Morphological diversity of dental and mandibular deformities in Microtus hartingi (Rodentia, Arvicolinae)

Processes limiting the growth of cyclic vole populations have stimulated considerable research and debate over several decades. In Fennoscandia, the peak density of cyclic vole populations occurs in fall, and is followed by a severe winter decline. Food availability and intestinal parasites have been demonstrated to independently and synergistically limit wildlife populations. The purpose of this study was to directly compare competing food and parasite hypotheses on the limitation of overwintering high‐density vole populations. Moreover, we evaluated the ability of food limitation and nematode infection to interact and thereby intensify population declines. A two‐factor experiment with food supplementation and antihelminthic medication was conducted on replicated, enclosed field vole (Microtus agrestis) populations in central Finland over one full boreal winter. Population abundance, survival, and demographic attributes were monitored through live trapping. Vole feces were concurrently examined for the eggs of Heligmosomidae nemadotes and oocysts of eimerian coccidians. We found that vole density declined in all treatment groups throughout winter. However, food supplementation mitigated this decline through positive effects on reproduction, and voles in food‐supplemented populations were generally in better physiological condition than non‐supplemented voles. Food supplementation and antihelminthic treatment reduced the prevalence of Heligmosomidae nematodes, while neither food nor medication affected the prevalence of eimerians, or infection intensity of either parasite group. Although food supplementation and antihelminthic medication aided in the clearance of Heligmosomidae nematodes, their prevalence did not influence vole population growth, and this parasite group is therefore unlikely to contribute to the cyclic winter decline of boreal vole populations. Instead food resources acting alone were the primary factor limiting vole population growth.

Simple SummarySkull size and shape have been widely used to study domestic animal populations and breeds. Although several techniques have been proposed to quantify cranial form, few attempts have been made to compare the results obtained by different techniques. In this study, two morphometric methods were compared for their ability in describing external morphology. The use of geometric morphometrics combined with multivariate statistical methods is an efficient way to characterize shape and size, thus allowing greater understanding of locally adapted breeds. The Araucanian horse from Colombia inhabits the eastern plains of Arauca. The objective was to compare linear and geometric morphometrics applied to the morphology of the skull of the Araucanian horse, specifically in the basal cranial region. Twenty dry skulls of adult males were examined and were separated into two age groups based on molar eruption and wear. A photograph was taken and a 100 mm scale was placed over each sample. Linear values were obtained from the distance between homologous points from a set of reference points. For the geometric morphometrics analysis, eight paired and five mid-sagittal reference points were used. The geometric morphometric method was more discriminant than linear morphometry and it provides more information about the contour and shape of the face. Future studies should aim to understand the role of phenotypic plasticity in equine race variations and their genetic basis.Skull size and shape have been widely used to study domestic animal populations and breeds. Although several techniques have been proposed to quantify cranial form, few attempts have been made to compare the results obtained by different techniques. While linear morphometrics has traditionally been used in breed characterization, recent advances in geometric morphometrics have created new techniques for specifically quantifying shape and size. The objective of this study was to compare two morphometric methods for their ability to describe external morphology. For this purpose, 20 skull specimens of adult male Araucanian horses were examined. Two age categories were established (the “mature group”, M3 not fully erupted to moderately worn, n = 7; and the “senile group”, M3 totally erupted and highly worn, n = 13). Both methods showed that there were statistical differences between generations, but discrimination rates were different between methods with the geometric morphometric analysis obtaining a rate of 97.5%. Although linear morphometrics was found to be compatible with geometric morphometrics, the latter was better able to discriminate the two groups and it also provides more information on shape.

Meadow vole (Microtus pennsylvanicus L.) populations, feeding activity, and damage to young apple (Malus domestica Borkh.) trees were monitored by direct observation, trap counts, and a feeding activity index in different groundcover management systems (GMSs) for five years in a New York orchard. Vole populations differed greatly among GMSs, with consistently higher populations and more damage to tree trunks in crownvetch (Coronilla varia L.), hay-straw mulch, and red fescue (Festuca rubra L.)sodgrass GMSs. Vole populations were highest in the fall and lowest during the spring seasons each year. Anticoagulant rodenticides and natural predation did not result in adequate control of voles in GMSs that provided favorable habitat for nesting and feeding of this pest. The percent of soil surface vegetation coverage was not, but the amount of groundcover biomass was, a significant predictor of vole populations and damage to trees, independent of groundcover vegetation species. Trunk applications of thiram fungicide were less effective than 40-cm-high plastic mesh trunk guards, but better than no protective measures for controlling vole depredation in groundcover management systems (GMSs) with high rodent populations. A combination of late fall vole trapouts, close and consistent mowing of orchard floor vegetation, tree trunk protection with mesh guards, ample surrounding habitat for natural predators of voles, and suppression of tree row groundcover species with herbicides provided adequate control of meadow voles without the use of rodenticides at this orchard.

The role of predators, particularly small mustelids, in regulating vole (Microtus spp.) populations has been the subject of much scientific inquiry over the past several decades. From a management perspective, voles cause economic damage by feeding on seedlings planted on cutover forest land in temperate and boreal zones. Because of the close relationship between small weasels (Mustela erminea and M. nivalis) and voles, could the indirect effect of weasel scent disrupt vole populations and reduce their damage to forest plantations? This study was designed to test the hypotheses that synthetic weasel odor would: (1) reduce abundance, reproduction, survival, and movement of montane (Microtus montanus) and meadow (M. pennsylvanicus) vole populations; (2) enhance the activity of small weasels; and (3) reduce feeding damage by voles to tree seedlings. Study areas were located near Summerland and Gavin Lake in south‐central British Columbia, Canada. Vole populations were intensively live‐trapped on replicate sites from April 1994 to May 1995 during a peak year in abundance. Synthetic weasel odor was continually present on treatment sites from early summer 1994 to spring 1995. Weasel activity was measured by the number of individuals captured in live‐traps and by the number of snow tracks on control and treatment sites. Overwinter mortality to planted lodgepole pine (Pinus contorta) seedlings from vole feeding was measured on all sites in May 1995.Mean vole abundance (n = 4) was similar between control (32–121 voles/ha) and treatment (37–118 voles/ha) sites. Montane voles declined by 17–36% on treatment sites during early summer when trappability of this species declined dramatically at Summerland. This pattern was not observed for meadow voles at Gavin Lake. Recruitment of new voles was generally similar between control and treatment sites. Weasel odor had no effect on reproduction, in terms of number of successful pregnancies and index of early juvenile survival, or on total survival, movements, or body mass of voles. Activity of small weasels appeared to be higher on treatment than control sites at Gavin Lake. Weasel odor did not reduce mortality of tree seedlings caused by vole feeding.This study is the first investigation of the population responses of free‐living voles to synthetic odor of the short‐tailed weasel, a principal predator of Microtus spp. Our results demonstrate that by the time voles have reached high densities, it is too late to reduce numbers or curtail feeding damage, regardless of weasel odor‐induced antipredatory behavior or enhanced activity of predators. Application of weasel odor during the low phase of the vole population cycle would be a critical test of the hypothesis that small mustelids could lengthen the period of low vole numbers and potentially protect forest plantations from vole damage.

Synthetic mustelid semiochemicals depress survival of long-tailed vole (Microtus longicaudus) populations and feeding damage

In the fields of Northern Europe, a tundra vole (Microtus oeconomus) population explosion could be going on right now. As they hit the reproductive jackpot, their numbers rocket. But with most booms there comes a bust, and the same is true for vole populations, which can collapse suddenly and unexpectedly. Ivan Calandra, from the University of Reims Champagne-Ardenne, France, explains that the cause of these dramatic population crashes was not clear, although there was one candidate that could account for the dramatic fall from grace: the vegetation upon which the voles feast. Plants are not as vulnerable as they may at first appear. ‘It has been known for at least 30 years that plants build up silica bodies (phytoliths) in response to intense grazing,’ says Calandra. But it was not clear whether these plant defences were directly responsible for the vole's demise, and if they were, how? Were the abrasive silica structures that accumulate in plant cells wrecking the rodents' teeth or damaging their intestines, leading to starvation and population collapse?Karol Zub, Andrzej Zalewski and Paulina Szafrańska, from the Polish Academy of Sciences, decided to feed voles on two diets – one composed of pellets containing high levels of sedge, which is reinforced with silica, and another in which the sedge was replace with lower-silica grasses – to find out how different levels of silica affected the rodents’ teeth. Then Zub and Szafrańska shipped the voles’ teeth to Gildas Merceron, a CNRS Researcher at the University of Poitiers, France, where he and Calandra could look for any damage using one of only four profilometers – confocal microscopes that scan surfaces to produce 3D representations of structures – that can analyse tooth wear.However, when the duo compared the damage on the surface of teeth that the voles had used to grind their food, they were surprised to see little difference between the patterns of wear in animals on the different diets, possibly because the lab diets were not optimal. However, Calandra's Polish colleagues also knew that voles switch diet from season to season, dining on high-silica sedges in the winter and spring before supplementing the diet with softer, low-silica leafy vegetation in the summer and autumn. In addition, Calandra explains that sedges retaliate as the vole population expands by arming themselves with increased silica levels. Could the team find differences in tooth wear if they investigated the wear patterns in different populations of voles across the years and seasons as the silica levels increased in response to the expanding populations?This time the team investigated vole teeth from animals that had been trapped in the wild from the late 1970s to 2001, including a period when the population crashed in 2000 after peaking the previous year. And this time, having scanned the surface of 47 teeth, they found evidence of changes in wear pattern as the voles shifted their diet through the seasons and as the sedges became more impregnated with silica.However, the team warns that this evidence of changes in tooth wear may not account for vole population crashes, saying, ‘Tooth wear rates might seem unimportant in voles since their molars are ever-growing’. They also add that there is no clear mechanism linking the effects of tooth wear to dramatic reductions in vole population, although they suspect that if the teeth are worn unevenly, the animals may have difficulties feeding and face starvation.

Removal of all vegetation with herbicides over the total orchard floor or only in tree rows significantly reduced montane vole (Microtus montanus Peale), meadow vole (M. pennsylvanicus Ord), and northern pocket gopher (Thomomys talpoides Richardson) populations and damage. Herbicide treatments in four test orchards were carried out during May, July, and Sept. 1983 to 1985. Average overwinter abundance of voles was reduced 53% to 99% on treatment areas. Several vole populations went to extinction in the third year of herbicide treatment. Incidence of tree damage was 40.6% and 9.6% with feeding intensities of 17.2 cm2 and 0.4 cm2 of bark and tissues removed per tree on control and treatment blocks, respectively, during a peak year in abundance of voles. Pocket gopher populations and damage were significantly lower in treatment than control blocks. Deer mouse (Peromyscus maniculatus Wagner) and yellow pine chipmunk (Eutamias amoenus J.A. Allen) populations generally increased on treated areas. Use of herbicides to control orchard floor vegetation is an effective means of rodent damage control.

Influence of diversionary foods on vole ( Microtus montanus and Microtus longicaudus) populations and feeding damage to coniferous tree seedlings

Considerable controversy exists over the role of density-dependent processes in controlling animal population size. In populations that fluctuate cyclically or erratically, for example many voles and insects, theory predicts that either density-dependence is weak, or that density-dependent responses lag behind density. One key mechanism for lagged density-dependence is a delay in regeneration of food resources following heavy exploitation. Here we show that meadow vole (Microtus pennsylvanicus) populations respond immediately to high density by reducing breeding effort and hence population growth, disproving the hypothesis that density-dependence is weak. In addition, vole populations do not show a delay in growth following marked reduction in plant biomass (their source of food and cover). We conclude that intrinsic density-dependence processes tend to stabilize vole populations, and that cyclic dynamics are not caused by lagged effects of resource exploitation.

Fenced enclosures were used to simulate peak populations of montane voles (Microtus montanus) for field bioassays of a stoat (Mustela erminea) scent mixture in various controlled-release devices. A 1∶ 1 mixture of 2-propylthietane and 3-propyl-1,2-dithiolane was dispensed in capillary tubes, clay pellets (activated alumina), rubber septa, and plastic rope. Release devices were placed near, or attached to, young apple trees planted in blocks in two enclosures containing high populations of voles. The stoat scent mixture in rubber septa and plastic rope significantly reduced vole attack of trees compared with a control, pellets, and capillary tubes. In terms of complete girdling (tree mortality), this odor in septa and rope also significantly reduced feeding compared with the control, and the rubber septa formulation was more effective than either the pellets or capillary tubes. Fenced populations of voles may be used effectively to conduct field bioassays during low years in vole cycles. Variations of release devices (with this stoat scent mixture) based on rubber septa for broadcast application to depress vole population density and survival, and plastic rope attached to individual trees to generate an avoidance response, should be used for forest and agricultural crop protection.

Historically, small mammals have been focal organisms for studying predator-prey dynamics, principally because of interest in explaining the drivers of the cyclical dynamics exhibited by northern vole, lemming, and hare populations. However, many small-mammal species occur at relatively low and fairly stable densities at temperate latitudes, and our understanding of how complex predator assemblages influence the abundance and dynamics of these species is surprisingly limited. In an intact grassland ecosystem in western Montana, USA, we examined the abundance and dynamics of Columbian ground squirrels (Spermophilus columbianus), deer mice (Peromyscus maniculatus), and montane voles (Microtus montanus) on 1-ha plots where we excluded mammalian and avian predators and ungulates, excluded ungulates alone, or allowed predators and ungulates full access. Our goal was to determine whether the relatively low population abundance and moderate population fluctuations of these rodents were due to population suppression by predators. Our predator-exclusion treatment was divided into two phases: a phase where we excluded all predators except weasels (Mustela spp.; 2002-2005), and a phase where all predators including weasels were excluded (2006-2009). Across the entire duration of the experiment, predator and/or ungulate exclusion had no effect on the abundance or overall dynamics of ground squirrels and deer mice. Ground squirrel survival (the only species abundant enough to accurately estimate survival) was also unaffected by our experimental treatments. Prior to weasel exclusion, predators also had no impacts on montane vole abundance or dynamics. However, after weasel exclusion, vole populations reached greater population peaks, and there was greater recruitment of young animals on predator-exclusion plots compared to plots open to predators during peak years. These results suggest that the impacts of predators cannot be generalized across all rodents in an assemblage. Furthermore, they suggest that specialist predators can play an important role in suppressing vole abundance even in lower-latitude vole populations that occur at relatively low densities.

Patterns of population dynamics are determined by the interaction between density—dependent and density—independent processes. To examine the responsiveness of various demographic and behavioral processes to population density, we maintained replicate meadow vole (Microtus pennsylvanicus) population at low, medium, and high densities inside field exclosures in southern New York. Density was manipulated by removing subadults during biweekly live—trapping sessions. Under higher density conditions voles exhibited: (1) a truncated breeding season; (2) reduction in growth rates of individuals; (3) increase in age (but not in size) at sexual maturity; and 4) reduction in movement distances of individuals. Extremely large—bodied voles were most frequent in low—density enclosures and least common in high—density ones. Survival rates of adults were delayed density—dependent. Reproductive rates during the middle of the breeding season and survival rates of juveniles and subadults were not affected by vole density. We conclude that vole populations are stabilized by density—dependent reductions in reproductive rate and recruitment, but destabilized by density—independent survival rates of young, and by density—dependent compression on individual movements, which accommodates population growth. The time delay in the effects of density on survival of adults may provide a mechanism for vole cycles in which lagged density—dependent mortality plays a central role.

Background Small rodents and their intricate population dynamics have long been a focus of research interest, but despite birds being one of the main predators of rodents, the impact of avian predation on rodent populations remains poorly studied. To fill this gap, we conducted a field experiment in a temperate grassland, in which we excluded bird predation in populations of the root vole (Microtus oeconomus) throughout the year. Methods We covered open plots in three locations with netting and used capture-mark-recapture method to estimate the effect of this treatment on vole survival and population size, accounting for body mass and sex of individuals. Results We found that avian predation exclusion increased vole survival in winter and spring (November to May). Survival of voles with bird predation was up to 22% lower compared to plots with no bird access. Large voles faced the highest mortality during this period, and avian predation did not affect this pattern. Conclusions This research contributes to our understanding of the causes of winter vole population collapses by demonstrating that bird predation has the greatest impact on vole survival and abundance during the winter-spring period, even in the presence of persistent snow cover.

Meadow vole ( Microtus pennsylvanicus Ord) populations, feeding activity and damage to young apple ( Malus ×domestica Borkh.) trees were monitored for several years in a New York orchard by direct observation, trap counts, and a feeding activity index in various groundcover management systems (GMSs). Meadow vole population density differed among GMSs, with consistently higher densities and more trees damaged in crown vetch ( Coronilla varia L.), hay-straw mulch, and red fescue ( Festuca rubra L.) turfgrass tree-row strips. Vole densities were high in autumn and low in spring each year. Anticoagulant rodenticides and natural predation did not adequately control voles in GMSs providing favorable habitat. Groundcover biomass per m 2 was weakly correlated with vole densities in 2 of 3 years, while the percentage of soil surface covered by vegetation was not significantly correlated with vole populations. Applications of thiram fungicide in white latex paint were better than no protection, but less effective than 40-cm-high plastic-mesh guards for preventing vole damage to tree trunks. A combination of late-autumn trapping, close and consistent mowing of the orchard floor, trunk protection with mesh guards, contiguous habitat for vole predators, and herbicide applications within the tree rows provided effective control of meadow-vole damage to trees at this orchard during 3 years without applications of rodenticide baits. Chemical names used: Tetramethylthiuram disulfide (thiram)

1. The relatedness of individuals can influence their behaviour and changes in the degree of female relatedness in spring may influence the demography of vole populations (Lambin & Krebs 1991a). Here we report on an experiment testing the effect of relatedness on the demography of Townsend's vole (Microtus townsendii) populations (kin and non-kin treatments) over three consecutive springs. 2. Most nestlings were marked before weaning such that we knew which recruits were related to one another and to which adult female. The average size of matrilineal groups was experimentally manipulated by selectively removing voles of known origin and by preventing predation by birds of prey. 3. Nearest neighbours had their nests closer to one another on the kin treatment, but there were no differences in home range size between treatments. Home-ranges of females present on both treatments were smaller in a spring of high density than in the springs with lower density. 4. Female survival was better on the kin treatment. Within the kin treatment, females with at least one first degree relative as a neighbour survived better than females without such a relative. No such difference was observed within the non-kin treatment. 5. Females in the kin treatment gave birth to their first spring litter 5-7 days later than females in the non-kin treatment, possibly as a consequence of space sharing with related neighbours. The weaning success of the first spring litter was significantly higher on the kin tratment than on the non-kin treatment, but there were no differences in the weaning success of females with and without related neighbours within treatments. The presence of immigrant females on the non-kin treatment and not on the kin treatment may have caused the difference in weaning success between the treatments. 6. We conclude that female relatedness influences the pattern of space use and the survival of females in spring. The presence of immigrant females attempting to establish in the population has a pronounced effect on the weaning success of residents.