Showing papers in "Journal of Zoology in 1970"
TL;DR: Regulation of the population studied was due to territorial intolerance acting to produce subsequent mortality, though it is not certain that this applies over a larger area.
Abstract: A long-term study was made (1947-59) of the numbers and breeding success of the Tawny owl (Strix aluco L.) in a woodland habitat near Oxford. Parallel studies were made of the numbers and distribution of the owl's two main prey species, the Wood mouse (Apodemus sylvaticus (L.)) and the Bank vole (Clethrionomys glareolus (Schr.)).
The life-cycles of all these three interrelated species were worked out and special attention was paid to the habit of strict territoriality of the owl (on the evidence of vocalizations and of the recovery, from the regurgitated pellets of the owl, of marking rings placed on the rodents) and to the sequence of losses which occurred during the breeding of the owl. The owls' vocal defence of their territories enabled an accurate census to be made of the adult population each spring and the fact that the fledged young remained for a long time in their parents' territories made it possible to count the number of young produced each year. Investigation of the breeding habits of the owls showed that the number of fledged young produced fell far short of what was possible: some pairs of owls refrained from breeding at all, others laid eggs but failed to hatch them, yet others hatched young but failed to rear them to fledging. By and large this degree of reproductive “failure” was associated with the numbers and availability of rodent prey. At an exceptionally low density of prey no owls even attempted to breed; as densities increased, correspondingly greater numbers of fledged young were produced up to a ceiling where no more young were produced however much higher the level of abundance of the rodents rose.
In spite of these wide variations in the numbers of prey and in the numbers of fledged young produced, the population of adult owls remained notably stable, increasing from a low level of 17 pairs in 1947, owing to the emergency mortality of an exceptionally hard winter, to about 30 pairs in 1955, after which the population remained stationary until the end of the study in 1959.
It is clear that this stability is maintained by those young which fail to find a territory either starving or moving outside the study area, which in most cases amounts to the same thing. Thus regulation of the population studied was due to territorial intolerance acting to produce subsequent mortality, though it is not certain that this applies over a larger area.
356 citations
TL;DR: More detailed information on reproduction, mortality and population counts are presented to give an outline of the population dynamics in this species.
Abstract: A general description of the life history of Mountain hares is given, base on a three year field study of about 200 wild hares on a moor near Morven, Aberdeenshire, and laboratory examination of over 360 dead specimens from surrounding areas. Growth and body size, behaviour, range and movements, food and reingestion are described. More detailed information on reproduction, mortality and population counts are presented to give an outline of the population dynamics in this species.
186 citations
TL;DR: Albino mouse pups develop homoiothermy during the first 19 days of their life and show three distinct stages during this period, where their acoustic response to cold is weak from day 1 to day 5 or 6 and very strong from day 6 or 7 to day 12 or 13.
Abstract: Albino mouse pups develop homoiothermy during the first 19 days of their life and show three distinct stages during this period. From day 1 to day 6 they are almost completely poikilothermic at low ambient temperatures; from day 7 to day 14 or 15 is a transitional period during which they develop homoiothermy at medium temperatures (e.g. 22°C); from day 15 or 16 to day 19 or 20 is the final stage when homoiothermy at very low ambient temperatures is developed. These changes are very closely correlated with changes in the ultrasounds produced by isolated pups within the 19 day period. Thus their acoustic response to cold is weak from day 1 to day 5 or 6 and very strong from day 6 or 7 to day 12 or 13, on exposure even to medium temperatures. From day 14 onwards the pups progressively stop producing ultrasounds depending on the ambient temperatures, and there is complete cessation of calling after day 19 or 20 even on exposure to temperatures as low as 2°C. In general, decreasing the ambient temperatures increases the rate and intensity of ultrasounds produced but very low ambient temperatures have an inhibiting effect and at 2–3°C breathing and calling cease completely after a time which varies with age of the pups.
137 citations
TL;DR: “Reliability” of identification is discussed in terms of the probability of there being more than one individual with a given spot pattern in the study population, and it is shown how reliability can be improved, when necessary, by adding together information from more thanone source.
Abstract: A method is described of identifying lions from the patterns of vibrissa spots. “Reliability” of identification is discussed in terms of the probability of there being more than one individual with a given spot pattern in the study population, and it is shown how reliability can be improved, when necessary, by adding together information from more than one source. Means of adapting the reliability calculation to identification in other species are indicated.
129 citations
TL;DR: The cuticle described by light microscopists on the skin of various fishes, has been studied by electron microscopy in several species of teleost and in two other actinopterygian fish.
Abstract: The cuticle described by light microscopists on the skin of various fishes, has been studied by electron microscopy in several species of teleost and in two other actinopterygian fish. Thelcuticle consists of an external coating layer, probably of mucopolysaccharide, which is secreted from the surface epidermal cells, not from the goblet mucous cells. The thickness of the cuticle is commonly of the order of 1 μm. It is particularly well developed in Trigla, where its thickness may vary from a fraction of a micron up to 50 μm, on different parts of the same individual. The cuticle has been detected in species from diverse orders, and is probably a normal constituent of the skin of all bony fishes. It is frequently lost during histological preparation. The external coat continues over the apertures of taste-buds, and may be continuous with the secretion at the mouths of chloride secreting cells. The secretion of the cuticle is partly from, or through, the outer membrane of the epidermal cells, but there is some evidence that cytoplasmic inclusions in the surface epidermal cells are also involved. There is striking variation in the appearance of these inclusions in electron micrographs of different species, and in some cases in different parts of the same fish, notably in Blennius. Certain of the inclusions are membrane-bounded vesicles whose contents are more electron-dense after staining with phosphotungstic acid than with lead citrate. In other cases, the inclusions are electron-transparent vacuoles. The cuticle is briefly compared with similar structures in other aquatic animals.
125 citations
TL;DR: The census data of the Great tit collected by Perrins (1965) and others in Marley Wood are analysed for density-dependence and Territorial behaviour has been shown experimentally to determine breeding density, and may produce a density-dependent effect outside the breeding season.
Abstract: The census data of the Great tit collected by Perrins (1965) and others in Marley Wood near Oxford are analysed for density-dependence. Clutch size and hatching success are density-dependent and sufficiently so to regulate the population at the observed level (assuming that there is in addition a fairly large density-independent mortality). There may also be some weak density-dependent mortality outside the breeding season. The density-dependent variations in clutch size are probably in the main due to shortage of available food and density-dependent hatching failure is caused by predation. Territorial behaviour has been shown experimentally to determine breeding density, and may produce a density-dependent effect outside the breeding season. These three factors are responsible for regulation of the Great tit population in Marley Wood.
114 citations
TL;DR: The systematics of the gorilla are reviewed in the light of abundant new material, examined with the aid of techniques of multivariate analysis, and the existence of morphological intergradation is shown.
Abstract: The systematics of the gorilla are reviewed in the light of abundant new material, examined with the aid of techniques of multivariate analysis. Defects are pointed out in the usually accepted view that there are two clear-cut subspecies (G. g. gorilla and G. g. beringei); the existence of morphological intergradation is shown, and an intermediate subspecies, G. g. grueri, is recognized in addition.
110 citations
TL;DR: Using an ordinary optical microscope, it is demonstrated that a considerable variety of setae exist on the body and appendages of A. pallipes, and the significance of the distribution and the variation is discussed in relation to crayfish behaviour and function.
Abstract: The author presents here the results of an introductory study into the setal armature of the British species of crayfish, Austropotamobius pallipes (Lereboullet, 1858). Using an ordinary optical microscope, it is demonstrated that a considerable variety of setae exist on the body and appendages of A. pallipes. These setae are described, and their distribution indicated. The setae fall into two main groups:
(1) Setae with relatively thick walls and inconspicuous ampulla, and having no basal septum.
(2) Those setae with relatively thin walls, a well-developed ampulla and basal septum. Further subdivisions of these two groups are made on the bases of outgrowths and outlines of the setal wall. Finally, the significance of the distribution and the variation, is discussed in relation to crayfish behaviour and function, linking the observed morphological facts with the results of some current electro-physiological experiments performed on related decapods.
106 citations
TL;DR: Pressure changes have been recorded from the buccal cavities of nine species of teleost as they sucked food into their mouths, and peculiarities in the feeding movements of Taurulus, Ictalurus and Anguilla are described and discussed.
Abstract: Pressure changes have been recorded from the buccal cavities of nine species of teleost as they sucked food into their mouths. Some of the pressures recorded are discussed in relation to the sizes of the muscles responsible. Cinematograph films have been used to estimate how much the volume of the orobranchial chamber increases as food is sucked in. Some peculiarities in the feeding movements of Taurulus, Ictalurus and Anguilla are described and discussed.
104 citations
TL;DR: The dentition of the African lizard Agama agama was examined in a range of material from late embryos and hatchlings to individuals of advanced age and a connection suggested between polyphyodent reptilian dentitions and the diphyodont mammalian dentition.
Abstract: The dentition of the African lizard Agama agama was examined in a range of material from late embryos and hatchlings to individuals of advanced age. Most of the skulls were prepared as dry specimens, but observations were also made on the living lizards in captivity and some records of tooth replacement collected.
The gross anatomy of the dentition is described and its growth and elaboration from the hatchling to the adult. Attachment of the two types of tooth, both acrodont and pleurodont, is considered and the replacement process is found to be sufficiently different from that of other lizards to justify a separate descriptive category.
Evidence from both dead and living material as to the order of tooth replacement in Agama is analysed and found to conform to the hypothesis of Edmund (1960). Other agamid genera are briefly described.
The similarity between agamid and mammalian dentitions is pointed out and a connection suggested between polyphyodent reptilian dentitions and the diphyodont mammalian dentition which is more correctly regarded as being composed of two Zahnreihen.
83 citations
TL;DR: Tactile stimuli, like environmental temperature changes, can evoke ultrasonic responses from albino mouse pups, but the changes with age in the intensity of ultrasounds so produced follow a different pattern from those due to temperature changes.
Abstract: Tactile stimuli, like environmental temperature changes, can evoke ultrasonic responses from albino mouse pups. But the changes with age in the intensity of ultrasounds so produced follow a different pattern from those due to temperature changes. The responses begin with very high intensity pulses in the very young pups and then gradually decline with the age of the pups. The present report arises from a systematic study of this phenomenon, the results of which are discussed in relation to those of previous ones.
TL;DR: Differences in survival, rate of water-loss and behaviour under conditions of low humidity in laboratory studies are reflected in differences in distribution in parts of Britain.
Abstract: Cepaea nemoralis L., C. hortensis Mull, and Arianta arbustorum L. show differences in survival, rate of water-loss and behaviour under conditions of low humidity in laboratory studies. C. nemoralis survives better, ceases activity more rapidly, and loses proportionally less weight in low humidity than C. hortensis, which in turn shows the same properties with respect to A. arbustorum. The differences between these three species are reflected in differences in distribution in parts of Britain.
TL;DR: There is little diurnal rhythm in activity at 0°C, but all species become moreNocturnal as temperature increases; C. nemoralis is most, and A. arbustorum least nocturnal.
Abstract: The activity of the land snails Cepaea nemoralis (L.), C. hortensis (Mull.) and Arianta arbustorum (L.) was measured over 24 hours at the constant temperatures of 0, 3, 8, 17, 22 and 26°C at 100% relative humidity and with 16 hours light and 8 hours dark. The activity of all three species varies significantly with temperature and light, and there are differences in the activities of the species at each temperature. A. arbustorum is relatively more active than Cepaea at low rather than high temperatures, as is C. hortensis with respect to C. nemoralis, though to a lesser extent. There is little diurnal rhythm in activity at 0°C, but all species become more nocturnal as temperature increases; C. nemoralis is most, and A. arbustorum least nocturnal. The results obtained assist in explaining the observed geographical and local distributions of the species concerned.
TL;DR: Evidence is presented to show that seasonal differences in temperature influence the pattern of ammocoete growth throughout the year, while local differences in the density of food are responsible for differences in growth rates in different areas.
Abstract: The life cycles and ecology of two closely related species of lampreys of the genus Mordacia were studied in various rivers in south-eastern Australia. In the Moruya River in southern New South Wales, the anadromous parasitic species, M. mordax (Richardson), has a larval life of three and a half years with metamorphosis occurring in late February or early March. The nonparasitic species, M. praecox Potter, metamorphoses at a different time (late October or November) and at a significantly longer length than M. mordax. The latter probably reflects a longer larval life in M. praecox, an estimate of which could not be obtained from the available data. Thus an extension of the larval phase, as well as a reduction in the post-metamorphic stages, may have occurred in the evolution of nonparasitic lampreys from parasitic forms. Evidence is presented to show that seasonal differences in temperature influence the pattern of ammocoete growth throughout the year, while local differences in the density of food are responsible for differences in growth rates in different areas. The effect of flooding and reduction in the water levels on the distribution of ammocoetes is discussed. A description is given of the behaviour of metamorphosing and transformed M. mordax prior to their migration out to sea. The above data is collated with that obtained from other studies to produce an overall picture of the life cycles of the two species of Mordacia.
TL;DR: The shore distribution, growth and reproduction of the siliceous monoaxonid sponge Hymeniacidon perleve has been studied over a two year period in a population of the sponge in Langstone Harbour, Hampshire.
Abstract: The shore distribution, growth and reproduction of the siliceous monoaxonid sponge Hymeniacidon perleve has been studied over a two year period in a population of the sponge in Langstone Harbour, Hampshire. The zonla distribution of the sponge is described, together with details of the seasonal variation in growth and changes in population size, and experimental determinations of the minimum growth temperature. The results of investigations of larval settlement are given and the relative importance of sexual and asexual reproduction in maintaining the population are considered.
TL;DR: Six other species of Excirolana examined in the course of this investigation show evidence of internal incubation, and ovoviviparity appears to be characteristic of the entire genus, members of which live on exposed sand beaches throughout tropical and warm temperate regions of the world.
Abstract: Studies on the intertidal sand-beach isopod, Excirolana chiltoni, have shown the species to be ovoviviparous. Large yolk-filled eggs are deposited into paired uteri of the female where they remain throughout gestation. Intrauterine development progresses through five stages and terminates upon birth of the manca which is morphologically similar to the adult but lacks the eighth pair of thoracic legs. The oostegites while present are much reduced and form a genital operculum rather than a brood pouch as they do in the majority of free living isopods. Six other species of Excirolana examined in the course of this investigation show evidence of internal incubation. Ovoviviparity thus appears to be characteristic of the entire genus, members of which live on exposed sand beaches throughout tropical and warm temperate regions of the world. Internal retention of embryonic stages provides protection against a number of environmental stresses peculiar to this sort of habitat.
TL;DR: Study of skulls from 145 Ribbon seals disclosed much greater variation in form than was indicated by earlier descriptions, and the Ribbon, Harp, Harbor, and Ringed seals are re-assigned to subgeneric rank, under the inclusive genus Phoca (sensu luto).
Abstract: Study of skulls from 145 Ribbon seals, mainly from the Bering Sea, disclosed much greater variation in form than was indicated by earlier descriptions. The characters of greatest diagnostic value in the Ribbon seal are the short rostrum, broad cranium with reduced temporal fossae. short, wide palate with small, widely spaced teeth, and the elongate, thickwalled bullae with massive, widely exposed petrosals. Comparison of these skulls with examples from each of the other recognized genera of Phocidae revealed several deficiencies in the referred cranial characteristics of taxa at all ranks below the family. Provisional support for J. E. King's recently proposed division of the Phocidae into two subfamilies, Phocinae and Monachinae, is reported; the distinctions formerly employed for diagnosis of a third subfamily, Cystophorinae, can be ascribed to convergent evolution. Craniologically, the subfamily Phocinae is divisible into three tribes: Erignathini, Cystophorini, and Phocini. The first two are monotypic; the third is polytypic. The subtribes Phocina and Histriophocina are untenable; while Histriophoca's nearest structural relative is Pagophilus, the latter shows equal or closer relationship with Phocu. Within the tribe Phocini, only the Grey seal, Hlichoerus grypus, shows sufficient cranial differentiation for recognition as a monotypic genus. The other four major taxa within that tribe show a complex system of intergrading characters that disallows generic recognition, other than as a polytypic group. Therefore, the Ribbon, Harp, Harbor, and Ringed seals are re-assigned to subgeneric rank, under the inclusive genus Phoca (sensu luto).
TL;DR: The nature of these encounters indicated that the harem males are effective in driving off extragroup males and that females and juveniles are instrumental in maintaining space and social exclusiveness between heterosexual groups.
Abstract: Observations on the behaviour and ecology of Patas monkeys in Cameroon complement those made in Uganda by Hall (1965) and contribute to an understanding of the proximate factors involved in the maintenance of Patas social structure and to seasonal changes in their behaviour and ecology. The heterosexual groups had a mean size of 21. Five all-male groups were seen. High proportions of similarly sized infants indicate that there is a birth season at Waza from November to January inclusive. At the peak of the dry season intergroup contacts were very common at the water holes. The frequency of agonistic encounters increased remarkably at this time, especially between monkeys of different groups. The nature of these encounters indicated that the harem males are effective in driving off extragroup males and that females and juveniles are instrumental in maintaining space and social exclusiveness between heterosexual groups. The frequency of interspecific encounters also increased at the peak of the dry season.
TL;DR: The food preferences of an insular population of Rattus rattus inhabiting colonies of the Short-tailed shearwater Puffinus tenuirostris are described from results obtained during analyses of stomach contents and droppings collected from Big Green Island, Furneaux Group, Tasmania.
Abstract: The food preferences of an insular population of Rattus rattus inhabiting colonies of the Short-tailed shearwater Puffinus tenuirostris are described from results obtained during analyses of stomach contents and droppings collected from Big Green Island, Furneaux Group, Tasmania. It was found that rats on the island maintained themselves by eating a predominantly vegetarian diet and results suggest that there was some selective feeding on monocotyledons rather than the dicotyledons present in the area. Green parts of plants were taken throughout the year and rats may select these as a water source during the summer months. Plants made up 77.2% of the 254 stomach contents analysed and of this 57.7% was green material. Insect remains were found in 24.8% of the 1400 droppings examined and made up 14.3% of the stomach contents. Few feathers of the shearwater Puffinus tenuirostris were found in the stomachs or droppings and preliminary behavioural experiments suggested that the rat does not actively predate the bird though it may remove unattended eggs and eat dead chicks.
TL;DR: Threat displays, fighting, displacement feeding, and agitation feeding are recognizable behaviour patterns which have been observed in Scopimera inflata during the daytime periods of low tide.
Abstract: A sequence of activities all related to the feeding of Scopimera inflata H. Milne-Edwards, 1873 can be distinguished during the daytime periods of low tide. Emergence begins one to two hours after a feeding area is uncovered, reaches a peak after a further three hours but some crabs are still emerging after the tide has turned. Before feeding commences the burrow is cleared of waste sand down to the water-table. While feeding S. inflata forms a feeding trench which acts as an escape route back to the hole and is defended against other crabs of the same species. Agonistic behaviour becomes evident as feeding progresses. Threat displays, fighting, displacement feeding, and agitation feeding are recognizable behaviour patterns which have been observed.
TL;DR: Many aspects of the size, shape, colour and behaviour of the larvae and pupae of both species of Pieris appear to be adaptations to the selective pressures exerted by bird predation.
Abstract: The importance of bird predation as a selective pressure on the eggs, larvae and pupae of the cabbage butterflies, Pieris rapae L. and P. brassicae L. has been investigated in a rural garden and an allotment. Birds are the main predators of all stages in a well-tended garden whereas in a field the eggs and young larvae are mainly preyed upon by arthropods. The species of avian predators vary according to the stage of development and species of prey. Consequently the relative survival rate of P. rupae and P. brussicue varies with stage of development. This changing pattern of survival has in turn acted as a selective pressure on their two main braconid parasites. Many aspects of the size, shape, colour and behaviour of the larvae and pupae of both species of Pieris appear to be adaptations to the selective pressures exerted by bird predation.
TL;DR: The feeding methods of seven intertidal ophiuroids are described and the podia are used as an integral part of the feeding mechanism, and varying use of the spines has been observed.
Abstract: The feeding methods of seven intertidal ophiuroids are described. In each method the podia are used as an integral part of the feeding mechanism, and varying use of the spines has been observed. Both podia and spines contain mucous glands and certain similarities are apparent in their secretions. Where mucus is used directly for food capture, and ingested with the food, it is acid, rich in wboxyl groups and at least partly sulphated. Further, the mucus in spinal glands is fibrillar while that of the podia is granular. Some integumentary glands are basiphilic and highly sulphated while other are acidophilic. The possible functions of these glands are discussed.
TL;DR: It is concluded that sunlight and temperature are the most important factors influencing gonadal development and subsequent breeding in Tilapia even under equatorial conditions.
Abstract: The cichlid fish T. leucosticta (Trewavas) was studied by fortnightly seining an area of an equatorial lake (Lake Naivasha) in Kenya to study their reproductive and gonadal patterns. The study lasted 16 months during which period temperature, rainfall and (for the last 11 months) sunlight patterns were obtained and analysed. Testicular and ovarian development was lowest in the months of July-August. No evidence of breeding was detected during this period. This period is also marked by the lowest rainfall, the lowest temperatures and least sunlight. Slight but fluctuating breeding activity and gonadal development is resumed in October following increased sunlight and temperatures from September. The period December to February is marked by sustained high temperatures, high sustained maximal sunlight and low rainfall. It is also the period of rising gonadal development in most mature males and females reaching a peak in both sexes in February. This is followed shortly after by a sharp peak in reproductive activity. It is concluded that sunlight and temperature are the most important factors influencing gonadal development and subsequent breeding in Tilapia even under equatorial conditions. When preceded by conditions of sustained high temperatures and good sunlight which are conducive to the maximal development of the gonads of both sexes, the onset of rainfall seems to stimulate the initiation of the peak breeding activity. Sustained heavy rainfall on the other hand seems to check breeding.
TL;DR: The morphology of the oesophagus and stomach has been studied in several species of Tursiops, Delphinus and Stenella and correlated with the histological and ultrastructural characteristics of each region.
Abstract: The morphology of the oesophagus and stomach has been studied in several species of Tursiops, Delphinus and Stenella and correlated with the histological and ultrastructural characteristics of each region. The oesophagus opens into a saccular forestomach, lined by stratified squamous epithelium. A narrow opening leads into a globular main stomach with a plicated glandular mucous membrane possessing mucous, parietal and chief cells. The main stomach communicates with pyloric stomach by a narrow connecting channel possessing sphincteric constrictions. Variations in the connecting channel have been found in the species examined. The mucosae of the channel and the pyloric stomach are similar and contain typical pyloric glands. Argentaffin cells are present. The cytological and other characteristics of the component chambers have been interpreted in relation to feeding habits and digestion in dolphins.
TL;DR: An account is given of the way in which Priapulus caudatus burrows in the muddy sea-bed in which it lives, and the muscular activities of the larva are limited by the presence of a lorica which encases the trunk.
Abstract: An account is given of the way in which Priapulus caudatus burrows in the muddy sea-bed in which it lives. Three phases are distinguishable in the muscular activity which is responsible for locomotion. During the first phase the animal is able to feed and defaecate, during the second the proboscis becomes invaginated, and during the third the animal moves forward. The power for locomotion is provided by contraction of the longitudinal and circular muscles of the body wall, not, as has been suggested previously, by the retractor muscles of the praesoma. Invagination of the proboscis is apparently stimulated by the arrival of a wave of contraction in the body wall musculature, propagated from the trunk.
In general the animal burrows in a way common for soft-bodied animals; the anterior and posterior extremities acting in turn as “terminal” and “penetration” anchors in the substratum. The muscular activities of the larva are limited by the presence of a lorica which encases the trunk, and the animal's powers of movement at this stage are very restricted.
TL;DR: The menstrual cycles of 14 captive Talapoin monkeys (Miopithecus talapoin) were studied by making serial observations on the vaginal smears and sexual skin swellings for up to 15 months and preliminary observations indicated a more pronounced correlation between this behaviour pattern and an animal's position in the hierarchy.
Abstract: The menstrual cycles of 14 captive Talapoin monkeys (Miopithecus talapoin) were studied by making serial observations on the vaginal smears and sexual skin swellings for up to 15 months. Twelve of these females menstruated and the mean duration of their cycle was32–9 days (95% confidence limits 28.0-37.7). The corresponding value for the seven most regular females was 33.0 days (29.1-36.8). There were rhythmic changes in the vaginal smears and sexual skin during the menstrual cycle. Maximum cornification of the smears and maximum sexual skin swelling were observed at midcycle; the sexual skin deflated and the smear became less cornified during the luteal phase. The follicular phase—i.e. from menstruation to maximum skin swelling lasted 20.4 days with a wide distribution, in contrast to the mean duration of the luteal phase (13.7 days) which showed a pronounced peak at 14 days. The menstrual cycle of the talapoin thus resembles those of certain other Old World monkeys that exhibit perineal sexual skin swelling.
Sexual behaviour of the male and female was maximal near the female's midcycle and minimal during the luteal phase, with intermediate values in the follicular phase. The males were most aggressive towards other females of the group when one female was at midcycle; there were no consistent changes in aggression between the male and the female herself. The number of times one animal looks at another (a characteristic behaviour pattern in talapoins) was measured and occurred most often at midcycle, but other preliminary observations indicated a more pronounced correlation between this behaviour pattern and an animal's position in the hierarchy.
TL;DR: It was generally found that the more isolated the lagoon, the more impoverished it was in numbers of species, and suggests that the mat of floating vegetation, by reason of the de-oxygenated conditions that exist under it, acts as a form of biological filter.
Abstract: Between 1961 and 1964 the water levels of Lake Victoria increased abruptly. This increase produced changes around the shoreline of the lake, creating new habitats in the form of lagoons. Such lagoons were cut off from the main lake by differing widths of floating vegetation. Chemically and physically these new regions resembled small tropical fish ponds, with a nocturnal reduction in both dissolved oxygen and temperature.
The lagoons were occupied shortly after their appearance by characteristic groups of fishes, which depended for their species composition on the degree of isolation of the different bodies of water from the main lake. It was generally found that the more isolated the lagoon, the more impoverished it was in numbers of species. The most successful colonizers of these waters were Tilapia leucosticta and Haplochromis nubilus, which were present in all lagoons.
Populations of these two species showed a tendency to stunt, which was more marked in the more isolated populations. This, together with the population changes associated with isolation, suggests that the mat of floating vegetation, by reason of the de-oxygenated conditions that exist under it, acts as a form of biological filter. Thus fish from the lake can only penetrate to the nearer lagoons, the populations in the more isolated waters remaining more or less segregated.
TL;DR: The snake now caled Micropechis elapoides is transferred to a new genus Loveridgelaps, here believed to be closely related to Salomnelaps par, Ogmodon vitianus, and Vermicella annualata; an account of the variation in Loverid gelaps elopoides is presented.
Abstract: The snakes now called Denisonia par and D. woodfordi are considered conspecific, but generically distinct from Denisonia (for the Australian D. maculata and D. devisi); they are here termed Salomonelaps par and an account is presented of the considerable island-to-island variation in that species. the snake now caled Micropechis elapoides is transferred to a new genus Loveridgelaps, here believed to be closely related to Salomnelaps par, Ogmodon vitianus, and Vermicella annualata; an account (quite tentative and unsatisfactory because of the paucity of specimens) of the variation in Loveridgelaps elopoides is presented. Salomonelaps, Loveridgelaps, Ogmodon, and Vermicella make up a well defined (by the presence of an imperforate lateral process of the palatine) group of Australiasian elapids, the Vermicella group, and a key to the genera and generic descriptions for this group are presented. The New Guinea genus Micropechis (containing only M. ikaheka) is a member of a different group, here called the Pseudechis, containing also pseudechis, Austrelaps (for A. superbus), and Suta (for the genera Suta, Parasuta, and Unechis of Worrell, and the species Fasciata and Punctata, referred to Denisonia by Worrell, and Flagellum, referred to Cryptophis by Worrell). Some additional notes are given on the type of Denisonia boschmai Brongersma & Knaap-Van Meeurwen (here considered a geographic variation of Suta carpentariae), and a key to the genera of Pseudechis group is presented.
TL;DR: Observations on the foregut and dentition, together with field data, suggest that the climax of downstream migration and the onset of parastic feeding takes place in late March or April.
Abstract: Comparisons of metamorphosing and macrophthalmia stages of the closely related species, L. fluviatilis (L.) and L. Planeri (Bloch), have shown that these can be distinguished within a few weeks of the onset of metamorphosis by characteristic differences in colouration and body form. Measurements of several body intervals have disclosed differences between the macrophthalmia stages of the two species. A sharp distinction between the blunt teeth of L. planeri and the supposedly sharp teeth of L. fluviatilis has not been confirmed in these early stages, but significant differences have been found in the numbers of teeth in the anterior field of the oral disk and in the lateral and posterior marginal series. For material from several rivers, the range of length of metamorphosing and macrophthalmia stages of L. fluviatilis is83–119 mm (mean 99.3 mm). Weights varied from 0.71-2.5 g (mean 1.51 g). Regression coefficients for weight on length are much lower in the macrophthalmia of L. fluviatilis than in comparable stages of L. planeri. Total oocyte counts on macrophthalmia of L. fluviatilis gave values from8000–20,000 which are in general agreement with egg counts for adults of this species in the river Severn. Observations on the earliest metamorphosing forms have shown that it is not possible at this stage to distinguish the males of the two species by the structure of the testes. The development of the lumen in the adult foregut of L. fluviatilis has been shown to be variable and in some instances the gut does not become patent until early Spring. The possibility has also been raised that, in exceptional cases, a temporary lumen may also be present for a short period in L. planeri. Observations on the foregut and dentition, together with field data, suggest that the climax of downstream migration and the onset of parastic feeding takes place in late March or April.