Article

Invasions: The trail behind, the path ahead, and a test of a disturbing idea

Journal of Ecology

December 2011
100(1):116 - 127

DOI:10.1111/j.1365-2745.2011.01915.x

Authors:

Angela Moles

UNSW Sydney

Stephen Bonser

UNSW Sydney

David I Warton

UNSW Sydney

Show all 21 authorsHide

1. We provide a brief overview of progress in our understanding of introduced plant species. 2. Three main conclusions emerge from our review: (i) Many lines of research, including the search for traits that make species good invaders, or that make ecosystems susceptible to invasion, are yielding idiosyncratic results. To move forward, we advocate a more synthetic approach that incorporates a range of different types of information about the introduced species and the communities and habitats they are invading. (ii) Given the growing evidence for the adaptive capacity of both introduced species and recipient communities, we need to consider the implications of the long-term presence of introduced species in our ecosystems. (iii) Several foundational ideas in invasion biology have become widely accepted without appropriate testing, or despite equivocal evidence from empirical tests. One such idea is the suggestion that disturbance facilitates invasion. 3. We use data from 200 sites around the world to provide a broad test of the hypothesis that invasions are better predicted by a change in disturbance regime than by disturbance per se. Neither disturbance nor change in disturbance regime explained more than 7% of the variation in the % of cover or species richness contributed by introduced species. However, change in disturbance regime was a significantly better predictor than was disturbance per se, explaining approximately twice as much variation as did disturbance. 4. Synthesis. Disturbance is a weak predictor of invasion. To increase predictive power, we need to consider multiple variables (both intrinsic and extrinsic to the site) simultaneously. Variables that describe the changes sites have undergone may be particularly informative.

Non-native plant species richness and influence of greenhouses and human populations in the conterminous United States

Article

Full-text available

Jun 2023

Brice B. Hanberry

Background One issue in invasive plant ecology is identification of the factors related to the invasion process that increase number of non-native species. When invasion by non-native species increases, so does the probability that some non-native species will become harmful, or classified as invasive species, which disrupt natural ecosystems with attendant economic and social costs. I quantified patterns of how non-native species richness varied with vegetation types and human populations. To evaluate the relative importance of different predictor variables for invasion pathways in the conterminous United States, I modeled non-native plant species richness by county compared to current and historical human populations; greenhouses and nurseries; railroads, pipelines, transmission lines, and oil and gas wells; and land covers of impervious surface, development intensity categories, agriculture, and vegetation types. I also modeled these variables within vegetation types, excluding vegetation variables. Results To summarize patterns, non-native plant species richness increased from 72 to 200 with increasing human population density classes. Forests and forest land use mosaics had the greatest mean number of non-native plant species, ranging from 121 to 166, whereas grasslands and grassland mosaics had the least number of non-native plant species, about 70. For modeling variable importance, all combined variables had R ² values of 56% (random forests regressor) and 54% (cubist regressor) for predictions of withheld observations of non-native plant species richness, with greenhouse density and percent forestlands as most influential variables. Single variables of greenhouses ( R ² = 29%), historical and current human populations ( R ² = 27% and 23%), impervious surface (25%), and medium intensity development (23%) were most associated with non-native plant species richness. For vegetation types, greenhouse and historical human population densities were influential variables particularly in forestlands, shrublands, and wetlands. Conclusions Based on these models, human population measures and horticultural locations of greenhouses and plant nurseries may have stronger relationships than measures of land use disturbance and transport with non-native plant species richness.

Non-native plant associations with wildfire, tree removals, and deer in the eastern United States

Article

Full-text available

Oct 2022

Brice B. Hanberry

Wildfires, tree removals, and deer herbivory are potential pathways for spread of non-native plants. I modeled the number of recorded nonnative plant species by county compared to wildfire area, tree removals, and deer densities in the eastern United States and also eastern forests. Species richness of 1016 plant species in 780 primarily forested counties decreased with increased values of the three variables; models equally showed negative relationships. For model predictions, based on withheld samples of non-native species counts, percentage wildfire area alone had the greatest association (R2 value of 31%) for non-native species richness in eastern forests; non-native species richness decreased with wildfire area until stabilizing at >1% wildfire area to a neutral relationship. For 1581 species in 2431 counties in the eastern U.S., the three variables each had an overall negative relationship with non-native species richness (R2 value up to 14%), without a consensus by three regression types of most influential variables. These formal models suggest that wildfire, tree removals, and deer herbivory generally may be nominal pathways for non-native plant spread at landscape scales in the eastern United States.

Island biogeography of plants and humans

Thesis

Full-text available

Mar 2022

Fabio Mologni

Islands have always attracted considerable research effort due to their unique geography and biota. However, the biogeography of islands still presents substantial challenges. For instance, islands often sustain high rates of plant invasions. The distributional patterning of exotic species on islands though is still poorly understood. Additionally, while species vary strongly in their life histories, plant traits have been rarely integrated with the investigation of the island biogeography of plant species. Islands are also commonly struck by storms and strong winds of oceanic origin, yet how ocean-borne disturbances affect island plant communities is unclear. Finally, in the last 50 years, researchers investigated the insular distribution of virtually every known taxon, but very little is known about variation in human population sizes on islands. The goal of this thesis is to investigate these understudied aspects within the theory of island biogeography framework in vascular plant species and humans. To better understand plant invasions on islands, I compared the relationships between native and exotic species richness and island characteristics on 264 islands offshore Northern New Zealand. Native and exotic species displayed broadly similar biogeographical patterns; however, exotic species exhibited subtle, yet distinctive, invasion patterns. Trends in species richness were also scale-dependent, and increasingly for exotic species. Second, I integrated plant life-history traits within the theory of island biogeography framework to investigate how exotic species with different traits relate to island characteristics on 264 islands offshore Northern New Zealand. Exotic species with traits associated with high invasion rates (i.e. high island occupancy rates) were more similar to native species both in occupancy and in relationships with island characteristics. Moreover, they were less commonly associated with human-related variables. 6 Third, I assessed how distributional patterns of native and exotic plant species varied depending on different levels of ocean-borne disturbances on 97 small New Zealand islands. Overall results show that both native richness and composition varied with different levels of disturbance. In striking contrast, distributional patterns of exotic species remained unchanged. Differences between natives and exotics might reflect a lack of coastal specialists in the exotic species pool. Lastly, I explored relationships between human population sizes and island characteristics on 10 archipelagos worldwide, for a total of 486 islands. Overall results showed that, just like other animals, human distributions are associated to island characteristics. However, relationships between human population sizes and island characteristics varied markedly among archipelagos, often reflecting specific social, political and historical circumstances. This thesis combines with a growing body of research on plant invasions on islands. It provides a fresh perspective on the subject by assessing previously overlooked aspects of the invasion process, such as the scale-dependency of the relationships between exotic species richness and island characteristics. Additionally, it integrated a trait-based approach within the theory of island biogeography framework. It also provided a test of how species of different biogeographic origins respond to varying levels of ocean-borne disturbances. Lastly, this work includes what is, to my knowledge, the first global test of the island biogeography of humans.

Different levels of disturbance influence the distributional patterns of native but not exotic plant species on New Zealand small islands

Article

Full-text available

Jun 2022

Fabio Mologni

Disturbances of oceanic origin can severely affect plant communities on islands, but it is unclear whether they promote or deter biological invasions. Here, I collected floristic data from 97 small islands subject to different levels of ocean-borne disturbances (i.e. inside and outside Wellington Harbour, New Zealand). First, I tested how relationships between the richness of native and exotic species and island characteristics (e.g. area, isolation, height, distance from nearest dwelling) changed depending on island location. Next, I assessed compositional differences on inner and outer islands for both native and exotic species, and how they vary with geographic distance between islands (i.e. distance-decay). Results show that the richness of both native and exotic plant species was similarly related to island characteristics regardless of island location. Both native and exotic species richness consistently increased with area and nearest dwelling. However, only exotics richness always declined with isolation, while natives richness alone consistently increased with height (elevation). Natives on outer, more exposed islands were floristically more homogenous, and compositional differences changed less strongly with the distance between islands than inside Wellington harbour. In contrast, exotics exhibited similar distributional patterns regardless of island location. Different levels of ocean-borne disturbances might explain distinct distributional patterns in native species. Conversely, results for exotic species might reflect a lack of coastal specialists in the species pool. Perhaps time-lags in the invasion process and non-equilibrium dynamics play a role as well. Conservation bodies should similarly manage islands sustaining different levels of ocean-borne disturbances.

Historical Fire and Ventenata dubia Invasion in a Temperate Grassland

Article

Full-text available

Mar 2021

Ventenata (Ventenata dubia L.) is an invasive annual grass that has rapidly expanded its range across temperate grassland and shrub-steppe ecosystems in western North America. However, there is little published regarding its ecology, especially its relationship with fire on rangelands. The objective of this study was to examine the effect of fire on ventenata invasion in the Pacific Northwest Bunchgrass (PNB) Prairie. Given the influence of fire on the invasion of other annual grasses such as cheatgrass (Bromus tectorum L.), we expected that fire would facilitate the spread and increase in abundance of ventenata. In addition, we considered that annual variation in precipitation might mask the effect of fire and drive the year-to-year variation in production of ventenata. Therefore, we resampled 56 plots in 2015 and 2016 where frequency and foliar cover of ventenata had been recorded in 2008 and where 12 of these plots had burned in the past 15 yr. We then compared ventenata abundance (frequency and foliar cover) between burned and unburned plots within each sampling yr (2008, 2015, and 2016), as well as the change in abundance over time. Our data revealed that ventenata frequency and cover increased on all plots. However, there was not significantly higher abundance in burned plots in any of the sampling years. In addition, ventenata abundance did not increase more in burned plots over time. Our findings suggest that, unlike cheatgrass, fire may not be a driving factor in the spread and increase of ventenata across the PNB Prairie. This finding has important implications for the management and control of ventenata, as well as the conservation of the PNB Prairie.

Land‐use intensity and relatedness to native plants promote exotic plant invasion in a tropical biodiversity hotspot

Article

Full-text available

Apr 2024
J APPL ECOL

Exotic plant invasions threaten biodiversity and are costly to farmers. Land use is a major pathway promoting the spread of exotic plant species; however, little is known about the processes underlying the success of exotic plants in tropical agricultural landscapes. Focussing on the heterogeneous smallholder landscapes of north‐eastern Madagascar, we studied exotic plants of understorey communities across a land‐use intensity gradient from unburned lands (old‐growth forests, forest fragments and forest‐derived vanilla agroforests) to burned ones (fallow‐derived vanilla agroforests, woody fallows and herbaceous fallows). We quantified the absolute species richness, abundance and cover of exotic plants across land‐use types and their proportional contribution to community richness, abundance and cover as indicators of exotic plant invasion. We tested for the effects of land‐use parameters, namely land‐use history, canopy closure and landscape‐level forest cover, on exotic plants. Additionally, we tested whether the phylogenetic relatedness between exotic and native species in the same plot affected invasion success, testing Darwin's naturalisation and pre‐adaptation hypotheses. All indicators of exotic plant invasion were lowest in old‐growth forests and forest fragments and highest in fallow‐derived vanilla agroforests, woody fallows and herbaceous fallows. Absolute and proportional exotic richness were negatively affected by canopy closure, and landscapes with high forest cover had lower proportions of exotic plant richness. High phylogenetic relatedness between exotics and natives was associated with lower proportional richness but higher proportions of exotics in abundance and cover. However, individual exotic species showed contrasting responses to land‐use parameters and relatedness to natives. Synthesis and applications: Our results indicate that maintaining unburned lands, land‐use types with dense canopies and landscapes with high forest cover prevents the spread of exotic plants within the agricultural landscapes of north‐eastern Madagascar. Supporting Darwin's pre‐adaptation hypothesis, exotic plants that are phylogenetically closely related to native plants are more likely to become successful invaders in terms of abundance and cover. Nevertheless, individual species show different responses to land‐use changes and phylogenetic relatedness. Therefore, land‐use decisions and management choices can be tailored to limit the spread of exotic species and to preserve native plants in this global biodiversity hotspot.

Abiotic and biotic contexts shape the effect of disturbance on non‐native plant invasion

Article

Dec 2023

Making predictions about when and where a given mechanism of invasion will be weak or strong is crucial for the effective management of non‐native species. Despite the importance of disturbance on invasion, our understanding of how variation in abiotic and/or biotic conditions may modify the disturbance‐invasion relationship is scarce. Here, we aimed to evaluate how abiotic (soil type) and biotic (tree and shrub cover) contexts affect the disturbance–invasion relationship in disturbed and nearby non‐disturbed communities in the semi‐arid open forest of central Argentina (ca 36°S) using field sampling. We found that abiotic context modulated non‐native species success in disturbed communities, whereas both abiotic and biotic context modulated success in nearby non‐disturbed communities. These findings suggest that the plant invasion–disturbance relationship is context‐dependent. Our results hint at the possibility that the significance of disturbance in predicting invasion might diminish as the importance of abiotic filters increases.

Higher plant colonisation and lower resident diversity in grasslands more recently abandoned from agriculture

Article

Full-text available

Sep 2023
J ECOL

Rates of species colonisation and extirpation are increasing in plant communities world‐wide. Colonisation could potentially help compensate for, or compound, resident diversity loss that results from global environmental change. We use a multifactorial seed addition grassland experiment to examine relationships between plant colonisation, resident species diversity and key community assembly factors over 3 years. By manipulating colonist seed rate, imposing disturbance and examining abundance and diversity impacts of 14 formerly absent sown colonists in communities that varied in successional stage and time since agricultural abandonment, we were able to disentangle effects of global change factors (species introduction, novel disturbance and land use change) that are usually confounded. Evidence suggested that cover abundance of sown colonists was most strongly influenced by successional stage of recipient communities, though number of growing seasons was also important for the group of seven colonists with resource conservative ‘slow’ life history traits. Colonist type, seed rate and disturbance had weaker relationships with colonist cover. Factors affecting sown colonist cover were highly conditional. A negative relationship between plot‐level disturbance and colonist cover in early successional communities meant that, despite a positive relationship in late succession, colonisation was negatively related to disturbance overall, defying theoretical expectations. Non‐sown resident diversity was negatively related to colonist cover and positively related to successional stage. Resource acquisitive colonists with ‘fast’ life history traits appeared to limit cover of ‘slow colonists’ when the two groups were sown together, likely reflecting niche pre‐emption. Communities at earlier stages of succession had lower resident diversity and experienced higher levels of colonisation than communities at later stages of succession. Elevated colonisation and lower resident diversity both appeared to be symptoms of human‐induced land use change. However, results suggested that resource competition from plant colonists may also limit resident diversity in grasslands abandoned from agriculture more recently. Synthesis. Our findings point to the importance of resource availability and competition on plant colonisation and colonist impacts on residents. Although colonisation is potentially a source of biodiversity in the short term, our results suggest that plant colonists that reach high abundance may be a further threat to resident plant diversity in secondary grasslands recovering from a recent history of agriculture.

Spanish Scientists Working Abroad

Article

Full-text available

Apr 2003
SCIENCE

In Xavier Bosch's interview “Spain's science minister sees future in telecom” (News Focus, 31 Jan., p. 653), Josep Pique, Spanish Minister of Science and Technology, asserts that “[n]ow there are many more scientists from abroad working in Spain than there are Spanish scientists abroad.”

Native diversity buffers against severity of non-native tree invasions

Article

Full-text available

Aug 2023
NATURE

Determining the drivers of non-native plant invasions is critical for managing native ecosystems and limiting the spread of invasive species1,2. Tree invasions in particular have been relatively overlooked, even though they have the potential to transform ecosystems and economies3,4. Here, leveraging global tree databases5-7, we explore how the phylogenetic and functional diversity of native tree communities, human pressure and the environment influence the establishment of non-native tree species and the subsequent invasion severity. We find that anthropogenic factors are key to predicting whether a location is invaded, but that invasion severity is underpinned by native diversity, with higher diversity predicting lower invasion severity. Temperature and precipitation emerge as strong predictors of invasion strategy, with non-native species invading successfully when they are similar to the native community in cold or dry extremes. Yet, despite the influence of these ecological forces in determining invasion strategy, we find evidence that these patterns can be obscured by human activity, with lower ecological signal in areas with higher proximity to shipping ports. Our global perspective of non-native tree invasion highlights that human drivers influence non-native tree presence, and that native phylogenetic and functional diversity have a critical role in the establishment and spread of subsequent invasions.

6 - Network Scaling

Article

May 2022

Maps of global biomes or ecoregions show geographical clusters – unique assemblages of plants and animals that are spatially tied with associated geomorphologic and climatic features. Biomes are typically defined on the basis of broad vegetation types and the biophysical features that impose fundamental controls on the distribution of plants (Cox and Moore 2000). The concept of biomes has a deep history in ecology and has experienced waves of knowledge synthesis, reaching a recent consensus of seven points (Mucina 2019), one of which caught our attention: ‘A biome incorporates a complex of fine-scale biotic communities; it has its characteristic flora and fauna and it is home to characteristic vegetation types and animal communities.’ Macro-scale biodiversity patterns, therefore, reflect the overarching geophysical structures of the globe such as the well-known latitudinal gradients of biodiversity (Willig et al. 2003) and associated ecosystem functioning (e.g., litter decomposition in streams via detritivores; Boyero et al. 2015). Nevertheless, within constantly changing environments, the species composition and geographical boundaries of biomes (called ecotones) are not fixed, but are fluid over evolutionary timescales (Haywood et al. 2019). This biodiversity–environment coupling has been disrupted by agriculture and urbanisation, and the appetite of humans for resources and raw materials and their carelessness in handling waste. Humans are steadily altering land cover and modifying ecological processes across the globe, creating a new ecological order of anthropogenic biomes (anthromes; sensu Ellis and Ramankutty 2008). Natural biomes are facing unprecedented pressures to change, shift, dissolve, merge and emerge, at a pace on par with the most tumultuous periods of the biosphere’s history.

4 - Regimes and Panarchy

Article

May 2022

Before diving into a discussion of open adaptive systems, we need to revisit the definition of an ecological network. Material covered in Chapters 2 and 3 showed that ecological networks are webs of co-evolving and co-fitting interactions among species residing in an ecosystem. Such networks subjected to regular incursions of new members in the form of biological invasions are a good example of Open Adaptive Systems (OASs). OASs are different from Clements’ (1916) superorganism metaphor that was further developed and scaled up into the concept of Lovelock’s (1972) Gaia theory, which posits that organisms interact to form a synergistic and self-regulating complex system. The reason for considering an ecological network (or its embedded ecological community) a system, rather than an organism or an organisation (sensu Keller 2005), lies with the type of its boundaries. A system can have either permeable or closed boundaries, while an organism cannot survive with a closed boundary. More importantly, a system has more flexible and tenuous boundaries, the positions of which are often set by the beholder. Boundaries drawn around sampling areas based on what we call an ecological community or an ecosystem are largely subjective. In contrast, the boundary of an organism is clear-cut and plays important physiological and metabolic roles. The value of a system’s boundary, albeit usually subjectively defined, is to identify and differentiate its residents from alien visitors, thereby providing the foundation for labelling entities for management purposes. In contrast, the organic boundary is inseparable from the organism; they belong to an irreducible whole.

1 - Invasion Science 1.0

Article

May 2022

At the time of writing this book, we have witnessed an extreme case of biological invasion. A virus, through an evolutionary leap, has jumped onto a new host species, Homo sapiens, and has taken advantage of the new host’s ambitions and mobility in the zealous phase of globalisation, causing a worldwide pandemic and economic meltdown. The 2019 coronavirus outbreak (COVID-19) is a showcase of the core of invasion science. A list of questions spring to mind. Why this particular virus, and not others? Why now? How fast can it spread? How is its spread mediated by climatic and other environmental factors? What are its vectors and pathways of transmission? Which regions and populations are most susceptible? How much damage can it cause to public health and economies? What factors cause substantial variation in mortality between human populations in different countries? How can we control it? Can we forecast and prevent future outbreaks of emerging infectious diseases? While the whole world scrambles to make sense of COVID-19 and to combat the biggest crisis for humanity since World War II (WWII), we embark on a journey to address these questions to cover many more taxa and situations – the invasion of any biological organism into novel environments.

7 - Rethinking Invasibility

Article

May 2022

Until now, biological invasions have been conceptualised and studied mainly as a linear process: from introduction to establishment to spread. This volume charts a new course for the field, drawing on key developments in network ecology and complexity science. It defines an agenda for Invasion Science 2.0 by providing new framings and classification of research topics and by offering tentative solutions to vexing problems. In particular, it conceptualises a transformative ecosystem as an open adaptive network with critical transitions and turnover, with resident species heuristically learning and fine-tuning their niches and roles in a multiplayer eco-evolutionary game. It erects signposts pertaining to network interactions, structures, stability, dynamics, scaling, and invasibility. It is not a recipe book or a road map, but an atlas of possibilities: a 'hitchhiker's guide'.

Invading Ecological Networks

Book

Jan 2022

Disturbance and indirect effects of climate warming support a plant invader in mountains

Article

Full-text available

Feb 2022
OIKOS

Climate warming and increased disturbance (resulting from intensified land use) are expected to enhance the invasibility of plant communities and the performance of exotic species also at high elevations, and thus pose additional threats to mountain ecosystems. The invasion success of introduced genotypes will also depend on their degree of pre‐adaption to high elevation climatic conditions, which may vary intra‐specifically across source populations. For populations currently spreading in the lowlands, climate warming might reduce the climatic distance to high‐elevation sites and thus remove a barrier to upwards spread. Here, we investigated the various facets of mountain invasions in a single, integrative experimental study. We applied a community transplant approach between high‐ and low‐elevation sites in the European Alps to address effects of climate warming and disturbance through land use on community invasibility and the performance of the exotic species Senecio inaequidens , a potential future plant invader in the Alps. Additionally, the transplant sites served as common gardens to test the influence of climatic pre‐adaptation to current (high site) and future (low site) climatic conditions on the performance of S. inaequidens in the transplanted communities. The 16 invasive central and western European S. inaequidens source population locations covered a wide geographic range, and thus a wide amplitude of climatic distances and presumed pre‐adaptation to our gardens. Our results attest to a strong effect of disturbance, which increased community invasibility, and promoted the performance of the exotic species. Contrary to our expectation, experimentally induced climate warming did not increase community invasibility. However, the performance of the S. inaequidens populations was positively related to their pre‐adaptation to the climatic conditions of our common gardens. Climate warming might thus promote the invasion of exotic species by reducing the climatic distance between mountain ranges and locations of potential source populations.

Six central questions about biological invasions to which NEON data science is poised to contribute

Article

Full-text available

Sep 2021

Biological invasions are a leading cause of rapid ecological change and often present a significant financial burden. As a vibrant discipline, invasion biology has made important strides in identifying, mapping, and beginning to manage invasions, but questions remain surrounding the mechanisms by which invasive species spread and the impacts they bring about. Frequent, multiscalar ecological monitoring such as that provided through the National Ecological Observatory Network (NEON) can be an important tool for addressing some of these questions. We articulate a set of major outstanding questions in invasion biology, consider how NEON data science is positioned to contribute to addressing these questions, and provide suggestions to help equip a growing contingent of NEON data users in solving invasion biology problems. We demonstrate these ideas through four case studies examining the mechanisms of plant invasions in the U.S. Intermountain West. In Case Study I, we evaluate the relationships between native species richness, non‐native species richness, and probability of invasion across scales. In Case Studies II and III, we explore the relationship between environmental factors and non‐native species presence to understand invasion mechanisms. Case Study IV outlines a method for improving the ability to distinguish invasive plants from native vegetation in remotely sensed data by leveraging temporal patterns of phenology. There are many novel elements in the NEON sampling design that make it uniquely poised to shed light on the mechanisms that can help us understand invasibility, prediction, and progression, as well as on the variability, longevity, and interactions of multiple invasive species’ impacts. Thus, knowledge gained through analysis of NEON data is expected to inform sound decision‐making in unique ways for managers of systems experiencing biological invasions.

Invasive Species Response to Natural and Anthropogenic Disturbance

Chapter

Full-text available

Feb 2021

Much of the literature dealing with the biology and management of invasive species has focused on the damaging ecological and economic consequences of invasions (see Chaps. 10.1007/978-3-030-45367-1_2 , 10.1007/978-3-030-45367-1_3 , and 10.1007/978-3-030-45367-1_14 of this volume for review). In this chapter, we shift the focus to the causes of invasion, with the goal of proactively limiting or preventing invasions rather than reacting to them once they have occurred. Preventing the introduction of invasive species is one key element in this proactive approach (Chap. 10.1007/978-3-030-45367-1_6 , this volume). Here, we specifically focus on ecosystem attributes that affect whether or not an ecosystem is vulnerable to invasion, that is, the features that affect its invasibility (Lonsdale 1999), with particular emphasis on the role of natural and anthropogenic disturbance.

Alliance between invasive plants management and farming: Cutting and livestock browsing reduce resprout and fruit production in an invasive shrub

Article

Full-text available

Feb 2024
FOREST ECOL MANAG

Biological invasions and land use change for extensive livestock are among the main threats to biodiversity and ecosystem functioning in the Anthropocene. Mechanical management actions against invasive plants are important to restore some of nature's contributions to people (e.g., water provisioning). Mountain Chaco Woodlands in central Argentina have been occupied by livestock production for centuries and during the last three decades invasive woody plants have been increasing their invaded surface. Pyracantha angustifolia is a thorny invasive shrub that facilitates other exotic species establishment and is rapidly invading many areas of this system. Moreover, the advance of the invasion is not uniform across the landscape (i.e., plant density is higher along water courses). The necessity to establish a low-cost, low-impact management strategy (e.g., without chemicals), motivates the integration of livestock production with mechanical actions against P. angustifolia advance. In this regard, we evaluate if livestock browsing complements mechanical control of invasive shrubs in mountain woodlands to reduce posterior resprout and fruit production. Using individual livestock exclusions we tested the effect of browsing and topography on P. angustifolia resprout and fruiting in a period of two years after mechanical cutting in an invaded basin of Mountain Chaco Woodlands. Our study demonstrates that the combined effect of plant cutting and subsequent livestock browsing on resprout contributes to reducing the propagule pressure of the targeted invasive shrub by temporarily limiting resprout and fruiting. Moreover, the livestock browsing on individuals located near the watercourse showed higher resprout and fruit production after the second year post-cutting compared to individuals on the slopes. This result highlights that the livestock effect is affected by topographic characteristics of the area (i.e., proximity to a watercourse). Furthermore, after two years of post-cutting, all the treatments showed a decrease in the effect of livestock browsing but the treatment with the highest fruit production remains much lower than the expected fruit production without management actions. Our study represents a contribution to the knowledge about how the interaction between human activity, such as livestock production, and invasive plant mechanical control can impact the invasion process of alien plants in mountain woodlands of central Argentina. The understanding of this relationship is an essential step for evaluating the success of a plant invasion management strategy in mountain systems.

Foundations of Science in Invasive Technologies

Preprint

Full-text available

Feb 2024

Mario Coccia

This study proposes that one of the drivers of technological change is due to technological invasion of path-breaking technologies and innovations. Invasion is anything that breaks into a place, occupying it or spreading in large quantities. This aspect is present in botany with invasive plants, in biology with invasive organism or in medicine with invasive cancer cells. The extension of this concept in the field of technologies can clarify main dynamics of technological change. In a perspective of generalized Darwinism, the theory here suggests the invasive behavior of technologies that expands the space of adjacent possible by introducing novelties and radical innovations with a dynamic interaction between the actual and possible. The prediction of the theory, given by acceleration rates of invasive technologies that conquer space of alternative technologies, is tested in emerging path-breaking technology of transformer (a type of deep learning architecture used in natural language processing-NPL- and in generative Artificial Intelligence). Transformer technology, introduced in 2017, and from 2018 is developing radical innovations in pretrained language models (Generative Pretraining Transformers, GPTs), such as OpenAI's GPT series, Google's Bidirectional Encoder Representations from Transformers (BERT) model with main products of ChatGPT introduced in November 2022 and Microsoft Copilot started on February 2023. Transformer technology and related radical innovations are spreading rapidly, invading and destroying other established technologies, changing the space of possibilities in human society. One significant way to understand the invasive behaviour of technologies is to estimate and analyze rates of spread. Statistical evidence here, based on patent analyses, reveals that the growth rate of transformer technology is 55.82% (over 2016-2023) more than double compared to 23.02% of all other technologies. The last three years (2021-2023) show that the growth rate is 25.81% for transformer models with an invasive and disruptive force of other technologies, having mere 0.76% of growth. Results are confirmed with a model of technological evolution that reveals a growth rate of invasive technology of transformers of 0.30 versus 0.13 for other technologies. Comparative analysis with a previous technology in neural network, Convolutional Neural Network (CCN), suggests that transformer architecture has a higher disruptive force that spreads rapidly invading the space of other technologies (technological invasion) with radical innovations, generating a drastic technological shift and change in the space of possibilities. This accelerated dynamics of transformer technology driving generative AI that mimics human ability is due to leading firms (such as OpenAI with ChatGPT, Microsoft with Copilot, Google with BERT, Apple with forthcoming his GPT, etc.) that are creating the innovation ecosystem based on new platforms and products directed to applications and diffusion in markets for a main technological and industrial change. Overall, the invasive behaviour of transformer technologies and related innovations is fueling continuous innovations in the space of adjacent possible in generative AI and explains, in current world of knowledge-based competition, the 'creative destruction' that has revolutionized the field of NLP with new products that invade current and new markets. Implications for management of technology and innovation policy are suggested to support invasive technologies.

Contribution of soil seed banks to vegetation resilience in coastal freshwater wetlands of subtropical Australia

Article

Full-text available

Jan 2024

Questions What role do soil seed banks play in the resilience of coastal freshwater wetland vegetation communities? How might soil seed bank composition and similarity to standing vegetation drive changes in vegetation expression, particularly given projected changes in climate? Location Sixty wooded coastal freshwater wetlands in southeast Queensland, Australia. Methods We surveyed standing vegetation and investigated soil seed bank composition through an 8‐month‐long emergence experiment. Results Soil seed bank assemblages were dominated by forb and sedge species (23% exotic), but composition varied throughout the study region. Spatial (north–south) and land‐use (urban–rural) gradients explained some variation in soil seed bank composition. Soil moisture and groundwater dependence also influenced species distributions, particularly for freshwater wetland species. The similarity of soil seed banks to standing vegetation was low. Species present in both extant and soil seed bank assemblages were commonly native wetland taxa, including one salt marsh species ( Juncus kraussii ). Conclusions Projected climatic changes will likely drive changes in coastal freshwater wetland vegetation communities through increases in the frequency and intensity of disturbances (e.g., storm surge). Our results suggest that regeneration from soil seed banks could promote four potential scenarios: (1) expansion of weed communities, (2) expansion of salt marsh communities, (3) maintenance and expansion of wetland/terrestrial species, and (4) transformation to an unvegetated open water zone because of reduced regeneration success under changing conditions. These diverse vegetation futures highlight the vulnerability of wooded coastal freshwater wetlands and the need for research and management interventions to maintain their biodiversity and ecosystem services.

Journal of Tropical Mycorrhiza Management of the mycorrhizal and rhizobial associations to mitigate the negative effects of Grevillea banksii on the development of Dalbergia trichocarpa an endemic tree species

Article

Full-text available

Oct 2023

This study aims to improve the development of Dalbergia trichocarpa, a Malagasy native tree species, on a soil invaded by Grevillea banksii, an invasive plant species in eastern part of Madagascar, by inoculating seedlings with mycorrhizal fungal, Rhizophagus irregularis and AMFn strains or rhizobial STM609 and Rn strains, or a mixed rhizobial-mycorrhizal strains. After five months of growth, the results showed that single or dual inoculation boosted significantly the development of D. trichocarpa, compared to control treatments and all parameters measured were markedly different between the time periods of plant invasions. Indeed, the dry mass of aerial biomass was significantly higher in inoculated seedlings than in control seedlings. It was also observed that the number of nodules and the arbuscular mycorrhizal colonization rates of D. trichocarpa increased significantly with inoculated plantlets. However, soil inoculated with the rhizobial strain STM609 alone showed a significantly high global soil microbial activity and the dual inoculation has promoted the soil acid phosphatase activity. These results suggest that dual inoculation with rhizobial and arbuscular mycorrhizal strains was significantly beneficial to the growth, nodulation and mycorrhizal colonization rates of D. trichocarpa in the soil overgrown by G. banksii, an invasive exotic plant species. Thus, this biotechnology can be used for restoration of degraded ecosystems in Madagascar with native tree species.

Assessing the mechanisms and impacts of shrub invasion in forests: A meta‐analysis

Article

Full-text available

Aug 2023
J APPL ECOL

The encroachment of invasive shrubs in forest understories can have detrimental effects on native plant recruitment. As a result, removal of invasive species is a common practice although long‐lasting success is rare. In order to effectively conserve and manage invaded forests, it is crucial to understand the mechanisms that drive shrub invasion, that is, high propagule pressure, low native resistance and exploitation of empty niches. To gain a deeper understanding of the invasion process in forest ecosystems we conducted a meta‐analysis of the work done in this topic. We collected data on invasive species and native community performance, and on the abiotic conditions of forest understories under low and high levels of shrub invasion. We analysed data from 124 articles that yielded 377 unique observations. Our results revealed that while invader performance did not vary by the mechanism of invasion, the impact on the native community was significantly detrimental when invasion occurred via low biotic resistance, and only marginally significant via propagule pressure. Invasive species performance was associated with increases in light availability, but not with other resources (soil water or nutrients). When assessing impact on native performance as a function of invasive performance, results were again only significant under the low biotic resistance mechanism. Lastly, impacts were stronger when invasion took place by a single invader. Synthesis and applications. Taken together, these results suggest that restoration efforts should focus on (i) increasing the presence of strong native competitors or functionally diverse native communities, (ii) decreasing sources of invasive shrub propagules while keeping the canopies closed when invasion occurs via high propagule pressure, (iii) avoiding management techniques that degrade or diminish canopy cover and (iv) prioritizing management of forest understories dominated by particularly impactful invasive shrubs.

Space use by Callosciurus erythraeus in a fragmented landscape

Article

Jul 2023
MAMMALIA

Tree squirrel species that are successful invaders may modify their behaviour according to the characteristics of the invaded community. We studied the use of space by Callosciurus erythraeus in the main invasion focus established in Argentina, where suitable habitat is highly fragmented and immersed in a rural-urban landscape of the Pampas region. We evaluated habitat use in relation to the dominant arboreal vegetation (evergreen vs. deciduous) based on seasonal trapping data throughout two years and home range size and overlap based on seasonal radio-tracking data in two consecutive years. We captured 476 squirrels with a higher trapping success in areas dominated by evergreen vegetation. Effective home ranges were smaller for females (0.10-0.77 ha, n = 12) than for males (0.9-3.78 ha, n = 3). We observed home range overlap between and within both sexes, suggesting no or low territoriality. Our results support the two working hypotheses on the relatively higher use of areas dominated by evergreen vegetation and on the relatively small home range sizes and large overlapping areas associated to high squirrel density. The flexibility in the use of different type of arboreal patches would be another attribute linked to the invasion success of this species.

Warming promotes non-native invasive ants while inhibiting native ant communities

Article

Full-text available

May 2023

1. Non‐native species may be the cause of native species declines or an effect of habitat degradations that promote the former and damage the latter. Social insects are extraordinarily successful organisms, and non‐native social insects, such as ants, often are very successful invaders of novel habitats. 2. The red imported fire ant ( Solenopsis invicta ) and the Asian needle ant ( Brachyponera chinensis ) are widespread non‐native invaders in the eastern United States that bring ecological, economic and social impacts, but their putative effects on native ant communities may be concomitant with habitat degradation rather than inherent in their invasion. 3. Given this gap in understanding, our goal was to examine how experimental warming influenced native and non‐native ant communities. Specifically, we hypothesised that (a) non‐native ant abundance and species richness will increase in warmed plots and that (b) warming‐induced increases in the non‐native ant populations will correspond with decreases in native ant abundance and species richness. 4. To test these hypotheses, we used three levels of experimental forest edge soil warming (warming targeted at +0, +3, and +5°C above ambient soil temperature) in a mixed deciduous forest in the Georgia (USA) Piedmont. We used repeated pitfall trapping to investigate how the experimental warming influenced the composition of native and non‐native ant communities with a focus on how warming combined with S. invicta and B. chinensis invasion impacted native ant communities. 5. Our results suggest that experimental warming promoted the non‐native invasive ants, particularly S. invicta and B. chinensis . We also found that B. chinensis somewhat inhibited native ant communities, but not because of warming. The warmed environment benefited both non‐native invasive ants at the expense of native ants but, given that B. chinensis negatively impacted the native ants with far fewer workers than S. invicta , B. chinensis may pose a greater threat to native ant communities than S. invicta in a warmer world.

Global change drivers synergize with the negative impacts of non-native invasive ants on native seed-dispersing ants

Article

Full-text available

Oct 2022
BIOL INVASIONS

Non-native species invasion, habitat fragmentation and climate change individually impose negative impacts on natural systems, but their synergistic effects may do more harm than the sum of their parts. We examined the combined effects of these global change drivers by studying the impacts of experimental warming on seed-dispersing forest ant nesting and foraging in the Southeastern U.S. to determine if warming and forest fragmentation facilitated non-native ant invasion effects on native ants. Spring ant phenology and activities were monitored for two years (2019–2020) at weekly bait stations and in artificial nest occupancy. We found that, when combined, forest edge habitat and experimental warming favored invasive non-native ant frequency, but the experimental warming alone did not appear to facilitate non-native ant incursion into forested habitat. We did find, however, that experimental warming exacerbated the negative effects of non-native ants on native ant foraging. Moreover, fragmented edge habitat strongly limited native forest ant foraging and experimental warming increased the negative effects of non-native ant invaders on native ants. Ultimately, the non-native ants displaced native seed-dispersing ants from artificial nests, and the displacement progressively increasing with greater experimental warming. Our results suggest that global change drivers such as warming, habitat fragmentation and species invasion imposed negative impacts individually, but their combined effects were worse than the sum of their parts. Moreover, our results indicate that predicting species reactions to global change poses great challenges given that the strongest impacts were the non-additive effects.

A general hypothesis of forest invasions by woody plants based on whole‐plant carbon economics

Article

Full-text available

Oct 2022
J ECOL

Although closed‐canopy forests are characterized by low‐light availability and slow population dynamics, many are under threat from non‐native, invasive woody species that combine high colonization ability and fast growth potential with high low‐light survival. This ‘superinvader’ phenotype contravenes expected trade‐offs predicted by successional niche theory, posing a challenge to both invasion and forest succession theory. We propose a parsimonious conceptual model based on the whole‐plant light compensation point (WPLCP) that, across a variety of plant strategies and growth forms, can explain greater competitive abilities of forest invaders in the context of both high‐light growth rate and shade tolerance. The model requires only that non‐native species experience relatively fewer carbon costs than native species, enabling resource‐acquisitive species to establish in low‐light conditions. We review evidence for lower carbon costs in invasive species resulting from (1) enemy release, (2) recent environmental changes that favour less stress‐tolerant phenotypes and (3) phylogenetically constrained native floras. We also discuss implications of invader shade tolerance in the context of other life‐history strategies that, combined with canopy disturbances, facilitate their rapid numerical dominance. Synthesis. An invasion framework driven by carbon dynamics suggests renewed focus on whole‐plant carbon costs, including below‐ground respiration and tissue turnover, which are rarely measured in functional studies of forest invaders.

Weedy and seedy: the rapid evolution of life-history characteristics in an introduced daisy

Article

Full-text available

Aug 2022

Despite the importance of life-history characteristics in determining a species’ success, we still lack basic information about some fundamental life-history elements found across the life cycle of introduced plants. Our study assesses rapid evolutionary divergence in life-history characteristics of the beach daisy Arctotheca populifolia by comparing introduced Australian and source South African plants and measuring eight key variables including seed mass, germination, reproductive output and survival. This is the first study that compares the life-history of an introduced plant species with its single original source population, providing a precise and powerful method for detecting evolutionary divergence. We found that introduced A. populifolia has evolved a suite of weedy life-history characteristics in less than 90 years: the introduced plants use a live-fast die-young strategy of germination and survival and produce significantly more inflorescences and more seeds that germinate faster. This knowledge adds to the remarkable data that we already have on the rapid evolutionary divergence occurring in the morphology, physiology and defence of this introduced plant and highlights the speed and scope of evolutionary divergence possible in plants. To fully understand and manage the future of our plant species we must consider their potential for ongoing change in key aspects of life-history.

Evolution of increased competitive ability may explain dominance of introduced species in ruderal communities

Article

Full-text available

May 2022
ECOL MONOGR

The evolution of increased competitive ability (EICA) hypothesis encapsulates the importance of evolution and ecology for biological invasions. According to this proposition, leaving specialist herbivores at home frees introduced plant species from investing limited resources in defense to instead use those resources for growth, selecting for individuals with reduced defense, enhanced growth, and, consequently, increased competitive ability. We took a multispecies approach, including ancestral and non‐native populations of seven weeds, as well as seven coexisting local weeds, to explore all three predictions (i.e., lower defense, greater growth, and better ability to compete in non‐native than ancestral populations), the generality as an invasion mechanism for a given system, and community‐level consequences of EICA. We assessed plant defenses by conducting herbivory trials with a generalist herbivore. Therefore, finding that non‐native populations are better defended than ancestral populations would lend support to the shifting defense (SD) hypothesis, an extension of EICA that incorporates the observation that introduced species escape specialists, but encounter generalists. We also manipulated water additions to evaluate how resource availability influences competition in the context of EICA and plant plasticity in our semiarid system. We found that non‐native populations of one study species, Centaurea solstitialis, were better defended, grew faster, and exerted stronger suppression on locals than ancestral populations, offering support to EICA through the SD hypothesis. The other species also displayed variation in trait attributes between ancestral and non‐native populations, but they did not fully comply with the three predictions of EICA. Notably, differences between those populations generally favored the non‐natives. Moreover, non‐native populations were, overall, superior at suppressing locals relative to ancestral populations under low water conditions. There were no differences in plasticity among all three groups. These results suggest that evolutionary change between ancestral and non‐native populations is widespread and could have facilitated invasion in our system. Additionally, although trading growth for shifted defense does not seem to be the main operational path for evolutionary change, it may explain the dominance of some introduced species in ruderal communities. Because introduced species dominate communities in disturbed environments around the world, our results are likely generalizable to other systems.

Fast but steady: An integrated leaf‐stem‐root trait syndrome for woody forest invaders

Article

Full-text available

Jan 2022
ECOL LETT

Successful control and prevention of biological invasions depend on identifying traits of non‐native species that promote fitness advantages in competition with native species. Here, we show that, among 76 native and non‐native woody plants of deciduous forests of North America, invaders express a unique functional syndrome that combines high metabolic rate with robust leaves of longer lifespan and a greater duration of annual carbon gain, behaviours enabled by seasonally plastic xylem structure and rapid production of thin roots. This trait combination was absent in all native species examined and suggests the success of forest invaders is driven by a novel resource‐use strategy. Furthermore, two traits alone—annual leaf duration and nuclear DNA content—separated native and invasive species with 93% accuracy, supporting the use of functional traits in invader risk assessments. A trait syndrome reflecting both fast growth capacity and understorey persistence may be a key driver of forest invasions. We show that non‐native, invasive woody plants of North American deciduous forests express a unique functional syndrome combining traits associated with both high growth potential and high shade tolerance. This syndrome was absent in all native species examined and involves an integrated growth strategy reflecting leaf, stem and root traits.

Towards a better understanding of the effect of anthropogenic habitat disturbance on the invasion success of non-native species: slugs in eastern Canadian forests

Article

Full-text available

May 2022
BIOL INVASIONS

The disturbance hypothesis postulates that habitat disturbance favours the invasion success of non-native species. Its unspecific formulation has led invasion biologists to evaluate either the effect of the occurrence of a disturbance or its characteristics (e.g., its intensity) on the invasion success of non-native species. However, the hypothesis is unclear about these two effects, which might explain why studies offer ambivalent support for this hypothesis. Our objective was to determine the effects of the occurrence of an anthropogenic disturbance (i.e., logging), its intensity, and the time since its occurrence on the invasion success (i.e., abundance) of the non-native slug species complex Arion subfuscus s.l. (hereafter Arion). We used pitfall trapping in stands located in two boreal and two temperate forest ecosystems in eastern Canada. We sampled unlogged and logged stands that differ in harvesting intensity (from partial to complete removal of standing live trees and downed biomass) and time since logging (from 1 to 66 years). Our results revealed a positive effect of logging occurrence on Arion abundance in only one of the four study sites, whereas it had a negative or no effect at the three other study sites. Our results also showed that Arion abundance decreased with increased biomass removal intensity and usually increased with time-since-logging. Given the varying response of non-native species to logging and its characteristics, future studies should aim to reformulate the disturbance hypothesis to make more specific predictions of the conditions under which habitat disturbance promotes the invasion success of non-native species.

Addressing context dependence in ecology

Article

Full-text available

Oct 2021
TRENDS ECOL EVOL

Context dependence is widely invoked to explain disparate results in ecology. It arises when the magnitude or sign of a relationship varies due to the conditions under which it is observed. Such variation, especially when unexplained, can lead to spurious or seemingly contradictory conclusions, which can limit understanding and our ability to transfer findings across studies, space, and time. Using examples from biological invasions, we identify two types of context dependence resulting from four sources: mechanistic context dependence arises from interaction effects; and apparent context dependence can arise from the presence of confounding factors, problems of statistical inference, and methodological differences among studies. Addressing context dependence is a critical challenge in ecology, essential for increased understanding and prediction.

Article

Full-text available

May 2021

Aim A better understanding of plant invasions on islands can be gained from comparing patterns of exotic and native species richness. We asked four questions: (1) Is exotic species richness on islands related to native species richness? (2) If they are related, does this result from similar responses of native and exotic species to specific island characteristics? (3) Is residual variation in native‐exotic richness relationships associated with distinctive island characteristics? (4) Are relationships between species richness and island characteristics scale‐dependent, and do they differ between native and exotic species? Location This study was conducted in Northern New Zealand. Taxon Vascular plants. Methods We conducted field surveys and augmented our field data with previously published surveys to quantify the number of native and exotic plant species on 264 islands. We then explored the relationship of species richness and several island characteristics (e.g. area and isolation) using multiple and iterative regression techniques. Results Seventy‐two percent of among‐island variation in exotic species richness was positively related to native species richness. Both native and exotic richness increased with island area and declined with isolation and exposure to ocean‐borne disturbances (a proxy for salt spray, wave action, etc). However, exotic species responded more strongly to these three variables. Exotic richness also decreased with latitude and the distance from the nearest urban area, but native species did not. Island area was a better predictor of species richness on larger islands, whereas isolation and exposure were better predictors on smaller islands. Scale‐dependent relationships between species richness and island characteristics were stronger for exotic species. Main Conclusions Insular distribution patterns of native and exotic plant species richness are governed by similar biogeographic principles. However, in New Zealand, exotic species exhibited subtle, yet distinctive, invasion patterns preferring larger, less isolated, less exposed islands that were located at higher latitudes and closer to urban areas.

Soil biotic and abiotic effects on seedling growth exhibit context‐dependent interactions: evidence from a multi‐country experiment on Pinus contorta invasion

Article

Full-text available

Jun 2021
NEW PHYTOL

The success of invasive plants is influenced by many interacting factors, but evaluating multiple possible mechanisms of invasion success and elucidating the relative importance of abiotic and biotic drivers is challenging, and therefore rarely achieved. We used live, sterile or inoculated soil from different soil origins (native range and introduced range plantation; and invaded plots spanning three different countries) in a fully factorial design to simultaneously examine the influence of soil origin and soil abiotic and biotic factors on the growth of invasive Pinus contorta. Our results displayed significant context dependency in that certain soil abiotic conditions in the introduced ranges (soil nitrogen, phosphorus or carbon content) influenced responses to inoculation treatments. Our findings do not support the enemy release hypothesis or the enhanced mutualism hypothesis, as biota from native and plantation ranges promoted growth similarly. Instead, our results support the missed mutualism hypothesis, as biota from invasive ranges were the least beneficial for seedling growth. Our study provides a novel perspective on how variation in soil abiotic factors can influence plant–soil feedbacks for an invasive tree across broad biogeographical contexts.

Non-native weed reaches community dominance under the canopy of dominant native tree

Article

Full-text available

Apr 2021
BIOL INVASIONS

Whether facilitation from native plants is strong enough to trigger community dominance by non-natives remains unclear. We explored the possibility that facilitation from Prosopis caldenia, the dominant native tree in the semiarid open forest of central Argentina, drives local community dominance by Chenopodium album, an annual herb native to Europe. We assessed this hypothesis by conducting extensive field sampling in which we recorded the relative abundance of species growing under the canopy of P. caldenia (caldén microsites) and in adjacent locations free of this tree (open microsites). If our hypothesis is correct, then the relative abundance of C. album will be greater than that of the rest of the species only when growing under P. caldenia. Also, we measured C. album performance, estimated its soil seed bank, and characterized growing conditions in caldén and open microsites. We found that the relative abundance of C. album was over seven times greater than that of any other species in communities occurring in caldén microsites; by contrast, C. album co-dominated communities with several other species in the open. Chenopodium album density, cover, biomass, and fecundity were all several times greater in caldén than open microsites. Similarly, C. album seed bank displayed an eight-fold increase in caldén as compared to open microsites. Growing conditions were markedly different between microsites, which could explain positive responses from C. album. Our results suggest that facilitation from natives is indeed strong enough to trigger local community dominance by non-natives, advancing the understanding of community-level consequences of this interaction.

Effects of clonal integration on allelopathy of invasive plant Wedelia trilobata under heterogeneous light conditions

Article

Full-text available

Mar 2021
J PLANT ECOL-UK

Aims Plant invasion is one of the most serious threats to ecosystems worldwide. When invasive plants with the ability of clonal growth invading or colonizing in new habitat, their interconnected ramets may suffer from heterogeneous light. Effects of clonal integration on allelopathy of invasive plants are poorly understood under heterogeneous light conditions. Methods To investigate the effects of clonal integration on allelopathy of invasive plant Wedelia trilobata under heterogeneous light conditions, a pot experiment was conducted by using its clonal fragments with two successive ramets. The older ramets were exposed to full light, whereas the younger ones were subjected to 20% full light. The younger ramets of each clonal fragment were adjacently grown with a target plant (one tomato seedling) in a pot. Stolon between two successive ramets was either severed or retained intact. In addition, two tomato seedlings (one as target plant) were adjacently grown in a pot as contrast. Important findings Compared with severing stolon, biomass accumulation, foliar chlorophyll and nitrogen contents, chlorophyll fluorescence parameters and net photosynthetic rates of the target plants as well as their root length and activity, were significantly decreased when stolon between interconnected ramets of Wedelia trilobata retained intact. Under heterogeneous light conditions, transportation or sharing of carbohydrate between two successive ramets enhanced allelopathy of the young ramets subjected to 20% full light treatment. It is suggested that clonal integration may be important for invasion or colonization of invasive plants with ability of clonal growth under heterogeneous light conditions.

How disturbance history alters invasion success: biotic legacies and regime change

Article

Full-text available

Jan 2021
ECOL LETT

Disturbance is a key factor shaping ecological communities, but little is understood about how the effects of disturbance processes accumulate over time. When disturbance regimes change, historical processes may influence future community structure, for example, by altering invasibility compared to communities with stable regimes. Here, we use an annual plant model to investigate how the history of disturbance alters invasion success. In particular, we show how two communities can have different outcomes from species introduction, solely due to past differences in disturbance regimes that generated different biotic legacies. We demonstrate that historical differences can enhance or suppress the persistence of introduced species, and that biotic legacies generated by stable disturbance history decay over time, though legacies can persist for unexpectedly long durations. This establishes a formal theoretical foundation for disturbance legacies having profound effects on communities, and highlights the value of further research on the biotic legacies of disturbance. Disturbance has many effects on communities, and much is still not known about how these effects accumulate over time. We use an annual plant model to demonstrate how legacies of disturbance can affect future community composition, long after disturbance regimes have changed. In particular, we show that differences in disturbance history can alter invasion success even when present disturbance regimes are identical.

Insect ecology and conservation in urban areas: An overview of knowledge and needs

Article

Mar 2024

Urban expansion across the globe profoundly impacts local biodiversity. The growing body of urban ecology research on animals has largely focused on mammals and birds, whereas knowledge of insect ecology and conservation in urban areas remains limited. To anchor this Special Issue (SI), we have taken a broad approach to editorial and conducted a structured literature search to set the scene. We provide here an overview of existing literature reviews on urban insect ecology and conservation, indicate where the articles included in this SI contribute to developing our understanding and point to priority areas for further investigation. Key themes in the growing literature (at individual, species, and/or community level) include the influence of habitat quality, quantity and land use type on insect diversity; the impacts of anthropogenic pollution (for instance, heat, noise, light and chemicals); habitat connectivity and changes in habitat structure and impacts of urban density on genetic diversity. Insect diversity and abundance broadly decline with urban density and loss of habitat. Beyond this, variation in responses of different taxa, or in different regions, and methodological limitations of individual studies make it challenging to identify general patterns. Insect ecology and conservation research in urban environments should focus on applying ecological theory to understand variation in diversity patterns; investigating interactions between climate change and urban contexts; identifying impacts of novel environments on insect biodiversity; addressing methodological limitations and harmonising methodological approaches; and exploring the influence of social and historical factors on urban insect biodiversity. Insect conservation must also consider research into how best to communicate the value of urban insects to urban humans.

Native versus non-native dominance after disturbance varies with environmental context

Article

Feb 2024
J ARID ENVIRON

Prioritizing the Risk and Management of Introduced Species in a Landscape with High Indigenous Biodiversity

Article

Jul 2023

How ecological and evolutionary theory expanded the ‘ideal weed’ concept

Article

Full-text available

Jun 2023
OECOLOGIA

Since Baker’s attempt to characterize the ‘ideal weed’ over 50 years ago, ecologists have sought to identify features of species that predict invasiveness. Several of Baker’s ‘ideal weed’ traits are well studied, and we now understand that many traits can facilitate different components of the invasion process, such as dispersal traits promoting transport or selfing enabling establishment. However, the effects of traits on invasion are context dependent. The traits promoting invasion in one community or at one invasion stage may inhibit invasion of other communities or success at other invasion stages, and the benefits of any given trait may depend on the other traits possessed by the species. Furthermore, variation in traits among populations or species is the result of evolution. Accordingly, evolution both prior to and after invasion may determine invasion outcomes. Here, we review how our understanding of the ecology and evolution of traits in invasive plants has developed since Baker’s original efforts, resulting from empirical studies and the emergence of new frameworks and ideas such as community assembly theory, functional ecology, and rapid adaptation. Looking forward, we consider how trait-based approaches might inform our understanding of less-explored aspects of invasion biology ranging from invasive species responses to climate change to coevolution of invaded communities.

Mechanisms behind elevational plant species richness patterns revealed by a trait‐based approach

Article

Dec 2022

Aims Elevational patterns of plant species richness may be caused by multiple underlying mechanisms, and the same pattern can be predicted by different mechanisms. Using the steep elevational gradient of Tenerife as a model system, we aimed to test if the application of a trait‐based approach can help disentangle the role of potential mechanisms behind local elevational plant species richness patterns. Location Tenerife, Canary Islands, Spain. Methods Based on vegetation relevés from natural vegetation and disturbed roadside habitat, along an elevational gradient of 2300 m, we observed a peak of plant species richness in the lowest third of the gradient. We considered three mechanisms potentially shaping this pattern: environmental filtering (temperature and precipitation), effects of area and disturbance. For these mechanisms, we hypothesized a distinct pattern of functional trait–elevation relationships. These were tested with in‐situ data of nine functional leaf traits, from which we calculated community‐weighted means (CWM) of traits and functional diversity (Rao's Q ). Results While species richness was significantly positively correlated with temperature, area and disturbance, filtering through temperature was the only mechanism for which we could confirm most of our mechanism‐specific hypotheses about elevational trait changes: with increasing elevation, CWMs of most traits indicated shifts from acquisitive to conservative growth strategies, and functional diversity decreased. The shift of growth strategies also supported the disturbance effect, as we found overall more acquisitive communities at roadsides compared to natural habitats. Conclusions Our results indicate that simple correlations between species richness and abiotic variables are not necessarily causal. Additional testing of mechanism‐specific hypotheses for elevational patterns of both CWMs and functional diversity can help distinguishing between correlational and mechanistic relationships between species richness and environmental variables. The trait‐based framework presented here can be fruitfully applied to better understand species richness patterns in other regions and across other types of environmental gradients.

Twenty‐two years of vegetation succession on the constructed Danish island Peberholm

Article

Nov 2022

Staffan Nilsson

Peberholm is a constructed Danish island in the Øresund strait. It was primarily constructed by calcareous clay from the sea floor, and is traversed by a highway and a railway. Being constructed from material without a seed bank, Peberholm constituted a good opportunity to study primary succession in an anthropogenic context. In this study, data from a survey of the vascular plant community of Peberholm was studied. The data span over a 22 year‐period, between 1999 and 2020. The development of the flora was analysed with regards to indicators for environmental factors and vegetation types, as well as occurrence of alien species or species of conservation concern. Peberholm experienced a rapid succession during its first five years. The effects of the initial ground disturbance quickly wore off, resulting in a relative decline in plant communities associated with ruderal land. These highly anthropogenic habitats were replaced with grasslands. The shrubification also began early on. The rapid initial changes were then replaced with a much slower but also more continuous change, resulting in the development of both more natural grasslands and an increased shrubification. Although several rare or threatened species colonized Peberholm from the beginning, the conservation value of the flora on a whole increased during the succession process of forming more natural vegetation types. The succession process demonstrated at Peberholm has more in common with the succession at urban soils than with naturally occurring primary succession.

Synergistic effects of soil nutrient level and native species identity and diversity on biotic resistance to Sicyos angulatus, an invasive species

Article

Full-text available

Sep 2022
OECOLOGIA

Sicyos angulatus is a serious threat to riverine ecosystem functions and services worldwide. Here, we studied the effect of species identity and diversity on biotic resistance to S. angulatus under two different soil nutrient levels (unfertilized vs. fertilized). Soil nutrient levels showed no significant effect on invasion by S. angulatus in the control treatment, where intervention by native plants was absent. Species identity of native plants and its interaction with soil nutrient levels had a significant effect on biotic resistance to S. angulatus. For instance, Pennisetum alopecuroides and Lespedeza cuneata best resisted invasion in fertilized soil, whereas Lespedeza bicolor and Lactuca indica best resisted invasion in unfertilized soil. In addition, a mixture of four plant species resisted invasion equally as well as the monoculture of a species in unfertilized soil, whereas the mixed treatment resisted invasion much better in fertilized soil compared with unfertilized soil. Structural equation modeling revealed that species identity and diversity as well as fertilizer application significantly influenced biotic resistance to S. angulatus invasion, while soil nutrients did not influence invasion success directly. Based on these results, we strongly suggest sowing seed mixtures of various species after eradicating S. angulatus plants to prevent re-invasion. Overall, these results demonstrate how native plants rely on resource availability to resist colonization by an invasive plant, such as S. angulatus. This information can be used for the development of improved guidelines for plant restoration and invasive species control.

Invasive and native grasses exert negative plant–soil feedbacks on the woody shrub Artemisia tridentata

Article

Full-text available

Aug 2022
OECOLOGIA

Displacement of diverse native plant communities by low-diversity invasive communities is a global problem. In the western United States, the displacement of sagebrush-dominated communities by cheatgrass has increased since the 1920s. Restoration outcomes are poor, potentially due to soil alteration by cheatgrass. We explored the poorly understood role of plant–soil feedbacks in the dominance of cheatgrass in a greenhouse study where uninvaded sagebrush soils were conditioned with either cheatgrass, a native bunchgrass or sagebrush. Sagebrush seedlings were grown in the soils that remained following the removal of conditioning plants. We expected cheatgrass to strongly suppress sagebrush due to a change in belowground microbial communities, conspecifics to have neutral effects and the native bunchgrass to have intermediate effects as it coevolved with sagebrush but belongs to a different functional group. We assessed the effects of conditioning on sagebrush growth, tissue nutrients, and carbon allocation. We also characterized the abundance, diversity and community composition of root microbial associates. Cheatgrass strongly suppressed sagebrush growth at high and low conditioning densities, the native bunchgrass showed suppression at high conditioning densities only and conspecific effects were neutral. Tissue nutrients, amount of root colonization by soil fungi or root microbial community composition were not associated with these plant–soil feedbacks. Although we did not identify the precise mechanism, our results provide key evidence that rapid soil alteration by cheatgrass results in negative plant–soil feedbacks on sagebrush growth. These feedbacks likely contribute to cheatgrass dominance and the poor success of sagebrush restoration.

Functional traits explain non-native plant species richness and occupancy on northern New Zealand islands

Article

Full-text available

Jul 2022
BIOL INVASIONS

Plant functional traits can greatly influence invasion success on islands. However, interrelationships between traits and invasion success are rarely integrated with the island biogeography theory. Here, we explored relations between functional traits and plant distributions to assess which traits are associated with invasion success (i.e. high island occupancy), test whether non-native richness and seed mass of species with distinct growth forms and dispersal modes vary differently with island characteristics (e.g. area, isolation, exposure to ocean-borne disturbances, distance from the nearest urban area, and whether islands were managed for conservation), and whether results differ from native species. We assembled a database of 264 northern New Zealand offshore islands, amalgamating species lists from field surveys and previously published data, and comprising 822 native and 855 non-native species. Non-native graminoids occurred on islands more frequently than forbs and woody species, and long-distance dispersal modes (wind, animal, unspecialized) more than species with short-distance dispersal modes. Most differences among trait categories of non-native species were associated with human-related variables (i.e. distance from the nearest urban area, and whether islands were conservation areas). Non-native plant species with high island occupancy were less commonly associated with human-related variables than non-native species with low island occupancy. Instead, they were more similar in their distributional patterns to native species within the same trait category, suggesting comparable processes regulate both sets of species. Our results illustrate that integrating trait-based approaches in the island biogeography framework can be a useful tool in understanding and predicting plant invasions.

Uncovering the Drivers of Non-Native Plant Invasions Using Ecological Data Synthesis

Thesis

Full-text available

Jan 2019

Marina Golivets

Understanding what promotes invasiveness of species outside their native range and predicting which ecosystems and under which conditions will be invaded is an ultimate goal of the field of invasion ecology. Obtaining general answers to these questions requires synthesis of extensive yet heterogeneous empirical evidence, coupled with a solid theoretical background. In this dissertation, I sought to provide insight into the drivers of non-native plant invasions through combining and synthesizing ecological data from various sources using advanced statistical techniques. The results of this work are presented as three independent research studies. In the first study, I aimed to understand what determines competitive advantage of non-native over native plants: the ability to suppress other plants, tolerate them, or both. For this, I collected data from 192 studies on plant competition and analyzed them within a Bayesian multilevel meta-analytic framework. I showed that non-native plants outperform their native counterparts due to the high tolerance of competition, as opposed to strong suppressive ability. Competitive tolerance ability of non-native plants was driven by neighbor’s origin and was expressed in response to native species and not to other non-native species. This synthesis demonstrates that non-native plants are competitively distinct from native plants and challenges the common notion that neighbor suppression is the primary strategy for plant invasion success. In the second study, I quantified the extent to which regional, landscape and local environmental factors individually and jointly affect understory non-native invasive plants across northern US forests. I used boosted regression trees and Bayesian nonlinear regressions to analyze forest inventory data spanning 14 northern US states in combination with data on climate, land use, and disturbance. Regionally, the highest level of plant invasion was observed in hotter regions with lower annual precipitation and climate seasonality and higher summer precipitation. Locally, young forests with moist to wet soils and relatively flat topography in open, human-altered landscapes at low elevation were most susceptible to invasion. Climate and land use strongly interacted in their effect on plant invasions. This study refines the understanding of the non-native plant invasion process in northern US forests and the obtained models can be used to generate predictions under current and future environmental regimes to inform management. In the third study, I tested the relationship between the long-term history of recurrent canopy disturbance by a non-native invasive defoliator, the gypsy moth (Lymantria dispar), and the level of non-native plant invasion in northeastern US forests. I reconstructed 46 years (1970–2015) of gypsy-moth defoliation history and quantified the cumulative effect of defoliation on understory non-native invasive plant species using multivariate techniques and Bayesian nonlinear regressions. Contrary to what is commonly expected, the cumulative severity of gypsy moth defoliation tended to be negatively associated with the presence and richness of invasive plant species, although this association was weak. This study suggests that the effect of biotic disturbance on forest plant invasions may vary in both the magnitude and direction depending on characteristics of disturbance regime and its effect on resident biota, and this needs to be explicitly taken into account when predicting future plant invasions.

Land-use history and abiotic gradients drive abundance of non-native shrubs in Appalachian second-growth forests with histories of mining, agriculture, and logging

Article

Aug 2021
FOREST ECOL MANAG

Invasion by non-native species is a consequence of previous anthropogenic disturbance that can be expected to differ between land-use histories with contrasting impacts on the physical and biotic environment. Mining, agriculture, and logging all alter environmental character in different ways through their different effects on soils and surrounding vegetation. We used second-growth forests with histories of mining, agriculture, logging, and older forest (>120 years) with no recent disturbance history to test the hypotheses that invasion is driven by 1) lasting environmental impacts of land use or 2) colonization following niche opening due to disturbance. We sampled shrub cover, environmental variables, and soils in forests with histories of mining, agriculture, logging, and older second-growth with no recent history of land use in four 10-meter² plots per site. Our analysis focused on the two most common non-native shrubs, Berberis thunbergii and Rosa multiflora. Cover of B. thunbergii was marginally significantly higher in post-agricultural and mined forests than logged sites or older second growth, whereas R. multiflora was most frequent in mined sites. Both species showed a significant relationship with environmental variables such as soil pH, water-holding capacity, and elevation. Soil texture differed with land-use history: post-agricultural sites were significantly higher in silt and clay, and lower in sand, than the mined, logged, or old forest sites, reflecting the interaction of land-use history with landform. Most environmental variables did not differ between land-use histories. Non-native shrubs were associated with land-use histories involving soil disturbance despite the lack of lasting contrasts in most soil variables, indicating that invasion primarily reflects past opportunities for colonization and environmental gradients that are not impacted by land use. We conclude that the presence of non-native shrubs is a biotic legacy of past disturbance that outlasts altered environmental conditions that may be present at the time of abandonment.

Invasive plants and climate change

Chapter

Jan 2021

This chapter provides a broad overview of the interactions between invasive alien plants and climate change. Invasive alien plants are harmful nonnative plant species that have been introduced by humans outside of their “natural” geographical range. Both climate change and alien plant invasions result from human activities and can cause major environmental and socioeconomic damage. Although they can operate as independent environmental and economic threats, they can also interact. Climate change can facilitate alien plant invasions (1) by altering background environmental conditions; (2) by increasing disturbance through extreme climatic events; and (3) through human responses to climate change. While all plants, regardless of whether they are native or alien, will likely be affected by environmental change, it is widely expected that climate change will favor invasive alien plants at the expense of native plants. The way in which invasive alien plants impact the environment (e.g., modifying hydrology and soil properties, altering fire regimes) can to some extent either contribute to or exacerbate the effect of climate change. Here, we consider why and how climate change is predicted to exacerbate alien plant invasions and provide examples of how invasive alien plants can contribute to climate change. We first briefly describe what makes a plant invasive, how and why a plant becomes invasive, what stages must it go through, and what the drivers of invasion are.

The relative importance of multiple invasion mechanisms

Article

Full-text available

Dec 2020

Aim: Plant invasions are driven by suites of factors in nature. To better understand the success of invasive plants, it is crucial to quantify the relative importance of multiple invasion mechanisms during plant invasions. Location: Eastern China. Methods: We surveyed 300 pairs of uninvaded and invaded quadrats by Solidago canadensis across its entire invaded range, quantified its invasion intensities, and identified the relative importance of 19 causal factors and 11 invasion hypotheses using the multimodel inference approach. Results: The relative contributions of all the 19 factors to S. canadensis invasion varied depending on different invasion intensities, so did the relative importance of 11 different hypotheses vary with invasion intensities. At the low invasion intensity, abiotic factors dominated over biotic factors; in contrast, biotic factors dominated over abiotic factors at the high invasion intensity. The role of S. canadensis-recipient community interactions was highly important. Main conclusions: These fi ndings suggest that the relative importance of multiple invasion mechanisms may be staged in a real invasion. Based on our results, we propose a novel nature-sieve hypothesis, which provides a universal framework for an understanding of successful invasion.

Nonadditive changes to cytosine methylation as a consequence of hybridization and genome duplication in Senecio (Asteraceae)

Article

Full-text available

Jun 2011

The merger of two or more divergent genomes within an allopolyploid nucleus can facilitate speciation and adaptive evolution in flowering plants. Widespread changes to gene expression have been shown to result from interspecific hybridisation and polyploidy in a number of plant species, and attention has now shifted to determining the epigenetic processes that drive these changes. We present here an analysis of cytosine methylation patterns in triploid F1Senecio (ragwort) hybrids and their allohexaploid derivatives. We observe that, in common with similar studies in Arabidopsis, Spartina and Triticum, a small but significant proportion of loci display nonadditive methylation in the hybrids, largely resulting from interspecific hybridisation. Despite this, genome duplication results in a secondary effect on methylation, with reversion to additivity at some loci and novel methylation status at others. We also observe differences in methylation state between different allopolyploid generations, predominantly in cases of additive methylation with regard to which parental methylation state is dominant. These changes to methylation state in both F1 triploids and their allohexaploid derivatives largely mirror the overall patterns of nonadditive gene expression observed in our previous microarray analyses and may play a causative role in generating those expression changes. These similar global changes to DNA methylation resulting from hybridisation and genome duplication may serve as a source of epigenetic variation in natural populations, facilitating adaptive evolution. Our observations that methylation state can also vary between different generations of polyploid hybrids suggests that newly formed allopolyploid species may display a high degree of epigenetic diversity upon which natural selection can act.

Economic and environmental threats of alien plant, animal, and microbe invasions

Article

Full-text available

Jan 2001

Bootstrap Methods and Their Application

Article

Full-text available

Mar 2012
TECHNOMETRICS

Debashis Kushary

This book gives a broad and up-to-date coverage of bootstrap methods, with numerous applied examples, developed in a coherent way with the necessary theoretical basis. Applications include stratified data; finite populations; censored and missing data; linear, nonlinear, and smooth regression models; classification; time series and spatial problems. Special features of the book include: extensive discussion of significance tests and confidence intervals; material on various diagnostic methods; and methods for efficient computation, including improved Monte Carlo simulation. Each chapter includes both practical and theoretical exercises. Included with the book is a disk of purpose-written S-Plus programs for implementing the methods described in the text. Computer algorithms are clearly described, and computer code is included on a 3-inch, 1.4M disk for use with IBM computers and compatible machines. Users must have the S-Plus computer application. Author resource page: http://statwww.epfl.ch/davison/BMA/

Don't judge species on their origins

Article

Full-text available

Jun 2011
NATURE

Mark A. Davis

Vegetation Change: a reunifying concept in plant ecology

Article

Full-text available

Jan 2005
PERSPECT PLANT ECOL

Specialization can become detrimental to a discipline if it fosters intellectual isolation. A bibliographic analysis of several research areas in plant ecology (invasion biology, succession ecology, gap/patch dynamics, and global change effects on plants) revealed that plant ecologists do not regularly make use of the findings and insights of very similar studies being conducted in other research subdisciplines, nor do they try to make their findings and insights easily accessible to researchers in other areas. Invasion papers were least likely to be cross-linked (6%) with other fields, whereas gap/patch dynamics papers were most likely to be cross-linked (15%). This tendency toward intellectual isolation may be impeding efforts to achieve more powerful generalizations in ecology by reducing the number of potentially productive exchanges among researchers. In this paper, we illustrate this problem using the example of several speciality areas that study vegetation change. We argue that, rather than characterizing studies of vegetation change on the basis of what distinguishes them from one another, plant ecologists would benefit from concentrating on what such studies have in common. As an example, we propose that several speciality areas of plant ecology could be reunified under the term ecology of vegetation change. Individual researchers, journals, and ecological societies all can take specific steps to increase the useful exchange of ideas and information among research areas. Promoting rapid and more effective communication among diverse researchers may reduce the proliferation of narrow theories, concepts, (M.A. Davis). and terminologies associated with particular research areas. In this way, we can expedite our understanding of the ecological mechanisms and consequences associated with plant communities.

A theory of seed plant invasiveness: The first sketch

Article

Full-text available

Oct 1996
BIOL CONSERV

Marcel Rejmanek

Although biological invasions are clearly one of the most important impacts humans have had on the Earth's ecosystems, we still do not have reliable tools which can help us to predict which species are potential invaders. At present, several limited generalizations are available for seed plants: (1) invasiveness of woody species in disturbed landscapes is significantly associated with small seed mass, short juvenile period, and short mean interval between large seed crops; (2) vertebrate dispersal is responsible for the success of many woody invaders in disturbed as well as ‘undisturbed’ habitats; (3) primary (native) latitudinal range of herbaceous Gramineae, Compositae, and Fabaceae seems to be the best predictor of their invasiveness, at least for species introduced from Eurasia to North America; (4) low nuclear DNA content (genome size) seems to be a result of selection for short minimum generation time and, therefore, may be associated with plant invasiveness in disturbed landscapes; (5) analysis of exotic Gramineae and Compositae introduced from Europe to California supports Darwin's suggestion that alien species belonging to exotic genera are more likely to be invasive than alien species from genera represented in the native flora. Fortunately, these seemingly disparate stories can be brought together and provide a foundation for building a general theory of seed plant invasiveness.

Effects of biodiversity on ecosystem functioning: a consensus of current knowledge: Ecological Monog

Article

Full-text available

Nov 2004

Dry Sheep Equivalents for Comparing Different Classes of Livestock

Article

Full-text available

Jan 1997

Colin Mclaren

Disentangling the role of environmental and human pressures on biological invasions across Europe

Article

Full-text available

Jul 2010
P NATL ACAD SCI USA

The accelerating rates of international trade, travel, and transport in the latter half of the twentieth century have led to the progressive mixing of biota from across the world and the number of species introduced to new regions continues to increase. The importance of biogeographic, climatic, economic, and demographic factors as drivers of this trend is increasingly being realized but as yet there is no consensus regarding their relative importance. Whereas little may be done to mitigate the effects of geography and climate on invasions, a wider range of options may exist to moderate the impacts of economic and demographic drivers. Here we use the most recent data available from Europe to partition between macroecological, economic, and demographic variables the variation in alien species richness of bryophytes, fungi, vascular plants, terrestrial insects, aquatic invertebrates, fish, amphibians, reptiles, birds, and mammals. Only national wealth and human population density were statistically significant predictors in the majority of models when analyzed jointly with climate, geography, and land cover. The economic and demographic variables reflect the intensity of human activities and integrate the effect of factors that directly determine the outcome of invasion such as propagule pressure, pathways of introduction, eutrophication, and the intensity of anthropogenic disturbance. The strong influence of economic and demographic variables on the levels of invasion by alien species demonstrates that future solutions to the problem of biological invasions at a national scale lie in mitigating the negative environmental consequences of human activities that generate wealth and by promoting more sustainable population growth.

Tree-Grass Interactions in Savannas

Article

Full-text available

Nov 2003
Annu Rev Ecol Systemat

▪ Abstract Savannas occur where trees and grasses interact to create a biome that is neither grassland nor forest. Woody and gramineous plants interact by many mechanisms, some negative (competition) and some positive (facilitation). The strength and sign of the interaction varies in both time and space, allowing a rich array of possible outcomes but no universal predictive model. Simple models of coexistence of trees and grasses, based on separation in rooting depth, are theoretically and experimentally inadequate. Explanation of the widely observed increase in tree biomass following introduction of commercial ranching into savannas requires inclusion of interactions among browsers, grazers, and fires, and their effects on tree recruitment. Prediction of the consequences of manipulating tree biomass through clearing further requires an understanding of how trees modify light, water, and nutrient environments of grasses. Understanding the nature of coexistence between trees and grass, which under other ci...

The Population Biology of Invasive Species

Article

Full-text available

Nov 2001

■ Abstract Contributions from the field of population biology hold promise for understanding and managing invasiveness; invasive species also offer excellent oppor- tunities to study basic processes in population biology. Life history studies and demo- graphic models may be valuable for examining the introduction of invasive species and identifying life history stages where management will be most effective. Evolution- ary processes may be key features in determining whether invasive species establish and spread. Studies of genetic diversity and evolutionary changes should be useful for

Biotic Globalization: Does Competition from Introduced Species Threaten Biodiversity?

Article

Full-text available

Jan 2003

Mark A. Davis

The introduction of new predators and pathogens has caused numerous well-documented extinctions of long-term resident species, particularly in spatially restricted environments such as islands and lakes. However, there are surprisingly few instances in which extinctions of resident species can be attributed to competition from new species. This suggests either that competition-driven extinctions take longer to occur than those caused by predation or that biological invasions are much more likely to threaten species through intertrophic than through intratrophic interactions. The likely threat of introduced species to resident controphics (species in the same trophic level) can be assessed with the help of existing biodiversity and extinction data sets and of two recent theories: (1) the fluctuating resource availability hypothesis, developed to account for changes in the invasibility of communities, and (2) the unified neutral theory, proposed to account for patterns of biodiversity at the community and metacommunity levels. Taken together, theory and data suggest that, compared to intertrophic interactions and habitat loss, competition from introduced species is not likely to be a common cause of extinctions of long-term resident species at global, metacommunity, and even most community levels.

Pimental, D., S. Mcnair, J. Janecka, J. Wrightman, C. Simmonds, C. O'Connell, and E. Wong. Economic and environmental threats of alien plant, animal and microbe invasions. Agriculture, Ecosystems and Environment

Article

Full-text available

Mar 2001
AGR ECOSYST ENVIRON

Over 120,000 non-native species of plants, animals and microbes have invaded the United States, United Kingdom, Australia, South Africa, India, and Brazil, and many have caused major economic losses in agriculture and forestry as well as negatively impacting ecological integrity. Some introduced species, like corn (Zea mays L.), wheat (Triticum spp.), rice (Oryza sativa L.), plantation forests, domestic chicken (Gallus spp.), cattle (Bos taurus), and others, are beneficial and provide more than 98% of the world’s food supply. Precise economic costs associated with some of the most ecologically damaging alien species are not available. Cats (Felis cattus) and pigs (Sus scrofa), for example, are responsible for the extinction of various animal species, however, it is impossible to assign monetary values to species forced to extinction. The estimate is that non-native species invasions in the six nations are causing more than US$ 314 billion per year in damages.

Rickart , E.A. , D.S. Balete , R.J. Rowe , and L.R. Heaney . Mammals of the northern Philippines: tolerance for habitat disturbance and resistance to invasive species in an endemic fauna. Diversity and Distributions

Article

Full-text available

Mar 2011
DIVERS DISTRIB

Aim Island faunas, particularly those with high levels of endemism, usually are considered especially susceptible to disruption from habitat disturbance and invasive alien species. We tested this general hypothesis by examining the distribution of small mammals along gradients of anthropogenic habitat disturbance in northern Luzon Island, an area with a very high level of mammalian endemism. Location Central Cordillera, northern Luzon Island, Philippines. Methods Using standard trapping techniques, we documented the occurrence and abundance of 16 endemic and two non‐native species along four disturbance gradients where habitat ranged from mature forest to deforested cropland. Using regression analysis and AIC c for model selection, we assessed the influence of four predictor variables (geographic range, elevational range, body size and diet breadth) on the disturbance tolerance of species. Results Non‐native species dominated areas with the most severe disturbance and were rare or absent in mature forest. Native species richness declined with increasing disturbance level, but responses of individual species varied. Elevational range (a measure of habitat breadth) was the best predictor of response of native species to habitat disturbance. Geographic range, body size and diet breadth were weakly correlated. Main conclusions The endemic small mammal fauna of northern Luzon includes species adapted to varying levels of natural disturbance and appears to be resistant to disruption by resident alien species. In these respects, it resembles a diverse continental fauna rather than a depauperate insular fauna. We conclude that the long and complex history of Luzon as an ancient member of the Philippine island arc system has involved highly dynamic ecological conditions resulting in a biota adapted to changing conditions. We predict that similar responses will be seen in other taxonomic groups and in other ancient island arc systems.

A new framework for predicting invasive species

Article

Full-text available

Nov 2007
J ECOL

Summary • Many studies have searched for traits that characterize successful invaders. Unfortunately, very few generalizations have emerged from this work. It seems that the traits of successful invaders are idiosyncratic and context-dependent. Unless we are to study each potential invader in each possible target community individually, we will need a new approach. • We introduce a framework for predicting traits that are likely to confer success in a given ecosystem. Our approach considers the prevailing environmental conditions, the traits of resident species, and the traits of potentially invading species. • Our approach can be applied to ecosystems where the environmental conditions and/or disturbance regime have recently changed, to predict the range of trait space occupied by (i) native species at risk of local extinction, (ii) native species that can persist under the present conditions, and (iii) successful invaders. Our approach can also be used to identify unoccupied viable trait space (i.e. vacant niches) that might be at risk of invasion. • Synthesis. Understanding invasions resulting from rapid changes in environmental conditions and invasions resulting from the colonization of vacant niches would be a major step forward for invasion biology. The conceptual framework described here is not limited to plant invasions: the same approach can be used for any taxa (e.g. insects, fish, mammals and marine invertebrates) and could also be used to predict species responses to environmental change.

GLOBAL PATTERNS OF PLANT INVASIONS AND THE CONCEPT OF INVASIBILITY

Article

Jul 1999

W. M. Lonsdale

EPISTASIS AND THE EVOLUTION OF ADDITIVE GENETIC VARIANCE IN POPULATIONS THAT PASS THROUGH A BOTTLENECK

Article

Aug 1999
EVOLUTION

Traditional models of genetic drift predict a linear decrease in additive genetic variance for populations passing through a bottleneck. This perceived lack of heritable variance limits the scope of founder-effect models of speciation. We produced 55 replicate bottleneck populations maintained at two male-female pairs through four generations of inbreeding (average F = 0.39). These populations were formed from an F2 intercross of the LG/J and SM/J inbred mouse strains. Two contemporaneous control strains maintained with more than 60 mating pairs per generation were formed from this same source population. The average level of within-strain additive genetic variance for adult body weight was compared between the control and experimental lines. Additive genetic variance for adult body weight within experimental bottleneck strains was significantly higher than expected under an additive genetic model This enhancement of additive genetic variance under inbreeding is likely to be due to epistasis, which retards or reverses the loss of additive genetic variance under inbreeding for adult body weight in this population. Therefore, founder-effect speciation processes may not be constrained by a loss of heritable variance due to population bottlenecks.

Disturbance and biological invasions. Direct effects and feedback

Article

Jan 1999

The evolution of weeds

Article

Jan 1974

H.G. Baker

Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory

Article

Jan 1977

J.P. Grime

An introduction to Urban Ecology as an interaction between humans and nature

Book

Jan 2008

Urban Ecology is the study of ecosystems that include humans living in cities and urbanizing landscapes. It is an emerging, interdisciplinary field that aims to understand how human and ecological processes can coexist in human-dominated systems and help societies with their efforts to become more sustainable. It has deep roots in many disciplines including sociology, geography, urban planning, landscape architecture, engineering, economics, anthropology, climatology, public health, and ecology. Because of its interdisciplinary nature and unique focus on humans and natural systems, the term "urban ecology" has been used variously to describe the study of humans in cities, of nature in cities, and of the coupled relationships between humans and nature. Each of these research areas is contributing to our understanding of urban ecosystems and each must be understood to fully grasp the science of Urban Ecology. Therefore, in Urban Ecology: An International Perspective on the Interaction Between Humans and Nature, we introduce students and practitioners of urban ecology to its roots, bases, and prospects by way of a diverse collection of historical and modern foundational readings. The editors are urban ecologists from the United States, Italy, and Germany who together view these readings as a fair representation of the importance of both natural and social sciences to Urban Ecology. This book presents important papers in the field of Urban Ecology that both set the foundations for the discipline and to illustrate modern approaches, from a variety of perspectives and regions of the world. The editors do this by reprinting important publications, filling gaps in the published literature with a few targeted original works, and translating several key works originally published in German. The aim of this collection is to provide students, practitioners, and professionals with a rich background in some of the core facets of Urban Ecology. © 2008 Springer Science+Business Media, LLC. All rights reserved.

The fundamentals of vegetation change

Article

W.S. Cooper

The Ecology of Invasions by Animals and Plants.

Article

Jul 1959

An Experimental Study of Plant Community Invasibility

Article

Apr 1996

A long-term field experiment in limestone grassland near Buxton (North Derbyshire, United Kingdom) was designed to identify plant attributes and vegetation characteristics conducive to successful invasion. Plots containing crossed, continuous gradients of fertilizer addition and disturbance intensity were subjected to a single-seed inoculum comprising a wide range of plant functional types and 54 species not originally present at the site. Several disturbance treatments were applied; these included the creation of gaps of contrasting size and the mowing of the vegetation to different heights and at different times of the year. This paper analyzes the factors controlling the initial phase of the resulting invasions within the plots subject to gap creation. The susceptibility of the indigenous community to invasion was strongly related to the availability of bare ground created, but greatest success occurred where disturbance coincided with eutrophication. Disturbance damage to the indigenous dominants (particularly Festuca ovina) was an important determinant of seedling establishment by the sown invaders. Large seed size was identified as an important characteristic allowing certain species to establish relatively evenly across the productivity-disturbance matrix; smaller-seeded species were more dependent on disturbance for establishment. Successful and unsuccessful invaders were also distinguished to some extent by differences in germination requirements and present geographical distribution.

Short-Term Evolution of Reduced Dispersal in Island Plant Populations

Article

Feb 1996

1 Dramatic reductions in dispersal potential are characteristic of many diverse taxa, both plants and animals, on oceanic islands. This paper documents the same trend of reduced dispersal ability over the course of just a few generations in some weedy, short-lived and wind-dispersed plants of inshore islands in British Columbia, Canada. 2 We measured dispersal-related morphological characteristics of diaspores from island populations of known ages, and from mainland populations. In two of three species with sufficiently large sample sizes, older island populations show increasingly reduced dispersal potential relative to mainland populations or to young island populations. 3 These and other morphological differences are consistent with results expected from strong selection for reduced dispersal potential, and may be striking examples of short-term evolution in small and isolated natural populations.

The good, the bad and the reified

Article

Jan 2001
EVOL ECOL RES

L. B. Slobodkin

In their search for generalizations, ecologists have postulated many concepts and processes. Some of these have become reified. Reification consists of accepting a designation as if it has empirical meaning when, in fact, its existence has either never been tested or it has been found empty. The distinction between a hypothesis and a reification is that hypotheses are created to be tested and replaced, whereas a reification is taken as an untestable axiom. When a research area loses its dynamism, its hypotheses become reifications. Conversely, if reifications are permitted to accumulate, they can destroy the dynamism of a research area. If a science retains an excess number of reifications, it stagnates and ultimately loses its status as a science. Reified concepts include the logistic equation (together with the theoretical constructs based on it), the idea of constant ecological efficiency, the concept of an integrated community, and certain aspects of species diversity, particularly in the context 'good', 'bad' and alien species. Also, there are reified metaphors, which, if taken seriously, can be obfuscatory. For example, natural communities have been likened to aeroplanes, and each species to parts of an aeroplane. A metaphor is then constructed in which the removal of a species from a community is likened to the removal of an aeroplane part. Just as removal of one or more parts will cause the plane to crash, the metaphor asserts that the removal of one too many species from a community will result in collapse of the community. On closer examination, this is seen as empty. There is no 'aeroplane'. Also, the designation of certain kinds of species as good or bad – specifically, alien species are bad and 'native' species are good – is empty and misleading. While invasive species, in some cases, actually do damage native species, the generalization that invaders will reduce species diversity is not well founded. Fields that are required to focus on research defined by social needs, like ecology and medi-cine, rather than on scientific capabilities, like astronomy and hydrodynamics, generate reifica-tions. Reifications are dangerous to the health of a research area and should be avoided. Only vigorous extirpation of reifications permits a field to preserve scientific integrity.

Disturbance, Diversity, and Invasion: Implications for Conservation

Article

Sep 1992
CONSERV BIOL

Disturbance is an important component of many ecosystems, and variations in disturbance regime can affect ecosystem and community structure and functioning. The “intermediate disturbance hypothesis” suggests that species diversity should be highest at moderate levels of disturbance. However, disturbance is also known to increase the invasibility of communities. Disturbance therefore poses an important problem for conservation management, Here, we review the effects of disturbances such as fire grazing, soil disturbance and nutrient addition on plant species diversity and invasion with particular emphasis on grassland vegetation. Individual components of the disturbance regime can have marked effects on species diversity, but it is often modifications of the existing regime that have the largest influence. Similarly, disturbance can enhance invasion of natural communities, but frequently it is the interaction between different disturbances that has the largest effect. The natural disturbance regime is now unlikely to persist within conservation areas since fragmentation and human intervention have usually modified physical and biotic conditions. Active management decisions must now be made on what disturbance regime is required and this requires decisions on what species are to be encouraged or discouraged.

Richardson, D. M. and P. Pysek. Plant invasions: merging the concepts of species invasiveness and community invasibility. Progress in Physical Geography

Article

Apr 2006
PROG PHYS GEOG

This paper considers key issues in plant invasion ecology, where findings published since 1990 have significantly improved our understanding of many aspects of invasions. The review focuses on vascular plants invading natural and semi-natural ecosystems, and on fundamental ecological issues relating to species invasiveness and community invasibility. Three big questions addressed by the SCOPE programme in the 1980s (which species invade; which habitats are invaded; and how can we manage invasions?) still underpin most work in invasion ecology. Some organizing and unifying themes in the field are organism-focused and relate to species invasiveness (the tens rule; the concept of residence time; taxonomic patterns and Darwin's naturalization hypothesis; issues of phenotypic plasticity and rapid evolutionary change, including evolution of increased competitive ability hypothesis; the role of long-distance dispersal). Others are ecosystem-centred and deal with determinants of the invasibility of communities, habitats and regions (levels of invasion, invasibility and propagule pressure; the biotic resistance hypothesis and the links between diversity and invasibility; synergisms, mutualisms, and invasional meltdown). Some theories have taken an overarching approach to plant invasions by integrating the concepts of species invasiveness and community invasibility (a theory of seed plant invasiveness; fluctuating resources theory of invasibility). Concepts, hypotheses and theories reviewed here can be linked to the naturalization-invasion continuum concept, which relates invasion processes with a sequence of environmental and biotic barriers that an introduced species must negotiate to become casual, naturalized and invasive. New research tools and improved research links between invasion ecology and succession ecology, community ecology, conservation biology and weed science, respectively, have strengthened the conceptual pillars of invasion ecology.

Competition between Native Populus deltoides and Invasive Tamarix ramosissima and the Implications for Reestablishing Flooding Disturbance

Article

Dec 2008
CONSERV BIOL

Changes in historical disturbance regimes have been shown to facilitate non-native plant invasions, but reinstatement of disturbance can be successful only if native colonizers are able to outcompete colonizing invasives. Reintroduction of flooding in the southwestern United States is being promoted as a means of reestablishing Populus deltoides subsp. wislizenii, but flooding can also promote establishment of an introduced, invasive species, Tamarix ramosissima. We investigated competition between Populus and Tamarix at the seedling stage to aid in characterizing the process by which Tamarix may invade and to determine the potential ability of Populus to establish itself with competitive pressure from Tamarix. We planted seedlings of Tamarix and Populus in five ratios at three densities for a total of 15 treatments. The growth response of each species was measured in terms of height, above-ground biomass, and tissue concentrations of nitrogen and phosphorous. These measurements across treatments were modeled as three-dimensional response surfaces. For both species, Populus density was more important than Tamarix density for determining growth response. Both species were negatively affected by increasing numbers of Populus seedlings. Due to the larger size of the native Populus, we predict that its superior competitive ability can lead to its dominance when conditions allow native establishment. Our results suggest that even in the presence of an invader that positively responds to disturbance, reestablishment of historical flooding regimes and post-flood hydrology can restore this ecosystem by promoting its dominant plant species.

The effect of long-term exclusion of large herbivores on vegetation in Murchison Falls National Park, Uganda

Article

Dec 1985
BIOL CONSERV

The floristic and structural changes in the vegetation resulting from the long-term exclusion of large herbivores from experimental plots in the Murchison Falls National Park, Uganda, are described.Two experimental plots were surveyed, one in Sporobolus-Setaria grassland and the other in Combretum-Terminalia woodland. The survey shows that long-term removal of grazing and browsing pressure results in (1) marked tree regeneration in both grassland and woodland plots; (2) a relatively species-poor herbaceous layer in the grassland plot; and (3) the development of a more diverse all-aged stand in the woodland plot. These results are discussed in the context of the poaching of large herbivores during the 1978 civil war and the concomitant vegetation changes, especially Acacia sieberiana regeneration, that are now occurring throughout the Park. The implications for future management of the Park are discussed.

The Ecology of Invasions by Animals And Plants

Article

Jan 1958

Cs Elton

Much as Rachel Carson's "Silent Spring" was a call to action against the pesticides that were devastating bird populations, Charles S. Elton's classic "The Ecology of Invasions by Animals and Plants" sounded an early warning about an environmental catastrophe that has become all too familiar today-the invasion of nonnative species. From kudzu to zebra mussels to Asian long-horned beetles, nonnative species are colonizing new habitats around the world at an alarming rate thanks to accidental and intentional human intervention. One of the leading causes of extinctions of native animals and plants, invasive species also wreak severe economic havoc, causing $79 billion worth of damage in the United States alone. Elton explains the devastating effects that invasive species can have on local ecosystems in clear, concise language and with numerous examples. The first book on invasion biology, and still the most cited, Elton's masterpiece provides an accessible, engaging introduction to one of the most important environmental crises of our time. Charles S. Elton was one of the founders of ecology, who also established and led Oxford University's Bureau of Animal Population. His work has influenced generations of ecologists and zoologists, and his publications remain central to the literature in modern biology. "History has caught up with Charles Elton's foresight, and "The Ecology of Invasions" can now be seen as one of the central scientific books of our century."-David Quammen, from the Foreword to "Killer Algae: The True Tale of a Biological Invasion"

Quantifying Threats to Imperiled Species in the United States

Article

Aug 1998
BIOSCIENCE

Biologists are nearly unanimous in their belief that humanity is in the process of extirpating a significant portion of the earth's spe cies. The ways in which we are doing so reflect the magnitude and scale of human enterprise. Everything from highway construction to cattle ranch ing to leaky bait buckets has been implicated in the demise or endan germent of particular species. Ac cording to Wilson (1992), most of these activities fall into four major categories, which he terms "the mind less horsemen of the environmental apocalypse": overexploitation, habi tat destruction, the introduction of non-native (alien) species, and the spread of diseases carried by alien species. To these categories may be added a fifth, pollution, although it can also be considered a form of habitat destruction. Surprisingly, there have been reIa tively few analyses of the extent to which each of these factors-much less the more specific deeds encomDavid S. Wilcove is a senior ecologist at the Environmental Defense Fund, Wash ington, DC 20009. David Rothstein re ceived his J.D. in 1997 from Northeastern

Bootstrap Methods and Their Application, Vol. 10

Article

Oct 1997

Ac Davison

Characteristics and modes of origin of weeds

Article

Jan 1965

H. G. Baker

Mechanisms underlying the impacts of exotic plant

Article

Jan 2003

Although the impacts of exotic plant invasions on community structure and ecosystem processes are well appreciated, the pathways or mechanisms that underlie these impacts are poorly understood. Better exploration of these processes is essential to understanding why exotic plants impact only certain systems, and why only some invaders have large impacts. Here, we review over 150 studies to evaluate the mechanisms underlying the impacts of exotic plant invasions on plant and animal community structure, nutrient cycling, hydrology and fire regimes. We find that, while numerous studies have examined the impacts of invasions on plant diversity and composition, less than 5% test whether these effects arise through competition , allelopathy, alteration of ecosystem variables or other processes. Nonetheless, competition was often hypothesized, and nearly all studies competing native and alien plants against each other found strong competitive effects of exotic species. In contrast to studies of the impacts on plant community structure and higher trophic levels, research examining impacts on nitrogen cycling, hydrology and fire regimes is generally highly mechanistic, often motivated by specific invader traits. We encourage future studies that link impacts on community structure to ecosystem processes, and relate the controls over invasibility to the controls over impact.

Evidence for the Existence of Three Primary Strategies in Plants and Its Relevance to Ecological and Evolutionary Theory

Article

Nov 1977

J. P. L. Grime

It is suggested that evolution in plants may be associated with the emergence of three primary strategies, each of which may be identified by reference to a number of characteristics including morphological features, resource allocation, phenology, and response to stress. The competitive strategy prevails in productive, relatively undisturbed vegetation, the stress-tolerant strategy is associated with continuously unproductive conditions, and the ruderal strategy is characteristic of severely disturbed but potentially productive habitats. A triangular model based upon the three strategies may be reconciled with the theory of r- and K-selection, provides an insight into the processes of vegetation succession and dominance, and appears to be capable of extension to fungi and to animals.

Performance Comparisons of Co-Occurring Native and Alien Invasive Plants: Implications for Conservation and Restoration

Article

Nov 2003

Curtis Daehler

■ Abstract In the search to identify factors that make some plant species trou- blesome invaders, many studies have compared various measures of native and alien invasive plant performance. These comparative studies provide insights into the more general question "Do alien invasive plants usually outperform co-occurring native species, and to what degree does the answer depend on growing conditions?" Based on 79 independent native-invasive plant comparisons, the alien invaders were not statisti- cally more likely to have higher growth rates, competitive ability, or fecundity. Rather, the relative performance of invaders and co-occurring natives often depended on grow- ing conditions. In 94% of 55 comparisons involving more than one growing condition, the native's performance was equal or superior to that of the invader, at least for some key performance measures in some growing conditions. Most commonly, these con- ditions involved reduced resources (nutrients, light, water) and/or specific disturbance regimes. Independently of growing conditions, invaders were more likely to have higher leaf area and lower tissue construction costs (advantageous under high light and nutrient conditions) and greater phenotypic plasticity (particularly advantageous in disturbed environments where conditions are in frequent flux). There appear to be few "super in- vaders" that have universal performance advantages over co-occurring natives; rather, increased resource availability and altered disturbance regimes associated with hu- man activities often differentially increase the performance of invaders over that of natives.

Epistasis and the Evolution of Additive Genetic Variance in Populations That Pass Through a Bottleneck

Article

Aug 1999
EVOLUTION

Traditional models of genetic drift predict a linear decrease in additive genetic variance for populations passing through a bottleneck. This perceived lack of heritable variance limits the scope of founder-effect models of speciation. We produced 55 replicate bottleneck populations maintained at two male-female pairs through four generations of inbreeding (average F = 0.39). These populations were formed from an F-2 intercross of the LG/J and SM/J inbred mouse strains. Two contemporaneous control strains maintained with more than 60 mating pairs pet generation were formed from this same source population. The average level of within-strain additive genetic variance for adult body weight was compared between the control and experimental lines. Additive genetic variance for adult body weight within experimental bottleneck strains was significantly higher than expected under an additive genetic model. This enhancement of additive genetic variance under inbreeding is likely to be due to epistasis, which retards or reverses the loss of additive genetic variance under inbreeding for adult body weight in this population. Therefore, founder-effect speciation processes may not be constrained by a loss of heritable variance due to population bottlenecks.

Evolution of Increased Competitive Ability in Invasive Nonindigenous Plants: A Hypothesis

Article

Oct 1995

The Evolution of Weeds

Article

Nov 2003
Annu Rev Ecol Systemat

Herbert G. Baker

Ehrenfeld JG. Ecosystem consequences of biological invasions. Annu Rev Ecol Evol S

Article

Nov 2010

Joan G. Ehrenfeld

Exotic species affect the biogeochemical pools and fluxes of materials and energy, thereby altering the fundamental structure and function of their ecosystems. Rapidly accumulating evidence from many species of both animal and plant invaders suggests that invasive species often increase pool sizes, particularly of biomass, and promote accelerated flux rates, but many exceptions can be found. Ecosystem dynamics are altered through a variety of interacting, mutually reinforcing mechanistic pathways, including species' resource acquisition traits; population densities; ability to engineer changes to physical environmental conditions; effects on disturbance, especially fire; regimes; the ability to structure habitat for other species; and their impact on food webs. Local factors of landscape setting, history, and other sources of disturbance constrain ecosystem responses to invasions. New research directions are suggested, including the need for whole-system budgets, the quantification of abundance-impact rel...

The Role of Propagule Pressure in Biological Invasions

Article

Dec 2009
ANNU REV ECOL EVOL S

Daniel Simberloff

Although most studies of factors contributing to successful establishment and spread of non-native species have focused on species traits and characteristics (both biotic and abiotic), increasing empirical and statistical evidence implicates propagule pressure—propagule sizes, propagule numbers, and temporal and spatial patterns of propagule arrival—as important in both facets of invasion. Increasing propagule size enhances establishment probability primarily by lessening effects of demographic stochasticity, whereas propagule number acts primarily by diminishing impacts of environmental stochasticity. A continuing rain of propagules, particularly from a variety of sources, may erase or vitiate the expected genetic bottleneck for invasions initiated by few individuals (as most are), thereby enhancing likelihood of survival. For a few species, recent molecular evidence suggests ongoing propagule pressure aids an invasion to spread by introducing genetic variation adaptive for new areas and habitats. This phenomenon may also explain some time lags between establishment of a non-native species and its spread to become an invasive pest.

Global Patterns of Plant Invasions and the Concept of Invasibility

Article

Jul 1999

W. M. Lonsdale

With a simple model, I show that comparisons of invasibility between regions are impossible to make unless one can control for all of the variables besides invasibility that influence exotic richness, including the rates of immigration of species and the characteristics of the invading species themselves. Using data from the literature for 184 sites around the world, I found that nature reserves had one-half of the exotic fraction of sites outside reserves, and island sites had nearly three times the exotic fraction of mainland sites. However, the exotic fraction and the number of exotics were also dependent on site area, and this had to be taken into account to make valid comparisons between sites. The number of native species was used as a surrogate for site area and habitat diversity. Nearly 70% of the variation in the number of exotic species was accounted for by a multiple regression containing the following predictors: the number of native species, whether the site was an island or on the mainland, and whether or not it was a nature reserve. After controlling for scale, there were significant differences among biomes, but not continents, in their level of invasion. Multiple biome regions and temperate agricultural or urban sites were among the most invaded biomes, and deserts and savannas were among the least. However, there was considerable within-group variation in the mean degree of invasion. Scale-controlled analysis also showed that the New World is significantly more invaded than the Old World, but only when site native richness (probably a surrogate for habitat diversity) is factored out. Contrary to expectation, communities richer in native species had more, not fewer, exotics. For mainland sites, the degree of invasion increased with latitude, but there was no such relationship for islands. Although islands are more invaded than mainland sites, this is apparently not because of low native species richness, as the islands in this data set were no less rich in native species than were mainland sites of similar area. The number of exotic species in nature reserves increases with the number of visitors. However, it is difficult to draw conclusions about relative invasibility, invasion potential, or the roles of dispersal and disturbance from any of these results. Most of the observed patterns here and in the literature could potentially be explained by differences between regions in species properties, ecosystem properties, or propagule pressure.

Invasion Ecology

Book

Jan 2007
AUSTRAL ECOL

This book provides a comprehensive introduction to all aspects of biological invasion by non-native species. Highlighting important research findings associated with each stage of invasion, Invasion Ecology provides an overview of the invasion process from transportation patterns and causes of establishment success to ecological impacts, invader management, and post-invasion evolution.--Jacket.

The invasive potential of Australian Banksias in South African fynbos: A comparison of the reproductive potential of Banksia ericifolia and Leucadendron laureolum

Article

Jul 2006
AUSTRAL ECOL

The invasive potential of Banksia ericifolia (Proteaceae) was investigated by comparing its recruitment potential with that of an indigenous proteaceous shrub, Leucadendron laureolum. Both species are overstorey shrubs that are killed by fire and rely on canopy-stored seeds (serotiny), for recruitment. Eight year old B. ericifolia shrubs produced an average of 16 500 seeds per plant, which is 30 times more than average of 570 seeds produced by 10 yr old L. laureolum. The seed bank of B. ericifolia was not only larger than that of L. laureolum (1098 vs 525 viable seeds m-2 projected canopy cover), but also considerably larger than that described for the species in its native environment (200-330 seeds m-2 in a 9 yr old stand near Sydney). Leucadendron released most of its seed a few days after the cones were burnt, whereas seed release in B. ericifolia was spread over 12 wk. Seeds of B. ericifolia had lower wingloading and fall rates than L. laureolum and were dispersed over greater distances. The relative seedling growth rates of the two species were very similar (0.03 g per day), but below-ground biomass was greater and proteoid roots were more developed in B. ericifolia seedings than in L. laureolum after 100 days. Four year old B. ericifolia plants growing in the field had attained over twice the height of indigenous proteoids and accumulated up to 10 times the fresh biomass of L. xanthoconus, a species which is ecologically similar to L. laureolum. The Bioclimatic Prediction System (BIOCLIM) was used to create a bioclimatic profile of B. ericifolia and identify climatically suitable areas in the Cape Province. Results show that its potential distribution covers most fynbos areas in the SW Cape. B. ericifolia has the potential to be highly invasive in fynbos. -from Authors

Influence of fire and soil nutrients on native and non-native annuals at remnant vegetation edges in the Western Australian Wheatbelt

Article

Feb 2009
J VEG SCI

The effect of fire on annual plants was examined in two vegetation types at remnant vegetation edges in the Western Australian wheatbelt. Density and cover of non-native species were consistently greatest at the reserve edges, decreasing rapidly with increasing distance from reserve edge. Numbers of native species showed little effect of distance from reserve edge. Fire had no apparent effect on abundance of non-natives in Allocasuarina shrubland but abundance of native plants increased. Density of both non-native and native plants in Acacia acuminata-Eucalyptus loxophleba woodland decreased after fire. Fewer non-native species were found in the shrubland than in the woodland in both unburnt and burnt areas, this difference being smallest between burnt areas. Levels of soil phosphorus and nitrate were higher in burnt areas of both communities and ammonium also increased in the shrubland. Levels of soil phosphorus and nitrate were higher at the reserve edge in the unburnt shrubland, but not in the woodland. There was a strong correlation between soil phosphorus levels and abundance of non-native species in the unburnt shrubland, but not after fire or in the woodland. Removal of non-native plants in the burnt shrubland had a strong positive effect on total abundance of native plants, apparently due to increases in growth of smaller, suppressed native plants in response to decreased competition. Two native species showed increased seed production in plots where non-native plants had been removed. There was a general indication that, in the short term, fire does not necessarily increase invasion of these communities by non-native species and could, therefore be a useful management tool in remnant vegetation, providing other disturbances are minimised.

A unified approach to model selection using the likelihood ratio test

Article

Aug 2010
Methods Ecol. Evol.

1. Ecological count data typically exhibit complexities such as overdispersion and zero-inflation, and are often weakly associated with a relatively large number of correlated covariates. The use of an appropriate statistical model for inference is therefore essential. A common selection criteria for choosing between nested models is the likelihood ratio test (LRT). Widely used alternatives to the LRT are based on information-theoretic metrics such as the Akaike Information Criterion. 2. It is widely believed that the LRT can only be used to compare the performance of nested models – i.e. in situations where one model is a special case of another. There are many situations in which it is important to compare non-nested models, so, if true, this would be a substantial drawback of using LRTs for model comparison. In reality, however, it is actually possible to use the LRT for comparing both nested and non-nested models. This fact is well-established in the statistical literature, but not widely used in ecological studies. 3. The main obstacle to the use of the LRT with non-nested models has, until relatively recently, been the fact that it is difficult to explicitly write down a formula for the distribution of the LRT statistic under the null hypothesis that one of the models is true. With modern computing power it is possible to overcome this difficulty by using a simulation-based approach. 4. To demonstrate the practical application of the LRT to both nested and non-nested model comparisons, a case study involving data on questing tick (Ixodes ricinus) abundance is presented. These data contain complexities typical in ecological analyses, such as zero-inflation and overdispersion, for which comparison between models of differing structure – e.g. non-nested models – is of particular importance. 5. Choosing between competing statistical models is an essential part of any applied ecological analysis. The LRT is a standard statistical test for comparing nested models. By use of simulation the LRT can also be used in an analogous fashion to compare non-nested models, thereby providing a unified approach for model comparison within the null hypothesis testing paradigm. A simple practical guide is provided in how to apply this approach to the key models required in the analyses of count data.

Effect of disturbance and nutrient addition on native and introduced annuals in plant communities in the Western Australian wheatbelt

Article

Jul 2006
AUSTRAL ECOL

To investigate factors affecting the ability of introduced species to invade natural communities in the Western Australian wheatbelt, five communities were examined within a nature reserve near Kellerberrin. Transect studies indicated that introduced annuals were more abundant in woodland than in shrub communities, despite an input of introduced seed into all communities. The response of native and introduced annuals to soil disturbance and fertilizer addition was examined. Small areas were disturbed and/or provided with fertilizer prior to addition of seed of introduced annuals. In most communities, the introduced species used (Avena fatua and Ursinia anthemoides) established well only where the soil had been disturbed, but their growth was increased greatly when fertilizer was also added. Establishment and growth of other introduced species also increased where nutrient addition and soil disturbance were combined. Growth of several native annuals increased greatly with fertilizer addition, but showed little response to disturbance. Fertilizer addition also significantly increased the number of native species present in most communities. This indicates that growth of both native and introduced species is limited by nutrient availability in these communities, but also that introduced species respond more to a combination of nutrient addition and soil disturbance.

Functional composition controls invasion success in a California serpentine grassland

Article

Jul 2010

1. Recent debates about the role of biotic resistance in controlling invasion success have focused on effects of species richness. However, functional composition could be a stronger control: species already in the community with similar functional traits to those of the invaders should have the greatest competitive effect on invaders. Still, experiments assessing effects of functional similarity have found contradictory results. 2. We used experimental communities in a serpentine grassland in California, USA, to assess the extent to which functional composition and functional diversity influenced success of two different types of invading plants: early season annuals (E) and late-season annuals (L) that have been previously shown to differ in patterns of resource acquisition. 3. We seeded known quantities of seed of six different species (three in each functional group) into experimental plots containing established communities differing in functional composition and functional diversity. The experimental communities contained different combinations of E, L, perennial bunchgrass (P) and nitrogen-fixer (N) functional groups, with functional diversity ranging from 0 to 4 groups. Each invading species was seeded into a separate quadrat within each plot to minimize competitive effects of invaders on each other. We measured both seedling and adult success of invaders for two full growing seasons to further understand mechanisms underlying biotic resistance. 4. More functionally diverse communities were less invaded overall, as measured by the average success of individual invaders. However, assessment of invaders by functional groups was more informative: Es in the extant community suppressed E invaders the most, and Ls in the extant community suppressed L invaders the most. 5. We observed a variety of interactions among extant functional groups in reducing invader success, including synergism, complementarity and ‘basement’ effects, where two or more groups negatively affected invaders, but combinations of groups were no more suppressive than single groups. The extant community influenced invaders more strongly through suppression of adult plant growth than through effects on seedling establishment. 6.Synthesis. Contrary to predictions from neutral theory, these results indicate that niche overlap was an important component of biotic resistance in these experimental plant communities and summed up to significant effects of species richness.

Invasibility and species richness of a community: A neutral model and a survey of published data

Article

Dec 2004

A widespread but controversial idea in ecology states that the number of invaders of a species assemblage depends on its species richness. Both negative and positive relationships have been reported. We examined whether a simple neutral model where assemblages are generated by drawing individuals from two pools of identical species (native and alien) can predict this relationship. We performed a meta-analysis of published data on this relationship. The neutral model showed that in communities with low and fixed numbers of indi-viduals, the relationship between the number of aliens and native species is strong and negative. This becomes weaker as the proportion of species from both pools already present in the community increases. The relationship between alien and native species richness becomes positive when the number of individuals is allowed to vary, because the richness depends on number of individuals and/or area sampled. The meta-analysis showed that scale-dependence of the relationship between alien and native species richness is universal and compatible with the neutral model. Unless more evidence is available to refute it, the relationship between native and alien species richness should be considered a result of a neutral processes due to constraints on the number of individuals in the community.

Invasions: The trail behind, the path ahead, and a test of a disturbing idea

Abstract

No full-text available

Recommended publications

Short-term responses of two collembolan communities after abrupt environmental perturbation: a field...

Modeling fire and nutrient flux

Invasive species in Kamchatka: Distribution and communities

Plant invasions in Central Europe: historical and ecological aspects