Evidence for demographic bottlenecks and limited gene flow leading to low genetic diversity in a rare thistle

European calcareous grasslands have decreased dramatically in area and number during the last two centuries. As a result, many populations of calcareous grassland species are confined to small and isolated fragments, where their long-term survival is to some extent uncertain. Recently, several restoration projects have been initiated to enlarge the current grassland area in order to maintain the exceptionally high species richness. However, from a genetic point of view, the success of these restoration measures is not necessarily guaranteed, as strong historical decreases in population size and limited gene flow may have led to low genetic diversity through genetic bottlenecks and drift. In this study, we investigated genetic diversity and structure of 16 populations of the calcareous grassland specialist Cirsium acaule in a severely fragmented landscape in south-western Belgium. The overall distribution of this species in the study area was significantly and positively related to patch area, suggesting that small patches do not allow survival of this species. Both allelic richness and genetic diversity were significantly and positively related to population size. Estimation of observed and expected gene diversity provided evidence for population bottlenecks in the history of not less than 31% of all sampled populations. Reconstruction of the historical land use showed that patch area decline in populations that went through a recent bottleneck was significantly larger than that in populations that showed no evidence of a bottleneck. Assignment analyses showed low migration rates, suggesting that replenishment of lost alleles through gene flow is highly unlikely. Overall, our results indicate that in the absence of gene flow strong decreases in calcareous grassland area may have long-lasting effects on genetic diversity of plant populations and may hamper the success of restoration projects that simply aim at restoring initial habitat conditions or enlarging population fragments, as indicated by the fact that none of the recently restored areas has been occupied by C. acaule.     

Effects of predation and habitat structure on the population dynamics of house mice in large outdoor enclosures

This paper examines the effect of different levels of protection from predation on feral house mice. Mice were contained in eight 50×50 m outdoor enclosures. Enclosures allowed access to a suite of freeliving vertebrate predators from the surrounding area, including feral foxes, feral cats and Australian raptors. A 10–15% cover of small, felled cypress pine trees was added in strips to low grassland to increase habitat complexity. Mice were not protected from predation when compared with low grassland pens, possibly because predators were able to focus their hunting activity in the strips. However, when felled trees were covered with wire netting, hence providing higher quality refuge, mouse populations achieved higher densities than in low grassland pens. A predator exclusion treatment was used to confirm the refuge effect was due to a reduction in the impact of predation. Survival rates under the different treatments were generally consistent with population level responses, with mice having lower survival in low grassland pens than in high refuge pens. This is the first study with mammals that confirms the importance of refuges from predators for prey populations.     

Small mammal populations in relation to hedgerow structure in an arable landscape

The population ecology of small mammals in hedgerows in arable farmland in eastern England is described. Features of hedgerows of importance to individual species are examined. Some 97% of the total 3042 mammals captured were wood mouse Apodemus sylvaticus , yellow-necked mouse Apodemus flavicollis , bank vole Clethrionomys glareolus and common shrew Sorex araneus . Small numbers of harvest mice Micromys minutus , field voles Microtus agrestis , pygmy shrews Sorex minutus and water shrews Neomys fodiens were also caught. Wood mouse, the most numerous species, showed a typical pattern of large numbers in autumn and winter, followed by a simultaneous decline over all hedges in early spring. Population changes were less clear in yellow-necked mouse and bank vole but the yellow-necked mouse was more scarce in the second year of study. Common shrews were most numerous in summer and declined rapidly in autumn. Hedgerow coppicing had a marked effect on yellow-necked mouse numbers but not on wood mouse. In an extensive survey of mammal numbers in relation to hedgerow features, ground cover was found to be the single largest factor influencing size of bank vole populations. Hedgerow condition (lack of gaps) was important to yellow-necked mice, which thrived only in well-established hedgerows. Wood mice appeared little influenced by the characteristics of the hedge. Common shrews were more abundant in hedgerows with adjacent permanent water.     

Woodland small mammal population ecology in Britain: a preliminary review of the Mammal Society survey of Wood Mice Apodemus sylvaticus and Bank Voles Clethrionomys glareolus, 1982–87

The Mammal Society has co-ordinated a population survey of Wood Mice Apodemus sylvaticus and Bank Voles Clethrionomys glareolus in 13 0.81 -hectare sites in Britain. Numbers of mice and voles live-trapped using standard methods were collated every May/June and November/December from 1982 to 1987. The data were analysed with results from four independent studies in England and the corresponding assessments of tree seed crop size. Wood Mouse numbers are usually higher in winter than in summer but Bank Vole fluctuations are less regular. In deciduous woodland, Wood Mouse mean relative densities are significantly greater in the winter and the following summer after a good seed crop than after a poor one; rates of population change from summer to winter are significantly higher when a good seed crop falls. Bank Vole relative densities are significantly greater in the summer following a good seed crop than after a poor one, and rates of change from winter to summer are significantly higher. In Wood Mouse populations, tests for density dependence suggest that it is strong from summer to winter but absent from winter to summer; in Bank Voles weaker density dependence is present in both halves of the year. Thus, Wood Mouse numbers are regulated in autumn but are also influenced by seed crop size in winter and the following summer; Bank Vole numbers are less strongly regulated during both autumn and spring and are influenced by seed crop size in the following summer. Evidence is presented suggesting that populations of each species in deciduous woodlands are synchronized over the country in summer and that Wood Mice are also synchronized in winter; highs and lows tend to coincide between different sites. The yield of tree seed is shown to vary significantly from year to year and may be the cause of the synchrony, but weather effects may also be involved.     

The ecology of Wood mice (Apodemus sylvaticus) on arable farmland

The ecology of Wood mice ( Apodemus sylvaticus ) was studied by live trapping and by examining the stomach contents of killed animals on an arable farm in West Suffolk. The study area included several fields but only a short length of hedgerow and was distant from other hedges and woods. Wood mice were trapped in the open fields throughout the year and their burrows were also found there. Population densities were comparable with those reported from deciduous woodland and seasonal population changes, ranging behaviour and timing of the breeding season were also broadly similar. The survival rate of juvenile mice varied greatly within and between breeding seasons tending to improve when young of the year replaced overwintered animals in the adult breeding population. Wood mice showed no marked preference for fields with different crops in winter when the main foods were grain, waste sugar beet roots, weed seeds and soil invertebrates. In spring and early summer they preferred winter wheat fields where seeding weeds provided most of their food.     

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 ecology of Mus musculus on Mana Island, New Zealand

Feral house mice ( Mus musculus ) living on 217 ha Mana Island, New Zealand, with no mammalian predators, were snap-trapped and autopsied. A 7-month breeding season took the population from a spring low to extremely high density in autumn. Litters were largest in the middle of the breeding season, and significantly larger on Mana than on the New Zealand mainland. Litter size in early pregnancy was similar for young and old mice but more embryos were resorbed by old females. The breeding season ended in April when adult females stopped ovulating and young failed to mature. When the population declined over winter no animals bred, they all lost weight, and even previously mature males lost their reproductive ability. Mice continue to grow throughout life and become larger than mice in most populations on the New Zealand mainland. The regular and pronounced seasonal pulse in Mana's mouse population contrasts with longer-term fluctuations generally seen in mainland populations at lower density in indigenous forest. These differences may be explained by absence of predators, habitat features or lack of any chance to disperse on the island.     

Seasonal variability of free amino acids in two marine bivalves, Macoma balthica and Mytilus spp., in relation to environmental and physiological factors

The seasonal variability of the intracellular free amino acid (FAA) concentration was studied in 5 Macoma balthica populations and 7 Mytilus spp. populations along their European distribution. Because of the well known physiological role of FAA as organic osmolytes for salinity induced cell volume regulation in marine osmoconformers, FAA variations were compared in bivalve populations that were exposed to high vs. low intraannual salinity fluctuations. In general, seasonal FAA variations were more pronounced in M. balthica than in Mytilus spp. In both bivalve taxa from different locations in the Baltic Sea, highest FAA concentrations were found in autumn and winter and low FAA concentrations were measured in summer. Seasonal patterns were less pronounced in both taxa at locations with constant salinity conditions. In contrast to Baltic Sea populations, Atlantic and Mediterranean bivalves showed high FAA concentrations in summer and low values in winter, regardless of seasonal salinity fluctuations. Significant seasonal FAA variations at locations with constant salinity conditions showed that salinity appeared not to be the main factor in determining FAA concentrations. The seasonal patterns of the main FAA pool components, i.e. alanine, glycine and taurine, are discussed in the context of seasonal variations in environmental factors (salinity, temperature) and physiological state (glycogen content, reproductive stage).     

Genie differentiation in M. m. domesticus populations from Europe, the Middle East and North Africa: geographic patterns and colonization events

Geographic patterns of genie differentiation were investigated in the commensal house mouse subspecies, M. m. domesticus . The analysis by protein electrophoresis of 40 populations throughout Europe, the Middle East and North Africa indicated that genie differentiation was not highly structured on a macrogeographic scale. Mean genie distances between regions showed, however, that populations fell into three levels of differentiation: a low level in southern Europe within which interregional distances were no larger than intraregional ones, an intermediate level between southern European populations and North European and African ones, and finally, a higher level between all the latter and the Middle Eastern populations.
Gene flow estimates indicated that the homogeneity of southern European populations does not result from present high levels of gene flow, but more likely from a very recent ancestry. These data when argumented with the fossil records of mice from the Mediterranean Basin suggest a two-step colonization process, the most recent of which occurred very rapidly and resulted in the multiple founding of populations in southern Europe. The relationship of M. m. domesticus to other subspecies of mice is discussed in relation to introgression and taxonomy.
Microdifferentiation patterns with low levels of within population substructuring and of gene flow suggest that genie differentiation in the western European house mouse is largely determined by genetic drift and/or founder effects. Although historical factors are determinant in the large scale patterns of genie variation in commensal house mice, dispersal by man no longer seems to be a prominent feature moulding the genetic structure of M. m. domesticus .     

Numerical response of predators to large variations of grassland vole abundance and long‐term community changes

Voles can reach high densities with multiannual population fluctuations of large amplitude, and they are at the base of predator communities in Northern Eurasia and Northern America. This status places them at the heart of management conflicts wherein crop protection and health concerns are often raised against conservation issues. Here, a 20‐year survey describes the effects of large variations in grassland vole populations on the densities and the daily theoretical food intakes (TFI) of vole predators based on roadside counts. Our results show how the predator community responded to prey variations of large amplitude and how it reorganized with the increase in a dominant predator, here the red fox, which likely negatively impacted hare, European wildcat, and domestic cat populations. This population increase did not lead to an increase in the average number of predators present in the study area, suggesting compensations among resident species due to intraguild predation or competition. Large variations in vole predator number could be clearly attributed to the temporary increase in the populations of mobile birds of prey in response to grassland vole outbreaks. Our study provides empirical support for more timely and better focused actions in wildlife management and vole population control, and it supports an evidence‐based and constructive dialogue about management targets and options between all stakeholders of such socio‐ecosystems.

A 20‐year survey describes the effects of large variations in grassland vole populations on the densities and the daily theoretical food intakes of a vole predator community based on roadside counts. Our results show how the predator community responds to prey variations of large amplitude and how it reorganized with the increase of the red fox, which likely negatively impacted hare, European wildcat, and domestic cat populations.     

The population dynamics of small mammals living in set-aside and surrounding semi-natural and crop land

Small mammals were found on set-aside and surrounding farmland. Wood mice showed a different pattern of demography at two sites, with higher densities, greater survival, heavier weights and longer breeding seasons at Aldroughty than at Newburgh. These differences were thought to be due to a difference in habitat productivity at the two sites. Field voles showed less of a difference in population dynamics between the two sites, and both species of vole maintained populations at low densities.     

Tawny Owl Strix aluco as an indicator of Barn Owl Tyto alba breeding biology and the effect of winter severity on Barn Owl reproduction

In the temperate zone, food availability and winter weather place serious constraints on European Barn Owl Tyto alba populations. Using data collected over 22 years in a Swiss population, we analysed the influence of early pre‐breeding food conditions and winter severity on between‐year variations in population size and reproductive performance. To estimate pre‐breeding food conditions, we attempted a novel approach based on an index that combines Tawny Owl Strix aluco reproductive parameters and the occurrence of wood mice Apodemus sp. in their diet. Tawny Owls breed earlier in the season than Barn Owls and are strongly dependent on the abundance of wood mice for breeding. This index was strongly positively associated with the number of breeding pairs and early breeding in the Barn Owl. Winter severity, measured by snow cover and low temperatures, had a pronounced negative influence on the size of the breeding population and clutch size. Food conditions early in the breeding season and winter severity differentially affect the Barn Owl life cycle. We were able to use aspects of the ecology and demography of the Tawny Owl as an indicator of the quality of the environment for a related species of similar ecology, in this case the Barn Owl.     

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)     

鼠类种群密度、性比对其数量的调节作用 Ⅰ.不同密度、性比对雌小白鼠繁殖的影响

种群调节问题作为阐明种群数量变动机制的重要领域,现已引起生态学界很大关注,并已从不同角度进行了各种探讨。特别关于种群密度的反馈调节作用方面,近20多年来已有许多工作予以论证,但其作用原理是多方面的,至今尚未完全阐明,而且争论甚多(Christian,1975;杨荷芳,1982)。     

Genetic diversity within and between remnant populations of the endangered calcareous grassland plant <Emphasis Type="Italic">Globularia bisnagarica</Emphasis> L.

Changes in agricultural production methods over the last century have caused a massive reduction and fragmentation of the area of European semi-natural grasslands. It remains unclear whether small and isolated grassland fragments can support viable plant populations in a sustainable way. In our study area in southern Belgium, the extent of calcareous grasslands was reduced from c. 650 ha in 1775 to less than 30 ha in 2004. We used AFLP markers to quantify the effects of present and historical grassland fragmentation on the genetic structure of 27 populations of the rare perennial plant species Globularia bisnagarica. Given the mixed breeding system of the species and the relatively small area of the studied system, the populations were characterized by high genetic differentiation (F _st range: 0.42–0.48; Φ_st=0.53). A Mantel test revealed significant isolation by distance of the populations. Average within population genetic diversity, measured as expected heterozygosity or gene diversity, was low (H _j =0.081) and was negatively related to population isolation. This suggests more gene flow into less isolated populations. Population size and local habitat characteristics did not significantly influence population genetic diversity. Both, high selfing rates in G. bisnagarica and a population genetic response to habitat fragmentation may explain our findings. Finally, a clear geographical clustering was observed, with cluster membership partially explainable by historical grassland connectivity. If populations indeed started to differentiate after fragmentation, this process was not (yet) strong enough to erase the genetic similarity between fragments that historically belonged to the same large grassland fragment.     

Mandibles and molars of the wood mouse, Apodemus sylvaticus (L.): integrated latitudinal pattern and mosaic insular evolution

Aim The distinct nature of island populations has traditionally been attributed either to adaptation to particular insular conditions or to random genetic effects. In order to assess the relative importance of these two disparate processes, insular effects were addressed in the European wood mouse, Apodemus sylvaticus (Linnaeus, 1758). Location Wood mice from 33 localities on both mainland and various Atlantic and western Mediterranean islands were considered. This sampling covers only part of the latitudinal range of A. sylvaticus but included the two main genetic clades identified by previous studies. Islands encompass a range of geographical conditions (e.g. small islands fringing the continent through large and isolated ones). Methods The insular syndrome primarily invokes variations in body size, but ecological factors such as release from competition, niche widening and food availability should also influence other characters related to diet. In the present study, the morphology of the wood mice was quantified based on two characters involved in feeding: the size and shape of the mandibles and first upper molars. The size of the mandible is also a proxy for the body size of the animal. Patterns of morphological differentiation of both features were estimated using two‐dimensional outline analysis based on Fourier methods. Results Significant differences between mainland and island populations were observed in most cases for both the mandibles and molars. However, molars and mandibles displayed divergent patterns. Mandible shape diverged mostly on islands of intermediate remoteness and competition levels, whereas molars exhibited the greatest shape differentiation on small islands, such as Port‐Cros and Porquerolles. A mosaic pattern was also displayed for size. Body and mandible size increased on Ibiza, but molar size remained similar to mainland populations. Mosaic patterns were, however, not apparent in the mainland populations. Congruent latitudinal variations were evident for the size and shape of both mandibles and molars. Main conclusions Mosaic evolution appears to characterize insular divergence. The molar seems to be more prone to change with reduced population size on small islands, whereas the mandible could be more sensitive to peculiar environmental conditions on large and remote islands.     

农田生态保留带中小林姬鼠的种群动态和结构

栖息地状况对小型兽类种群动态具有明显影响。在质量好,食物资源丰富,隐蔽条件优良的栖息地中小型兽类具有较高的存活率,种群繁殖时间更长,体重比较高。有关栖息地和种群动态方面国内外已有研究报道（Brown,1988;Corp et al．,1997;Quinn et al．,2003;Schnurr et al．,2004）。     

Landscape composition and vole outbreaks: evidence from an eight year study of Arvicola terrestris

This study investigates the relationships between landscape composition and the population dynamics of the fossorial water vole Arvicola terrestris. Land use patterns were studied based on agricultural and forestry data from the French Ministry of Agriculture collected in 1955 and 1988. In the Massif Central, France, water vole populations were monitored from 1985 to 1993 by using index methods. Outbreaks of water vole populations occurred in many dispersed epicentres and spread suddenly and widely over > 7500 km². At a regional scale, the fluctuation lasts six years on average with an outbreak period lasting from two to three years. Density variation patterns are positively correlated with the proportion of permanent grassland to agricultural land. A high risk of outbreak is linked to a high proportion of permanent grassland (over 90%), whereas a low risk of outbreak is linked to a proportion of < 80%, Conversely, density variation patterns are negatively correlated with the proportion of temporary grassland to agricultural land and with the proportion of forest to total land in the western (major) part of the study area. Temporary grassland thus appears to be a marginal habitat for water voles and extensive forests could act as a brake on outbreaks. The increase in the area of permanent grassland from 1955 to 1988 was apparently the major cause of chronic high densities of water voles. Therefore, land use and landscape management could be one way to control water vole outbreaks.     

The dynamics and regulation of small rodent populations in the woodland ecosystems of Killarney, Ireland

Populations of Wood mice Apodemus sylvaticus and Bank voles Clelhrionomys glareolus were studied by mark-recapture techniques in five different woodlands but concentrated on an oak Quercus petraea wood and a yew Taxus baccata wood, where food supply was also investigated. Much of the yew wood was on limestone pavement which was greatly creviced thus providing static and quantifiable cover. Indices of the intensity with which food was being searched for were obtained on all areas by seed-removal experiments.
Trappability varied within the populations and seasonally, being highest in summer. Unusually high densities of mice were recorded in the yew wood but not elsewhere; vole densities were always low. There was an inverse relationship between range length and density: mean range length in the yew wood was exceptionally low. Males generally ranged further than females, voles further than mice. Females outnumbered males in the oak wood, where cover was minimal, when the population was low. In the two areas with most cover, males outnumbered females. In a further area, where numbers were initially exceedingly low, the population consisted entirely of males for almost a year. Sexes differed in habitat preference but numbers, especially of males, were significantly correlated with cover. Voles usually bred for shorter periods than mice. Overwinter breeding and increased overwinter survival followed good seed years. Individuals recruited when food was plentiful lived longest. In seed-removal experiments rate of removal increased with shortage of natural seed.
Food and intraspecific aggression were the probable major factors in regulating population size, of mice at least. Cover probably modifies intrinsic mechanisms by reducing numbers of encounters between individuals.     

Global diversity and genetic contributions of chicken populations from African,Asian and European regions

Genetic diversity and population structure of 113 chicken populations from Africa, Asia and Europe were studied using 29 microsatellite markers. Among these, three populations of wild chickens and nine commercial purebreds were used as reference populations for comparison. Compared to commercial lines and chickens sampled from the European region, high mean numbers of alleles and a high degree of heterozygosity were found in Asian and African chickens as well as in Red Junglefowl. Population differentiation (F_ST) was higher among European breeds and commercial lines than among African, Asian and Red Junglefowl populations. Neighbour‐Net genetic clustering and structure analysis revealed two main groups of Asian and north‐west European breeds, whereas African populations overlap with other breeds from Eastern Europe and the Mediterranean region. Broilers and brown egg layers were situated between the Asian and north‐west European clusters. structure analysis confirmed a lower degree of population stratification in African and Asian chickens than in European breeds. High genetic differentiation and low genetic contributions to global diversity have been observed for single European breeds. Populations with low genetic variability have also shown a low genetic contribution to a core set of diversity in attaining maximum genetic variation present from the total populations. This may indicate that conservation measures in Europe should pay special attention to preserving as many single chicken breeds as possible to maintain maximum genetic diversity given that higher genetic variations come from differentiation between breeds.