The statistical mechanics of community assembly and species distribution (original) (raw)
Related papers
Ecology
Communities comprising alien species with different residence times are natural experiments allowing the assessment of drivers of community assembly over time. Stochastic processes (such as dispersal and fluctuating environments) should be the dominant factors structuring communities of exotic species with short residence times. In contrast, communities should become more similar, or systematically diverge, if they contain exotics with increasing resident times, due to the increasing importance of deterministic processes (such as environmental filtering). We use zeta diversity (the number of species shared by multiple assemblages) to explore the relationship between the turnover of native species and two categories of alien species with different residence times (archaeophytes [introduced between 4000 BC and 1500 AD] and neophytes [introduced after 1500 AD]) in a network of nature reserves in central Europe. By considering multiple assemblages simultaneously, zeta diversity allows us to determine the contribution of rare and widespread species to turnover. Specifically, we explore the relative effects of assembly processes representing isolation by distance, environmental filtering, and environmental stochasticity (fluctuating environments) on zeta diversity using Multi-Site Generalized Dissimilarity Modelling (MS-GDM). Four clusters of results emerged. First, stochastic processes for structuring plant assemblages decreased in importance with increasing residence time. Environmental stochasticity only affected species composition for neophytes, offering possibilities to predict the spread debt of recent invasions. Second, native species turnover was well explained by environmental filtering and isolation by distance, although these factors did not explain the turnover of archaeophytes and neophytes. Third, native and alien species compositions were only correlated for rare species, whereas turnover in widespread alien species was surprisingly unrelated to the composition of widespread native species. Site-specific approaches would therefore be more appropriate for the monitoring and management of rare alien species, whereas species-specific approaches would suit widespread species. Finally, the size difference of nature reserves influences not only native species richness, but also their richness-independent turnover. A network of reserves must therefore be designed and managed using a variety of approaches to enhance native diversity, while controlling alien species with different residence times and degrees of commonness.
The relationship between community diversity and exotic plants: cause or consequence of invasion?
Invasive Plants: Ecological and Agricultural Aspects
Introduction Biological diversity is the modern unifying metric by which the health and status of communities and ecosystems are assessed throughout the world. Diversity is used to identify areas of special conservation concern while threats to biodiversity are the focus of remediation and legal action. Although the greatest threats to biodiversity are typically thought of as being the direct or indirect result of habitat loss and fragmentation, biological invasions follow closely behind. Despite this high priority position, our knowledge of the relationship between invasions and diversity remains relatively early in its development. The invasion of terrestrial communities by exotic plant species is a major concern for ecologists and natural resource managers. With the increased speed of planned and unplanned movement of species throughout the world and greater rates of disturbance, exotic plants are becoming a larger component of regional floras [1-4]. Furthermore, exotic species already cover vast areas of many community types and sometimes dominate local plant communities. Invasions affect both natural and agricultural systems and cause financial, as well as biological problems in areas of heavy invasion. While there has been an increase in awareness of the problem of exotic invasive plant species, their community-level impacts remain relatively unknown [5-8]. A frequently observed pattern within plant communities is a negative relationship between diversity, typically expressed as species richness, and the cover of exotic plants (Fig. 1A). This simple pattern has been explained by two community-level mechanisms that differ in the cause/consequence relationship between diversity and invasion. In the first mechanism, diversity regulates the invasibility of the local plant community, causing the diversity/invasion relationship. This view comes from theoretical and experimental community ecologists over the past several decades starting with Elton [9] and continues with empirical work (e.g., [10-12]). In the second mechanism, plant invasion results in the reduction of community diversity by driving other species from the local community. Changes in diversity in this context are a consequence of invasion. Conservationists largely present this view as justification for the control and regulation of exotic plant species [13, 14].
High species mobility in species-rich plant communities: An intercontinental comparison
Folia Geobotanica et Phytotaxonomica, 1994
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.
Journal of Vegetation Science, 2010
Questions: To what extent can Shipley et al.'s original maximum entropy model of trait-based community assembly predict relative abundances of species over a large (3000 km 2) landscape? How does variation in the species pool affect predictive ability of the model? How might the effects of missing traits be detected? How can non-trait-based processes be incorporated into the model? Location: Central England. Material and Methods: Using 10 traits measured on 506 plant species from 1308 1-m 2 plots collected over 3000 km 2 in central England, we tested one aspect of Shipley et al.'s original maximum entropy model of ''pure'' trait-based community assembly (S 1), and modified it to represent both a neutral (S 2) and a hybrid (S 3) scenario of community assembly at the local level. Predictive ability of the three corresponding models was determined with different species pool sizes (30, 60, 100 and 506 species). Statistical significance was tested using a distribution-free permutation test. Results: Predictive ability was high and significantly different from random expectations in S 1. Predictive ability was low but significant in S 2. Highest predictive ability occurred when both neutral and traitbased processes were included in the model (S 3). Increasing the pool size decreased predictive ability, but less so in S 3. Incorporating habitat affinity (to indicate missing traits) increased predictive ability. Conclusions: The measured functional traits were significantly related to species relative abundance. Our results both confirm the generality of the original model but also highlight the importance of (i) taking into account neutral processes during assembly of a plant community, and (ii) properly defining the species pool.
Exotic plants establish persistent communities
Plant Ecology, 2006
Many exotic plants utilize early successional traits to invade disturbed sites, but in some cases these same species appear able to prevent re-establishment of late-successional and native species. Between 2002 and 2004, I studied 25 fields that represent a 52-year chronosequence of agricultural abandonment in a shrub-steppe ecosystem in Washington State, USA, to determine if exotic plants behaved as early successional species (i.e., became less abundant over time) or if they established persistent communities. Exotics maintained dominance in tilled (73% of total cover) relative to never-tilled (6% of total cover) fields throughout the chronosequence. Exotic community composition, however, changed on annual and decadal timescales. Changes in exotic community composition did not reflect typical successional patterns. For example, some exotic perennial species (e.g., Centaurea diffusa and Medicago sativa) were less common and some exotic annual species (e.g., Sissymbrium loeselii and S. altissimum) were more common in older relative to younger fields. Exotics in the study area appeared to establish communities that are resistant to re-invasion by natives, resilient to losses of individual exotic species, and as a result, maintain total exotic cover over both the short- and long-term: exotics replaced exotics. Exotics did not invade native communities and natives did not invade exotic communities across the chronosequence. These results suggest that, in disturbed sites, exotic plants establish an alternative community type that while widely variable in composition, maintains total cover over annual and decadal timescales. Identifying alternative state exotic communities and the mechanisms that explain their growth is likely to be essential for native plant restoration.
The emergence of diversity in plant communities
Comptes Rendus de l'Académie des Sciences - Series III - Sciences de la Vie, 2000
The diversity of functional forms and strategies in plant communities is essential to the maintenance of the services that ecosystems provide humanity, and ultimately to the homeostasis of the biosphere. This diversity emerges from evolutionary forces operating at lower levels; these exploit the opportunities for specialization presented by exogenous and endogenous spatial and temporal heterogeneity. Two major theoretical approaches have been taken to understand how strategies arise and are maintained: optimization models, which consider the fitnesses of types in isolation, and game-theoretic methods, which take frequency dependence into account. The gametheoretic approach is more powerful, but also more challenging to apply. For some relatively simple problems in the study of biodiversity, we show how the game-theoretic formulation can be translated into an equivalent problem in optimization. More generally, however, new techniques will be needed to explore the dynamics of multiple coexisting types and strategies. © 2000 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS biodiversity / evolutionary stable strategy / heterogeneity / life history / dispersal / seed size Résumé -Émergence de la diversité dans les communautés de plantes. La diversité des formes fonctionnelles et des stratégies dans les communautés de plantes est essentielle au maintien des services rendus à l'humanité par les systèmes écologiques, et en dernier lieu à l'homostase de la biosphère. Cette diversité émerge des forces de l'évolution opérant aux niveaux inférieurs ; celles-ci exploitent les opportunités de spécialisation présentées par l'hétérogénéité spatiale et temporelle exogène et endogène. Deux approches théoriques majeures ont été utilisées pour comprendre comment les stratégies naissent et comment elles perdurent : les méthodes d'optimisation qui considèrent la valeur adaptative des espèces en isolation et les méthodes de la théorie des jeux qui considèrent les interactions dépendant de la fréquence. Les méthodes de la théorie des jeux sont plus puissantes mais plus difficiles à appliquer. Nous démontrons comment une formulation utilisant la théorie des jeux peut être traduite en un problème équivalent d'optimisation pour certains problèmes simples dans l'étude de la biodiversité. Plus généralement, pourtant, nous démontrons que des techniques nouvelles seront nécessaires pour explorer les dynamiques des espèces et stratégies multiples coexistantes. © 2000 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS biodiversité / hétérogénéité / histoire de la vie / dispersion
Native and Exotic Plant Species Exhibit Similar Population Dynamics During Succession
Ecology, 2007
A growing body of literature has led to the debate in invasion biology whether exotic species perform within communities differently than native taxa due to inherent advantages. To address this issue, the population dynamics of native and exotic plant species were assessed from a 48-year record of permanent plot data from the Hutcheson Memorial Forest Center (New Jersey, USA) to determine rate of increase, lag time, maximum frequency, and the year of peak frequency. Overall, native and exotic species exhibited very similar population dynamics. Rates of increase and length of lag times were similar between native and exotic taxa but were strongly influenced by plant life form. Short-lived species were characterized by rapid population growth rates and short lag times. Growth rates decreased and lag times increased with species longevity. Overall, correlations between population metrics were the same in native and exotic taxa, suggesting similar trade-offs in life history patterns. The one difference observed was that, in native species, peak frequency was negatively associated with the year of peak frequency (i.e., early-successional species tended to become more abundant), while there was no relationship in exotic species. These analyses show that exotic species behave in essentially the same way as native taxa within dynamic communities. This suggests that abundant native and exotic plant species are exploiting the same range of ecological strategies resulting in similar roles within communities.
Invasion impacts diversity through altered community dynamics
Journal of Ecology, 2005
Invading plant species often alter community structure, composition and, in some instances, reduce local diversity. However, the community dynamics underlying these impacts are relatively unknown. 2 Declines in species richness with invasion may occur via displacement of resident species and/or reduction of seedling establishment by the invader. These two mechanisms differ in the demographic stage of the interaction. 3 We document turnover dynamics using long-term permanent plot data to assess the mechanism(s) of invasion impacts of four exotic species on a mixed community of native and exotic species. These mechanisms were evaluated at both the neighbourhood (1-m 2 plot) and population (individual species) scales. 4 During invasion, species richness declined with increasing invader cover for three of the four invaders. All invaders reduced colonization rates, but had no effect on extinction rates at the neighbourhood scale. Populations differed in their susceptibility to invasion impacts, with significant reductions in colonization for 10 of 25 (40%) species and increases in extinction for only 4 of 29 (14%) species. 5 At neighbourhood and population scales, influences of invasion on community dynamics were essentially the same for all invaders regardless of life-form. While individual resident species had some increase in extinction probability, community richness impacts were largely driven by colonization limitation. 6 The consistency of invasion impacts across life-forms suggests establishment limitation as a general mechanism of invasion impact. This common causal mechanism should be explored in other systems to determine the extent of its generality.