摘要:

Seasonal and diel behaviour of six sharptooth catfish,Clarius gariepinus(Burchell), was monitored in Lake Ngezi, Zimbabwe, from May 1986 to February 1987. All specimens were equipped with surgically‐implanted radiotransmi tters, 48–49 mHz, after they were anaesthetized in 6 mg l‐1quinaldine. This represented the first known use of this methodology in subSaharan Africa.It was determined thatC. gariepinusexhibited three movement patterns on a day‐to‐day basis: long‐distance movements ( 2200 m), moderate movements (c. 40–200 m) and local movements (<40 m). Major movements were not restricted to night‐time conditions, nor were inshore/offshore movements related to time of day. Seasonal activity peaks occurred in July/August 1986 and again in January 1987, with rate of swimming exceeding 470 m/h on some occasions. Home range of some individuals encompassed the entir

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02575.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A simplified population equation for Monodon Pnonoceros shows that current estimates of the values of the life history variables are inconsistent with the hypothesis of a stationary population. Instantaneous adult mortality must be less than 0,10/yr, not the published estimate of 12–13%/yr, for accepted values of the other variables to be consistent with stationarity. For sustainable harvest, permissible exploitation rates are no larger than 3–4%/yr, and instantaneous natural mortality must then be well below 10%/yr. Present uncertainty in the values of survival rates, both of adults and young, contributes twice as much to uncertainty in population growth rate as does uncertainty in reproductive ra

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02576.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Stadia 11‐VII and adults of Chondromorpha kelaarti (Humbert) can be separated by segment number, length, breadth and paired legs. Sexes are distinguished from stadium IV and the sex ratio vaned around SO%, though females were prevalent in May and June.In females, a positive and significant correlation was found between number ofeggs present and body width at the 17th Segment.Population density and biomass of C. kelaarti varied from 0.06 to 12.94 and 1.75 mg to 811.24 mg per 0.1 mz, respectively. From May to November, populations of C. kelaartiare aggregated in distribution.Chondronrorphu keluurti passed the dry season in late stadia (VI, VII and adult) and may complete the life cycle in one or two year

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02577.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Experiments were performed to determine the mechanical importance of the fascia lata in stopping the hind limb during its rearward extension and reversing the direction of leg swing. Samples of fascia lata from a number of different mammals were subjected to tensile tests. Tangent Young's moduli reached about 0.5 GPa and stresses at failure about 50 MPa for fascia from each of the species examined. Energy losses incurred in a loading‐unloading cycle were generally about 20%. The moment arms of the fascia lata, in combination with its muscle, about the hip and knee joints were determined and the extension of the fascia lata while its muscle is active was estimated. Calculations suggest that the fascia lata could help to reverse the backward swing of the hind limb by recoiling elastically shortly after the foot leaves the ground. Substantial savings of internal kilnetic energy could be mad

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02578.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The diets of Erpobdella octoculata, Glosiphonia complanata and Helobdella stagnalis on the stony littoral zone of eutrophic Crose Mere were examined over two years using the precipitin test. The abundances of food organisms were measured. For all leech species, juvenile mortality was greatest in locations where a low ratio of prey abundance to recruited leech abundance occurred, and the intensity of feeding byErpobdella and Helobdellafell slightly in late summer when large numbers of juveniles of these species were present; these suggest the involvement of food in juvenile mortality, Seasonal changes in feeding intensity were similar for all leech species, with the exceptions outlined above and forGlossiphoniain April when feeding by brooding adults ceased, at which time the severity of any interspecific competition would have been reduced. Within a leech species, there was little change in the food spectrum as the leeches grew. Niche breadth was lowest forErpobdellaand highest forHelobdella.Niche overlap was greatest between Glossiphonia and Helobdella, and there was a trend for overlap values to be lower betweenGlossiphoniaandErpobdelluthan betweenHelohdelluandErpohdellu. Erpobdellafed mainly on chironomids and oligochaetes,Glossiphoniaon molluscs, oligochaetes and chironomids, andHelobdellaon oligochaetes, chironomids,Asellus,molluses and amphipods, all in decreasing order of importance. It is suggested that coexistence in the leech species may be due in part toErpobdellaandGlossiphoniahaving ‘food refuges’ in chironomids and molluscs, respectively, withHelobdellubeing more of a general preda

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02579.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

In rockhopper penguins (Eudyptes crestatus), liver concentrations of retinol (vitamin A) were significantly higher in post‐moult than in pre‐moult birds. In Magellanic penguins (Spheniscus magelianicus), plasma concentrations of retinol were significantly higher in post‐moult than in pre‐moult birds; liver retinol concentrations were also higher, but not significantly so.The pre‐ and post‐moult Magellanics had higher liver and lower plasma retinol concentrations than the pre‐ and post‐moult rockhoppers.Captive blackfooted (jackass) (Spheniscus demersus), king (Aptenodytes patagonica) and Humboldt (Spheniscus humboldti) penguins had liver vitamin A stores significantly lower than those of the free‐living rockhopper, Magellanic, gentoo (Pygoscelis papua), emperor (Aptenodytes forsteri), chinstraps (Pygoscelis antarctica) and Adélie (Pygoscelis

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02580.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The skin ofMyxine glutinosncontains both velocity‐sensitive and displacement‐sensitive mechanoreceptors. These can be distinguished from each other by the different time course of their response to skin indentation. Velocity receptors gave a brief response, consisting usually of three to four action potentials which could only be elicited by movement of the skin. No velocity receptor was spontaneously active. Displacement receptors, some of which were spontaneously active, gave a prolonged discharge which continued, with only slight adaptation, while the skin was indented. Velocity receptors code for velocity of indentation and continue to respond to repeated stimuli. Displacement receptor action potentials occur irregularly, with a Poisson‐like distribution of interspike interval. The mean frequency of displacement receptor discharge increases with depth of skin indentation, while the interspike interval distribution becomes progressively biased towards shorter intervals. The threshold of displacement receptors is related to displacement velocity; sinusoidal indentations of the skin produce a minimum threshold around 60 Hz. These receptors fail to respond to oscillations in excess of 120 Hz. The structure of the skin is described. Stress‐strain curves are given both for static and dynamic compression of the skin and these are discussed in relation to the properties of the skin mechanore

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02581.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A total of 622 skin specimens, 527 skeletons, and myological data compiled by Schreiweis (1972) were used to investigate morphometric patterns within and among the 18 Recent species of Spheniscidae, and to compare the family with a fighted species, the common diving‐petrel (Pelecanoides urinator), considered by some authorities to be similar to the flighted ancestor of penguins. Fossil penguins also were studied using measurements from 111 skeletal elements representing 18 species. Most external and skeletal measurements follow interspecific rankings in body mass; the latter span a 30‐fold range from 1 kg inEudyptula minorto 30 kg inAptenodytes forsteri.FlightedPelecanoidesis only one‐tenth the mass of the smallest spheniscid. Wing areas and body masses of penguins maintain approximate geometric similitude among species; the allometric coefficient is 0.62 ± 0.04. Several skeletal elements are less derived in conformation in the fossil penguins than in modern confamilials. Despite great variation in the lengths of wing and leg skeletons, penguins show relative consistency in proportions of wing elements; pelvic proportions were more variable within the Spheniscidae. Proportions within both limbs are distinctly different from those ofPelecanoides.Analysis of correlation structures within species of penguin revealed three major subsets of skeletal variables that are highly intercorrelated: trunk‐skull lengths, appendicular‐trunk widths, and appendicular lengths. Within these groups, measurements tend to separate by anatomical region and, to a lesser degree, by limb.Canonical analysis of skin and skeletal measurements revealed groupings of spheniscids on the basis of size and relatively complex shape variables. Cluster analyses of taxa on the canonical variates confirmed the similarity of congeners inEudyptes, EudyptulaandSpheniscus; species ofAptenodytesand, to a lesser degree,Pygoscelis, are more heterogeneous. A cluster analysis of principal components of myological measurements tabulated by Schreiweis (1972) corresponded closely with phenetic groupings using external and skeletal variables. A canonical contrast between spheniscids andPelecanoidesindicated that the families differ in a relatively complex skeletal dimension that only in part reflects overall size.Multivariate assessment of sexual dimorphism in external and skeletal variables indicated that:Eudyptulais least dimorphic;Aptenodytes, Eudyptes, MegadyptesandSpheniscusare moderately dimorphic; andPygoscelisis most dimorphic.Pelecanoidesshows comparatively low dimorphism.Among‐species and within‐species first principal components of skeletal measurements (multivariate axes of skeletal ‘size’) differ from one another in their orientation, and both deviate from isometric size. The first principal component for skeletons ofPelecanoidesalso deviated from isometric size, but the direction of this allometry is fundamentally different from that in penguins.Estimates of body mass for fossil penguins, based on principal components of available skeletal measurements, indicate that fossil species ranged from 3 kg to 81 kg in total mass; the largest fossil species was approximately 2.5 times as massive as the largest extant spheniscid.Much of the morphometric variation in the Spheniscidae is explainable on locomotory, ecological and thermodynamic grounds, and the associated phenetic groupings conform broadly with traditional generic classifications. The evolutionary significance of mensural correlations, allometric trends and differences between fossil and Recent species are discussed, and the need for a phylogenetic analysis of this highly specialized family of winged‐propelled divi

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02582.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The growth dynamics of the American alligator (Alligator mississippiensis) were studied in the subtropical Florida Everglades using extensive mark‐recapture data from over 2000 recaptures of known‐aged and unknown‐aged animals. A model based on the power curve best describes growth of Everglades alligators. The nonasymptotic character of this curve leads to rejection of the hypothesis that alligator growth is determinate. A model consisting of piece‐wise linear equations better described growth in the first year, and suggested a period of arrested growth occurred in the first winter. A comparison of predictions from growth models derived from several populations indicated that Everglades alligators grew more slowly than did those in more temperate areas, leading to the rejection of the hypothesis that growth rates in subtropical Florida would be elevated because of the long growing season. We attribute this result to a combination of increased maintenance costs and a limited resource base in the Everglades.Analyses considered the extent to which growth model evaluation and use can be affected by data selection. Mathematical constraints posed by negative growth data can be alleviated by including growth records over combined recapture intervals to achieve a positive growth increment. However, periods of no to negative growth may be real, and such deviations are obscured by fitting growth data to monotonically increasing

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02583.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

In this paper, we critically evaluate the view that eutherian life history diversity arises because of constraints imposed by the allometric consequences of body size, rather than selection acting on a broad array of possible life histories. Using life history data from over 700 species of eutherians, we examine covariation of life history variables across the 18 orders represented. Eutherian orders can be arranged from those characterized by small rapidly reproducing, rapidly developing, short‐lived species, such as lagomorphs, to large, slowly developing, slowly reproducing, long lived species, such as elephants. When the effect of body weight is controlled for, this pattern remains, but the relative positions ofthe orders on the new fast‐slow continuum are very different. There is a trade‐off between the weight and number of offspring in a litter which is independent of adult body weight. Maximum recorded lifespan is the best identified predictor of annual fecundity: high fecundity is associated with short lives. This is not easily explained as a cost of reproduction, because it is a function of the whole lifetime, rather than just the maximum reproductive lifespan. Those mechanisms said to underlie the allometric scaling of life histories, and which make testable predictions–growth constraints imposed by basal metabolic rate, brain weight and the rate of neuronal tissue growth–are not associated with life history variation once the effects of body weight are removed. Thus these variables have no greater explanatory power than body weight itself, since they cannot explain the variation in life histories which is not correlated with weight. Rates of litter growth rate are associated with life history variation independent of body weight, but until we understand why litter growth rates vary, they are unable, on their own, to explain considerable amounts of life history diversity. Differences in life histories among orders, whether or not the effect of body weight is controlled for, are associated with differences in mortality rates. We suggest that eutherian life histories are better thought of as adaptive strategies, and that mortality patterns offer considerably more promise in the understanding of eutherian life history diversity than loosely defined ideas about scaling principles and the allometric consequences of

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02584.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY