Breeding occupancy and success of two hole-nesting passerines: the impact of fragmentation caused by forestry

We studied the distribution and the reproductive success of the pied flycatcher Ficedula hypoleuca and the redstart Phoenieurus phoenicurus in relation to forest patch size, edge type (clearcut vs natural), distance from the forest edge, and vegetation characteristics in a forest-dominated landscape. Breeding performances were recorded in up to 72 forest patches during 1992–1994 for birds breeding in nest-boxes. In the spring, breeding individuals of both species arrived earlier in large forest patches (> 1 ha) than in smaller ones. Pied flycatchers arrived earlier on clearcut edges than natural edges but in the redstart there was no preference for a particular edge type. The territory distance from the forest to open land edge did not affect the arrival dates of either species. In the case of the pied flycatcher, the proportion of unpaired males was highest in patches < 1 ha in size and in the case of the redstart this applied to patches < 5 ha in size. Pairing success was not related to the forest edge type or the nest's distance from the edge. Nest predation was not patch-size nor edge-related for either of the species, but in the combined data for both species nest predation was higher at clearcut edges than at natural edges. Clutch size, brood size and the survival of nestlings to the fiedgling stage (fledgling/egg. %) were independent of the patch size, edge type and nest's "distance from the forest edge.     

Nest quality limits the number of hole-nesting passerines in their natural cavity-rich habitat

We experimentally tested whether the lack of high-quality nest holes may limit the number of secondary cavity-nesters in cavity-rich habitats. We mapped and measured natural tree-holes in 10 mature aspen forests in Estonia. In five experimental plots, we provided nest-boxes on trees having suitable cavities for hole-nesting passerines. This improved the quality of available cavities but retained their total number (due to territoriality, sites in the same tree could not be occupied simultaneously) and location on the landscape. In the next breeding season, the density of hole-nesting passerines increased in experimental plots but remained at the same level in control plots. The increase was due to the species that used boxes: Parus major that preferred these over natural cavities, and Ficedula hypoleuca that used both nest types more opportunistically. We concluded that the quality of cavities can influence the numbers of hole-nesting birds in old cavity-rich forests, also; probably, adaptive habitat selection is the proximate mechanism in this case.     

Spatial variation in population growth rate and community structure affects local and regional dynamics

1. Theory predicting that populations with high maximum rates of increase (r(max)) will be less stable, and that metapopulations with high average r(max) will be less synchronous, was tested using a small protist, Bodo, that inhabits pitcher plant leaves (Sarracenia purpurea L.). The effects of predators and resources on these relationships were also determined. 2. Abundance data collected for a total of 60 populations of Bodo, over a period of 3 months, at six sites in three bogs in eastern Canada, were used to test these predictions. Mosquitoes were manipulated in half the leaves partway through the season to increase the range of predation rates. 3. Dynamics differed greatly among leaves and sites, but most populations exhibited one or more episodes of rapid increase followed by a population crash. Estimates of r(max) obtained using a linear mixed-effects model, ranged from 1 x 5 to 2 x 7 per day. Resource levels (captured insect) and midge abundances affected r(max). 4. Higher r(max) was associated with greater temporal variability and lower synchrony as predicted. However, in contrast to expectations, populations with higher r(max) also had lower mean abundance and were more suppressed by predators. 5. This study demonstrates that the link between r(max) and temporal variability is key to understanding the dynamics of populations that spend little time near equilibrium, and to predicting and interpreting the effects of community structure on the dynamics of such populations.     

Regional variation in seasonality affects migratory behaviour and life-history traits of two Mediterranean passerines

Migratory birds may improve fecundity by moving to seasonal breeding areas, but may also suffer higher mortality rates as a cost of movement. However, the covariation among seasonality, migratoriness and life histories should change between species if their ecological features affect site-tenacity, survival or fecundity. In frugivorous birds, for instance, wandering in search of fruits may trigger broader migrations than territorial defence, and also may improve nonbreeding survival by preventing food shortages that eventually happen in discrete territories. We studied the variation in spatio-temporal distribution, life expectancy and fecundity in robins (Erithacus rubecula) and blackcaps (Sylvia atricapilla) distributed in three Iberian regions with a low, mid or high degree of environmental seasonality. In the Iberian Peninsula, robins and blackcaps are the two most intensive frugivores in winter; however, robins are territorial while blackcaps track fruit abundance among habitat patches. In the most seasonal area, robins and blackcaps decreased abundance in winter and showed a lower breeding-site tenacity, a shorter life expectancy and a larger clutch size. However, blackcaps tended to be more migratory than robins in all regions. Despite their stronger migratory behaviour, blackcaps showed a longer life expectancy and a smaller clutch size than robins in all regions. In robins, winter territoriality could decrease nonbreeding survival but also improve fecundity, because survivors are dominant and hence more efficient breeders. In blackcaps, however, the use of the most profitable habitat patches could improve nonbreeding survival, thereby allowing a similar recruitment than in robins with a lower reproductive investment. These results support that regional-scale changes in seasonality may affect migratory behaviour and hence the tradeoff between reproduction and survival in birds, doing so differently depending on the idiosyncrasy of each species.     

Climate and spatio-temporal variation in the population dynamics of a long distance migrant, the white stork

1. A central question in ecology is to separate the relative contribution of density dependence and stochastic influences to annual fluctuations in population size. Here we estimate the deterministic and stochastic components of the dynamics of different European populations of white stork Ciconia ciconia. We then examined whether annual changes in population size was related to the climate during the breeding period (the 'tap hypothesis' sensu Saether, Sutherland & Engen (2004, Advances in Ecological Research, 35, 185 209) or during the nonbreeding period, especially in the winter areas in Africa (the 'tube hypothesis'). 2. A general characteristic of the population dynamics of this long-distance migrant is small environmental stochasticity and strong density regulation around the carrying capacity with short return times to equilibrium. 3. Annual changes in the size of the eastern European populations were correlated by rainfall in the wintering areas in Africa as well as local weather in the breeding areas just before arrival and in the later part of the breeding season and regional climate variation (North Atlantic Oscillation). This indicates that weather influences the population fluctuations of white storks through losses of sexually mature individuals as well as through an effect on the number of individuals that manages to establish themselves in the breeding population. Thus, both the tap and tube hypothesis explains climate influences on white stork population dynamics. 4. The spatial scale of environmental noise after accounting for the local dynamics was 67 km, suggesting that the strong density dependence reduces the synchronizing effects of climate variation on the population dynamics of white stork. 5. Several climate variables reduced the synchrony of the residual variation in population size after accounting for density dependence and demographic stochasticity, indicating that these climate variables had a synchronizing effect on the population fluctuations. In contrast, other climatic variables acted as desynchronizing agents. 6. Our results illustrate that evaluating the effects of common environmental variables on the spatio-temporal variation in population dynamics require estimates and modelling of their influence on the local dynamics.     

Spatial synchrony in Drosophila suzukii population dynamics along elevational gradients

1. Spotted wing drosophila (SWD; Drosophila suzukii Matsumura, 1931) is a polyphagous invasive crop pest native of Southeast Asia able to attack a wide array of host plant species in both cultivated and natural habitats. SWD is now widespread in several mountain regions, but it is still unclear how the species moves to different elevations across the seasons, and how this depends on environmental conditions and food resources. 2. The temporal dynamics of several SWD populations were studied along elevational gradients in the Alps using a synchrony analysis. Twelve transects were selected, covering an overall elevational gradient of 2100 m. SWD abundance was monitored every 2 weeks during the growing season (from June to November 2015) when cultivated and wild hosts are potentially susceptible (i.e. fruits are ripe). 3. Spotted wing drosophila were widely distributed along all the tested elevations, revealing synchrony in population dynamics across ranges in elevation and geographic distance. Synchronised populations were observed at distances of up to 100 km at sites with similar temperatures. The high dispersal potential of the pest together with the seasonal variation in temperature are likely to be the dominant mechanisms causing the observed spatial synchrony. A factor that seemed to reduce synchrony is the large concentration of host plants (i.e. crop) in lowland agricultural landscapes. 4. The spatial synchrony in pest abundance at large spatial scale indicates that the risk of SWD outbreaks is highly dependent on drivers beyond the control of traditional field‐scale management. These findings could help in developing monitoring and predictive models of SWD population dynamics.     

Geographical gradients in the population dynamics of North American prairie ducks

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.     

Historic and contemporary levels of genetic variation in two New Zealand passerines with different histories of decline

We compared historic and contemporary genetic variation in two threatened New Zealand birds (saddlebacks and robins) with disparate bottleneck histories. Saddlebacks showed massive loss of genetic variation when extirpated from the mainland, but no significant loss of variation following a severe bottleneck in the 1960s when the last population was reduced from approximately 1000 to 36 birds. Low genetic variation was probably characteristic of this isolated island population: considerably more genetic variation would exist in saddlebacks today if a mainland population had survived. In contrast to saddlebacks, contemporary robin populations showed only a small decrease in genetic variation compared with historical populations. Genetic variation in robins was probably maintained because of their superior ability to disperse and coexist with introduced predators. These results demonstrate that contemporary genetic variation may depend more greatly on the nature of the source population and its genetic past than it does on recent bottlenecks.     

Seasonal forcing on the dynamics ofClethrionomys rufocanus: Modeling geographic gradients in population dynamics

We interpret gradients in population dynamics of the gray-sided vole from the southwestern part of the island of Hokkaido to its northeastern part within the framework of a phenomenological model involving the relative length of summer and winter. In Hokkaido, as in other northern regions, both spring and fall is considered as short transition periods between the two main seasons — summer (the primary breeding season) and winter (the non-reproductive or secondary breeding season). We show that the geographic transition in dynamics may be understood as the combined consequence of different patterns of density-dependence during summer and winter, and geographically varying season lengths. Differences are shown to exist between summer and winter with respect to strength of density-dependence. Direct density-dependence, in particular, is stronger during winter than during summer. A model is presented to show how relative lengths of seasons can induce both stable and periodically fluctuating population dynamics. The results are compared and contrasted with what is otherwise known about the gradient in rodent dynamics in Fennoscandia.     

Adaptive feeding across environmental gradients and its effect on population dynamics

This paper analyzes a consumer's adaptive feeding response to environmental gradients. We consider a consumer-resource system where resources are distributed among many discrete resource patches. Each consumer exhibits a feeding morphology allowing it to remove resources from a patch down to some threshold density (or level) before having to seek resources elsewhere. Assuming consumers trade off resource extraction with patch access and predation, we show that for a given environment there often exists a single evolutionarily stable feeding threshold and it is an evolutionary attractor. We then investigate how the population dynamics of the resource and the consumer change as the environment changes. Two cases are considered: (i) all consumers exhibit a fixed feeding threshold that is adaptive for an intermediate environment; and (ii) the consumer population adapts and adopts the evolutionarily stable feeding threshold associated with the current environment. In less harsh environments (i.e., environments where consumers experience a lower risk of predation, or environments where resource patches are more abundant) the adaptive consumer population is predicted to evolve so that resources within a patch are depleted to lower densities. We show that the change in consumer density due to environmental change can be rather different depending on whether or not the population can adapt. In some situations we observe that when the consumer's environment becomes harsher, the consumer population may increase in density before a rapid crash to extinction. This result has implications for monitoring and managing a population.     

Ecological and evolutionary constraints on regional avifauna of passerines in China

Strong correlations between species diversity and climate have been widely observed, but the mechanism underlying this relationship is unclear. Here, we explored the causes of the richness–climate relationships among passerine birds in China by integrating tropical conservatism and diversification rate hypotheses using path models. We found that assemblages with higher species richness southwest of the Salween–Mekong–Pearl River Divide are phylogenetically overdispersed and have shorter mean root distances (MRDs), while species-rich regions northeast of this divide (e.g., north Hengduan Mountains–south Qinling Mountains) are phylogenetically clustered and have longer MRDs. The results of the path analyses showed that the direct effect of climatic factors on species richness was stronger than their indirect effects on species richness via phylogenetic relatedness, indicating that neither tropical conservatism nor diversification rate hypotheses can well explain the richness–climate relationship among passerines in China. However, when path analyses were conducted within subregions separately, we found that the tropical conservatism hypothesis was well supported in the southwestern Salween–Mekong–Pearl River Divide, while the diversification rate hypothesis could explain the richness–climate relationship well in the northeastern divide. We conclude that the diversity patterns of passerines in different subregions of the Eastern Himalayas-Mountains of Southwest China may be shaped by different evolutionary processes related to geological and climatic histories, which explains why the tropical conservatism or diversification rate hypothesis alone cannot fully explain the richness–climate relationships.     

Evolutionary games and two species population dynamics

Competition between species has long been modeled by population dynamics based on total numbers of each species. Recently, the evolution of strategy frequencies has been used successfully for competition models between individuals. In this paper, we illustrate that these two views of competition are compatible. It is shown that the rate of intra and interspecific competitions between individuals largely determines the population dynamics. Competition models over a single common resource and predator-prey models are developed from this individual competition approach. In particular, the equilibrium strategies in a co-evolving predator-prey system are shown to be more stable than the predicted strategy cycling of standard evolutionary game theory.     

Historical distribution and regional dynamics of two Brassica species

Plants often show a patchy distribution. This can be related to the discontinuous distribution of environmental variables that define suitable habitat. Metapopulation theory suggests that additional patchiness may be caused by the dynamics of local extinctions and recolonisations. However, the contribution of these two mechanisms to explaining the observed patterns, and thus the applicability of metapopulation theory to plants remains controversial partly because population turnover may occur at long time‐scales not usually covered by ecological studies. We analyzed the role of environmental variation and population turnover in determining the distribution of two Brassica species, an annual and a perennial, along 44 km of coastline in Dorset, UK. Mapped occurrence and abundance of both species in recent years was compared with distributions from a 70 yr‐old dataset and a survey of present‐day environmental parameters. Abiotic and vegetation parameters were correlated with the occurrence of both species in binary logistic regression models and explained spatial auto‐correlation in the Brassica distributions. These regression models suggest that neither species is occupying all potential habitat in the region studied. The relationship between historical and present distributions differed between the species. While an historical signal was very weak in the annual B. nigra, it had a large influence in predicting the present distribution of the perennial B. oleracea. This suggests local extinction and colonisation events for B. nigra over the 70 yr period, but not for B. oleracea which showed little evidence of population turnover. Our results demonstrate that the consideration of large time‐scales can reveal patterns of regional dynamics. We conclude that metapopulation dynamics might be possible for our annual but can be ruled out for our perennial study species over the past 70 yr. We argue that beyond this time‐scale possible metapopulation dynamics may be overridden by faster processes of environmental change.     

Stochastic population dynamics and life-history variation in marine fish species

Abstract We examined whether differences in life-history characteristics can explain interspecific variation in stochastic population dynamics in nine marine fish species living in the Barents Sea system. After observation errors in population estimates were accounted for, temporal variability in natural mortality rate, annual recruitment, and population growth rate was negatively related to generation time. Mean natural mortality rate, annual recruitment, and population growth rate were lower in long-lived species than in short-lived species. Thus, important species-specific characteristics of the population dynamics were related to the species position along the slow-fast continuum of life-history variation. These relationships were further associated with interspecific differences in ecology: species at the fast end were mainly pelagic, with short generation times and high natural mortality, annual recruitment, and population growth rates, and also showed high temporal variability in those demographic traits. In contrast, species at the slow end were long-lived, deepwater species with low rates and reduced temporal variability in the same demographic traits. These interspecific relationships show that the life-history characteristics of a species can predict basic features of interspecific variation in population dynamical characteristics of marine fish, which should have implications for the choice of harvest strategy to facilitate sustainable yields.     

Richards-like two species population dynamics model

The two-species population dynamics model is the simplest paradigm of inter- and intra-species interaction. Here, we present a generalized Lotka–Volterra model with intraspecific competition, which retrieves as particular cases, some well-known models. The generalization parameter is related to the species habitat dimensionality and their interaction range. Contrary to standard models, the species coupling parameters are general, not restricted to non-negative values. Therefore, they may represent different ecological regimes, which are derived from the asymptotic solution stability analysis and are represented in a phase diagram. In this diagram, we have identified a forbidden region in the mutualism regime, and a survival/extinction transition with dependence on initial conditions for the competition regime. Also, we shed light on two types of predation and competition: weak, if there are species coexistence, or strong, if at least one species is extinguished.