摘要:

The costs and benefits of fighting in bovids are high in terms of injury and reproductive success, respectively. The breakage of a horn would curtail reproductive success permanently. Therefore, the horns of bovids should include sufficient material so that they are strong enough to be unlikely to break in fighting but without being too heavy to carry around. The forces developed during fighting were measured in a computerized analysis of film of blackbuck and bighorn sheep. All possible modes of failure were investigated using a mechanical analysis to see how the horns are most likely to fail.The maximum possible force developed during fighting is 3400 N for the bighorn sheep and 456 N for the blackbuck. Bending stress, shear stress, deflection, strain energy and critical crack lengths were calculated for the horns of these two bovids. Horns are most likely to fail in bending as indicated by safety factors. Most of the force is taken in compression due to the curvature of horns. Shear stresses are insignificant and deflections are negligible during the most forceful encounters.The safety factor in bending of the horn of the bighorn sheep is greater (10) than that of the horn of the blackbuck (3.4) because the forces are probably more variable and unpredictable in the fighting of the former.All of the energy of fighting is absorbed by the body musculature because horns store less than 1% of the energy produced in fighting as strain energy when they bend. Cracks and scratches mustbe more than 60% of the transverse basal dimensions of horns in order for there to be catastrophic failure at the maximum stresses developed during fighting.The horns of the blackbuck and the bighorn sheep appear to be minimum weight structures given the variability of the forces acting on them and are unlikely to break in fighting given the forces calculated from the analyses of films.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04983.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Factors influencing the rate of sibling cannibalism in larval and juvenile sharptooth catfish,Clarias gariepinus, were investigated under controlled conditions. The circum‐oral barbels were found to be more important for the capture of prey than the eyes. Cannibalism starts at a mean total length of 8 mm, three and a half days after the start of feeding and ceases to be of significance at approximately 80 mm, 47 days after the start of feeding. Two distinct types of cannibalism were evident, both of which are primary functions of the relationships between predator mouth width and prey head width. Type I cannibalism, which occurs in the length range from 8 to 45 mm, is characterized by the prey being caught tail‐first and swallowed up to the head, which is subsequently bitten off and discarded. Type II cannibalism on the other hand is characterized by the prey being swallowed head first and whole. During this phase, the larger fish in the population have a mouth width exceeding the head width of the smaller fishes. Type I induced mortality was higher than that induced by Type II. It was concluded that the rate of cannibalism is a consequence of intraspecific aggressive behaviour, the level of which is determined by experimental conditions. Sibling cannibalism was found to be positively density dependent, significantly suppressed by shelter and negatively correkated to food availability. Food availability was shown to have the greatest effect on the behaviour of the fish and hence on the rate of cannibalism. Cannibals grow at a faster rate than non–cannibals. It was concluded that the high rate of Type 1 cannibalism enhances the natural differential growth rate of the fish which leads to Type I1 cannibalism. There is a strong positive correlation between predator and prey size. Electivity analysis showed that the larvae and the juveniles appear to select for larger prey items. The applied implications of these observations are discussed. It was concluded that sibling cannibalism is a highly specialized predation strategy which, under a given set of environmentally induced limiting factors, acts as a density dependent population regulatory mech

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04984.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In the Cervidae, sexual dimorphism in body mass, armament and structure of the breeding pelage appears to be, as in African antelope, a curvilinear function on openness of habitat. Sexes converge in characteristics towards male‐like monomorphism in deer that hide in dense cover, as well as in gregarious, cursorial dwellers in open terrain. Relative antler mass correlates with weight dimorphism. The most cursorial species, the wapiti (Cervus elaphus canadensis) and the caribou (Rangifer farandus) converge towards male monomorphism, with the wapiti showing strong reduction in weight dimorphism (compared to red deer C.elaphus hippelaphus), and structure of the breeding pelage, but not in weaponry. Male and female caribou converge strongly in the structure of the breeding pelage, less so in weaponry, and least in weight dimorphism; antlers in female caribou are thus comparable to horns in male‐like females of plains bovids. In weight dimorphism, wapiti have almost reached the level of the African grazing antelopes of the tribes Alcelaphini and Orygini. Sexual dimorphism is maximal in mixed and concentrate feeders from semi‐open lands

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04985.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Daily activity levels of black‐backed jackalsCanis mesomeluswere determined in southern Africa through direct observation and radio‐tracking. Jackals have a bigeminus activity pattern that is closely paralleled by the activity levels of some of their most important prey. Although differences due to sex, age, study area and season of year were found, this activity pattern was most markedly influenced by light conditions during both the crepuscular and the nocturnal peri

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04986.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Two new species of Phytoseiidae (Acari: Mesostigmata) from southern England,Neoseiulus paramarinusandTyphlodromus ulexare described. A redescription is given ofTyphlodromus tiliaeOudemans, 1929 based on the examination of the holotype female.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04987.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Aspects of the morphology of the opercular region of siluroids (catfishes) were examined to determine the homologies of the opercular bones of loricarioid catfishes, a diverse monophyletic neotropical group. Homology of the component structures was inferred by examination of three criteria: (1) functional relations to the jaw abduction mechanism of primitive halecostome fishes; (2) positional relations to the bones of the suspensorium and the path of the preopercular laterosensory canal; and (3) pattern of development of the preopercular canal and lateral cheek plates of loricarioid catfishes. The majority of siluroids have lost one or more of the preopercular canal exit branches to the skin surface present in most primitive siluroids. A number of specializations of the canal pathway and components of the opercular series have occurred in loricariids. Trichomycterids have the preopercular canal reduced to a short branch from the pterotic. Callichthyids share the presence of a preopercular canal with primitive siluroids, but have lost the communication of the canal between the preopercle and pterotic bones. Callichthyids and scoloplacids share one additional loss of a preopercle exit. The second of two subopercular elements of astroblepids is homologous with the interhyal. Astroblepids and loricariids have lost one additional preopercle exit, the interoperculo‐mandibular ligament and the corresponding biomechanical couple for lower jaw abduction. Loricariids have probably lost the interopercle as well. These derived features of loricariids and astroblepids are viewed as specializations for a particular feeding behaviour: scraping algae and detritus from the substratu

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04988.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Georychus capensisis a seasonal breeder with the reproductive potential of producing two litters during the summer breeding season (August to December). These solitary mole‐rats signal to each other through the soil, by drumming with their hind feet. This drumming is probably important in spacing the burrow systems and in triggering the onset of reproductive behaviour. In a captive male the onset of drumming was accompanied by a rise in urinary testosterone concentrations and the enlargement of testes and accessory reproductive glands. The male appeared to drum with a different frequency to the female. Courtship is initiated by the male and copulation involves brief multiple intromissions. The gestation period is about 44 days and the mean litter size is 5.9 with a maximum of 10 pups. Development of the pups is relatively rapid. Inter‐sibling aggression begins to develop at 35 days, eventually resulting in the pups dispersing when about 60 days old. Body mass increases exponentially from birth to day 60 and the asymptote is reached around day 260. These features are compared with those of other solitary subterranean rodents and with those of the social Bathyergidae (Cryptomys hottentotus, Cryptomys damarensis and Heterocephalus glab

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04989.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Red acouchies were observed in French Guiana, and compared with agoutis. Acouchies frequent all forest habitats except disturbed areas. Strictly diurnal, they show most activity in early morning. Males prefer open forests, females closed habitats. The size of home ranges and the level of activity decrease in the dry season when food resources are at a minimum. The social unit is the family, one male and one female with juveniles. Family units are separated from each other. Each individual occupies a small home range which has several much‐frequented areas and many resting places, often located in hollow logs and consisting of one nest in use and several old leafheaps. There are no food reserves in the nest: fruits are buried over the whole home range. Within each social unit, every individual mainly lives alone and home ranges have little overlap. The percentage of males decreases from the juvenile to the adult stage. Populations show large year to year density variations. The red acouchy is not similar to the agouti, but instead represents an unique adaptation among the terrestrial forest herbivore

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04990.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Forty‐nine samples of skin from the mid‐ventral, ventrolateral and mid‐dorsal regions of six species of snakes were mechanically tested in uniaxial extension at 0.05 strain/sec. The species of snakes studied ranged from generalists to specialists for arboreal or aquatic habitats. Analysis of the loading curves revealed substantial variation in loads and maximum stiffnesses among samples from different dorsoventral regions within an individual and among homologous samples from different species. Skin thickness varied by a factor of more than five, but this only partially accounts for the differences in the force per width of sample at a given extension. Qualitative differences in the dermal collagen fibres are implied by the shapes of the loading curves and the terminal elastic modulus which varied from about 15 to 585 MN/m2. The strain at beginning of failure ranged from 0.12 to 0.60. The size of the scales within a skin sample was not a reliable predictor of the loading behaviour of the sample. Correlations between the mechanical behaviour of skin and specializations in locomotion and associated musculature are disc

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04991.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In the adult maleSaguinus fuscicollis, the scrotal skin and the area above the root of the penis are raised in a sharply defined cushion, which extends cranially into a rectangular suprapubic pad. The circumgenital area of the adult female resembles that of the male, except that the suprapubic pad is relatively and absolutely larger. A complex glandular organ, composed of holocrine and apocrine glands, is located beneath the epidermis of the circumgenital skin. In males, specialized holocrine glands associated with hair follicles predominate. They form a layer, 2‐3 mm deep beneath the epidermis. These holocrine glands have a complex alveolar structure and possess numerously branched excretory ducts. Each group of glands empties into a common duct which enters the hair follicle. In males, the apocrine glands are located predominantly at the periphery of the glandular pad and between the scrotal and perineal areas. The excretory ducts of most apocrine glands empty on to the skin surface in close spatial association with hair follicles. However, independent openings were also observed. In females, the specialized holocrine glands resemble those of males but are more frequently interspersed with apocrine glands. The apocrine glands are larger and much more numerous than in males, especially in the region of the labia majora. Gonadectomy of an adult male and female resulted in a reduction in the size of the holocrine glands but had much less effect on the apocrine glands of the scent organ. In addition, the sexual dimorphism in gland histology was retained years after castratio

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1988.tb04992.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY