摘要:

The reproductive tracts of male sub‐Antarctic fur sealsArctocephalus tropicalis(n= 123), taken at Gough Island (40° 20'S, 9° 54'W) between November 1977 and October 1978, were examined. The presence of spermatozoa in the epididymal tubules showed that all males ≥4 years old had reached puberty, and the marked slower increase in mean testis weight and baculum length suggested that sexual (social) maturity was approached by 8‐year‐olds. Full adulthood was attained at 10–11 years of age based on the peak in mean testis and prostate weights, and mean baculum length. Secondary sexual characteristics were only fully developed in males ≥9 years old. A significant decline in mean testosterone concentration, and in testis, epididymis and prostate weights showed that adult males were reproductively quiescent during winter from May to July when seminiferous and epididymal tubules had lowest mean diameters with no spermatozoa present. Both the mean plasma testosterone concentration and mean testis weight peaked twice during the austral summer. The first peak coincided with the breeding season, and the second peak with the moulting period when adult males were impotent. Photoperiodic cueing might explain this s

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05670.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Drift samples were taken with paired nets on 19 occasions over a 12‐month period in Tai Po Kau Forest Stream (TPKFS), Hong Kong. Mean drift density (±1 S.E.) was 277·9 ± 25·0 individuals 100 m‐3; peaks in density were apparent during autumn and spring. One hundred and two taxa were recovered from the drift, and the total number of taxa drifting was positively related to water temperatures. Over 99% of the aquatic animals collected in drift samples were insects, 10 taxa of which constituted 67·3% of the entire catch. Baetid mayflies dominated the composition of the drift, comprising 40·4% of individuals caught.Seasonal changes in the drift of individual taxa were evident, reflecting significant relationships between drift densities and water temperature:SimuliumT1(Diptera).Anisocentropus maculatus(Trichoptera) andAmphinemura chui(Plecoptera) drifted most in winter, whereasChimarraT1,Polymorphanisus astictus(Trichoptera),Helodes#1 and cf.Rhantussp. (Coleoptera) were most numerous in summer. Drifting mayflies showed spring (Indobaetissp.,CinygminaT1,SerratellaT2), autumn (Baetiellasp.,PseudocloeonT2), or spring and autumn (Baetisnrpseudofrequentus) peaks which were not clearly related to water temperature. In only two cases (A. maculatusandP. astictus) was TPKFS drift seasonality associated with life‐cycle events. Overall, there was no evidence of community‐level trends in the periodicity of stream drift in this seasonal tro

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05671.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The growth of black kitesMilvus migranswas studied in 1981, 1982 and 1984 at the Doñana Biological Reserve (south‐west Spain). Fifteen variables were submitted to a principal component analysis in order to characterize the growth pattern of the young. In general, in the nestlings that fledged, rapid weight gain corresponded to rapid growth of the tarsus and feathers. For nestlings that starved, tarsus growth took priority over weight gain. Within the same brood, the last‐hatched sibling grew more slowly than its older sibling and the differences between them increased in proportion to the hatching asynchrony. Brood size did not affect growth as clearly as hatching order and hatching asynchrony. Increased rainfall and lower maximum temperature, factors that seem to make the search for food more difficult, had negative effects on the youngest sibling in a multiple brood and on single nestlings. The only environmental variable that had an effect on all of the nestlings was the hatching

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05672.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The effects of diets differing in energy and water content on the energy turnover rates and water flux of fourGerbillurusspecies have been examined in the laboratory.Gerbillurus tytonis.a dune species, had higher than predicted daily energy expenditure (DEE) and high water turnover rates (WTR) for a small desert mammal. The largeGerbillurus setzeri, which occurs on gravel plains, has slightly lower than predicted DEE and lower WTR than the other gerbil species studied. TheGerbillurusspecies examined have DEE and WTR that are affected by the protein content and potential water yield of food eaten. The importance of diet selection for water and energy budgets are discussed as adaptive strategies employed for survival and reproduction within the southern African arid zone.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05673.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The elephant with its low surface‐to‐volume ratio presents an interesting problem concerning heat dissipation. To understand how such large mammals remain in thermal balance, we determined the major avenues of heat loss for an adult African elephant and an immature Indian elephant. Because conventional physiological measurements are difficult for these animals, the present study used a non‐invasive technique, infrared thermography, to measure skin temperatures of each elephant. Detailed surface temperature profiles and surface area measurements of each elephant were used in standard equations for convective, conductive and radiant heat transfer. Results demonstrated that heat transfer by free convection and radiation accounted for 86% of the total heat loss for the elephants atTa= 12·6 °C. Heat transfer across the ears, an important thermal window at high ambient temperatures, represented less than 8% of the total heat loss. Surface area of the animals, and metabolic heat production calculated from total heat loss of the African elephant, scaled predictably with body mass. In contrast, the thermal conductance of the elephants (71·6W/°C, African; 84·5W/°C, Indian) was three to five times higher than predicted from an allometric relationship for smaller mammals. The high thermal conductance of elephants is attributed to the absence of fur and appears to counteract reduced heat transfer associated with a low surface‐to

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05674.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The breeding biology of the gentoo penguin,Pygoscelis papua, was studied over a three‐year period (1986–1988) at Bird Island, South Georgia, with particular reference to birds of known age or breeding experience. Laying date varied significantly between all three years, being three weeks later in 1987, when the breeding population decreased markedly. Factors involved in the timing of breeding are discussed. Within years egg‐laying was highly synchronous: 95% of clutches were initiated in 14·5 days or less. The incubation period was 35 days and the laying interval, between the two eggs, 3·3–3·4 days. Chicks creched when 25–30 days old, and this varied between years, possibly related to food supply and chick growth. Chicks left the colony for the first time between 75 and 85 days of age. The breeding population at Bird Island decreased by 20% and increased by 84% in successive years during the study period. Breeding success (chicks fledged per egg laid) varied between 0·33 and 0·65 within colonies, but for the whole island was very consistent over the three years: 0·45, 0·51 and 0·47. Overall, colony differences were not correlated between years. Disturbance from Antarctic fur seals,Arctocephalus gazella, is suggested as the cause of consistently lower breeding success at one colony. Mean egg weight varied annually, and with age of the breeding bird, nest location and, in one year, with laying date. Young, first‐time breeders laid smaller eggs and had lower breeding success compared to older, experienced birds, similar to other seabirds. However, they differed from other species in laying on average earlier than older birds. The relationship between age, egg weight, laying date and breeding success is discussed in relation to predation and s

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05675.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The specific composition and diversity of the zooplankton in 18 impoundments in Zimbabwe were analysed on the basis of samples taken in July and August 1983. All the lakes lay at altitudes over 1200 m, with the highest at 2270 m.Thirty species of Rotifera and 20 species of Crustacea were identified, but the mean numbers of species per lake were 5·7 rotifers and 4·5 crustaceans. Some records represent considerable extensions of known ranges.Daphnia laeviswas the most widespread and frequently dominant crustacean, while among the rotifersKeratella cochleariswas most frequently dominant, particularly in the lakes at the upper part of the altitudinal range.Ordination and cluster analysis of the associations revealed a group of lakes with closely interrelated similarities which could be attributed to their lying on tributaries of the same river system and receiving trout from the same hatchery. These analyses also picked out the lowest locality as the most divergent and the one showing the most typically tropical zooplankton association. Although all the lakes were well within the tropics, their altitudes seem to have excluded some of the widespread tropical African zooplankters.The possibility that these associations could be formed by random colonization is discussed and dismissed.The momentary species composition of these Zimbabwean zooplankton associations was similar to that given by Pennak (1957) for the world average, although the mean number of species of Copepoda was significantly lower than the world average. Comparisons with data from Brazil and Lake Maggiore indicate the need for a further geographical analysis.A comparative study of the species diversity in impoundments of different sizes indicates that, over several orders of magnitude of area, the number of species of Ciadocera and Copepoda shows a small increase, but the number of species of Rotifera shows a much larger and more variable increas

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05676.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Salmon (Salmo salar) formed the largest proportion by mass offish found in the stomachs of red‐breasted mergansers (Mergus serrator) shot during the smolt run in north‐east Scotland. Salmon parr represented approximately two‐thirds by mass of juvenile salmon eaten, whilst smolts were present in a smaller proportion than previously predicted. The median lengths of parr and smolts eaten were 70 and 115 mm, respectively; the latter being significantly smaller than the smolt population sampled during annual production estimates on the

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05677.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The current consensus is that only one type of horn, the ossicone, exists in the giraffe and that the central or median horn is both structurally and developmentally similar to the paired parietal horns. We have shown that the paired ossicones are composites of three structures: an innermost large frontoparietal boss base, the ossicone, and outermost layers of secondary bone growth. The median hom, to which we assign the name ‘giraffacone’, is a composite of only two structures: the median frontonasal boss and the overlying secondary bone growth. In older males, secondary bone growth due to combat clashes covers the entire calvaria. In females, there is little or no such secondary bone growth over the ossicones and the rest of the skull roof. Consequently, the median horn consists only of the frontal boss. The shape of the ossicones without the secondary bone layer, as revealed in young males and females, is herein described. It is shown how a distinction can be made between the variation in shape due to secondary bone growth and the variation of the ossicone. It is apparent that ossicone shape is not as variable as previously thought. We found secondary bone growth in the horns ofPalaeomeryxand in the ossicones of Giraffinae,Giraffokeryx punjabiensis, Samotherium africanumand Sivatherii

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05678.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Eggs of the tuatara,Sphenodon punctatus, were incubated either buried or half buried in vermiculite at constant temperatures of 15, 18, 20, 22 and 25 °C and constant water potentials between —90 and —400 kPa. Many clutches failed completely, possibly because they had been taken from females prior to proper shell development. Failed eggs were significantly smaller than successful eggs. Incubation is unsuccessful at 15 °C. Hatching success is high between 18 and 22 °C but low at 25 °C, but equally successful between 18 and 22°C. Incubation is strongly influenced by temperature, with mean incubation periods of 328 days at 18 °C, 259 days at 20 °C, 169 days at 22 °C and 150 days at 25 °C. Water potential generally has little influence on incubation time at a given temperature. Buried eggs hatch sooner than partially buried eggs at 20 °C but the large range makes significance dubious.Eggs on the driest substrata at 18 and 20 °C lose water initially but then gain water through the rest of incubation. Eggs in all other conditions gain water throughout incubation, with the rate of i water absorption being maintained or increasing late in incubation. The suggestion that increasing rate of water absorption late in incubation facilitates explosive hatching is not supported. Egg mass at the time of hatching varies from 132 to 398% of initial values, depending on incubation conditions. Final egg mass is not affected significantly by incubation temperature. Hence, rates of absorption increase with temperature.Water potential has no influence on hatchling size. However, hatchlings from buried eggs generally are significantly larger than those from partial

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb05679.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY