摘要:

The dental apparatus or Aristotle's lantern of sea‐urchins is a complex system of interacting skeletal ossicles, joints, muscles and ligaments arranged in a rigorous geometry and involved in a variety of activities. In this paper we study the movement of the whole lantern system modelled as a rigid body. The model lantern is constrained at its apex by the peristomial membrane and its movement is controlled by five pairs of antagonistic forces (retractor and protractor muscles). The other main forces applied to the lantern are the elastic reactions of both muscles and ligamental structures (compass depressors and peristomial membrane). The lantern is allowed to perform vertical movements and lateral inclinations but cannot rotate around its main axis. The equilibrium conditions of the system have been found by means of a numerical iterative procedure for solving non‐linear equations. The results of the present analysis allow simulation of the overall mechanical activity of the lantern taking into account the experimental data regarding active and passive muscular forces and the tensile constraints due to ligame

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04312.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Eremitalpa granti namibensisis a small, blind insectivorous mole endemic to the sand dunes of the Namib Desert. Unlike most other subterranean mammals,E. g. namibensislacks a permanent burrow system and forages for its prey on the dune surface at night. This study examines the natural dietary habits and foraging behaviour ofE. g. namibensisin relation to resource abundance and distribution in the Namib dunes.Stomach content analysis revealed termites as the major dietary item with other invertebrates being of only minor importance. Biomass of potential prey items was found to be low and food resources patchily distributed. It is suggested that desert moles opportunistically exploit a sedentary prey resource which occurs in patches of high concentrations, hence avoiding the energetic costs implicit in pursuing more mobile prey. Qualitative and quantitative descriptions of nocturnal foraging paths were undertaken so that searching behaviour could be related to the variation and distribution of food items. It is concluded that movement patterns of moles are effective in encountering localized areas of high prey concentrations and in minimizing energy expenditure in an energy‐sparse environmen

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04313.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A hedgehog population in southern Sweden was studied by capture‐mark‐recapture during 1972–1979. Each animal was weighed, sexed and marked with one numbered clip in each ear.The number of subadult and adult hedgehogs was about 20 in the first two years, 1972–1973. Numbers then increased and approximately doubled and the population peaked in 1978. A decrease came in 1979.The estimated number of juveniles produced varied between years with the lowest figure (15 juv.) in 1974 when the population was low and the highest in 1977 (39 juv.) when the population was high. As no captured subadult female had suckled young, estimates of recruitment rate assumed that females did not reproduce until they were adult. The average number of juveniles per adult female was 2.8. Recruitment rate did not show any correlation with non‐juvenile population densities.For both juveniles and non‐juveniles the annual mortality varied greatly between years. Average yearly mortality was 47% for non‐juveniles and 34% for juveniles.For non‐juveniles, most of the total mortality occurred during winter, ranging between 26% and 43% (average 33%), and increased with increasing densities of non juveniles. Juvenile winter mortality varied between 6% and 94%, averaging 33%.Summer mortality of non‐juveniles averaged 15%, ranging between 3% and 22%. Traffic kills were the predominant cause of death. Only a few juveniles were found dead during summer and autumn.There were no statistical differences in age‐specific survival rate between males and females and, generally, no differences in survival rate between the age categories within each sex. It is argued that the population size appears to be more influenced by environmental factors, such as food availability, winter nest sites and winter climate, than by densit

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04314.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

OttersLutra lutraL. which feed in the sea in Scotland frequently wash in fresh water. Experiments were carried out with otter pelts and with captive otters, to study the biological function of this behaviour.In vitro, the fur of otters lost much of its thermal insulation after five soakings in sea water and subsequent drying. Otters were fed in sea water or fresh water, with or without simultaneous access to alternative fresh water. When fed in sea water, otters used the alternative fresh water much more than when fed in fresh water, they were more reluctant to enter sea water if no alternative fresh water was present, and without this alternative fresh water they showed signs of hypothermia. After swimming in sea water the animals spent more time grooming and rolling. Without fresh water present the otters' fur lost its capacity for retaining air under water. These observations suggest an explanation for the restricted distribution of otters living along the coast, and for the lack of use of marine habitats by small mammals in general.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04315.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Recent comparative studies point to the importance of mortality schedules as determinants in the evolution of life‐history characteristics. In this paper, we compare patterns of mortality from natural populations of mammals with a variety of life histories. We find that, after removing the effects of body weight, mortality is the best predictor of variation in life‐history traits. Mammals with high levels of natural mortality tend to mature early and give birth to small offspring in large litters after a short gestation, before and after body size effects are factored out. We examine the way in which life‐history traits relate to juvenile mortality versus adult mortality and find that juvenile mortality is more highly correlated with life‐history traits than is adult mortality. We discuss the necessity of distinguishing between extrinsic sources of mortality (e.g. predation) and mortality caused by intrinsic sources (e.g. costs of reproduction), and the role that ecology might play in the evolution of patterns of mortality and fecundity. We conclude that these results must be explained not simply in the light of the demographic necessity of balancing mortality and fecundity, but as a result of age‐specific costs and benefits of reproduction and parental investment. Detailed comparative studies of mortality patterns in natural populations of mammals offer a promising avenue towards understanding the evolution of life‐history

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04316.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Water vole latrines were studied on four of the principal rivers in the North Yorkshire Moors National Park. Water voles occupied ‘core’ and ‘peripheral’ sites on these rivers. Core sites were marked by latrines and held breeding colonies of voles; animals at core sites were readily captured. Peripheral sites were not marked by latrines, but showed erratic water vole activity as measured by activity indices (tracks m‐1of muddy bank month‐1). It was never possible to catch voles at these peripheral sites, and there was no evidence of breeding.Latrines on core sites were not maintained outside the breeding season. The appearance of latrines coincided with the start of the breeding season, and while they were maintained, latrines provided a useful guide to the number of animals in the area. A curvilinear response was obtained between latrine production and date, with production rising steadily from early spring until mid‐to‐late summer, which suggests that latrines signal sexual activity.Future studies on the distribution of water voles should use a variety of techniques. Latrine surveys will only be applicable during the breeding season at core sites. Similarly, live‐trapping will only detect water voles at core sites. Tracking provides the best evidence that water voles are present at peripheral sites even though they may not be breeding

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04317.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The ultrastructure of the intrapigmented aesthetes which occur in specific areas of the different valves ofCallochiton achatinusare described. The possible functions of the aesthete and the pigmented body are discussed in the light of their ultrastructure and the ecological requirements of the animal. The properiostracum inC. achatinusis unusually thick and has a structure very similar in appearance to that of collagen.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04318.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The relative ages of individuals in a complete wild‐captured colony of 13Cryptomys hottentotus hottentotusand a complete wild‐captured colony of 25Cryptomys damarensiswere determined by means of tooth wear and eruption patterns and through the degree of ossification of their skeletons.From sequential tooth wear and eruption patterns four relative age classes were discerned inC. h. hottentotusand five inC. damarensis. These relative age class allocations were supported by the studies on the ossification of the skeletons.InC. damarensis, older animals are not necessarily the larger‐sized individuals. InC. h. hottentotus, however, older animals are usually the larger‐sized individuals. The reproductive pair in each of theCryptomysspecies are the oldest or amongst the oldest individuals in the colony.Individuals in a second colony ofC. damarensiskept under laboratory conditions for three years maintained greatly disparate body masses which were correlated with the role of the individual within the colony and not, where it was known, with the age of the animal.An analysis of 13 body and skull measurements performed on a complete colony of 13C. h. hottentotusand a complete colony of 25C damarensisrevealed that onlyC. damarensisshowed sexual dimorphism. This dimorphism was apparent from an early age but became more pronounced in older

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04319.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Diamond terrapins,Malaclemys terrapinLatreille, inhabit salt marshes and estuaries where they may encounter sustained high salinities for weeks or months. Terrapins can discriminate between salinities. When salt‐loaded they avoid drinking high salinities (27.2–34.0%), drink small amounts of salinities which are a little more concentrated than the blood (13.6–20%), and drink copious quantities of lower salinities (0–10.2%). After seven days in full sea water (34%) they can rehydrate themselves in<15 min if given access to fresh water. Terrapins are capable of drinking from the thinnest of freshwater films (1.6 mm), exploit menisci and have specific postural responses to collect small quantities of fresh water from horizontal and vertical surfaces. Specimens ofMalaclemys terrapinrespond to the vibration of simulated rainfall by rapid emergence followed by drinking from thin films, either on the exposed substratum or from the surface of the water column. Under simulated conditions of heavy rainfall they collect rain directly fro

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04320.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A detailed histological study showed that in two protogynous sparids,Chrysoblephus laticeps(Cuvier) andC. cristiceps(Cuvier), gametogenesis follows a pattern typical of temperate sparids and marine teleosts in general. Fertilization is external and both species produce numerous small eggs which are pelagic. They have a restricted summer breeding season and gonadal recrudescence is well correlated with temperature and photoperiod. Behavioural observations showed that C. laticeps are pair‐spawners, releasing their gametes well above the substratum after an elaborate courtship routine. The testes of these fishes are small in relation to those of other sparids and are thought to reflect basic differences in the mating systems of sex‐changing and gonochoristic spec

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1990.tb04321.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY