Ecological Monographs
SCOPUS (SonsInc.)SCIE-ISI
0012-9615
1557-7015
Mỹ
Cơ quản chủ quản: WILEY , John Wiley & Sons Inc.
Lĩnh vực:
Ecology, Evolution, Behavior and Systematics
Các bài báo tiêu biểu
An Ordination of the Upland Forest Communities of Southern Wisconsin
Tập 27 Số 4 - Trang 325-349 - 1957
Pseudoreplication and the Design of Ecological Field ExperimentsPseudoreplication is defined as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with an error term inappropriate to the hypothesis being considered. Scrutiny of 176 experimental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential statistics. The incidence of pseudoreplication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on an experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assured only by dispensing with strict randomization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre—layout (or conventional) and layout—specific alpha (probability of type I error). Suggestions are offered to statisticians and editors of ecological journals as to how ecologists' understanding of experimental design and statistics might be improved.
Tập 54 Số 2 - Trang 187-211 - 1984
EFFECTS OF BIODIVERSITY ON ECOSYSTEM FUNCTIONING: A CONSENSUS OF CURRENT KNOWLEDGE
Tập 75 Số 1 - Trang 3-35 - 2005
Modeling Survival and Testing Biological Hypotheses Using Marked Animals: A Unified Approach with Case StudiesThe understanding of the dynamics of animal populations and of related ecological and evolutionary issues frequently depends on a direct analysis of life history parameters. For instance, examination of trade—offs between reproduction and survival usually rely on individually marked animals, for which the exact time of death is most often unknown, because marked individuals cannot be followed closely through time. Thus, the quantitative analysis of survival studies and experiments must be based on capture—recapture (or resighting) models which consider, besides the parameters of primary interest, recapture or resighting rates that are nuisance parameters. Capture—recapture models oriented to estimation of survival rates are the result of a recent change in emphasis from earlier approaches in which population size was the most important parameter, survival rates having been first introduced as nuisance parameters. This emphasis on survival rates in capture—recapture models developed rapidly in the 1980s and used as a basic structure the Cormack—Jolly—Seber survival model applied to an homogeneous group of animals, with various kinds of constraints on the model parameters. These approaches are conditional on first captures; hence they do not attempt to model the initial capture of unmarked animals as functions of population abundance in addition to survival and capture probabilities. This paper synthesizes, using a common framework, these recent developments together with new ones, with an emphasis on flexibility in modeling, model selection, and the analysis of multiple data sets. The effects on survival and capture rates of time, age, and categorical variables characterizing the individuals (e.g., sex) can be considered, as well as interactions between such effects. This "analysis of variance" philosophy emphasizes the structure of the survival and capture process rather than the technical characteristics of any particular model. The flexible array of models encompassed in this synthesis uses a common notation. As a result of the great level of flexibility and relevance achieved, the focus is changed from fitting a particular model to model building and model selection. The following procedure is recommended: (1) start from a global model compatible with the biology of the species studied and with the design of the study, and assess its fit; (2) select a more parsimonious model using Akaike's Information Criterion to limit the number of formal tests; (3) test for the most important biological questions by comparing this model with neighboring ones using likelihood ratio tests; and (4) obtain maximum likelihood estimates of model parameters with estimates of precision. Computer software is critical, as few of the models now available have parameter estimators that are in closed form. A comprehensive table of existing computer software is provided. We used RELEASE for data summary and goodness—of—fit tests and SURGE for iterative model fitting and the computation of likelihood ratio tests. Five increasingly complex examples are given to illustrate the theory. The first, using two data sets on the European Dipper (Cinclus cinclus), tests for sex—specific parameters, explores a model with time—dependent survival rates, and finally uses a priori information to model survival allowing for an environmental variable. The second uses data on two colonies of the Swift (Apus apus), and shows how interaction terms can be modeled and assessed and how survival and recapture rates sometimes partly counterbalance each other. The third shows complex variation in survival rates across sexes and age classes in the roe deer (Capreolus capreolus), with a test of density dependence in annual survival rates. The fourth is an example of experimental density manipulation using the common lizard (Lacerta vivipara). The last example attempts to examine a large and complex data set on the Greater Flamingo (Phoenicopterus ruber), where parameters are age specific, survival is a function of an environmental variable, and an age × year interaction term is important. Heterogeneity seems present in this example and cannot be adequately modeled with existing theory. The discussion presents a summary of the paradigm we recommend and details issues in model selection and design, and foreseeable future developments.
Tập 62 Số 1 - Trang 67-118 - 1992
Organization of a Plant‐Arthropod Association in Simple and Diverse Habitats: The Fauna of Collards (Brassica Oleracea)Collards were grown at Ithaca, New York, in two experimental habitats: pure stands and single rows that were bounded on each side by diverse, meadow vegetation. The arthropods associated with these plants were sampled on 20 dates over a 3—year period. The status of the herbivore species was measured by their rank in biomass in each sample. The two most prominent species, Phyllotreta cruciferae and Pieris rapae, maintained high status throughout the investigation, but another important species, Brevicoryne brassicae, was absent for an entire season. Pit feeders usually formed the most important herbivore guild. Nevertheless, the guild spectrum, which describes the functional structure of the fauna, varied widely in time and space. The size distributions of species and of individuals were both highly skewed toward the smaller sizes. Herbivore loads, the mean biomass of herbivores per 100 g of consumable foliage, were consistently higher in the pure stands. Moreover, herbivore loads varied significantly with season in each experimental habitat. Both the number of herbivore species and the diversity of the herbivore load were greater in the diverse habitat. Biomass was more heavily concentrated among the prominent herbivores in the pure stands; increased dominance, rather than differences in species richness, appeared to be the major cause for the lower herbivore diversity in this habitat. The diversity of predators and parasitoids was higher in the pure stands. Most of the abundant species found on collards shared a similar narrow range of hosts. As a result the species in this core group of herbivores and parasitoids were regularly associated with each other. Predators and the less abundant herbivores tended to be less specialized and served to link the collard association with the surrounding community. Plant—arthropod associations are representative of component communities, well—integrated systems that form portions of larger compound communities. This distinction facilitates the analysis of community structure. Microclimates and the effectiveness of "enemies" did not appear to differ sufficiently in the two experimental habitats to account for the observed differences in the herbivore load. The results suggest a new proposition, the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments; and that, as a result, biomass tends to become concentrated in a few species, causing a decrease in the diversity of herbivores in pure stands.
Tập 43 Số 1 - Trang 95-124 - 1973
Competition, Disturbance, and Community Organization: The Provision and Subsequent Utilization of Space in a Rocky Intertidal CommunityAn understanding of community structure should be based on evidence that the growth and regulation of the component populations in the community are affected in a predictable manner by natural physical disturbances and by interactions with other species in the community. This study presents an experimental evaluation of the effects of such disturbances and competitive interactions on populations of sessile organisms in the rocky intertidal community, for which space can be demonstrated to be the most important limiting resource. This research was carried out at eight stations on the Washington coastline which have been ranked according to an exposure/desiccation gradient and subjected to comparable manipulation and observation. Physical variables such as wave exposure, battering by drift logs, and desiccation have important effects on the distribution and abundance of many of the sessile species in the community. In particular, wave exposure and desiccation have a major influence on the distribution patterns of all the algae and of the anemone Anthopleura elegantissima. The probability of damage from drift logs is very high in areas where logs have accumulated along the intertidal. Log damage and wave exposure have complementary effects in the provision of free space in a mussel bed, as wave shock enlarges a patch created by log damage by wrenching the mussels from the substratum at the periphery of the bare patch. Competition for primary space results in clear dominance hierarchies, in which barnacles are dominant over algae. Among the barnacles, Balanus cariosus is dominant over both B. glandula and Chthamalus dalli; B. glandula is dominant over C. dalli. The mussel Mytilus californianus requires secondary space (certain algae, barnacles, or byssal threads) for larval settlement, but is capable of growing over all other sessile species and potentially is the competitive dominant of space in the community.
Tập 41 Số 4 - Trang 351-389 - 1971
DISTANCE-BASED REDUNDANCY ANALYSIS: TESTING MULTISPECIES RESPONSES IN MULTIFACTORIAL ECOLOGICAL EXPERIMENTS
Tập 69 Số 1 - Trang 1-24 - 1999
PERMANOVA, ANOSIM, and the Mantel test in the face of heterogeneous dispersions: What null hypothesis are you testing?ANOSIM, PERMANOVA, and the Mantel test are all resemblance‐based permutation methods widely used in ecology. Here, we report the results of the first simulation study, to our knowledge, specifically designed to examine the effects of heterogeneity of multivariate dispersions on the rejection rates of these tests and on a classical MANOVA test (Pillai's trace). Increasing differences in dispersion among groups were simulated under scenarios of changing sample sizes, correlation structures, error distributions, numbers of variables, and numbers of groups for balanced and unbalanced one‐way designs. The power of these tests to detect environmental impacts or natural large‐scale biogeographic gradients was also compared empirically under simulations based on parameters derived from real ecological data sets. Overall, ANOSIM and the Mantel test were very sensitive to heterogeneity in dispersions, with ANOSIM generally being more sensitive than the Mantel test. In contrast, PERMANOVA and Pillai's trace were largely unaffected by heterogeneity for balanced designs. PERMANOVA was also unaffected by differences in correlation structure, unlike Pillai's trace. For unbalanced designs, however, all of the tests were (1) too liberal when the smaller group had greater dispersion and (2) overly conservative when the larger group had greater dispersion, especially ANOSIM and the Mantel test. For simulations based on real ecological data sets, PERMANOVA was generally, but not always, more powerful than the others to detect changes in community structure, and the Mantel test was usually more powerful than ANOSIM. Both the error distributions and the resemblance measure affected results concerning power. Differences in the underlying construction of these test statistics result in important differences in the nature of the null hypothesis they are testing, their sensitivity to heterogeneity, and their power to detect important changes in ecological communities. For balanced designs, PERMANOVA and PERMDISP can be used to rigorously identify location vs. dispersion effects, respectively, in the space of the chosen resemblance measure. ANOSIM and the Mantel test can be used as more “omnibus” tests, being sensitive to differences in location, dispersion or correlation structure among groups. Unfortunately, none of the tests (PERMANOVA, Mantel, or ANOSIM) behaved reliably for unbalanced designs in the face of heterogeneity.
Tập 83 Số 4 - Trang 557-574 - 2013
Cross‐Scale Morphology, Geometry, and Dynamics of EcosystemsThis paper tests the proposition that a small set of plant, animal, and abiotic processes structure ecosystems across scales in time and space. Earlier studies have suggested that these key structuring processes establish a small number of dominant temporal frequencies that entrain other processes. These frequencies often differ from each other by at least an order of magnitude. If true, ecosystems therefore will have a few dominant frequencies that are endogenously driven and that are discontinuously distributed. This paper additionally tests the proposition that these structuring processes should also generate a discontinuous distribution of spatial structures coupled with the discontinuous frequencies. If that is the case, animals living in specific landscapes should demonstrate the existence of this lumpy architecture by showing gaps in the distribution of their sizes. This proved to be the case for birds and mammals of the boreal region forest and the short—grass prairie. Alternative hypotheses to explain the body mass clumps include architectural, developmental, historical, and trophic causes. These were all tested by comparing body—mass clump distributions (1) in ecosystems having different spatial structures (forest, grassland, and marine pelagic) and (2) in different animal groups having different body plans (birds and mammals) or feeding habits (carnivore, omnivore, and herbivore). The only hypothesis that could not be rejected is that the body—mass clumps are entrained by discontinuous hierarchical structures and textures of the landscape. There is evidence for at least eight distinct habitat "quanta," each defined by a distinct texture at a specific range of scales. These eight quanta together cover tens of centimetres to hundreds of kilometres in space and at least months to millennia in time. There is a striking similarity, but not identity, between the clump structure of prairie and boreal animals. This indicates that many processes that form qualitative habitat structure are common to both landscapes or ecosystems, but a few are landscape specific, particularly over larger scales. That conclusion is extended to all terrestrial ecosystems by an analysis of the body—mass clump structure of all North American birds. In contrast, there are striking differences in clump structure between landscapes and "waterscapes," indicating that fundamentally different processes shape structure in terrestrial and open ocean systems. The discontinuous body—mass structure provides a bioassay of discontinuous ecosystem structure. Mammalian carnivores, omnivores, and herbivores all show the same number of body—mass clumps, and the gaps in these distributions occur at the same body masses. Mammals and birds show the same number of body—mass clumps, but the mass gaps for mammals occur at larger sizes than those for birds in such a way that the log—transformed body—mass gaps for mammals are correlated linearly with those for birds. Hence there is a simple cross—calibration between the mammal and bird bioassays. I compiled and analyzed published data on home ranges in order to convert body masses into an absolute linear measure of geometric structures in the landscape. A new and general equation was developed relating home—range size to body mass, and was tested by reanalyzing published data for mammalian carnivores, omnivores, and herbivores and for birds. I conclude: (1) Birds and mammals of all trophic levels utilize resources in their foraging areas in the same way by measuring the spatial grain of habitat patches with a resolution defined as a function of their size (i.e., the animal's step length or minimum unit of measurement). The step length is a morphological function of the size of animals and is not significantly affected by trophic status or taxonomy of the groups considered. That explains why all trophic levels and both birds and mammals show the same qualitative body—mass clump structure. (2) Home—range data can convert the body—mass data to a quantitative estimate of texture, i.e., of fractal dimension of the landscape. The landscape forms a hierarchy that contains breaks in object sizes, object proximities, and textures at particular scales. Animals also demonstrate a hierarchy of decisions whose target suddenly shifts at specific scales in space and time. The interaction between these two hierarchies produces the discontinuous body—mass clump structure. The breaks in geometry in the landscape occur because structuring processes exert their influence over defined ranges of scale. The temporal and architectural structure of habitat quanta are in general determined by three classes of processes, each dominating over three different ranges of scale. Vegetative processes that determine plant growth, plant form, and soil structure dominate the formation of texture at fine microscales of centimetres to tens of metres in space and days to decades in time. At the other, macroscale extreme, slow geomorphological processes dominate the formation of a topographic and edaphic structure at large scales of hundreds to thousands of kilometres and centuries to millennia. At the mesoscales in between, contagious disturbance processes such as fire, insect outbreak, plant disease, and water flow dominate the formation of patterns over spatial scales of hundreds of metres to hundreds of kilometres. In addition, the direct impacts of grazing by large herbivores and of human activities, and the indirect effects of large predators and animal disease, further transform spatial patterns over these meso—scales. These processes operate on time scales of years to decades, making them critically important in determining whether present local, regional, and global human influences will trigger a transition in vegetation types, and, if so, how rapidly. The paper provides a direction for the development of programs to evaluate, monitor, and predict ecosystem and community changes across scales. The necessary research elements include (1) models that incorporate a few scale—dependent structuring processes to allow cross—scale analysis; (2) comparative studies of different disturbed and undisturbed landscapes using the animal body—mass bioassay technique to identify critical scales of ecosystem geometry; (3) analysis of remote imagery to identify spatial discontinuities and regions of scale invariance; and (4) behavioral studies of the hierarchy of animal decisions to identify species groups vulnerable to predicted (using models) or observed (using remote imagery) changes in vegetation geometry.
Tập 62 Số 4 - Trang 447-502 - 1992