Isotopic partitioning by small mammals in the subnivium

In the Arctic, food limitation is one of the driving factors behind small mammal population fluctuations. Active throughout the year, voles and lemmings (arvicoline rodents) are central prey in arctic food webs. Snow cover, however, makes the estimation of their winter diet challenging. We analyzed the isotopic composition of ever‐growing incisors from species of voles and lemmings in northern Finland trapped in the spring and autumn. We found that resources appear to be reasonably partitioned and largely congruent with phylogeny. Our results reveal that winter resource use can be inferred from the tooth isotopic composition of rodents sampled in the spring, when trapping can be conducted, and that resources appear to be partitioned via competition under the snow.     

Seasonal dynamics of a flea number (Siphonaptera) on the common shrew (Sorex araneus) in the north part of the Novgorod oblast

In the course of 5-year stationary investigations of the common shrew Sorex araneus in the north part of the Novgorod oblast, 12 flea species have been recorded on this host. Among them, Palaeopsylla soricis and Doratopsilla dasycnema are specific parasites of small insectivores, including the common shrew. Hystrichopsylla talpae is a polyxenous species, parasitizing both rodents and insectivores. Other 9 flea species are not common parasites of S. araneus and apparently have come to this host from other mammal species inhabiting the forest biotopes in the area of investigation. P. soricis and D. dasycnema have similar phenology of parasitism. These fleas appear in spring (April), are present during summer and autumn and disappear in winter. During a year, the abundance of these species shows three pikes, which correspond to three generations: spring (April), summer (June-July) and autumn (September-October) generation. The first species dominates in spring (April-May) and in the autumn-winter period, while the second species predominates in summer. These two species comprise over 90% of total number of fleas collected and determine general dynamics of the flea number on the shrews; during the year the flea number has a sinusoidal increasing from spring to autumn and minimum in winter.     

Population dynamics of a diverse rodent assemblage in mixed grass-shrub habitat, southeastern Colorado, 1995-2000

We followed seasonal and year-to-year population dynamics for a diverse rodent assemblage in a short-grass prairie ecosystem in southeastern Colorado (USA) for 6 yr. We captured 2,798 individual rodents (range, one to 812 individuals per species) belonging to 19 species. The two most common species, deer mice (Peromyscus maniculatus) and western harvest mice (Reithrodontomys megalotis), generally had population peaks in winter and nadirs in summer; several other murid species demonstrated autumn peaks and spring nadirs; heteromyids were infrequently captured in winter, and populations generally peaked in summer or autumn. Inter-annual trends indicated an interactive effect between temperature and precipitation. Conditions associated with low rodent populations or population declines were high precipitation during cold periods (autumn and winter) and low precipitation during warm periods (spring and summer). Severity of adverse effects varied by species. Heteromyids, for example, were apparently not negatively affected by the hot, dry spring and summer of 2000. Cross-correlations for the temporal series of relative population abundances between species pairs (which are affected by both seasonal and interannual population dynamics) revealed positive associations among most murids and among most heteromyids, but there were negative associations between murids and heteromyids. These results have important implications for those attempting to model population dynamics of rodent populations for purposes of predicting disease risk.     

Evidence for different bottom-up mechanisms in wood mouse ( Apodemus sylvaticus ) and bank vole ( Myodes glareolus ) population fluctuations in Southern Norway

Animals that feed on forest tree seeds, such as Apodemus mice, increase in number after a mast year. At high latitudes, there is a similar delayed response by Myodes voles to high seed crops of bilberry (Vaccinium myrtillus), but here the mechanism is hypothesised to be increased forage quality, caused by a trade-off between reproduction and defence in the plants. Both Apodemus mice and Myodes voles eat berries, but only the latter feed on bilberry plants. Hence, only Myodes voles are predicted to respond to bilberry peak years. A second prediction is that the effect should last longer than any possible direct impacts of bilberries, because the plants would not be able to rebuild their defence until the succeeding summer. During a 21-year snap-trapping study of small rodents in Southern Norway, the spring population of bank vole (Myodes glareolus) was positively related to a bilberry seed index of the previous year, indicating increased winter survival, whereas the wood mouse (Apodemus sylvaticus) was not affected. Also the succeeding autumn population index of the bank vole was positively related to the bilberry index of the previous year, even when controlling for spring population levels. The wood mouse population responded to mast years of sessile oak (Quercus petraea), whereas seeds of Norway spruce (Picea abies) seemed to have some impact on both species. It is concluded that these rodents are mainly limited from below, but by different mechanisms for the granivorous and the herbivorous species.     

The bionomics of the free-living larvae and the transmission of Dictyocaulus filaria between lambs in North-East England.

The bionomics of the free-living larvae of Dictyocaulus filaria on pasture, and the transmission of infection between lambs, were studied during different seasons of the year in North-East England. The rate of development of first-stage larvae to the third stage took 4-9 days in late spring and summer, 1 1/2-4 weeks in autumn and 5 1/2-7 weeks in winter. The proportion of first-stage larvae developing to the third stage ranged from 10-28% in autumn and winter, and 2-25% in spring and summer. The rate of mortality of the third-stage larvae was approximately logarithmic in nature, although the survival time was shorter in spring and summer than in autumn and winter. Third stage larvae were able to survive from autumn until the spring of the following year in sufficient numbers to perpetuate transmission but not to cause clinical disease. In a transmission study, the survival of the infective larvae on the experimental plot was poor in summer, but the larval population increased in the autumn and then declined slowly throughout the winter. Infection in the susceptible lambs was related to the level of infection on the herbage increasing in severity from early summer to late autumn. However, those lambs infected in the summer were resistant to the heavy autumn challenge of larvae on pasture.     

Activity patterns and interactions of red foxes (Vulpes vulpes) in Oxford city

The activity patterns of red foxes ( Vulpes vulpes L.) living and breeding in urban areas of Oxford, and the interactions between individuals, were analysed from detailed radio-tracking data on 17 adults. Foxes were nocturnal and active during the night for a mean of 6h 52min min, irrespective of the time of year. The number of active/resting periods increased in autumn and winter, and in winter and spring the night was characteristically divided into several short cycles of activity of 2–2 1/2 h each, interspersed with similar periods of rest. The foxes occupied mutually exclusive group ranges and group members remained within 50m of each other for up to one-third of the time spent active at night. The implications of fox spatial relationships for rabies transmission are discussed.     

Population structure and dynamics of sympatric Apodemus species (Rodentia: Muridae)

This paper describes the population biology of sympatric populations of Apodemus sylvaticus and A. flavicollis in western England. Annual changes in population siie closely resembled those seen in allopatric populations such that simultaneous peaks in number occurred only in autumn and early winter. Numbers of A. sylvaticus were low and stable in early summer increasing rapidly in late summer and autumn and remaining high throughout winter before a sharp decline in spring. Numbers of A. flavicollis increased after the start of reproduction and continued to rise throughout summer and autumn. The period of major decline of this species was during early winter. Densities of A. sylvaticus and A. flavicollis were comparable with those cited in allopatric studies. Spring populations of both species consisted of cohorts first appearing in the late summer and autumn of the previous year. Few individuals present in spring survived the summer. Reproduction of A. flavicollis commenced four to six weeks before that of A. sylvaticus . Seasonal variation in mean weight of adult males and females also indicates that those changes, due to the acquisition of secondary sex characteristics and reproductive maturity, occur earlier in A. flavicollis than in A. sylvaticus . Data presented contain no evidence of interspecific competition and it is concluded that interspecific differences, chiefly asynchrony in reproduction and annual population cycles, contribute to their stable coexistence.     

Modeling Seasonal Rabies Epidemics in China

Human rabies, an infection of the nervous system, is a major public-health problem in China. In the last 60 years (1950–2010) there had been 124,255 reported human rabies cases, an average of 2,037 cases per year. However, the factors and mechanisms behind the persistence and prevalence of human rabies have not become well understood. The monthly data of human rabies cases reported by the Chinese Ministry of Health exhibits a periodic pattern on an annual base. The cases in the summer and autumn are significantly higher than in the spring and winter. Based on this observation, we propose a susceptible, exposed, infectious, and recovered (SEIRS) model with periodic transmission rates to investigate the seasonal rabies epidemics. We evaluate the basic reproduction number R ₀, analyze the dynamical behavior of the model, and use the model to simulate the monthly data of human rabies cases reported by the Chinese Ministry of Health. We also carry out some sensitivity analysis of the basic reproduction number R ₀ in terms of various model parameters. Moreover, we demonstrate that it is more reasonable to regard R ₀ rather than the average basic reproduction number [`(R)]₀\bar{R}_{0} or the basic reproduction number [^(R)]₀\hat{R}_{0} of the corresponding autonomous system as a threshold for the disease. Finally, our studies show that human rabies in China can be controlled by reducing the birth rate of dogs, increasing the immunization rate of dogs, enhancing public education and awareness about rabies, and strengthening supervision of pupils and children in the summer and autumn.     

Ecology of wildlife rabies in Europe

• 1 The number of wildlife rabies cases has increased in Europe in recent years. We review the epizootiology of wildlife rabies in Europe, paying special attention to recent changes to the situation of two important vector species: the red fox and the raccoon dog. Red fox Vulpes vulpes has been the main vector of rabies since 1945, but the number and proportion of raccoon dog Nyctereutes procyonoides cases has rapidly increased during the past few years, particularly in north‐eastern Europe.
• 2 The transmission rate (average number of susceptible animals infected by each rabid animal) is critical for rabies spread and is partly determined by population density. Both raccoon dogs and foxes live in pairs. Foxes also live in family groups. Pairs and groups share their territories. Home range size usually correlates negatively with population density. Fox home ranges are 50–1500 ha, those of raccoon dogs 150–700 ha. The threshold value for rabies spread among foxes is estimated to be 0.63 individuals/km². Although fox density in eastern and northern Europe may be lower than this, the pooled density of foxes and raccoon dogs exceeds the threshold density.
• 3 Animal movements, especially dispersal of young, pose a risk for rabies spread. Although the likelihood of an epizootic is highest where fox and raccoon dog densities are highest, rabies may spread fastest where population densities are lower, because dispersal distances tend to correlate negatively with population density.
• 4 Oral vaccinations have been more effective in rabies control than culling foxes. Where two vector species exist, vaccination should be conducted twice a year, because most raccoon dogs disperse in autumn but some foxes do not disperse before mid‐ or late winter.
• 5 New rabies models, based on two vector species and their interaction, and which take into account the hibernation period of raccoon dogs, are needed for north‐eastern Europe.

     

Density-dependence vs. density-independence - linking reproductive allocation to population abundance and vegetation greenness

1. Recent studies have shown that optimal reproductive allocation depends on both climatic conditions and population density. We tested this hypothesis using six years of demographic data from eight reindeer (Rangifer tarandus) populations coupled with data on population abundance and vegetation greenness [measured using the Enhanced Vegetation Index (EVI)]. 2. Female spring body mass positively affected summer body mass gain, and lactating females were unable to compensate for harsh winters as efficiently as barren ones. Female spring body mass was highly sensitive to changes in population abundance and vegetation greenness and less dependent on previous autumn body mass and reproductive status. Lactating females were larger than barren females in the spring. Moreover, female autumn body mass was positively related to female autumn body mass and reproductive success and was not very sensitive to changes in vegetation greenness and population abundance. 3. Offspring autumn body mass was positively related to both maternal spring and autumn body mass, and as predicted from theory, offspring were more sensitive to changes in vegetation greenness and population abundance than adult females. A lagged cost of reproduction was present as larger females who were barren, the previous year produced larger offspring than equally sized females that successfully reproduced the previous year. 4. Reproductive success was negatively related to female autumn body mass and positively related to female spring body mass. Moreover, females who successfully reproduced the previous year experienced the highest reproductive success. The fact that negative density-dependence was only present for females that had successfully reproduced the previous year further support the hypothesis that reproduction is costly. 5. This study shows that female reindeer buffer their reproductive allocation according to expected winter conditions and that their buffering abilities were limited by population abundance and a lagged cost of reproduction and enhanced by vegetation greenness.     

Influence of weather factors on population dynamics of two lagomorph species based on hunting bag records

Weather conditions can have a significant influence on short-term fluctuations of animal populations. In our study, which is based on time series of hunting bag records of up to 28?years from 26 counties of The Netherlands and Germany, we investigated the impact of different weather variables on annual counts of European rabbits (Oryctolagus cuniculus) and European hares (Lepus europaeus). Overall, the long-term dynamics of both species could be described by higher-order polynomials. On a smaller time scale, the number of European hares shot was lower in years with higher amounts of precipitation during late summer/autumn, and the number of European rabbits shot was lower in years with high precipitation in spring of the respective year. We suggest that rainy weather conditions might have lowered the survival of young rabbits in spring and might have generally facilitated the outbreak or spread of diseases in rabbits as well as in hares, specifically in autumn. In addition, the results showed a time-delayed, interactive effect between precipitation in spring and winter weather on European rabbit dynamics: rabbit numbers were limited by low temperatures of the prior winter season, but only when precipitation was high during spring of the previous year. The latter result might be explained by the lowering effects of rainy spring weather on the body condition of the animals, leading to higher sensitivity to harsh winter conditions. In conclusion, our study provides evidence for the impact of weather conditions on the population dynamics of both study species and particularly highlights complex interactions between the prevailing weather conditions during different seasons in the European rabbit.     

Morphological and Functional Changes in Small Mammals Exposed to Technogenic Pressure

The effect of technogenic pressure on the weight indices of major endocrine glands responsible for adaptation to adverse environmental conditions was studied in murine rodents. The data obtained in technogenic and natural ecosystems were compared. Using the method of morphophysiological indicators, it was shown that exposure to heavy pollution (emissions from lead and zinc smelters) caused a significant increase in the adrenal index of virgin animals (0.45–0.56 mg/g, compared to 0.15–0.33 mg/g in the norm); conversely, the liver index decreased to 39.0–49.0 mg/g (below the lower limit of the norm). The simultaneous increase in the adrenal index and decrease in the liver index of rodents in autumn are indicative of exhaustion, which leads to an energy breakdown and mass mortality. The core of the population in the next spring consists of juveniles coming from the neighboring biotopes with more favorable conditions. Thus, under the effect of technogenic pressure, a temporary population of small mammals is formed every year.     

Seasonal population dynamics of Eisenia fetida (Savigny, 1826) (Oligochaeta, Lumbricidae) in the field

In order to assess the response of epigeic earthworms to seasonal changes we monitored the population dynamics of Eisenia fetida (Oligochaeta, Lumbricidae) in a manure heap in the field during a year. Earthworms were hand-sorted from five 0.25 x 0.25 x 0.20 m blocks around the heap in November (autumn) 1999 and in January (winter), April (spring) and August (summer) 2000 to determine earthworm population dynamics. Earthworms of each block were classified into different age classes: mature, preclitellate, juvenile, hatchling and cocoon, and afterwards counted and weighed. Seasonality had a strong effect on the density, biomass and reproductive activity of the population. The population of E. fetida was characterized by a high density of individuals and the predominance of mature individuals throughout the year. Maximum density, mating activity and size of cocoons were achieved in spring, but there were not changes in the number of cocoons per mature earthworm throughout the year. Unexpectedly, the smallest cocoons were produced in winter by the largest individuals. These results suggest that E. fetida is able to allocate resources to growth and/or reproduction in response to environmental fluctuations.     

Seasonal changes of semen quality and freezability in Franches-Montagnes stallions

The objective of this study was to investigate seasonal changes of semen quality parameters in Franches-Montagnes stallions and to compare the freezability of ejaculates collected in autumn and winter. Experiments were performed using 15 stallions from the National Stud Farm in Avenches (Switzerland). Ejaculates were collected and evaluated every month during 1 year as well as cryopreserved in autumn and winter (September to February). In fresh semen the gel-free volume, concentration, motility and morphology (normal sperm, major defects, vacuoles and acrosome defects) were evaluated and in frozen-thawed semen the motility as well as the viability (SYBR-14/PI) were performed. To analyse seasonal differences four periods of 3 months each were defined as autumn (September, October, November), winter (December, January, February), spring (March, April, May) and summer (June, July, August). During the 1-year experiment all fresh semen quality parameters demonstrated a clear seasonal and individual pattern. The gel-free volume was significantly (P<0.05) higher in spring and summer compared to autumn and winter while sperm concentration was significantly (P<0.05) lower in spring than at any other time of the year. Total sperm number was significantly (P<0.05) higher and sperm motility significantly (P<0.05) lower in summer than in other seasons. Regarding sperm morphology, normal sperm was significantly (P<0.05) higher in autumn than in winter and summer and major defects were lowest (P<0.05) in autumn. In frozen-thawed semen motility was significantly (P<0.05) improved in the ejaculates collected in autumn compared to winter, while viability showed no obvious differences. Our results clearly demonstrate that individual and seasonal differences occurred in semen quality of Franches-Montagnes stallions. Ejaculates collected in autumn (September, October, November) demonstrated good quality, especially regarding sperm morphology, and were more suitable for cryopreservation because of better motility in frozen-thawed semen collected during autumn than in winter.     

Seasonal variability of macroinvertebrate assemblages in two regions of South Africa: implications for aquatic bioassessment

Seasonal variability of macroinvertebrate assemblages was examined in two regions of South Africa: Western Cape and Mpumalanga. Sampling was undertaken at reference sites using the rapid bioassessment method SASS4 (South African Scoring System, Version 4). This study examined the influence of sampling season on the occurrence of taxa, macroinvertebrate assemblages and SASS scores. In the Western Cape a few taxa were more common at certain times of the year, and multivariate analysis of macroinvertebrate assemblages showed that assemblages grouped by season. The number of taxa and the Average Score per Taxon (ASPT) were significantly different among seasons in the Western Cape, with fewer taxa recorded in winter compared to summer, and significantly higher ASPT values recorded in winter and spring than summer and autumn. Whereas more taxa were recorded in autumn than in spring, a higher proportion of sensitive and high-scoring taxa were recorded in spring. In Mpumalanga macroinvertebrate assemblages did not group by season, and differences in SASS scores were not significant, although more taxa were recorded in winter than in spring or autumn, and ASPTs were slightly higher in winter than in spring. Results are discussed in relation to ecological reference conditions and the interpretation of bioassessment data.     

Performance of the green spruce aphid, Elatobium abietinum (Walker) on previously defoliated Sitka spruce

Abstract 1 The green spruce aphid, Elatobium abietinum, is an important defoliator of Sitka spruce in the U.K. However, it is usual for years in which high E. abietinum populations occur to be followed by a year with low aphid densities. The possibility that the performance of E. abietinum is reduced on previously infested Sitka spruce, and that this is the cause of year‐to‐year fluctuations in population density, was investigated by comparing population development and the growth rate of individual aphids on experimentally defoliated trees. 2 Separate experiments were performed to determine whether aphid performance was reduced either in the autumn immediately after defoliation in the spring, or was reduced in the spring of the next year. Different rates of initial defoliation on trees used to test aphid performance were created by artificially infesting the trees with aphids in the spring before the experiments, and varying the time of infestation. 3 Population development and the mean relative growth rate (MRGR) of individual aphids on previously defoliated and undefoliated Sitka spruce did not differ significantly in the spring of the next year. No differences were observed in the nutrient content of the 1‐year‐old needles of previously defoliated or undefoliated trees at this time. 4 In the autumn and winter immediately after spring defoliation, aphid MRGR was significantly higher on trees that had been heavily defoliated earlier in the season compared with trees that had been lightly defoliated. However, the difference in MRGR decreased over the winter period. Nitrogen, phosphorous and potassium concentrations were 9.4–12.2% higher, at the beginning of the autumn, in the current year needles of heavily defoliated trees than in the current year needles of lightly defoliated trees. 5 The experiments indicate that high populations of E. abietinum in the spring do not induce any defensive mechanisms in Sitka spruce that adversely affect subsequent generations of the aphid. By contrast, the results suggest that high spring densities of the aphid improve the nutritional quality of the current year's foliage for autumn generations.     

Observational evidence of risk-sensitive reproductive allocation in a long-lived mammal

Organisms should adopt a risk-sensitive reproductive allocation when summer reproductive allocation competes with survival in the coming winter. This trade off is shown through autumn female body mass, which acts as an insurance against unpredictable winter environmental conditions. We tested this hypothesis on female reindeer in a population that has experienced a time period of dramatic increase in abundance. Environmental conditions during winter were fairly stable (with the exception of 1 year). We conclude that increased population abundance (perhaps in interaction with winter environmental conditions) could have represented a worsening of winter environmental conditions as both autumn offspring and spring female body mass decreased during the course of the study. Moreover, we found that the cost of reproduction was related to environmental conditions as: (1) autumn body mass was larger for barren than for lactating females, and this difference was temporally highly variable; (2) lactating females produced smaller offspring than barren ones in the following year; and (3) reproductive output (offspring size) decreased over time. We also found evidence of quality effects as lactating females had a higher reproductive success in the following year. In sum, a worsening of winter conditions lead to: (1) decreased reproductive output; (2) lowered autumn body mass for lactating females; and (3) increased body mass for barren females. Since females reduce their reproductive allocation as winter conditions becomes more severe, we conclude that reindeer have adopted a risk-sensitive reproductive allocation.     

A time series and geographical analysis of population dynamics of the red-backed vole in Hokkaido,Japan

Summary A time series and geographical analysis of the long term (25-years and 16-years) census data of the red-backed vole, Clethrionomys rufocanus bedfordiae, populations in Hokkaido, Japan was carried out. Eighty seven populations from all over Hokkaido were grouped into the following 4 types according to their flucturation patterns: type A: low density-constant type; type B: medium density-gradual increase type; type C: medium density-wavy change type; type D: high density-large amplitude type. The border between type B and type C was not clear. Although the distribution of the fluctuation types did not show any geographical cline, the high density type (type D) occurred in limited areas where the winter was severe and spring came later and almost all the populations in the Oshima peninsula were the low density type (type A). The most common type of population in Hokkaido, type C, greatly fluctuated from year to year with the maximum density level/the minimum one being over 10. The periodicity of the peak years was not statistically significant, although peaks often occurred at 3 or 4 year intervals. The population grew from spring to autumn in almost all years so that the pattern of the seasonal change was qualitatively constant. The population density levels in spring were not significantly different between peak years and others, while those in autumn were greatly different between them, so that the population growth rates from spring to autumn were variable from year to year. This differential pattern was also found between high and low density areas.     

The dynamics of Wood mouse (Apodemus sylvaticus) populations in the Camargue

The ecology of two monospecific populations of Wood mice ( Apodemus sylvaticus ) was studied using mark-recapture techniques in a high grassland and a low grassland of the Camargue. Annual changes in population size resembled the classical pattern of variation for European Wood mice. Numbers were low in summer, and peaks in numbers occurred in autumn and decreased sharply in early spring. However, the densities of the populations in winter were higher than many other European Wood mouse populations. The Wood mouse population in the high grassland area was dense and showed regular variations throughout the year. In the low grassland area, the population was lower and showed less regular variations, especially in winter, coinciding with soil flooding. Reproduction-related differences between the demographic parameters of the two sexes pointed to the use of differential space use strategies by males and females.