The population ecology of house mice (Mus domesticus) on the Isle of May, Scotland

The colonizing ability, catholic habitat utilization and wide distribution of house mice ( Mus domesticus , Rutty) are indicators of their ecological resilience. Numerous studies have been made of commensal, caged and free-living mouse populations though few have assessed the relative importance of physiological and genetical components of adaptability in a simple ecosystem. This paper reports such findings, derived from live-trapping which formed part of an inter-disciplinary study of adaptability in a feral population of house mice living on a small Scottish island (57 ha).
The population size ranged from450–3250 animals. A high proportion of mice showed homerange tenacity, though15–20% shifted their range during winter. This 'churning' of the population is consistent with the island population forming an effectively panmictic unit rather than fragmented demes. The breeding season, survival of individuals and change in population size related to patterns of gross climatic variation (temperature and rainfall) so that rates of reproduction and survival were lowest in cold, wet conditions. Thermoregulatory adjustment of the mice to lowered ambient temperatures and its contribution to overwinter survival are discussed. Genetical monomorphism of May Island mice is discussed in relation to their biological performance compared with other populations, especially that of the ecologically comparable Skokholm Island (Wales).     

The general biology of Verruca stroemia (O. F. Müller). III. Seasonal changes in body weight and biochemical composition

The seasonal changes in body weight, DNA, total carbohydrate, total lipid, and two nitrogen fractions are described for Verruca stroemia (O. F. Müller). Events are dominated by the fact that the spring brood is virtually synchronous throughout the population. Values for all the above rise during the autumn and early winter and fall at copulation during February as the animals are fertilized. Subsequently there may be some storage of nutrients which is later utilized. In general, there are only small changes in all these constituents during the summer. Although this species has escaped from the limitation of a single annual brood the seasonal changes in weight and composition closely resemble those in Balanus balanoides and B. balanus although their phasing is different.     

Seasonal shifts within juvenile recruit sex ratio of Pampas mice (Akodon azarae)

Sex ratio (SR) variation of Akodon azarae juvenile recruits was analysed during 1985–86 on a Pampean grassland in central Argentina. Rodents were intensively live-trapped on a 0.81 ha grid. The SR (proportion of males) of the overall population did not differ significantly from evenness (0.49). In contrast, juvenile recruits (0.5–2.0 months of age) showed SR fluctuations according to their time of birth. SR was strongly female-biased among spring and autumn juveniles (0.13 and 0.33, respectively), while males were predominant (0.72) among the summer juveniles.
Social and demographic implications of these results are discussed in the framework of current SR theory. Spring female recruits should be selected for summer reproduction and autumn female recruits for winter survival and spring reproduction. The overwintered population was characterized by 1:1 SR and an age structure composed of males older than females. Most of these males had been recruited as juveniles during the summer. They also made up most of the resident male population in the spring. A selective allocation of energy by the mothers among their offspring is the mechanism proposed to explain the seasonal changes in SR, as pregnant females which gave birth to the summer recruits were in better physical condition than the mothers of both spring and autumn recruits. These results are consistent with the predictions of Werren & Charnov (1978), based on temporal overproduction of one or the other sex according to differential changes in the life-history expectations for both sexes.     

Seasonal changes in the invertebrate community of small shallow ephemeral pans at Bain's Vlei, South Africa

Changes in invertebrate population numbers and composition were monitored in six small shallow ephemeral pans during four consecutive inundations of spring, summer and autumn 1988/1989. The community was generally characterized by crustaceans and was invaded by insect larvae in summer. Community changes and succession were prominent in spring but less so in summer and autumn. Large pans supported more species than small pans. During longer inundation there was less difference between the initial and the final population composition than during shorter inundation, although the total population density did not increase significantly. This indicated that population composition stabilized as inundation lengthened. Population changes of six representative taxa were not correlated to changes in the physical and chemical characteristics of the water.     

The impact of changing the season in which cereals are sown on the diversity of the weed flora in rotational fields in Denmark

1. Surveys have shown that there has been a dramatic decrease in the weed flora of fields under rotational cultivation during the last 30 years. This trend has been particularly noticeable in winter cereals, a crop of increasing importance in the landscape.
2. The weed flora of spring and winter cereals was compared in 19 unsprayed fields during a 5-year study to test the hypothesis that cereal type exerts no effect on the flora or on the absolute and relative abundance of single species.
3. Plant and species densities, and accumulated species richness, were lower in winter than in spring cereals.
4. Floristic similarity was greater among spring cereal fields and between spring and winter cereals within the same fields than among winter cereal fields.
5. Species that occurred with unequal density in spring and winter cereals occurred at higher densities in the spring cereals; these species germinated mainly in the spring. However, for a few species the relative plant abundance was highest in winter cereals; these species were able to germinate both in the spring and autumn.
6. Some species – on the relative scale – occurred indifferently of season of sowing; all but one of these species were able to germinate both in the spring and autumn.
7. Plant species and taxa that are important food resources for arthropod herbivores occurred at greater densities in spring than in winter cereals and, in addition, occurred with the highest relative abundance in spring cereals.
8. Change in land use from spring to winter cereals involves not only an immediate reduction of more than 25% in the density of plants and species, but also a change and increased uncertainty in the composition of the weed flora. These findings may have serious implications for the ecology of wildlife in the agricultural landscape.     

Vagility in an island population of the House mouse

The chance of encounter—and hence mating—between two animals may be limited by social as well as spatial factors, thus dividing a population into a series of discrete territories with little movement between them. Only within the sub-units will random mating take place, and drift may cause a considerable amount of non-adaptive genetical change if the units are very small. Work on House mouse ( Mus musculus ) populations in the laboratory and particular ecological situations have suggested that the effective breeding size of these units may be as small as four. This would mean that a considerable amount of random change would be expected in mouse populations. However, a six year study (1964–69) of movement and territoriality on the 244 acre (100 ha) Welsh island of Skokholm during which over 3000 animals were marked and released, showed that more than 20% of individuals breed in an area other than the one in which they were born, i.e. a considerable amount of population churning takes place. This conclusion is supported by evidence of the spread of three rare biochemical variants in the population. Chance seems to play little part in the determination of the genetical constitution of the Skokholm mice. In general, estimates of the size of effective breeding units must always be qualified by an understanding of the ecology of the population in question.     

Blood groups and natural selection by genetical environment

A survey is given of a number of investigations indicating the importance in natural selection of the genetical environment of populations and individuals.In the introduction it is observed that blood group frequency patterns are very stable, even in very small populations, and appear independent of environmental factors. They appear to be race-specific, maintained by a process of natural selection which is dependent of the racial genetical composition. Indications in favour of this hypothesis are obtained from several studies carried out in populations of mixed origin:The introduction on a small scale into the populations of New Guinea of foreign elements with some S genes may result in a population with relatively high S frequencies; the frequencies of certain of the blood group genes in the mixed negroid populations of Curaçao are not in agreement with the racial compositions of the mixtures as they have been calculated from the frequencies of other blood group genes, and the same appears to be the case in the populations of the Himalayas. The marked variation of MNSsHe frequencies in Africa may perhaps be explained by a powerful selective pressure exercized by the genetical backgrounds of the various populations, as is demonstrated by the absence of some expected genotypes among male Bush Negroes in Surinam.The effects of natural selection by genetical environment can also be demonstrated by family studies:In families with elliptocytosis Rhesus segregation shows some deviation from Mendelian laws, and the ratio of elliptocytosis-positive and-negative children appears to depend on the Rh genotype of the elliptocytosis-positive parent. From blood group studies in selected pedigrees and dizygotic twins it appears that twin pairs are more often doubly concordant for both MN and Rh than is to be expected.Some implications of the observed effects of natural selection in the study of human genetics and population dynamics are briefly discussed.     

Possible impact of mild winters on zooplankton succession in eutrophic lakes of the Atlantic European area

1. We report on a long-term study (1975–94) of water temperatures and plankton in a eutrophic lake (Heiligensee, Berlin, Germany). Using a phenomenological approach, we use historical data to infer how an increase in air temperature has influenced a natural zooplankton community.
2. Air temperatures in Berlin showed a significantly rising trend between 1975 and 1994. Mean winter air temperatures in the last 8 years always exceeded the long-term mean.
3. A rising trend was also found for April water temperature, which increased significantly beginning in 1988–89. An increase of 2.58°C in the last 21 years was recorded using a linear model. A significantly decreasing trend was found in June but no trend was noted for the other summer months.
4. Phytoplankton composition shifted from a dominance of diatoms and cryptophytes during winter and spring in the 1980s towards a dominance of cyanobacteria in 1990–94.
5. The dominant zooplankton species in spring shifted in recent years from the large-bodied Daphnia galeata to the smaller D. cucullata . Cyclops kolensis , previously the only invertebrate predator during winter, decreased in abundance while C. vicinus , usually present during spring and autumn, increased in abundance and was numerous during winter, a season passed in diapause in the earlier years.
6. Because direct and indirect temperature effects are species specific, we put forward the hypothesis that zooplankton species, rather than functional groups, are the nexus between environmental stress, such as rising air temperatures, and ecosystem changes.     

GENETIC VARIATION AND TERRITORIALITY IN WILLOW PTARMIGAN (LAGOPUS LAGOPUS LAGOPUS)

We examined eight polymorphic esterase loci in 526 juvenile and adult willow ptarmigan (Lagopus lagopus lagopus) collected during autumn and spring over five years. The genetic structure of territorial birds during spring differed from birds on the study area in autumn. This can not be explained by selective winter mortality since juvenile birds in the autumn had the same genetic structure as the adults who had lived through at least one winter. In the spring, birds with intermediate heterozygosity had the largest territories and were more frequently mated than expected from random mating among autumn birds. The results suggest selective access to territories by genotype and stabilizing selection, especially among males, since natural selection is assumed to favor large territories and reproduction. Our data also suggest that the spring population consisted of both territorial and non-territorial birds. The genetic relationship between birds of established pairs in spring was lower than that between randomly drawn birds on the study area in the autumn. This together with the finding that parents with an intermediate level of genetic relationship produced the largest broods, suggest that optimal rather than maximal outbreeding is the most successful breeding strategy in this species.     

Seasonal variation in haematological parameters in male and female Tinca tinca

This study was designed to investigate any seasonal (spring, summer, autumn and winter) changes in haematological parameters in the blood of Tinca tinca measuring the number of red blood cells (RBC), haematocrit, white blood cells, and total plasma proteins.The results show significant changes in RBC and haematocrit in males comparing spring and summer with autumn and winter, whereas in females the RBC remained constant for all 4 seasons but the haematocrit decreased in autumn and winter compared to spring and summer. The white blood cells of male and female animals were significantly lower in spring and winter compared to summer and autumn. In male fish total protein contents significantly decreased in autumn and winter compared to spring and summer, whereas in females protein output significantly decreased in winter compared to the other seasons. The results indicate marked seasonal variation in the blood of male and female Tinca tinca. This variation may play a important protective role for the survival of the animals.     

Possible impact of mild winters on zooplankton succession in eutrophic lakes of the Atlantic European area

1. We report on a long-term study (1975–94) of water temperatures and plankton in a eutrophic lake (Heiligensee, Berlin, Germany). Using a phenomenological approach, we use historical data to infer how an increase in air temperature has influenced a natural zooplankton community.
2. Air temperatures in Berlin showed a significantly rising trend between 1975 and 1994. Mean winter air temperatures in the last 8 years always exceeded the long-term mean.
3. A rising trend was also found for April water temperature, which increased significantly beginning in 1988–89. An increase of 2.58°C in the last 21 years was recorded using a linear model. A significantly decreasing trend was found in June but no trend was noted for the other summer months.
4. Phytoplankton composition shifted from a dominance of diatoms and cryptophytes during winter and spring in the 1980s towards a dominance of cyanobacteria in 1990–94.
5. The dominant zooplankton species in spring shifted in recent years from the large-bodied Daphnia galeata to the smaller D. cucullata . Cyclops kolensis , previously the only invertebrate predator during winter, decreased in abundance while C. vicinus , usually present during spring and autumn, increased in abundance and was numerous during winter, a season passed in diapause in the earlier years.
6. Because direct and indirect temperature effects are species specific, we put forward the hypothesis that zooplankton species, rather than functional groups, are the nexus between environmental stress, such as rising air temperatures, and ecosystem changes.     

The biology and epidemiology of Eimeria exigua, a parasite of wild rabbits invading the host cell nucleus.

Prevalence and intensity of infection with Eimeria exigua were studied by monthly sampling of caecal faeces of 254 wild rabbits (Oryctolagus cuniculus) from 5 localities in France (Arjuzanx, Versailles, Donzere-Mondragon, Massereau, Gerstheim) and by a single sampling in autumn in a small island off the coast of Britany (Beniguet). Intensity was heavier in young than in adult rabbits but usually remained low. It decreased from north to south, was at a maximum during autumn and winter, and declined in spring. Prevalences were relatively high and their rank (4th or 5th out of 10) was constant in all localities. Prevalences decreased from north-west to south-east; they increased progressively during autumn and winter, were at a maximum during spring and declined in summer. E. exigua developed in the ileum, at the top of the villi and inside the host-cell nucleus. It is distinguished from congeneric species by a number of features: micro-localisation, multiplication in autumn and winter rather than in summer, low intensity and high prevalence. These characteristics may be the consequence of a short schizogony phase and of strong resistance of oocysts.     

Comparison of life-history characteristics of island and mainland populations of the swamp antechinus

The reproductive ecology of the swamp antechinus Antechinus minimus , a small dasyurid (Dasyuridae) marsupial with obligate male semelparity, was investigated in populations inhabiting the mainland coast and on a nearby offshore island in south-eastern Australia. The size and sex ratios of litters, individual body mass and size, timing of births and female longevity were determined from live-trapped animals. The island population had significantly smaller litter sizes and greater adult body mass in comparison with the mainland population. This is consistent with features of the 'island syndrome', which predicts directional selection for these traits in high-density populations with reduced extrinsic mortality. However, inter-annual variability in litter sizes in the island population suggests that litter size is more responsive to fluctuating local conditions, such as population density, which is likely to affect food availability, rather than directional genetic changes. In contrast with other antechinus species, biased sex ratios were not evident. In addition, large variations of the timing of births were estimated at both sites and these appear to be related to seasonal conditions such as autumn rainfall and female body mass before mating.     

Intraspecific differentiation of social behavior and shelter selection in Mesobuthus gibbosus (Brullé, 1832) (Scorpiones: Buthidae)

We compared seasonal shelter selection and social behavior of Mesobuthus gibbosus from autumn to mid-summer in two similar phryganic ecosystems, in continental Greece (near Volos city) and in insular Greece (eastern Crete), and in the laboratory under simulated abiotic conditions. Our results showed that shelter selection is a critical indicator of the seasonal social behavior of the species. The abrupt climatic changes in spring caused a differentiation in shelter selection between the cold period (November–February) and the warm period (March–June) at both sites. Sociality was exhibited only during winter in the field and was more extensive under cold conditions in the laboratory. Co-occurrence of scorpions proved to be age-specific, facilitated by population density and by harsh abiotic conditions during winter, and negatively influenced by intraspecific competition, which was higher in continental Greece. The response of scorpions to changes of abiotic factors reveals synchronization of seasonal shelter selection with climatic changes.     

Surviving north of the natural range: the importance of density independence in determining population size

The relative importance of density-dependent and -independent processes in determining population density has been predicted to vary according to whether the population concerned is located near the centre or the periphery of the species' range. Thus, density-independent processes should be more pronounced near the periphery. The long-tailed wood mouse Apodemus sylvaticus in Iceland is at the northern and western edge of its geographical range. We estimated the autumn population density in an open habitat in south-western Iceland in 9 years out of 10 during 1996–2005 in order to monitor the annual maximum population size. Furthermore, we estimated population density and survival at c . 5-week intervals from September 2001 to October 2003 and from September 2004 to November 2005 in order to reveal the causes of variation in maximum population size. The estimated autumn population density was low, ranging from 2.7 to 8.9 mice ha⁻¹ while spring densities ranged from 0.4 to 0.8 mice ha⁻¹. Apparent monthly survival probabilities ranged from 0.4 to 0.7 per month in autumn and 0.7 to 0.9 in winter. Our results suggest that low temperature in early winter (October–December) is the major determinant of population density in the following autumn, explaining 74% of the variation in autumn population density. No significant correlation was found between either the NAO index or the NAO winter index and variation in wood mouse population density in autumn. Differential mortality in early winter results in variation in spring population size. This study shows clear evidence of density-independent control of a mammal population at the edge of its geographical range as opposed to the mostly density-dependent control previously recorded near its centre of distribution.     

Age variation in a fluctuating population of the common vole

We analysed variation in age in a fluctuating population of the common vole (Microtus arvalis) in southern Moravia, Czech Republic, to test the assumption of the senescence hypothesis that the age of voles increases with increasing population density. Between 1996 and 1998, we monitored the demographic changes by snap-trapping and live-trapping in a field population passing through the increase, peak and decline phase of the population cycle. We used the eye lens mass method to determine the age of snap-trapped animals and those that died in live-traps. The average age of winter males was clearly higher after the peak phase breeding season than before it. No such phase-dependent shift in age, however, was observed in the female component. Male age continued to increase from autumn to spring over the pre-peak winter, and the highest age was in spring of the peak phase year. However, after the peak phase breeding season the highest age was achieved in winter, with the decline phase males during the next spring tending to be younger. The average age of females in spring populations was always lower than in winter populations. The average age of voles from live-traps was always higher than voles from snap-traps, particularly in winter and spring populations, suggesting the presence of senescent animals. Although the density-dependent changes in age are consistent with those observed for other voles, they provide only weak evidence that population cycles in the common vole are accompanied by pronounced shifts in individual age, particularly in female voles.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Seasonal patterns in feeding ecology of three small fishes in the Biandantang Lake, China

Feeding ecology of three small fish species, Hypseleotris swinhonis, Ctenogobius giurinus and Pseudorasbora parva was studied seasonally in the Biandantang Lake, a small, shallow lake in central China. Gut length, adjusted for total body length, was significantly higher in spring than in other seasons for all the three species. Seasonal changes in gut length were not associated with changes in food quality. Weight of fore-gut contents, adjusted for body weight, was significantly higher in winter and spring than in summer and autumn in H. swinhonis and C. giurinus , and significantly higher in autumn than in spring and summer for P. parva. Percentage of empty fore-guts was highest in summer and lowest in spring for H. swinhonis and C. giurinus , and highest in winter and lowest in autumn for P. parva. Diet of the three small fishes showed apparent seasonal changes, and these changes reflected partly the seasonal fluctuations of food resources in environment. Diet breadth was high in winter and low in autumn for H. swinhonis , high in winter and low in spring and summer for C. giurinus , and high in autumn and low in spring for P. parva. Diet overlaps between pairs of species were biologically significant in most cases, except between H. swinhonis and P. parva in summer and autumn and between C. giurinus and P. parva in autumn.     

Seasonal population dynamics of Paraquimpevia tenevvima (Linstow) (Nematoda) in the European eel Anguilla anguilla (Linnaeus) in three localities of southwest England

Seasonal population dynamics of Puraquzmperia tenerrima (Linstow) in the European eel Anguillu anguillu (Linnaeus) have been investigated in three localities in Devon, southwest England. The nematode is common and exhibits very similar seasonal patterns in changes of prevalence and abundance in the three localities. The population increases over winter through to late spring or early summer as the recruitment of the new generation occurs throughout this period. Reproduction of the nematode starts in spring. A sharp decrease of prevalence and abundance accompanies or follows reproduction, and infection levels are very low in autumn and early winter. The dispersion pattern of the nematode varies with the infection levels from over-dispersion in spring and early summer to almost random dispersion in autumn and winter. It is suggested that P. tenerrimu is a common specific parasite of eels, especially in small streams or rivers and that insect larvae or species of crustaceans might serve as intermediate hosts for the nematode.     

Turnover, age and sex ratios of kestrels (Falco tinnunculus) in south Scotland

This paper examines the composition and turnover of a population of European kestrels Falco tinnunculus L. in the Southern Uplands of Scotland. Turnover was generally high, with most birds staying in the area for only one summer or winter. The rate at which birds arrived or left was highest in autumn and spring, and was independent of population size. During winter, breeding males were more likely to stay on their territories than females, and males that did so were more likely to retain their partners the following year. Breeding success was associated with a greater likelihood of return the following year, except in first-year females which were unlikely to return anyway. The sex ratio was biased toward males in winter, especially in poor vole years when there were also few first-year birds present. The study confirmed the high rate of turnover reported elsewhere in small raptors, and further indicated that the composition and turnover of the population were related to food supply and seasonal patterns of migration.