Reproductive biology and ecology of a deep-demersal fish, alfonsino Beryx splendens, over the seamounts off New Caledonia

The reproductive biology of the alfonsino Beryx splendens was studied by histological examinations, gonadosomatic index and macroscopic scales of maturation of a large sample of gonads. Alfonsino is a gonochoric species. The size-frequency distribution of the sex ratio was bimodal and considered to be due to size dimorphism. In New Caledonia, the breeding period of this species occurs during the southern summer, with a peak in December to January. The spawning stage is attained at a minimum fork length of 28 cm for females and 33 cm for males. The size at which 50% of the population attain sexual maturity (FL₅₀) is 33.2 cm for females and 34.5 cm for males. Maximum potential fecundity is estimated to lie between 270 000 to 675 000 eggs for fish between 34 and 40 cm in fork length. It was possible to differentiate vegetative zones, in which juvenile alfonsino grow until they reach maturity, from reproductive zones (fishing grounds) which are inhabited by mature individuals. The larvae and juveniles could be carried from the reproductive zone to the vegetative zone by currents in an oceanic eddy system. Received: 26 April 1996 / Accepted: 20 September 1996     

Reproductive parameters of female Hawaiian damselfish<Emphasis Type="Italic"> Dascyllus albisella</Emphasis> with comparison to other tropical and subtropical damselfishes

The reproductive ecology of female Hawaiian damselfish Dascyllus albisella (Gill) was studied at Kaneohe Bay, Oahu, Hawaii (21°27'N; 157°47'W) during two peak reproductive seasons (June–September 1997, July–August 1998). In both years, spawning occurred cyclically every 5–7 days, with all spawning in the study area in each cycle concluding within 2–3 days. The study period encompassed 16 spawning cycles in 1997 and 10 cycles in 1998. Some females spawned in almost all cycles, whereas others spawned in as few as one. Mean spawning interval of individual females ranged from 6.4 to 11.7 days in 1997 and from 5.5 to 29.0 days in 1998. Batch fecundity increased exponentially with body length, and ranged from 23,100 to 52,800. Spawning duration increased linearly with body length and ranged from 20 to 286 min. On a single day, large females spawned earlier than small females. Females mated with several different males over a season, but typically mated with only one male on a single spawning day. Female spawning frequency and interval, spawning duration, batch fecundity, as well as diel timing of spawning in D. albisella were comparable to those reported for other large, planktivorous, non-territorial damselfishes.     

Mortality in the pheasant Phasianus colchicus during the breeding season

Summary Mortality of wild radio-tagged pheasants was analysed over six breeding seasons (1984–1987 and 1989–1990) in the Revinge area in southernmost Sweden. The aim of the study was to compare morphology and behaviour of birds found dead with those that survived the breeding season (from the first week of April to 30 June). The pheasants were kept over winter in an outdoor enclosure, equipped with radio transmitters, and released during the first week of April. In all, 49 females and 43 males were found dead and the average breeding-season mortality was 25% in males and 26% in females (not including birds that disappeared). The main predators were goshawk Accipiter gentilis and red fox Vulpes vulpes. Mortality among males peaked in late April whereas female mortality was highest in late May. Measurements of morphology included: length of tail, tarsus and wing, body mass and for males, spur length. The only morphological trait that differed between survivors and non-survivors was spur length in males; survivors had longer spurs. This difference was only found when allometric effects of age and body size on spur length were controlled for. Attractiveness and spacing behaviour of non-surviving males were recorded by telemetry from release until the last day of life, and compared with the average performance of survivors in that year. Non-surviving males moved shorter distances between days but did not differ from survivors in calling activity and attractiveness. Calling activity was higher in males that died early in the season compared to those dying late in the season. No differences were found between surviving and non-surviving females.     

Evidence for seasonal mate limitation in populations of an intertidal amphipod, Corophium volutator (Pallas)

Potential rates of reproduction (PRR) differ between the sexes of many animal species. Adult sex ratios together with PRR are expected to determine the operational sex ratio (OSR) defined as the ratio of fertilizable females to sexually active males at any given time. OSR is expected to determine the degree to which one sex competes for another—the limiting sex. We explored the potential for mate limitation in an intertidal amphipod, Corophium volutator (Pallas). Males have higher PRR than females, but males may be limiting because of extreme female-biased sex ratios observed in this species. Consistent with this idea, late season females were less likely to be ovigerous and had smaller size-specific clutches, both of which were associated with seasonal declines in availability of males of reproductive size. Seasonal changes in ovigery could not be explained by seasonal changes across sites in other factors (e.g., female body size or phenology of breeding). Smaller females were less likely to become ovigerous later in the season at three of four sites. Seasonal reductions in clutch size also occurred among small females expected to be reproducing for their first time. In complimentary laboratory experiments, reduced likelihood of ovigery and reduced fecundity occurred when the number of receptive females was increased relative to availability of a reproductively active male. Our results suggest male mate limitation can occur seasonally in this species and that male limitation is regionally widespread and may affect recruitment.     

Sexual dimorphism and the mating ecology of polar bears (Ursus maritimus) at Svalbard

We assessed the role of size, mass, and age in mating and non-mating polar bears (Ursus maritimus) at Svalbard, Norway, during the spring breeding season. The ratio of male to female mass, in male-female pairs, ranged from 1.00 to 3.02 ([`(x)] = 1.99 \overline x = 1.99 ) indicating that mating males were larger than mating females but with substantial variation. Paired males were older than unpaired males and male mass was related to age. However, males paired with females were not significantly different in body mass from those males caught alone. Wounds and scars resulting from fights between males began at about 6 years of age and peaked at about 17 and 20 years of age, respectively. The frequency of broken canines in males, presumably due to increased male-male conflicts, increased with age but showed little increase in females. The wide range of male size in male-female pairs and the age-related signs of injury suggest that male polar bears engage in both scramble competition and contest competition for access to breeding females. The mating system of polar bears is variable but is best described as female defense polygyny or serial monogamy.     

Reproductive biology of the lanternfish Benthosema pterotum from the Indian Ocean

Samples of Benthosema pterotum (Alcock) were obtained from the Arabian Sea (1976, 1979, 1981, 1983, 1984), off Mozambique (1978) and from the Bay of Bengal (1979). The sexual maturity stages are described. For females, the size of the largest oocytes was found to be most useful for size of the largest oocytes was found to be most useful for assessing maturity. Mature and spawning fish were found in all seasons. Samples from November 1983 differed from all others in having very few mature females. A few apparently spent fish were observed in July to August 1979 and November 1983. Some females mature at 25 mm and males at 20 mm, whereas others can still be immature at 45 and 40 mm, respectively. Of the total number of stations, four had significantly more males than females, twelve significantly more females, and forty-seven displayed no difference in the sex ratios. The vertical migration of the mature and spawning fish did not differ significantly from that of other individuals. Batch fecundity ranged from ca. 200 to 3 000 eggs fish ranging from 27 to 52 mm, relative fecundity from ca. 2 000 to 7 000 eggs g^-1 maternal dry weight. There are indications that B. pterotum spawns only once, but no firm conclusions could be drawn.     

Abundance, growth and life cycle of the mesopelagic amphipod Primno abyssalis (Hyperiidea: Phrosinidae) in the Oyashio region, western subarctic Pacific

Abundance and life-cycle features of the mesopelagic hyperiid amphipod Primno abyssalis (formerly P. macropa) in the Oyashio region, western subarctic Pacific, were investigated using samples collected between July 1996 and July 1998. P. abyssalis was collected throughout the entire survey period, with abundance peaks occurring in spring to autumn. While all maturity stages of males and females were observed throughout the study period, the peak reproduction season was in summer. Instar analysis based on the segment number of the pleopod rami indicated that hatched juveniles molted 10 times before becoming adult males and 13 times before becoming adult females. Judging from the dry and ash-free dry weights of each instar, males and females continued to feed throughout the final instar stage. Based on cohort analysis of seasonal samples and laboratory observations on molting frequencies, growth in body length of P. abyssalis was linear with time, and estimated generation lengths were 2.3-3.8 years for females and 1.4-1.9 years for males. Brood size of females ranged from 66 to 337 and increased with increasing female body length. Lifetime fecundity, calculated as the sum of six successive broods, was 1,004. Compared with P. abyssalis in the southern Sea of Japan, those in the Oyashio region have a larger number of adult instars (six versus five for females, three 3 vs one for males), a lower growth rate (0.014 mm day^-1 vs 0.021 mm day^-1), and mature earlier (instar 13 vs instar 15 for females; instar 10 vs instar 11 for males). These characteristics are considered to be advantageous life-history traits to counteract higher niche competition within the mesopelagic community and higher predation pressure by mesopelagic fishes in the Oyashio region than in the Sea of Japan.     

Parental care and the cost of reproduction in a Mediterranean fish

Summary Symphodus tinca is a common near-shore Mediterranean labrid fish in which females may sometimes spawn their eggs over hundreds of square meters, or alternatively spawn into well-defined algal nests. Eggs spawned in either manner are fertilized, but widely scattered eggs receive no parental care, whereas eggs spawned into nests are usually guarded by the male until they hatch. Here, I report weight changes of individual marked fish that engaged in a variety of different reproductive behaviors during three breeding seasons. Males gained weight at 0.15% per day outside the spawning season, and added 29–78% to their overall body weight between reproductive seasons, even following substantive weight losses in a spawning season (up to 20% among nesting males). Nesting and nest-guarding males lost an average of 0.32% and 0.41% of their body weight per day in 1986 and 1987. This cost is four times greater than reproduction for nonnesting males, which registered a 0.03% daily weight gain. Actively spawning females lost 0.06% of their body weight daily during the spawning season. While long-term growth rates did not appear to be substantially affected by reproduction in either sex or by parental care in males, present work does not exclude the possibility that such long-term effects may exist.     

Reproduction and growth of the freshwater prawn, Palaemon paucidens (Decapoda: Palaemonidae) in a lake of Korea

This study analyzed the reproduction and growth of freshwater prawn, Palaemon paucidens De Haan 1844 from Suk-dang lake(Korea). The analysis of the sex ratio showed a higher proportion of males than that of females. The average size of the eggs was 6.12 (+/-0.55) mm3 in the non-eyed stage (stageA) and 7.20 (+/-0.86)mm3 in the eyed stage (stage B). The reproductive output (RO) calculated with the dried-body weight of an incubating female and the weight of the eggs in dried condition was 26.97% (n = 17) of the average females weight. Incubating prawn appeared in April, and the gonadosomatic indices(GSI) showed the highest value during three months from January to March. Based on the month when there was a high proportion of incubating females with a high GSI, the estimated spawning season of P. paucidens was April. The maturity of the female was evaluated by the development of the ovaries and the existence of eggs. The average body length when 50% of the females in the group reached maturity was 8.55 (+/-2.74) mm. The analysis of the length-frequency distribution showed that the life span of P. paucidens ranged from 12 to 13 months. Females mature faster than males.     

Determinants of ejaculate size in a grasshopper (Chorthippus parallelus)

Models for the evolution of ejaculate expenditure predict that ejaculate size (ES) depends on male body condition, on female fecundity, or on the risk of sperm competition. These ideas were tested in the grasshopper Chorthippus parallelus. ES ranged over four orders of magnitude, around a mean of 442,000 sperm. ES was independent of male body size and female fecundity. None of the male condition parameters - age, degree of parasitism, macropterism score (a measurement of competitive energy allocation to other sources), and the mass-femur length residuals - explained variation in ES. As expected in species where females are cyclically non-receptive after mating, male-male encounters before copulation were a more reliable indicator of the risk of sperm competition than the number of males present during copulation. In particular, the summative number of male-male encounters rather than the male-male encounter frequency was a significant predictor of ES variation (24.9%).     

Polygyny and male parental care in Savannah sparrows: effects on female fitness

Summary To determine the effects of male mating status on female fitness, we compared the reproductive success, survival, and future fecundity of female Savannah sparrows (Passerculus sandwichensis) mated to monogamous vs. polygynous males in a 5-year study on Kent Island, New Brunswick, Canada. The proportion of males with more than one mate varied from 15 to 43% between years and sites. Polygynous and monogamous males fledged young of equal size in every year of the study. Females who shared paternal care with other females laid as many eggs per clutch and clutches per season as monogamously mated females. In most years polygynously mated females showed no delay in laying a second clutch, and they suffered no reduction in fecundity the following year. Recruitment of a female's offspring into the breeding population was generally independent of her mating status. Fitness costs of being mated to a polygynous male were only apparent in one year of the study, during which females mated to polygynous males had higher over-winter mortality than those mated to monogamous males. That same year, young raised by polygynous males were only one-third as likely to survive to reproductive maturity (as inferred by returns) as those raised by monogamous males. A male's mating status had no effect on his own survivorship. A male's mating status did not necessarily reflect his contributions to raising nestlings, which may partially explain why monogamously and polygynously mated females had equal fitness. At 35 nests the proportion of food deliveries brought by individual males varied from 0 to 75%; on average, males brought fewer than 30% of all food deliveries. Yet parental care by polygynous males was no less than that of monogamous males, at least at the nests of their primary females. Secondary females tended to receive less male assistance during the nestling stage, but their reproductive success was indistinguishable from that of primary females. Females feeding young without male assistance made as many food deliveries/h as did pairs in which males brought at least 30% of all food deliveries. Unassisted females did not suffer diminished fledging success or produce smaller fledglings. The benefits of polygyny for male Savannah sparrows are clear: polygynous males recruit more surviving offspring into the breeding population than monogamous males. The fitness of females, on the other hand, appears to be unaffected by whether their mate was monogamous or polygynous except in occasional years. Polygyny may be maintained in this population by the constraints of a female-biased sex ratio, the inability of females to predict a male's paternal care based on his morphology or behavior, the poor correlation between a male's mating status and his assistance at the nest, and inconsistent natural selection against mating with a polygynous male. Correspondence to: N.T. Wheelwright     

Fecundity of the freshwater fish, Notopterus notopterus (Pallas) in natural and heavy metal contaminated water

The knowledge of fecundity of fish from a specific aquatic body is extremely important in the successful management and exploitation of its fishery. In the present investigation the fecundity of the freshwater fish, Notopterus notopterus was studied in fish collected from a natural aquatic body (Sirnoor nala) near Gulbarga and also in fish exposed to some heavy metal contamination (HgCl2, CdCl2 and their combination) at sublethal concentration for 15 days in the laboratory. The mathematical relationship between fecundity and total length, body weight, ovary length and ovary weight were determined in both unexposed and exposed fish. The fish, N. notopterus has bigger oocytes and are few in number. Studies in the fish exposed to heavy metals indicate that significant reduction in these parameters after exposure to heavy metals at sublethal concentration was noticed. The fecundity has straight line relationship with total length, body weight, ovary length and ovary weight in control fish which did not alter after heavy metal exposure. This study provides the viability of species in only specific environment.     

Polyandrous female butterflies forage for matings

Butterfly mating systems exhibit great variation and range from strict monandry to strong polyandry. During mating males transfer ejaculates containing both sperm and accessory substances to females. In the polyandrous green-veined white butterfly, Pieris napi (Lepidoptera, Pieridae) these ejaculates average 15% of male body mass, but can represent up to 23% of body mass for individual males. Hence, mating is costly to males, and recently mated males increase copula duration but decrease ejaculate mass transferred to females. Substances transferred to females during mating are later incorporated into female soma and reproductive tissues, and multiply mated female butterflies have higher lifetime fecundity, lay proportionately larger eggs, and live longer compared to once mated females. Here we report that females of P. napi allowed to mate at liberty with recently mated males only (i.e. males that delivered a small ejaculate) increased their lifetime number of matings compared to females allowed to mate with virgin males only (i.e. males that delivered large ejaculates), the former group mating on average 5.1 times (range 2–10) and the latter group mating on average 2.8 times (range 1–4). The lifetime fecundity of the two groups of females did not differ significantly. Because nutrient donation from males is essential for females to realize their potential fecundity, we conclude that females of the polyandrous green-veined white actively forage for matings.     

Role of sex and breeding status in grooming and total tick load of impala

The lesser mouse lemur (Microcebus murinus) is a prosimian primate which presents evidence of sex ratio bias of offspring that agrees with the direction of bias predicted by the local resource competition model for facultative sex ratio adjustment. That is, females overproduced sons when grouped prior to mating, whereas isolated females exhibited the opposite tendency. In this solitary species, social communication relies heavily on urinary chemical signals. To test the hypothesis that sex biases induced by social factors may be linked to urinary cues, isolated females were exposed (n = 76) or not (control group, n = 16) to urinary cues from other reproductively active females from the beginning of the breeding season (induced by long photoperiod) until oestrus. During that period, females were either continuously (n = 17) or partially (n = 59) exposed to chemosignal stimulation. Females in oestrus were placed in contact with a breeding male and subsequently isolated until they gave birth. All females entered oestrus but the timing of oestrus was significantly delayed by 1 week in urine-exposed females. A general depressive effect of long-term urine exposure on fecundity was demonstrated, involving fewer impregnations, higher abortion frequency and smaller litter sizes. Among females giving birth (n = 55) to a total of 129 young, a significant positive correlation was found between sex ratio bias towards males and the duration of urine exposure. However, the shift in sex ratio at birth depended on the duration of urine stimulation during a sensitive period extending from the beginning of the long photoperiod until the beginning of the follicular phase. In the absence of urinary cues during the sensitive period, females significantly overproduced daughters (32% males of 53 newborn). As urine exposure increased during the sensitive phase, the proportion of males in litters increased from 54% males (n = 50) in partially urine-exposed females to a significant bias towards males (69.2% of 26 newborn) in totally exposed females. The biased sex ratio in response to chemical cues did not show consistent relationships with maternal body weight, parity or litter size. Although the intrinsic mechanisms involved in sex-biased conceptions are not known, chemical cues could interact with the photoperiodic control of gonadotropin secretions. Received: 14 January 1995/Accepted after revision: 26 November 1995     

Seasonal changes in the diet of a critically endangered seabird and the importance of trawling discards

Pelagic seabirds obtain food from oceans where the availability of their prey changes rapidly both seasonally and spatially. Here, we investigated changes in the trophic habits of the critically endangered Balearic shearwater (Puffinus mauretanicus) through the breeding season and tested for dietary differences between sexes and age classes. We analysed δ¹⁵N and δ¹³C values in blood of adults during the pre-incubation, incubation and chick-rearing periods and of their chicks. Using a two-isotope mixing model, we estimated dietary contributions based on isotope values from potential prey species which included small pelagic species available naturally and demersal fish species available only from trawling discards. Balearic shearwaters showed clear isotopic and dietary variation through the breeding season. During pre-incubation, breeding adults appeared to exploit demersal fish, whereas during the incubation and chick-rearing period, they fed mainly on pelagic anchovies (Engraulis encrasicolus) and pilchards (Sardina pilchardus). Similarly, chicks were fed mainly with anchovies, a resource with a high energetic value. This variation in the dietary habits of adult shearwaters during the breeding season was probably related to both natural and fishery-induced seasonal changes in the availability of potential prey species within their main feeding grounds. However, changes in the nutritional requirements of the shearwaters could also play an important role. Indeed, diet differed between sexes during pre-incubation: females fed less on trawling discards and more on small pelagic fish than males. This sexual segregation in diet could be the consequence of higher nutritional requirements of females during this period. Our study reveals the differential importance of both trawling discards and small pelagic fish species for a pelagic seabird depending on the breeding period and illustrates the importance of considering the entire breeding season when making inferences about the importance of specific prey in seabird dietary studies.     

Seasonal changes in plasma calcium and inorganic phosphate levels in relation to parathyroid structure of the grey quail, Coturnix coturnix coturnix Linnaeus

Plasma Ca concentration (annual mean) in males Coturnix cotumix coturnix was 10.27 +/- 0.14 mg/100 ml while it was slightly higher (11.85 +/- 0.15 mg/100 ml) among females. Plasma Pi levels (annual mean) in males and females were 5.62 +/- 0.12 mg/100 ml and 6.52 +/- 0.20 mg/100 ml, respectively. While the males did not exhibit marked fluctuation in plasma Ca and Pi levels either in winter or summer, the females did record significant elevation in the levels of both these electrolytes during breeding season. The peak values of plasma Ca (17.66 +/- 0.38 mg/100 ml) and Pi (8.64 +/- 0.22 mg/100 ml) in females were observed during June. Parathyroid gland of the grey quail exhibited hyperactivity (hypertrophy and hyperplasia) during breeding season, however, the activity was more conspicuous among females than in males. The maximum increase in cell and nuclear diameters were observed in females during May-July. The follicles were also filled with AF- and PAS-positive materials during these months. The glands depicted signs of hypoactivity and degeneration during peak winter season (November-December) as evident by decrease in cell and nuclear diameters as well as vacuolation in the chief cells.     

Male preference for large females and assortative mating for body size in the sand lizard (Lacerta agilis)

Summary Male sand lizards (Lacerta agilis) are polygynous and guard individual females for several hours to days after copulation. Even though the copulation itself only lasts 2–4 min, the total time that a male invests per female is considerably more and may constitute a substantial investment during a mating season. In such situations, when male copulation frequency is constrained, or when variation in female fecundity is high, mate choice by males may be adaptive. Large body size in female sand lizards is correlated with higher fecundity. In choice experiments performed in the laboratory, male sand lizards preferred to court large females rather than small females. In addition, when there was little difference in size between the females in the experiment, the males visited the two females more often before they started to court the preferred female. The results from a field study during 1984 and 1987–1990 showed that females are non-aggressive, have small neighboring home ranges (c. 100 m²) and may share burrows and sites for thermoregulation. This means that females can be found close together and thus gives males the opportunity to choose a mate. Assortative mating with respect to size was observed in a natural population, as well as a limited number of direct choices of females by males. These results support the results of the choice experiment.     

Maturation and diel reproductive periodicity of round scad (Carangidae: Decapterus punctatus)

The diel reproductive periodicity of Carangidae is poorly known but appears to be highly variable between species. Some species spawn during the day, others are believed to spawn at night, and it is demonstrated here that round scad, Decapterus punctatus, spawn at dusk. We collected D. punctatus in the eastern Gulf of Mexico during three April cruises (1995, 1996, and 1997). Based on histological criteria, size at 50% maturity was 113 mm fork length (FL) for males and 128 mm FL for females. The gonad-somatic index (GSI) of mature males was significantly different between hours and appeared to show diel periodicity. Diel periodicity was also observed in changes in female GSIs, whole oocyte diameters, and ovarian histology. The average GSI of mature females fluctuated two-fold between day and night, and the size distribution of whole oocytes in some fish was bimodal (at 0.3-0.4 and 0.7-0.8 mm diameter) at dusk rather than unimodal during most of the diel cycle. Histological preparations revealed that these rapid changes in ovarian GSIs and oocyte size distributions were the result of final oocyte maturation. Germinal vesicle migration was observed from 0900 to 1400 hours eastern standard time (EST), germinal vesicle breakdown was evident as early as 1100 hours EST, and ovulation occurred as early as 1800 hours EST. Spawning frequency (approximately every 5 days) was similar whether calculated from the proportion of females with hydrated oocytes during the afternoon or from the proportion of females with postovulatory follicles during the morning. Batch fecundity correlated with fish size and ranged from 5,500 to 34,700 hydrated eggs per individual. These findings do not support published hypotheses that young-of-the-year D. punctatus reproduce before their first winter or that D. punctatus reproductive output is bimodal within a year.     

Seasonal variation in male-female competition,cooperation and selfish hoarding in a monogamous songbird

Both cooperation and conflict between the sexes are commonplace in monogamous mating systems. However, little is known about how cooperation and competition varies seasonally in monogamous species that maintain permanent territories. We presented territorial pairs of male and female New Zealand robins (Petroica australis) with a large supply of insect prey at monthly intervals for 2 years. Behavioural observations after food presentation were then made to quantify seasonal and sexual differences in aggressive interactions over prey, prey acquisition rates, mate provisioning, offspring provisioning, selfish food hoarding and cache retrieval. Data were used to evaluate sex-specific behavioural strategies of mediating competition for food. Results showed that males aggressively excluded females from experimental food sources year-round. Females only accessed food sources when males left them unattended. Consequently, females acquired fewer prey than males. After controlling for differences in prey acquisition, both sexes consumed similar amounts of prey in the non-breeding season. Even though males aggressively excluded females from accessing food sources directly, males fed large amounts of prey to females during the breeding season. Both sexes provisioned young at similar rates. Males cached less prey than females in the breeding season but more prey than females in the non-breeding season. Females showed similar caching intensities year-round. Although males tried to defend their hoards, females frequently retrieved male-made caches. Overall, results showed that although New Zealand robins cooperate to raise offspring during the breeding season, conflict between the sexes occurs year-round. Males and females display different behavioural strategies to gain access to experimental food sources, which appear to lessen male–female competition for food and evenly distribute food resources between the sexes.     

Dynamics of space use and male vigour amongst wood mice,Apodemus sylvaticus,in the cereal ecosystem

The spatial organisation of male and female wood mice,Apodemus sylvaticus, was investigated in a large-scale radio-tracking study on arable farmland near Oxford, United Kingdom, during the breeding season. Both sexes had significantly larger home ranges in the breeding season than at other times, and the breeding season home ranges of male (X = 1.44 ha) were significantly larger than those of females (X = 0.49 ha). Home range overlap was significantly greater between males, and between males and females, than it was between females. Overlap between males tended to be greatest in heavily utilised areas. Except during sexual consortship, there was minimal evidence of dynamic interaction among individuals. Home range sizes of breeding males varied widely, as did their body weights. There was no relationship between male body weight and home range size or any other movement parameter. However, males with the largest home ranges had the highest scores on all other movement parameters, indicating that they expended more energy in movement. These more vigorous males had access to the home ranges of more females than did males with small home ranges.