A Perplexing Outbreak of Mice in Patagonia,Argentina

Early in spring, 1997, remarkably large numbers of mice appeared in the dense forests near the western end of Lago Nahuel Huapi, Argentina. Dead mice that washed up on nearby beaches at this time were fat, had full stomachs and were young or young-adults born unusually late in the preceding autumn and winter. These mice represented an aperiodic outbreak that extended over 300 km along the Andes. By analysis of trapped samples, the demographics of the two main species in this outbreak (Oligoryzomys longicaudatus and Abrothrix longipilis) were compared with demographics of the same species during the preceding 21 years. In spring of 1997, trap success for O. longicaudatus in areas of the outbreak was as high as 46%; for A. longipilis it was 22%. Neither males nor females of either species entered breeding condition in 1997 during the usual season of reproduction in spring, nor in the following summer, leading to the collapse of the populations. Numbers of Oligoryzomys decreased steadily to 15% in autumn and a normal 2% in the following spring, at which time reproduction resumed. The 1997 springtime populations in adjacent ecotone and steppe habitats to the east had not increased, contained no young individuals, and overwinter individuals reproduced normally. During the breeding season, O. longicaudatus in these populations increased more rapidly than did A. longipilis, and during the winter, they decreased faster. The unusual winter reproduction preceding the outbreak may have resulted from an increase in some deep-forest food source that in turn was responding to two successive, unusually warm winters. Predation played a negligible role in the population collapse. The mouse outbreak was not accompanied by an increase in human cases of hanta pulmonary syndrome, a disease for which O. longicaudatus is a reservoir.     

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.     

Population biology of small mammals in Pureora Forest Park .2. The feral house mouse (

Over five years from November 1982 to November 1987, we examined 395 mice collected from unlogged and logged native forest and from exotic forest at Pureora Forest Park, in the central North Island of New Zealand. Sex ratio, litter size, and breeding effort (pregnancy rate in females, proportion of males with visible tubules) were similar in all samples. By contrast, both density (captures per 100 trap-nights = C/ 100TN) and recruitment (proportion of young mice of age classes 1-3) were higher in densely vegetated habitats (along the road edge or in a young exotic plantation) than in the forest interior, whether logged or not. The age structures of the road edge and interior forest samples were significantly different (road edge, 33-35% young; interior, 10-11% young, means adjusted for sex, season and year by GLM). Mice of a given age caught in summer were larger, especially the females, implying that young mice grew faster in summer than at other seasons, and that older mice, especially females, also put on extra weight in summer. Most pregnant mice were found in spring and summer, but there was no winter quiescence in mature mice of either sex, and three of 29 pregnant females were collected in August. In five of 29 litters of embryos, at least one embryo was resorbing, totalling 12 of 161 embryos (7.4%). Litter size (viable embryos only) ranged from 5 to 8 (average 6) in 23 spring and summer pregnancies, but only 1-5 in four autumn and winter pregnancies. At high densities during 1984 in the young plantation (41.1 C/100TN in May) mice were significantly smaller in autumn, though somewhat larger in spring, and fewer young were recruited in 1984 and 1985. In these years we found significantly fewer males fertile, litters smaller and pregnancy rates lower, both in the plantation and in other habitats. The population Peak was much higher than most apparently similar post-seedfall Peaks in beech forest documented by the same methods, but it was different because (1) it developed very suddenly in autumn rather than building up slowly over winter and spring and Peaking in summer; (2) it was not preceded by winter breeding; and (3) it was made up mostly of mice born in the previous summer, whereas Peak populations in beech forests are usually made up of mice born during the previous winter and spring.     

Delayed female reproduction in equilibrium and chaotic populations

Behavioural and life history polymorphisms are often observed in animal populations. We analyse the timing of maturation and reproduction in risky and resource-limited environments. Field and laboratory evidence suggests that female voles and mice, for example, can adjust their breeding according to the level of risk to their own survival and to survival probabilities and recruitment of young produced under different environmental conditions. Under risky or harsh conditions breeding can be postponed until later in the current breeding season or even to the next breeding season. We develop a population dynamics and life history model for polymorphism in reproduction (co-existence of breeding and non-breeding behaviours) of females in an age-structured population, with two temporally distinct mating events within the breeding season. We assume that, after overwintering, the females can breed in spring and again in summer or they can delay breeding in spring and breed in summer only. Young females born in spring can either mature and breed in summer or stay immature and postpone breeding over the winter to the next breeding season. We show that an evolutionarily stable breeding strategy is either an age-structured combination of pure breeding behaviours (old females breed and young delay maturity) or a mixed breeding behaviour within age-classes (a fraction of females breed and the rest of the age class postpones breeding). Co-occurrence of mixed reproductive behaviour in spring and summer within a single breeding season is observed in fluctuating populations only. The reproductive patterns depend on intraspecific, possibly interspecific, and ecological factors. The density dependence (e.g. social suppression) and predation risk are shown to be possible evolutionary mechanisms in adjusting the relative proportions of the different but co-existing reproductive behaviours.     

Age structure and reproduction in feral New Zealand populations of the house mouse (Mus musculus), in relation to seedfall of southern beech

Abstract

After good seedfalls by southern beech (Nothofagus spp.), density indices for mice increased, the breeding season for adult females was brought forward, and winter breeding was observed. The end of the breeding season of the following summer was brought forward only slightly if the maximum density achieved was not great; incomplete data on 2 very high-density populations suggested a much earlier end to breeding. In early winter following a good seedfall the recruitment of juveniles was temporarily increased. After spring, few young mice entered the population, though breeding continued. The distribution of age classes shifted steadily upwards as population density rose. The peak population of 1976–77 comprised mainly old mice, still breeding, but without significant recruitment. No effects of density on sex ratio, litter size, or body weight could be detected from these data. In all populations studied, density decreases were ultimately due to failure of recruitment and the disappearance of ageing, non-breeding mice. The proximate causes of this mortality were probably the onset of cold weather in 1976–77 and predation by stoats in 1979–80.     

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.     

Breeding biology of Tenagomysis tasmaniae Fenton,Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea: Mysidacea)

The number, size and developmental stage of young in the brood pouch of female Tenagomysis tasmaniae, Anisomysis mixta australis and Paramesopodopsis rufa was recorded throughout the year. Breeding was intensive from spring till the end of autumn for the three species. Calculation of the egg ratio for each species showed that their major reproductive peaks occurred during spring and summer. A winter depression in the breeding cycle was observed for T. tasmaniae and P. rufa, but A. mixta australis ceased breeding during winter. Seasonal variation in the length of gravid females and number of young carried was evident for these three species. Females were longer in spring and summer and carried more young than in autumn and winter. A linear relationship between female length and brood size was demonstrated for each species; annual and seasonal equations were calculated for females carrying each developmental stage. The seasonal equations showed that for a female of given length fecundity was greater during spring than any other season. Natality was estimated to be highest during late spring, summer and early autumn for the three species. No seasonal variation in the size of eggs was evident for the three species. The reproduction pattern of T. tasmaniae, A. mixta australis and P. rufa appears to be very similar to that reported for the majority of iteroparous coastal temperate mysids throughout the world.     

Trends in annual and seasonal survival of Pink-footed Geese Anser brachyrhynchus

Adult Pink-footed Geese Anser brachyrhynchus from the Svalbard breeding population were neck-banded and resighted in staging and wintering areas outside the breeding season 1990–1999. We estimated annual and seasonal survival using capture–recapture statistical models. Mean annual survival was 0.829, declining over the study period from 0.90 to 0.79. The annual cycle was partitioned into three periods: summer (1 April–30 September), including both spring and autumn migration, autumn (1 October–31 December), including most shooting, and winter (1 January–31 March). The parsimonious model selected to describe seasonal survival included a declining trend in summer survival, constant autumn and winter survival with lower survival in the severe winter of 1996, and an additive effect of sex on summer and winter survival. Monthly survival was highest during winter. Decreasing summer survival was the main contributor to the overall decline in annual survival, and was attributed mainly to increasing natural mortality on the breeding grounds. Mean annual survival based on the seasonal survival probabilities was 0.835 for females and 0.805 for males. The effect of sex was most pronounced during summer and remains to be explained.     

Composition of cyclic and non-cyclic vole populations: On the causes of variation in individual quality among Clethrionomys glareolus in Sweden

A cyclic Clethrionomys glareolus population from north Sweden was compared with a non-cyclic population from south Sweden regarding age structure, body weight, reproductive development and suppression, and sex ratios.The non-cyclic population, after years with winter breeding, was characterized by especially early and intense breeding in spring and many post-reproductive animals in autumn. Non-cyclic populations with no winter reproduction were similar to increase years in cyclic populations. In peak and especially in decline phases of cyclic populations reproduction decreased clearly below the level in non-cyclic populations. Animal weights varied insignificantly between years in the non-cyclic population but changed greatly in the cyclic population.A unifying hypothesis for explaining variations in animal quality between different populations is proposed: Maternal conditions related to food supply are assumed to affect body growth and sexual maturation of the young. Predictions from this hypotheses are outlined and compared with those from competing ideas.     

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.     

Reproductive characteristics of free-livingCalomys venustus (Rodentia, Muridae)

Calomys venustus showed a cyclic seasonal pattern of reproductive activity characterized by a period of repose and a variable length of the period of sexual activity between August—September to May—June. The study was done from 1983 to 1999. During this time the population density increased from October—November to the end of autumn and sharply decreased in winter. Three peaks in rate of pregnancy were recognized in the breeding period: spring, summer and late summer. The average litter size was different among the three peaks in rate of pregnancy. The reproductive pattern had a peak at the beginning of the spring produced by overwintering animals, and another peak in summer-autumn caused by the reproductive activity of young born in the same period in which they breed. The spring cohort exhibited the greatest breeding contribution suggesting that this cohort is principally responsible for the yearly peak in abundance.     

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.     

On the virtue of being the first born: the influence of date of birth on fitness in the mosquitofish, Gambusia affinis

We found in an earlier study that mosquitofish (Gambusia affinis and G. holbrooki) ceased reproduction in the late summer, long before the end of warm weather, stored fat, then utilized reserves to survive the winter and initiate reproduction the following spring. We hypothesized that this pattern of fat utilization was a life history adaptation that enabled the fish to acquire food resources in the autumn then allocate them to reproduction the following spring when the fitness of the young would be greater. Here we evaluate one aspect of this hypothesis by evaluating the probability of survival to maturity and fecundity of young as a function of date of birth. We placed cohorts comprising eight to ten litters of young born early‐, mid‐ or late in the reproductive season in replicate field enclosures. The entire experiment was repeated in two different years. Early‐born young had a significantly higher probability of survival to maturity but did not differ in fecundity relative to the last cohort of the season. Early‐born young also attained maturity early enough to reproduce in their year of birth while late‐born young had to overwinter before reproduction. The fitness consequences to the mother of either producing one more litter of young at the end of the season, versus instead storing fat and reproducing the following spring are not as determinate as are the effects of date of birth on offspring fitness. Females most often gain fitness by not producing one last litter and instead over‐wintering. If, however, the overwinter survival of offspring is not influenced by their size at the end of the season, then a female's fitness could be enhanced by producing one more litter late in the season. If instead the probability of overwinter survival is strongly influenced by the size of offspring at the end of the season, then our results suggest that a female gains more by deferring reproduction and storing for overwinter survival and reproduction the following spring.     

Species composition, host association and niche differentiation in fleas of small mammals in the Ilmen-Volkhov lowland

Species composition, abundance, annual cycles, and host association of fleas parasitizing small mammals were investigated. The problem of niche differentiation in these insects is considered on the base of the comparative analysis of their annual cycles. The annual cycles of the fleas are revealed to be similar in the case of few number of flea species in parasite community. Thus, two species parasitizing Sorex araneus (Doratopsylla dasycnema and Palaeopsylla soricis), as well as three species associated with Apodemus uralensis (Megabothris turbidus, Ctenophthalmus agyrtes, and Ct. uncinatus) have equal phenology of parasitizing. The fleas community of Clethrionomys glareolus is characterized by a large species number and high diversity of the annual cycles. The differentiation by the seasons of parasitizing is observed most clearly in the dominant flea species, namely Amalaraeus penicilliger, Ct. uncinatus, and Peromyscopsylla bidentata. The periods of imaginal life are overlapped significanly in these species, but they are differed by the season of dominance. Ct. uncinatus predominates in spring and summer, while P. bidentata predominates in autumn, and A. penicilliger predominates in winter and early spring. It may be noted also, that niche partitioning was not observed in the fleas having wide range of hosts. The imaginal life of such fleas usually does not go beyond the warm season.     

Fire season effects on the recruitment of non‐sprouting serotinous Proteaceae in the eastern (bimodal rainfall) fynbos biome,South Africa

Abstract Research in Mediterranean‐climate shrublands in both South Africa and Australia shows that recruitment of proteoid shrubs (non‐sprouting, serotinous Proteaceae) is best after warm‐season (summer and autumn) fires and worst after cool‐season (winter and spring) ones. This pattern has been attributed to post‐dispersal seed attrition as well as size of pre‐dispersal seed reserves. Here we investigate patterns of post‐fire recruitment for four proteoid species in the eastern part of South Africa's fynbos biome, which has a bimodal (spring and autumn) rainfall regime. Despite the lack of significant differences in recruitment between cool‐ and warm‐season burns, we find some evidence for favourable recruitment periods following fires in spring and autumn, immediately before, and coinciding with, the bimodal rainfall peaks. This suggests that enhanced recruitment is associated with conditions of high soil moisture immediately after the fire, and that rapid germination may minimize post‐dispersal seed attrition. In two of the species, we also find a shift from peak flowering in winter and spring in the Mediterranean‐climate part of the fynbos biome, to summer and autumn flowering in the eastern part. Because these two species are only weakly serotinous, warm‐season flowering would result in maximal seed banks in spring, which could explain the spring recruitment peak, but not the autumn one. We conclude that eastern recruitment patterns differ significantly from those observed in the western and central parts of the biome, and that fire management protocols for the east, which are currently based on data and experience from the winter‐rainfall fynbos biome, need to be adjusted accordingly. Fire managers in the eastern fynbos biome should be less constrained by requirements to burn within a narrow seasonal range, and should therefore be in a better position to apply the required management burns.     

Babesia divergens in France: descriptive and analytical epidemiology

Babesia divergens cause of bovine babesiosis transmitted by Ixodes ricinus, is widely spread especially in West, Central and South-West parts of France. It occurs with two annual peaks, in spring and autumn. The study was carried out during a period of two years (1991-1993) in four farms in the Sarthe area, in order to know the distribution and the ecology of I. ricinus, and to show the presence of B. divergens. Cattle are parasitised as early as March essentially by adult ticks, according to a seasonal distribution (spring, autumn). The flag method allows to catch essentially the larvae and the nymphs on the pastures; nymphs appear as early as March, and larvae one to two months later. Ectoparasite collection on trapped micromammals (Apodemus sylvaticus, Clethrionomys glareolus, etc.) in pastures hedges, is used to detect small I. ricinus populations, mostly larvae. A new ELISA method has been used for the study of the kinetics of anti-B. divergens antibodies in 236 cattle during two years. Most of the animals (60%) show a high antibody level, essentially at the end of the pasture season; the percentage of positive animals decreases during winter and increases again during the pasture season. Calves become seropositive since their first months on pastures. Adults show asymptomatic infections several times along the year, mostly during spring and autumn; only three clinical babesiosis cases have been observed during the whole study, in animals exhibiting nevertheless a high specific antibody level.     

Population-Dynamics and Diet of Rodents on Rangitoto Island, New Zealand, Including the Effect of a 1080 Poison Operation

The objective of this study was to quantify the population dynamics, morphological characteristics, and diet of rodents on Rangitoto Island (Hauraki Gulf, New Zealand) to provide information for the future development of an eradication strategy. An aerial 1080 operation to eradicate possums and wallabies was carried out two months after the study began. The effects of this operation on rodent population dynamics are discussed. Both ship rats (Rattus rattus) and mice (Mus musculus) were trapped on Rangitoto Island over a 15 month period. A two month decline in mouse abundance was noticed following poisoning; following this the population recovered rapidly, reaching a Peak of 12 captures per hundred trap nights (12 C100TN(-l)) in autumn and then declining over winter. A longer decline in ship rat abundance was observed, although this reached a pre-poisoning level of 1.6 C100TN(-l) in April. Thereafter the population did not reach pre-poisoning levels again. Total body length and weight were significantly related to age, and were similar to those of mice and ship rats recorded in other New Zealand studies. The majority of breeding appeared to occur between September and May for both species. There was evidence of delayed reproductive maturity for female mice and mts born at the end of summer. A relatively large number of young mice were caught in autumn, with very few being caught in spring. Invertebrates were the major component of both species' diet, with weta (Hemideina thoracica) predominant, while plant matter was a minor constituent. The nematodes Physoloptera getula and Mastophorus muris were present in the stomachs of 22% of mice and 59% of ship rats.     

Annual variation in energy reserves in male three-spined stickleback, Gasterosteus aculeatm L. (Pisces, Gasterosteidae)

Wet and dry weights of tissue were measured and concentrations of glycogen, lipid and protein were estimated for the liver, gonad and carcass of male sticklebacks from an annual population collected each month over one complete year. In young-of-the-year there is one period of rapid weight gain, in all three body regions (liver, carcass and gonads) but particularly of the carcass, in the autumn and a second in spring and early summer. This is accompanied by an increase in the water content of all three body regions. The gonadosomatic index also increases sharply in spring and early summer. Young sticklebacks accumulate lipid and glycogen slowly during the autumn and winter of their first year of life and more rapidly from late winter to early summer. Thus, the period of most rapid accumulation of these reserves coincides with the time when body weight and gonad maturation are also increasing sharply. Lipid and glycogen levels fall during the reproductive season in those males that breed, so that by July they are reduced to 43% and 37% (respectively) of their peak values in May. Levels of protein increase throughout the year as the fish grow, but in breeding males by July the concentration of protein in the carcass falls to 70% of pre-breeding levels. Breeding males therefore reach the end of the reproductive season with their total energy reserves severely reduced, and consequently they suffer a very high mortality. In contrast, adult males that fail to reproduce survive beyond the breeding season. They continue to gain weight and to accumulate lipid and glycogen from August to September, but these energy reserves fall (to levels comparable to those of post-breeding fish) in December, when these fish probably die. These results demonstrate that in male sticklebacks, growth and gonad maturation can be sustained in parallel with the accumulation of energy reserves, which are subsequently extensively depleted as a result of reproductive activities.     

Seasonal changes in density, demography and body composition of small mammals in a southern temperate forest

Eleven small mammal species (nine rodents and two shrews) were recorded in 16 months of trapping in the Karkloof Forest, Natal. Total densities varied seasonally, ranging from 60.7 animals/ha in the dry autumn and winter to 29.1 animals/ha at the onset of the rains in spring and early summer. Peaks in breeding coincided with high body fat and water content in the five common species during summer: in winter, when body fat and water levels were low, there was no breeding. This may be related to poor food quality at this time. Annual changes in density, breeding season and juvenile recruitment of Rhabdomys pumilio, Mastomys natalensis and Myosorex varius are the same as recorded in conspecific populations from other habitat types and do not seem modified by the habitat stability of the forest environment. Of the five common species, only Grammomys dolichurus , one of the few forest-associated small mammals in southern Africa, and Graphiurus murinus demonstrated stable, K-selectéd life-history styles.