摘要:

Age‐specific patterns of maternal weight, litter size, litter weight and reproductive effort were investigated for polar bears (Ursus maritimus) from western Hudson Bay. Most relationships were described by quadratic equations. Maternal weight in spring and autumn increased until 17 and 15 years of age, respectively, and then declined. Age‐related increases in maternal weight were thought to be associated with improving hunting skills. The relationships between age and litter size, litter weight and reproductive effort, in both the spring and autumn, increased until 14 to 16 years, followed by a decline. We speculate that age‐related decreases in reproductive performance are due to undetennined processes associated with ageing that impair the accumulation of fat stores necessary for reproduction. Pregnant females lost an average of 127 kg overwinter which represented an average of 43.5% of their autumn weight. Fat stores remaining after the overwinter fast may be critical for maintaining an energy supply to cubs once they return to the sea ice where the distribution and abundance of their prey is unpredictable. We suggest that maternal condition is an important factor contributing to lifetime reproductive success in polar

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04863.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Few wind tunnel studies of animal flight have controlled or corrected for distortions to behaviour, physiology or flight aerodynamics representing the difference between flight in the tunnel and flight in free air. Aerodynamic correction factors are derived based on lifting‐line theory and the method of images for an animal flying freely within closed‐ and open‐section wind tunnels; the method is very similar to that used to model flight in ground effect, and as in ground effect the corrections to induced drag may be substantial. These correction factors are used to estimate bound wing circulation, drag and mechanical power for comparison with free flight, and to derive testable predictions of optimum flight strategies for an animal in a tunnel. In an open‐section tunnel, mechanical power is increased compared to free flight, and the animal should fly at the tunnel centre. In a closed tunnel mechanical power is usually reduced, and substantial savings are available, particularly at low speeds, if the animal flies close to the tunnel roof. Anecdotal observations confirm that birds and bats adopt this strategy. The mechanical power‐speed curve in a closed tunnel is flatter than the curve for free flight, and this may explain the flat metabolic power‐speed curves for birds and bats obtained in some m

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04864.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Fertile eggs obtained from alligators reared in captivity typically exhibit high rates of embryonic mortality. Also, the fatty acid composition of the yolk lipid of the captive eggs is markedly different from that observed in eggs from wild alligators, possibly as a result of differences in maternal diet in the two situations. The fatty acid compositions of tissue lipids during the embryonic development of wild and captive alligators were compared. The lipids of liver, adipose tissue and heart of the two types of embryo displayed fatty acid profiles which generally reflected the acyl compositions of the respective yolks. Thus the lipids from these tissues of the captive embryos contained markedly higher proportionate levels of linoleic and linolenic acids, lower levels of palmitoleic acid, and, in general, lower levels of docosahexaenoic acid and other C20 and C22 polyunsaturates, in comparison to the values for the wild embryos. In contrast, the fatty acid composition of the brain phosphoglycerides was very similar in the two types of embryo. Thus, at least in those embryos which had survived during the developmental period studied, the brain was able to maintain a relatively constant fatty acid composition, in spite of major differences between the wild and captive eggs in the proportions of the various fatty acids supplied from the yolk. It is suggested that a major cause of embryonic mortality in the captive embryos could be a failure to maintain an adequate level of docosahexaenoic acid in the developing brain.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04865.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The elevational distribution of small mammals was surveyed by three transects during 1989–90 at Yushan National Park in subtropical central Taiwan. As a result of this survey, a sample of 1205 animals was obtained. Based on the sample, the sampling regime and elevational distribution of these species is reported with consideration of the spatial and temporal components. To detect the presence of all species and to estimate their relative abundances at any elevational site, one must trap consecutively for a minimum of five days.‘Trap competition’is common in trap lines, resulting in a few traps being responsible for all the captures. Besides, common and rare species at each elevation have different trap responses. The elevational distribution of small mammals shows substantial seasonal and spatial variation. Furthermore, the plant succession is demonstrated to influence the species composition and relative abundances of the small mammal community at the same elevation. Despite the variation, some general patterns of elevational distribution emerge.Tamiops muritimusoccurs above 2000 m and is common at 2000–3000 m.Apodemus semotusis widely distributed from 1400 to 3700 m, but becomes rare below 1500 m and above 3600 m. The congenericA. ugruriusis known only from lowlands in Taiwan and reaches no higher than 1000 m.Niviventer culturutusoccurs at about 2000–3000 m, whereasN. coxingioccurs no higher than 2000 m and is common below 1300 m. Two species of microtine also show replacement in elevational distribution.Eothenomys melunogusteroccurs from 1400 to 3000 m andMicrotus kikuchiibecomes abundant only above 3000 m. Two shrews,Anourosorex squumipesandSoriculus fumidus, are widely distributed at different elevations, but their distribution seems to be little related to

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04866.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

In the frog,Rana esculenta(L.), the liver can change in volume by over 25%, depending on the respiratory conditions of the animal: in well‐oxygenated specimens the organ can hoard about half of the total amount of erythrocytes in its sinusoids, and release them into the bloodstream under conditions of hypoxia. This phenomenon can be observed at a temperature of 6°C by comparing the liver volumes and haematic values of chlorobutanol‐anaesthetized animals exposed to the air or submerged in still water (a condition which induces hypoxia): the blood volume remains constant, at about 5 ml per 100g of body weight, but red blood cell count and haematocrit value differ by as much as 50%. At 18°C there is an increase in oxygen demand and in anaesthetized animals, which rely totally on cutaneous respiration, the compensatory liver mechanism can no longer be observed, since all the available erythrocytes are already circulating in a blood volume which, depending on respiratory conditions, can vary between about 7 and 8ml/100g. At 30°C, cutaneous respiration alone does not allow the anaesthetized animals to survive long enough to stabilize their haematic para

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04867.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Changes in the water quality and temperature relationships of ponds may affect the structure of amphibian assemblages. The survival, time to hatching, hatching size and hatching stage of newt embryos were studied in the three British species (Triturus cristatus, T. helveticusandT. vulgaris), at two temperatures and two pHs. AllT. cristatusembryos failed to hatch at pH 4.5, whereas over 80% ofT. helveticusandT. vulgarisembryos hatched successfully at the same pH. At pH 7.5,T. cristatussurvival was the same as the other two species, after the 50% mortality due to the homomorphism of chromosome 1 was taken into account. Temperature had no effect on survival of embryos. Time to hatching was two to four times longer at 12°C than at 17°C. Low pH shortened development time inT. vulgarisbut not inT. helveticus. Low pH, but not temperature, affected size at hatching, withT. helveticusandT. vulgarisembryos emerging at a smaller size and earlier stage of development under acidic conditions. This reduction of size at low pH affectedT. vulgarismore thanT. helveticus. We predict thatT. cristatusembryos will be the most vulnerable of the three species to acidification in nature. Warm ponds will result in rapid embryonic development, butT. helveticusandT. vulgarislarvae hatching in acid ponds will do so at a smaller size and earlier stage of development. The pattern of vulnerability to acidification within amphibian assemblages may change during ontogen

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04868.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

We studied the epidemiology ofHeligmosomoides polygyrus(Nematodd) in the wood mouse (Apodemus sylvaticus) in an arable ecosystem, and investigated any association between infection and the movement patterns of male mice by manipulating worm burdens. Methods included the live‐trapping of mice, estimation of worm burdens by faecal analysis, administration of either an anthelminthic or water (as a control) and the radio‐tracking of selected animals.Heligmosomoides polygyrusshowed an overdispersed distribution pattern, with prevalence tending to be higher in males and heavier mice. Prevalence and intensity peaked in spring and declined in autumn both in the entire population and in adults. This seasonality in the arable ecosystem in comparison to woodland may arise due to the direct and indirect impact of agricultural practice.To investigate the link between infection and movements, radio‐tracked mice were classed as either‘Uninfected’or‘Infected’; mice were also classed as either‘Control’or‘Dosed’. There were no significant differences in movement parameters between‘Infected/Dosed’and‘Infected/Control’, possibly because treatment was not administered sufficiently frequently. Both‘Infected’classes of mice moved significantly faster than‘Uninfected’ones, and‘Infected/Dosed’mice moved significantly further than‘Uninfected’ones. The percentage of time spent moving was also greater, and the home range area was larger, for‘Infected/Dosed’and‘Infected/Control’than for‘Uninfected’mice. The observed differences in movement may have been the result of either the behaviour of mice influencing

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04869.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The effect of different variables on the territory size and defence level of tawny owl (Strix alucoL.) populations was studied in two habitats: mixed farmland (1976–1978) and town (1986–1988). Territory size was determined by plotting the position of territorial challenges (hoots) of males which were individually recognizable in most cases. No differences were found in size, defence, number of competitors and biomass between territories in farmland and in town, but territories in town were more fragmented and showed a larger nearest neighbour distance. Size of rural territories was adequately predicted both by some structural habitat features and food supplies, while size of urban territories was affected only by habitat structure and by years of territory occupancy. No effect on territory size by competing neighbours was found in either habitat, thus confirming that behavioural interactions between the owners of territories and potential settlers prevent a decrease of territory size.Defence level of urban territories was affected by 'social’variables (nearest neighbour distance and years of occupancy), structural variables (percentage of poplar grove and diversity), and food supply, while in rural territories only structural variables (fragmentation or natural vegetation) and food supplies affected defence level.This was due to different settlement tactics in the two areas, depending on the extent and quality of suitable ha

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04870.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04871.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1994.tb04872.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY