Geographic differences in the sociability of voles in relation to cyclicity

Bank voles, Clethrionomys glareolus, and field voles, Microtus agrestis, redistribute food hoards and alter the location of their activity upon the introduction of a foreign conspecific in laboratory experiments. This behaviour showed geographic variation in C. glareolus but no clear geographic variation in M. agrestis; north Swedish cyclic C. glareolus were repelled by the new animals while southern non-cyclic C. glareolus were attracted. There were no differences between animals from various population phases at the same locality. The geographic differences were retained in laboratory-born animals kept in an abnormal social environment. Other studies have demonstrated similar differences in M. agrestis. Cyclic voles may be negatively affected by density-related stimuli while non-cyclic ones may instead gather in environments that are fairly safe from predators.     

The effect of diet quality on gut anatomy in British voles (Microtinae)

Three species of British voles, the bank vole Clethrionomys glareolus, the field vole Microtus agrestis and the water vole Arvicola terrestris were maintained on diets of seed and plant leaf material to investigate changes in gut anatomy. C. glareolus and M. agrestis showed significant changes in most regions of the gut; they developed longer and heavier tracts when on a highfibre diet. This response may be important in enabling these animals to withstand seasonal changes in diet quality.     

Parental investment related to social systems in microtines

Summary Laboratory offspring of wild-caught voles Clethrionomys glareolus and Microtus agrestis, bred for 1 year under constant conditions, were examined with regard to sex ratios and weights at weaning and at 2 months of age. C. glareolus exhibits female territoriality and M. agrestis male territoriality in summer. The adults die away in late summer-autumn. Early-summer young mature in the year of birth but late-summer young do not reach maturity until the following year. C. glareolus young showed a male bias in early summer and a female bias in late summer. Conditions were the opposite but less clear in M. agrestis. C. glareolus males grew comparatively faster than M. agrestis males and showed a markedly higher early summer male: female weight ratio at 2 months of age. Maternal investment thus appears clearly related to the social system; the sex with the largest number and highest quality of young was that which was not limited in number by territoriality. However, the investment depended also on the time until maturation of the young.     

有色环境噪音对空间异质种群动态同步性的影响

随着种群动态和空间结构研究兴趣的增加,激发了大量的有关空间同步性的理论和实验的研究工作。空间种群的同步波动现象在自然界广泛存在,它的影响和原因引起了很多生态学家的兴趣。Moran定理是一个非常重要的解释。但以往的研究大多假设环境变化为空间相关的白噪音。越来越多的研究表明很多环境变化的时间序列具有正的时间自相关性,也就是说用红噪音来描述更加合理。因此,推广经典的Moran效应来处理空间相关红噪音的情形很有必要。利用线性的二阶自回归过程的种群模型,推导了两种群空间同步性与种群动态异质性和环境变化的时间相关性(即环境噪音的颜色)之间的关系。深入分析了种群异质性和噪音颜色对空间同步性的影响。结果表明种群动态异质性不利于空间同步性,但详细的关系比较复杂。而红色噪音的同步能力体现在两方面:一方面,本身的相关性对同步性有贡献;另一方面,环境变化时间相关性可以通过改变种群密度依赖来影响同步性,但对同步性的影响并无一致性的结论,依赖于种群的平均动态等因素。这些结果对理解同步性的机理、利用同步机理来制定物种保护策略和害虫防治都有重要的意义。     

Landscape genetics highlights the role of bank vole metapopulation dynamics in the epidemiology of Puumala hantavirus

Rodent host dynamics and dispersal are thought to be critical for hantavirus epidemiology as they determine pathogen persistence and transmission within and between host populations. We used landscape genetics to investigate how the population dynamics of the bank vole Myodes glareolus, the host of Puumala hantavirus (PUUV), vary with forest fragmentation and influence PUUV epidemiology. We sampled vole populations within the Ardennes, a French PUUV endemic area. We inferred demographic features such as population size, isolation and migration with regard to landscape configuration. We next analysed the influence of M. glareolus population dynamics on PUUV spatial distribution. Our results revealed that the global metapopulation dynamics of bank voles were strongly shaped by landscape features, including suitable patch size and connectivity. Large effective size in forest might therefore contribute to the higher observed levels of PUUV prevalence. By contrast, populations from hedge networks highly suffered from genetic drift and appeared strongly isolated from all other populations. This might result in high probabilities of local extinction for both M. glareolus and PUUV. Besides, we detected signatures of asymmetric bank vole migration from forests to hedges. These movements were likely to sustain PUUV in fragmented landscapes. In conclusion, our study provided arguments in favour of source‐sink dynamics shaping PUUV persistence and spread in heterogeneous, Western European temperate landscapes. It illustrated the potential contribution of landscape genetics to the understanding of the epidemiological processes occurring at this local scale.     

Population growth and habitat distribution in cyclic small rodents: to expand or to change?

Habitat selection determined by intraspecific interactions (social behaviour), being either free or despotic, should result in the largest densities in the most favourable habitat at least in late increase and decline phases of cyclic populations. Habitat distribution determined by interspecific effects such as herbivore-plant or predator-prey interactions may result in higher densities in inferior habitats at late peaks and/or declines due to overgrazing of preferred habitats, or invasion of such habitats by specialist predators. An examination of the distributions of the rodent species Clethrionomys glareolus and Microtus agrestis during a population cycle on forest clearcuts at Grimsö, south-central Sweden, demonstrated clear changes towards less preferred habitats during the decline phase, particularly in M. agrestis. Intraspecific competition could be excluded as a cause since the numbers of both species declined simultaneously. There was no sign of overgrazing, while weasels, Mustela nivalis, invaded the preferred M. agrestis habitat during peak–decline. Predation thus appears more important for the local occurrence at early decline, rather than territoriality or other social behaviour. It is concluded that distributions in various habitats do not always reveal any primary habitat selection but, rather, habitat-dependent survival.     

Experiments on habitat selection in voles: Implications for the inverse distribution of two common European species

Summary Several pairs of species of microtine rodents show inverse distributions or abundance. Here I determine if the inverse abundance relationship of the bank vole Clethrionomys glareolus (a forest species) and the field vole Microtus agrestis (an open field species) could be explained by habitat selection. Habitat selection was examined by choice experiments with combinations of soil and vegetation types, and with separate habitat factors. The effects of early experience and social behaviour were also studied, e.g. in a large outdoor enclosure. M. agrestis showed a stronger dependence on shelter (e.g. easily excavated soil or thick grassy vegetation) than C. glareolus, while the presence of preferred food did not affect habitat selection for either species. In both species, laboratory-bred specimens showed considerably fewer preferences. Habitat selection in subadult C. glareolus was influenced by social clumping, while territorial behaviour made more even distributions in M. agrestis.The less rigid habitat selection and weaker territorial behaviour observed in the forest species (Clethrionomys) compared with a species from temporary habitats (Microtus) is not consistent with present concepts of r- and K-selection.     

Gradients in density variations of small rodents: the importance of latitude and snow cover

Summary Microtine rodents are known to show extreme population variations (cycles) but non-cyclic populations have also been recognized during recent years. The cyclic populations have been widely thought to be regulated by intrinsic mechanisms. However, such predictions for cyclic populations are usually not applicable to non-cyclic ones and extrinsic factors may have to be included in any explanation.A hypothesis that the degree of fluctuations in small rodent numbers is related to the sustainable number of generalist predators was tested on mainly literature data by computing indices of cyclicity for local populations. These indices were related to latitude and snow cover (two measures) as these variables will affect the amount of alternative prey available for these generalists. Within Fennoscandia such indices for Clethrionomys glareolus and Microtus agrestis were clearly positively related to latitude and snow cover. The fraction of populations with summer declines in numbers, characterizing highly cyclic populations, increased in the same way. Cyclicity indices in Great Britain were similar to those in southern Fennoscandia, both areas being poor in snow, but were higher at the same latitudes in eastern Europe with more snow. Indices of density variations were generally low in North American Clethrionomys species and very variable in Microtus species.The gradients observed and differences between continents are interpreted as due to microtine-vegetation interactions in northern European areas poor in generalist predators but with important small mustelid predation, and to similar snowshoe hare-vegetation interactions in mainly Canada-Alaska, where small rodents may serve as alternative prey for numerically fluctuating hare predators, at least in the forests. Western European microtine populations, and probably many others, seem to be regulated by generalist predators.     

Effects of range position,inter-annual variation and density on demographic transition rates of <Emphasis Type="Italic">Hornungia petraea</Emphasis> populations

The central-marginal model assumes unfavourable and more variable environmental conditions at the periphery of a species’ distribution range to negatively affect demographic transition rates, finally resulting in reduced population sizes and densities. Previous studies on density-dependence as a crucial factor regulating plant population growth have mainly focussed on fecundity and survival. Our objective is to analyse density-dependence in combination with the effect of inter-annual variation and range position on all life stages of an annual plant species, Hornungia petraea, including germination and seed incorporation into the seed bank. As previous studies on H. petraea had revealed a pattern opposite to existing theory with lower population densities at the distribution centre in Italy than at the periphery in Germany, we hypothesised that (1) demographic transition rates are lower, (2) the inter-annual variation in demographic transition rates is higher and (3) the intensity of density-dependence is weaker in Italy than in Germany. To analyse demographic transition rates, we used an autoregressive covariance strategy for repeated measures including density and inter-annual variation. All the three hypotheses were confirmed, but the impact of range position, density-dependence and inter-annual variation differed among the transition steps. All transition rates except fecundity were higher in the German populations than in the Italian populations. Germination rate and incorporation rate into the seed bank were strongly density-dependent. Central populations showed a larger inter-annual variation in fecundity and winter survival rate. Winter survival rate was the only transition step with a stronger density-dependence in peripheral populations. In most cases, these differences between distribution centre and periphery would not have emerged without taking density-dependence and inter-annual variation into account. We conclude that including range position, inter-annual variation and density-dependence in one single statistical model is an important tool for the interpretation of demographic patterns regarding the central-marginal model. Electronic Supplementary Material Supplementary material is available for this article at     

Spatio‐temporal covariation in abundance between the cyclic common vole Microtus arvalis and other small mammal prey species

Populations of the common vole Microtus arvalis in mid‐western France show cyclic dynamics with a three‐year period. Studies of cyclic vole populations in Fennoscandia have often found inter‐specific synchrony between the voles and other small mammals which share the voles' predators. Although predators are central to the favoured mechanism to explain Fennoscandian vole cycles and the spatial variation of small mammal populations, their role in vole cycles elsewhere, including France, is less clear. Establishing whether alternative prey species in France cycle in parallel with voles as they do in Fennoscandia is thus an important step towards understanding the generality of predators' influence on cyclic vole populations. We applied spatial and temporal autocorrelation and cross‐correlation methods to French populations of M. arvalis and two sympatric non‐cyclic small mammal species, Apodemus sylvaticus and Crocidura russula. Patterns of time‐lagged cross‐correlation between the abundance of M. arvalis and the other two species suggested synchrony in their dynamics beyond that expected of stochastic environmental variation, and indicated a weak three‐year cycle in A. sylvaticus and C. russula that was in phase with that of M. arvalis. We interpret the synchrony between these species as the effect of shared predators and environmental stochasticity. Abundance within species showed weak spatial autocorrelation in June at scales consistent with dispersal being the mechanism responsible, but a more general lack of spatial structure within and between species was consistent with the strong spatial synchrony at regional scales often found in fluctuations of small mammal abundance.     

The population dynamics of the voleClethrionomys rufocanus in Hokkaido, Japan

Population dynamics of the gray sided-vole,Clethrionomys rufocanus, in Hokkaido, Japan were described on the basis of 225 time series (being from 12 to 31 years long); 194 of the time series have a length of 23 years or longer. The time series were classified into 11 groups according to geographic proximity and topographic characteristics of the island of Hokkaido. Mean abundance varied among populations from 1.07 to 21.07 individuals per 150 trap-nights. The index of variability for population fluctuation (s-index) ranged from 0.204 to 0.629. Another index for population variability (amplitude on log-10 scale) ranged from 0.811 to 2.743. Mean abundance and variability of populations were higher in the more northern and eastern regions of the island. Most populations, except for the southernmost populations, exhibited significant direct density-dependence in population growth. Detection rate for delayed density-dependence varied among groups from 0% to 22.6%. Both direct and delayed density-dependence tended to be stronger in the more northern and eastern populations. The proportion of cyclic populations was higher in the northern-eastern areas than that in the southern-western areas. There was a clear gradient from the asynchronous populations in southwest, to the highly synchronized populations in the northeast.     

The Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) populations of Windermere,UK: population trends associated with eutrophication,climate change and increased abundance of roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>)

The north and south basins of Windermere in the English Lake District, UK, support autumn- and spring-spawning populations of Arctic charr, Salvelinus alpinus, which have been studied since the 1930s. Continuous investigations of the population dynamics of Arctic charr at this lake have involved gill netting since 1939, collection of fishery catch-per-unit-effort data since 1966, and hydroacoustic surveys since 1990. Analysis of these and associated long-term data on the abiotic environment and other components of the fish communities revealed recently contrasting fortunes of the Arctic charr populations of the north and south basins, the latter of which has been significantly impacted by eutrophication while both basins have shown elevated water temperatures and increasing roach, Rutilus rutilus, populations. Despite the introduction of phosphate stripping in 1992 and some subsequent initial improvement, the hypolimnion of the south basin still remains significantly eutrophicated and the fishery catch-per-unit-effort in this basin is now at record low levels. In addition, the spatial distribution of roach has expanded to form significant components of the fish communities of inshore and offshore surface habitats, where this cyprinid may compete with Arctic charr for zooplanktonic prey. It is concluded that the Arctic charr populations of Windermere, particularly those of the south basin, currently face a number of significant environmental pressures and continued management action is required to ensure their survival.     

Density regulation in the Mediterranean leaf-toed gecko <Emphasis Type="Italic">Euleptes europaea</Emphasis>

Isolated populations are particularly prone to extinction, and understanding their temporal dynamics is relevant for conservation and management. In this study, the abundance of a population of the nocturnal leaf-toed gecko Euleptes europaea was estimated by mark-recapture over a 12-year period in northwest Italy. Simulation tests showed the presence of density-dependence, and autoregressive analyses indicated that direct density dependence was responsible for a large part of the variation in population growth rates. Density-dependent recruitment was suggested as the main demographic mechanism controlling population dynamics, which was also affected by solar radiation measured during the active gecko season. These results may contribute to implement conservation strategies in other small and isolated leaf-toed gecko populations.     

Spatial variation in springtime food resources influences the winter body mass of roe deer fawns

It is well established that the dynamics of mammalian populations vary in time, in relation to density and weather, and often in interaction with phenotypic differences (sex, age and social status). Habitat quality has recently been identified as another significant source of individual variability in vital rates of deer, including roe deer where spatial variations in fawn body mass were found to be only about a tenth of temporal variations. The approach used was to classify the habitat into blocks a priori, and to analyse variation in animal performance among the predefined areas. In a fine-grained approach, here we use data collected over 24 years on 1,235 roe deer fawns captured at known locations and the plant species composition sampled in 2001 at 578 sites in the Chizé forest to determine the spatial structure at a fine scale of both vegetation and winter body mass of fawns, and then to determine links between the two. Space and time played a nearly equal role in determining fawn body masses of both sexes, each accounting for about 20% of variance and without any interaction between them. The spatial distribution of fawn body mass was perennial over the 24 years considered and predicted values showed a 2 kg range according to location in the reserve, which is much greater than suggested in previous work and is enough to have strong effects on fawn survival. The spatial distribution and the range of predicted body masses were closely similar in males and females. The result of this study is therefore consistent with the view that the life history traits of roe deer are only weakly influenced by sexual selection. The occurrence of three plant species that are known to be important food items in spring/summer roe deer diets, hornbeam (Carpinus betulus), bluebell (Hyacinthoides sp.) and Star of Bethlehem (Ornithogalum sp.) was positively related to winter fawn body mass. The occurrence of species known to be avoided in spring/summer roe deer diets [e.g. butcher's broom (Ruscus aculeatus) and beech (Fagus sylvatica)], was negatively related to fawn body mass. We conclude that the spatial variation in the body mass of fawns in winter in this forest is as important as the temporal variation, and that the distribution of plant species that are actively selected during spring and summer is an important determinant of spatial variation in winter fawn body mass. The availability of these plants is therefore likely to be a key factor in the dynamics of roe deer populations.     

Landscape and habitat dependence in cyclic and semi-cyclic small rodents

Habitat dependence and foraging for bark of semi-cyclic and cyclic voles were examined on clearcuts in central and northern Sweden. Both populations showed inconsistent and weak relationships to habitat variables. Population dynamics of the northern cyclic population was more clearly related to landscape composition. Snow depth explained a large proportion of the total variation between clearcuts when the populations were pooled. Snow and landscape effects agree with recent hypotheses that 3–4 yr cyclic densities are related to predator impact. The negligible effects of other habitat variables may be due to generalized habitat selection by northern rodents and the historical growth of populations in different macrohabitats since population crashes. The relations between density and bark consumption differed between the two regions, indicating a threshold density for more intense bark use. From an applied point of view, areas with seedling damage can be predicted at regional rather than at local scales.     

Regional patch dynamics of Cirsium arvense and possible implications for plant‐animal interactions

Abstract. Plant population biology considers the dynamics of plant modules within stands. However, stands themselves may have considerable regional turnover in space and time. These changes in the number, distribution and size of plant stands generate a dynamic spatial pattern with important implications for the spatial and temporal dynamics of phytophagous insects using these plants as a host. During five successive years we studied the regional distribution and patch dynamics of the creeping thistle Cirsium arvense and the distribution of associated populations of the herbivore Urophora cardui (Diptera: Tephritidae), a specialist stem gall former. The study conducted was in a 15 km² heterogeneous, agricultural area in northeastern Bavaria. The distribution of the number of plants per patch was skewed with many more small C. arvense patches than large ones. During the five years of study, there was a 50% increase in the number of C. arvense patches, and a decrease in the mean number of plants per patch (= patch size) to less than half the patch size of the first year. Whilst patch size was randomly distributed in space, patch density showed a consistent, non‐random spatial pattern. Patch density was spatially auto‐correlated, with areas of high or low patch density having a characteristic dimension of ca. 1 km. Patch size was predictable in time and appeared to be regulated by size dependent processes, with the extinction probability of a patch being negatively correlated with its size. Correlated with the decline of C. arvense patch size during the study, the occupancy and total numbers of the herbivore U. cardui had a marked decrease, suggesting that the regional distribution of the stem gall former is not only influenced by patch number but more importantly by the mean patch size. With decreasing patch sizes, U. cardui was faced with an increasingly dynamic landscape due to higher extinction rates of small patches, although the mean distance between host plant patches decreased.     

Density-dependent dispersal may explain the mid-season crash in some aphid populations

Aphid population dynamics during the season show a characteristic pattern with rapid increase in numbers at the beginning followed by a sudden drop in the middle of the season. This pattern is usually associated with predation and/or change in food quality during the summer. By developing a mechanistic model of aphid population dynamics we show that this pattern can arise from density-dependent dispersal behaviour of aphids. The dynamics produced by the model were similar to those observed in real populations of the alder aphid (Pterocallis alni). The two mechanisms required for these oscillations to arise were the perception of density through the number of contacts with other individuals and the inter-generational transfer of information (the maternal effect). Both mechanisms are examples of delayed density-dependence and, therefore, this study adds to the evidence that delayed density-dependence might cause complex population dynamics. To reproduce the seasonal dynamics of the alder aphid with the model, the maternal effect was essential, indicating that this could be an important factor in alder aphid dynamics. According to our model, external regulations (e.g., predation and/or change in food quality) were not required to explain the highly oscillatory population dynamics of aphids during a season.     

The genetic underpinnings of population cyclicity: establishing expectations for the genetic anatomy of cycling populations

Despite extensive research into the mechanisms underlying population cyclicity, we have little understanding of the impacts of numerical fluctuations on the genetic variation of cycling populations. Thus, the potential implications of natural and anthropogenically‐driven variation in population cycle dynamics on the diversity and evolutionary potential of cyclic populations is unclear. Here, we use Canada lynx Lynx canadensis matrix population models, set up in a linear stepping‐stone, to generate demographic replicates of biologically realistic cycling populations. Overall, increasing cycle amplitude predictably reduced genetic diversity and increased genetic differentiation, with cyclic effects increased by population synchrony. Modest dispersal rates (1–3% of the population) between high and low amplitude cyclic populations did not diminish these effects suggesting that spatial variation in cyclic amplitude should be reflected in patterns of genetic diversity and differentiation at these rates. At high dispersal rates (6%) groups containing only high amplitude cyclic populations had higher diversity and lower differentiation than those mixed with low amplitude cyclic populations. Negative density‐dependent dispersal did not impact genetic diversity, but did homogenize populations by reducing differentiation and patterns of isolation by distance. Surprisingly, temporal changes in diversity and differentiation throughout a cycle were not always consistent with population size. In particular, negative density‐dependent dispersal simultaneously decreased differences in genetic diversity while increasing differences in genetic differentiation between numerical peaks and nadirs. Combined, our findings suggest demographic changes at fine temporal scales can impact genetic variation of interacting populations and provide testable predictions relating population cyclicty to genetic variation. Further, our results suggest that including realistic demographic and dispersal parameters in population genetic models and using information from temporal changes in genetic variation could help to discern complex demographic scenarios and illuminate population dynamics at fine temporal scales.     

Spatial variability of an invasive earthworm (<Emphasis Type="Italic">Amynthas agrestis</Emphasis>) population and potential impacts on soil characteristics and millipedes in the Great Smoky Mountains National Park,USA

European and Asian earthworm invasions are widespread in North America. European earthworms especially are well-known to cause dramatic changes in ecosystems in northern, formerly glaciated portions of the continent, but less is known about the impacts of earthworm invasions in unglaciated areas inhabited by indigenous earthworms. We monitored fluctuations in the spatial extent of an Amynthas agrestis (Megascolecidae) population in the Great Smoky Mountains National Park in eastern Tennessee, USA. Two years of monthly growing-season observations revealed that the distribution of the earthworm population was dynamic, but overall distribution was closely linked to temperature and moisture with dramatic reductions of earthworm numbers associated with very dry conditions. In plots where A. agrestis were more often detected, we measured increased A-horizon soil aggregation and decreased thickness of the Oe/Oa-horizon. However, A. agrestis was not related to A-horizon microbial biomass, A-horizon C:N, Oi-horizon (litter) thickness, or mass of forest floor (O-horizon). Reductions in millipede species richness and density were associated with frequency of A. agrestis presence, possibly due to direct competition for food resources (Oe/Oa material). This evidence for potentially negative interactions between millipedes and A. agrestis suggests that expansion of the non-native earthworm into new habitats in the Park may alter soil physical properties and could pose a threat to native millipede diversity.     

Long-term pattern of population dynamics in the field vole from central Europe: cyclic pattern with amplitude dampening

The subject of population cycles is regarded as controversial due to a number of unsettled questions such as whether or not cyclic patterns are governed by the same processes at high and low latitudes in Europe. Recent evidence suggests that the dynamics at high and low latitudes share the common temporal pattern of vole dynamics referred to as collapsing population cycles. Despite concurrent interest, the key contention around the causal mechanisms that drive population cycles remains a hot topic in ecology. The aims of this study are to supplement information on the seasonal population dynamics of the field vole Microtus agrestis in the Czech Republic by analysing 25 years of time series data. By applying robust estimation procedures, we estimated several parameters to describe population dynamics, such as population variability, amplitude dampening, cycle period, order of the dynamics and the structure of density dependence. The parameters indicate that field vole dynamics in central Europe are highly variable, cyclic dynamics of order two, with peaks in abundance occurring regularly at intervals of 4–5 years. In addition to exhibiting population cycles, the field vole populations show a pattern of dampened amplitude as observed elsewhere in Europe, including northern latitudes. By analysing temporal trends in seasonal abundances, population growth rates and environmental temperatures, we did not obtain evidence to support the hypothesis that amplitude dampening results from the negative effect of increasingly mild winters on winter population growth rates.