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Different prey species can vary in their significance to a particular predator. In the simplest case, the total available density or biomass of a guild of several prey species might be most relevant to the predator, but behavioural and ecological traits of different prey species can alter the picture. We studied the population dynamics of a predator-prey setting in Finland by fitting first-order log-linear vector autoregressive models to long-term count data from active breeding sites of the northern goshawk (Accipiter gentilis; 1986-2009), and to three of its main prey species (1983-2010): hazel grouse (Bonasa bonasia), black grouse (Tetrao tetrix) and capercaillie (T. urogallus), which belong to the same forest grouse guild and show synchronous fluctuations. Our focus was on modelling the relative significance of prey species and estimating the tightness of predator-prey coupling in order to explain the observed population dynamics, simultaneously accounting for effects of density dependence, winter severity and spatial correlation. We established nine competing candidate models, where different combinations of grouse species affect goshawk dynamics with lags of 1-3 years. Effects of goshawk on grouse were investigated using one model for each grouse species. The most parsimonious model for goshawk indicated separate density effects of hazel grouse and black grouse, and different effects with lags of 1 and 3 years. Capercaillie showed no effects on goshawk populations, while the effect of goshawk on grouse was clearly negative only in capercaillie. Winter severity had significant adverse effects on goshawk and hazel grouse populations. In combination, large-scale goshawk-grouse population dynamics are coupled, but there are no clear mutual effects for any of the individual guild members. In a broader context, our study suggests that pooling data on closely related, synchronously fluctuating prey species can result in the loss of relevant information, rather than increased model parsimony.

We study the dynamics of the capercaillie, black grouse, hazel grouse and willow grouse in Kainuu game management district in northeastern Finland in the years 1989 – 2004. It appears that the 6 – 7 year periodicity that prevailed in this region from 1960s up to 1980s has now vanished in all species. Th e grouse data are modelled using a linear autoregressive model with lag terms for population dynamics including grouse harvest as annual bag and an index of winter severity (winter-time area of Baltic Sea ice cover). We use the Akaike information criterion for selecting the best model for each species; fi rst order lag is forced to the models. It turns out that a term is needed for harvesting (with a negative coeffi cient) in models for all species. For the capercaillie and the hazel grouse second order lag was included, for the black grouse and the willow grouse fi rst order lag suffi ces. Th e willow grouse is the only species where the index of winter strength (with a negative coeffi cient) is needed in the model.

The ongoing climate change has improved our understanding of how climate affects the reproduction of animals. However, the interaction between food availability and climate on breeding has rarely been examined. While it has been shown that breeding of boreal birds of prey is first and foremost determined by prey abundance, little information exists on how climatic conditions influence this relationship. We studied the joint effects of main prey abundance and ambient weather on timing of breeding and reproductive success of two smaller (pygmy owl Glaucidium passerinum and Tengmalm's owl Aegolius funereus) and two larger (tawny owl Strix aluco and Ural owl Strix uralensis) avian predator species using long-term nation-wide datasets during 1973-2004. We found no temporal trend either in vole abundance or in hatching date and brood size of any studied owl species. In the larger species, increasing late winter or early spring temperature advanced breeding at least as much as did high autumn abundance of prey (voles). Furthermore, increasing snow depth delayed breeding of the largest species (Ural owl), presumably by reducing the availability of voles. Brood size was strongly determined by spring vole abundance in all four owl species. These results show that climate directly affects the breeding performance of vole-eating boreal avian predators much more than previously thought. According to earlier studies, small-sized species should advance their breeding more than larger species in response to increasing temperature. However, we found an opposite pattern, with larger species being more sensitive to temperature. We argue that this pattern is caused by a difference in the breeding tactics of larger mostly capital breeding and smaller mostly income breeding owl species.

Isolation-by-distance (IBD) is a widely used model explaining population structure and how gene flow decreases with increasing distance. It is biologically intuitive that populations which rarely exchange individuals should drift apart genetically. However, the model is based on the assumptions that populations are large, equal in size and stable over time — conditions that are unlikely to occur in natural conditions. The model has been challenged in the past, for example, in the light of metapopulations or variance in reproductive success. However, an appraisal of the assumption of a large and stable population size per se is lacking. We investigate the robustness of the results concerning IBD patterns when smaller and fluctuating population sizes, or differences in population size are allowed. Through computer simulations we show that allowing for different population sizes and random fluctuations lead to unpredictable patterns regarding the results concerning gene flow and IBD. A pattern of IBD could be the result of high gene flow or no gene flow at all, depending on how populations differ in size and how they fluctuate. Adding environmental noise (white, red and blue noise corresponding to random, positive and negative autocorrelation respectively) gives even more unpredictable results concerning patterns of IBD. Our results have important implications for genetic and conservation research. Interpreting an IBD pattern, or lack thereof, is not as easy as earlier thought and needs to be more thoroughly explored.

Juveniles of the signal crayfish reside during daylight hours in shelters. At twilight they leave for food, at daybreak they either return or find another shelter. We examined conflicts over burrow ownership. At low densities with equal numbers of shelters and crayfish 1/5 of the burrows were occupied. Increasing both the number of crayfish and shelters improved the occupancy close to 50%. Doubling the number of crayfish in relation to the number of shelters increased the occupancy up to 75%. In an experiment with 30 randomly selected crayfish and 15 sheltering holes available the burrow holders were about 1–2 mm longer in carapace length than those found freely moving in the aquarium. Shelter owners were rarely newly moulted individuals. Size asymmetry (2 mm difference in carapace length) between owner and intruder affected the outcome of the contest over burrow ownership. When intruders were larger than owners, takeovers occurred in about 80% of the cases tested. If the owner was large and the intruder small the takeover frequency was about 20%. When the owner and the intruder were of matching size takeovers were still observed in about 45% of the cases. The outcome of the ownership contest has a true meaning. In a nursery-pond experiment, where low-protein food was randomly scattered all around, no size differences were found in carapace lengths of crayfish juveniles residing in different shelters. However, when high-protein food was introduced in a single spot, owners of burrows were significantly larger and more numerous in the nearby shelters than in the shelters furthest away from the food source. Therefore, when food is unevenly distributed the burrow ownership contests may potentially lead to size asymmetries between individuals. This may lead to large individuals nearby the food growing faster than small individuals further away from the food source, a process likely to further enhance size differences.

Determining whether the composition of ecological communities (species presence and abundance), can be predicted from species demographic traits, rather than being a result of neutral drift, is a key ecological question. Here we compare the similarity of community composition, from different community assembly models run under identical environmental conditions, where interspecific competition is assumed to be either neutral or niche-based. In both cases, species colonize a focal patch from a network of neighbouring patches in a metacommunity. We highlight the circumstances (rate and spatial scale of dispersal, and the relative importance of ecological drift) where commonly used community similarity metrics or species rank-abundance relationships are likely to give similar results, regardless of the underlying processes (neutral or non-neural) driving species' dynamics. As drift becomes more important in driving species abundances, deterministic niche structure has a smaller influence. Our ability to discriminate between different underlying processes driving community organization depends on the relative importance of different drift processes that operate on different spatial scales.

A changing climate induces shifts in the location of biomes. Tracing such a shift may pose problems for life history traits adapted to the prior conditions, so that, e.g. the timing of reproduction and the time with sufficient resources for rearing hatchlings do not match. We show that the timing of breeding of Finnish common buzzards Buteo buteo, has advanced with over ten days as a response to the warming of early spring, during 1979―2004. During the same period the isoclines of the onset of breeding have moved about 200 km to the north-east. However, the reproductive performance of the common buzzard has not increased as a response to these changes. Despite increasing temperatures during early spring, the temperatures of early summer have remained the same since the 1970s. Combined, the early onset of breeding and the unchanged temperatures of early summer have lead to decreased post-hatching temperatures. Under these circumstances, common buzzard offspring now face a higher risk to hatch into less favourable weather conditions than three decades ago. Furthermore, summer precipitation, harmful for nestlings, has been predicted to increase in the future, thus possibly further worsening the circumstances for breeding common buzzards. Our results demonstrate that even if common buzzards in Finland breed at the northern limit of the species' distribution, and could therefore be expected to gain advantage from a warming climate, the opposite is the case.

Competition is assumed to generate compensatory dynamics where an increase in one species is compensated by a decrease in others. Recently, using a community covariance technique, Houlahan et al. found that compensatory dynamics are only visible in 25-30% of natural communities studied. The study was based on scoring the sum of covariances of population densities. In contrast to the theory, and as a cautionary reminder to the interpretation of natural time series data, we show that negative community covariance can be absent even in strongly competitive communities and can be found present in communities without competitive interactions. Precise knowledge of various features of the underlying species' biology and characteristics of the environmental variation is required before community covariance can be correctly interpreted as a proxy for the importance of competition or environmental forcing in driving community fluctuations. Other tools may therefore be more appropriate, e.g. explicit modelling of competition using modern time series analytical tools.

Harvest data are commonly used as proxy for count data, especially in studies of long-term temporal and spatial patterns of population fluctuations. However, usually the concurrence of the conclusions based on different types of data is impossible to verify due to the lack of count data. Here, we use annual (1964–2004) harvest and population census data for capercaillie, black grouse and hazel grouse from 14 game management districts covering Finland, and demonstrate some mismatch in the information that these data sets provide. Overall, linear regressions of annual harvest against population count give a reasonable fit, but the slopes are less than 1 in every species. Harvest bags have been proportionally larger in north and eastern Finland than in southwestern Finland, with marked species-specific differences. Considering population variation, the CV% in the census data (30–50%) is consistently smaller than it is in the harvest data (60–70%). Most importantly, conclusions on the spatio-temporal patterns of the population dynamics are different if based on harvest rather than count data. In capercaillie, synchrony decreases faster with distance according to the harvest data, while in black grouse and hazel grouse the census data show the steeper decline. In addition, the autocorrelation coefficients in the census time series are higher in capercaillie and black grouse than in harvest data, but in hazel grouse the opposite is true. Finally, the parameter estimates for a second order autoregressive model using different data sets differ, and these differences are species-specific. Despite the fact that annual harvest is a positive and linear function of annual grouse population density, the pattern of population dynamics derived from the bag data is different from that shown by the census data. This result urges caution in using wildlife bag data as reliable indices of population dynamics. deceased August 2008.

The invasion of alien species and genotypes is an increasing concern in contemporary ecology. A central question is, what life-history traits enable invasion amidst populations of wild species and conventional cultivars? In order to invade, the initially rare species must perform better than their resident competitors. We conducted a mathematical analysis and simulation of a two-species extension of the Maynard Smith and Slatkin model for population dynamics in discrete time to study the role of density dependence as different types of competition in the invasion of new species. The type of density dependence ranged from scramble to contest competition. This led to intrinsic dynamics of the species range from point equilibrium to cycles and chaos. The traits were treated either as free parameters or constrained by a trade-off resulting from a common fixed strength of density dependence or equilibrium density. Resident and intruder traits had up to ten-fold differences in all of the parameters investigated. Higher equilibrium density of the intruder allowed invasion. Under constrained equilibrium density, an intrinsically stable intruder could invade an unstable resident population. Scramble competition made a population more susceptible to invasion than contest competition (e.g., limitation by light or territory availability). This predicts that a population which is mainly limited by food (or nutrients in plants) is more likely to be invaded than a population limited by a hierarchical competition, such as light among plants. The intruder population may have an effect on the resident population’s dynamics, which makes the traditional invasion analysis unable to predict invasion outcome.

Many species from diverse taxa are known to display synchronous fluctuations across vast geographical ranges. It is often thought that climate factors influencing the growth of conspecific populations are correlated over large distances and hence produce the synchronous population dynamics - an effect known as the Moran effect. However, for species embedded in a food web the Moran effect needs not necessarily influence the focal species directly, but can act indirectly through other species. Such an indirect synchronization can also occur in an age-structured population, where the correlated environment of one age-class causes synchronous fluctuations of another. Here, we investigate this indirect Moran effect. We find first of all that synchrony is readily transferred through food webs or between age classes, which complicates the identification of the underlying synchronizing factor. Secondly, we find puzzling cases, where synchrony is enhanced as it is filtered through a food web or between age-classes. Our results also apply to systems of different species, but with closely matching dynamics.

Understanding the effects of population management on the community a target species belongs to is of key importance for successful management. It is known that the removal or extinction of a single species in a community may lead to extinctions of other community members. In our study, we assess the impacts of population management on competitive communities, studying the response of both locally stable and unstable communities of varying size (between four and 10 species) to three different management strategies; harvesting of a target species, harvesting with non-targeted catch, and stocking of the target species. We also studied the consequences of selecting target species with different relative abundances, as well as the effects of varying environmental conditions. We show here how the effects of management in competitive communities extend far beyond the target population. A crucial role is played by the underlying stability properties of the community under management. In general, locally unstable communities are more vulnerable to perturbation through management. Furthermore, the community response is shown to be sensitive to the relative density of the target species. Of considerable interest is the result that even a small (2.5%) increase in the population size of the target species through stocking may lead to extinction of other community members. These results emphasize the importance of considering and understanding multi-species interactions in population management.

Linkage between environmental variability and population renewal processes is assumed invariable in standard population models. We explored adaptive, density-dependent population dynamics in a setting where population consists of individuals differing in location of their optimum performance relative to a stochastic and autocorrelated environmental variable, such as temperature, humidity or salinity. Relative growth rates of phenotypes are determined by a Gaussian unimodal function of the environmental variable, which also has a unimodal distribution. Adaptive dynamics causes a significant increase in mean population growth performance and decreases its variance. Population growth fluctuates more rapidly, i.e. has a blue-shifted spectrum. This also causes a blue-shift in density-dependent population dynamics in a wide range of population growth rates and autocorrelation of the environment. The blue-shift is most pronounced when the breadth of environmental response is moderately smaller that the breadth of environmental fluctuations. The causes of the blue-shift are discussed. The blue-shift caused by adaptive dynamics is in contrast with views that evolutionary processes redden population time series, i.e. cause slow fluctuations, due to slow changes in population properties. Mean genetic variance is maximised in rapidly fluctuating blue and white noise environments, and when genotype performance breadth is small. In contrast, genotype diversity is maximised in slowly fluctuating red environments and in populations with large performance breadth. Genetic variance and genetic diversity also have marked temporal fluctuations. Temporal variability of genetic variance increases with noise redness and small response breadth. However, genetic diversity is maximised in slightly reddened environments and narrow performance breadth populations. That genetic variance and diversity are affected by the spectrum of environmental noise and also fluctuate temporally, suggest that models assuming constant amount of genetic variability (equilibrium variance) may not be successful in predicting the consequences of environmental changes.

A key question of evolutionary importance is what factors influence who becomes dominant. Individual genetic variation has been found to be associated with several fitness traits, including behaviour. Could it also be a factor influencing social dominance? We investigated the association between social status and the amount of intra-individual genetic variation in juvenile brown trout (Salmo trutta). Genetic variation was estimated using 12 microsatellite loci. Dominant individuals had higher mean heterozygosity than subordinates in populations with the longest hatchery background. Heterozygosity–heterozygosity correlations did not find any evidence of inbreeding; however, single-locus analysis revealed four loci that each individually differed significantly between dominant and subordinate fish, thus giving more support to local than general effect as the mechanism behind the observed association between genetic diversity and a fitness-associated trait. We did not find any significant relation between mean d 2 and social status, or internal relatedness and social status. Our results suggest that individual genetic variation can influence dominance relations, but manifestation of this phenomenon may depend on the genetic background of the population.

The classical theory of the ideal free distribution (IFD) predicts that the spatial distribution of consumers should follow the distribution of the resources they depend on. Here, we study consumer-resource matching in a community context. Our model for the community is a food chain with three levels. We study whether the primary consumers are able to match resources both under predation risk and in its absence. Both prey and predators have varying degrees of knowledge of the global and local resource distribution. We present two versions of the model. In the "resource maximising" model, the consumers consider the availability of their resource only. In the "balancing" model, individual consumers minimise predation risk per unit of resource that they can gain access to. We show that both models can lead to perfect matching of consumers on resources and predators on consumers, assuming that individuals have full knowledge of the whole environment. However, when the consumers' information and freedom of movement are greater than those of the predators, then the predators generally undermatch the consumers. In the opposite case, we observe overmatching and high consumer movement rates. Furthermore, undermatching of predators on consumers tends to induce overmatching of consumers on resources.

Semi-automated fluorescent genotyping of eight polymorphic microsatellite loci was used to assess the level of genetic diversity and population differentiation in Nordic stocks of non-anadromous Arctic charr, Salvelinus alpinus, of both wild and hatchery origin. Highly significant genetic heterogeneity was detected globally across wild and/or hatchery populations and even between populations from lakes separated by as little as six kilometres. The overall level of genetic differentiation among wild populations (FST= 0.360) was substantially higher than that observed between populations of anadromous Arctic charr in Canada using microsatellite data. Cavalli-Sforza and Edward's chord distance was used to construct a neighbour-joining tree and three population clusters were supported with relatively high bootstrap values which included the populations from north-west, north-east and southern Finland respectively. Use of Paetkau et al's individual assignment test further supported the strong differentiation of most populations as well as their classification into the three predicted geographical areas. No significant difference in average allele number or heterozygosity was observed between populations of wild and hatchery origin. However, the effects of hatchery rearing were revealed by a strong increase in the number of deviations from Hardy-Weinberg equilibrium as well as of linkage disequilibrium events in the hatchery stocks compared to natural populations. The population from Lake Saimaa, in south-east Finland, is completely reliant upon aquaculture assistance for its survival. The broodstocks of this population exhibited particularly low levels of genetic variability. Although the hatchery stocks of this population suffer from increased egg and alevin mortality and disease susceptibility, it remains to be determined if this is due directly to a lack of genetic variation as some abundant unstocked natural populations possessed similarly low levels of microsatellite variability.

Non-linearities are commonly observed in the responses of organisms to environment. They potentially modify the qualitative and quantitative properties of population dynamics. We studied how non-linear responses to environment, or “noise filters”, influence population variability and extinction risk by introducing coloured noise to the growth rate in the Hassell single-species model. The consequences of noise filtering were analysed by comparing the model dynamics with linearly filtered and non-linearly filtered noise that have the same mean. Three biologically plausible filters we used: saturating, unimodal optimum type, and sigmoid responses. Filtering can either decrease or increase population variability when compared to linear noise response. The effect of noise filtering on variability is most pronounced with stable population dynamics and the outcome depends on the filter type, population growth rate, and noise colour. Non-linear noise filtering predominantly increases extinction risks when population growth rate is low (R

By simulating all possible offspring genotypic combinations based on pair-wise matings in three vulnerable or endangered populations of salmonids (two Atlantic salmon Salmo salar and one Arctic charr Salvelinus alpinus), family level estimates of potential offspring genetic diversity were calculated using several commonly used genetic diversity estimators (d 2 EST, d 2 scaled-EST and H EST ). By using this approach. the genetic variability of offspring could be predicted accurately based solely on parental genotype data. In addition, significant associations between offspring genetic variability and fitness-related traits were observed in the two Atlantic salmon populations and these associations were consistent between fitness measures and either estimated or observed genetic diversity. This indicates that associations with offspring fitness measures can be predicted without genetic analysis of the offspring themselves.

We assessed how non-linear biological responses to environmental noise, or “noise filtering”, impact the spectra of density-dependent population dynamics, and the correlation between noise and population dynamics. The noise was assumed to affect population growth rate in a discrete-time population model by Hassell [J. Anim. Ecol. 44 (1975) 283–295] where the population growth rate was linked to the environment with an optimum type filter. When compared to unfiltered noise, the filtered noise can distort the stationary distribution of population values. The optimum type filter can make cyclic population dynamics more regular and low population values can become more frequent or rare depending on the strength of density dependence. Filtering can cause blue shifted and red shifted population dynamics and determine the strength of correlation between environmental noise and population size. In most cases, optimum type filtering makes linear correlation between population dynamics and noise weaker. The filter effect on population spectra and noise versus population correlation is sensitive to changes in population model parameters, the location where noise hits the filter, and noise colour.

It has recently been shown that damped endogenous dynamics is a common feature in Finnish grouse species; In this paper, we demonstrate that time-variant harvesting may turn damped dynamics to quasi-periodic fluctuations. Exploited populations, e.g. grouse, may therefore fluctuate more than expected if we do not manage to keep the harvest fraction constant over time. However, the harvest fraction of Finnish grouse varies with the phase of the cycle. Such a harvesting strategy could potentially change the periodicity of the fluctuations, as can a threshold harvest strategy where a constant fraction is harvested above a density threshold. The two non-linear harvesting strategies investigated here can modulate the dynamic properties of the population in a way not predicted by linear models. We argue that the behaviour of exploited populations and the role of harvesting can only be understood if we identify and understand the interplay of endogenous and exogenous components of population dynamics. (Less)

Summary 1. Local population studies have shown that sex allocation among many birds and mammals seems to be partly non-random and in connection to surrounding factors, such as environmental or parental quality. In this scenario, if environmental quality varies in space and time, it is feasible that environmental quality also comes to influence offspring sex ratio on larger geographical scales. 2. Investigating this idea - using nation-wide data sets on size-dimorphic Finnish northern goshawks Accipiter gentilis from 1989 to 1998 - we found that offspring sex ratio is related to spatial and temporal variation in availability of their main prey, woodland grouse species. 3. In a majority of locations ( n = 73), broods are large and male-biased when grouse density is high, while small and female-biased broods are found in areas and times with low grouse density. When adjusted for grouse density, the correlation between brood size and sex ratio disappears, but the correlation between grouse density and sex ratio remains. 4. We also found evidence indicating a mechanism balancing local offspring sex ratios towards the previously rarer sex with a time lag of 1 year. That is, local sex ratios in subsequent years are negatively correlated. 5. Our study highlights the importance of inclusion of both time and space in sex ratio studies. Ignorance of these dimensions could explain a great deal of the inconsistency in many earlier local sex ratio studies. 6. Irrespective of whether the observed pattern is the result of facultative manipulation, sex biased mortality, or both, it is suggested that the male-biased sex ratio during periods of high grouse availability maximizes goshawk reproductive success.

Seed bank is a plant life history strategy against the unpredictability of the biotic and the abiotic environment. We simulated competition between a seed banking and a non-banking morph of an annual plant. A constant fraction of the banker morph seeds was allocated to the seed bank, where they had a constant mortality and germination rate. All surviving seeds of the non-banker morph germinated in the next generation. The seedlings of both morphs experienced similar density-dependent mortality. Whether one of the morphs wins or the morphs coexist was evaluated from parameter space plots and statistically with logistic regression analysis. All parameters of the model had a significant, nonlinear effect on the persistence of the morphs, supporting our approach of numerically covering a wide range of parameter values. The seed production of a focal morph increased its survival and decreased the survival of the other morph. Otherwise, the morphs showed opposite response to changes in the model parameters. The banker morph was usually the winning strategy when it had a higher seed production than the non-banker morph. The banker morph benefitted from high germination probability, while the non-banker benefitted from high allocation to seed bank and high seed mortality. The coexistence of the morphs was inhibited by high banker morph seed production and seed mortality and promoted by high values of all other parameters. The system showed complex dynamics when banking was the winning strategy or the morphs coexisted. In addition, a part of the parameter space where the non-banker morph wins showed complex dynamics. Our results suggest that seed banking is a beneficial strategy if seed number is increased consequently, e.g. due to a decreased seed size. If banking decreases seed number, the non-banker morph wins or the two morphs coexist.

Research on the evolution of life histories addresses the topic of fitness trade-offs between semelparity (reproducing once in a lifetime) and iteroparity (repeated reproductive bouts per lifetime). Bulmer (1994) derived the relationship v+P(A)

Evidence from wildlife and human populations indicates that conditions during early development can have marked effects on the subsequent performance of individuals and cohorts. Likewise, the effects of maternal and, more generally, parental environments can be transferred among individuals between generations. These delayed life-history effects are found consistently and suggestions have been made that they can be one source of both variability and of delayed density dependence in population dynamics. Assessments of several different time series indicate that population variability and delayed density dependence are common and that understanding the mechanisms giving rise to them is crucial for the interpretation and application of such models to basic and applied research. Therefore, it is necessary to assess the different ways in which history in the life history might give rise to variability and delayed density dependence in population dynamics. Here, we build on recent appraisals of the pervasive influence of past environmental conditions on current and future fitness and link the details of these life-history studies to classic features of population dynamics.

The interpretation of ecological data has been greatly improved by bridging the gap between ecological and statistical models. The major challenge is to separate competing hypotheses concerning demography, or other ecological relationships, and environmental variability (noise). In this paper we demonstrate that this may be an arduous, if not impossible, task. It is the lack of adequate ecological theory, rather than statistical sophistication, which leads to this problem. A reconstruction of underlying ecological processes can only be done if we are certain of either the demographic or the noise model, which is something that can only be achieved by an improved theory of stochastic ecological processes. Ignoring the fact that this is a real problem may mislead ecologists and result in erroneous conclusions about the relative importance of endogenous and exogenous factors in natural ecosystems. The lack of correct model identification may also have far-reaching consequences for population management and conservation.

Per Lundberg and Jorgen Ripa, Dept of Theoretical Ecology, Lund Univ., Ecology Building, SE-223 62 Lund, Sweden (per.lundberg@teorekol.lu.se). Veijo Kaitala, Dept of Biological and Environmental Science, Univ. of Jyvaskyld, P.O. Box 35, FIN-40351 Jyvaskyll, Finland. Esa Ranta, Integrative Ecology Unit, Div. of Population Biology, Dept of Ecology and Systematics, P.O. Box 17, FIN-00014 University of Helsinki, Finland

Climate change has ignited lively research into its impact on various population–level processes. The research agenda in ecology says that some of the fluctuations in population size are accountable for by the external noise (e.g. weather) modulating the dynamics of populations. We obeyed the agenda by assuming population growth after a resource–limited Leslie matrix model in an age–structured population. The renewal process was disturbed by superimposing noise on the development of numbers in one or several age groups. We constructed models for iteroparous and semelparous breeders so that, for both categories, the population growth rate was matching. We analysed how the modulated population dynamics correlates with the noise signal with different time–lags. No significant correlations were observed for semelparous breeders, whereas for iteroparous breeders high correlations were frequently observed with time–lags of −1 year or longer. However, the latter occurs under red–coloured noise and for low growth rates when the disturbance is on the youngest age group only. It is laborious to find any clear signs of the (red) noise– and age group–specific fluctuations if the disturbance influences older age groups only. These results cast doubts on the possibility of detecting the signature of external disturbance after it has modulated temporal fluctuations in age–structured populations.

The moose Alces alces population in Finland has been managed for sustained harvest since 1970 by regulating annual hunting quotas. However, against all expectations the population size declined in the 1990s. An ecological risk analysis approach was used to build a growth model with annual harvest for the moose population. In the model there is stochasticity in the parameters representing population dynamics. We shall address: 1) whether the population decline could be due to a mismatch between harvest and anticipated population growth rate, and 2) to what extent hunting the moose population down to a much lower target size succeeds. A central element in this is the assumption that the estimate of the pre-hunting population size errs. First, the probability of a population decline due to hunting increases from values close to 0% up to 100% in a very narrow range (15–25%) of harvest rates. Even with high birth rates the risk of a population decline was substantial when the hunting rate exceeded 25% for cows and 37.5% for calves and bulls. The 1974–1994 moose harvest rate was, on average, ca 45% of the population size in autumn. The high rate suggests that the harvest might have been too intense in that period to keep the population stable. Second, we set the target to reduce the moose population drastically (to say 50% of the existing population size). Assuming that the estimates of the population size may err, our analysis shows that the achieved population size after the severe harvest is far below the size we aimed at.

We report an individual-based single-species model producing temporal scale-free, self-similar dynamics in time. Individuals in the population renew in an explicit space with a large number of loci. We show that reproduction, subsequent dispersal of the offspring, and mortality will organise population fluctuations such that the emerging dynamics represent power law and scale-free structures. Further, we show that spatially structured population dynamics may show red frequency spectra, a property that the simple nonlinear population models are generally lacking.

Summary 1. It is widely appreciated that complex population dynamics are more likely in systems where there is a lag in the density dependence. The transmission of maternal environmental conditions to offspring phenotype is a potential cause of such a lag. Maternal effects are increasingly found to be common in a wide range of organisms, and might thus be a frequent cause of nonequilibrium population dynamics. 2. We show that a maternal effects’ lag generally increases population variability. This may result from the lag inducing cycles (or more complex dynamics) in a deterministic environment or, in a stochastic environment, from the lag interacting with environmental noise to produce more variable dynamics than would otherwise occur. This may happen whether the underlying dynamics are equilibrium, periodic or more complex.

We investigate conditions enabling long-term coexistence of semelparity (reproducing only once per lifetime) and iteroparity (repeated spells of reproduction in subsequent breeding seasons). Bulmer (1985, 1994) has transferred the study of the fitness merit of reproducing semelparously vs. iteroparously into a density-dependent system, using an invasion scenario with an abundant resident population of one reproductive strategy and a rare mutant invader population of another reproductive strategy. For stable population dynamics, Bulmer (1994) derived condition v + PA < 1 (PA is adult survival and v is the ratio of offspring number of the iteroparous type over that of the semelparous type) where a semelparous population cannot be invaded by an iteroparous strategy. In order to study the generalisation of Bulmer's results in spatial population dynamics, we generate a population system consisting of a linear string of habitable sub-units. The sub-units are semi-independent, obeying discrete-time Ricker dynamics in renewal, but they are close enough for dispersing individuals to couple them together. At each time step, a random fraction of individuals in each sub-unit disperses into neighbourhood. In this setting, we observe long-term persistence of semelparity and iteroparity when dispersal is stochastic and positively autocorrelated. Stochasticity in dispersal creates fluctuating local dynamics and thus permits long-term persisting coexistence of semelparity and iteroparity even in the parameter region where Ricker dynamics are stable and the Bulmer inequality is true. Positively autocorrelated, in contrast to negatively autocorrelated dispersal time-series, promoted coexistence between semelparity and iteroparity.

Egg size contributes to other life history traits of an individual. It is traditionally considered as a maternally determined characteristic to which the male does not have any direct contribution. However, a recent finding in insects suggests that males can affect egg size also directly. In fish, the male effect could take place only during egg swelling, as the final egg size is reached after that. We studied egg size in four freshwater salmonid species (the land-locked Atlantic salmon, the brown trout, the Arctic charr and the lake trout) right after fertilisation (initial egg size) and after the swelling phase (final egg size). The results showed that the final egg size is affected not only by the initial egg size but also by both the female and the male through the process of egg swelling. This study suggests that paternal contribution may form a previously largely ignored source of variation in early life history traits in salmonid fish.

Birth and death rates, as so many other biological processes, are usually not linearly related to environmental variation. Common examples of non-linear response forms include unimodal ‘‘optimum-type’’ responses and various saturating responses. These responses filter the signal coming from the environment to a corresponding biological process. We explored how different types of environmental signal may be transformed to a biological process. We were interested in the effect of the filter on modulation of (1) the variance of the signal, on (2) the variance-covariance structure between the signal and the filtered signal, and on (3) the match between the power spectra of the signal and the filtered signal. We found that the filters will change the frequency distribution (mean, variance, modality) of the signal. Especially symmetric filters that have a single peak of optimum will change signal structure so that there either exists or does not exist a correlation between the signal and the filtered signal. When the correlation exists it may be either positive or negative depending on the signal’s mode relative to the filter structure. Also, the power spectrum properties of the signal may be dramatically transformed after passing the filter, e.g., blue noise can turn into red noise. Our results strongly suggest that studies on the influence of external signals on biological processes, such as population dynamics, should explicitly consider how the signal is transferred to biological processes.

We study resource matching – the relationship between resource supply and forager numbers – under conditions of fluctuating population dynamics in a two-patch system. For the inter-patch dispersal we apply the patch-departure rule following the principle of the ideal free distribution: leave the current patch of residence if local conditions are worse than conditions elsewhere on average. We show that such a dispersal rule synchronises cyclic and chaotic local population dynamics, but unlike many other dispersal rules, leaves the underlying population dynamics untouched. We also show that the IFD dispersal rule is not very sensitive to biased information and navigation failures during the dispersal phase. Even under such circumstances we observe a quick process of populations becoming synchronised, even when the population dynamics are chaotic. We conclude that an IFD patch-departure rule represents an ESS dispersal behaviour towards which the dispersal patterns should evolve.

Global extinction of a species is sadly irreversible. At a local scale, however, extinctions may be followed by re-invasion. We here show that this is not necessarily the case and that an ecological community may close its doors for re-invasion of species lost from it. Previous studies of how communities are assembled have shown that there may be rules for that process and that limitations are set to the order by which species are introduced and put together. Instead of focusing on the assembly process we randomly generated simple competitive model communities that were stable and allowed for two to 10 coexisting species. When a randomly selected single species was removed from the community, the cascading species loss was recorded and frequently the resulting community was more than halved. Cascading extinctions have previously been recorded, but we here show that the relative magnitude of the cascade is dependent on community size land not only trophic structure) and that the reintroduction of the original species lost often is impossible. Hence, species loss does not simply leave a void potentially refilled, bur: permanently alters the entire community structure and consequently the adaptive landscape for potential re-invaders.

In stark contrast to other species within the Salmonidae family, phylogeographic information on European grayling, Thymallus thymallus, is virtually nonexistent. In this paper, we utilized mitochondrial DNA polymerase chain reaction-restriction fragment length polymorphism (mtDNA PCR-RFLP) and sequence variation to infer the postglacial dispersal routes of T. thymallus into and within northern Europe, and to locate geographically, potential evolutionarily distinct populations. Mitochondrial analyses revealed a total of 27 T. thymallus haplotypes which clustered into three distinct lineages. Average pairwise interlineage divergence was four and nine times higher than average intralineage divergence for RFLP and sequence data, respectively. Two European grayling individuals from the easternmost sample in Russia exhibited haplotypes more genetically diverged from any T. thymallus haplotype than T. arcticus haplotype, and suggested that hybridization/introgression zone of these two sister species may extend much further west than previously thought. Geographic division of the lineages was generally very clear with northern Europe comprising of two genetically differentiated areas: (i) Finland, Estonia and north-western Russia; and (ii) central Germany, Poland and western Fennoscandia. Average interpopulation divergence in North European T. thymallus was 10 times higher than that observed in a recent mtDNA study of North American T. arcticus. We conclude that (i) North European T. thymallus populations have survived dramatic Pleistocene temperature oscillations and originate from ancient eastern and central European refugia; (ii) genetic divergence of population groups within northern Europe is substantial and geographically distinct; and (iii) the remainder of Europe harbours additional differentiated assemblages that likely descend from a Danubian refugium. These findings should provide useful information for developing appropriate conservation strategies for European grayling and exemplify a case with a clear need for multinational co-operation for managing and conserving biodiversity.

For most animals their foraging environment consists of a patch network. In random environments there are no spatial autocorrelation at all, while in fine-grained systems positive autocorrelations flip to negative ones and back again against distance. With increasing grain size the turnover rate of spatial autocorrelation slows down. Using a cellular automaton with foragers having limited information about their feeding environment we examined how well consumer numbers matched resource availability, also known as the ideal free distribution. The match is the better the smaller the size of the environmental grain. This is somewhat contrary to the observation that in large-grained environments the spatial autocorrelation is high and positive over long distances. In such an environment foragers, by knowing a limited surrounding, should in fact know a much larger area because of the spatially autocorrelated resource pattern. Yet, when foragers have limited knowledge, we observed that the degree of undermatching (i.e., more individuals in less productive patches than expected) increases with increasing grain size.

The ability to distinguish among chemical cues from multiple predators is of key adaptive value for many prey fish. We examined the attractiveness and repulsiveness of chemical stimuli from different coexisting fish species fed on different diets on the behaviour of hatchery reared Arctic charr young in a Y-maze fluviarum, where the charr could choose between two sides either with control water or stimulus water with fish odour. We used stimuli from (1) matching sized conspecifics, large (2) Arctic charr, (3) salmon, (4) brown trout and (5) brown trout fed on Arctic charr fry. Other salmonids were given pellet food. Additional fish odour treatments included piscivorous (6) pike and (7) burbot. In the control trials both sides received control water. Arctic charr young were expected to respond adaptively to the stimuli from coexisting piscivorous fish. The charr most strongly preferred water with the odour of their matching sized conspecifics, which was the only fish odour they were familiar with before the experiments. They also showed significant preference for other salmonid odours, even though these fish are potential predators on small charr. Chemical stimuli from pike and burbot, on the contrary, were strongly avoided, and burbot odour even prevented the charr to swim and enter the lateral halves of the fluviarum. Moreover, odour from brown trout fed on Arctic charr fry was avoided when compared to stimuli from trout fed on pellets. Although the Arctic charr young were completely naive regarding piscivores, the fact that they could distinguish between different predator taxa and diets on the basis of chemical cues only reflects the long coevolutionary history of these fish populations.

According to Fisherian sex allocation theory, parents that can adjust their offspring sex ratio in response to skews in population sex ratio will maximize their fitness over parents lacking this ability. There is good evidence that adaptive sex ratio adjustment occurs in many natural populations, but deviations from theoretical predictions have also been observed. These anomalies may be more apparent than real. When the spatial dimension of sex ratio variation is ignored, then a mismatch between empirical data and theoretical predictions based on panmictic mating is to be expected. We illustrate this with data on human sex ratio variation in 21 preindustrial populations, and with a cellular automaton model built to obey Fisherian sex allocation rules. The results from the model generally match with the data. When information about the ambient sex ratio is limited, then the sex allocation decisions may appear locally maladaptive. In general, the results indicate that Fisher’s sex-ratio theory may have greater explanatory power than previously thought.

We investigated the evolution of monogamy (one male, one female) and polygyny (one male, more than one female). In particular, we studied whether it is possible for a mutant polygynous mating strategy to invade a resident population of monogamous breeders and, alternatively, whether a mutant monogamy can invade resident polygyny. Our population obeys discrete-time Ricker dynamics. The role of males and females in the breeding system is incorporated via the harmonic birth function. The results of the invasability analysis are straightforward. Polygyny is an evolutionarily stable strategy mating system; this holds throughout the examined range of numbers of offspring produced per female. So that the two strategies can coexist, polygyny has to be punished. The coexistence of monogamy and polygyny is achieved by reducing the offspring number for polygyny relative to monogamy. This yields long-term persistence of the strategies for all offspring numbers studied. An alternative punishment is to increase the sensitivity of polygynous breeders to population density. The coexistence is possible only with a limited range of offspring produced. The third way to achieve coexistence of the two mating strategies is to assume that individuals live in a spatially structured population, where dispersal links population subunits to a network. Reducing the dispersal rate of polygynous breeders relative to that of monogamous individuals makes the coexistence feasible. However, for monogamy to persist, the number of offspring produced has to be relatively high.

We studied whether social environment in the form of different body size regimes in rearing groups affects the growth of juvenile Arctic char (Salvelinus alpinus) in hatchery conditions. Young-of-the-year Arctic char were divided into groups of three different compositions (a wide, a bimodal, and a narrow size-frequency distribution) in which individuals would be subjected to different dominance and competitive relationships. After a 9-month growth period the fish in the narrow size distribution had grown the fastest in both length and weight. Also, total biomass gains were highest for fish originating from the narrow size distribution treatment. The adjusted mean biomasses for wide, bimodal, and narrow size regime treatments were 5400, 5000, and 5900 g, respectively. Our results give support to the hypothesis that individuals in size-sorted groups should show enhanced growth compared with individuals originating from a wider size-frequency distribution where more aggressive interactions are to be expected.

Spatially synchronous population dynamics have been documented in many taxa. The prevailing view is that the most plausible candidates to explain this pattern are extrinsic disturbances (the Moran effect) and dispersal. In most cases disentangling these factors is difficult. Theoretical studies have shown that dispersal between subpopulations is more likely to produce a negative relationship between population synchrony and distance between the patches than perturbations. As analyses of empirical data frequently show this negative relationship between the level of synchrony and distance between populations, this has emphasized the importance of dispersal as a synchronizing agent. However, several weather patterns show spatial autocorrelation, which could potentially produce patterns in population synchrony similar to those caused by dispersal. By using spatially extended versions of several population dynamic models, we show that this is indeed the case. Our results show that, especially when both factors (spatially autocorrelated perturbations and distance-dependent dispersal) act together, there may exist groups of local populations in synchrony together but fluctuating asynchronously with some other groups of local populations. We also show, by analysing 56 long-term population data sets, that patterns of population synchrony similar to those found in our simulations are found in natural populations as well. This finding highlights the subtlety in the interactions of dispersal and noise in organizing spatial patterns in population fluctuations.

In social foraging, scroungers take a disproportionately large share of the food found relative to their own food-searching efforts, while producers find more food than they manage to monopolize. We present a model of social foraging acknowledging the finder's advantage and foraging role asymmetries among individuals but incorporating the possibility that producers and scroungers differ in vigilance level and in vulnerability to predators. This allows simultaneous examination of both foraging benefits and anti-predatory aspects of grouping behaviour. Instead of seeking for equal payoff conditions, we first look for groups in which foraging character combinations and anti-predatory properties of producers and scroungers minimize the phenotype-specific predation hazard over food-intake rate, Ri/Ii, that is, fixed phenotype Ri/Ii minima. In the second approach, we allow individuals to change their foraging status to achieve lower Ri/Ii and look for combinations where it no longer pays for either producers or scroungers to change their roles, that is, evolutionarily stable group compositions, ESS. Various character combinations allow the phenotype-specific minima. In most cases, however, producers' and scroungers' minima are achievable only in different group compositions. The ESS combinations of producers and scroungers deviate widely from those combinations yielding phenotype-specific minima of Ri/Ii. If individuals are allowed to be flexible in adopting either a producer or a scrounger role, ESS group compositions will emerge, even though they are more expensive for both producers and scroungers in terms of Ri/Ii than group compositions yielding the phenotype-specific Ri/Ii minima. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Successful predictions of population fluctuations are valuable in game management, as population estimates are instrumental in increasing the time available for management decisions. However, finding a population model which produces predictions accurate enough to be used for management purposes is often precluded due to scarcity and noisiness of population data. Using two long-term population data sets, 1964-1984 data on Finnish grouse (Tetrao urogallus, T. tetrix and Bonasa bonasia) and 1914-1950 data on coloured fox Vulpes fulva from Canada, we demonstrate the use and power of an artificial neural network in predicting population fluctuations. The performance of an artificial neural network model is compared to two benchmark forecasts: time series mean and the previous data value. Unfortunate as it is, in practise management decisions often have to be made with limited data. Therefore, a notable advantage of neural network modelling is the forecast accuracy even in cases when the time series available are short and noisy, and the processes underlying population fluctuations are not fully understood.

A common ‘rule of thumb' in conservation biology is that populations of more than 100 individuals are not threatened by demographic stochasticity alone. However, the effect of demographic stochasticity on population survival may be strengthened if the population has a non-homogeneous demography. A recently developed measure, the demographic effective population size ND, scales population size by taking the differential contribution of individuals into account. We exemplify the estimation of ND with the current population of the Saimaa ringed seal, comprising about 200 individuals. The estimate of ND is shown to be dependent on how independently individuals can be assumed to reproduce. Completely independent reproduction leads to ND∼ 250, suggesting a safe future for the population. However, when acknowledging the potential of breeding failure due to habitat limitation and difficulties of dispersal among the different subareas of Lake Saimaa, ND lies in an alarming range from six to 30 individuals. The effective means to increase the ND value are limited. Although subdivision itself decreases the value of ND, improving dispersal of individuals is shown to be of limited aid. Instead, the most effective way to enhance future prospects of the Saimaa seal population is to improve pup survival to maturity.

The records of Canadian lynx fur returns indicate rather regular self-repeating pattern with 9–11 yr cycles That the lynx populations over a vast geographical range fluctuate in synchrony appears to be well established The finding that the degree of synchrony levels off with increasing distance among provinces compared to increase again between the furthest–away provinces (O–shape) has largely escaped notice in previous analyses Moreover, the pattern of synchrony against distance varies depending on the period of time used m the analysis, sometimes there is O–shape, sometimes mere negative correlation, and sometimes no relationship whatsoever The entire rich pattern of lynx dynamics in space and time can be emulated by sets of local subpopulations acknowledging dispersal among populations This all suggest that local dynamics of populations cannot be fully understood unless the significance of spatial linkage of subpopulations via dispersal of individuals is acknowledged