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.     

Sex-chromosome heterochromatin variation in the wood mouse,Apodemus sylvaticus

Variation in heterochromatin content, as revealed by G- and C-banding, was studied in the sex chromosomes of the wood mouse, Apodemus sylvaticus. The sex-chromosome heterochromatin was also characterized by DAPI staining. Variation in sex chromatin was recorded in extremely large (giant) sex chromosomes in certain individuals and populations. In some individuals, the Y chromosome was the largest element of the complement. Different variants of both the X and Y chromosomes were found within a single population. The variation is therefore a type of population polymorphism and should not be used for taxonomic discrimination.     

Some population dynamics of the Bank vole, Clethrionomys glareolus and the Wood mouse, Apodemus sylvaticus in mixed woodland

The population dynamics of Clethrionomys glareolus Schr.and Apodemus sylvaticus (L.) in mixed woodland in County Durham, were studied from March 1963 to January 1965. Two areas of 0.9 ha (2.25 acres) each were trapped monthly and information was obtained on population size, reproduction, survival and growth from marked animals.
Clethrionomys populations increased from June to an autumn peak; then declined, at first rapidly, but then more slowly in winter, before reaching a spring trough. The breeding season of Clethrionomys was from May to December; juveniles were caught from mid-June to December. Survival was in general poor during the breeding season but good at other times. Survival of young born early in the summer was particularly good on one of the areas and some individuals lived long enough to breed in two successive years. On both areas young born early in the year matured rapidly and bred in the year of their birth. Young born in late summer and early autumn ceased growing at a weight of about 14.5 g, remained immature, and formed the bulk of the overwintering population. Growth was completed at the time of sexual maturation the following spring.
Trapping failed to provide adequate samples of juvenile Apodemus in summer to account for subsequent recruitment. The possibility that a substantial proportion of the adult population of this species was also either trap shy or had emigrated temporarily is discussed. Breeding occurred from April until the following January, but the numbers trapped remained very low throughout the early months of the breeding season. Large scale recruitment of young fecund animals into the trap-revealed population occurred during the autumn. Apodemus males continued to grow rapidly during the winter.     

Ovarian interstitial tissue of the wood mouse, Apodemus sylvaticus

The ovary of the wood mouse contains an unusually large amount of interstitial tissue which appears to develop from undifferentiated cells of the ovarian stroma and also by transformation of theca or granulosa cells of atretic follicles. The cells are characterized by the presence of smooth endoplasmic reticulum, rounded mitochondria with tubular cristae, and abundant, large (1.5 micron diameter) lipid droplets containing cholesterol and its esters. 3 beta-Hydroxysteroid dehydrogenase activity occurs in the interstitial cells. Their ultrastructural characteristics suggest that the cells are not very active, but their abundance and the considerable amount of steroid hormone precursor they contain may compensate for low secretory activity and they may be an important and (from a developmental viewpoint) early source of steroid hormone.     

Studies on the helminth parasites of the Long-tailed field mouse, Apodemus sylvaticus sylvaticus from Wales

The incidence and degree of infestation of the Long-tailed field mouse, Apodemus sylvaticus with helminth parasites have been studied from a rough grassland and woodland area, Aberystwyth and from Skomer Island in Wales. With few exceptions, adult mice were more heavily infested than juveniles.
In Aberystwyth, where the composition of the helminth fauna was found to be more varied than that from the island of Skomer, three species of helminths, one digenean and two nematodes, showed evidence of seasonal variation in the degree of infestation of mice. The factors affecting this fluctuation in parasite numbers throughout the year are discussed.
It is suggested the distribution of helminths in the mouse population may be represented by a negative binomial, indicating that the infective eggs, larvae or intermediate hosts of the respective helminths were aggregated in their distribution in the selected areas of study.     

Notes on the activity of wild Wood mice, Apodemus sylvaticus, in artificial enclosures

The activity of Wood mice, Apodemus sylvaticus , was monitored by light beams and photoelectric cells placed in runways. In outdoor enclosures it is shown that weather and time of the year both modify the activity pattern. The nature of the activity in an indoor residential maze is described and the effects of a food shortage noted.     

Observations on trap response in confined populations of Wood mice, Apodemus sylvaticus

Three laboratory studies of trap response in confined Wood mouse populations at various densities and using various densities of traps are described. Individual variation in trap response and whether captures were made at random are examined, and factors which affect trap response in confined populations of mice are discussed.     

Seasonal variations in infestations of parasites in a Wood mouse Apodemus sylvaticus population in the West of Ireland

Seasonal variation in most of the metazoan parasites of a Wood mouse population was investigated by a statistical analysis of their frequencies in 11 samples of about 30 mice trapped regularly over one year. Numbers of the flea Ctenophthalmus nobilis , most mesostigmatid mites and the beetle Leptinus testaceus were correlated with breeding in the mouse population and may have been directly linked with it as all ofthese arthropods are common in Wood mouse nests. The tick Ixodes ricinus was abundant over the summer but scarce in winter. Its preponderance on male hosts is doubtless because they cover more ground than females. Flukes were commonest in summer, probably as a result ofthe period of intensive feeding on invertebrates by the mice which usually occurs in early summer. Female mice were more heavily infected, perhaps because of their increased food requirements in the breeding season. Abundance of flukes declined with the turnover in the mouse population in autumn. The infestation pattern of the nematode Capillaria muris sylvatici is similar and the possibility of an invertebrate vector is discussed. While older mice were generally more heavily infected with helminths than were young, this was least marked in the tapeworm Cataenotaenia lobata (which most likely has a mite as an intermediate host and may be picked up as soon as juveniles start grooming) and the roundworm Syphacia stroma (eggs of which are almost certainly transferred by body contact between hosts)     

Geographical variation in body size of the Wood Mouse Apodemus sylvaticus L.

This paper analyses the geographical variation in body size of the Wood Mouse. A size increase is observed from north to south, contrary to Bergmann's rule. This increase is related to regions of sympatry and allopatry with the Yellow-necked Mouse, a closely related, potentially competing species. The possibility of character displacement playing an important role in determining the observed variation in body size is discussed.     

Growth in field and laboratory populations of Wood mice (Apodemus sylvaticus)

Intrinsic growth rate and asymptotic body weight parameters were estimated for two laboratory and three field populations of the Wood mouse, Apodemus sylvaticus , using a logistic model fitted by an ordinary least squares method. The data upon which the growth equations were based were differences in body weight for individual animals between sampling occasions. Suckling mice in one of the laboratory studies suffered high mortalities and poor body growth which was related to disturbance to the mothers and their young during examination. Growth in weaned mice appeared normal and was compared with growth in autumn and winter populations of wild mice with poor and good natural seed supplies. Males tended to have higher growth rates, and to a lesser extent, higher body weight asymptotes than females in all groups. Growth rates were highest in the autumn field population with a good seed supply; differences between the other groups were less marked. These results are discussed and it is suggested that, despite the approximations inherent in the method, the method will be a useful tool for studying the the productivity of wild populations of small mammals.     

Population structure and dynamics of wood mouse Apodemus sylvaticus in Iceland

Five-year-studies of two wood mouse populations (Apodemus sylvaticus L.) were carried out outside the village Vík. S. Iceland, and in a birch forest close to the lake Mývatn, N. Iceland. The population at Vík was studied on a 1.10 ha grid on a slope covered with Angelica archangelica L., the seeds of which constituted a major food resource for the mice. Altogether 948 individuals were caught, marked and followed during 1973–1978. No other free-living small mammals occur in Iceland, and predator pressure is low and considered non-existent on the Angelica slope. The population density was extremely high; highest autumn density recorded was 150 ind ha^?1. Like other Apodemus populations, the one at Vík showed a typical seasonal pattern in numbers: a winter decrease, relatively stable numbers in late summer, and an autumn peak. Breeding started in late April or early May and ended in late September; no winter breeding was observed. Three or four litters were produced, and the last litter(s) of the season greatly contributed to the autumn increase. The output of young per reproductive female throughout the year was negatively correlated with spring density, and autumn peak density with the number of females in August. Also overwinter success and weight changes appeared to be associated with population density (and weather). Survival rates did not vary much between years and seasons and were consistently rather high. Autumn survival of juveniles was positively correlated with mean minimum temperatures. Juvenile survival was, at least at times, negatively affected by the presence of adult males. Trapping outside the main grid did not indicate any marked dispersal, though some immigration to the grid must have occurred, especially in spring and early summer. Among the factors governing the population density and dynamics of wood mouse at Vík we emphasize the absence of interspecific competition and predation, the rich and dependable food resources (mainly Angelica seeds), the mild (though moist and windy) climate, the shelter of dense Angelica stands, the abundance of crevices (e.g. nest-sites), and the social interactions. The birch forest in northern Iceland was low productive and the wood mouse population differed from the Vík population by exhibiting low density, short breeding season, and high vagility; characteristics we consider to be representative for most Apodemus populations in Iceland.     

The ovary of the wood mouse, Apodemus sylvaticus, during late pregnancy and lactation

Female wood mice, Apodemus sylvaticus, were killed on day 18 of pregnancy (P 18) and on days 0, 3, 6, 9, 12, 15, and 18 of lactation (L 0, L 3, L 6, L 9, L 12, L 15, and L 18 respectively), and the ovaries were studied. The weight of the ovaries was recorded at dissection. The corpora lutea and the follicles of the right ovary were counted and measured, and the appearance of the interstitial tissue was noted. A decline in weight from day P 18 to day L 6 coincided with a decrease in mean diameter of the corpora lutea. The mean number of corpora lutea did, however, not change over the period. The corpora lutea present throughout lactation were probably from the gestation period; the females did not appear to ovulate post-partum. The interstitial tissue was not affected, as far as could be judged with light microscopy. Ovulatory follicles were only present at times close to expected ovulation; on days P 18 and L 18. A lactational anoestrous is suggested for the wood mouse.     

The diet of the wood mouse Apodemus sylvaticus on set-aside land

The diet of wood mice on set-aside consisted of 87% plant material, 65% of which was green leaf materials. This diet contains very much less seed or animal material than does that of wood mice studied in other habitats. The poor diet reflected what was available in the area.     

Home range and mating system of two sympatric field mouse species,Apodemus speciosus andApodemus argenteus

The size and spatial distribution of home ranges in two sympatric field mouse species,Apodemus speciosus andApodemus argenteus, were revealed by the capture-recapture method in a temperate deciduous forest from June 1987 to June 1990. InA. speciosus, the home ranges of males were significantly larger tha those of females, and overlapped with those of other males and females during the breeding season. InA. argenteus, the home range of each male overlapped only that of a single female throughout the year. These results suggested thatA. speciosus was promiscuous or polygynous andA. argenteus was monogamous.