Showing papers in "Journal of Zoology in 2009"

To cut a long tail short: a review of lizard caudal autotomy studies carried out over the last 20 years

Abstract: Caudal autotomy, the ability to shed the tail, is common in lizards as a response to attempted predation. Since Arnold's substantial review of caudal autotomy as a defence in reptiles 20 years ago, our understanding of the costs associated with tail loss has increased dramatically. In this paper, we review the incidence of caudal autotomy among lizards (Reptilia Sauria) with particular reference to questions posed by Arnold. We examine tail break frequencies and factors that determine occurrence of autotomy in natural populations (including anatomical mechanisms, predation efficiency and intensity, microhabitat preference, sex and ontogenetic differences, as well as intraspecific aggression). We also summarize the costs associated with tail loss in terms of survivorship and reproduction, focusing on potential mechanisms that influence fitness (i.e. locomotion costs, behavioural responses and metabolic costs). Finally, we examine the factors that may influence the facility with which autotomy takes place, including regeneration rate, body form and adaptive behaviour. Taking Arnold's example, we conclude with proposals for future research.

Anatomical studies of the insect central nervous system: A ground-plan of the midbrain and an introduction to the central complex in the locust, Schistocerca gregaria (Orthoptera)

Abstract: The supra-oesophageal ganglion (brain) of Schistocerca gregaria Forskal has been studied at the light-microscopical level using Wigglesworth's osmic acid-ethyl gallate method. Particular attention was paid to the midbrain. A structural ground-plan is described which incorporates the ocellar nerve roots, the antenno-glomerular bundles, the corpora cardiaca nerves I roots, the antennal lobes, the corpora pedunculata and the central complex. The “undifferentiated” midbrain is described in terms of the distribution of the main features of 15 unique pairs of large neurones all of which have their cell bodies in the brain and which project, either ipsilaterally or contralaterally, to the circumoesophageal connectives. In addition a single unique neurone with bilateral distribution restricted to the brain is described. All these neurones provide a conspicuous and constant framework for further investigation. A ground-plan based on the distribution of 64 individual neurones (central complex system I) is presented for the central complex. This system indicates that the central complex is fundamentally organized on the basis of 16 repetitive groups of neurones.

An analysis of social behaviour in wild rats

Abstract: SUMMARY Wild rats (Battus norvegicus Berkenhout and R. rattus L.) were kept in large cages fitted with nest boxes and supplied with excess food and water. Colonies varied in size from four to twenty rats, and were usually maintained for at least nine weeks. The rats were individually identified and their behaviour studied in detail. Rattus norvegicus. In all-male colonies there was a low mortality and most of the rats increased in weight. In colonies containing both males and females, mortality was high among the males, very low among the females; most of the males declined in weight, though some grew well. There was however no fighting for females. It is suggested that the extra fighting which took place in these colonies resembled displacement behaviour and was due to excitement evoked by the presence of females combined with frequent frustration. There were no deaths in all-female colonies, or in colonies of litter mates. Unless parturient, normal females did not display aggressive behaviour except in ‘play’. Males, but not females, added to established colonies, were attacked by resident males and usually died, sometimes within a few hours and often without visible injury. At the beginning of an experiment there was much exploration, both of the cage and of the other rats. Social relationships were established early. Male members of the colonies fell into three classes: (i) alphas, which were the equals or superiors of other males in the colony, and attacked newcomers; (ii) betas, which adapted themselves to a subordinate role, and were ingratiating towards newcomers; (iii) omegas, which were persecuted by one or more alphas and soon died. Alphas and betas gained in weight; omegas lost weight. There were more omegas in male-female colonies than in those consisting only of males. Amicable behaviour (apart from coitus and care of young) was shown by both sexes and was based mainly on contact ‘releasing’ stimuli: the most specific of a number of amicable responses was crawling under the belly of another rat. Fighting involved a series of stereotyped acts, including tooth chattering and a characteristic threat posture; there was much wild leaping, but biting produced only superficial damage. Rattus rattus. A small number of experiments with R. rattus showed that this species possesses all the components of amicable and aggressive behaviour observed in R. norvegicus, but that it is less fierce and more agile. There was no evidence of extra conflict in male-female colonies. All-male colonies containing both species were usually peaceful. R. rattus of either sex added to norvegicus colonies were usually attacked, but not with such intensity or consistency as were male norvegicus; if attacked, they died. R. norvegicus males added to rattus colonies were sometimes attacked, but they did not die. Displacement behaviour and abnormaľ sexual and aggressive behaviour were observed in both species. General. There is no reason to think that dominance hierarchies ever develop in wild rat colonies. Members of a single family do not attack each other. The fighting of wild rats is essentially territorial, not for any specific object. Aggression is most readily evoked in males established in a familiar area, faced with a strange adult male of the same species. In normal females aggression occurs only in defence of a nest containing young. Social responses consist of stereotyped behaviour patterns which are probably innate; but learning plays an important part in determining the choice of response and in secondary adjustments of behaviour to particular circumstances.

Trend‐surface analysis of transformation grids

Abstract: Computer methods are described for trend-surface analysis of D'Arcy Thompson transformation grids, illustrated by data on skulls and jaws of hominoids. In comparing two diagrams the following steps are required. First, corresponding points on each diagram are marked, and their co-ordinates are recorded. Second, the diagrams are scaled and fitted to give the best possible fit; this gives measures of size and shape difference. Third, the displacements of each point relative to its partner on the other diagram are subjected to trend-surface analysis. The displacements are analysed in terms of linear, quadratic, cubic and higher order trends. Fourth, the differences based on the trends alone can now be estimated. The results on the illustrative examples are discussed, together with the difficulties in applying such methods. The nature of taxonomic (phenetic) affinity is also discussed, with suggestionsfor measuring different components of this concept. The techniques show promise for a wide variety of taxonomic and morphological applications.

The anatomy of the nervous system of the mesothorax of locusta migratoria migradorioides r. & f.

Abstract: A description is given of those nerves which arise from the mesothoracic ganglion of Locusta migratoria migratorioides R. & F. There are six pairs of nerves, of which the sixth and most posterior are referred to as recurrent nerves since they join the first nerve of the ganglion in the metathorax. The median nerve is also described. The posterior median nerve of the prothoracic ganglion is noted as its branches make a connection with the branches of the first mesothoracic nerve. Wherever possible an attempt has been made to relate the observations to those of some other authors.

Polyspecific associations and niche separation of rain‐forest anthropoids in Cameroon, West Africa

Abstract: A 19 month field study of rain-forest anthropoids at Idenau and several other rain forests, and a similar 15 month study at Southern Bakundu were conducted in Cameroon, West Africa. The study areas and their primate fauna are described. Polyspecific associations of primates were temporary, but not random, some species occurring together more frequently than others, and with statistical significance. Seasonal environmental factors affecting the composition of polyspecific cercopithecid associations are described. Interspecific social behaviour was infrequent and hybridization rare; instances of each are described. Observations on vertical stratification, habitat preference, seasonal movements and food habits indicated that all these factors contribute to niche separation among five sympatric species of rain-forest Cercopithecus. The major predator of anthropoids in Cameroon is man. To a much lesser extent the Crowned hawk-eagle, Stephanoaetus coronatus (Linnaeus) preys on Cercopithecus species. It is suggested that polyspecific associations, by increasing the effective group size, give advantages in food location and avoidance of predators without increasing interspecific competition for food and competition between males for females.

The functions and mechanisms of the protrusible upper jaws of some acanthopterygian fish

Abstract: Photographs of Pterophyllum and Gasterosteus feeding indicate that they suck food into their mouths by expansion of the buccal and opercular cavities. The premaxillae are protruded as the mouth opens, and remain protruded as it closes. The mechanisms whereby these movements can be performed, by these and by more generalized acanthopterygians, are described. It is shown that the palatines of generalized acanthopterygians are so arranged as to prevent retraction of the premaxillae when the mouth is closed with the buccal cavity expanded. It is estimated, from rough measurements on a few species, that a teleost cannot suck into its mouth food that is further from its mouth opening than about one-quarter of the length of its head. It is shown that protrusion of the premaxillae can be useful in getting the mouth opening close to food that is to be sucked in, expecially when it is to be taken from the bottom. The possible advantages of closing the mouth with the premaxillae protruded are discussed. The origin of the acanthopterygian protrusile mechanism is discussed.

Dynamics of Mara-Serengeti ungulates in relation to land use changes

Abstract: Animal population dynamics can be driven by changing climatic forcing, shifting habitat conditions, trophic interactions and anthropogenic influences. To understand these influences, we analyzed trends in populations of seven ungulate species counted during 15 years (1989-2003) of monthly monitoring using vehicle ground counts in the Maasai Mara National Reserve, Kenya. Abundance of six species declined markedly and persistently throughout the reserve during this period. The declines were contemporaneous with progressive habitat deterioration due to changing land use in pastoral ranches bordering the reserve, habitat desiccation due to rising temperatures, recurrent severe droughts and an exceptional ENSO flood in 1997-1998. The effect of progressive habitat deterioration was accentuated by illicit harvest, competition with livestock and elevated predation. After factoring out the influence of rainfall, ungulate populations declined more markedly in sections of the reserve experiencing greater livestock incursions and poaching. The declines were significantly correlated with increasing number of settlements and people in the pastoral ranches for five species. Heightened predation following a crash in the buffalo Syncerus caffer population during a severe drought in 1993 had little support as the primary cause of the declines.

Variations in body weight, wing length and condition of Mallard Anas platyrhynchos platyrhynchos and their relationship to environmental changes

Abstract: This paper describes the analysis of over 15,000 weights of Mallard caught for ringing at Borough Fen Decoy, Northamptonshire, during a 13 year period. Weights are corrected to give condition indices by using wing length to give an indication of body size. The weight of pectoral muscles varies with body weight but as the fat stores increase in weight the proportion of body weight made up of flight muscles decreases. Body weight corrected for size gives a better indication of the bird's condition (defined as its fitness for its present and future needs) than the relative weight of the pectoral muscles or the shape of the breast. The relationships between food availability and weather, and condition are examined. Only occasionally can a drop in condition following hard weather be detected; the birds normally emigrate to the coast after a few days of adverse conditions. There is a relationship between the condition of Mallard in autumn and the amount of grain left on their stubble feeding grounds after harvest. The implications of variations in winter condition on survival and breeding success are briefly discussed.

The foraging decisions of a central place foraging seabird in response to fluctuations in local prey conditions

Abstract: During reproduction, seabirds need to balance the demands of self- and offspring-provisioning within the constraints imposed by central place foraging. To assess behavioral adjustments and tolerances to these constraints, we studied the feeding tactics and reproductive success of common murres (also known as common guillemots) Uria aalge, at their largest and most offshore colony (Funk Island) where parents travel long distances to deliver a single capelin Mallotus villosus to their chicks. We assessed changes in the distance murres traveled from the colony, their proximate foraging locations and prey size choice during two successive years in which capelin exhibited an order of magnitude decrease in density and a shift from aggregated (2004) to dispersed (2005) distributions. When capelin availability was low (2005), parental murres increased their maximum foraging distances by 35% (60 to 81 km) and delivered significantly larger capelin to chicks, as predicted by central place foraging theory. Murres preferred large (>140 mm) relative to small capelin (100–140 mm) in both years, but unexpectedly this preference increased as the relative density of large capelin decreased. We conclude that single prey-loading murres target larger capelin during long foraging trips as parents are ‘forced’ to select the best prey for their offspring. Low fledgling masses suggest also that increased foraging time when capelin is scarce may come at a cost to the chicks (i.e. fewer meals per day). Murres at this colony may be functioning near physiological limits above which further or sustained adjustments in foraging effort could compromise the life-time reproductive success of this long-lived seabird.

Further studies on the mechanical properties of mollusc shell material

Abstract: Values of tensile strength, compressive strength, bending strength, hardness and modulus of elasticity are reported for the shell material of various species of bivalve, gastropod and cephalopod mollusc. Nacre is the strongest structural type, but crossed lamellar structure is the hardest. Possible selective reasons for these differences are discussed but no firm conclusions are drawn.

The importance of conservancies for enhancing the value of game ranch land for large mammal conservation in southern Africa

Abstract: Legislative changes during recent decades resulted in a massive shift away from livestock towards game ranching in southern Africa, resulting in significant increases in the abundance and distribution of many wildlife species. However, there are problems associated with game ranching from a conservation perspective, including persecution of predators, overstocking, introductions of exotic species and genetic manipulation of ‘huntable’ species. We suggest here that most of these problems could be overcome through promoting the formation of conservancies, where adjacent ranches remove internal fencing to form larger collaborative wildlife areas. Larger areas permit the reintroduction of the full range of indigenous mammals, tending to result in a land-use shift from high-offtake, low-value consumptive utilization towards higher value forms of hunting and ecotourism. Under these land-use conditions, ranchers tend to be more tolerant of predators and often actively reintroduce them. Freedom of movement for wildlife populations increases resilience to environmental shocks. The collaborative management agreements typical of conservancies tend to align more closely with conservation objectives than on single ranches. Fortuitously, there are financial advantages associated with conservancies: land-use options in conservancies are more profitable and there are economies of scale associated with cooperative management. Land within conservancies is likely to appreciate in value and attract external investment. In addition, conservancies are more conducive to developing partnerships with indigenous communities and investors and may thus increase the political and social sustainability of game ranching. However, ranchers are fiercely independent and may be resistant to removing fences due to the perception that they may relinquish control over their land and wildlife. Strategies are required to overcome such reluctance and promote the formation of conservancies to enhance the conservation value of game ranch land.

The use of the tongue and hyoid apparatus during feeding in lizards (Ctenosaura similis and Tupinambis nigropunctatus)

Abstract: The use of the tongue and hyoid is examined in cineradiographic and electromyographic investigations of feeding in two species of lizards, Ctenosaura similis (Iguanidae) and Tupinambis nigropunctatus (Teiidae). In both animals food is transported through the oral cavity by regular cycles of the tongue. Tongue movements correlate with jaw and hyoid movement. Similarities between the two animals in the use of the tongue in food transport, lapping, pharyngeal packing, and pharyngeal emptying are detailed. Mechanisms of tongue protrusion are examined and it is shown that the tongue in Tupinambis is relatively more protrusible than in Ctenosaura. This difference is complementary with data on the greater reliance of Tupinambis on the tongue as a sensory organ. Tupinambis further differs from Ctenosaura in possessing a greater mobility of the hyoid. In many features of tongue use in food transport, lizards resemble mammals, supporting postulations of a basic pattern of intra-oral food transport. However, whether this pattern can be attributed to convergence or a common, primitive neural pattern of control cannot be distinguished. Lizards lack two major characteristics of mammalian food transport: regular masticatory cycles and an internal swallowing mechanism.

A comparative study of territory in the Reed warbler (Acrocephalus scirpaceus) and Sedge warbler (A. schoenobaenus)

Abstract: Various aspects of territoriality were studied comparatively in a marked population of Reed and Sedge warblers at the Attenborough Nature Reserve, Nottinghamshire. Differences in arrival patterns, establishment of territory and particularly territory size were detected. In view of the dynamic nature of territory boundaries, a method is described for obtaining measures of mean territory size for comparative purposes. The sympatric species were largely separated by different breeding and feeding habitats, but there was also a degree of interspecific competition in some areas and interspecific territorialism was found to occur. Adults of both these migratory species were found to exhibit strong site fidelity, and there was some evidence to suggest that early post-fledging experience may influence initial selection of a particular area and territory for first breeding. The adaptive significance of territory is discussed in relation to the findings presented and current hypotheses. There was some evidence which suggests that reduction of predation pressure and intraspecific interference through spacing out, as well as provision of a nest-site may be important functions of territory in these species, but no evidence that food supply or population regulation are involved. The significance of interspecific territorialism is considered in relation to interspecific competition. The various factors effecting territory size and the patterns of nesting dispersion are also considered in an attempt to account for the striking interspecific differences found between these closely related species. It is concluded that although a multiplicity of factors may well be interacting in complex fashion, the more important of these stem from contrasts in the physical properties of the two habitats.

Implications of predatory specialization for cranial form and function in canids

Abstract: The shape of the cranium varies widely among members of the order Carnivora, but the factors that drive the evolution of differences in shape remain unclear. Selection for increased bite force, bite speed or skull strength may all affect cranial morphology. We investigated the relationship between cranial form and function in the trophically diverse dog family, Canidae, using linear morphometrics and finite element (FE) analyses that simulated the internal and external forces that act on the skull during the act of prey capture and killing. In contrast to previous FE-based studies, we compared models using a newly developed method that removes the effects of size and highlights the relationship between shape and performance. Cranial shape varies among canids based on diet, and different selective forces presumably drove evolution of these phenotypes. The long, narrow jaws of small prey specialists appear to reflect selection for fast jaw closure at the expense of bite force. Generalists have intermediate jaw dimensions and produce moderate bite forces, but their crania are comparable in strength to those of small prey specialists. Canids that take large prey have short, broad jaws, produce the largest bite forces and possess very strong crania. Our FE simulations suggest that the remarkable strength of skulls of large prey specialists reflect the additional ability to resist extrinsic loads that may be encountered while struggling with large prey items.

Spatial ecology of the European wildcat in a Mediterranean ecosystem: dealing with small radio-tracking datasets in species conservation

Abstract: Despite some populations of European wildcat Felis silvestris in central Europe are stable or increasing, the Iberian subpopulation is in decline and is listed as ‘vulnerable’. In Portugal, little is known about wildcat populations, making conservation policies extremely difficult to define. Furthermore, the secretive behaviour of these mammals, along with low population densities, make data collection complicated. Thus, it is crucial to develop efficient analytical tools to interpret existing data for this species. In this study, we determine the home-range size and environmental factors related to wildcat spatial ecology in a Mediterranean ecosystem using a combined analysis of habitat selection and maximum entropy (Maxent) modelling. Simultaneously, we test the feasibility of using radio-tracking locations to construct an ecologically meaningful distribution model. Six wildcats were captured and tracked. The average home-range size (MCP95) was 2.28 km2 for females and 13.71 km2 for one male. The Maxent model built from radio-tracking locations indicated that the abundance of the European rabbit Oryctolagus cuniculus and limited human disturbance were the most important correlates of wildcat presence. Habitat selection analysis revealed that wildcats tend to use scrubland areas significantly more than expected by chance. A mosaic of scrublands and agricultural areas, with a higher proportion of the former, benefits wildcat presence in the study area; however, species distribution is mainly constrained by availability of prey and resting sites. The Maxent model validation with camera-trapping data indicated that highly adequate model performance. This technique may prove useful for recovering small radio-tracking datasets as it provides a new alternative for handling data and maximizing the ecological information on a target population, which can then be used for conservation planning.

Ecomorphological correlates of craniodental variation in bears and paleobiological implications for extinct taxa: an approach based on geometric morphometrics

Abstract: Relative warp analyses of landmarks describing cranial and mandibular shape are used for investigating patterns of morphological variation among extant bears (Mammalia, Carnivora, Ursidae) indicative of diet and feeding behavior. These patterns are used for deriving inferences about the autecology of two extinct species previously assumed to have had different dietary preferences, the North American giant, short-faced bear Arctodus simus and the Eurasian cave bear Ursus spelaeus. Results reveal a set of shared craniodental traits among the herbivorous bears, including short and vaulted skulls with well-developed zygomatic arches, lateralized orbits and small canines, concave jaws with a highly positioned condyle, large moment arms for the temporalis and masseter muscles, and long cheek teeth. In contrast, those bears that consume animal resources have long skulls with small zygomatic arches, frontalized orbits and well-developed canines, and long jaws with a deep mandibular symphysis, low muscle leverages, a condyle situated at the level of the tooth row and reduced cheek teeth. The craniodental morphology of omnivorous bears is intermediate between those of faunivores and herbivores. This is also the case of the short-faced bear and the cave bear, which suggests that previous reconstructions of the feeding ecology of these extinct species (highly carnivorous for A. simus and herbivorous for U. spelaeus) should be revised.

Population density and the evolution of male aggression

Abstract: In some cases male animals engage in aggressive contests for access to females, in others they adopt more passive strategies and invest in traits that assist them in detecting females or in competing with rivals in other ways, such as sperm competition. One possible factor determining the fitness of these different strategies is population density. Theoretically, aggressive tactics should be found at intermediate population densities. At low densities males that invest in traits related to searching for mates could be favoured, whereas at the highest densities males that fight over females might pay excessive costs for this behaviour because of the number of rival males that they will encounter. Current empirical evidence is mostly consistent with this scheme: in some cases it seems that traits that are associated with locating mates are favoured at low densities, with aggression related traits favoured at higher densities, and in other cases aggression is selected but as density increases less aggressive strategies become more common. There remain substantial differences between species, however, and I discuss how variation in mating system, in the costs of aggression and in the nature of sperm competition, plus ecological differences between species, can change the relationship between population density and the fitness consequences of aggressive and passive behavioural strategies.

Non-indigenous ungulates as a threat to biodiversity

Abstract: Non-indigenous ungulate species pose a problem for conservation. They can be socially and economically valuable, but are also potentially harmful to biodiversity. Therefore, their introduction requires an explicit assessment of risk relative to benefit. To conduct such risk assessments, information regarding the impacts of non-indigenous ungulates on biodiversity is required. Here, we review the available evidence for the biodiversity impacts of non-indigenous ungulates. Hybridization, exploitation and apparent competition, vegetation impacts, predation, facilitation, trophic cascades and soil system functioning were assessed using a hierarchical set of criteria for the strength of the evidence. Strong evidence was lacking for risks posed by competition. Numerous reports exist of hybridization in captivity between ungulate species that normally do not co-occur, but conclusive evidence for introgression in the wild was restricted to one case. Strong evidence (using exclosure experiments) for the impacts of introduced ungulates on vegetation structure and composition was found and in some cases introduced ungulates caused the extirpation of plant species. Predation by Sus scrofa is a substantial threat to island faunas and systems, and impacts on soil system functioning elsewhere have also been found. Facilitation by ungulates has been shown to be substantial in promoting invasive plant species. By contrast, little evidence exists for apparent competition. The largest impacts from introduced ungulates are likely to be in cases where they perform novel functions in the new environment. However, to determine which types of impacts are likely to be most problematic, further evidence is required, ideally from well-designed field experiments.

Locomotory aspects of squid mantle structure

Abstract: Morphological aspects of squid (Loligo, Lolliguncula) mantle relevant to locomotory function were studied. Methods used included polarized light microscopy of frozen sections of untreated tissue taken from animals immediately after death and electron microscopy. The mantle consists of circular and radial muscles arranged in alternating rings along the whole length of the mantle. The muscle is obliquely striated. Connective tissue fibres are found in the body of the muscle and in the outer and inner tunics. The outer tunic consists of layers of large collagenous fibres. The fibres run in superimposed right- and left-handed helical courses that lie at an angle of 27° to the long axis of the animal. The tunics and the intramuscular connective fibres are thought to resist length changes in the mantle while permitting the changes in girth required for the jet power stroke. Both the intramuscular and the tunic fibre systems may provide elastic energy for the return phase of the jet cycle. Tunic fibres appear to be a geodesic tensile reinforcing system ensuring smooth shape changes in the mantle.

Aspects of the structure and functional anatomy of the Middle Triassic cynodont Luangwa

Abstract: The study concerns an incomplete skull and postcranial skeleton of the traversodontid cynodont Luangwa drysdalli Brink, from the Middle Triassic Ntawere Formation of Zambia. The incisor teeth had cutting edges maintained by tooth abrasion, and the post-canines functioned more by a puncture-crushing mechanism than by shearing. The jaw muscles, in conjunction with the teeth, were arranged to avoid stresses at the jaw articulation. Both the region of the orbit, and the braincase show certain tendencies towards mammalian structure. The forelimb operated in a primitive, sprawling fashion. The equivalent of the therian supraspinatus muscle had evolved, but not the infraspinatus. The hindlimb was more or less erect, and the hip musculature was very close to mammalian. Expanded costal plates were still present on the posterior thoracic and lumbar ribs, and functioned to maintain the vertebral column virtually rigid.

Feeding habits and niche partitioning in a predator guild composed of tigers, leopards and dholes in a temperate ecosystem in central Bhutan

Abstract: We describe the food habits, niche overlap and prey preferences in a predator guild comprised of tigers Panthera tigris, leopards Panthera pardus and dholes Cuon alpinus in a mountainous region of central Bhutan. Scat analyses revealed that these predators consumed 11 different prey species including livestock and rodents, of which leopards consumed 11. The combined relative occurrence of the three species, sambar Cervus unicolor, muntjac Munticus muntjac and wild pig Sus scrofa, constituted 42.7, 33.7 and 71.1% of the tiger, leopard and dhole diets, respectively, while livestock comprised 44.5, 73.4 and 15.9% of the prey consumed, respectively. Regression equations from earlier feeding trials were used to estimate the relative biomass and the numbers of prey consumed. Results showed that sambar featured more frequently than did muntjac and wild pig in the diets of tiger, leopard and dhole and contributed more relative biomass than did muntjac and wild pig. Sambar, muntjac and wild pig together provided 36.9, 28 and 63.1% of the biomass consumed by tigers, leopards and dholes respectively. All else being equal, there was evidence that all three predators ate livestock less than might have been expected on the basis of the abundance and high biomass of this prey category in the area. There was a high dietary niche overlap between the predators (Pianka's overlap index of 0.58–0.92), with a greater overlap between the two felid species than between the felids and the canid. This study provides evidence of a substantial diet overlap among the three sympatric carnivores, and thus highlights the potential for high intra-guild competition among them, especially given the relatively low density of prey.

Factors affecting ultrasound production in infant rodents

Abstract: Studies on the motivation for the production of ultrasound in rodents revealed that two principal factors influence this phenomenon in the infants. These have already been reported in full for white mice and partially for Wistar rats and Golden hamsters. The present paper completes the report on all five species that were investigated and makes a general assessment of the findings.

Hunting patterns and geographic profiling of white shark predation

Abstract: Predators can play important roles in structuring their communities through topdown effects on the distribution and abundance of their prey. Sharks are top predators in many marine communities, yet few studies have quantified those factors influencing their distribution and hunting behaviour. Here, we use location data from 340 predatory interactions between white sharks Carcharodon carcharias (Linnaeus), and Cape fur seals Arctocephalus pusillus pusillus (Schreber), data on associated environmental factors, and spatial analysis, including a novel application of geographic profiling – a tool originally developed to analyse serial crime – to investigate spatial patterns of shark attack and search behaviour at Seal Island in False Bay, South Africa. We found that spatial patterns of shark predation at this site are nonrandom. Sharks appear to possess a well-defined search base or anchor point, located 100 m seaward of the seal’s primary island entry–exit point. This location is not where chances of intercepting seals are greatest and we propose it may represent a balance among prey detection, capture rates, and competition. Smaller sharks exhibit more dispersed prey search patterns and have lower predatory success rates than larger conspecifics, suggesting possible refinement of hunting strategy with experience or competitive exclusion of smaller sharks from the most profitable hunting locations. As many of the features of this system will be common to other instances of foraging, our conclusions and approach employed may have implications and applications for understanding how large predators hunt and for studying other predator–prey systems.

The structure of the gonad during natural sex reversal in Monopterus albus (Pisces: Teleostei)

Abstract: A detailed study on the structure of the gonad of Monopterus albus was made as a basis for analysis of gonadal steroids in this sex-reversing teleost. Two types of males were identifiedand their existence appeared to be a result of the difference in gonadal ontogeny among the individuals in natural populations. The germinal area of the gonad, the gonadal lamellae, exhibited a zoned nature with regard to the location of the female and male germ cells. Observations suggested that the male germ cells originated from gonia pre-existing in the inner zone of the gonadal lamellae before sex reversal. Natural reversal of sex in this protogynous hermaphrodite was found to be usually a postnuptial event and was always accompanied by loss of ovarian tissue and by development of interstitial (Leydig) cells. In the mesogonial region of the gonadal wall, peculiar mesenchyme cells were found, their significance remained uncertain.