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Environmental Stochasticity (environmental + stochasticity)
Selected AbstractsProjected population-level effects of thiobencarb exposure on the mysid, Americamysis bahia, and extinction probability in a concentration-decay exposure systemENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2005Sandy Raimondo Abstract Population-level effects of the mysid, Americamysis bahia, exposed to varying thiobencarb concentrations were estimated using stage-structured matrix models. A deterministic density-independent matrix model estimated the decrease in population growth rate (,) with increasing thiobencarb concentration. An elasticity analysis determined that survival of middle stages provided the largest contribution to ,. Decomposing the effects of , in terms of changes in the matrix components determined that reduced reproduction had a large influence on population dynamics at lower thiobencarb concentrations, whereas reduced survivorship had the largest impact on populations at higher concentrations. A simulation model of a concentration-decay system was developed to demonstrate the importance of integrating chemical half-life and management practices in determining population viability. In this model, mysids were originally exposed to a high thiobencarb concentration (300 ,g/L) that decayed an order of magnitude in the number of mysid generations corresponding to thiobencarb half-life values under three different exposure regimes. Environmental stochasticity was added to the model to estimate the cumulative extinction probability of mysids exposed to fluctuating concentrations of thiobencarb in random environments. The cumulative extinction probability increased with thiobencarb half-life, stochasticity, and concentration present at the time of a new exposure. The model demonstrated the expansion of population projection models in determining the ecological impact of a population exposed to pesticides. [source] Estimating the growth of a newly established moose population using reproductive valueECOGRAPHY, Issue 3 2007Bernt-Erik Sæther Estimating the population growth rate and environmental stochasticity of long-lived species is difficult because annual variation in population size is influenced by temporal autocorrelations caused by fluctuations in the age-structure. Here we use the dynamics of the reproductive value to estimate the long-term growth rate s and the environmental variance of a moose population that recently colonized the island of Vega in northern Norway. We show that the population growth rate was high (,=0.26). The major stochastic influences on the population dynamics were due to demographic stochasticity, whereas the environmental variance was not significantly different from 0. This supports the suggestion that population growth rates of polytocous ungulates are high, and that demographic stochasticity must be assessed when estimating the growth of small ungulate populations. [source] Setting the absolute tempo of biodiversity dynamicsECOLOGY LETTERS, Issue 7 2007Andrew P. Allen Abstract Neutral biodiversity theory has the potential to contribute to our understanding of how macroevolutionary dynamics influence contemporary biodiversity, but there are issues regarding its dynamical predictions that must first be resolved. Here we address these issues by extending the theory in two ways using a novel analytical approach: (1) we set the absolute tempo of biodiversity dynamics by explicitly incorporating population-level stochasticity in abundance; (2) we allow new species to arise with more than one individual. Setting the absolute tempo yields quantitative predictions on biodiversity dynamics that can be tested using contemporary and fossil data. Allowing incipient-species abundances greater than one individual yields predictions on how these dynamics, and the form of the species-abundance distribution, are affected by multiple speciation modes. We apply this new model to contemporary and fossil data that encompass 30 Myr of macroevolution for planktonic foraminifera. By synthesizing the model with these empirical data, we present evidence that dynamical issues with neutral biodiversity theory may be resolved by incorporating the effects of environmental stochasticity and incipient-species abundance on biodiversity dynamics. [source] The paradox of invasionGLOBAL ECOLOGY, Issue 5 2000Dov F. Sax Abstract It is paradoxical that exotic species invade and displace native species that are well adapted to local environments. Yet, even those exotics that eventually become abundant and widespread, often do so only after having failed to establish following multiple earlier introductions. The first pattern, while not generally discussed in this context, is usually explained by exotic species pre-adaptations for human-altered environments and by a release from enemies. It can be understood further by examining the superior quality of colonists from large species-rich regions and the historical contingency of evolution. The second pattern is generally explained by invoking demographic and environmental stochasticity; however, it can be understood further by examining the role of environmental variation over space and by metapopulation dynamics. These processes provide a context in which these patterns of invasion are not paradoxical, but instead, expected. [source] Overcompensatory population dynamic responses to environmental stochasticityJOURNAL OF ANIMAL ECOLOGY, Issue 6 2008James C. Bull Summary 1To quantify the interactions between density-dependent, population regulation and density-independent limitation, we studied the time-series dynamics of an experimental laboratory insect microcosm system in which both environmental noise and resource limitation were manipulated. 2A hierarchical Bayesian state-space approach is presented through which it is feasible to capture all sources of uncertainty, including observation error to accurately quantify the density dependence operating on the dynamics. 3The regulatory processes underpinning the dynamics of two different bruchid beetles (Callosobruchus maculatus and Callosobruchus chinensis) are principally determined by environmental conditions, with fluctuations in abundance explained in terms of changes in overcompensatory dynamics and stochastic processes. 4A general, stochastic population model is developed to explore the link between abundance fluctuations and the interaction between density dependence and noise. Taking account of time-lags in population regulation can substantially increase predicted population fluctuations resulting from underlying noise processes. [source] Effect of experimentally altered food abundance on fat reserves of wintering birdsJOURNAL OF ANIMAL ECOLOGY, Issue 5 2003Christopher M. Rogers Summary 1Current models of adaptive fat regulation make opposing predictions concerning the effect of increased winter food supply on size of the avian winter fat reserve. To distinguish between models, food supply was varied experimentally in nature and two measures of size of the fat reserve were taken at food-supplemented sites and non-supplemented sites. 2In two winters, most of the seven species sampled showed slightly higher visible subcutaneous fat class at supplemented than at non-supplemented sites; treatment and species factors were statistically significant. Body mass corrected for wing length showed a similar if non-significant trend. 3A parallel dispersal study of birds colour-banded at non-supplemented sites showed that these birds did not move 0·8 or 1·5 km to use supplemental food at private feeding stations in the study areas. In addition, accipiter hawk attack rate did not differ between supplemented and non-supplemented sites. 4These results are consistent with a model of adaptive fat regulation (based on between-day environmental variability caused by severe weather events) that predicts an increase in the winter fat reserve at increased food supply. Other published studies, all from the north temperate zone, showed the same pattern. 5The present results are inconsistent with a second model (based on within-day foraging interruption) which predicts a decrease in the fat reserve under increased food supply. However, a set of published studies, all from tropical regions or regions with mild maritime climate, showed the decrease at higher food predicted by the second but not the first model. 6Models of adaptive fat regulation in small birds are therefore limited in their predictive power, perhaps because they are developed for environments that differ in the time scale of environmental stochasticity. New studies are needed that explore further the complexities of environment-specific adaptive fat models, e.g. a winter feeding experiment in a tropical bird species. [source] A test of the metapopulation model of the species,area relationshipJOURNAL OF BIOGEOGRAPHY, Issue 8 2002Stephen F. Matter Abstract Aim The species,area relationship is a ubiquitous pattern. Previous methods describing the relationship have done little to elucidate mechanisms producing the pattern. Hanski & Gyllenberg (Science, 1997, 275, 397) have shown that a model of metapopulation dynamics yields predictable species,area relationships. We elaborate on the biological interpretation of this mechanistic model and test the prediction that communities of species with a higher risk of extinction caused by environmental stochasticity should have lower species,area slopes than communities experiencing less impact of environmental stochasticity. Methods We develop the mainland,island version of the metapopulation model and show that the slope of the species,area relationship resulting from this model is related to the ratio of population growth rate to variability in population growth of individual species. We fit the metapopulation model to five data sets, and compared the fit with the power function model and Williams's (Ecology, 1995, 76, 2607) extreme value function model. To test that communities consisting of species with a high risk of extinction should have lower slopes, we used the observation that small-bodied species of vertebrates are more susceptible to environmental stochasticity than large-bodied species. The data sets were divided into small and large bodied species and the model fit to both. Results and main conclusions The metapopulation model showed a good fit for all five data sets, and was comparable with the fits of the extreme value function and power function models. The slope of the metapopulation model of the species,area relationship was greater for larger than for smaller-bodied species for each of five data sets. The slope of the metapopulation model of the species,area relationship has a clear biological interpretation, and allows for interpretation that is rooted in ecology, rather than ad hoc explanation. [source] The evolutionary ecology of vegetative dormancy in mature herbaceous perennial plantsJOURNAL OF ECOLOGY, Issue 5 2009Richard P. Shefferson Summary 1.,I present an evolutionary ecology interpretation of vegetative dormancy in mature herbaceous perennials. This kind of vegetative dormancy has been noted for at least 40 years, but has only recently become a topic of study. 2.,Vegetative dormancy may be considered in a life-history context. Both vegetative dormancy and mortality typically decrease with increasing size. Vegetative dormancy's relationship to reproduction is more complex, because some species increase flowering and fruiting after dormancy while others do the opposite. 3.,If vegetative dormancy is adaptive, then it is most likely a bet-hedging trait. Dormancy-prone plants are often long-lived, and in such organisms, bet-hedging traits should counter the effects of environmental stochasticity on adult survival. This adaptive context may vary by life span, because in shorter-lived plants, fitness is most sensitive to changes in reproduction rather than survival. 4.,Vegetative dormancy could evolve if the costs of sprouting ever outweigh the benefits. The benefits of sprouting include: (i) photosynthesis and (ii) the opportunity to flower and reproduce. The costs include: (i) greater chance of herbivory, (ii) greater need for limiting nutrients, and (iii) greater maintenance costs. The many losses of photosynthesis among plants suggest that these benefits may not always outweigh the costs. 5.,Vegetative dormancy may be an evolutionary step towards the loss of photosynthesis. Many non-photosynthetic plants acquire carbon from their mycorrhizal fungi. Many autotrophic, dormancy-prone plants also acquire some carbon from their mycorrhizal fungi. Further, non-photosynthetic plants often become dormant to an even greater extent than autotrophic, dormancy-prone plants. 6.Synthesis,Vegetative dormancy often occurs in clades with non-photosynthetic, myco-heterotrophic plants, with implications for the evolution of traits involved in carbon nutrition. The links between vegetative dormancy, other life-history traits, mycorrhizas and the loss of photosynthesis should provide exciting directions for further research in plant evolutionary ecology. Particularly needed is an assessment of the physiology of vegetative dormancy, including whether the mycorrhiza is a carbon source in all dormancy-prone plant species. Equally important is a better understanding of the genetic relationships among photosynthesis, myco-heterotrophy and dormancy. [source] Demographic variation and population viability in Gentianella campestris: effects of grassland management and environmental stochasticityJOURNAL OF ECOLOGY, Issue 3 2001Tommy Lennartsson Summary 1,Transition matrix models were used to evaluate the effects of environmental stochasticity and four different methods of grassland management on dynamics and viability of a population of the biennial Gentianella campestris (Gentianaceae) in species-rich grassland. Data were collected between 1990 and 1995. 2,Continuous summer grazing, the prevailing management strategy in Scandinavian grasslands, resulted in high recruitment of new plants, mainly because litter accumulation was prevented and gaps were created by trampling. Trampling and repeated grazing, however, caused damage which reduced seed production. Lambda for the average matrix was c. 0.77, and a stochastic matrix model yielded an extinction probability for the total population of c. 0.08 within 50 years. 3,Mowing in mid-July (used as a conservation tool) increased seed production, but litter accumulation following re-growth of the vegetation prevented establishment. Lambda and extinction risk were similar to continuous grazing. 4,Mowing in October (another conservation tool) promoted recruitment because of low litter accumulation, but the seed output decreased because plant growth was impaired by tall vegetation. Lambda was 0.64, while the extinction probability was very high (c. 0.98 within 50 years). 5,Mid-July mowing followed by autumn grazing (the historical management regime) yielded high values for both seed production and establishment of rosettes. Lambda was 0.94 and the probability of extinction within 50 years was below detection level. 6,Log-linear analysis showed that the matrices differed significantly both between treatments and between years. The latter indicates environmental stochasticity, here caused by summer drought that increased the extinction risk. Lambda may be slightly underestimated because drought occurred in one out of five summers during the study period, which is high compared with the natural frequency. 7,We conclude that traditional grassland management is more favourable for G. campestris than the methods that prevail in Scandinavia today. This indicates a serious conservation problem, because grazing has replaced traditional management in many of the remaining semi-natural grasslands throughout Europe. [source] Spatially heterogeneous stochasticity and the adaptive diversification of dormancyJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 10 2009E. Rajon Abstract Diversified bet-hedging, a strategy that leads several individuals with the same genotype to express distinct phenotypes in a given generation, is now well established as a common evolutionary response to environmental stochasticity. Life-history traits defined as diversified bet-hedging (e.g. germination or diapause strategies) display marked differences between populations in spatial proximity. In order to find out whether such differences can be explained by local adaptations to spatially heterogeneous environmental stochasticity, we explored the evolution of bet-hedging dormancy strategies in a metapopulation using a two-patch model with patch differences in stochastic juvenile survival. We found that spatial differences in the level of environmental stochasticity, restricted dispersal, increased fragmentation and intermediate survival during dormancy all favour the adaptive diversification of bet-hedging dormancy strategies. Density dependency also plays a major role in the diversification of dormancy strategies because: (i) it may interact locally with environmental stochasticity and amplify its effects; however, (ii) it can also generate chaotic population dynamics that may impede diversification. Our work proposes new hypotheses to explain the spatial patterns of bet-hedging strategies that we hope will encourage new empirical studies of this topic. [source] Is life-history buffering or lability adaptive in stochastic environments?OIKOS, Issue 7 2009David N. Koons It is commonly thought that temporal fluctuations in demographic parameters should be selected against because of the deleterious impacts variation can have on fitness. A critical underpinning of this prediction is the assumption that changes in environmental conditions map linearly into changes in demographic parameters over time. We detail why this assumption may often break down and why selection should not always favor buffering of demographic parameters against environmental stochasticity. To the contrary, nonlinear relationships between the environment and demographic performance can produce asymmetric temporal variation in demographic parameters that actually enhances fitness. We extend this result to structured populations using simulation and show that ,demographic lability' rather than ,buffering' may be adaptive, particularly in organisms with low juvenile or adult survival. Finally, we review previous ecological work, and indicate cases where ,demographic lability' may be adaptive, then conclude by identifying research that is needed to develop a theory of life-history evolution that encompasses both demographic buffering and lability. [source] Which traits promote persistence of feral GM crops?OIKOS, Issue 1 2005Part 2: implications of metapopulation structure Transgenes may spread from crops into the environment via the establishment of feral populations, often initiated by seed spill from transport lorries or farm machinery. Locally, such populations are often subject to large environmental variability and usually do not persist longer than a few years. Because secondary feral populations may arise from seed dispersal to adjacent sites, the dynamics of such populations should be studied in a metapopulation context. We study a structured metapopulation model with local dispersal, mimicking a string of roadside subpopulations of a feral crop. Population growth is assumed to be subject to local disturbances, introducing spatially random environmental stochasticity. Our aim is to understand the role of dispersal and environmental variability in the dynamics of such ephemeral populations. We determine the effect of dispersal on the extinction boundary and on the distribution of persistence times, and investigate the influence of spatially correlated disturbances as opposed to spatially random disturbances. We find that, given spatially random disturbances, dispersal slows down the decline of the metapopulation and results in the occurrence of long-lasting local populations which remain more or less static in space. We identify which life history traits, if changed by genetic modification, have the largest impact on the population growth rate and persistence times. For oilseed rape, these are seed bank survival and dormancy. Combining our findings with literature data on transgene-induced life history changes, we predict that persistence is promoted by transgenes for oil-modifications (high stearate or high laurate) and, possibly, for insect resistence (Bt). Transgenic tolerance to glufosinate herbicide is predicted to reduce persistence. [source] Ecological dynamics of extinct species in empty habitat networks.OIKOS, Issue 3 2003This paper explores the relative effects of host plant dynamics and butterfly-related parameters on butterfly persistence. It considers an empty habitat network where a rare butterfly (Cupido minimus) became extinct in 1939 in part of its historical range in north Wales, UK. Surviving populations of the butterfly in southern Britain were visited to assess use of its host plant (Anthyllis vulneraria) in order to calibrate habitat suitability and carrying capacity in the empty network in north Wales. These data were used to deduce that only a portion (,19%) of the host plant network from north Wales was likely to be highly suitable for oviposition. Nonetheless, roughly 65,460 eggs (3273 adult equivalents) could be expected to be laid in north Wales, were the empty network to be populated at the same levels as observed on comparable plants in surviving populations elsewhere. Simulated metapopulations of C. minimus in the empty network revealed that time to extinction and patch occupancy were significantly influenced by carrying capacity, butterfly mean dispersal distance and environmental stochasticity, although for most reasonable parameter values, the model system persisted. Simulation outputs differed greatly when host plant dynamics was incorporated into the modelled butterfly dynamics. Cupido minimus usually went extinct when host plant were at low densities. In these simulations host plant dynamics appeared to be the most important determinant of the butterfly's regional extirpation. Modelling the outcome of a reintroduction programme to C. minimus variation at high quality locations, revealed that 65% of systems survived at least 100 years. Given the current amount of resources of the north Wales landscape, the persistence of C. minimus under a realistic reintroduction programme has a good chance of being successful, if carried out in conjunction with a host plant management programme. [source] Trophic-dynamic considerations in relating species diversity to ecosystem resilienceBIOLOGICAL REVIEWS, Issue 3 2000KRIS H. JOHNSON ABSTRACT Complexity in the networks of interactions among and between the living and abiotic components forming ecosystems confounds the ability of ecologists to predict the economic consequences of perturbations such as species deletions in nature. Such uncertainty hampers prudent decision making about where and when to invest most intensively in species conservation programmes. Demystifying ecosystem responses to biodiversity alterations may be best achieved through the study of the interactions allowing biotic communities to compensate internally for population changes in terms of contributing to ecosystem function, or their intrinsic functional redundancy. Because individual organisms are the biologically discrete working components of ecosystems and because environmental changes are perceived at the scale of the individual, a mechanistic understanding of functional redundancy will hinge upon understanding how individuals' behaviours influence population dynamics in the complex community setting. Here, I use analytical and graphical modelling to construct a conceptual framework for predicting the conditions under which varying degrees of interspecific functional redundancy can be found in dynamic ecosystems. The framework is founded on principles related to food web successional theory, which provides some evolutionary insights for mechanistically linking functional roles of discrete, interacting organisms with the dynamics of ecosystems because energy is the currency both for ecological fitness and for food web commerce. Net productivity is considered the most contextually relevant ecosystem process variable because of its socioeconomic significance and because it ultimately subsumes all biological processes and interactions. Redundancy relative to productivity is suggested to manifest most directly as compensatory niche shifts among adaptive foragers in exploitation ecosystems, facilitating coexistence and enhancing ecosystem recovery after disturbances which alter species' relative abundances, such as extinctions. The framework further explicates how resource scarcity and environmental stochasticity may constitute ,ecosystem legacies' influencing the emergence of redundancy by shaping the background conditions for foraging behaviour evolution and, consequently, the prevalence of compensatory interactions. Because it generates experimentally testable predictions for a priori hypothesis testing about when and where varying degrees of functional redundancy are likely to be found in food webs, the framework may be useful for advancing toward the reliable knowledge of biodiversity and ecosystem function relations necessary for prudent prioritization of conservation programmes. The theory presented here introduces explanation of how increasing diversity can have a negative influence on ecosystem sustainability by altering the environment for biotic interactions - and there by changing functional compensability among biota - under particular conditions. [source] | ||||||||||