Multiannual Cycles Research Articles

Multiannual Vole Cycles and Population Regulation during Long Winters: An Analysis of Seasonal Density Dependence

Multiannual Vole Cycles and Population Regulation during Long Winters: An Analysis of Seasonal Density Dependence

Body mass dynamics in the Mediterranean pine vole Microtus duodecimcostatus

The occurrence of large individuals in fluctuating populations of microtine rodents (the Chitty effect) has received considerable attention. Recent studies showed that there are no causal relationships between the Chitty effect and the multi-annual population cycles of voles and lemmings. We studied five populations of Microtus duodecimcostatus in southern France with capture-recapture methods. Mean body mass was constant in all populations. Maximum observed body mass was more variable, and slightly positively correlated with density, except in the most fluctuating population where the correlation was strong. A careful study of the occurrence of large voles in these populations showed that most were pregnant females, and that the few large males were present when density was high and sample sizes were large. Comparison with published studies indicates that the Chitty effect, though not restricted to microtines, is not a general phenomenon in small mammal populations. Our field results and laboratory data on the same species suggest that M. duodecimcostatus has a determinate body growth, contrary to some Microtus species which have an indeterminate growth.

Long-term changes (1979–1994) in two coastal benthic communities (English Channel): analysis of structural developments

The long-term variations of two coastal benthic communities (Eastern English Channel, France) were studied between 1979 and 1994 by means of factor correspondence analysis (FCA), trophic structure and rank-frequency diagrams (RFD). FCA identified periods of relative homogeneity and periods of strong variation in the structure of the two communities. The first community, established on heterogeneous sand, showed a multi-annual cycle linked to grain-size variations in the sediment. As passive supplies of organic matter were not important and suspension feeders could hardly live in these conditions, the community remained poor and stable and was dominated by deposit-feeders and carnivores. The other one, a rich and diverse mussel ( Mytilus edulis) bed, showed great variations in the abundance of the main species which generated the enrichment of the community by its suspension-feeding behaviour (biodeposition). Beyond these variations, the community remained stable until 1990 as no continuous trend or permanent change could be seen. Since 1990, no recruitment of M. edulis occurred and the relative dominance of suspension feeders, as well as the number of species, strongly decreased. During the following years, several species of tunicates (sessile suspension feeders with gregarious recruitment) recruited and partly took the ecological niche of M. edulis but they did not induce an increase of biodeposition and the previous richness was not restored. After a strong and rapid shift in the structure, a new equilibrium has been established within the community.

Cyclicity and stability of grey-sided voles, Clethrionomys rufocanus , of Hokkaido: spectral and principal components analyses

A spatio-temporal data panel of abundances of the grey-sided vole of Hokkaido (Japan) is analysed. The data consist of annual censuses of 90 populations from 1962-1992. The region studied covers approximately 160 x 220 km. The 90 time series spanning 31 years are analysed using a combination of spectral analysis, principal components analysis and graphical methods. Through this we demonstrate that vole populations in the northwestern coastal region of Hokkaido exhibit seasonal population dynamics, whereas those in the more mountainous northeastern and central regions exhibit multiannual cycles. The multiannual cycles have a period of 3.5-4 years. The findings are related to other studies from Hokkaido as well as studies of North European microtines.

Predation on Competing Rodent Species: A Simple Explanation of Complex Patterns

We extend a predator-prey model previously parameterized for voles and weasels to two prey species, a 'Microtus' (field vole) type which is competitively superior to but more vulnerable to predation than a 'Clethrionomys' (bank vole) type. The model explains four patterns in the dynamics of multispecies rodent assemblages in Fennoscandia : a predictable shift in the relative abundances of different prey species during one multiannual population cycle ; long-term (supracyclic) variation in relative prey abundances ; an association between the amplitude of population oscillations and the type of the numerically dominant prey species ; and increasing rodent species number with increasing latitude. The model results illustrate the complex and often unexpected behaviour of strongly connected multispecies assemblages, of which the Fennoscandian rodent-predator community is a prime example. Since the mid 1980s, rodent oscillations in many, though not all, parts of northern Fennoscandia have become distinctly less regular (non-cyclic), a change which is reflected in the entire animal community linked to the keystone species, the arvicoline rodents. We demonstrate that such long-term changes in the amplitude and regularity of rodent oscillations are not unexpected in multispecies prey-predator assemblages.

POPULATION CYCLES IN NORTHERN SMALL MAMMALS

I. The regular multiannual oscillations of small mammals at northern latitudes have been a subject of intensive study from the beginning of this century. The existence of a subjective bias in the research due to different schools of study together with a long series of failures and seemingly contradictory results in experiments testing a multitude of hypotheses have brought confusion to the field of study. Much of this confusion has resulted from a failure to recognize sharply the problem studied, which in turn has masked the progress made during the years. Northern mammal cycles are not a single problem but a composition of many related problems. Every problem may have a single-factor explanation, but even with a single-factor explanation, one factor is not necessarily an answer to all of the related problems. 2. At present, we can state that the cyclicity is caused by a predator-prey interaction. Both the 8-11-year and the 3-5-year cycles may be special cases of a more general cycle, most likely caused by a herbivore-resident specialist predator interaction, where the period of the cycles is determined by size-related constraints affecting the increase rate of the populations. The factors determining the amplitude of the cycles probably vary regionally and/or temporally. The operation of generalist and nomadic predators is largely responsible for the regional and geographic synchrony in cycles, although climatic factors may also contribute to the geographic synchrony. The northern distribution of animal communities; both these factors affect the density of generalist predators, which act as a stabilizing factor in the system. The age-related survival pattern seems to be mainly caused by predation, and the cyclically fluctuating reproductive output and mean body mass may be caused by changes in prey behaviour in response to fluctuating predation risk. Thus, we can already give a plausible explanation for most problems related to northern mammal cycles. 3. In all problems discussed, predation seems to be involved, and in most problems, it seems to be the factor which explains the observed patterns. Thus, as a generalization, it can be said that predation seems to be the key factor in the explanation of the northern multiannual cycles of small mammals. 4. There seems to be a linkage between diversity and cyclicity, probably because the diversity of the community (the number of prey species available) may determine the diet choice of a predator, which in turn determines whether the predators have a stabilizing or a destabilizing impact on prey populations.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid or Delayed Tracking of Multi-Annual Vole Cycles by Avian Predators?

1. The relationship between the yearly densities of avian predators and their microtine prey in western Finland was studied. Predator densities were determined by checking nest-boxes in forests [Tengmalm's owl (Aegolius funereus), hawk owl (Surnia ulula) and Ural owl (Strix uralensis)] and by searching for nests in farmland [short-eared owl (Asio flammeus), long-eared owl (Asio otus) and kestrel (Falco tinnunculus)]. Tengmalm's, Ural and hawk owls overwinter in Fennoscandia, long-eared owls are partially migratory, and short-eared owls and kestrels are migratory. 2. Prey densities were estimated by snap-trapping in spring (early May) and autumn (mid-September), and by snow-tracking in late February to early March (early spring) and late November to early December (late autumn)

Reproductive investment under fluctuating predation risk: Microtine rodents and small mustelids

We studied the reproductive investment of microtine rodents (bank vole (Clethrionomys glareolus),Microtus epiroticus andMicrotus agrestis) in western Finland under predation risk from small mustelids. During 1984–1992, the yearly mean litter size of overwintered bank voles was smaller at high least weasel and stoat densities than at low densities (close to 3 versus 4–5). In addition, the annual mean litter size of young bank voles was negatively correlated to the least weasel density. In youngM. agrestis voles, the yearly late summer litter size was negatively associated with the autumn density of small mustelids. In the crash phase of the vole cycle (1989 and 1992), we removed small mustelids (mainly least weasels) from four unfenced areas in late April to late May and studied the reproduction of voles in four removal and comparable control areas (each 2–4 km2). Reduction of small mustelids significantly increased the proportion of pregnant bank vole females, but not that of pregnantMicrotus vole females. We conclude that predation risk apparently reduced reproductive investment of free-living bank vole females; these voles appear to trade their current parental investment against future survival and reproductive prospects. Accordingly, the presence of small mustelids (or their scent) may slow down the reproductive rate of voles. As antipredatory behaviours occurred on a large scale, our results add evidence to the hypothesis that crashes in multiannual vole cycles are driven by small mustelid predators.

Successful surf-riding on size spectra: the secret of survival in the sea

All ecosystems require constituent species to survive against a backcloth of biotic and abiotic scenery. How this scenery shapes the life-history strategies of the players and how they in turn shape the scenery are important themes of the play of life. Species surviving in temperate and Arctic shelf seas do so against a scenery dominated by seasonal changes in the size-spectrum of other players. Successful survival in such an environment requires species to ride the big wave of annual productivity as it rolls through the extended size spectrum from phytoplankton to large fish. This wave flattens and broadens as it moves towards higher sizes. We speculate that in a seasonal shelf seas environment the wave shape is such that the Sheldon-Sutcliffe spectrum of equal biomass per log size interval is approximately true as an annual average although it may not be true at any particular moment in the year. Such spectra are structured by biomass being moved up the size spectrum mainly by predation processes, with growth of individuals being a second order process. However, the problem for an individual is to grow up through a size spectrum from its size at birth to its size at reproduction. Hence species need to find survival paths through the fluctuating scenery. This scenery is composed of the biomass of the prey, that of animals of a similar size, and larger predators. The paths followed dictate the life-history strategies of the species. This central problem for sea dwellers in temperate and Arctic shelf seas generates a broad similarity in the choice of life-history strategy for many key players over quite wide geographic areas of the globe. In these seas, strategies of high fecundity, high mortality and high growth rate are particularly common while strategies of low fecundity and parental care are rare for much of the size range. These seas also seem to favour longer trophic chains than terrestrial systems and either several generations per year or multiannual life cycles rather than annual cycles.

Qualitative analysis of a predator-prey system with limit cycles

Fairly regular multiannual microtine rodent cycles are observed in boreal Fennoscandia. In the southern parts of Fennoscandia these multiannual cycles are not observed. It has been proposed that these cycles may be stabilized by generalist predation in the south.

Long-term changes (1979–1990) in three benthic communities (eastern English Channel): Use of factor analysis and rank-frequency diagrams for studying structural developments

Long-term variations (1979–1990) of three benthic communities (Eastern Channel, France) were analysed by means of factor correspondence analysis (FCA), a multivariate method of ordination in reduced space, and rank-frequency diagrams (RFD). FCA distinguished periods of relative homogeneity and periods of strong variations in the structure of the communities. Two communities, the pebbles community and a rich and diverse mussel (Mytilus edulis) bed, showed great variations in the abundance of the main species (Ophiothrix fragilis in the first one, andM. edulis in the second one) which generated the enrichment of the community by their suspension-feeding behaviour. Beyond the multi-annual cycle induced by these variations, both communities seemed to be quite stable as no continuing trends could be seen. The third community, established on heterogeneous sand, also showed a multi-annual cycle linked to granulometric variations of the sediment. As passive supplies of detritus were not important and suspension feeders could hardly live in these conditions, the community stayed poor and was dominated by carnivores and deposit-feeders.

Regulation of Multiannual Vole Cycles by Density-Dependent Avian and Mammalian Predation?

A mortality factor should be density-dependent to regulate population density. In western Finland, vole (Microtus spp.) populations fluctuated in 3-4 yr cycles in a farmland area. During 1977-1987, the mortality by breeding avian predators was positively correlated with vole density in spring. Accordingly, vole mortality by avian predators directly depended on prey density, and avian predators have thus a potential to reduce the amplitude of the multiannual vole cycle

Extra-Large Body Size in California Voles: Causes and Fitness Consequences

Extra-large body size in microtine rodents is a ubiquitous feature of peak population densities, and it has been hypothesized that these giant individuals represent a genetically based morphotype that has high fitness under increasing and high densities, and may represent a key element of a genetic polymorphism driving multi-annual cycles (Chitty/Krebs model). We examine this large-size phenomenon (Chitty Effect) in the California vole utilizing three approaches : analyzing the weight distribution in a non-cyclic population over a 13 yr period with comparisons to cyclic populations, analyzing body composition, especially fat content, as a function of body size, and observing the microhabitat distribution of extra-large males in two populations, one of which cycles

Bark consumption by voles in relation to mineral contents

Recent field experiments with impregnated wooden sticks have demonstrated a pronounced use by small rodents of mineral supplies, especially sodium, and such findings seemed related to vole damage to forestry seedlings. Consumption of the bark of experimentally introduced aspen twigs and of sodium-impregnated sticks by voles (mainly or onlyMicrotus agrestis) correlated significantly on clear-cuts but not on unmanipulated abandoned fields. Such a correlation appeared when abandoned fields were cut continuously in summer. At vole peak densities, bark of pine seedlings experimentally fertilized with sodium was consumed but not bark of seedlings fertilized with calcium or control seedlings. Field pine seedlings attacked by voles had significantly higher levels of calcium, sodium, and phosphorus than the nearest untouched seedling. However, sodium and phosphorus contents correlated strongly. Sodium and calcium supply to voles in laboratory feeding trials did not diminish the moderate interest in pine bark. Such conditions are, however, assumed to mimic a situation of bark sampling in low-density populations. Sodium, and possibly also calcium, requirements are concluded to be partial determinants of the destructive bark consumption by voles at the peaks of their multiannual population cycles.

The Influence of Sex Ratio on Dispersal in the Prairie Vole, Microtus ochrogaster

The Influence of Sex Ratio on Dispersal in the Prairie Vole, Microtus ochrogaster

The first born, their dispersal, and vole cycles

On the basis of some empirical data and the existing theory of vole cycles, a new hypothesis is proposed. It explains cyclicity as an effect of obligatory dispersal of the first seasonal cohort of young (Y1) from their natal (optimal) habitats into vacant (suboptimal) habitats. This behaviour could evolve, because it increases contribution of genetic lineages with dispersing Y1, to subsequent generation. It is assumed that the dispersal of Y1 is common among vole species, it does not change during consecutive phases of the cycle, and it does not vary between cyclic and non-cyclic populations. It results in multiannual cycles only under a certain set of spatial and climatic conditions, which are discussed in a paper. Otherwise it results in annual dynamics.

Multi-Annual Cycles in Populations of Ischnura e. elegans Induced by Crowding and Mediated by Sexual Aggression (Odonata: Coenagrionidae )

L'agression sexuelle des mâles de I. e. varie avec la surpopulation. Cette aggressivite dependant de la densite constituerait une des forces qui provoque un cycle pluriannuel des populations. Au dessous d'un certain seuil de population, il existe une certaine agression sexuelle. Au dessus, le harcelement sexuel, qui provoque la chute du taux global d'accouplement, provoque une augmentation de la frequence des accouplements avec des femelles immatures. Lors du pic de densite de population, l'agressivite generale disparait et l'agression sexuelle revient a son niveau de base.

Solving the Enigma of Microtine "Cycles"

A frequently expressed opinion is that despite massive efforts the multi-annual cycles in density exhibited by many microtine rodents remain mysterious; moreover, understanding awaits completion of one or a few clever experiments or elegant mathematical models that will discredit all but the one true hypothesis. I contend in this brief, personal essay that, on the contrary, we are actually quite close to an adequate understanding of microtine cycles. This optimistic perspective requires that we adopt a multi-factorial model of vole demography, a position that allows us to comprehend how many extrinsic and intrinsic factors act synergistically and sequentially to produce the density changes we observe. I argue that this approach is not only supported by a modern systems view of reality, but is consistent with the extensive data base accumulated over a 60 year period. A multi-factorial perspective is illustrated by data for Microtus californicus , a well-studied species that shows considerable geographic and temporal variation in demographic pattern. At least eight key factors (four extrinsic and four intrinsic) are required to explain the multi-annual cycles in this species. The resulting model is complex, but not chaotic or non-testable.

Does social behavior drive vole cycles? An evaluation of competing models as they pertain to California voles

The literature contains a number of verbal and mathematical models that assert that social behavior drives the multiannual density cycles characteristic of many vole species. Many of the assumptions about vole behavior on which the models are based remain unverified. In this paper we briefly review these models and their underlying assumptions. We then use natural history data on the social behavior of California voles (Microtus californicus) to critically examine the plausibility of these assumptions. We do not attempt to explain vole cycles, but only to evaluate models that rely strongly on social behavior as a critical component. Our results indicate that (i) critical assumptions of the behavioral polymorphism, social stress, and social breakdown hypotheses are not met; (ii) some assumptions of the kin selection hypothesis are met whereas others are not; and (iii) assumptions of the habitat patchiness – dispersal hypothesis are met. However, published models of dispersal and habitat patchiness must invoke additional factors, such as resource depletion or predation, before cycles result. We conclude that social behavior is unlikely to be a driving force in the generation of cycles in the California vole. We hope that our approach will stimulate further research specifically directed at assumptions of these models.

The Role of Dispersal in Models of Small Rodent Population Dynamics

Five papers containing mathematical models of dispersal recently submitted to Oikos are basically devoted to the same topic: the consequences of dispersal on population dynamics. The conclusions reached in the papers, however, are often contradictory: social interaction affecting dispersal may produce cyclicity (Hestbeck 1988); social factors cannot destabilize population dynamics (= drive density cycles) Stenseth 1988). presaturation dispersal may contribute to the generation and maintenance of microtine cycles (Stenseth and Antonsen 1988); presaturation dispersal (resulting from territorial behaviour of mature females) cannot operate as a destabilizing factor (Stenseth et al. 1988). Bondrup-Nielsen and Ims (1988) call it saturation dispersal, but according to Lidicker's idea on dispersal (Lidicker 1975) this is presaturation dispersal, since it takes place before the population space is saturated with the species. multi-annual density cycles require heterogeneous space (Hestbeck 1988, Stenseth 1988); cyclic populations occur in more homogeneous habitats than stable populations (Bondrup-Nielsen and Ims 1988).