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This paper explores the correspondence between the parameters of an extinction model analysedoeby Lande, Foley and Middleton et al. and the parameters of the incidence function model of metapopulation dynamics. The parameters of the extinction model, the intrinsic rate of population increase (r), its variance (v) and the population ceiling (K), can be mapped to the parameters of the incidence function model describing the scaling of the probability of local extinction (E) with area (A), E = e/Ax, via the equations s = x and r = eDs / s, where s = 2r / v, D is population density and K = DA. Iexplore this correspondence with two empirical examples, a mainland-island metapopulation of the European common shrew (Sorex araneus) onislands in lakes and a classical metapopulation of the American pika(Ochotona princeps). The most robust result is the correspondence x = 2r / v, which value decreases with increasing strength of environmental stochasticity. Thus the impact of environmental stochasticity onpopulation dynamics can, in principle, be inferred from the pattern of habitat patch occupancy in a metapopulation. [ABSTRACT FROM AUTHOR]

Species distributions often show an aggregated pattern, which can be due to a number of endo- and exogenous factors. While autologistic models have been used for modelling such data with statistical rigour, little emphasis has been put on disentangling potential causes of aggregation. In this paper we ask whether it is possible to infer sources of aggregation in species distributions from a single set of occurrence data by comparing the performance of various autologistic models. We create simulated data sets, which show similar occupancy patterns, but differ in the process that causes the aggregation. We model the distribution of these data with various autologistic models, and show how the relative performance of the models is sensitive to the factor causing aggregation in the data. This information can be used when modelling real species data, where causes of aggregation are typically unknown. To illustrate, we use our approach to assess the potential causes of aggregation in data of seven bird species with contrasting statistical patterns. Our findings have important implications for conservation, as understanding the mechanisms that drive population fluctuations in space and time is critical for the development of effective management actions for long-term conservation. [ABSTRACT FROM AUTHOR]

This paper reports the effects of food supply, predation and the interaction between them on the population dynamics of root voles,Microtus oeconomus, by adopting factorial experiments in field enclosures. This two-factor experiment proved the general hypothesis that food supply and predation had independent and additive effects on population dynamics of root voles. The experimental results proved the following predictions: (1) predation reduced population density and recruitment significantly; (2) food supply increased population density; (3) predation and food supply influenced spacing behavior of root voles separately and additively: Exposure to predation reduced long movements of root voles between trapping sessions; additional food supply reduced aggression level and home range size of root voles. Less movement of individuals that exposed to predators possibly reduced their opportunity of obtaining food and lessened population survival rate, which led population density to decrease. Smaller home range and lower aggression level could make higher population density tolerable. The interactive effect of predation and food on home range size was highly significant (P=0.0082<0.01). The interactive effect of food and predation on dispersal rate was significant (P<0.01). From the experimental results, we conclude that the external factors (predation, food supply) were more effective than internal factors (spacing behavior) in determining population density of root voles– under the most favorable external conditions (−P, +F treatment), the mean density and mean recruitment of root vole population was the highest; under the most unfavorable external conditions (+P,−F treatment), the mean density and mean recruitment of root vole population was the lowest. [ABSTRACT FROM AUTHOR]

Landscape connectivity is critical to the maintenance of spatially-structured populations and consists of both a structural component, which describes the shape, size and location of landscape features; and a biological component, which consists of both the response of individuals to landscape features, and the patterns of gene flow that result from those individual responses. Traditional studies of landscape connectivity have attempted to discern individual behavioral responses to landscape features, but this methodology is intractable for many species. This paper is an attempt to relate the components of landscape connectivity through the explicit treatment of their spatial and temporal scales. Traditional measures of structural and biological components of connectivity are reviewed and more recently developed methods for the analysis of scale for each are introduced. I then present a framework for the comparison of scalar phenomena based on Watt's unit pattern, describe the potential outcomes of the comparison and discuss the implications of each. Several testable hypotheses emerge from the analysis that may serve as a useful framework for the investigation of landscape connectivity in the future . [ABSTRACT FROM AUTHOR]

Recent studies on metapopulation dynamics have emphasized the need for improved methods for quantifying individual movements between local populations and habitat patches. In this paper, we report on a 6-yr study in which a network of 12 habitat patches occupied by the bog fritillary, Proclossiana eunomia , was surveyed, with special focus on quantifying movements between the habitat patches. We applied the Virtual Migration model which has been designed to estimate survival and migration parameters in a metapopulation of several connected local populations. The model was parameterized using mark-release-recapture data collected during 6 yr. Generally, the estimated parameter values indicated a high level of movements, with roughly half of butterfly-days spent outside the natal patch. Mortality within patches was higher in males than in females. Females tended to be more mobile and spent more time outside their natal patch than males. Further analysis of the MRR data shows that in this protandrous species males tend to move very little between habitat patches before substantial numbers of females have emerged. [ABSTRACT FROM AUTHOR]

To understand the dynamics of spatially structured populations, we need to know the level of movements at different spatial scales. This paper reports on Aphodius dung beetle movements at two scales: movements between dung pats within pastures, and movements between pastures. First, I test an assumption common to many recent models of spatially structured populations – that the probability of an individual moving between habitat patches decreases exponentially with distance. For dung beetles, I find sufficient evidence to reject this assumption. The distribution of dispersal distances was clearly leptokurtic, with more individuals moving short and long distances than expected on the basis of an exponential function. In contrast, the data were well described by a power function. I conclude that dung beetle movements include an element of non-randomness not captured by the simplistic exponential model. The power function offers a promising alternative, but the actual mechanisms behind the pattern need to be clarified. Second, I compare several species of Aphodius to each other. Although these species occur in the same network of habitat patches, their movement patterns are different enough to result in a mixture of different spatial population structures. Movements between pastures were more frequent the larger the species, the more specific its occurrence in relation to pat age, and the more specialized it is on cow dung and open pasture habitats. Within pastures, all species form “patchy” populations, with much movement among individual pats. [ABSTRACT FROM AUTHOR]

It is well known that ecological communities are spatially and temporally dynamic. Quantifying temporal variability in ecological communities is challenging, however, especially for time-series data sets of less than 40 measurement intervals. In this paper, we describe a method to quantify temporal variability in multispecies communities over time frames of 10–40 measurement intervals. Our approach is a community-level extension of autocorrelation analysis, but we use Euclidean distance to measure similarity of community samples at increasing time lags rather than the correlation coefficient. Regressing Euclidean distances versus increasing time lags yields a measure of the rate and nature of community change over time. We demonstrate the method with empirical data sets from shortgrass steppe, old-field succession and zooplankton dynamics in lakes, and we investigate properties of the analysis using simulation models. Results indicate that time-lag analysis provides a useful quantitative measurement of the rate and pattern of temporal dynamics in communities over time frames that are too short for more traditional autocorrelation approaches. [ABSTRACT FROM AUTHOR]

Theoretical models indicate that natural populations may be structured in such a way that many individuals occur in habitats where reproduction is insufficient to balance mortality. The persistence of such Isinka populations depends on immigration from neighboring Isourcea habitats where local reproduction exceeds mortality. While source-sinkdynamics has become a fundamental concept in ecological theory, there has been virtually no experimental test for the existence of sources and sinks in natural populations. This paper reports the results ofa four-year study that was designed to experimentally test for source-sink population dynamics in desert annual communities. Based on evidence from a variety of desert ecosystems indicating that patchiness caused by the presence of shrubs is important in structuring desert annual communities, we distinguished between two types of habitats: areas beneath the canopy of shrubs and the open areas between the shrubs. If, as suggested in previous studies, source-sink dynamics are important in structuring such annual communities, one would expect that removal of populations from one habitat would lead to extinction of some species in the other habitat. We tested this prediction using removal experiments. We monitored density responses of annual populations inhabiting open areas to the repeated removal of conspecific populations from under shrubs and vice versa. Four years after establishment of the experiment, none of the 34 species studied responded to the removal treatments with habitat-specific extinction. Only one speciesexhibited a significant habitat-specific decrease in density in response to the removal of conspecific populations from the other habitat. These findings contradict our expectations based on conventional theory and point to the importance of applying an experimental approachin studies of source-sink dynamics. [ABSTRACT FROM AUTHOR]

Previous studies have indicated that the relationship between community biomass and species density can be represented by a multivariate model in which abiotic variables influence species density both through effects on biomass and through effects on the species pool. In this paper, we use data from grazed and ungrazed coastal meadows in Finland to evaluate and extend this general conceptual model of the factors controlling species density. Structural equation analysis was usedto evaluate a model for all meadows and then to perform a multigroupanalysis to determine how grazed and ungrazed meadows differ. By itself, biomass could explain only 12% of the variation in species density while the multivariate model was able to explain 47% using five types of predictor variables: site, soil, flooding, grazing, and biomass. Analyses found that flooding explained the greatest amount of variability in species density, primarily through negative effects on thespecies pool. Grazing was also found to have a strong effect on species density and results suggest that its negative influence may be largely through reductions in the species pool in grazed meadows. The most important difference found between grazed and ungrazed meadows was that species density had a strong negative relationship to biomass in the ungrazed meadows but no significant relationship in the grazedones. Thus, it appears that the influence of competition on species density was much greater in ungrazed meadows compared to grazed ones. [ABSTRACT FROM AUTHOR]

The numbers of published macroecological studies are increasing dramatically. Yet, progress within the field of macroecology, and a wideracceptance of its goals and rationale, do not seem to be developing at an equivalent rate. In this paper we examine the criticisms which have been, and can be, made. Attention is drawn to those which withstand scrutiny and are therefore of concern, and some solutions are proffered. We attempt to dispel those criticisms which are misplaced or ill-considered. We conclude that macroecology is likely to progress most effectively in the immediate future, and to make the greatest contribution to the broader study of ecology, if research follows three paths. It needs first to establish a more balanced and better documented body of published patterns, second to establish not simply the presence of patterns but also how in an 'anatomical' sense they come about, and third to expand the program of tests of multiple hypotheses that have been generated to explain observed patterns. [ABSTRACT FROM AUTHOR]

We study the dynamics of a metapopulation in which the rates of colonization and/or extinction change along an environmental gradient. Spatially explicit simulations are applied to compare two cases: in parent-dependent colonization (PDC) the rate of colonization is limited by the production of new individuals; in offspring-dependent colonization (ODC) it is limited by the success of establishment of the offspring. Thus, PDC depends on the quality of the parent's site, while ODC is dependent on the offspring's site. We combine PDC and ODC in a spatially implicit model. We study the steady-state distribution of a metapopulation, and ask whether the local densities of occupied sites at each position x along the gradient could be predicted from the local rates of colonization c(x) and extinction e(x). This prediction is not trivial, since the sites are connected, enabling a flow of individuals from more favorable to less favorable sites. The results show that at ODC a single parameter, c(x)/e(x), is sufficient for the prediction. Therefore, different species and geographic regions can be directly compared by appropriate rescaling: choosing the local average lifetime of occupancy, 1/e(x), for a time unit at each point along the gradient. This permits generalizations about the shape of range edges, and can help to predict the position of the boundary of a species’ distribution. At PDC, rescaling is not possible: the whole profile of c(x) and e(x) along the gradient has to be taken into consideration. Nevertheless, rescaling gives a good approximation when the parent-dependent component of colonization does not change abruptly across space. [ABSTRACT FROM AUTHOR]

Within the paradigm of population dynamics a central task is to identify environmental factors affecting population change and to estimate the strength of these effects. We here investigate the impact of observation errors in measurements of population densities on estimates of environmental effects. Adding observation errors may change the autocorrelation of a population time series with potential consequences for estimates of effects of autocorrelated environmental covariates. Using Monte Carlo simulations, we compare the performance of maximum likelihood estimates from three stochastic versions of the Gompertz model (log–linear first order autoregressive model), assuming 1) process error only, 2) observation error only, and 3) both process and observation error (the linear state–space model on log-scale). We also simulated population dynamics using the Ricker model, and evaluated the corresponding maximum likelihood estimates for process error models. When there is observation error in the data and the considered environmental variable is strongly autocorrelated, its estimated effect is likely to be biased when using process error models. The environmental effect is overestimated when the sign of the autocorrelations of the intrinsic dynamics and the environment are the same and underestimated when the signs differ. With non-autocorrelated environmental covariates, process error models produce fairly exact point estimates as well as reliable confidence intervals for environmental effects. In all scenarios, observation error models produce unbiased estimates with reasonable precision, but confidence intervals derived from the likelihood profiles are far too optimistic if there is process error present. The safest approach is to use state–space models in presence of observation error. These are factors worthwhile to consider when interpreting earlier empirical results on population time series, and in future studies, we recommend choosing carefully the modelling approach with respect to intrinsic population dynamics and covariate autocorrelation. [ABSTRACT FROM AUTHOR]

Evidence for synchronous fluctuations of spatially separated populations is ubiquitous in the literature, including accounts within and across taxa. Among the few mechanisms explaining this phenomenon is the Moran effect, whereby independent populations are synchronized by spatially correlated environmental disturbances. The body of research on the Moran effect predominantly assumes that environmental disturbances within a local site are serially uncorrelated; that is, successive observations in time at a particular local site are independent. Yet, many environmental variables are known to possess strong temporal autocorrelation – a character which has often been described as ‘colour’. The omission of environmental colour from research on the Moran effect may be due in part to the lack of methods capable of generating sets of time series with a desired colour and spatial correlation. Here I present a novel and simple method designated as ‘phase partnering’ to generate such sets of time series and I investigate the combined impact of spatial correlation and environmental colour on population synchrony in two common models of population dynamics. For linear population dynamics, and for a subset of nonlinear population dynamics, coloured environments intensify the Moran effect when population dynamics are spatially heterogeneous; in coloured environments the spatial correlation between populations more closely mimics the spatial correlation between their respective environments. Given that most environmental variables are coloured, these results imply that the Moran effect may be a far more significant driver of regional-scale population and interspecific synchrony than is currently believed. [ABSTRACT FROM AUTHOR]

Explaining the variance of local communities in a spatial-environmental matrix is one of the core interests of ecology today. Recent progress in metacommunity theory has made a substantial contribution to this field, however good empirical data in support of available theories are still relatively scarce. In this study we sampled a cluster of 36 temporary rock pools four times during one season to assess invertebrate metacommunity structure and dynamics and to search for steering processes and variables. Both Mantel tests and redundancy models indicate that local abiotic factors were dominant over spatial factors in explaining community structure and both were acting independently. Spatial variables were only important for passive dispersers and significantly explained 11% of variation in this community component. Pools connected by temporary overflows hosted more similar communities of passive dispersers than unconnected ones while community dissimilarity significantly increased with inter-pool distance. A negative curvilinear relation was discovered between taxon richness and isolation in passive dispersers, providing some support for existing theoretical models of Mouquet and Loreau. Of different metacommunity perspectives, a combination of species sorting and mass effects best explains the observed patterns. Additionally, priority effects and monopolization may buffer against the homogenising effects of dispersal and contribute to the distinctness of isolated communities. This is one of the first studies to present evidence for spatial patterns in aquatic communities on such a small spatial scale (a rock ledge of ±9000 m2). Bridging the gap between theory and observed patterns in natural systems is one of the main challenges for future metacommunity research. Small aquatic habitats such as pitcher plants and freshwater rock pools may well have an important role to play as model systems to study ecological processes in a natural spatially explicit environment. [ABSTRACT FROM AUTHOR]

The recently proposed metabolic theory of ecology (MTE) claims to provide a mechanistic explanation for long known allometric relationships between mass and metabolic rate. The MTE postulates that these patterns of allometry are driven by the primary selective constraint of transport of energy and materials. However, recent evidence along several different lines has called into question both the adequacy and the universality of this mechanism. We review the accumulating body of literature on this subject, adding our own concerns and criticisms. In addition to other difficulties, we argue that MTE fails as a mechanistic explanation of mass versus metabolic rate allometries because: 1) circulatory cost minimization is not a tenable criterion for evolutionary optimization, 2) the Boltzmann type relationships on which MTE depends are inadequate descriptors of complex metabolic pathways, and 3) most of the hypotheses advanced by the MTE do not, in fact, depend on the proposed mechanism and therefore cannot be used to test the theory. We conclude that the MTE should be abandoned as a monolithic explanation for allometric patterns, and that a more realistic path toward a better understanding of allometry would be to consider multiple explanatory mechanisms for physiological allometries. [ABSTRACT FROM AUTHOR]

The populations of many species fluctuate in synchrony across large geographical areas. This synchrony is often attributed to the Moran effect, that is, shared environmental fluctuations across the region. In this article, I use a series of simple metapopulation models to show that the degree of synchrony among populations separated by different distances is strongly affected by the particular way that environmental stochasticity is represented in the models. Furthermore, when multiple types of stochasticity are acting simultaneously, the synchronizing effect of any one type is difficult to discern from the resulting pattern of population synchrony. These effects can be exacerbated under certain demographic conditions or if population dynamics are affected by interspecific interactions. In general, it should be extremely difficult to determine if synchrony is caused by the Moran effect using only the synchrony–distance relationship of natural populations. [ABSTRACT FROM AUTHOR]

Individual traits are often assumed to be linked in a straightforward manner to plant performance and processes such as population growth, competition and community dynamics. However, because no trait functions in isolation in an organism, the effect of any one trait is likely to be at least somewhat contingent on other trait values. Thus, to the extent that the suite of trait values differs among species, the magnitude and even direction of correlation between values of any particular trait and performance is likely to differ among species. Working with a group of clonal plant species, we assessed the degree of this contingency and therefore the extent to which the assumption of simple and general linkages between traits and performance is valid. To do this, we parameterized a highly calibrated, spatially explicit, individual-based model of clonal plant population dynamics and then manipulated one trait at a time in the context of realistic values of other traits for each species. The model includes traits describing growth, resource allocation, response to competition, as well as architectural traits that determine spatial spread. The model was parameterized from a short-term (3 month) experiment and then validated with a separate, longer term (two year) experiment for six clonal wetland sedges, Carex lasiocarpa, Carex sterilis, Carex stricta, Cladium mariscoides, Scirpus acutus and Scirpus americanus. These plants all co-occur in fens in southeastern Michigan and represent a spectrum of clonal growth forms from strong clumpers to runners with long rhizomes. Varying growth, allocation and competition traits produced the largest and most uniform responses in population growth among species, while variation in architectural traits produced responses that were smaller and more variable among species. This is likely due to the fact that growth and competition traits directly affect mean ramet size and number of ramets, which are direct components of population biomass. In contrast, architectural and allocation traits determine spatial distribution of biomass; in the long run, this also affects population size, but its net effect is more likely to be mediated by other traits. Such differences in how traits affect plant performance are likely to have implications for interspecific interactions and community structure, as well as on the interpretation and usefulness of single trait optimality models. [ABSTRACT FROM AUTHOR]

Despite the importance of community-structuring processes operating at both local and regional scales, there is relatively little work examining both forces within a single system. I used a combination of observational and experimental approaches to examine the processes structuring larval dragonfly distributions in lentic habitats that encompass a gradient of both permanence and top predator type. I compared the relative vulnerability of species to predators from different portions of this gradient to assess the role of predation as a local force structuring communities. I also assessed the role of regional processes on species’ distributions by examining species’ propensity to disperse to and colonize artificial ponds distributed across a landscape. In both studies I contrasted habitat specialist species, which had larvae restricted to permanent lakes, with habitat generalist species, which had larvae that occur broadly across the habitat permanence and top predator transition. Results from this work suggest that dispersal and colonization behavior were critical mechanisms restricting the distributions of habitat specialist species, but that predation may act to reinforce this pattern. The habitat specialists dispersed less frequently, colonized artificial ponds less often when they did reach them, and most moved shorter distances than the habitat generalist species. Habitat specialists were also more vulnerable than habitat generalists to an invertebrate top predator with which they do not co-exist. Results from these studies suggest that species distributions can be shaped by processes operating at both regional and local spatial scales. The role of dispersal and recruitment limitation may be generally underestimated as a force shaping species distributions and community structure across habitat gradients in which there is a transition in both the biotic interactions and the disturbance interval across that gradient. [ABSTRACT FROM AUTHOR]

Time series analysis of herbivore data with weather included as covariate is commonly used as a mean to shed light on the state and ecology of the studied population. Conclusions about the herbivore population are drawn from statistical parameter values and presence/absence in the most parsimonious model. However, this procedure is only reliable if the statistical parameters have general interpretations regardless of system characteristics. Here we investigated the extent to which this is true by deriving six different vegetation–herbivore-systems and analyzing their respective statistical parameters. The analysis was done in both continuous and discrete time. It turned out that both density parameters (a1 and a2) and rainfall coefficients change with biological interactions and amount of average rainfall, and they do so in different ways in different systems. This means that there is no valid general interpretation of them and, most important, the probability of detecting density dependence and effects of rainfall vary between systems. Hence, you can not make inference about the biological processes from statistical analysis without knowing the system that you study and what model best describes the interactions within it. [ABSTRACT FROM AUTHOR]

Large data requirements may restrict the use of matrix population models for analysis of population dynamics. Less data are required for a small population matrix than for a large matrix because the smaller matrix contains fewer vital rates that need to be estimated. Smaller matrices, however, tend to have a lower precision. Based on 37 plant species, we studied the effects of matrix dimensionality on the long-term population growth rate (λ) and the elasticity of λ in herbaceous and woody species. We found that when matrix dimensionality was reduced, changes in λ were significantly larger for herbaceous than for woody species. In many cases, λ of woody species remained virtually the same after a substantial decrease in matrix dimensionality, suggesting that woody species are less susceptible to matrix dimensionality. We demonstrated that when adjacent stages of a transition matrix are combined, the magnitude of a change in λ depends on the distance of the population structure from a stable stage distribution, and the difference in the combined vital rates weighted by their reproductive values. Elasticity of λ to survival and fecundity usually increased, whereas elasticity to growth decreased both in herbaceous and in woody species with reduced matrix dimensionality. Changes in elasticity values tended to be larger for herbaceous than for woody species. Our results show that by reducing matrix dimensionality, the amount of demographic data can be decreased to save time, money, and field effort. We recommend the use of a small matrix dimensionality especially when a limited amount of data is available, and for slow-growing species having a simple matrix structure that mainly consists of stasis and growth to the next stage. [ABSTRACT FROM AUTHOR]

A major question at the interface of community and behavioural ecology is whether optimal foraging influences patterns of population dynamics. One productive route towards addressing this question has been to treat the solution to an optimal foraging model as an “adaptive” functional response, capable of varying with resource density. Here I integrate resource density into an optimal foraging model by allowing consumption rates, part of the time constraint in the foraging model, to vary in a linear or saturating manner with resource density. Using field estimates to parameterize the model for 11 herbivore mammals and four herbivore Orthoptera, the modeling effort produces a novel set of functional responses that display unique combinations of traditional functional response shapes. These new adaptive functional response shapes arise because of the assumptions about physiology, resource quality and environmental conditions that are embedded in a foraging model. The results of the study indicate that there is 1) resource and body size specific changes in resource intake as resource density varies; 2) a sensitivity of intake to the shape and magnitude of the cropping rate variation; and 3) that herbivores may regulate their resources via the functional response. [ABSTRACT FROM AUTHOR]

Species distributional limits may coincide with hard dispersal barriers or physiological thresholds along environmental gradients, but they may also be influenced by species interactions. We explore a number of models of interspecific interactions that lead to (sometimes abrupt) distribution limits in the presence and absence of environmental gradients. We find that gradients in competitive ability can lead to spatial segregation of competitors into distinct ranges, but that spatial movement tends to broaden the region of sympatry between the two species, and that Allee effects tend to sharpen these boundaries. We generalize these simple models to include metapopulation dynamics and other types of interactions including predator–prey and host–parasite interactions. We derive conditions for range limits in each case. We also consider models that include coevolution and gene flow and find that character displacement along environmental gradients can lead to stable parapatric distributions. We conclude that it is essential to consider coevolved species interactions as a potential mechanism limiting species distributions, particularly when barriers to dispersal are weak and environmental gradients are gradual. [ABSTRACT FROM AUTHOR]

Understanding the boundaries of species’ ranges and the variations in population dynamics from the centre to margin of a species’ range is critical. This study simulated spatial-temporal patterns of birth and death rates and migration across a species’ range in different seasons. Our results demonstrated the importance of dispersal and migration in altering birth and death rates, balancing source and sink habitats, and governing expansion or contraction of species’ ranges in changing environments. We also showed that the multiple equilibria of metapopulations across a species’ range could be easily broken following climatic changes or physical disturbances either local or regional. Although we refer to our models as describing the population dynamics across whole species’ range, they should also apply to small-scale habitats (metapopulations) in which species abundance follows a humped pattern or to any ecosystem or landscape where strong central-marginal (C-M) environmental gradients exist. Conservation of both central and marginal populations would therefore be equally important considerations in making management decisions. [ABSTRACT FROM AUTHOR]

Variation in demographic rates within a spatially structured population could have important consequences for management decisions, harvesting strategies and offtake rates. Although there is a growing body of evidence suggesting that demographic rates vary within populationsover a range of spatial scales, there has been little research investigating the consequences of this variation for population management. In this paper, data on the dynamics of two female red deer sub-populations on Rum are analysed, and evidence is presented for differences between the fecundity and mortality rates of the two sub-populations. A simple harvesting model is developed to represent the dynamics of the two sub-populations, including density-independent migration between sub-populations and spatially correlated environmental variability. The highest monetary yield in the model is obtained by harvesting the more resilient sub-population at a higher rate. Surprisingly the losses involved in harvesting both sub-populations at the same rateare insignificant. However, if migration were density-dependent, thesize of one sub-population would be more relevant to harvesting policy for the other sub-population. The results of this empirical study are compared to theoretical work on spatially structured populations;it is shown that when a species has complex age- and sex-structured population dynamics, previous theoretical results may not hold. [ABSTRACT FROM AUTHOR]

The ideal despotic distribution, whereby the lifetime reproductive success a territory's owner achieves is unaffected by population density, is a mainstay of behaviour-based population models. We show that the population dynamics of an island population of Seychelles warblers ( Acrocephalus sechellensis) cannot be modelled with an ideal despotic distribution, and suggest the effects of both territory shrinkage and territorial disputes on reproductive success must be included to adequately model the population dynamics of this species. To do this we introduce two different approaches. The first is reductionist, using data on how population density affects individuals’ reproductive success to predict population growth rates. Because such a model is mechanistic, it can be used to predict population dynamics in novel environments, making it a desirable long-term solution. However, because territorial populations are typically tightly regulated, birth and death rate data at low population densities are often unavailable. Hence, our second approach statistically infers the relationship between population density and per territory reproductive success, and thus provides a stop-gap solution for the shorter term. Our analysis indicates that although the Cousin population of Seychelles warblers is highly resilient to environmental stochasticity, the degree of resilience is considerably underestimated by approaches that ignore intrinsic regulation through territory shrinkage and territorial disputes. [ABSTRACT FROM AUTHOR]

Individuals allocate resources to the expansion of their foraging area and those resources are no longer available for the traits that determine how well those individuals are able to protect their foraging area against competitors. The resulting trade-off between foraging area size and the traits associated with the ability to compete for the resources within the foraging area applies to ecological scenarios as different as territorial defence by individuals and colonies, and light competition in plants. Whether the trade-off affects species performance in competition for resources at the area of overlap between foraging areas depends on the symmetry of resource division. In symmetric competition resources are divided equally between the competitors, while in asymmetric competition the individual with the smallest foraging area, and consequently the greatest competitive ability, gains all the resources. Competition may also be a combination of the symmetric and asymmetric processes. I studied the effects of competitive asymmetry on population dynamics and coexistence of two annual species with different sized foraging areas using an individual-based spatially explicit simulation model. Symmetric competition favoured the species with the larger foraging area and did not allow coexistence. Competitive asymmetry favoured the species with smaller foraging area and allowed coexistence, which was due to the consequences of losing an asymmetric competition being more severe than losing a symmetric competition. The mechanism of coexistence is the larger foraging area's superiority in low population densities (little competition) and the smaller foraging area's ability to win a large foraging area when competition was intense. Competitive asymmetry and small size of both foraging areas led to population dynamics dominated by long-term fluctuations of small intensity. Symmetric competition and large size of the foraging areas led to large short-term fluctuations, which often resulted in the extinction of one or both of the species due to demographic stochasticity. [ABSTRACT FROM AUTHOR]

Ecological traps, poor-quality habitat that nonetheless attract individuals, have been observed in both natural and human-altered settings. Until recently, ecological traps were considered a kind of source–sink system, but source–sink theory does not model maladaptive habitat choice, and therefore cannot accurately represent ecological traps or predict their population-level consequences. Although recent models of ecological traps addressed this problem, they used patch-based models containing only two habitats that were very different from one another, but were internally homogeneous. These sorts of patch models may not apply to many real populations, and using them for populations in landscapes with mosaic or gradient habitat structures may be misleading. I developed models that treat source–sink dynamics and ecological traps as special cases of a single process, in which the attractiveness and quality of the habitat are separate variables that can be either positively or negatively related, and in which habitat quality varies continuously throughout the landscape. As expected, sinks are less detrimental to populations than ecological traps, in which preferential use of poor habitat elevates extinction risk. Furthermore, ecological traps may be undetected, and may even appear to be sources, when population sizes are large, but may still prevent recovery in spite of the availability of high-quality habitat when populations drop below threshold levels. Conservation biologists do not routinely consider the possibility that apparent sinks are actually traps, but since traps should be associated with the rapidly changing and novel habitat characteristics primarily produced by human activities, ecological traps should be considered an important and potentially widespread conservation concern. [ABSTRACT FROM AUTHOR]

It has been suggested that climatic variation has the effect on the dynamics of arid and semi-arid grazing systems of reducing animal numbers below the level at which they have much impact on vegetation or soils, and that spatial heterogeneity in resource availability serves to buffer herbivores against climatic variation. Modelling was used to test these hypotheses and to examine the interacting effects of temporal and spatial variability in plant production on animal population dynamics and defoliation intensity. The model distinguishes areas of the range that are accessible during wet and dry seasons, and examines the effect of seasonal restrictions in foraging area. It was established that the animal population is in long-term equilibrium with dry-season resources, on which it depends for survival; that dry season resource areas and outlying areas thus operate in a source-sink manner; and that the ratio of these areas determines the strength of consumer-resource coupling outside the dry-season range. A high ratio of dry season to wet season resources may support a sufficiently large animal population to impose non-trivial defoliation impacts on the outlying range. Increasing degrees of variability in primary production on areas used by animals for surviving the dry season increased the annual variation in animal abundance and reduced the mean. By comparison with a stable environment, for which the model predicts virtually stable animal numbers and constant, low defoliation intensity, variation in annual rainfall causes wide fluctuations in animal numbers and defoliation intensity. Under climatic variation, animal numbers can build up enough to impose much higher defoliation intensities than under a constant regime. Periodic intense defoliation is a consequence of climatic variability which is likely to make these environments more, not less, prone to ecological change. [ABSTRACT FROM AUTHOR]

Fluctuations in essential resources cause a strong selection pressure on the ability to adjust parental investment accordingly. In the dog family, Canidae, variance in female prebirth investment is adjustedby litter size. The arctic fox, Alopex lagopus , is a small canid living on the northern tundras of the world. It has the largest known litter size in the order Carnivora, up to 18 young, and litter size ishighly variable. We have analysed data from arctic fox populations throughout the species circumpolar range. In some areas, arctic foxes feed on strongly fluctuating populations of small rodents. In contrast, they have more stable food resources at bird cliffs and along coast lines. Food availability determines arctic fox litter and population sizes. A comparison between fluctuating and stable arctic fox populations showed that fluctuations are associated with large litter sizes. There were significant differences in litter size means, maxima and variances, as well as in placental scar count means. We have discussed five hypotheses on the determination of variation in litter size:one energetic, one genetic (based on density variation), one diet-determined, one based on reproductive allocation and one based on differences in reaction norms. Our findings suggest that litter size in the arctic fox is determined by the combined effect of immediate resource levels and the degree of resource predictability. We describe reaction norms that suggest how litter sizes result from adaptive plasticity within each of two genetic strategies where, according to the jackpot hypothesis, populations with unpredictable food resources generally have larger litter sizes. Within each genetic strategy, or reaction norm, litter sizes are adjusted through a number of plastic traits. These traits are influenced by nutritional limitations and include reduced ovulation rates, prenatal losses, and litter size reduction during the lactation period. [ABSTRACT FROM AUTHOR]

The concept of a cost of reproduction has associations with a variety of other ideas in population biology, among them trade-offs and antagonistic pleiotropy. Within the concept of a cost of reproduction, avariety of components can be distinguished, such as physiological and ecological costs of reproduction. This article concentrates on the former type of cost. Empirically, a variety of approaches can be, andhave been, used to analyze the cost of reproduction. Three are distinguished: genetic, environmental, and physiological. These are discussed first in general terms and second with specific reference to research on laboratory evolution in Drosophila. The latter discussion serves to focus and to instantiate the general analysis of the field. Emerging themes from this area of research include the environmental plasticity of costs of reproduction, the difficulties facing simple trade-off theories, and the critical role of physiological integration in determining costs at the organismal level. [ABSTRACT FROM AUTHOR]

For a spatial population assemblage, extinction risk should be greatly affected by features of local population dynamics and interpatch migration patterns. In a variable environment, the magnitude of environmental correlation between local population patches may have great impact on local dynamics and thereby global extinction isk. We examined the effect of correlated environmental variation on global extinction risk in a coupled lattice model consisting of local populations governed by density dependent population growth and density independentinterpatch migration. We let each local population experience a stochastic environment expressed as a variation in maximum birth rate andlet this environmental variation be correlated among local populations. We simulated global population growth under different magnitudes of environmental variability, correlation of environmental variability, emigration rate and migration survival, in order to evaluate the magnitude of their effect on local population dynamics and global extinction risk. The risk of global extinction increases with increasing magnitude of environmental correlation and environmental variability.The major determinant of global extinction risk is the balance between local population variability and the synchrony in local populationfluctuations. A low rate of successful interpatch migration connectsthe local populations to each other, exposing them to less extinction risk than when they are isolated. High levels of interpatch migration are often negative for population persistence. The reason for thisis that increased migration survival causes an increased risk of population crashes, due to overcompensatory population growth. This effect is amplified by a high emigration rate. Thus, local dynamics are affected by temporal and spatial variability in birth rates as well asinterpatch migration levels. An assemblage of local populations in avariable environment will suffer least risk of global extinction when enviro [ABSTRACT FROM AUTHOR]

I analyse the importance and influence of noise with positive autocorrelation ('red noise') to extinction risk in spatially structured populations using a set of simple population dynamical simulation models. Noise colour has a major influence on both local and global extinction risk, level of synchrony in population dynamics, and spatial patterns of the synchrony. Generally, the stronger the autocorrelation in the noise is, the higher is the global extinction risk -- even though local extinction risk may decrease. Populations with high intrinsic growth rate are more prone to global extinction than populations with low growth rate. The influence of autocorrelated noise on population synchrony depends strongly on the way in which environmental noiseis introduced into the model. [ABSTRACT FROM AUTHOR]

Based on data from radio-collared individuals, we present an analysis of the viability of two small populations of the Scandinavian brownbear, Ursus arctos. The northern and southern populations had different demographic characteristics, even though the population growth rate (r) and the demographic variance (sd2) were high in both populations (r = 0.13 and sd2 = 0.180 in the north, and r = 0.15 and sd2 = 0.155 in the south). In the northern population the environmental variance (se2) was not significantly different from 0, whereas in the south se2= 0.003. In the south, this was related to high environmental stochasticity in the survival rate of the youngest animals, which resulted in an increase in survival with age in this population. In contrast, in the north, the probability of survival showed a slight decrease with age. Uncertainties were obtained from the joint distribution of bootstrap replications of r, sd2 and se2. Although the uncertainty in these estimates is quite large, it is unlikely that even relatively small populations (N > 10 females 1 year old) will decline to less than 1 after 100 years. Analysis of the distribution of the critical population size (i.e. the population size where the population's logarithmic growth rate is zero) shows that these brown bear populations must be larger than 3-4 females 1 year or older to secure a positive growthrate. Similarly, if we define a viable population as the population size where the chance of survival is greater than 90% during a periodof 100 years, 8 females 1 year old must be present in the north and 6 females in the south. This high viability of even small brown bear populations is due to high reproductive and survival rates. A relatively small increase in the mortality rate will strongly reduce the viability of even relatively large brown bear populations. [ABSTRACT FROM AUTHOR]

Classical biological control (natural enemy introductions) has long served as a paradigm for the role of predators and parasitoids in insect herbivore population dynamics, and it is widely held that there is no fundamental difference between successful biological control andthe action of native natural enemies ('natural control'). We ask if biological control is really a natural phenomenon. To address this, we focus on two aspects of biological control that potentially influence the ability of natural enemies to exert top-down control of victimpopulations: (1) control is most often attempted against insect herbivores occupying habitats that have been substantially simplified in diversity and structure, and (2) the enemy-herbivore-plant food web in biological control systems is often composed entirely of exotic species that share few evolutionary or ecological links with the native biota, further simplifying the web in which the enemies operate. Using the insect life table literature, we found no differences in the frequencies of all types of natural enemies acting as key factors in the dynamics of exotic and native insect populations. However, top-downcontrol, when it occurs, is more frequently due to a single parasitoid species for exotic insect herbivores on exotic plants in cultivated habitats, whereas for native insect herbivores on native plants in natural habitats it is more frequently due to a suite of generalist predators. We also found from the historical record of biological control that success rates are substantially greater in exotic, simplified, managed habitats than in natural habitats, particularly when involving parasitoids. We suggest that biological control is not strictly a 'natural' phenomenon, because it overestimates the extent to which parasitoids exert top-down control on insect populations, and it results most often from the formation of a single strong link in simplified food webs, in contrast to the 'natural control' that results from mul [ABSTRACT FROM AUTHOR]

Positive interspecific and intraspecific relationships between localabundance and regional occupancy have been widely documented. The former are essentially pervasive. These patterns have some potentially significant applied implications: (1) Biodiversity inventorying - there can be no simple and effective trade-off between the intensity andspatial extent of biodiversity inventorying, (2) Population monitoring - intraspecific, and to a more limited extent interspecific, population monitoring may be based on measures of occupancy, particularly where only crude indications of marked shifts in abundance are required, (3) Harvesting - harvesting of local populations may often resultin a reduction in wider occupancy, but if local extinctions are caused by over-exploitation this may not generally result in a reduction in local abundance elsewhere in the range of a species, (4) Conservation - species of conservation concern may face the double jeopardy oflow abundance and small range size, but depending on the extent of acausal link between levels of abundance and occupancy it may be possible to cheat the abundance-occupancy relationship and maintain species at relatively high local densities for their range sizes, and (5) Invasions - pest species may become more of a problem in those areas in which they already occur, because their local densities will increase, as they spread. [ABSTRACT FROM AUTHOR]

Over 100 allometric regressions on rate [kg kg-1 d-1=d-1], age [d] and density [kg [kg km-2] parameters often used in ecological models were collected in a literature review. For each parameter, typical coefficients and exponents that covered most of the correlations found were selected. The parameters were checked for consistency by comparing them to each other, e.g. mortality versus age and to independent data, e.g. production and respiration rate constants versus production efficiency. Exponents forconsumption, production and respiration rates on the one hand and slopes for maturation, average and maximum age on the other, scale to size with an exponent of the same magnitude but opposite sign. Most values are between 10.25 and 10.33. No consistent differences between parameters and species were found. Coefficients for production and respiration were largely consistent with those for ingestion and with independent data on assimilation and production efficiencies. The same was concluded for production versus mortality, for mortality versus age as well as maximum versus average production and consumption. Warm-blooded animals consume, produce and respire at rates about 10 timeshigher than equally sized cold-blooded species. The reverse was noted for age and possibly density. Population density of individual species and biota density of geometric size classes are nearly independent of size for regressions that span a wide size range. The coefficients for density vary up to two orders of magnitude, depending on localconditions. Most allometric regressions reported apply to aquatic invertebrates or terrestrial birds and mammals of the biophageous food chain. Yet, the rate and age regressions that include other species do not indicate substantial deviations for bacteria, micro- and macrophytes and for terrestrial (saprophageous) invertebrates. The set of typical values derived may facilitate parameter estimation for genericmod [ABSTRACT FROM AUTHOR]

Presence and stability of populations of Microtus ochrogaster, M. pennsylvanicus and Blarina brevicauda were studied in tallgrass prairiehabitat in central Illinois for 25 yr; 52 yr of autumn data were available for M. ochrogaster. M. ochrogaster displayed erratic, very lowamplitude population fluctuations in tallgrass; it was absent from the study site 49% of the time. Multiannual cycles were not obvious. Population fluctuations in adjacent alfalfa and bluegrass sites were higher, more frequent and in synchrony with those in tallgrass. Densities recorded in the autumn from 1944-1996 revealed distinct, erratic multiannual population cycles. M. pennsylvanicus populations were continuously present at relatively high densities in tallgrass; neither annual nor multiannual fluctuations were evident. Infrequent annual cycles were recorded in the other two habitats. B. brevicauda was persistent and displayed a synchronous annual cycle in the three habitats. [ABSTRACT FROM AUTHOR]