Predation and competition within an assemblage of larval newts (Triturus)

The impact of crested newts (Triturus cristatus) on the smaller-bodied palmate and smooth newts (T helveticus and T vulgaris) was studied during the larval stages using a combination of field and laboratory experiments In pond enclosures T cristatus larvae had no effect on the two smaller species over the first four weeks of development By eight weeks, however. T cristatus had achieved a size advantage which enabled it to eliminate T helveticus and severely reduce T vulgaris by predation In laboratory trials under food-limited conditions, T helveticus and T vulgaris were slightly smaller when raised with T cristatus, suggesting that this predatory effect was complemented by interspecific competition during early development Predation of the smaller species started when T cristatus reached a threshold size of c 27 mm No reciprocal effects on T cristatus growth or survival were observed Although T cristatus may be a significant predator of congeneric species in natural ponds, other factors, such as differences in microhabitat selection, higher-order predator-prey interactions and the occasional desiccation of pond habitats may facilitate coexistence between the species     

Differential effects of pH and temperature on embryonic development in the British newts (Triturus)

Changes in the water quality and temperature relationships of ponds may affect the structure of amphibian assemblages. The survival, time to hatching, hatching size and hatching stage of newt embryos were studied in the three British species ( Triturus cristatus, T. helveticus and T. vulgaris ), at two temperatures and two pHs. All T. cristatus embryos failed to hatch at pH 4.5, whereas over 80% of T. helveticus and T. vulgaris embryos hatched successfully at the same pH. At pH 7.5, T. cristatus survival was the same as the other two species, after the 50% mortality due to the homomorphism of chromosome 1 was taken into account. Temperature had no effect on survival of embryos. Time to hatching was two to four times longer at 12°C than at 17°C. Low pH shortened development time in T. vulgaris but not in T. helveticus . Low pH, but not temperature, affected size at hatching, with T. helveticus and T. vulgaris embryos emerging at a smaller size and earlier stage of development under acidic conditions. This reduction of size at low pH affected T. vulgaris more than T. helveticus . We predict that T. cristatus embryos will be the most vulnerable of the three species to acidification in nature. Warm ponds will result in rapid embryonic development, but T. helveticus and T. vulgaris larvae hatching in acid ponds will do so at a smaller size and earlier stage of development. The pattern of vulnerability to acidification within amphibian assemblages may change during ontogeny.     

Limitation of similarity and feeding habits in three syntopic species of newts (Triturus, Amphibia)

Differences in body size between both species and sex were observed to be close to Hutchinsonian ratios in an assemblage of three species of newts (Triturus italicus, T alpestris and T carnifex) in southern Italy According to feeding, differences in body size were not related with a strict food niche segregation The diet of larger newt included indeed all the prey eaten by smaller newts but showed new prey types Differences between species were more marked than between sexes of the same species, despite a strong sexual dimorphism in body size Larger newts foraged in a wider range of microhabitats and exhibited a greater diversity of foraging tactics Triturus italicus fed essentially on plankton and chironomids in shallow water at the banks of the pond Triturus alpestris foraged also in deeper water, particularly on lsopods in vegetation Prey fallen on the water surface constituted the main part of T carnifex diet According to recent data on newt evolution, speciation consisted in the reduction of body size Our data show that this process has been related with a specialization of the diet and of habitat use     

Resource partitioning by three species of newts during their aquatic phase

This paper describes the multidimensional niche of syntopic smooth newts Triturus vulgaris. alpine newts Triturus alpestris. and Italian crested newts Triturus carnifex. which constitute a complex community of eight components (the three species and their larvae, plus juvenile and neotenic alpine newts) All the potentially limiting resources (seasonal time, diel time, habitat and food) are analyzed as single niche dimensions, and then the real multidimensional niche is calculated Resource states are objectively defined, using an algorithm that groups the significant resource categories The larvae were segregated by prey, season, habitat, and water depth, in order of decreasing importance, their overlap was very low when their complete multidimensional niche was considered, and therefore they have few opportunities for present–day competition The adults were largely segregated by season and water depth, and to a lesser degree by habitat and prey, their multidimensional niches overlapped to a certain degree, thus leaving conditions for ongoing competition Considenng all the species and the life stages together, the order of importance for segregation was season, prey, habitat, water depth and diel activity, with a low overlap in the complete niche Differences m prey size were probably due to morphological constraints, differences in diel activity had very little effect on segregation except m separating larvae from the adults, and were likely promoted by need to avoid mutual predation and cannibalism It remains to be tested whether seasonal, habitat, and water depth differences are due to competitive pressures or to ecophysiological constraints     

Food niche overlap and ecological separation in a multi-species community of shrews in the Siberian taiga

An investigation of the feeding habits and prey availability in a community of seven species of shrew (Insectivora: Soricidae) inhabiting the taiga of Central Siberia was carried out with the aim of quantifying levels of niche overlap and elucidating modes of ecological separation amongst these coexisting species. All species took a wide range of invertebrate prey, and overlap in the numbers of shared prey taxa was high, but differences in dietary composition of certain taxa reduced overlap between most species. Small species fed almost exclusively on small arthropods, mostly Araneae, Chilopoda and Coleoptera, while medium and large-sized species took high proportions of oligochaetes. Prey were mostly taken in proportions approximately equal to their availability, although certain prey appeared to be selected. All shrews took prey in a range of sizes, and the high dietary occurrence of small invertebrates reflected their availability and high encounter rate in field samples. Dietary occurrence of small prey was negatively correlated, and large prey positively correlated, with body size of shrew. Smaller shrews were predominantly ground-surface foragers while larger species were more subterranean, with body size and dietary occurrence of soil prey being positively correlated. Differences in prey size and foraging mode reduced niche overlap between shrew species of widely differing sizes. Each shrew species did not occupy a separate, well-defined food niche. Instead, the community was sub-divided into three functional groups: large and small species which tended towards specialization with relatively low levels of overlap, and intermediate, generalist species with higher levels of overlap.     

Population ecology of Trituras cristatus and T. vulgaris (Urodela) in SW Sweden

The population ecology of newts was investigated between 1969 and 1974 in two localities near Gothenburg, SW Sweden: the Gunnebo park pond (about 300 m²) where Triturus cristatus Laurenti and T. vulgaris L. are sympatric, and a rock-pool (6 m²) in Billdal with only T. vulgaris. At Gunnebo, a population of about 350 breeding T. cristatus was found with about as many males as females but males being more aquatic than females. An annual survival of 0.7–0.8 was estimated for the adults. The T. vulgaris population at the same locality was estimated to about 250–300 breeding adults with a sex ratio possibly in favour of males. The survival of adults was found to be extremely low and a very small percent of the adults seems to breed more than once. The Billdal T. vulgaris population was estimated to contain nearly 70 breeding adults with a sex ratio very near to 1:1. The annual survival of adults was found to be 0.5. The different survival of the two T. vulgaris populations are discussed with particular reference to predation. The age at which newts breed for the first time seems to vary; for T. vulgaris five years may well be the normal age. Factors that may limit the sizes of the populations, possible reasons for differences in frequency of occurrence in water, and possible predators are discussed.     

Growth and size of Triturus vulgaris and T. cristatus (Amphibia) in different parts of Norway

The growth and size of the newts, Triturus vulgaris (L.) and T. cristatus (Laurenti) in different parts of Norway (+ Jämtland, Sweden) were studied. Age was estimated from skeletal growth marks, size-frequency histograms and, for the males, from the number of testis lobes.
On average, the T. vulgaris Larvae in central Norway and Jämtland are smaller than those in southeastern Norway, although in good localities, at the same altitude, they are of approximately the same size and complete their development already within 2½–3 months. Larvae living in eutrophic habitats are larger than those in oligotrophic-dystrophic habitats. In bog habitats at similar times of year the T. cristatus larvae from central Norway are about the same size as those from similar habitats in southwestern and southeastern Norway, but somewhat smaller than those from eutrophic ponds in the Oslofjord area.
No significant differences in the mean size of adult T. vulgaris from southeastern Norway and from central Norway were found. The maximum lengths attained were recorded from central Norway, however. In eutrophic habitats T. vulgaris adults BK usually larger than those in oligotrophic/dystrophic habitats.
In southeastern Norway, where growth is rapid, T. vulgaris may become sexually mature when 2+ yr-old, in central Norway usually a year later, in Jämtland. on average, still later, and in their northernmost locality (Vefsn) they probably do not breed until 5+ or 6+ yr-old.
On average, T. cristatus adults from southeastern Norway are slightly larger than those from central Norway, and may become mature at 2+ yr-old. compared with 4 + yr-old, at the earliest, in the latter area. The differences in the growth rates of both larvae and metamorphosed stages, of both species, most probably represent a response to climatic differences, although biotope quality is also an important factor.     

Fish community structure,spatial distribution and feeding ecology in a beaver pond

Synopsis The fish community of a small (2.7 ha) Ontario beaver pond was analyzed relative to predictions based on its small size, shallow depth, brief existence and isolation from more permanent water bodies. The predictions were: (1) species richness will be lower than that of more permanent water bodies in the area, (2) fish will be mainly of small body size, (3) species will be randomly distributed across habitats, and (4) there will be a high degree of diet overlap between species and age classes. The first and second predictions were supported. The pond consisted of 10 resident species in 1985, and at least seven in 1988. Species richness was below the average of 13.2 found in four lakes in the vicinity, but greater than the 3.1 predicted by a species-area curve for non-acidified lakes in Ontario. All species except pumpkinseed, yellow perch and brown bullheads were small-bodied with short life spans and high population turnover rates, and few fish above 100 mm were present. Predictions 3 and 4 were not supported. Habitat occupation was nonrandom, and high diet separation occurred, particularly in August when food limitation was evident. While beaver ponds lack the range of habitats and the diversity of species of lake environments, low prey density and high fish density nevertheless appear to foster resource partitioning.     

Influence of introduced fish Percottus glenii (Odontobutidae, Pisces)

Monitoring of 28 waterbodies has been carried out since 1994 in the region of reserve "Lake Glubokoe" (Moscow region, Russia). It was revealed that species diversity as well as abundance of larval amphibians correlate negatively with presence of introduced fish, rotan, Perccottus glenii (Odontobutidae). Newts (Triturus cristatus, T. vulgaris) and frogs (Rana temporaria, R. arvalis, R. lessonae) as a rule are not capable to breed in waterbodies colonised by rotan. In contrast, toads (Bufo bufo) breed successfully in such sites. Larvae of toads are comparatively less edible for rotan and pass their metamorphosis. Persistence of amphibians to predation of rotan decreases in the row: B. bufo (R. temporaria, R. arvalis and R. lessonae), T. vulgaris, T. cristatus. The Crested newt (T. cristatus) is the most endangered species and could extinct in next years.     

Diet niche relationships among North American grassland and shrubsteppe birds

Summary We consider the dietary relationships of the numerically dominant breeding bird species in four North American grassland/shrubsteppe habitats, sampled over 2–3 consecutive years. Overall, the diets of these species contained primarily insects: orthopterans comprised 29% of the diet biomass, coleopterans 24%, and lepidopteran larvae 23%, while seeds contributed 15% of the average diet. These diets varied substantially, however, and we evaluated several aspects of this variation. Intersexual differences in diets within a species were few, despite the occurrence of significant sexual size dimorphism in several species. For many species, however, there were substantial shifts in dietary composition between years at a given location; overall, the average between-year similarity of species' dietary composition was 70%. Different species exhibited rather different diet patterns. Horned Larks were relatively omnivorous, had broad diet composition niches, and varied considerably in diets between different locations. Meadowlarks were also broad-niched and geographically variable in their diets, but were the most highly carnivorous of the species we considered. Dietary niche breadths of Grasshopper Sparrows were intermediate, but diet composition was rather stable, both between years and between locations. Chestnut-collared Longspurs exhibited narrow diet niches, but substantial annual variation: each year this species apparently exploited a different but limited set of prey types rather heavily. Larger avian predators generally consumed a broader array of functional groups of prey, but did not differ in the taxonomic variety of their diets from small birds. Variation in diet composition between individuals within local populations was considerable; in most species, an individual contained on the average 30–40% of the prey taxa represented in entire population smaples.Patterns of dietary overlap among species were quite inconsistent from year to year at most locations, although at the shrubsteppe site overlap among all species present was consistently quite high. Relatively few cooccurring species pairs exhibited low diet overlap. The degree of diet niche overlap was unrelated to body size differences of the birds, despite as much as six-fold differences in weight among some coexisting species. Relationships of the bird species on another dimension of the trophic niche, prey size, also differed substantially between sites and years. The ranking of co-occurring species by the mean sizes of the prey they consumed generally did not parallel their rankings by body sizes, and in some cases the smallest and the largest species present ate prey of similar sizes. At the shrubsteppe site, all the breeding species exhibited quite similar frequency distributions of prey sizes in their diets.As species number and diversity increased in the breeding avifaunas, diet niche breadths generally decreased, species packing by prey size decreased, and diet composition niche overlap remained relatively unchanged. These trends are in at least partial agreement with predictions of diffuse competition theory, but the patterns were derived from broad inter-site comparisons of overall site averages, and the relationships generally did not hold within local assemblages of species. In general, our attempts to match values of dietary niche features with site characteristics failed to demonstrate close agreement with the predictions of prevailing ecological theory based upon assumptions of resource limitation and competition. Instead, our findings seem generally most consistent with the suggestion that food is not normally limiting to bird populations in these systems, and individuals and populations are exploiting the food resources in an opportunistic fashion, which leads to considerable individual, between-year, and between-location variation in diet compositions and interspecific overlaps.Our attempts to discern clear relationships that accord with theoretical expectations in these avian assemblages are thwarted by our lack of detailed information on the resource base and by the lack of clear tests that will separate alternative hypotheses of community organization and structuring. We suggest that these complications may compromise the findings of many community studies.     

The effect of pH on embryonic and larval development in smooth and palmate newts, Triturus vulgaris and T. helveticus

The distribution of smooth newts, Triturus vulgaris , and palmate newts, Triturus helveticus , in north-west Europe is related to geology and water quality. This study compared the development of the eggs and larvae of the two species under sublethal acidic and neutral conditions. Newt embryos raised under low pH hatched at an earlier stage of development, at a smaller size, and before those raised under neutral conditions. T. vulgaris hatched at a smaller size than T. helveticus , but pH did not affect the species differentially. Larvae of both species grew to a larger size under neutral than under acid conditions. Larvae raised in heterospecific pairs grew at least as well as those raised in conspecific pairs. Feeding was depressed under acid conditions, and reduced growth may therefore be associated with changes in the behaviour of newt larvae and their prey.     

Complex interactions between components of individual prey specialization affect mechanisms of niche variation in a grasshopper-hunting wasp

1.?Individual foraging behaviour defines the use of resources by a given population and its variation in different ways such as, for example, unpredictable interactions between taxon-biased and size-biased selection. Here we investigated how the environmental availability of prey and individual specialization, for both prey taxa and prey size, shape niche variation across generations in the grasshopper-hunting digger wasp Stizus continuus. 2.?The population of S.?continuus expressed selective predation, females mainly hunting species encountered on large bushes; diet changed across generations, due more to size increase in potential prey than to changes in the orthopteran community. 3.?Individual females of both generations weakly overlapped the size and taxa of prey, and the niche width of the second generation increased for both prey size and taxa. 4.?The greater variance in prey size in the environment accounted for the enlarged prey size niche of the second generation, but the load-lifting constraints of the wasps maintained individual prey size specialization constant. In contrast, the enlarged prey taxon niche paralleled a smaller overlap of diets between wasps in the second generation. 5.?Increased niche width in the S.?continuus population was thus achieved in two ways. Regarding prey size, all individuals shifted towards the use of the full set of available resources (parallel release). For prey taxa, according to the classical niche variation hypothesis, individuals diverged to minimize resource use overlap and perhaps intraspecific competition. These two mechanisms were observed for the first time simultaneously in a single predator population.     

Feeding habits and diet overlap of marine fish larvae from the peri-Antarctic Magellan region

The Magellan region is a unique peri-Antarctic ecosystem due to its geographical position. However, the knowledge about the distribution and feeding ecology of fish larvae is scarce. Since this area is characterized by low phytoplankton biomass, we hypothesize that marine fish larvae display different foraging tactics in order to reduce diet overlap. During austral spring 2009–2010, two oceanographic cruises were carried out along southern Patagonia (50–56°S). Larval fish distribution and feeding of the two most widely distributed species were studied, the smelt Bathylagichthys parini (Bathylagidae) and black southern cod Patagonotothen tessellata (Nototheniidae). Larvae of B. parini showed a lower increase in the mouth gape at size, primarily feeding during daytime (higher feeding incidence during the day) mostly on nonmotile prey (invertebrate and copepod eggs, appendicularian fecal pellets, diatoms). They showed no increase in feeding success (number, total volume of prey per gut and prey width) with increasing larval size, and the niche breadth was independent of larval size. Larvae of P. tessellata showed a large mouth gape at size, which may partially explain the predation on motile prey like large calanoid copepods (C. simillimus) and copepodites. They are nocturnal feeders (higher feeding incidence during night) and are exclusively carnivorous, feeding on larger prey as the larvae grow. Nonetheless, niche breadth was independent of larval size. Diet overlap was important only in individuals with smaller mouth gape (<890 μm) and diminished as larvae (and correspondingly their jaw) grow. In conclusion, in the peri-Antarctic Magellan region, fish larvae of two species display different foraging tactics, reducing their trophic overlap throughout their development.     

Niche overlap of two sympatric-nesting hawks Accipiter spp. in the New Jersey-New York Highlands

The food and habitat niches of two nesting species of hawks Accipiter spp were studied in an extensively forested area of the Eastern Deciduous Forest Biome Nesting habitat was quantitated at 19 Cooper s hawk A cooperu nests and 16 northern goshawk A gentilis nests There was no significant trend for Cooper's hawks to nest in less mature forests than northern goshawks as reported previously for western North America Forest habitats did not differ markedly except that shrub cover was greater at Cooper's hawk nest sites, which were also on flatter terrain and closer to roads, forest openings, and human habitation However, these few differences resulted m reducing habitat-niche overlap considerably (0 538), as was calculated using principal components analysis Mean prey weight was significantly larger for the northern goshawk which follows its 2 2-fold body weight advantage over Cooper's hawk Although bird prey was of primary importance to both Accipiter, goshawks took twice the proportion of mammals compared to their smaller congener Food-niche overlap was lowest by prey species overlap (0 470), followed by prey size class overlap (0 529), and highest by vertical foraging zone overlap (0 816) The Cooper's hawk showed the greatest niche breadth for both food and habitat niches indicating it as more of a generalist Overall, niche complementarity of food and habitat dimensions resulted in niche overdispersion along food and habitat dimensions with a total niche overlap (0 504) that was below the competition threshold These results suggested that competition (past and current) was responsible for segregating niches     

Sexual Dimorphism of Head Size in Phrynocephalus przewalskii: Testing the Food Niche Divergence Hypothesis

Sexual size dimorphism （SSD） is a general phenomenon in lizards, and can evolve through sexual selection or natural selection. But natural selection, which was thought to operate mainly through reducing the competition be- tween the two sexes （niche divergence hypothesis）, gave rise to a lot of controversy. We tested the niche divergence hypothesis in the toad-headed lizard Phrynocephalus przewalskii by comparing diet composition and prey sizes between males and females. The species was found to be sexual dimorphic, with males having relatively larger snout-vent length, head width, head length, and tail length, while females have relatively larger abdomen length. Based on analysis of 93 studied stomachs, a total of 1359 prey items were identified. The most common prey items were formicid, lygaeid and tenebrionid. The two sexes did not differ in the relative proportions of prey size categories they consumed and the dietary overlap based on prey species was high （O = 0.989）. In addition, the meal size, the volume or any maximal dimension of the largest prey item in the stomach was not explained by the sexes. According to our results, food niche divergence might not play an important role in the SSD evolution ofP. przewalskii.     

Seasonal variation in prey preference,diet partitioning and niche breadth in a rich large carnivore guild

Large carnivore community structure is affected by direct and indirect interactions between intra-guild members. Co-existence between different species within a carnivore guild may occur through diet, habitat or temporal partitioning. Since carnivore species are highly dependent on availability and accessibility of prey, diet partitioning is potentially one of the most important mechanisms in allowing carnivores to co-exist. Intra-guild interactions may vary over time as carnivore prey preference and diet overlap can change due to seasonal changes in resource availability. We conducted scat analysis to compare the seasonal changes in prey preference, diet partitioning and niche breadth of four large carnivore species, namely leopard Panthera pardus, spotted hyena Crocuta crocuta, brown hyena Parahyaena brunnea and wild dog Lycaon pictus in central Tuli, Botswana. Large carnivores in central Tuli display a high dietary overlap, with spotted hyena and brown hyena displaying almost complete dietary overlap and the other carnivore species displaying slightly lower but still significant dietary overlap. Dietary niche breadth for both hyena species was high possibly due to their flexible foraging strategies, including scavenging, while leopard and wild dog showed a relatively low niche breadth, suggesting a more specialised diet. High dietary overlap in central Tuli is possibly explained by the high abundance of prey species in the area thereby reducing competition pressure between carnivore species. Our research highlights the need to assess the influence of diet partitioning in structuring large carnivore communities across multiple study sites, by demonstrating that in prey rich environments, the need for diet partitioning by carnivores to avoid competition may be limited.     

The effects of morphology,phylogeny and prey availability on trophic resource partitioning in an anuran community

Several factors influence the partitioning of trophic resources in ecological communities, such as morphology, evolutionary history, and resource availability. Although the effects of morphology, phylogeny, and resource availability on trophic ecology have long been explored by theoretical studies, little has been done to empirically test these relationships. Here, we tested whether phylogenetic and morphological distances correlate with trophic niche overlap using a path analysis of multiple partial regression of distance matrices. Also, we tested whether niche breadth is influenced by body size using Phylogenetic Generalized Least Squares analysis. Trophic niche overlap was better explained by morphology per se than by the phylogenetic distance. We also found that predator's body size influences niche breadth calculated considering prey traits and availability, but not when we do not include these availability data. Additionally, trophic niche breadth was usually smaller when we considered prey traits and availability, differently from niche overlap, whose values increased when we did not consider these data. Our findings show that the interpretation of trophic niche in communities changes if we consider availability data, affecting inferences about coexistence and trophic specialization. Our study contributes to understanding trophic specialization and emphasizes the importance of incorporating prey availability and their traits into diet analysis.     

El Niño events,the lean versus fat scenario,and long‐term guild dynamics of vertebrate predators in a South American semiarid ecosystem

Abstract Predator assemblages are complex systems in which asynchrony in the dynamics of resources and consumers, and the idiosyncratic perception of environmental conditions by the predators may obscure the detection of expected patterns. We disentangle the specific effects of these variables on the guild structure of a vertebrate predatory assemblage in a semiarid ecosystem of western South America. Over 16 years, this system faced dramatic fluctuations in prey availability associated with four El Niño events. After controlling for other sources of variation, we tested if increased resource availability is associated with higher niche overlaps, as expected from the lean/fat scenario. We determined the existence of two trophic guilds of predators (specialized mammal‐eaters and omnivorous species with emphasis on arthropods) and found that they responded to increased productivity both at the guild and whole assemblage levels. However, the population response of arthropod prey (almost simultaneous) and of different small mammal prey (delayed by 1 or 2 years) to productivity imposed a degree of asynchrony in prey availability and in the response of predators. This resulted in the between‐guilds exchange of predator species depending on mammal prey scarcity or abundance. As a consequence, the observed pattern was an apparent lack of response at the assemblage level. Despite differences in the perception of prey levels by predators, we conclude that each one of them responded accordingly to theoretical predictions following a simple rule: if prey resources are not limiting, predators behave opportunistically converging over the most abundant resources, thus increasing niche overlap; if prey shortages occur, predators specialize on those prey resources that they gather most efficiently, thus lowering niche overlap; if resources become even scarcer, all predators converge again upon the few prey resources still available, thus increasing overlap – out of necessity.     

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

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.     

FOOD PREFERENCE AND THE EXTENT OF OVERLAP IN SOME INSECTIVOROUS BIRDS, WITH SPECIAL REFERENCE TO THE TYRANNIDAE

Analysis of published records of the food of flycatchers (Tyrannidae), swallows (Hirundinidae) and vireos (Vireonidae) of North America, and terns (Laridae) of the Pacific Ocean showed that size, rather than taxonomic, differences in food appear to be the most important ones for these birds. Although the distribution of insect sizes in nature approaches a two-parameter log-normal distribution, the distributions of the sizes of food items taken by birds show no significant differences from log-normal. Birds of a given feeding type (e.g. flycatchers) show a strong correlation of average prey size with bird body weight, and a significantly less strong correlation with bill characteristics, indicating that body size is a better predictor of prey size than any single bill character. The slopes and/or intercepts of regressions of food size against body weight are different for birds of different foraging type. Values of overlap in food preference are proportional to the similarity of the two species compared, expressed as the ratio of their weights. Because insect taxa differ in size and because the amount of overlap in taxonomic composition of foods is therefore very roughly proportional to the amount of overlap in size, taxonomic differences in food may merely reflect differences in size preferences. Values for overlap in food are greater than for most cases involving spatial niche parameters, indicating space is more easily divided than food, a conclusion supported by the relative rarity of large flycatchers.