypotheses, differentiating among 1) indicators for enemy release, 2) types of comparisons, and 3) types of enemies. We identified 176 empirical tests and weighted each test according to the number of alien species studied and the research method (experimental vs observational, field vs enclosure vs laboratory). For the broadly formulated enemy release hypothesis, we found nearly as much supporting (36%) as questioning evidence (43%). At the sub‐hypotheses level, however, we found that some sub‐hypotheses are strongly supported by empirical evidence, whereas others receive hardly any support. These differences are further emphasized for some types of habitat and focal taxonomic groups. Our findings suggest that several specific formulations (i.e. sub‐hypotheses) of the broad enemy release hypothesis are useful, whereas other formulations should be viewed more critically. In general, the approach outlined here can help evaluate major ecological hypotheses and their specific sub‐hypotheses. Our study also highlights the need for a scientific debate on how much supporting evidence is sufficient to consider an ecological hypothesis to be useful.     

Invasion triangle: an organizational framework for species invasion

Species invasion is a complex, multifactor process. To encapsulate this complexity into an intuitively appealing, simple, and straightforward manner, we present an organizational framework in the form of an invasion triangle. The invasion triangle is an adaptation of the disease triangle used by plant pathologists to help envision and evaluate interactions among a host, a pathogen, and an environment. Our modification of this framework for invasive species incorporates the major processes that result in invasion as the three sides of the triangle: (1) attributes of the potential invader; (2) biotic characteristics of a potentially invaded site; and (3) environmental conditions of the site. The invasion triangle also includes the impact of external influences on each side of the triangle, such as climate and land use change. This paper introduces the invasion triangle, discusses how accepted invasion hypotheses are integrated in this framework, describes how the invasion triangle can be used to focus research and management, and provides examples of application. The framework provided by the invasion triangle is easy to use by both researchers and managers and also applicable at any level of data intensity, from expert opinion to highly controlled experiments. The organizational framework provided by the invasion triangle is beneficial for understanding and predicting why species are invasive in specific environments, for identifying knowledge gaps, for facilitating communication, and for directing management in regard to invasive species.     

Can optimality models and an ‘optimality research program’ help us understand some plant–fungal relationships?

In this paper we suggest that the field of fungal ecology may benefit from the use of optimality models in the context of an ‘optimality research program’ (ORP). An ORP is a research program in the sense of modern philosopher of science Lakatos' [1978. The Methodology of Scientific Research Programmes: philosophical papers, vol. 1. Cambridge University Press, Cambridge] seminal work. An optimality research program has a lengthy history and record of success in the field of behavioural ecology, but has been seldom employed in fungal ecology. We discuss the ORP and provide some examples of how optimality models may be useful in fungal ecology. We suggest that such an approach may benefit experimental fungal ecologists by: providing a framework for organizing knowledge; generating hypotheses; helping in the planning of experiments; aiding in the interpretation of results; and directing the next steps of an experimental research program. We illustrate these benefits by sketching out how an ORP might be used to answer some fundamental questions about the interactions between host plants and arbuscular mycorrhizal fungi.     

Can model species be used to advance the field of invasion ecology?

Hypotheses for explaining plant invasions have focused on a variety of factors that may influence invasion success, including propagule pressure, interactions of the introduced species with the biotic, abiotic, or disturbance properties of the new ecosystem, or the genetic characteristics of the invader itself. Evaluating the relative importance of these factors has been difficult because for most invaders key information about the introduced population or the introduction event is not available. We propose that natural experiments using model species is an important tool to test multiple invasion hypotheses at the same time, providing a complementary approach to meta-analysis and literature review. By focusing on a single candidate species, Pinus contorta, we explore several attributes that we propose constitute a good model, including: (a) intentional and relatively well documented introduction into a wide range of environments and countries across the world during the past century, where invasion success or failure has already occurred, (b) conspicuous growth form that simplifies assessment of growth rates, and comparisons across native and introduced ecosystems around the world, and, (c) documented and replicated variability of introduction intensity, genetic characteristics of the introduced populations, contrasting biotic communities present at sites of introduction, and abiotic conditions within and across introduced ecosystems. We propose that identifying model species with these characteristics will provide opportunities to disentangle the relative importance of different mechanisms hypothesized to influence invasion success, and thereby advance the field of invasion ecology.     

Ecological genetics of invasive alien species

There is growing realisation that integrating genetics and ecology is critical in the context of biological invasions, since the two are explicitly linked. So far, the focus of ecological genetics of invasive alien species (IAS) has been on determining the sources and routes of invasions, and the genetic make-up of founding populations, which is critical for defining and testing ecological and evolutionary hypotheses. However an ecological genetics approach can be extended to investigate questions about invasion success and impacts on native, recipient species. Here, we discuss recent progress in the field, provide overviews of recent methodological advances, and highlight areas that we believe are of particular interest for future research. First, we discuss the main insights from studies that have inferred source populations and invasion routes using molecular genetic data, with particular focus on the role of genetic diversity, adaptation and admixture in invasion success. Second, we consider how genetic tools can lead to a better understanding of patterns of dispersal, which is critical to predicting the spread of invasive species, and how studying invasions can shed light on the evolution of dispersal. Finally, we explore the potential for combining molecular genetic data and ecological network modelling to investigate community interactions such as those between predator and prey, and host and parasite. We conclude that invasions are excellent model systems for understanding the role of natural selection in shaping phenotypes and that an ecological genetics approach offers great potential for addressing fundamental questions in invasion biology.     

Phage co-transport with hyphal-riding bacteria fuels bacterial invasion in a water-unsaturated microbial model system

Nonmotile microorganisms often enter new habitats by co-transport with motile microorganisms. Here, we report that also lytic phages can co-transport with hyphal-riding bacteria and facilitate bacterial colonization of a new habitat. This is comparable to the concept of biological invasions in macroecology. In analogy to invasion frameworks in plant and animal ecology, we tailored spatially organized, water-unsaturated model microcosms using hyphae of Pythium ultimum as invasion paths and flagellated soil-bacterium Pseudomonas putida KT2440 as carrier for co-transport of Escherichia virus T4. P. putida KT2440 efficiently dispersed along P. ultimum to new habitats and dispatched T4 phages across air gaps transporting ≈0.6 phages bacteria⁻¹. No T4 displacement along hyphae was observed in the absence of carrier bacteria. If E. coli occupied the new habitat, T4 co-transport fueled the fitness of invading P. putida KT2440, while the absence of phage co-transport led to poor colonization followed by extinction. Our data emphasize the importance of hyphal transport of bacteria and associated phages in regulating fitness and composition of microbial populations in water-unsaturated systems. As such co-transport seems analogous to macroecological invasion processes, hyphosphere systems with motile bacteria and co-transported phages could be useful models for testing hypotheses in invasion ecology.Subject terms: Microbial ecology, Ecosystem ecology, Macroecology, Population dynamics     

Coexistence and Spread of Competitors in Heterogeneous Landscapes

Competition between species is ubiquitous in nature and therefore widely studied in ecology through experiment and theory. One of the central questions is under which conditions a (rare) invader can establish itself in a landscape dominated by a resident species at carrying capacity. Applying the same question with the roles of the invader and resident reversed leads to the principle that “mutual invasibility implies coexistence.” A related but different question is how fast a locally introduced invader spreads into a landscape (with or without competing resident), provided it can invade. We explore some aspects of these questions in a deterministic, spatially explicit model for two competing species with discrete non-overlapping generations in a patchy periodic environment. We obtain threshold values for fragmentation levels and dispersal distances that allow for mutual invasion and coexistence even if the non-spatial competition model predicts competitive exclusion. We obtain exact results when dispersal is governed by a Laplace kernel. Using the average dispersal success, we develop a mathematical framework to obtain approximate results that are independent of the exact dispersal patterns, and we show numerically that these approximations are very accurate.     

Experimental support for a resource-based mechanistic model of invasibility

Recent theory has suggested a mechanistic relationship between resource availability, competition and invasibility. In a field experiment, in which we manipulated resources and competition, we confirmed that changes in resource availability affected competition intensity, which in turn affected invasibility. We found that fluctuations in resource availability of as short as a few weeks had a large impact on plant invasion success (survival and percentage cover), including up to 1 year following the fluctuations. If resource availability is a primary mechanism controlling invasibility, it may serve as a unifying concept that can integrate earlier ideas regarding invasibility. The results emphasize the important role of history in the invasion process, particularly the occurrence of stochastic, short-lived events that temporarily reduce or suspend competition and increase invasibility. Therefore, it may be very difficult, or even impossible, to reconstruct the ecology of particular invasions after the fact.     

A conceptual framework for understanding arthropod predator and parasitoid invasions

Arthropods make up the largest group of invasive alien species (IAS) worldwide. Although invasion research has been biased towards alien plants and vertebrates, it has suggested potential mechanisms for the success of IAS and provided a theoretical framework for further investigation. Here we address key concepts from invasion biology that are essential to our understanding of the success of invasive alien arthropod predators and parasitoids including human intervention, environmental characteristics, propagule pressure, biological traits, and biological interactions. To gain a greater understanding of the factors most likely to influence the different stages of invasion (arrival, establishment, and spread) for alien arthropod predators and parasitoids, we use a comparative approach to compare and contrast the differential success of invasions by alien phytophagous and carnivorous arthropods. Insights gained from this comparison suggest that future research will require a multitrophic approach in order to enhance our understanding of invasions at higher trophic levels.     

Advancing impact prediction and hypothesis testing in invasion ecology using a comparative functional response approach

Invasion ecology urgently requires predictive methodologies that can forecast the ecological impacts of existing, emerging and potential invasive species. We argue that many ecologically damaging invaders are characterised by their more efficient use of resources. Consequently, comparison of the classical ‘functional response’ (relationship between resource use and availability) between invasive and trophically analogous native species may allow prediction of invader ecological impact. We review the utility of species trait comparisons and the history and context of the use of functional responses in invasion ecology, then present our framework for the use of comparative functional responses. We show that functional response analyses, by describing the resource use of species over a range of resource availabilities, avoids many pitfalls of ‘snapshot’ assessments of resource use. Our framework demonstrates how comparisons of invader and native functional responses, within and between Type II and III functional responses, allow testing of the likely population-level outcomes of invasions for affected species. Furthermore, we describe how recent studies support the predictive capacity of this method; for example, the invasive ‘bloody red shrimp’ Hemimysis anomala shows higher Type II functional responses than native mysids and this corroborates, and could have predicted, actual invader impacts in the field. The comparative functional response method can also be used to examine differences in the impact of two or more invaders, two or more populations of the same invader, and the abiotic (e.g. temperature) and biotic (e.g. parasitism) context-dependencies of invader impacts. Our framework may also address the previous lack of rigour in testing major hypotheses in invasion ecology, such as the ‘enemy release’ and ‘biotic resistance’ hypotheses, as our approach explicitly considers demographic consequences for impacted resources, such as native and invasive prey species. We also identify potential challenges in the application of comparative functional responses in invasion ecology. These include incorporation of numerical responses, multiple predator effects and trait-mediated indirect interactions, replacement versus non-replacement study designs and the inclusion of functional responses in risk assessment frameworks. In future, the generation of sufficient case studies for a meta-analysis could test the overall hypothesis that comparative functional responses can indeed predict invasive species impacts.     

Social personality polymorphism and the spread of invasive species: a model

Ecological invasions are a major worldwide problem exacting tremendous economic and ecological costs. Efforts to explain variability in invasion speed and impact by searching for combinations of ecological conditions and species traits associated with invasions have met with mixed success. We use a simulation model that integrates insights from life-history theory, animal personalities, network theory, and spatial ecology to derive a new mechanism for explaining variation in animal invasion success. We show that spread occurs most rapidly when (1) a species includes a mix of life-history or personality types that differ in density-dependent performance and dispersal tendencies, (2) the differences between types are of intermediate magnitude, and (3) patch connections are intermediate in number and widely spread. Within-species polymorphism in phenotype (e.g., life-history strategies or personality), a feature not included in previous models, is important for overcoming the fact that different traits are associated with success in different stages of the invasion process. Polymorphism in sociability (a personality type) increases the speed of the invasion front, since asocial individuals colonize empty patches and facilitate the local growth of social types that, in turn, induce faster dispersal by asocials at the invasion edge. The results hold implications for the prediction of invasion impacts and the classification of traits associated with invasiveness.     

A general eco-evolutionary framework for understanding bioinvasions

Studies of bioinvasions have revealed various strategies of invasion, depending on the ecosystem invaded and the alien species concerned. Here, we consider how migration (as a demographic factor), as well as ecological and evolutionary changes, affect invasion success. We propose three main theoretical scenarios that depend on how these factors generate the match between an invader and its new environment. Our framework highlights the features that are common to, or differ among, observed invasion cases, and clarifies some general trends that have been previously highlighted in bioinvasions. We also suggest some new directions of research, such as the assessment of the time sequence of demographic, genetic and environmental changes, using detailed temporal surveys.     

Invasive species profiling? Exploring the characteristics of non‐native fishes across invasion stages in California

1. The global spread of non‐native species is a major concern for ecologists, particularly in regards to aquatic systems. Predicting the characteristics of successful invaders has been a goal of invasion biology for decades. Quantitative analysis of species characteristics may allow invasive species profiling and assist the development of risk assessment strategies. 2. In the current analysis we developed a data base on fish invasions in catchments throughout California that distinguishes among the establishment, spread and integration stages of the invasion process, and separates social and biological factors related to invasion success. 3. Using Akaike's information criteria (AIC), logistic and multiple regression models, we show suites of biological variables, which are important in predicting establishment (parental care and physiological tolerance), spread (life span, distance from nearest native source and trophic status) and abundance (maximum size, physiological tolerance and distance from nearest native source). Two variables indicating human interest in a species (propagule pressure and prior invasion success) are predictors of successful establishment and prior invasion success is a predictor of spread and integration. 4. Despite the idiosyncratic nature of the invasion process, our results suggest some assistance in the search for characteristics of fish species that successfully transition between invasion stages.     

Soil biota and invasive plants

Interactions between plants and soil biota resist invasion by some nonnative plants and facilitate others. In this review, we organize research and ideas about the role of soil biota as drivers of invasion by nonnative plants and how soil biota may fit into hypotheses proposed for invasive success. For example, some invasive species benefit from being introduced into regions of the world where they encounter fewer soil-borne enemies than in their native ranges. Other invasives encounter novel but strong soil mutualists which enhance their invasive success. Leaving below-ground natural enemies behind or encountering strong mutualists can enhance invasions, but indigenous enemies in soils or the absence of key soil mutualists can help native communities resist invasions. Furthermore, inhibitory and beneficial effects of soil biota on plants can accelerate or decelerate over time depending on the net effect of accumulating pathogenic and mutualistic soil organisms. These 'feedback' relationships may alter plant-soil biota interactions in ways that may facilitate invasion and inhibit re-establishment by native species. Although soil biota affect nonnative plant invasions in many different ways, research on the topic is broadening our understanding of why invasive plants can be so astoundingly successful and expanding our perspectives on the drivers of natural community organization.     

Can ecological stoichiometry help explain patterns of biological invasions?

Several mechanisms for biological invasions have been proposed, yet to date there is no common framework that can broadly explain patterns of invasion success among ecosystems with different resource availabilities. Ecological stoichiometry (ES) is the study of the balance of energy and elements in ecological interactions. This framework uses a multi‐nutrient approach to mass‐balance models, linking the biochemical composition of organisms to their growth and reproduction, which consequently influences ecosystem structure and functioning. We proposed a conceptual model that integrates hypotheses of biological invasions within a framework structured by fundamental principles of ES. We then performed meta‐analyses to compare the growth and production performances of native and invasive organisms under low‐ and high‐nutrient conditions in terrestrial and aquatic ecosystems. Growth and production rates of invasive organisms (plants and invertebrates) under both low‐ and high‐nutrient availability were generally larger than those of natives. Nevertheless, native plants outperformed invasives in aquatic ecosystems under low‐nutrient conditions. We suggest several distinct stoichiometry‐based mechanisms to explain invasion success in low‐ versus high‐nutrient conditions; low‐nutrient conditions: higher resource‐use efficiency (RUE; C:nutrient ratios), threshold elemental ratios (TERs), and trait plasticity (e.g. ability of an organism to change its nutrient requirements in response to varying nutrient environmental supply); high‐nutrient conditions: higher growth rates and reproductive output related to lower tissue C:nutrient ratios, and increased trait plasticity. Interactions of mechanisms may also yield synergistic effects, whereby nutrient enrichment and enemy release have a disproportionate effect on invasion success. To that end, ES provides a framework that can help explain how chemical elements and energy constrain key physiological and ecological processes, which can ultimately determine the success of invasive organisms.     

Ecological Invasion,Roughened Fronts,and a Competitor’s Extreme Advance: Integrating Stochastic Spatial-Growth Models

Both community ecology and conservation biology seek further understanding of factors governing the advance of an invasive species. We model biological invasion as an individual-based, stochastic process on a two-dimensional landscape. An ecologically superior invader and a resident species compete for space preemptively. Our general model includes the basic contact process and a variant of the Eden model as special cases. We employ the concept of a “roughened” front to quantify effects of discreteness and stochasticity on invasion; we emphasize the probability distribution of the front-runner’s relative position. That is, we analyze the location of the most advanced invader as the extreme deviation about the front’s mean position. We find that a class of models with different assumptions about neighborhood interactions exhibits universal characteristics. That is, key features of the invasion dynamics span a class of models, independently of locally detailed demographic rules. Our results integrate theories of invasive spatial growth and generate novel hypotheses linking habitat or landscape size (length of the invading front) to invasion velocity, and to the relative position of the most advanced invader.     

Molecular systematics and population genetics of biological invasions: towards a better understanding of invasive species management

The study of population genetics of invasive species offers opportunities to investigate rapid evolutionary processes at work, and while the ecology of biological invasions has enjoyed extensive attention in the past, the recentness of molecular techniques makes their application in invasion ecology a fairly new approach. Despite this, molecular biology has already proved powerful in inferring aspects not only relevant to the evolutionary biologist but also to those concerned with invasive species management. Here, we review the different molecular markers routinely used in such studies and their application(s) in addressing different questions in invasion ecology. We then review the current literature on molecular genetic studies aimed at improving management and the understanding of invasive species by resolving of taxonomic issues, elucidating geographical sources of invaders, detecting hybridisation and introgression, tracking dispersal and spread and assessing the importance of genetic diversity in invasion success. Finally, we make some suggestions for future research efforts in molecular ecology of biological invasions.