Surplus Of Males Research Articles

Återfynd av kungsfåglar Regulus regulus funna i Sverige: tidsmässigt uppträdande samt köns- och åldersfördelning

In Sweden, 377 recoveries of Goldcrests Regulus regulus have been reported up to and including 1997. Of these, 274 (73%) were ringed outside of Sweden, mainly in neighbouring countries: Norway (45), Finland (70), Russia and the Baltic States (77), Poland (22) and Denmark (43). Three hundred recoveries were made during the autumn migration, 62 during spring migration and four during winter. Goldcrests ringed to the east of Sweden (e.g. in Finland) make up a relatively large proportion of the autumn recoveries, while comparatively few Goldcrests of eastern origin have been found in subsequent migratory seasons compared to birds of western origin (Norway). This indicates that Goldcrests of eastern origin adopt a more easterly route of migration in subsequent seasons. A large part of the recoveries consists of birds, which have been caught or otherwise found in connection with ringing activities. A majority of the Swedish bird observatories are situated along the Baltic Sea, on islands or close to the coast. The sex distribution during autumn migration among individuals handled at ringing sites shows a surplus of males (63.1%) among short-term recoveries. Among birds ringed during previous seasons (adult birds) the sex ratio is still, but slightly less, male biased (55.8%). At ringing, most Goldcrests (both newly ringed and recaptured) are aged based on the shape of rectrices. When recaptured, 26 of the adults were correctly aged as adults. However, 12 were wrongly assigned as juveniles and the remaining 14 were not aged. The fact that about one third of the aged, adult Goldcrests were recorded as juveniles (1Y) when controlled is assumed to reflect the difficulty to positively age Goldcrests using morphological criteria.

Sex differences in recovery pattern and migratory direction of Goldcrest Regulus regulus ringed in northern Europe during autumn migration

Among Goldcrests ringed in Denmark, Sweden and Finland, and recovered later the same autumn in the British Isles, a remarkably high proportion (30:5) of males are found , compared with the assumption of equal sex ratio or a surplus (55%) of males in the migrating population during autumn. Sex ratio bias was not found in birds ringed in Norway. Provided that males and females can be assumed to have on average the same relative fat deposits and that the sexes are morphologically similar, both sexes should have the same flight range. Differences in flight capacity can thus not be a main explanation to the sexual bias in the short time recoveries in the British Isles. An alternative explanation may be a difference in migratory strategy between the sexes when facing long sea passages. If there is a choice, e.g. an alternative migratory route along the coast, the females, although for unknown reasons, fly out over the sea to a lesser extent than the males. Different geographical situations, compared to the rest of southern Scandinavia, is assumed to explain why Goldcrests ringed in southern Norway and later recovered in the British Isles do not show the same sexual bias.

Population ecology of the squirrel glider (Petaurus norfolcensis) and the sugar glider (P. breviceps) (Maruspialia : Petauridae) at Limeburners Creek, on the central north coast of New South Wales

The population ecology of the squirrel glider (Petaurus norfolcensis) and the sugar glider (P. breviceps) was studied at Limeburners Creek Nature Reserve, on the central north coast of New South Wales. The study was undertaken between July 1986 and November 1988. Sugar and squirrel gliders at Limeburners Creek exhibited similar home-range sizes (2.54 ha) despite considerable differences in mean mass between the species (squirrel glider 192-213 g; sugar glider, 104-119 g). Squirrel gliders existed at higher densities (049-1.54 ha-') than did sugar gliders (0.24454 ha-') and populations of both species exhibited male-biased sex ratios. The timing of births was not consistent between years and, at least in the squirrel glider, occurred in almost all months of the year over the 2.5-year study. Usually a winter peak in births that extended into spring was apparent, sometimes following an autumn peak. Mean litter size for both species (1.8-1.9) was similar to that recorded for the sugar glider in Victoria. Most adult females of both species exhibited the capacity to raise two litters in a year. Hence, natality rates (2.3-2.4 young per year) at Limeburners Creek were high relative to those recorded for the sugar glider in Victoria. Recruit persistence time (3.0-3.5 seasons) was similar between the species and recruitment appeared to be most successful during years when heavy eucalypt and Banksia flowering was recorded. Populations of both species were characterised by high rates of juvenile dispersal and mortality. Young gliders dispersed at a mean age of 10.9 and 12.5 months in the sugar glider and the squirrel glider, respecti~e1y;SquirreI gliders nested in colonies of 2-Bindividuals. Usually at least one male and two females nested together, suggesting a polygynous mating strategy. The mating system of the sugar glider at Limebumers Creek was less clear, but colonies appeared to comprise at least monogamous pairs with or without a surplus of males. Sugar glider colonies at Limebumers Creek varied in size from two to seven individuals. The larger squirrel gliders were clearly dominant to the smaller sugar gliders in interspecific behavioural interactions. Inconsistencies in body-weight fluctuations between years for both species were thought to be a consequence of the unpredictable nature of the aseasonal, coastal climates and resulting food resource abundances.

Geographic distribution of human skin colour: A selective compromise between natural selection and sexual selection?

Modern humans have been shaped by the cumulative action of natural selection, non-adaptive random change, and sexual selection. The last of these is not universal and has prevailed in one of two circumstances: (1) A surplus of females due to high male mortality, combined with ecological constraints on female participation in food procurement which discourage males from taking second wives; (2) A surplus of single males due to generalized polygyny with relatively low male mortality. These circumstances are most likely to occur in (1) Arctic tundra environments, specifically the vast expanse of tundra covering most of Europe up to 10,000 B.P., and in (2) regions dominated by generalized polygyny, notably sub-Saharan Africa. Sexual selection often acts on existing sex differences, including perhaps sexual dimorphism in human skin colour. Whereas women are universally fairer in complexion, men are browner and ruddier; parallel to this, most human societies see lighter skin as more feminine and darker skin as more masculine. Hence, sexual selection should favour lighter pigmented women when a surplus of single females must compete for a mate. Since skin colour is only mildly sex-linked, both sexes would lighten in pigmentation within the population in question. Similarly, when a surplus of single males must compete for a mate, both sexes would darken. Geographic variation in human skin colour may thus represent a selective compromise between two counterbalancing forces: natural selection, as determined by latitudinal variation in sunlight; and sexual selection, as determined by variations in the following: male mortality rates, incidence of polygyny, and ecological constraints on female participation in food procurement.

Sex Differentials in Mortality Early in the Twentieth Century: Sri Lanka and India Compared

Sex differentials in mortality between 1921 and 1981 in Sri Lanka are examined and contrasted with India; the goal is to assess whether the patterns in Sri Lanka follow the patterns in the north and south of India. In northern India there was greater sex differentials than in the south which was attributed to lower labor force participation the presence of a dowry system exogamous marriage and lower female status. The findings show that Sri Lanka closely approximates the excess female mortality of northern India even though the social situation of women was more like conditions in southern India. Sri Lankan women had a high degree of autonomy endogamous marriages and agricultural practices which favored womens participation. Female mortality declined at all age groups between 1921-81. In 1921 female differentials in mortality exceeded males in most age groups with the exception of infant mortality and ages 45-54 years. Between 1921 and 1953 womens mortality declined for aged 5-9 and all ages between 15-54 years. In each decade after 1953 there was a shift from less female disadvantage to more male disadvantage. By contrast in India between 1872 and 1921 the census showed that female life expectancy exceeded males; between 1921 and 1931 male life expectancy exceeded females. Based on sex ratio data in the early 1960s for India by ethnic group there was a male surplus in the north and a slight female surplus in the south. In Sri Lanka for a comparable period were more disadvantaged than in India and more like north India. The explanation does not related to the similarity in language (Sinhalese) between the north and Sri Lanka because common social structural and ideological features were similar to the south. Levels of mortality also did not provide an explanation. The explanation is likely to have been that some causes of death disadvantaged one sex over the other. Famine was associated with greater male mortality and famine occurred in north India and not in Sri Lanka. Women in Sri Lanka were most affected by hookworm infestations and corresponding anemia malaria and maternal mortality which were not prevalent in south India. The mortality differentials between north India and Sri Lanka may be explained by the culture against females in north India.

Strategies of mate finding in the European field cricket (Gryllus campestris) at different population densities: a field study

Abstract. 1. Members of a field population of Gryllus campestris L. varied in their walking and calling activity. In both sexes, some individuals occupied burrows whereas others walked around in the observation area. Males at burrows could be either silent or calling.2. In the course of one summer, population density decreased and the initial balanced sex ratio changed to a large surplus of males.3. At high population density, there were equal numbers of non‐calling males at burrows, calling males at burrows and walking males, while walking females predominated over females at burrows. Non‐calling males at burrows achieved more encounters with females than did calling and walking males. Females met males by walking through the population and by waiting at burrows. Thus, calling and phonotaxis were not essential for mate finding and calling was less effective than previously thought.4. At low population density calling males predominated. Calling males at burrows achieved the most encounters with females. Females met males only by walking around in the population area. Calling was thus more important in mate finding than at high population density.5. Changes in sex ratio and population density may cause the flexibility in mate finding behaviour of individual crickets.

Sexual dimorphism in the energetics of reproduction and growth of North Sea plaice, Pleuronectes platessa L.

The chemical composition and energy content of North Sea plaice during the spawning period were examined in mature males and females and in immature fish, to study differences in the allocation of energy over reproduction and somatic growth between the sexes.At the beginning of the spawning period mature males and females had equal dry weights of lipid that were 70% higher than in immatures. Protein content in mature males was equal to that in immatures but was 23 % higher in mature females. Immature males and females did not differ in chemical composition. At the end of the spawning period, spent and immature fish had equal lipid contents, but protein content in spent females was 10% lower than in spent males, and 17% lower than in immatures. Gross energy content of the body decreased by 44% (65·2 to 36·3 J cm‐3) in mature females, 27% (55·0 to 40·OJ cm‐3) in mature males, and 9% (48·7 to 44·2J cm‐3) in immatures. Energy content of plaice eggs was estimated at 6·60 kJ per 1000 eggs.Reproductive investment was estimated from the energy loss during the spawning period and included the energy of sex products and spawning metabolism. Somatic growth comprised the annual increase in energy content of fish. The pattern of energy allocation over reproduction and somatic growth differed between males and females. Males started their reproduction at a smaller length and a younger age and allocated a higher proportion of the available energy into reproduction than females. Available energy resources for somatic growth and reproduction (surplus production) were equal between the sexes up to a length of about 30 cm. Beyond this length male surplus production levelled off whereas female surplus production continued to increase. The differences in surplus production and the allocation patterns are discussed.For female plaice the energy allocated into egg production was estimated as between 48 and 64% of the total amount of energy lost during spawning. The remaining energy is used for metabolism during the spawning period, yielding an estimate of the metabolic rate of mature females of between 6·4 and 9·1 kJ day‐1. A maximum estimate of the metabolic rate of mature males was 7·4 kJ day‐1.

Mating system and mate choice of Tengmalm's Owls Aegolius funereus

The mating system and mate choice of Tengmalm's Owls were studied in relation to population fluctuations of the staple food (voles) for seven years in western Finland. Three age classes of owls were differentiated: first‐year, second‐year and older owls. Despite a surplus of males, 11 % of them showed simultaneous bigyny in peak vole years. The mean distance between primary and secondary nests was 1158 m, and usually there was a free nest‐box between the two nests. Because primary nests produced more fledglings than secondary ones and secondary nests produced fewer fledglings than simultaneous or even eight‐days‐later monogamous nests, this bigyny could be best explained by the ‘deception’ hypothesis.In successive biandry, females deserted their first brood when young were still in the nest, thereby transferring the burden of raising the young to their males. The tendency of assortative mating by age (more yearling x yearling and + 2‐year‐old ×+ 2‐year‐old pairs than expected by chance) showed that females chose older males when these were available.

Dynamika populacji i cechy osobników w fazie spadku liczebności nornika burego

Halle S. & Lehmann U., 1987: Population dynamics and individual features during the phase of decline in the field vole Acta theriol., 32, 2: 21—29 (With 3 Figs.) A North Swedish population of the field vole Microtus agrestis (Linnaeus, 1761) in the phase of decline was studied in detail by the use of individual marking and brief trapping intervals over one re- productive season. In early spring, a distinct surplus of males was found. Reproduction started with a delay of about 4 weeks, thus the first juveniles could not be trapped earlier than the beginning of June. All the overwintered adults disappeared during 10 days just prior to the recruitment of the young, resulting in a total exchange of the pop- ulation. The members of the spring born cohort ceased growing at an age of about 25 days and maintained body weights of 20—30 g during the entire time of observation. Although sexual activity was obvious in both sexes, no juveniles could be trapped during summer. Both immigration and emigration was scarcely seen. Thus during summer, the population remained rather uniform with respect to number, age and weight, closely resembling a pattern found during winter. The reasons and implications of these findings are discussed. (Zool. Inst., Phys. Okol., Univ. Koln, Weyertal 119, 5000 Koln 41, FRG).

Breeder-Helper-Interactions in the Pied Kingfisher Reflect the Costs and Benefits of Cooperative Breeding

In most social species there is not only cooperation but also conflict between group members. Although various theoretical models have specified the conditions for, and the extent and direction of conflict and cooperation, there are few empirical data to test their predictions. This paper reports such a test for the pied kingfisher (Ceryle rudis), a cooperatively breeding bird species with two types of male helpers: primary (= related) and secondary (= unrelated). In a breeding colony at Lake Victoria (Kenya), the birds were studied with regard to: (a) aggressive and non-aggressive interactions between breeders and helpers before and after chicks hatched; (b) frequency and effect of prey transfer from helpers to breeders; and (c) sizes and types of prey brought to females and nestlings. The six major results of the study and their explanations are as follows: Result 1. Male breeders attack secondary male helpers more often than primary helpers (Table 1). Explanation: Because of a high male surplus, all helpers are also potential rivals, competing with male breeders for sexual access to the scarce females. Secondary helpers, however, impose higher costs and lower benefits on the male breeders' fitness than do primary helpers. This is because they provide less help, seem to be more capable of fertilizing eggs in the year of help, are more likely to displace breeders in subsequent years, and are more distantly related to breeders than are primary helpers. Result 2. Primary helpers treat secondary helpers in the same way as male breeders do (Table 1). Explanation: Primary helpers are closely related to the young they raise. Therefore, any competition from secondary helpers that affects the breeder will decrease the primary helpers inclusive fitness. Result 3. Female breeders tolerate secondary helpers more readily than do male breeders and primary helpers (Table 1). Explanation: Females do not incur the costs of male-male competition; indeed they even benefit from it, because (a) with additional males (= secondary helpers) they get a better food supply during egg formation than without them, and (b) secondary helpers lower the females' food contributions to nestlings more than those of male breeders and primary helpers. Result 4. By offering fish, secondary helpers reduce the probability that they will be attacked by the breeding pair and any primary helpers (Table I). Explanation: The helpers' food transfer is interpreted as a for being accepted as a group member. Receiving fish improves the breeders' and primary helpers' energy-budgets and their chances of fledging young and thus reduces the cost/benefit ratio of tolerating helpers. For females this holds already during egg formation, for males only after hatching, when the risk of kleptogamy is low, and when helpers can improve survival of the young. Result 5. After the young have hatched, primary helpers carry more food to nestlings (= usually their sibs) than to females, whereas secondary helpers carry more to females than to unrelated nestlings (Table 2 and Fig. 1). Explanation: Primary helpers increase their inclusive fitness mainly through raising close kin, secondary helpers mainly through improving their chances of finding a mate and reproducing themselves. Result 6. In groups with two or three secondary helpers, each helper tends to provide the nestlings with more food than in groups with only one helper (Fig. 2). Explanation: Groups with two or three secondary helpers differ from groups with only one helper (a) in the breeders' average gain from each helper, and (b) in the extent of male-male competition for females as prospective mates. The helpers' higher food contribution to nestlings in bigger groups is interpreted (a) as a higher payment for being tolerated, and (b) as increased effort to signal their parental qualities to the females. It is concluded that all behavioral interactions and food contributions closely reflect the costs and benefits of giving and receiving help, which vary with the sex of the breeder, the relatedness between the group members, and the period of the reproductive cycle.

Staphylococcus aureus bacteremia in a Dutch teaching hospital

During a period of 21 months an analysis was made of bacteremia caused by Staphylococcus aureus in a teaching hospital for adults. During the observation period staphylococcal bacteremia was detected in 77 patients, i.e. in 1.83 cases per 1,000 admissions. Not less than 81.8% of staphylococcal bacteremia cases were hospital-acquired. The age-specific attack rate increased consistently from the sixth decade onwards. The male/female ratio was 1.96: 1. If this ratio was related to the sex ratio of patients admitted to the hospital during the observation period, statistical significance was reached for the surplus of males. Staphylococcal bacteremia contributed to death in 14 of 47 patients, i.e. 18.2%. Intravascular infection was the most prevalent source of infection (25 of 77 cases, i.e. 32.5%). Serious complications were observed in 14 cases of staphylococcal bacteremia. Eight of these patients had endocarditis and four died. Tolerance was observed with nine of 77 strains and may have influenced the reaction to antimicrobial therapy in at least one case.

Spring Arrival Times and Assortative Mating of Kestrels in South Scotland

(1) In a partially migrant population of kestrels studied for 4 years in south Scotland, migrants settled in spring from late February until late April. Mean arrival time was earlier following a mild winter, but was not related to local food supply, so that the mean length of courtship (pairing to egg-laying) was longer in a poor vole year (when laying was late) than in good times (when laying was early). (2) Within years, migrants that arrived early tended to pair earlier, and lay earlier, than those that arrived late. Later pairing birds partly compensated for this by having shorter courtship than those that paired early. (3) Males and females arrived over roughly the same period and there was no difference in their mean arrival dates. However, within pairs, the males arrived about 4 days, on average before their females. The sex ratio of winter residents was biased towards males, so more early arriving females than males were able to pair with residents on arrival. This resulted in a surplus of unpaired males that persisted until the end of the settling period when all breeding birds were paired. (4) In the 2 years when they bred in substantial numbers, first-year birds arrived later than adults. In males, but not females, first-year birds resident over winter waited longer than adults before finding a mate. (5) Selective mating of first-year birds and adults occurred in 1978 but not 1979. The observed preponderance of yearling-yearling and adult-adult pairs in 1978 seemed largely due to the different arrival times of the two age groups, though this did not entirely explain the infrequency of yearling-male x adult-female pairs compared with adult-male x yearling-female. The data were consistent with the idea that females, but not males, preferred adult partners when these were available.

Lek structure and territoriality in the chryxus arctic butterfly, Oeneis chryxus (Satyridae)

The territorial and mating systems of the satyrid butterfly Oeneis chryxus were studied for 3 years on individually marked populations in algonquin Provincial Park, Ontario. Males defended territories in a dry open forest clearing by means of chases and spiral flights with conspecifies. Defended areas did not contain food or oviposition sites required by females. Territories were not uniformly distributed over the study area; the highest density of territories was clustered over bare ground covered with sand and small stones rather than areas of vegetation. This pattern of distribution of territories occurred during each year of the study. The patterns of occupancy of territories showed a high degree of consistency from one day to the next, some males defending a given territory for as many as 11 consecutive days. Removal experiments showed that a surplus of non-territorial males did not exist. Vacant territories in the high-density area were absorbed by neighboring males; those in the low-density area remained empty. Male size was not correlated with territory position in the study are. Wing patterning (i.e. size of spots) differed between males occupying territories on sandy/stony versus vegetated areas. The territorial and mating systems of O. chryxus resemble lek polygyny, and are more similar to some vertebrate lek systems than to hilltopping or landmark territoriality.

THE STARRED ROBIN IN NATAL, PART 3: BREEDING, POPULATIONS AND PLUMAGES

SUMMARY Oatley, T. B. 1982. The Starred Robin in Natal, Part 3: Breeding, populations and plumages. Ostrich 53: 206–221 The female Starred Robin Pogonocichla stellata constructs a domed nest of moss and dead leaves usually on sloping ground and well concealed in the herb layer. The normal clutch is three eggs laid on consecutive days. Incubation usually starts with the laying of the third egg. The mean size of 138 eggs was 22 x 16 mm. The female incubates the eggs for 16 to 18 days and intermittently broods the young for the fist five of the average 14-day nestling period. Both sexes feed the young from the time of hatching and parental care lasts for some 42 days after leaving the nest. Eggs are laid from October to December with 63% of clutches started in November. Data on sex ratios indicate a surplus of adult males in the population and annual survival rates are estimated at 0,84 for males and 0,76 for females. 51% of eggs laid in 60 nests give rise to fledged young. About 21.3% of eggs laid produce adults. The level of brood parasitism by cuckoos is relatively low. Most adult mortality occurs outside of the breeding seasons. Chilling and overnight starvation from January to March when incidence of late afternoon thunderstorms is highMaycause significant mortality. The subadult plumage appears to confer crypsis and enable the immature bird to reside in adult territories without harassment. AdultsMaybenefit through an effective reduction in competitive stress.

OBSERVATIONS OF GROUP BEHAVIOUR AND BREEDING BIOLOGY OF THE YELLOW‐BILLED SHRIKE CORVINELLA CORVINA

SummaryYellow‐billed Shrikes were found to live in groups throughout the year. Within the group, each member helped to defend the group's territory, warn against predators and feed the breeding female, nestlings and fledglings.During the study there was little change in the location of the boundaries and in the areas of the territories occupied by the majority of the groups. The densities of the larger groups were in general two to three times that of smaller groups. Numbers within one group varied by ±24% of the average (12) during a period of three years.Progeny remained in a group for some years before dispersing, sometimes in parties of the same sex. Both sexes exchanged groups, the females moving on average further than males. During successive periods in the history of a group the representation of the sexes varied from a surplus of females to a surplus of males. In the population as a whole the sex ratio was probably parity.Only one female bred in a group at a particular time and she alone incubated. Eggs were laid on consecutive days. Breeding started at the height of the dry season; the first peak in egg laying occurred at the beginning of the rains; laying continued through the wet season and ceased usually in August. The most frequent clutch size was four, and varied little within a breeding season or between seasons. The incubation period ranged from 15 to 18 days, the most frequently recorded being 17 days. The nestling period was 19 days. The percentage of total eggs laid that produced fledglings was 25% and yearlings 11%.Young shrikes were independent in the seventh week, participated in group displays in their tenth week and fed fledglings in their fourteenth week.The age of first breeding was not discovered. Two females in their sixth year were still helpers in a group at the end of the study.

Alternate Routes to Sociality in Jays—With a Theory for the Evolution of Altruism and Communal Breeding

The social systems of New World species of jays are compared behaviorally and ecologically. Two lines leading to sociality are identified, one connecting the pair-in-territory system with the colonial system and a second connecting the pair-in-territory system with the communal system. Ecological factors in the evolution of communal breeding and its associated altruistic behavior are considered mainly in the genus Aphelocoma , but other birds are treated briefly. Three principal origins of communality and altruism in birds are identified: from colonies, from a surplus of males, and by retention of young in the family, the latter being of greatest importance. The theory proposed for the evolution of communal breeding and altruism emphasizes three main processes: 1) K-selection, (2) kin selection, and (3) kin-group selection in the same chronological order.

The Water Mite Hydrachna Conjecta Koenike, 1895 (Acari, Hydrachnellae), Bionomics and Relation To Species of Corixidae (Hemiptera)

The Water Mite Hydrachna Conjecta Koenike, 1895 (Acari, Hydrachnellae), Bionomics and Relation To Species of Corixidae (Hemiptera)

Population Geography in Chittagon Hill Tracts, East Pakistan

The Chittagon Hill Tracts, the only mountain area of East Pakistan, were at first settled by the hill men, Mongoloid people, with the shifting cultivation. The immigration of the plains men, Bengali people, has brought the paddy cultivation, and the conflicts and acculturation between both peoples.The writer studied the population geography of this area at the field survey in 1964 with following results.1) The population density is higher than 70per square mile in the settlements of Chakma, Marma and Tippera tribes with the paddy cultivation, occupying broader valley floors in northern and central parts, and is less than 70per square mile in the settlements of Marma tribe with the paddy cultivation on mountain lands.2) Hill men consists of many tribes, whose places of origin and degree of acculturation are various. But they are equally enthusiastic to take the Bengali culture.3) The population of Bengali people shows male surplus, the high percentage of Islamism, and the inclination to the urban and the secondary and tertiary industries. The tribes are exclusively Buddists and are living on the agriculture, and their sex ratio is normal.4) The natural growth of population is generally high. The social growth is caused by the Bengali immigration to the westernmost region and the movement of hill men from the Kaptai reservoir area.

Fertility decline and female chances of marriage in Malaya

Abstract A feature of the demographic pattern of post-World War II Malaya has been its high rate of natural growth, which reached 31/2 per cent per annum in the mid-1950s. However, the average age at marriage of the female population has been rising for most of this period, and since 1956 there has been a considerable and sustained fall in the birth rate. In this paper simple models are developed to show that in a closed population a continuing high rate of population growth is incompatible with a pattern of universal female marriage, monogamy and a culturally imposed age difference of considerable size between spouses. The demonstration provided by the models is then offered as at least a partial explanation of the fertility and female marriage trends in contemporary Malaya. Discrepancies between the population of Malaya and the models have to be taken into account. A pattern of polygamous and unstable marriage does exist amongst the Malaysians and, to a much lesser extent, in the Chinese community. Furthermore, recent years have witnessed the passing of the large surplus of single males built up in the Chinese sector of the population during the years oflarge scale immigration. Such a transition is well under way in the Indian community too. It is suggested that a substantial average age gap between spouses may be an aspect of many contemporary societies which reacts against the persistence of extremely high rates of natural increase. Even where demographic pressures in the ‘marriage market’ act towards a lessening of this gap, there is a cultural lag, during which period many females are forced to marry late or not at all. Most of the study was made on a pan-Malayan basis (i.e. combining the Federation of Malaya and the State of Singapore) to achieve comparability with earlier censuses and as a recognition that with unrestricted migration between these areas they still form a single demographic unit. The terms Malaya and Malayans will be used when referring to this area or its inhabitants. The so-called major races of the country are Malaysians, Chinese and Indians. The first will be used in accordance with the census definition to cover the indigenous inhabitants of Malaya or the Malay Archipelago (Indonesia, British Borneo and the Philippines). As most of these people are either indigenous or have been in Malays for some generations they are usually called Malays (except for the aborigines). However, the all-embracing census term will be used here. Indians, in conformity with most local usage, will be used for the groups classified as Indians and Pakistanis at the 1957 censuses of the Federation of Malaya and Singapore. The group was very small.

Reproductive Performance of a Population of Woodchucks after a Change in Sex Ratio

A reciprocal relationship between density and reproductive performance in mammalian populations is now well established (Crew and Mirskaia 1931, Retzlaff 1938, Davis 1951, Calhoun 1952, Christian 1955a, b, and 1956, Christian and LeMunyan 1958, Clark 1955, Kalela 1957, Crowcroft and Rowe 1957, Hoffman 1958, Helmreich 1960). This relationship apparently depends upon social interactions which increase with increased population density and which operate through endocrine mechanisms to affect reproduction (Clhristian 1959). A corollary to this thesis is that actual numbers (density per se) are not wholly determinant. The intensity of social interaction also should be related to factors such as the sex ratio and age composition of a population, because present evidence shows clearly that competitive behavior changes with age and differs with sex. The present paper describes the reproductive performances of 3 different populations of woodchucks (Marmiota m. monax L.). In one population, a surplus of males was maintained by selectively removing a portion of the females at intervals in 1957 and 1958. In a 2nd population, males and females were removed selectively in large numbers in 1957 and 1958 to reduce density and eliminate older animals. The 3rd populatioln was disturbed as little as possible during this time. The reproductive performance of each population was assessed in 1959 by examining the reproductive tracts of females collected during the breeding seasonl. The main purpose of this paper is to describe the way in which each population was man-ipulated and to present an analysis of the reproductive data collected subsequently. Observations oni mortality, movements, and social interactions, and data colncerned with compensatory responses to the