There has been a recent rise in the number of experiments investigating the effect of dispersal on diversity, with many of the predictions for these tests derived from metacommunity theory. Despite ...the promise of linking observed relationships between dispersal and diversity to underlying metacommunity processes, empirical studies have faced challenges in providing robust tests of theory. We review experimental studies that have tested how dispersal affects metacommunity diversity to determine why shortcomings emerge, and to provide a framework for empirical tests of theory that capture the processes structuring diversity in natural metacommunities. We first summarize recent experimental work to outline trends in results and to highlight common methods that cause a misalignment between empirical studies and the processes described by theory. We then identify the undesired implications of three widely used experimental methods that homogenize metacommunity structure or species traits, and present alternative methods that have been used to successfully integrate experiments and theory in a biologically relevant way. Finally, we present methodological and theoretical insights from three related ecological fields (coexistence, food web and priority effects theory) that, if integrated into metacommunity experiments, could help isolate the independent and joint effects of local interactions and dispersal on diversity, and reveal the mechanisms underlying observed dispersal–diversity patterns. Together, these methods can provide stronger tests of existing theory and stimulate new theoretical explorations.
Synthesis
Although metacommunity experiments offer a unique opportunity to test classic and emerging theory on the relationship between dispersal and diversity, several common challenges have hindered robust tests of theory. We outline how emerging theory on the invasion criterion, food webs and priority effects could be help clarify when and how dispersal affects metacommunity diversity, and identify when experimental approaches that homogenize metacommunities fail to test existing theory. By forging better links between theoretical and empirical work, we hope to motivate novel and improved experimental approaches to understanding the joint effects of local and regional processes on diversity.
According to the invasion criterion, stable coexistence requires that all species in a community increase in abundance when rare, which occurs when stabilizing mechanisms cause intraspecific ...competition to be stronger than interspecific competition. This simple principle has traditionally been applied to tests of local coexistence in a narrow range of ecological systems. However, new theory founded on the invasion criterion is emerging across ecological fields ranging from eco-evolutionary dynamics to global change to macroecology. Concurrently, straightforward methods for testing the invasion criterion have been proposed, but remain underused. Here, we identify the invasion criterion as a common thread linking emerging ecological theory, and we bring this theory together with the methods that can be used to test it.
The invasion criterion has historically been applied to tests of local coexistence in a narrow range of ecological systems.New theory based on the invasion criterion is rapidly emerging, while new methods that allow researchers to test this principle across a broader range of systems have been introduced.We identify the invasion criterion as a common thread that links emerging theory across a range of ecological fields, and we bring this theory together with the methods that can be used to test it.We hope to facilitate the empirical application of the invasion criterion to a range of questions that reach beyond tests of local coexistence.
Ecological drift causes species abundances to fluctuate randomly, lowering diversity within communities and increasing differences among otherwise equivalent communities. Despite broad interest in ...ecological drift, ecologists have little experimental evidence of its consequences in nature, where competitive forces modulate species abundances. We manipulated drift by imposing 40-fold variation in the size of experimentally assembled annual plant communities and holding their edge-to-interior ratios comparable. Drift over three generations was greater than predicted by neutral models, causing high extinction rates and fast divergence in composition among smaller communities. Competitive asymmetries drove populations of most species to small enough sizes that demographic stochasticity could markedly influence dynamics, increasing the importance of drift in communities. The strong effects of drift occurred despite stabilizing niche differences, which cause species to have greater population growth rates when at low local abundance. Overall, the importance of ecological drift appears greater in non-neutral communities than previously recognized, and varies with community size and the type and strength of density dependence.
Plant invasions and extinction debts Gilbert, Benjamin; Levine, Jonathan M.
Proceedings of the National Academy of Sciences - PNAS,
01/2013, Letnik:
110, Številka:
5
Journal Article
Recenzirano
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Whether introduced species invasions pose a major threat to biodiversity is hotly debated. Much of this debate is fueled by recent findings that competition from introduced organisms has driven ...remarkably few plant species to extinction. Instead, native plant species in invaded ecosystems are often found in refugia: patchy, marginal habitats unsuitable to their nonnative competitors. However, whether the colonization and extinction dynamics of these refugia allow long-term native persistence is uncertain. Of particular concern is the possibility that invasive plants may induce an extinction debt in the native flora, where persistence over the short term masks deterministic extinction trajectories. We examined how invader impacts on landscape structure influence native plant persistence by combining recently developed quantitative techniques for evaluating metapopulation persistence with field measurements of an invaded plant community. We found that European grass invasion of an edaphically heterogeneous California landscape has greatly decreased the likelihood of the persistence of native metapopulations. It does so via two main pathways: (i) decreasing the size of native refugia, which reduces seed production and increases local extinction, and (ii) eroding the dispersal permeability of the matrix between refugia, which reduces their connectivity. Even when native plant extinction is the deterministic outcome of invasion, the time to extinction can be on the order of hundreds of years. We conclude that the relatively short time since invasion in many parts of the world is insufficient to observe the full impact of plant invasions on native biodiversity.
1. Statistical tests partitioning community variation into environmental and spatial components have been widely used to test ecological theories and explore the determinants of community structure ...for applied conservation questions. Despite the wide use of these tests, there is considerable debate about their relative effectiveness. 2. We used simulated communities to evaluate the most commonly employed tests that partition community variation: regression on distance matrices and canonical ordination using a third-order polynomial, principal components of neighbour matrices (PCNM) or Moran's eigenvector maps (MEM) to model spatial components. Each test was evaluated under a variety of realistic sampling scenarios. 3. All tests failed to correctly model spatial and environmental components of variation, and in some cases produced biased estimates of the relative importance of components. Regression on distance matrices under-fit the spatial component, and ordination models consistently under-fit the environmental component. The PCNM and MEM approaches often produced inflated R² statistics, apparently as a result of statistical artefacts involving selection of superfluous axes. This problem occurred regardless of the forward-selection technique used. 4. Both sample configuration and the underlying linear model used to analyse species-environment relationships also revealed strong potential to bias results. 5. Synthesis and applications. Several common applications of variation partitioning in ecology now appear inappropriate. These potentially include decisions for community conservation based on inferred relative strengths of niche and dispersal processes, inferred community responses to climate change, and numerous additional analyses that depend on precise results from multivariate variation-partitioning techniques. We clarify the appropriate uses of these analyses in research programmes, and outline potential steps to improve them.
A complete description of the state of the cell requires knowledge of its size, shape, components, intracellular reactions, and interactions with its environment—all of these as a function of time ...and cell growth. Adding to this list is the need for theoretical models and simulations that integrate and help to interpret this daunting amount of experimental data. It seems like an overwhelming list of requirements, but progress is being made on many fronts. In this review, we discuss the current challenges and problems in obtaining sufficient information about each aspect of a dynamical whole-cell model (DWCM) for simple and well-studied bacterial systems.
•Natural tracer profiles through clay rock, interpreted by paleo-hydrological modeling, can constrain rates of diffusion over geologic timescales•No combination of imaging, scattering or other ...approach has yet identified all types of shale porosity and their interconnection•Accurate prediction of solute transport must consider transport and reactions with mineral and organic phases•Carbonate minerals strongly affect pore water chemistry, porosity evolution, and the retardation of solutes•Interdisciplinary meetings and collaborations can accelerate progress for all communities studying clay rocks
Clay rocks are low permeability sedimentary formations that provide records of Earth history, influence the quality of water resources, and that are increasingly used for the extraction or storage of energy resources and the sequestration of waste materials. Informed use of clay rock formations to achieve low-carbon or carbon-free energy goals requires the ability to predict the rates of diffusive transport processes for chemically diverse dissolved and gaseous species over periods up to thousands of years. We survey the composition, properties and uses of clay rock and summarize fundamental science challenges in developing confident conceptual and quantitative gas and solute transport models.
Abstract
Trait variation underlies our understanding of the patterns and importance of biodiversity, yet we have a poor understanding of how variation at different levels of biological organization ...structures communities and ecosystems. Here, we use a mesocosm experiment to test for the effects of a larval dragonfly functional trait on community and ecosystem dynamics by creating artificial populations to mirror within‐ and between‐population trait variation observed in our study area. Specifically, we manipulate variation in activity rate, a key functional trait shaping food webs, across three levels of biological organization: within‐populations (differences in trait variation in a population), among‐populations (differences in population mean trait values), and among‐species (species‐level differences of co‐occurring dragonflies). We show that differences in activity rate alter prey communities, trophic cascades, and multiple ecosystem processes. However, trait variation among populations had much larger effects than differences between co‐occurring species or even the presence of a predator, whereas within‐population variation had a relatively minor impact. Interestingly, combined with earlier work in the same system, our study suggests that the relative importance of species vs. individual level differences for ecosystem functioning will depend on the spatial scale considered. Ecological processes, including biodiversity–ecosystem‐functioning relationships, cannot be understood without accounting for trait variation across biological scales of organization, including at fine scales.
Background Computer-assisted diagnosis of dermoscopic images of skin lesions has the potential to improve melanoma early detection. Objective We sought to evaluate the performance of a novel ...classifier that uses decision forest classification of dermoscopic images to generate a lesion severity score. Methods Severity scores were calculated for 173 dermoscopic images of skin lesions with known histologic diagnosis (39 melanomas, 14 nonmelanoma skin cancers, and 120 benign lesions). A threshold score was used to measure classifier sensitivity and specificity. A reader study was conducted to compare the sensitivity and specificity of the classifier with those of 30 dermatology clinicians. Results The classifier sensitivity for melanoma was 97.4%; specificity was 44.2% in a test set of images. In the reader study, the classifier's sensitivity to melanoma was higher ( P < .001) and specificity was lower ( P < .001) than that of clinicians. Limitations This is a retrospective study using existing images primarily chosen for biopsy by a dermatologist. The size of the test set is small. Conclusions Our classifier may aid clinicians in deciding if a skin lesion should be biopsied and can easily be incorporated into a portable tool (that uses no proprietary equipment) that could aid clinicians in noninvasively evaluating cutaneous lesions.
Ion exchange in nanoporous clay-rich media plays an integral role in water, nutrient, and contaminant storage and transport. In montmorillonite (MMT), a common clay mineral in soils, sediments, and ...muds, the swelling and collapse of clay particles through the addition or removal of discrete molecular layers of water alters cation exchange selectivities in a poorly understood way. Here, we show that ion exchange is coupled to the dynamic delamination and restacking of clay layers, which creates a feedback between the hydration state of the exchanging cation and the composition of the clay interlayer. Particles with different hydration states are distinct phases with unique binding selectivities. Surprisingly, equilibrium achieved through thermal fluctuations in cation concentration and hydration state leads to the exchange of both ions and individual MMT layers between particles, a process we image directly with high-resolution transmission electron microscopy at cryogenic conditions (cryo-TEM). We introduce an exchange model that accounts for the binding selectivities of different phases, which is likely applicable to many charged colloidal or macromolecular systems in which the structural conformation is correlated with the activities of water and counterions within spatially confined compartments.
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