Diet-dependent fecundity of the spiders Atypena formosana and Pardosa pseudoannulata, predators in irrigated rice

1 The fecundity of the spiders Atypena formosana and Pardosa pseudoannulata was assessed on diets of brown planthopper Nilaparvata lugens (BPH), green leafhopper Nephotettix virescens (GLH), Collembola (Entomobryidae), Droso phila melanogaster and three prey mixtures; BPH–GLH, BPH–GLH–Collembola and a full mixed diet of BPH–GLH–Collembola–D. melanogaster. 2 Egg production and hatching success was high in A. formosana except on the BPH, the GLH and the BPH–GLH diets. In P. pseudoannulata egg production and hatching success was lowest on diets of GLH and BPH–GLH, whereas this spider used BPH better. 3 Differences between offspring sizes were small. 4 Survival of A. formosana females was lowest on the GLH and BPH–GLH diets. In P. pseudoannulata survival did not differ significantly. 5 Food conversion efficiency was highest on the Collembola and the D. melanogaster diets for both spiders. 6 Overall, diets of Collembola and D. melanogaster had the highest quality for both spiders, the BPH–GLH–Collembola and the full mixed diets were intermediate in quality, the quality of the BPH diet was intermediate to low and quality of the GLH and BPH–GLH diets was low. 7 There need not be a contradiction between low dietary value of hoppers and successful natural biological control provided that the nutritional needs of the spiders are met by sufficient alternative prey. 8 The hopper‐spider relationship is comparable to that of aphids and spiders in temperate cereals, suggesting that low dietary quality of Homopterans to spiders may be widespread.     

Prey‐mediated changes in the selectivity of the predator Macrolophus pygmaeus (Heteroptera: Miridae)

When foraging in communities with mixed prey, generalist predators may be confronted with prey species that differ in quality, size and mobility and interact with one another. To examine prey selection, predation by Macrolophus pygmaeus (Heteroptera: Miridae) was recorded by providing a diet of either one or two prey species of Myzus persicae (third‐instar nymphs), Aphis gossypii (fourth‐instar nymphs), Trialeurodes vaporariorum (third‐instar nymphs) and Ephestia kuehniella (eggs). In the experiments, prey mobility, prey quality and prey biomass were considered. The biomass consumed by the predator was dependent on the combination of prey species and the quantity of biomass offered. In choice experiments with diets mixed of two prey species at equal densities, the predation to A. gossypii was significantly reduced in the presence of E. kuehniella but the rate of consumption of M. persicae, T. vaporariorum and E.kuehniella was not significantly affected by the coexistence of any other species in the mixed prey diet. When equal amounts of biomass from two prey species were provided in combination, the total consumed biomass was significantly reduced in the mixed prey diets composed of E. kuehniella eggs and aphid nymphs. Thus, under the mixed‐prey situation, prey selection by predators may be affected by interactions among prey species differing in traits such as quality, mobility and size.     

Invertebrate biodiversity affects predator fitness and hence potential to control pests in crops

Natural enemies that control pests usually allow farmers to avoid, or reduce, the use of pesticides. However, modern farming practices, that maximize yields, are resulting in loss of biodiversity, particularly prey diversity. Does this matter? Pests continue to thrive, and without alternative prey the predators should, perforce, concentrate their attentions upon the pests.We showed that a diverse diet significantly enhances predator fecundity and survival. Experiments were conducted using common generalist predators found in arable fields in Europe, the carabid beetle Pterostichus melanarius (Coleoptera: Carabidae) and the linyphiid spider Erigone atra (Araneae: Linyphiidae). We tested the hypothesis that mixed species diets were optimal, compared with restricted diets, with respect to parameters such as predator weights, egg weights, numbers of eggs laid, egg development times, egg hatching rates and predator survival. In carabids, an exclusive earthworm diet was as good as mixed diets containing earthworms for egg production and hatching, but less good than such mixed diets for increase in beetle mass and sustained egg laying. For spiders, aphids alone (Sitobion avenae) or with the Collembola Folsomia candida, drastically reduced survival. Aphids plus the Collembola Isotoma anglicana improved survival but only aphids with a mixed Collembola diet maximized numbers of hatching eggs.Predators offered only pests (slugs or aphids) had lowest growth rates and fecundity. We therefore demonstrated that conservation of a diversity of prey species within farmland, allowing predators to exploit a diverse diet, is essential if predators are to continue to thrive in crops and regulate agricultural pests.     

Invertebrate biodiversity affects predator fitness and hence potential to control pests in crops

Natural enemies that control pests usually allow farmers to avoid, or reduce, the use of pesticides. However, modern farming practices, that maximize yields, are resulting in loss of biodiversity, particularly prey diversity. Does this matter? Pests continue to thrive, and without alternative prey the predators should, perforce, concentrate their attentions upon the pests.We showed that a diverse diet significantly enhances predator fecundity and survival. Experiments were conducted using common generalist predators found in arable fields in Europe, the carabid beetle Pterostichus melanarius (Coleoptera: Carabidae) and the linyphiid spider Erigone atra (Araneae: Linyphiidae). We tested the hypothesis that mixed species diets were optimal, compared with restricted diets, with respect to parameters such as predator weights, egg weights, numbers of eggs laid, egg development times, egg hatching rates and predator survival. In carabids, an exclusive earthworm diet was as good as mixed diets containing earthworms for egg production and hatching, but less good than such mixed diets for increase in beetle mass and sustained egg laying. For spiders, aphids alone (Sitobion avenae) or with the Collembola Folsomia candida, drastically reduced survival. Aphids plus the Collembola Isotoma anglicana improved survival but only aphids with a mixed Collembola diet maximized numbers of hatching eggs.Predators offered only pests (slugs or aphids) had lowest growth rates and fecundity. We therefore demonstrated that conservation of a diversity of prey species within farmland, allowing predators to exploit a diverse diet, is essential if predators are to continue to thrive in crops and regulate agricultural pests.     

Prey selection of subadult male northern fur seals (Callorhinus ursinus) and evidence of dietary niche overlap with adult females during the breeding season

During the breeding season northern fur seals (Callorhinus ursinus) congregate on the Pribilof Islands in large numbers creating the potential for intraspecific competition. Due to the declining trend in the Pribilof Islands population of fur seals, it is important to understand how prey resources are partitioned among the population. Fur seals exhibit a high degree of sexual dimorphism resulting in energetic differences among age and sex classes. Therefore, we hypothesized that subadult male and adult female fur seals would differ in the type and size of prey consumed. We examined the diets of subadult male (age 2–8; mean mass 28–176 kg) and adult female (age ≥ 3 yr; mean mass 13–50 kg) seals on St. Paul Island from 1992 to 2000. Prey remains found in fecal samples were compared using niche overlap indices. There was nearly complete dietary niche overlap between subadult male and adult female fur seals. Walleye pollock (Theragra chalcogramma), Pacific salmon (Oncorhynchus spp.), Pacific herring (Clupeia pallasi), and cephalopods were common prey items found in the diets of both groups. We found differences in the size of pollock consumed and that geographic location of sample collection may be important in determining diet differences. Our results indicate high levels of dietary overlap among subadult male and adult female fur seals.     

Diet-shifts by an estuarine goby (Pomatoschistus microps) in the face of variable prey availability

Ontogenetic shifts in diet provide a mechanism for maximising fitness throughout development and are common where predators exhibit large increases in size. In order to maximise their fitness throughout development, benthic feeding fish can show diet-shifts that centre on the transition from meiofaunal to macrofaunal prey. Here we assessed whether such a shift was influenced by natural variation in prey-size availability by comparing the sizes of prey consumed by naturally foraging common gobies (Pomatoschistus microps). We tested explicitly for the presence of an ontogenetic shift by analysing the length of prey consumed and an index for prey importance for gobies of different lengths. We also tested the match between actual diets and those predicted by a foraging model. The goby size at which the diet-shift occurred was consistent among locations that differed in their availability of prey and through temporal changes in densities and types of prey. The mean sizes of ingested prey increased for gobies > 35 mm in length and the relative importance of macrofauna increased at 30 mm. The foraging model predicted that gobies > 30 mm would eat larger prey than would smaller gobies which differed from the observed changes in prey-size at 35 mm. Availability of prey did not appear to influence the lengths at which gobies changed diet but did affect the size of prey taken after the diet-shift. A relatively large abundance of large-bodied chironomids at two sites was reflected in the mean size of prey consumed by gobies > 30 mm at these sites. Our study indicates that intrinsic mechanisms can be more important than fluctuating environments in determining prey-choice and shifts in diet, although for the common goby, variability in prey-size may have implications for prey-choice later in ontogeny.     

Functional significance of Micraspis discolor (F.) (Coccinellidae: Coleoptera) in rice ecosystem

Coccinellids are key predators that are conserved and augmented in agricultural ecosystems, to achieve biological control of pests. Actual quantification of field predation has not been attempted for many of the beneficial coccinellids. Numerous reports show coccinellids as opportunistic, feeding on a variety of food material in addition to their preferred prey. Micraspis discolor is the most abundant species of coccinellid in rice ecosystems and touted as a biocontrol option for brown planthopper (BPH), Nilaparvata lugens (Stal), a key pest of rice. However, it has been reported as both entomophagous and phytophagous. Native polyacrylamide gel electrophoresis (PAGE) was used to separate esterases from whole‐body homogenates of Micraspis and its prey viz., green leafhopper (GLH) Nephotettix virescens (Distant), BPH N. lugens, whitebacked planthopper (WBPH) Sogatella furcifera (Horvath), aphid Rhopalosiphum padi L., thrips, Haplothrips sp., and pollen. Field‐collected beetles showed a range of bands, some corresponding with pollen and GLH, while others were different from prey offered, indicating a wider range of prey spectrum than envisaged. Feeding preference studies confirmed a preference for pollen and GLH in no‐choice (H = 20.724; P = 0.001) and multiple‐choice tests (H = 20.52; P < 0.001) and a significant preference for pollen over all insects offered in the paired‐choice test (t = 5.099; P = 0.007). The abundance of adult M. discolor in rice at flowering phase does not correspond to prey abundance in the field but rather reflects an inclination to pollen feeding more than entomophagy.     

Growth and reproduction of fungal feeding Collembola as affected by fungal species,melanin and mixed diets

Fungal feeding soil invertebrates feed on a wide spectrum of fungal species suggesting that mixed diets increase fitness. We investigated relationships between food preferences for seven saprophytic fungal species/forms and fitness parameters (mortality, growth, time to reproduction, reproduction, egg size) in two Collembola species, Folsomia candida and Protaphorura armata. The fungal species/forms studied included the wild type and a melanin-deficient form of Aspergillus fumigatus to investigate the role of melanin in collembolan nutrition. Also, three mixed diets consisting of a preferred fungal species (Cladosporium cladosporioides) and species of intermediate or low food quality were investigated. Both Collembola species preferred similar fungal species/forms as food. Food preference generally matched fitness parameters, i.e. growth and reproduction of Collembola was at a maximum when feeding on preferred fungi. This was not the case for A. fumigatus. The wild type and the melanin-deficient form ranked among the least preferred fungi. Growth and reproduction of Collembola were low when feeding on the wild type but high when feeding on the melanin-deficient form indicating that the Collembola misjudged the food quality of the latter in the preference tests. The results show for the first time that genes driving melanin syntheses (pksP) strongly affect the food quality of fungi for fungal feeding invertebrates. Feeding on mixed diets generally increased growth and reproduction of Collembola except when the diets included toxic species (Penicillium sp.). The results support the nutrient balance hypothesis and also show that the detection of toxic species in the diet is important. They indicate that the widespread generalist feeding mode of Collembola maximizes fitness if toxic fungal species are avoided. The fitness parameters growth, reproduction and time until onset of reproduction were correlated closely but egg volume, which also varied with fungal diet, correlated poorly with the other fitness parameters. Variation in egg size with fungal diet shows that the diet of Collembola may have transgenerational effects.     

Resistance to green leafhopper (Nephotettix virescens) and brown planthopper (Nilaparvata lugens) in transgenic rice expressing snowdrop lectin (Galanthus nivalis agglutinin; GNA)

Transgenic rice plants expressing snowdrop lectin (Galanthus nivalis agglutinin; GNA) were screened for resistance to green leafhopper (Nephotettix virescens; GLH), a major homopteran pest of rice. Survival was reduced by 29% and 53% (P<0.05) respectively, on plants where GNA expression was tissue-specific (phloem and epidermal layer) or constitutive. Similar levels of resistance in GNA-expressing transgenic rice were previously reported for rice brown planthopper (Nilaparvata lugens; BPH). GNA binding to glycoproteins in gut tissues showed that BPH contained more "receptors" than GLH, and that the binding affinity was stronger, particularly in the midgut. Subsequent toxicity of GNA is thus unlikely to be directly related to the amount of lectin bound. GNA was not detected in the honeydew of either insect species when they were fed on GNA-expressing plants, in contrast to results from artificial diet studies. This result suggests that GNA is not being delivered to the insect efficiently. When offered a free choice vs control plants, BPH nymphs tended to avoid plants expressing GNA; avoidance was less pronounced and took longer to develop on plants where GNA expression was tissue-specific, In contrast to BPH, GLH nymphs were attracted to plants expressing GNA, whether constitutively or in a tissue-specific manner.     

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 partitioning between breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in southern Brazil.

I examined the diet of breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in an agrarian area of southern Brazil by analyzing regurgitated prey remains. The objective was to evaluate how these raptors, which differ markedly in their hunting activity periods (owls are nocturnal and kites diurnal), share their mammalian food component. 2,087 prey consumed by Barn Owls and 1,276 by White-tailed Kites were identified. They presented a high overlap of food-niches (Piankas index was 0.98). Based on the daily activity period of their main small mammal prey, a lower overlap would be expected. The crepuscular/nocturnal Mus musculus was the main prey for the diet of breeding Barn Owls (81%) and White-tailed Kites (63%). This small exotic rodent provided 63% of the small mammal biomass ingested by owls and 44% by kites. Larger native small mammals were also considered important for the diet of kites, mainly because of their biomass contribution. Although these raptors differ markedly in their hunting activity periods, Barn Owls and White-tailed Kites are very similar predators in southern Brazil, overlapping their diets.     

The global relationship between climate,net primary production and the diet of spiders

Aim We compiled data on prey utilization of spiders at a global scale to better understand the relationship between current climate or net primary production (NPP) and diet breadth, evenness and composition in spiders. We test whether the productivity and the diversity–climatic‐stability (DCS) hypotheses focusing on diversity patterns may also explain global patterns in prey utilization by web‐building and cursorial spiders. Location A global dataset of 95 data points from semi‐natural and natural terrestrial habitats spanning 41.3° S to 56.1° N. Methods We collected data on spider prey (29 groups, mostly order‐level invertebrate taxa) through extensive literature research to identify the relationship between climatic conditions and NPP and spider diets based on 66 studies of prey composition in 82 spider species. Results The number of prey groups in spider diets was positively related to NPP, after accounting for differences in sampling effort in the original studies. In general, diet breadth was significantly higher for spider species in tropical environments. Prey individuals in spider diets were more evenly distributed among different prey groups in warmer environments with lower fluctuations in precipitation. Collembola and other spiders were more common prey for spiders with a cursorial hunting mode. Myriapoda and Collembola were more common prey in cooler climates with more stable precipitation, whereas Isoptera, Lepidoptera, Psocoptera and Coleoptera showed the opposite pattern. Main conclusions The positive relationship between diet breadth and NPP and the negative relationship between prey evenness and seasonality in precipitation support the productivity and the DCS hypotheses, respectively. This effect on global patterns of invertebrate predator–prey interactions suggests that trophic interactions between spiders and their prey are sensitive to climatic conditions. Climatic conditions may not only affect spider community composition, but also considerably alter the functional role of these abundant invertebrate predators in terrestrial ecosystems.     

Diet estimation in California sea lions,Zalophus californianus

We performed a captive feeding experiment using California sea lions to assess biases associated with estimating pinniped diet using scats and spews. Sea lions were fed nine of their natural prey species: anchovy, sardine, Pacific mackerel, jack mackerel, hake, steelhead smolts, shortbelly rockfish, pink salmon, and market squid. Recovery percentages varied among prey species using otoliths and were improved for adult salmon and sardine using the all‐structure method. Numerical and graded length correction factors provided better estimates of number and size of prey consumed. Four models used to determine the proportions of prey species consumed by a sea lion population were tested. The all‐structure method and variable biomass reconstruction model, in conjunction with numerical and graded length correction factors, provided more accurate estimates than without. We provide numerical correction factors for all prey species, including correction factors for specific salmon bones: vertebrae, branchials, radials, teeth, gill rakers, and hypurals.     

The combined effects of temperature and diet on development and survival of a crab spider,Misumenops tricuspidatus (Fabricius) (Araneae: Thomisidae)

In the present study, the combined effects of temperature and diet on development and survival of a crab spider, Misumenops tricuspidatus (Fabricius) (Araneae: Thomisidae) in laboratory conditions were investigated. The experiments were carried out at five constant temperatures ranging from 15°C to 35°C on two kinds of diets, fruit flies (Drosophila melanogaster) and a mixed diet of fruit flies and dung flies. It was found that development rate of eggs increased with successive temperature increments, reaching a maximum at 30°C, then declined at 32°C and that eggs survived well between 20°C and 30°C (>70%), but no eggs survived to hatching at 35°C regardless of whether the spiders were fed on single or mixed diet. Juveniles completed development on both diets at all constant temperatures tested, but survival was low at the extreme temperatures. Juvenile development times decreased over successive temperature increments up to 30°C, then increased at 32°C. Females developed faster than males. Diet also influenced development time, survival and number of moults to reach maturity. Juveniles raised on the mixed diet composed of fruit flies and dung flies developed faster, survived better, and required fewer moults to reach maturity than on a diet composed of only fruit flies. Plots of development rates (reciprocal of mean development times) and survival rates (expressed as percentages) against constant temperatures indicated that M. tricuspidatus is well adapted to low temperatures, but detrimentally affected by high temperatures. Using linear regression, the lower development threshold (LDT) and the sum of effective temperatures (SET) for all life stages of M. tricuspidatus on each diet were estimated. LDT and SET varied among developmental stages and between diets.     

Effects of contrasting omnivorous fish on submerged macrophyte biomass in temperate lakes: a mesocosm experiment

1. Freshwater fish can affect aquatic vegetation directly by consuming macrophytes or indirectly by changing water quality. However, most fish in the temperate climate zone have an omnivorous diet. The impact of fish as aquatic herbivores in temperate climates therefore remains unclear and depends on their dietary flexibility. 2. We tested the effects of a flexible omnivore and an herbivore on aquatic vegetation by comparing the effects of rudd (Scardinius erythrophthalmus, the most herbivorous fish in temperate climates) with grass carp (Ctenopharyngodon idella) in a mesocosm pond study. Exclosures distinguished herbivorous effects of fish on submerged macrophytes from indirect effects through changes in water quality, whereas stable isotope food‐web analysis provided information on fish diets. 3. We hypothesised that rudd, with its flexible diet and preference for animal food items, would only indirectly affect macrophytes, whereas grass carp, with its inflexible herbivorous diet, would directly affect macrophyte biomass. 4. Only grass carp significantly reduced macrophyte biomass through consumption. Rudd had no effect. Food‐web analysis indicated that rudd predominantly consumed animal prey, whereas grass carp included more plants in their diet, although they also consumed animal prey. Grass carp significantly affected water quality, resulting in lowered pH and increased N‐NH₄ concentrations, whereas more periphyton growth was observed in the presence of rudd. However, the indirect non‐herbivorous effects of both fish species had no effect on macrophyte biomass. 5. Both fish species should be considered as omnivores. Despite the fact that rudd is the most herbivorous fish in the western European climate zone, its effect on submerged macrophyte biomass is not substantial at natural densities and current temperatures.     

Seasonal diet by a generalist raptor: the case of the variable hawk (Geranoaetus polyosoma) at Atacama Desert,northern Chile

We determined the seasonal diet of the variable hawk, Geranoaetus polyosoma, in a hyperarid and threatened habitat in the Atacama Desert, northern Chile, by analysing the contents of the bird's pellets. We estimated the biomass and number of individuals of each prey species consumed. We compared our results with those of other studies on G. polyosoma in South America. In general, the diet was characterised by extremely low number of prey, low diversity of species consumed and high dietary breadth. In contrast with other biomes of Chile, in our study reptiles formed the dominant food item and accounted for the highest percentage of biomass consumed from autumn to spring, with rodents being a seasonally significant major food item. Arthropods were also consumed, but the biomass ingested was negligible. Statistically significant differences were noted across seasons in the prey items consumed, reflecting a flexible and opportunistic response to the scarcity of prey available. Our findings add to the data present on the basic natural history of G. polyosoma and can aid in its conservation in the Atacama Desert.     

Adult survival of Delphastus catalinae (Coleoptera: Coccinellidae), a predator of whiteflies (Hemiptera: Aleyrodidae), on diets of whiteflies, honeydew, and honey

Delphastus catalinae (Horn) is a coccinellid predator that is commercially sold for the management of whiteflies. A study was conducted to assay the effect of selected diets on the survival of adult D. catalinae. Treatments of water (as a control), 10% honey, honeydew, and whiteflies [Bemisia tabaci (Gennadius)] were provided to the beetles in laboratory assays. Newly emerged, unfed adult insects were used at the start of a survival experiment with trials lasting 50 d. Another survival experiment used mixed-aged adults from a greenhouse colony, and the trials lasted 21 d. Survival was poor on a diet of solely water; ~1% survived beyond a week at 26°C. Survival using the newly emerged insects was similar between those fed honeydew and honey diets, but those on the whitefly diet had the greatest survival (~60% on day 50). However, in the experiment with mixed-aged beetles, adults on honey, and whitefly diets performed the same over a 21-d experiment. Excluding those on the water diet, survival of beetles on the various diets ranged from ~50-80% after 21 d. In an open choice assay across 7 h, D. catalinae adults were found on the whitefly diet in a much greater incidence than on the other diets, and the number of beetles found on the whitefly diet increased over time. The data supports that when D. catalinae are employed in greenhouses or fields for whitefly management, during low prey populations, honeydew from the whitefly can help sustain the population of this predator. Moreover, a supplemental food such as a honey solution can help sustain the population of D. catalinae when the prey is decreased to low numbers. These results may help in the development of strategies to enhance the utility of predators for the management of whiteflies.     

Patterns of prey use by lesser scaup <Emphasis Type="Italic">Aythya affinis</Emphasis> (Aves) and diet overlap with fishes during spring migration

Recent decline in the lesser scaup Aythya affinis population has been linked to changes in wetland conditions along their spring migration routes. In particular, the use of amphipod prey by lesser scaup has declined in many regions of the upper Midwest U.S.A. and has been linked to expanded fisheries, although empirical data on diet overlap are lacking. To explore patterns of prey use by lesser scaup and diet overlap with fishes, we quantified diets of scaup and fishes during the 2003 and 2004 spring migration in eastern South Dakota, U.S.A. We compared diet overlap between lesser scaup and fishes collected from Twin Lakes, South Dakota—an important stopover location for spring-migrating scaup. Plant seeds occurred in >95% of lesser scaup diets (n = 118) and represented an appreciable amount of consumed biomass (>70%). Gastropods, amphipods, and chironomids were the most abundant invertebrate prey taxa and occurred in 29–34% of lesser scaup diets. Although relatively frequent, these taxa each contributed only 4–27% of the diet by weight. Percent dry mass of amphipods, a preferred prey by lesser scaup, was low (4%) indicating that amphipod availability may be reduced during spring migration. Analysis of fish diets showed that black bullhead Ameiurus melas and yellow perch Perca flavescens had the highest diet overlap with lesser scaup at 94% and 92%, respectively. Moreover, mean size of amphipods and chironomids found in fish diets were significantly larger than that consumed by lesser scaup. Our findings support the notion that amphipod use by spring-migrating lesser scaup has declined and that size-selective predation by fishes may influence prey availability for lesser scaup. Handling editor: K. Martens     

Diet of Eurasian lynx <Emphasis Type="Italic">Lynx lynx</Emphasis> in the northern Dinaric Mountains (Slovenia and Croatia)

The Eurasian lynx Lynx lynx (Linnaeus 1758) is an opportunistic predator that usually selects the smallest ungulate available. Its diet varies considerably among different regions; therefore it is important to study lynx diet in different parts of the species’ range. We studied the diet of lynx from the endangered Dinaric population in Slovenia and Croatia by analyzing lynx scats, prey remains, and stomach contents. Dinaric lynx mainly killed European roe deer Capreolus capreolus (0.64 frequency of occurrence, 79% of all consumed biomass), which were used more frequently during winter and spring. Ungulates were killed more often by adult males than by lynx of other age and sex groups. In contrast to studies from other regions, lynx in the northern Dinaric Mountains also frequently fed on the edible dormice Glis glis (0.18 frequency of occurrence, 7% of all consumed biomass). This large rodent appears to be an important alternative prey, especially for females and young lynx, and was the reason for the highest use of rodents reported so far for the Eurasian lynx. Edible dormice in Dinaric forests have highly variable numbers of active animals. Seasonal and possibly annual variation in dormouse availability obviously affects lynx diet. This is a rare example where variability in the availability of the alternative prey and not the preferred prey leads to the dietary shift. This study confirms the opportunistic nature of Eurasian lynx and the regional variability of its diet.     

Diet and prey profiles of three sympatric large carnivores in Bandipur Tiger Reserve, India

We conducted a field study of diets of three sympatric large carnivores, the tiger Panthera tigris , the leopard Panthera pardus and the dhole Cuon alpinus in Bandipur Tiger Reserve, India, based on analyses of 381, 111 and 181 scats, respectively. The frequency of occurrence of prey items in scats was converted to relative biomass and number of prey consumed using regression equations based on earlier feeding trials. The results showed that although these predators kill ∼11–15 species of vertebrate prey, relatively abundant ungulate species provide 88–97% of biomass consumed by them. Although the dietary niche overlap among the three species was high (Pianka's index of 0.75–0.93), some specialized predation was observed. The largest ungulates, gaur Bos gaurus and sambar Cervus unicolor , provided 73% of biomass consumed by tigers, whereas medium-sized chital Axis axis and wild pig Sus scrofa formed 65 and 83% of the biomass intake of leopards and dholes, respectively. In terms of the relative numbers of prey animals killed by the three predators, chital, which is the most abundant prey species, dominated their diets (tiger=33%, leopard=39% and dhole=73%). The results of the study, in conjunction with earlier work, support the prediction that abundance of ungulate prey species, as well as their availability in different size classes, are both critical factors that facilitate sympatry among the three predators.