FORUM Fluctuating resources in plant communities: a general theory of invasibility (original) (raw)
Related papers
Fluctuating Resources in Plant Communities: a General theory of invasibility
Journal of Ecology, 2000
1 The invasion of habitats by non-native plant and animal species is a global phenomenon with potentially grave consequences for ecological, economic, and social systems. Unfortunately, to date, the study of invasions has been primarily anecdotal and resistant to generalization. 2 Here, we use insights from experiments and from long-term monitoring studies of vegetation to propose a new theory in which¯uctuation in resource availability is identi®ed as the key factor controlling invasibility, the susceptibility of an environment to invasion by non-resident species. The theory is mechanistic and quantitative in nature leading to a variety of testable predictions. 3 We conclude that the elusive nature of the invasion process arises from the fact that it depends upon conditions of resource enrichment or release that have a variety of causes but which occur only intermittently and, to result in invasion, must coincide with availability of invading propagules.
The Disturbed Resource-Flux Invasion Matrix: a New Framework for Patterns of Plant Invasion
Biological Invasions, 1999
Attempts to classify certain habitats as vulnerable to invasion or plant traits as invasive have met with limited success and applicability. Clearly, not all plant invaders are able to exploit all habitats and not all habitats are equally susceptible to invasion. Here we argue that it is critical for a successful model for invasions to incorporate both environmental and species traits and present just such a framework. Although disturbance has been targeted as a crucial event which renders habitats vulnerable to invasion, disturbances are often integral parts of ecosystems (e.g. floods, tree-falls, fire, etc.) and are not always associated with invasion events. We argue that disturbances that are associated with invasions alter historical patterns of turnover, or flux, of resources in an ecosystem. Given this perspective on the relationship between invasions and disturbances, and the need to integrate species traits with those of invaded ecosystems, we have developed an approach to characterize plant invasion patterns that we call the 'Disturbed Resource-Flux Invasion Matrix' or DRIM. This is a 16-cell matrix that classifies habitats by the quality of changes in physical and chemical resource flux either increasing or decreasing flux relative to historical patterns. Within each matrix cell, it is then possible to apply basic ecological principles to target species traits that can facilitate successful invasion of habitats experiencing that particular kind of disturbance. We present examples from the literature of how habitats and species can be classified according to the DRIM, and demonstrate the application of this theoretical model.
Separating habitat invasibility by alien plants from the actual level of invasion
Ecology, 2008
Habitats vary considerably in the level of invasion (number or proportion of alien plant species they contain), which depends on local habitat properties, propagule pressure, and climate. To determine the invasibility (susceptibility to invasions) of different habitats, it is necessary to factor out the effects of any confounding variables such as propagule pressure and climate on the level of invasion. We used 20 468 vegetation plots from 32 habitats in the Czech Republic to compare the invasibility of different habitats. Using regression trees, the proportion of alien plants, including archaeophytes (prehistoric to medieval invaders) and neophytes (recent invaders), was related to variables representing habitat properties, propagule pressure, and climate. The propagule pressure was expressed as the proportion of surrounding urban and industrial or agricultural land, human population density, distance from a river, and history of human colonization in the region. Urban and industrial land use had a positive effect on the proportion of both archaeophytes and neophytes. Agricultural land use, higher population density, and longer history of human impact positively affected the proportion of archaeophytes.
Expanding the conceptual frameworks of plant invasion ecology
Perspectives in Plant Ecology, Evolution and Systematics, 2011
Numerous mechanisms driving alien plant invasions have been described in a rapidly growing body of literature. However these are frequently case specific, making generalizations across species and systems difficult. A number of conceptual approaches have been proposed to help synthesize the literature, stimulating healthy debate among scientists. We build on these syntheses, presenting an expanded framework that incorporates the processes contributing to invasions, and the context within which they must interact. We also provide a model template into which the framework we develop is incorporated, illustrating both with examples. Our general framework includes three contributing processes: these are (1) the characteristics of the introduced species, (2) system context, within which the invasion takes place, and (3) the features of the receiving habitat. System context refers to the influences arising outside of the receiving environment, both spatially and temporally. Each contributing process is comprised of specific mechanisms, drawn from literature on invasion ecology and other related fields. The framework invokes relevant mechanisms for a specific species or situation. Although, a number of frameworks already consider the characteristics of the invading species or those of the receiving habitat, they seldom include all possible characteristics of both. We propose that these approaches alone are inadequate to provide a comprehensive understanding of the invasion process, without explicitly examining the context within which the invasion takes place. The model template we present relates the contributing processes described for a particular invasion, to the change in habitat from one state to another. Each of the contributing processes defined in the framework modulates the degree to which the habitat is changed. We suggest that these additional tools and the explicit inclusion of all three contributing processes, provide for further synthesis and improved understanding of invasions by alien plants.
Global Plant Invasions
Due to numerous human activities, organisms have been transported and either accidentally or deliberately introduced all around the globe. Biological invasions are now considered to be one of the main drivers of global change because many invasive plants have severe ecological, economic, and health consequences. Thus, there is an ever-growing need to better understand invasions to determine how specific plant species are able to establish in communities and, in many cases, expand their range. Here, we describe the invasion process and how it contributes to the invasion of plant communities. We present an invasion-factor framework (IFF) model that uses three factors (climate dynamics, ecosystem resistance, and invader fitness) to explain how each plays a role in the introduction of plants and their ultimate failure or success (i.e., becoming inva
Journal of Ecology, 2009
A number of experimental studies have supported the hypothesis that diversity increases invasion resistance, but several mechanisms were proposed to explain this relationship. We studied spontaneous invasion in experimental grasslands varying in species richness (1-16 (60)) and plant functional group richness and identity (1-4; grasses, legumes, tall herbs small herbs) during the first 3 years after establishment on large-area plots of 20 × 20 m size. 2. Invader species number, biomass and density decreased with increasing community species richness. The identity of successful invaders changed through time as the relative importance of external invaders (= species not belonging to the experimental species pool) decreased, while internal invaders (= species belonging to the experimental species pool) became more important. The presence of legumes increased, while the presence of grasses in the plant communities decreased density, biomass and species number of external invaders and biomass of internal invaders in the second and third year after establishment. 3. Analyses of viable seeds in the topsoil, a higher invasion in communities with more potential invaders in adjacent plots and an edge effect with a higher invader density and species number at the margin of the plots suggested recruitment limitation of internal invader species in contrast to external invader species that were more strongly limited by community characteristics. 4. Resource availability, in particular percentage cover of resident species, root length density and soil nitrate, and propagule availability had significant effects on invasibility. However, statistical analyses revealed that these variables did not completely control for effects of community species richness and the presence of grasses and legumes respectively on invasion resistance. 5. Separate analyses of frequent invader species showed that the invasion success of individual species varied in response to biodiversity and resource niches. 6. Synthesis . Our results confirm that a more complete use of available resources in plant communities of increasing species richness generally decreases invasibility. However, the overall positive effects of biodiversity on invasion resistance are dependent on species identity of the invader species. Thus, mechanisms at species level are important to understand community invasion resistance.
PERSPECTIVE Invasiveness in plant communities with feedbacks
2007
The detrimental effects of invasive plant species on ecosystems are well documented. While much research has focused on discovering ecological influences associated with invasiveness, it remains unclear how these influences interact, causing some introduced exotic species to become invasive threats. Here we develop a framework that incorporates the influences of propagule pressure, frequency independent growth rates, feedback relationships, resource competition and spatial scale of interactions. Our results show that these ecological influences interact in complex ways, resulting in expected outcomes ranging from inability to establish, to naturalization, to conditional invasion dependent on quantity and spatial distribution of propagules, to unconditional takeover. We propose a way to predict the likelihood of these four possible outcomes, for a species recently introduced into a given target community. Such information could enable conservation biologists to craft strategies and target remediation efforts more efficiently and effectively in order to help maintain biodiversity in ecological communities.