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Parental care is assumed to be closely associated with individual differences in reproductive success. We investigated how feeding frequencies varied among parents and how this affected the subsequent reproductive success in insular populations of House Sparrows Passer domesticus in northern Norway. Female parents fed their offspring more than male parents did, and the feeding rates were positively related to the feeding rates of the partner. A positive relationship between feeding rates and bill depth was present in females. In males, the feeding rates were negatively related to total badge size and positively related to visible badge size, after the effect of other variables had been taken into account. A non-linear convex relationship between feeding frequency and hatch day was present in males, which could reflect either the seasonal change in weather conditions or the seasonal variation in food availability. For both sexes, feeding frequencies increased with increasing brood size, but at the same time the average feeding rate per nestling decreased with increased brood sizes. Finally, our results indicate that the amount of parental investment, measured as feeding rates during the nestling stage, may have a positive long-term influence both on the number of fledglings that recruit as well as the probability that fledglings survive until recruitment.

During the last 30 years, the proportion of males in the calf harvest of moose (Alces alces) in Norway has decreased, indicating a decline in proportions of males recruited to the autumn populations. At the same time, the percentages of exclusive calf hunting permits and of calves shot have increased. The change in calf sex ratio may thus simply be the result of hunter preferences for slightly larger (6.2% higher body mass) male calves combined with fewer opportunities for selective hunting due to increasing hunting quotas of calves. We examined this hypothesis by analyzing the variation in sex, number of siblings, carcass mass, date, and location of kill of 16,330 moose calves harvested during 1970–2004. In the presence of hunting selection for larger calves, we predicted larger proportions of male calves to be harvested in populations with large sexual size dimorphism among calves. Similarly, we expected more males to be harvested from twin than single litters because hunters then can more easily compare twins and select the larger calf, which is more often a male. Increasing proportions of single female calves were also expected to occur in the daily harvest as the accumulated number of harvested calves increased and the proportion of calves left in the population decreased. We found no positive relationship between the proportion of male calves and the level of sexual size dimorphism, no clear difference in sex ratio between harvested single and twin calves, and no increase in the proportion of single female calves as the accumulated number of calves in the harvest increased. This suggests that the spatiotemporal variation in the harvest calf sex ratio in Norway most likely reflects differences in population calf sex ratios prior to the hunting season and not varying degrees of hunting selectivity.

1. Geographic gradients in population dynamics may occur because of spatial variation in resources that affect the deterministic components of the dynamics (i.e. carrying capacity, the specific growth rate at small densities or the strength of density regulation) or because of spatial variation in the effects of environmental stochasticity. To evaluate these, we used a hierarchical Bayesian approach to estimate parameters characterizing deterministic components and stochastic influences on population dynamics of eight species of ducks (mallard, northern pintail, blue-winged teal, gadwall, northern shoveler, American wigeon, canvasback and redhead (Anas platyrhynchos, A. acuta, A. discors, A. strepera, A. clypeata, A. americana, Aythya valisineria and Ay. americana, respectively) breeding in the North American prairies, and then tested whether these parameters varied latitudinally. 2. We also examined the influence of temporal variation in the availability of wetlands, spring temperature and winter precipitation on population dynamics to determine whether geographical gradients in population dynamics were related to large-scale variation in environmental effects. Population variability, as measured by the variance of the population fluctuations around the carrying capacity K, decreased with latitude for all species except canvasback. This decrease in population variability was caused by a combination of latitudinal gradients in the strength of density dependence, carrying capacity and process variance, for which details varied by species. 3. The effects of environmental covariates on population dynamics also varied latitudinally, particularly for mallard, northern pintail and northern shoveler. However, the proportion of the process variance explained by environmental covariates, with the exception of mallard, tended to be small. 4. Thus, geographical gradients in population dynamics of prairie ducks resulted from latitudinal gradients in both deterministic and stochastic components, and were likely influenced by spatial differences in the distribution of wetland types and shapes, agricultural practices and dispersal processes. 5. These results suggest that future management of these species could be improved by implementing harvest models that account explicitly for spatial variation in density effects and environmental stochasticity on population abundance.

Taylor's spatial scaling law concerns the relation between the variance and the mean population counts within areas of a given size. For a range of area sizes, the log of the variance often is an approximately linear function of the mean with a slope between 1 and 2, depending on the range of areas considered. In this paper, we investigate this relationship theoretically for random quadrat samples within a large area. The model makes a distinction between the local point process determining the position of each individual and the population density described by a spatial covariance function. The local point process and the spatial covariance of population density both contribute to the general relationship between the mean and the variance in which the slope may begin at 1, increase to 2, and decrease to 1 again. It is demonstrated by an example that the slope theoretically may exceed 2 by a small amount for very regular patterns that generate spatial covariance functions that increase in certain intervals. We also show how properties of population dynamics in space and time determine this relationship.

The relative importance of genetic, demographic, environmental, and catastrophic processes that maintain population bottlenecks has received little consideration. We evaluate the role of these factors in maintaining the Puerto Rican Parrot (Amazona vittata) in a prolonged bottleneck from 1973 through 2000 despite intensive conservation efforts. We first conduct a risk analysis, then examine evidence for the importance of specific processes maintaining the bottleneck using the multiple competing hypotheses approach, and finally integrate these results through a sensitivity analysis of a demographic model using life-stage simulation analysis (LSA) to determine the relative importance of genetic, demographic, environmental, and catastrophic processes on population growth. Annual population growth has been slow and variable (1.0 ± 5.2 parrots per year, or an average λ = 1.05 ± 0.19) from 16 parrots (1973) to a high of 40–42 birds (1997–1998). A risk analysis based on population prediction intervals (PPI) indi...

Habitat selection of the Willow Warbler and the Chiffchaff was studied along a succession of grey alder forest in Central Norway (63oN) where both species breed. Both were found in all serai stages, but there was a slight tendency for the Willow Warbler to be found more often in the voungest stages than was the Chiffchaff. Foraging niches and horizontal spacing were studied within one particular forest. Most of the records of both Willow Warbler and Chiffchaff came from the tree layer, and the overlap between the species in their foraging niches was considerable. However, the species were found to occupy almost mutually exclusive territories.

Most population models assume that individuals have equal opportunities for survival and reproduction, although many natural populations consist of individuals with different vital parameters that remain different over time. Individual heterogeneity in vital parameters, which may depend on age or stage, can alter many population characteristics compared with a homogeneous population, affecting both deterministic and stochastic properties of the population process. Demographic variance is an important parameter influenced by heterogeneity. However, whether heterogeneity leads to increased or decreased demographic variance has been an unresolved question, except for special cases. Here, we present a general stochastic matrix model for a heterogeneous population that allows us to examine effects of heterogeneity on population dynamics, even when the degree of heterogeneity depends on age. Using this model, we found that the demographic variance may increase, decrease, or remain unaltered compared with a homogeneous comparison model, depending on the vital parameter values and on how these are distributed among individuals at each time step. Furthermore, if the reproductive value is the same for all individuals, heterogeneity has no effect on the demographic variance. Thus, we provide a general theoretical framework for analyzing how individual heterogeneity caused by different biological mechanisms affects fluctuations of especially small populations.

We show how the spatial structure of species diversity can be analyzed using the correlation between the log abundances of the species in the communities, assuming that two communities at different localities can be described by a bivariate lognormal species abundance distribution. A useful property of this approach is that the log abundances of the species at two localities can be considered as samples from a bivariate normal distribution defined by only five parameters. The variances and the correlation can be estimated by maximum likelihood methods even if there is no information about the sampling intensity and the number of unobserved species. This method also enables estimation of over-dispersion in the sampling relative to a Poisson distribution that allows sampling adjustment of the estimate of b-diversity. Furthermore, we also obtain a partitioning of species diversity into additive components of a-, b- and g-diversity. For instance, if the correlation between the log abundances of the species is close to one, the same species will be common and rare in the two communities and the b-diversity will be low. We illustrate this approach by analysing similarities of communities of rare and endangered species of oak-living beetles in south-eastern Norway. The number of recorded species was estimated to be only 48.1% of the total number of species actually present in these communities. The correlations among communities dropped rather quickly with distance with a scaling of order 200 km. This illustrates large spatial heterogeneity in species composition, which should be accounted for in the design of schemes of such series

Mechanisms generating inequalities among males in reproductive success are key to understanding the evolutionary significance of sexual selection. This paper develops a stochastic model to quantitatively describe and analyze mating systems on a continuous scale from strict monogamy to extreme polygyny. The variance in male mating success is shown to increase with increased differences among males, with decreased interdependence of mating events, with increased population size, and with an increased number of females per male. The latter condition decreases the opportunity for sexual selection. It is found that different combinations of mating system characteristics can lead to the same variance in male mating success, although the distribution differs. This emphasizes the importance of using a model of this type to study mating systems, rather than relying solely on the variance in reproductive success as a descriptor of different systems.

For an understanding of the effect of climate change on animal population dynamics, it is crucial to be able to identify which climatologic parameters affect which demographic rate, and what the underlying mechanistic links are. An important reason for why the interactions between demography and climate still are poorly understood is that the effects of climate vary both geographically and taxonomically. Here, we analyse interspecifically how different climate variables affect the breeding success of North Atlantic seabird species along latitudinal and longitudinal gradients. By approaching the problem comparatively, we are able to generalize across populations and species. We find a strong interactive effect of climate and latitude on breeding success. Of the climatic variables considered, local sea surface temperatures during the breeding season tend to be more relevant than the North Atlantic Oscillation (NAO). However, the effect of NAO on breeding success shows a clear geographic pattern, changing in sign from positive in the south to negative in the north. If this interaction is taken account of, the model explains more variation than any model with sea surface temperature. This superiority of the NAO index is due to its ability to capture effects of more than one season in a single parameter. Mechanistically, however, several lines of evidence suggest that sea surface temperature is the biologically most relevant explanatory variable.

Predicting the effects of the expected changes in climate on the dynamics of populations require that critical periods for climate-induced changes in population size are identified. Based on time series analyses of 26 Swiss ibex (Capra ibex) populations, we show that variation in winter climate affected the annual changes in population size of most of the populations after accounting for the effects of density dependence and demographic stochasticity. In addition, precipitation during early summer also influenced the population fluctuations. This suggests that the major influences of climate on ibex population dynamics operated either through loss of individuals during winter or early summer, or through an effect on fecundity. However, spatial covariation in these climate variables was not able to synchronize the population fluctuations of ibex over larger distances, probably due to large spatial heterogeneity in the effects of single climate variables on different populations. Such spatial variation in the influence of the same climate variable on the local population dynamics suggests that predictions of influences of climate change need to account for local differences in population dynamical responses to climatic conditions.

Inbreeding causes reduction of genetic variability that may have severe fitness consequences. In spite of its potentially huge impact on viability and evolutionary processes especially in small populations, quantitative demonstrations of genetic and demographic effects of inbreeding in natural populations are few. Here, we examine the relationship between individual inbreeding coefficients (F) and individual standardized multilocus heterozygosity (H) in an insular metapopulation of house sparrows (Passer domesticus) in northern Norway in order to evaluate whether H is a good predictor for F. We then relate variation in fitness (i.e. the probability of surviving from fledging to recruitment) to F and H, which enables us to examine whether inbreeding depression is associated with a reduction in genetic variability. The average level of inbreeding in the house sparrow metapopulation was high, and there was large inter-individual variation in F. As expected, standardized multilocus heterozygosity decreased with the level of inbreeding. The probability of recruitment was significantly negatively related to F, and, accordingly, increased with H. However, H explained no significant additional variation in recruitment rate than was explained by F. This suggests that H is a good predictor for F in this metapopulation, and that an increase in F is likely to be associated with a general increase in the level of homozygosity on loci across the genome, which has severe fitness consequences.

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 agestructure. Here we use the dynamics of the reproductive value to estimate the long-term growth rate s and the environmental variance s 2 of a moose population that recently colonized the island of Vega in northern Norway. We show that the population growth rate was high (s ˆ� 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.

An important issue concerning the introduction of non-indigenous organisms into local populations is the potential of the introduced individuals to spread and interfere both demographically and genetically with the local population. Accordingly, the potential of spatial dispersal among introduced individuals compared with local individuals is a key parameter to understand the spatial and temporal dynamics of populations after an introduction event. In addition, if the variance in dispersal rate and distance is linked to individual characteristics, this may further affect the population dynamics. We conducted a large-scale experiment where we introduced 123 house sparrows from a distant population into 18 local populations without changing population density or sex ratio. Introduced individuals dispersed more frequently and over longer distances than residents. Furthermore, females had higher probability of dispersal than males. In females, there was also a positive relationship between the wing length and the probability of dispersal and dispersal distance. These results suggest that the distribution and frequency of introduced individuals may be predicted by their sex ratio as well as their phenotypic characteristics.

Optimal research and management of species with age structure often depends on estimates of age-specific population parameters, which in turn depends on reliable methods for age determination. By counting annuli in the cementum of incisor root tips from 51 known-age moose (Alces alces) between 1 and 12 years old, we examined the variation in accuracy and repeatability of age estimates provided by three research technicians with different experiences of aging moose. The most experienced technician estimated the moose age correctly in up to 90% of the cases, while the technician with no prior experience estimated age correctly in up to 73% of the cases. The medium-experienced technician achieved a lower accuracy (up to 53%), indicating that experience alone is not sufficient if the basic training or lack of routine checks against other colleagues or a known-age material are not undertaken. The percentage moose aged within ±1 year from correct age was significantly higher in all technicians (94–98%). After the generally high accuracy, we also found high repeatability (0.980–0.994) within technicians. We conclude that this method of age-determination provides reliable estimates that can be used by management and research to gain information about age-specific patterns in moose populations. However, to obtain estimates of high accuracy the technicians should be well trained, have gained the necessary experience, and most preferably, have access to a sample of teeth from known-age moose.

The dynamics of reproductive value are used to provide a simple derivation of Tuljapurkar's approximation for the long-run growth rate and environmental variance of lnN, in a density-independent age-structured population in a random environment. With no environmental autocorrelation, the dynamics of total population size, N, generally shows time lags and autocorrelation caused by life history, which may strongly bias estimates of environmental variance obtained by ignoring age structure. In contrast, the total reproductive value, V, is Markovian and obeys a first-order autoregressive process. This suggests a simple method for estimating the environmental variance, and avoiding potentially large bias due to age-structure fluctuations, by converting a multivariate time series of age structure to a univariate time series of lnV. We illustrate the method by estimating the long-run growth rate and the environmental variance in an exponentially growing population of Bighorn Sheep.

We generalize a previous simple result by Lande et al. (1999) on how spatial autocorrelated noise, dispersal rate and distance as well as strength of density regulation determine the spatial scale of synchrony in population density. It is shown how demographic noise can be incorporated, what effect it has on variance and spatial scale of synchrony, and how it interacts with the point process for locations of individuals under random sampling. Although the effect of demographic noise is a rather complex interaction with environmental noise, migration and density regulation, its effect on population fluctuations and scale of synchrony can be presented in a transparent way. This is achieved by defining a characteristic area dependent on demographic and environmental variances as well as population density, and subsequently using this area to define a spatial demographic coefficient. The demographic noise acts through this coefficient on the spatial synchrony, which may increase or decrease with increasing demographic noise depending on other parameters. A second generalization yields the modeling of density regulation taking into account that regulation at a given location does not only depend on the density at that site but also on densities in the whole territory or home range of individuals. It is shown that such density regulation with a spatial scale reduces the scale of synchrony in population fluctuations relative to the simpler model with density regulation at each location determined only by the local point density, and may even generate negative spatial autocorrelations.

Empirical evidence strongly indicates that human exploitation has frequently led to rapid evolutionary changes in wild populations, yet the mechanisms involved are often poorly understood. Here, we applied a recently developed demographic framework for analyzing selection to data from a 20-year study of a wild population of moose, Alces alces. In this population, a genetic pedigree has been established all the way back to founders. We demonstrate harvest-induced directional selection for delayed birth dates in males and reduced body mass as calf in females. During the study period, birth date was delayed by 0.81 days per year for both sexes, whereas no significant changes occurred in calf body mass. Quantitative genetic analyses indicated that both traits harbored significant additive genetic variance. These results show that selective harvesting can induce strong selection that oppose natural selection. This may cause evolution of less favorable phenotypes that become maladaptive once harvesting ceases.

Fitness is a central concept in evolutionary biology, but there is no unified definition. We review recent theoretical developments showing that including fluctuating environments and density dependence has important implications for how differences among phenotypes in their contributions to future generations should be quantified. The rate of phenotypic evolution will vary through time because of environmental stochasticity. Density dependence may produce fluctuating selection for large growth rates at low densities but for larger carrying capacities when population sizes are large. In general, including ecologically realistic assumptions when defining the concept of fitness is crucial for estimating the potential of evolutionary rescue of populations affected by environmental perturbations such as climate change.

International audience; In many species, population dynamics are shaped by age-structured demographic parameters, such as survival, which can cause age-specific sensitivity to environmental conditions. Accordingly, we can expect populations with different age-specific survival to be differently affected by environmental variation. However, this hypothesis is rarely tested at the intra-specific level. Using capture–mark–recapture models, we quantified age-specific survival and the extent of annual variations in survival of females of alpine chamois in two sites. In one population, survival was very high (>0.94; Bauges, France) until the onset of senescence at approximately 7 years old, whereas the two other populations (Swiss National Park, SNP) had a later onset (12 years old) and a lower rate of senescence. Senescence patterns are therefore not fixed within species. Annual variation in survival was higher in the Bauges (SD = 0.26) compared to the SNP populations (SD = 0.20). Also, in each population, the age classes with the lowest survival also experienced the largest temporal variation, in accordance with inter-specific comparisons showing a greater impact of environmental variation on these age classes. The large difference between the populations in age-specific survival and variation suggests that environmental variation and climate change will affect these populations differently.

We develop an integrated population model for Svalbard reindeer Rangifer tarandus platyrhynchus, and demonstrate how this type of model can be used to extract more information from the data and separate different sources of variability in population estimates. Our model combines individual mark–recapture data with population counts and harvesting data within a Bayesian model framework, and accounts for observation error, environmental and demographic stochasticity,and age structure. From this model we obtain annual estimates of age-specific population size, survival and fecundity. The model provides estimates of age structure at a finer scale than that found in the census data, and enables us to estimate survival for the period before calves are first caught and marked, i.e. before they enter the individual mark–recapture data. The modeling framework provides an improved approach to studying age-structured populations that are imperfectly censused and where the demography of only a sample of individuals is known. We use data from independent censuses of the same population to evaluate population estimates obtained from the model, and show that it is successful at correcting for different types of observation error. Based on our model results, we suggest that allocating resources to the collection of supplementary mark–recapture data could improve the reliability of population projections more than making regular population censuses as exhaustive as possible. Our work demonstrates how integrated Bayesian population modeling can be used to increase the amount of information extracted from collections of data, identifying and disentangling sources of variation in individual performance and population size. This represents an important step towards increasing the predictive ability of population growth models for long-lived species experiencing changes in environmental conditions and harvesting regimes. This is the pre-peer reviewed version of the following article: An integrated population model for a long-lived ungulate: more efficient data use with Bayesian methods, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/oik.01924/epdf. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving

Evolution of body size is likely to involve trade-offs between body size, growth rate and longevity. Within species, larger body size is associated with faster growth and ageing, and reduced longevity, but the cellular processes driving these relationships are poorly understood. One mechanism that might play a key role in determining optimal body size is the relationship between body size and telomere dynamics. However, we know little about how telomere length is affected when selection for larger size is imposed in natural populations. We report here on the relationship between structural body size and telomere length in wild house sparrows at the beginning and end of a selection regime for larger parent size that was imposed for 4 years in an isolated population of house sparrows. A negative relationship between fledgling size and telomere length was present at the start of the selection; this was extended when fledgling size increased under the selection regime, demonstrating a persistent covariance between structural size and telomere length. Changes in telomere dynamics, either as a correlated trait or a consequence of larger size, could reduce potential longevity and the consequent trade-offs could thereby play an important role in the evolution of optimal body size. This is the authors’ manuscript to an article published by the Royal Society.

A central challenge in ecology is to predict long-term consequences of high herbivore densities on their resources. Here we describe vegetation changes during 26 years following the reintroduction of a wild Svalbard reindeer (Rangifer tarandus platyrhynchus) population that was not subject to predation. The population irrupted, crashed and subsequently fluctuated around lower densities throughout the study period. The irruption generated strong trophic top-down effects on the vegetation including a decline in the cover of mosses, vascular plants and lichens. Previously dominant fruticose lichens, which are preferred forage during winter, were almost depleted and showed no response to the relief in grazing pressure. This in turn indirectly affected rates of recovery in other plant groups subsequent to the crash. Mosses recovered completely and even exceeded pre-reindeer levels 6 years after the population peak. Recovery of vascular plants was more delayed and only partial due to a long-term suppression of common species that are important as reindeer forage. Thus, a suppression of major forage species and a sustained reduction in herbivore densities suggest that overgrazing occurred during the population irruption, possibly inducing a long-term decline in reindeer carrying capacity K. This supports the “exploitation ecosystem hypothesis” predicting top-down control of vegetation by herbivores when predators are absent.

Summary 1 Here we examine how sex ratio variation in house sparrow broods interacts with other demographic traits and parental characteristics to improve the understanding of adaptive significance and demographic effects on variation in sex ratio. 2 The sex ratio in complete broods did not deviate significantly from parity (54·9% males). 3 There was sex-specific seasonal variation in the probability of recruitment. Male nestlings that hatched late in the breeding season had larger probability of surviving than early hatched males. 4 An adaptive adjustment of sex ratio should favour production of an excess of males late in the breeding season. Accordingly, the proportion of male offspring increased throughout the breeding season. 5 A significant nonlinear relationship was present between sex ratio and age of the female. However, there was no relationship between parental phenotype and standardized hatch day that could explain the observed seasonal change in sex ratio. 6 The sex-specific number of offspring recruited by a pair to subsequent generations was closely related to the brood sex ratio. 7 These results indicate an adaptive adjustment of sex ratio to seasonal variation in environmental conditions that affects the offspring fitness of the two sexes differently. Our results also suggest that such a sex ratio variation can strongly influence the demography and structural composition of small passerine populations.

1. A general problem in population ecology is to predict under which conditions stochastic variation in the environment has the stronger effect on ecological processes. By analysing temporal variation in a fitness-related trait, body mass, in 21 Norwegian moose Alces alces (L.) populations, we examined whether the influence of temporal variation in different environmental variables were related to different parameters that were assumed to reflect important characteristics of the fundamental niche space of the moose. 2. Body mass during autumn was positively related to early access to fresh vegetation in spring, and to variables reflecting slow phenological development (low June temperature, a long spring with a slow plant progression during spring). In contrast, variables related to food quantity and winter conditions had only a minor influence on temporal variation in body mass. 3. The magnitude of the effects of environmental variation on body mass was larger in populations with small mean body mass or living at higher densities than in populations with large-sized individuals or living at lower densities. 4. These results indicate that the strongest influence of environmental stochasticity on moose body mass occurs towards the borders of the fundamental niche space, and suggests that populations living under good environmental conditions are partly buffered against fluctuations in environmental conditions.

Presence of phenotypic variation is necessary for selection to occur, yet processes affecting variation in sexually selected characters in natural populations are poorly understood. Here we examine whether variation in a sexual ornament (badge size) of male house sparrows (Passer domesticus) is dependent on individual variation in the conditions during early ontogenetic stages, and whether this variation and the population-wide effects of external variables such as weather or population size jointly will generate consistent differences among cohorts later in life. Variation in badge size was independent of adult body size, whereas heavier fledglings and fledglings in good body condition developed smaller visible badges as adults. Furthermore, strong cohort-effects were present, caused by a combined effect of density-dependence and weather during the early development in the moulting period and autumn after hatching. Thus, badge size is an environmentally-dependent trait in house sparrows, and likely to be under the influence of both natural and sexual selection.

The Moran effect for populations separated in space states that the autocorrelations in the population fluctuations equal the autocorrelation in environmental noise, assuming the same linear density regulation in all populations. Here we generalize the Moran effect to include also nonlinear density regulation with spatial heterogeneity in local population dynamics as well as in the effects of environmental covariates by deriving a simple expression for the correlation between the sizes of two populations, using diffusion approximation to the theta-logistic model. In general, spatial variation in parameters describing the dynamics reduces population synchrony. We also show that the contribution of a covariate to spatial synchrony depends strongly on spatial heterogeneity in the covariate or in its effect on local dynamics. These analyses show exactly how spatial environmental covariation can synchronize fluctuations of spatially segregated populations with no interchange of individuals even if the dynamics are nonlinear.

The overfishing of an increasing number of fish populations has put focus on the need for development of robust sustainable harvest strategies that can be easily implemented. This requires estimates and modelling of the deterministic and stochastic components of the population dynamics as well as an evaluation of the contribution of different harvest strategies to future population fluctuations. Here we present an example of such an approach, using the collapse of Norwegian spring-spawning herring stock as a case. We demonstrate that the collapse probably was due to overfishing, and that the large influence of the environmental stochasticity could only influence the timing of the collapse. We suggest that a proportional threshold strategy with a threshold around 14 billion individuals (4 200 000 tons), combined with a harvest of 30 -40% of the individuals above this threshold will give a sustainable yield with little annual variation. The choice of harvest strategy should also be strongly influenced by the uncertainty in the assessment of stock size. When the population stock is estimated with uncertainty, the proportional threshold strategy give a mean annual yield close to the optimum for known population size.

The use of Population Viability Analysis has recently been criticized mainly because uncertainties in population predictions are often ignored. We analyzed the viability of Scandinavian wolverine Gulo gulo populations that allow for the inclusion of uncertainties in parameter estimates and stochastic effects on population dynamics. We used the insight gained from analyses of stochastic population models to quantitatively analyze different management options for the wolverine. These management options were based on data from an individual-based demographic study in the Sarek National Park, Sweden, and data from monitoring schemes in Norway and Sweden. Stochastic components in population dynamics of the wolverine were large. Strong density regulation occurred around the carrying capacity. According to the World Conservation Union (2001), the carrying capacity of populations must exceed 46 sexually mature (≥3-yr-old) females to be considered not vulnerable. Continuation of the current levels of offt...

Summary 1. A key issue in ecology is the prediction of future population fluctuations. Such population predictions are fundamental for population-viability analysis and are essential for assessing the implications of various management actions. Development of reliable population predictions is however, difficult because it requires estimation and modelling of the separate effects of the deterministic components of the population dynamics as well as the stochastic influences on the population fluctuations. Here we model the stochastic dynamics of an introduced population of muskox Ovibos moschatus in the Dovrefjell mountains of central Norway, using a simple model without density regulation. Our aim is to examine quantitatively factors affecting the accuracy of the population projections by applying the concept of Population Prediction Interval (PPI). 2. The long-term growth rate was % = 0·0511, assuming no density dependence. The environmental variance was relatively large ( = 0·0159). This gives a deterministic growth rate of r = 0·0591. However, accounting for losses due to various kinds of human activities resulted in a nearly doubling of s ( % = 0·0980). 3. Autumn temperature and late winter snow depth were each able to explain a significant proportion of the annual variation in population growth rates. 4. The impact of environmental stochasticity made the PPI wide after only a few years. Uncertainties in the estimates of the population parameters were quite small and had a minor impact on the PPI. 5. A sensitivity analysis showed that ignoring demographic stochasticity led to an overestimate of the environmental variance , but that the impact on the width of the PPI was small. 6. This study shows that reliable projections of future population growth, even based on simple population models without density regulation, are dependent on assessment of the accuracy in the population predictions that must be based on estimating and modelling the stochastic influences on the population dynamics.

Previous theories on the effective size of age-structured populations assumed a constant environment and, usually, a constant population size and age structure. We derive formulas for the variance effective size of populations subject to fluctuations in age structure and total population size produced by a combination of demographic and environmental stochasticity. Haploid and monoecious or dioecious diploid populations are analyzed. Recent results from stochastic demography are employed to derive a two-dimensional diffusion approximation for the joint dynamics of the total population size, N, and the frequency of a selectively neutral allele, p. The infinitesimal variance for p, multiplied by the generation time, yields an expression for the effective population size per generation. This depends on the current value of N, the generation time, demographic stochasticity, and genetic stochasticity due to Mendelian segregation, but is independent of environmental stochasticity. A formula for the effective population size over longer time intervals incorporates deterministic growth and environmental stochasticity to account for changes in N.

Theoretical analyses have shown that the spatial scaling of environmental autocorrelation, strength of density regulation, and the dispersal of individuals determine the scaling of synchrony in population fluctuations. By modeling the separate effects of density regulation, environmental stochasticity, and demographic stochasticity, we estimate the spatial scaling of the component that is due to environmental stochasticity in the population dynamics of roe deer (Capreolus capreolus) in Norway. The estimated spatial scaling of the environmental noise was ∼200 km. An examination of how different weather variables influenced the scaling indicated that snow depth was the major weather variable affecting the scaling of synchrony in population fluctuations, and was negatively related to population growth rates in 97.4% of the 151 populations included in the study. A large-scale climatic phenomenon, the North Atlantic Oscillation, was positively related to population growth rates in 94.7% of the populations but ...

Migratory birds are subject to the effects of various weather systems during the year. Fluctuations in population size may depend on survivorship of juveniles and adults at various stages of the annual cycle. Severe weather conditions can lower survival, especially in migrating passerines that feed on insects. We investigated the effects of climate and density dependence on survival in a population of Common House-Martins (Delichon urbicum), including variables of weather experienced both in their breeding areas and during autumn migration. Unfavorable weather conditions during autumn migration had a severe negative effect on adult apparent survival, irrespective of sex; whereas temperature in the breeding area and population size explained a significant proportion of variance in juvenile survival. Thus, weather conditions experienced in different areas can regulate various age classes in different ways, which suggests that climate change can have a significant but complex influence on demography in passerine populations.

The risk of extinction of populations has not previously been empirically related to parameters characterizing their population dynamics. To analyze this relationship, we simulated how the distribution of population dynamical characters changed as a function of time, in both the remaining and the extinct populations. We found for a set of 38 bird populations that environmental stochasticity had the most immediate effect on the risk of extinction, whereas the long-term persistence of the population was most strongly affected by the specific population growth rate. This illustrates the importance of including information on temporal trends in population size when assessing the viability of a population. We used these relationships to examine whether time to extinction can be predicted from interspecific life history variation. Two alternative hypotheses were examined. (1) Time to extinction should decrease with increasing clutch size or decreasing survival rate because of the larger stochastic components in the population dynamics of such species. (2) Time to extinction should increase with decreasing clutch size or longer life expectancy if extinction rates are most strongly influenced by variation in the specific population growth rate. In the present data set, time to extinction increased with decreasing clutch size because of larger stochastic influences on the population dynamics of species with large clutch sizes located toward the fast end of the “slow–fast continuum” of life history variation. This demonstrates that interspecific variation in extinction risk can be predicted from knowledge of general life history characteristics. Such information can therefore be useful for assessing minimum sizes of viable populations of birds. [KEYWORDS: birds; clutch size; comparative analyses; demography; environmental stochasticity; life history variation; PVA; stochastic population dynamics; population growth rate; time to extinction; viable population size]

All Together Now Environmental drivers, such as extreme weather events, impact population dynamics and can synchronize such dynamics across populations within a species. Given that many species depend on similar resources, such events might also be expected to synchronize dynamics across species, but the complexity of multispecies communities makes it difficult to reveal potential drivers in common. Hansen et al. (p. 313 ) took advantage of the simplicity of the year-round community on the high-arctic island of Spitsbergen to test for the presence of synchrony. Population fluctuations were synchronized across the three herbivore species (Svalbard reindeer, Svalbard rock ptarmigan, and sibling vole) and the single resident predator, the arctic fox, was in lagged synchrony. The driver of these fluctuations appears to be extreme winter rain-on-snow events that reduce the availability of winter forage due to ice cover.

Knowledge about the potential spatial dynamics of species is important. Already in 1922, the American ornithologist Joseph Grinnell (Grinnell 1922) noted that in order to understand the population consequences of dispersal, its role in the stochastic nature of rare longdistance movements and the interplay between innate and environmental factors in triggering dispersal, have to be known. Furthermore, Grinnell claimed, we need knowledge of the role of dispersal in the colonisation (or re-colonisation) of unoccupied areas of suitable habitats. Although many animals are regarded as relatively sedentary and specialised in marginal parts of their geographical distribution (Thomas et al. 2001), several species (Spivak et al. 1991, Hill et al. 1999) develop more dispersive forms at range fronts, which increases rates of range expansion. Such physiologically plastic responses to new environments are unlikely to occur in larger species (Weisser 2001). Here we report that a medium-sized cervid / the roe deer (Capreolus capreolus ) increases its expansion rate 3to 20-fold in marginal habitats by performing a conditional dispersal strategy in accordance with the balanced-exchange dispersal model (Doncaster et al. 1997). A bi-sexual dispersal behaviour (Wahlstrom and Liberg 1995a, Linnell et al. 1998) and an inverse relationship between local patch quality and local dispersal probability are shown to have profound implications for expansion rates, by decreasing the rate of local extinction (i.e. the rescue effect, sensu Brown and Kodric-Brown 1977) and increasing the rate of colonisation (i.e. the establishment effect, sensu Lande et al. 1998).

Summary 1. Population viability models usually consider only the female segment of the population. However, random variation in sex ratio as well as the mating system may also affect variation in fitness among females. Here we develop population models incorporating demographic stochasticity in both sexes. Furthermore, we consider the effects on the estimated time to extinction and whether density regulation acts only on females or on total population size. 2. We applied these models to two populations of polygynous great reed warblers Acrocephalus arundinaceus L. with differences in population trends to investigate the importance of considering sex in population viability models. 3. Demographic stochasticity was larger in a polygynous than in a monogamous mating system. 4. The estimated time to extinction was considerably shorter for a monogamous than for a polygynous mating system, particularly if density regulation acted only on females than rather on the total population. 5. This study demonstrates that structure of mating system must be included when making population viability analysis based on counts of total population sizes. It is especially important to model the specific effects of density regulation on the two sexes.

Lifetime reproductive success in relation to morphology in house sparrow (Passer domesticus)

In most of Fennoscandia, moose Alces alces is intensively managed by the use of age and sex specific harvesting. This includes strong male biased harvesting, which over the last decade has resulted in a change in the sex and age composition of the populations. During the same period of time, a reduction in the proportion of male calves in the harvest has occurred all over Norway, probably reflecting a change in the secondary sex ratio. In order to examine for any causal link between these two patterns, we manipulated the structural composition of an isolated island population of moose in northern Norway and at the same time closely monitored the variation in the secondary sex ratio. In the first stage of the project, which was assumed to represent the conditions in a natural, unhunted moose population, the proportion of male calves increased significantly with the age of their fathers. Potentially, as a consequence of the high mean adult male age in the population, the secondary sex ratio was highly male biased. When we altered the male segment of the population, leaving only young (≤ 2½ years old) males as potential mates for the females, a significant increase in the proportion of female calves occurred in the population. Finally, in the last 3-years stage of the project, we reduced the adult sex ratio in the population to about 23% males and kept the adult male age relatively high. This again led to an increasing secondary sex ratio. These results suggest that the age composition of males in the population may affect the secondary sex ratio. The general significance of these results was supported by a larger temporal decrease in the proportion of males that were shot in the areas of Norway with larger changes in the sex composition of the hunting quotas than in the regions in which a less extreme harvest strategy were practised.

We model the effects of stochastic fluctuations in sex ratio on the demographic stochasticity in populations with two sexes. Two different mating systems, purely polygamous and purely monogamous, are considered. For both systems, the fluctuation in sex ratio adds a large component to the demographic variance. For long-lived species, there will be a large temporal autocorrelation in the sex ratio that affects the components of the demographic variance. For monogamous mating systems, the fluctuations in sex ratio may also cause an Allee effect. These effects need to be taken into account when modeling two-sex populations without explicitly using separate counts of males and females, but only the total population size.

Using a long-term data set on the fluctuations of a reintroduced Swiss population of ibex we estimated the parameters in a stochastic population model with theta-logistic density regulation, and how the environmental stochasticity was related to different climate variables. Our aim was to examine quantitatively the relative effects of variation in parameters describing the expected dynamics and the environmental stochasticity as well as the uncertainties in them for the development of reliable population projections. The specific growth rate r1 was 0.14. Density regulation mainly happened close to the carrying capacity K, indicating that the commonly used assumption in population ecology of loglinear density regulation is not always valid. Annual variation in the point estimates of the environmental stochasticity was correlated with winter climate. Uncertainties in parameter estimates were high, especially in the estimates of density regulation and r1. In order to examine the dynamical consequences of the...

Using a spatially homogeneous population model with migration (random individual dispersal) and spatially autocorrelated environmental noise, we show how migration and local density regulation affect the spatial scale of fluctuations in the log of population sizes as well as the 1-yr differences in these. The difference between the squares of these two spatial scales of population fluctuations does not depend on the spatial scale of the noise but only on migration rate and strength of local density regulation. We also show how migration, local density regulation, and spatially correlated environmental noise affect the realized population process at a specific location. As the migration increases, the realized local density regulation and the expected population size increase, while the realized environmental noise decreases. This approach also enables us to analyze the dynamics of the total population size within quadrats of different sizes. The risk of local quasi extinction is strongly reduced by increasing quadrat size or migration rate, while an increase in environmental stochasticity or spatial correlation in the environmental noise increases the risk of quasi extinction.

A central question in population ecology is to understand why population growth rates differ over time. Here, we describe how the long–term growth of populations is not only influenced by parameters affecting the expected dynamics, for example form of density dependence and specific population growth rate, but is also affected by environmental and demographic stochasticity. Using long–term studies of fluctuations of bird populations, we show an interaction between the stochastic and the deterministic components of the population dynamics: high specific growth rates at small densities r 1 are typically positively correlated with the environmental variance σ e 2 . Furthermore, θ, a single parameter describing the form of the density regulation in the theta–logistic density–regulation model, is negatively correlated with r 1 . These patterns are in turn correlated with interspecific differences in life–history characteristics. Higher specific growth rates, larger stochastic effects on the population dynamics and stronger density regulation at small densities are found in species with large clutch sizes or high adult mortality rates than in long–lived species. Unfortunately, large uncertainties in parameter estimates, as well as strong stochastic effects on the population dynamics, will often make even short–term population projections unreliable. We illustrate that the concept of population prediction interval can be useful in evaluating the consequences of these uncertainties in the population projections for the choice of management actions.

Recruitment rate has declined in many Norwegian moose Alces alces populations during the last two decades and at the same time the population size has increased and the proportion of males to females has decreased. Although density-dependent food limitation may explain part of the decrease in productivity, we evaluated to what extent the decline could also be a result of an insufficient number of males in the populations to fertilise all females. To test this hypothesis, we compared, based on ovary analyses, the age-specific variation in fecundity rates in eight Norwegian moose populations with annual variation in the adult sex ratio. Differences in female age and body mass explained a significant proportion of the variance in the probability of pregnancy. In addition, there was a significant relationship between the population sex ratio and the probability of pregnancy among 2-year-old females, but not the probability of pregnancy of older females. Because biased sex ratio only affects first-time breeders, the effect on the population recruitment rate may be limited. However, we also call attention to other possible effects of biased sex ratio, e.g. delayed parturition date, which in the long term may decrease population productivity through effects on survival and fecundity.

During recent decades there has been a change in the circulation of atmospheric pressure throughout the Northern Hemisphere. These variations are expressed in the recently described Arctic Oscillation (AO), which has shown an upward trend (associated with winter warming in the eastern Arctic) during the last three decades. We analysed a 12-year time series on growth of Cassiope tetragona (Lapland Cassiope) and a 21-year time series on abundance of a Svalbard reindeer population. High values of the AO index were associated with reduced plant growth and reindeer population growth rate. The North Atlantic Oscillation index was not able to explain a significant proportion of the variance in either plant growth or reindeer population fluctuations. Thus, the AO index may be a better predictor for ecosystem effects of climate change in certain high-arctic areas compared to the NAO index.

One important question in ecology is how large-scale regional phenomena affect the demography and dynamics of local populations. The purpose of the present study was to examine how climate affected spatial and temporal variation in demography within an insular metapopulation of House Sparrows (Passer domesticus). Daily weather conditions during the breeding season were highly correlated within the study region, and because the onset of breeding differed significantly among the five study islands, fledgling success was also affected. Thus, local recruitment was reduced by the occurrence of bad weather during the nestling period, and the asynchronous breeding phenology among the islands led to a significant island × year interaction in recruitment rate. Interaction between climate and the local environment provides a mechanism by which spatial synchrony in population dynamics can be reduced even in strongly spatially autocorrelated environments.

A continuous stochastic population model in space and time is presented. The model includes migration and spatially correlated environmental noise, and it accounts for spatial heterogeneity in habitat quality using a general spatial autocorrelation in the local carrying capacities. The model is analyzed by Fourier methods based on linearizations which are realistic when the population fluctuations are not too large. An expression for the spatial autocorrelation for the population density is derived together with some relatively simple relations for the scaling of these autocorrelations under the assumption that the migration rate is constant. For strong local density regulation, the spatial density pattern is approximately the same as the pattern of spatial heterogeneity in habitat quality. For weak density regulation the scaling increases with migration rate and distance and is approximately the same as the scaling of the environmental noise if the migration rate and distance are large. A required distinction between the spatial autocorrelation function and the function describing the spatial variation in the synchrony of population fluctuations is made. The effects of migration distance, migration rate, heterogeneity in carrying capacities, strength of local density regulation, and the magnitude and spatial autocorrelation in the environmental noise are discussed. Numerical examples illustrating the general findings are presented.

Stochasticities in population dynamics as well as uncertainties in parameters often make it difficult to obtain reliable predictions of future population fluctuations. Here we use a long-term data set to model the fluctuations of a Willow Ptarmigan (Lagopus lagopus) population in Central Sweden. We use this model to examine how different harvest strategies affect mean annual yield, and how these results are influenced by uncertainties in parameter estimates. Restricted proportional harvest (each hunter is allowed to shoot only a limited number of grouse per day) gave slightly higher mean annual yields than proportional threshold harvesting (harvesting only a fixed proportion of the difference between the estimated population size and the threshold when this difference is positive). However, variance in annual yield was reduced by restricted proportional harvesting because periods with low population size became shorter. Uncertainties in population parameters did not affect which strategy was optimal although those uncertainties strongly influenced the expected yield and the uncertainties in the hunting statistics. Inaccuracies in population projections are therefore important to estimate and to model when developing sustained harvest strategies for fluctuating populations.

The population growth rate of the European dipper has been shown to decrease with winter temperature and population size. We examine here the demographic mechanism for this effect by analysing how these factors affect the survival rate. Using more than 20 years of capture-mark-recapture data (1974-1997) based on more than 4000 marked individuals, we perform analyses using open capture-mark-recapture models. This allowed us to estimate the annual apparent survival rates (probability of surviving and staying on the study site from one year to the next one) and the recapture probabilities. We partitioned the variance of the apparent survival rates into sampling variance and process variance using random effects models, and investigated which variables best accounted for temporal process variation. Adult males and females had similar apparent survival rates, with an average of 0.52 and a coefficient of variation of 40%. Chick apparent survival was lower, averaging 0.06 with a coefficient of variation of 42%. ...

Models describing fluctuations in population size should include both density dependence and stochastic effects. We examine the relative contribution of variation in parameters of the expected dynamics as well as demographic and environmental stochasticity to fluctuations in a population of a small passerine bird, the pied flycatcher, that was newly established in a Dutch study area. Using the theta-logistic model of density regulation, we demonstrate that the estimated quasi-stationary distribution including demographic stochasticity is close to the stationary distribution ignoring demographic stochasticity, indicating a long expected time to extinction. We also show that the variance in the estimated quasi-stationary distribution is especially sensitive to variation in the density regulation function. Reliable population projections must therefore account for uncertainties in parameter estimates which we do by using the population prediction interval (PPI). After 2 years the width of the 90% PPI was already larger than the corresponding estimated range of variation in the quasi-stationary distribution. More precise prediction of future population size than can be derived from the quasi-stationary distribution could only be made for a time span less than about five years.