Relating body size to the role of aquatic subsidies for the riparian spider <Emphasis Type="Italic">Nephila clavata</Emphasis>

We examined the relationship between body size of the riparian spider Nephila clavata and the contribution of allochthonous (aquatic insects) and autochthonous (terrestrial insects) sources to its diet using stable isotope analysis. During the study period from July to September, the body size of the females increased remarkably (about 60-fold) but that of males remained small. The biomass of both aquatic and terrestrial insects trapped on the spider webs increased with spider size, with the biomass of the former ranging between 30 and 70% of that of the terrestrial insects. The average relative contribution of aquatic insects to the diet of the spiders, calculated from δ¹³C values, was 40–50% in spiders in the early juvenile and juvenile stages, 35% in adult males and 4% in adult females. There was a significant negative relationship between the relative contribution of aquatic insects and body size of the female spiders. We conclude that aquatic insects might be an important seasonal dietary subsidy for small spiders and that these allochthonous subsidies may facilitate the growth of riparian spiders, which may in turn enable the spiders to feed on larger prey.     

Diet spectra and resource partitioning in the larvae and juveniles of three species and six cohorts of cyprinids from a subalpine lake

Summary Diet composition based on gut analyses was studied in larvae and juveniles belonging to six (out of eight) age groups (cohorts) of three species of cyprinids (Rutilus rutilus L., Leuciscus cephalus L., Scardinius erythrophthalmus L.) from a small meso-oligotrophic lake in Tyrol, Austria.A basic pattern of ontogenetic shifts of resource use is postulated for the first weeks after hatching, consisting of the sequence: phytoplankton-rotifers-crustaceans-chironomid larvae. However, there are several variations to this general theme.Diet overlap is of about the same magnitude between representatives of different species or different cohorts, and between members of schools belonging to one cohort. This points to the importance of random food selection in all larvae and juveniles during this phase of life.Prey size is a very poor predictor of food choice by young cyprinids, but there is greater similarity in diet between the larger juveniles than between the smaller larvae, irrespective of whether the fish compared represent different species, different cohorts or are members of homogeneous groups.The lack of correlation between prey size and predator size may be explained by assuming that out of a limited range of available prey size the fish always try to include in their diet also the largest items they are able to swallow. This would be a good strategy considering that growth rates are positively correlated with food size.One clearcut interspecific difference in resource use may be noted: The larvae of L. cephalus are distinguished from those of the other two species by the absence of rotifers and nauplii in their diet, and by their greater ability to handle both adult copepods and chironomid larvae.     

Size related variability in the summer diet of the blackfin tuna (Thunnus atlanticus Lesson, 1831) from Tobago,the Lesser Antilles

Blackfin tuna (Thunnus atlanticus) is a small epipelagic oceanic species known only from the western Atlantic. In Tobago, the Lesser Antilles, blackfin tuna is caught by the artisanal fishery. The diet of this species was examined during the summer of 2004 for fish landed at the Charlotteville fish market in Tobago. T. atlanticus ranged from 32 to 91 cm FL (0.7–12.4 kg). Overall numerical abundance of prey items comprised fish (48%), crustaceans (46%) and cephalopods (6%). Prey species included small pelagics such as anchovies (ranked as most important prey overall), juveniles of larger pelagics such as jacks, juveniles of fish found in coral reef communities as adults, e.g. squirrelfishes, and some mesopelagic species. The importance of major diet categories differed significantly with predator size, with fishes becoming more important and crustaceans less important with increasing size of the blackfin tuna. This study has improved our scant knowledge of the blackfin tuna diet in the Lesser Antilles.     

Intraspecific and seasonal differences in the diet of feral ferrets (

This study reports the diet of feral ferrets (Mustela furo) in a pastoral habitat, East Otago, South Island, New Zealand. Rabbits (Oryctolagus cuniculus) were the most common prey of ferrets, occurring in 86.7% of seats, but birds (12.4%) and invertebrates (11.3%) were also frequently eaten. Female ferrets ate more non-lagomorph prey items, especially invertebrates and birds than males. No significant dietary differences were found between juvenile and adult ferrets except in summer when juveniles ate more lagomorph prey. There were seasonal differences in the consumption of rabbits, invertebrates, skinks, possums (Trichosurus vulpecula) and small and large secondary prey items. Seasonal differences in ferret diet are likely to be related to the relative abundance of the various prey items. Lagomorph availability may also be a determinant of the frequency of occurrence of other prey items in the diet. Dietary differences may differentially influence the functional response of adults and juveniles and/or males and females to rabbit control or other manipulations of prey populations. Bovine tuberculosis (Mycobacterium bovis) infections in ferret populations show intraspecific variation with more males than females and more adults than juveniles infected. Intraspecific dietary differences in diet were not observed in the species (possums and hedgehogs (Erinaceus europaeus)) considered to be the main sources of infection for ferrets.     

Foraging ecology of the California gnatcatcher deduced from fecal samples

The California gnatcatcher is a threatened species essentially restricted to coastal sage scrub habitat in southern California. Its distribution and population dynamics have been studied intensely, but little is known about its diet. We identified arthropod fragments in 33 fecal samples of the California gnatcatcher to gain insight into its foraging ecology and diet. Fecal samples were collected from adult males, adult females, fledglings, and nestlings. Leaf- and planthoppers (Homoptera) and spiders (Araneae) predominated numerically in samples. Spider prey was most diverse, with eight families represented. True bugs (Hemiptera) and wasps, bees, and ants (Hymenoptera) were only minor components of the gnatcatcher diet. Gnatcatcher adults selected prey to feed their young that was larger than expected given the distribution of arthropod size available in their environment, and chicks were provisioned with larger prey items and significantly more grasshoppers and crickets (Orthoptera) and spiders than adults consumed themselves. Both adults and young consumed more sessile than active prey. Further studies are needed to determine whether arthropods sampled in coastal sage scrub that are common in fecal samples are good indicators of California gnatcatcher habitat. Received: 30 December 1998 / Accepted: 28 April 1999     

Field predation of twospotted spider mite in a New Zealand strawberry crop

Predation by naturally occurring predatory arthropods was investigated to explain variations in population numbers of twospotted spider mite (Tetranychus urticae Koch) between first and second season strawberry crops. Araneomorph spiders. European harvestman [Phalangium opilio (L.)], Tasmanian lacewing [Micromus tasmaniae (Walker)] and Pacific damsel bug [Nabis kinbergii Reuter] were the only predators found in high numbers. However, spiders and harvestment were more prevalent than lacewings and nabids. Laboratory feedings trials indicated spiders build horizontal webs in the plants and prey predominantly on small flying insects that shelter in the crops. Similar feeding trials cofirmed the palatability of TSSM to spiders and harvestmen. Immunological testing for proteins of TSSM, aphids, Collembola and leafrollers in the intestines of field collected European harvestman, spiders, Tasmanian lacewing and Pacific damsel bug confirmed European harvestman includes TSSM in its diet, but not in large enough quantities to exert a significant regulating pressure on TSSM populations. Lacewings and nabids include TSSM in their diets but only in very small quantities (2% and 1% respectively). Spiders do not take TSSM unless they drop or spin down onto the spider webbing. The immunological testing also showed European harvestman to be a polyphagous and opportunistic feeder. Prey residues were detected more frequently in harvestmen intestines at times of prey abundance which indicated a seasonality to harvestmen diet.      

Cross‐ecosystem disturbance influences on the life history and population size structure of a riparian predator

Cross‐ecosystem transfers of resources could alter the life history traits of consumers in adjacent systems by changing the nature and availability of prey. However, large‐scale influences, such as natural disturbances, that control the magnitude of prey subsidies are likely to modify these effects. To investigate impacts of cross‐ecosystem subsidies on the life history traits of a riparian predator we measured the size, sex and condition of riparian fishing spiders (Dolomedes aquaticus) across a gradient of flooding frequency and intensity. These spiders rely on adult aquatic insects for a large proportion of their diet and previous research demonstrated that increased flooding decreased the abundance of aquatic insect prey. In this study, laboratory experiments indicated that increased prey availability hastened the first moult of the spiders after winter and decreased the propensity for cannibalistic interactions of individuals of the same size. However, despite the likely positive influences of increased food supply, in the field the highest abundance and proportion of large, potentially reproductive females occurred at the most flood‐prone rivers, where aquatic prey availability was the lowest. It is likely that other factors modified by the disturbance regime, such as habitat availability, flood‐related mortality and intra‐specific interaction rates, altered the influence of cross‐ecosystem subsidies on the life history traits of these spiders. Thus, our results indicate that disturbance‐related effects can flow across ecosystem boundaries and alter the life history traits of predators relying on allochthonous resources.     

Food habits of the barbastelle bat Barbastella barbastellus

The diet of Barbastella barbastellus was investigated through analysis of droppings collected from three maternity roosts in Germany and Switzerland The results showed a high dominance of moths (Lepidoptera). which accounted for 73-94% of the recovered items by volume Flies (Diptera). ranging in size from blow flies (Calliphoridae) and large crane flies (Tipulidae) to small Nematocera, were the second most important prey items (4-17%) Prey types recovered also included small numbers of Trichoptera, Neuroptera, Homoptera. Hymenoptera. Coleoptera and spiders (Araneae) The diet of the barbastelie differs from that of most other bats in Europe m the predominance of moths and the corresponding virtual absence of dung beetles (Coleoptera, Searabaeidae) and midges (Diptera. Chironomidae) Conservation measures for barbastelles should therefore consider facilitation of the diversity and abundance of moths     

Feeding ecology of the orb-weaving spiderArgiope aurantia [Araneae: Araneidae] in a cotton agroecosystem

Twenty females of the orb-weaving spiderArgiope aurantia Lucas were introduced into a cotton field in east Texas in order to study the feeding ecology of this spider. In the 24 h after the release of these spiders in the cotton field, one had moved over a distance of 53 m. The released spiders spun webs with an average diameter of 33.5 cm with the hub an average of 39 cm above the ground. The diet ofA. aurantia was diverse which characterizes this species as a food generalist. Major food components were aphids (30%), Diptera (26.8%), grasshoppers (17.9%), and Hymenoptera (12.6%). The spiders' prey length ranged from 0.4 to 47 mm (mean =7.7±0.83 mm). Adult females ofA. aurantia have the potential to kill prey of up to ca. 200% of their own size. However, two-thirds of the prey items had a length of <3 mm, while only 25% of the prey items had a length of ≥20 mm.A. aurantia was found to be a predator of the cotton fleahopper (about 1% of the spiders' diet), which is a key pest of cotton.      

Foraging behaviour in the jumping spider Phidippus audax: bases for selectivity

The hunting and feeding behaviour of the jumping spider Phidippus audax was examined in the laboratory under single and multi-prey conditions. When given the choice, spiders consistently selected insects with high activity levels and crawling velocities. Selection was not correlated with insect length, mass, or length/width ratio. However, cine analysis of single predator-prey encounters indicated that, at the time of detection, prey size (length and mass) was evaluated by the predator; spiders pursued large insects at significantly slower rates (i.e. more cautiously) than small insects. Prey size also significantly affected handling times. Time invested in handling preferred items was similar whether these were encountered alone or with alternate prey available. However, as predicted by the optimal foraging theory, spiders spent significantly less time feeding on lower ranked items in the presence of alternative prey.     

Food habits of an endangered Japanese frog, Rana porosa brevipoda

We examined the diet of an endangered frog, Rana porosa brevipoda inhabiting rice fields of western Japan, by forced regurgitation of stomach contents. The frog diet consisted of a wide variety of arthropods, and ants, beetles, dipterans, bugs, orthopterans, and spiders, which were especially prominent. These prey taxa were also collected in large numbers by sweep-net samplings made in the frog habitat, and relative abundances of prey taxa in frog diet and those in sweep samples were found to be significantly correlated. Aquatic forms did not contribute much to the frog diet, but were found to be taken more frequently and in larger numbers in irrigated fields than in drained fields. These findings suggest that prey availability around frog habitat is very important to regulate the food items of R. p. brevipoda. On the other hand, terrestrial components of frog habitats are indicated to be important because the frog highly depended on terrestrial invertebrates. From these results, we consider it imperative to preserve terrestrial components linked with aquatic environments to conserve biodiversity in rice field ecosystems.     

Optimal foraging by the swallow (Hirundo rustica, L): Prey size selection

The foraging ecology of the swallow (Hirundo rustica) was investigated in the field and compared with predictions of optimal foraging theory. Prey items were selected primarily by size. The inclusion of an item in the diet depended on the absolute abundance of the high-ranking prey and not of the low-ranking ones. Small items of low profitability were, however, included when food was abundant and more small items were taken when they were relatively abundant. Energetics data are used to show that it is profitable in terms of net energy gain for the swallow to take a mixture of large and small items, whereas optimal foraging theory would predict exclusive specialization on large, high-ranking items. Other possible explanations for the inclusion of small items in the diet are discussed.     

Behavior, Diet, and Movements of the Sulawesi Crested Black Macaque (Macaca nigra)

We present the first field study of activity budgets, diet and ranging patterns of the Sulawesi crested black macaque, Macaca nigra, one of seven macaque species endemic to Sulawesi, Indonesia. We studied three crested macaque groups, ranging in size from 50 to 97 individuals, for 18 months in the Tangkoko-DuaSudara Nature Reserve, North Sulawesi. They spent 59% of the day moving and procuring food, especially fruits, and 41% of the day resting and socializing. Their diet is composed of more than 145 species of fruit (66% of observed feeding bouts), vegetative material (2.5%), invertebrates (31.5%), and occasional vertebrate prey. Group differences were more pronounced than seasonal or diurnal differences. Specifically, the largest group moved farther during the day, moved at a faster and more uniform rate, ate less fruit, rested more, and socialized less than the smaller groups did. The largest group had the largest home range, but it included less primary forest and more disturbed habitat than the ranges of smaller groups. There are individual differences in activity budgets of adult males and females in time spent moving, resting, feeding, and socializing that may reflect differences in reproductive strategies of males versus females. The behavior of large juveniles is more similar to that of adults than to that of small juveniles. Daily movements and use of home range are correlated with diet. Macaques moved shorter distances as the proportion of time spent feeding on fruit increased, and the top four dietary items accounted for most of the variance in entry into hectare blocks of home range.     

A comparison of prey lengths among spiders

Summary Field observations and laboratory experiments were carried out to determine the influence of body length of preys on the acceptance rate by spiders. Feeding experiments with 13 spider species and a model prey (crickets) reveal a decreasing acceptance rate with increasing prey size. Prey sizes of 50–80% of the spiders' size yielded the highest acceptance rates, crickets of double the spiders' size were accepted by two species only. By fitting the acceptance rate Y versus prey size X by Y(x)=Y(0) (1-x²), two coefficients could be calculated: Y(0), the size-independent palatibility of the prey and , a coefficient of size-induced refusal of the prey. These values describe the degree of specialisation towards (a) crickets and (b) large prey, respectively. Further comparison showed (a) that labidognath (= araneomorph) spiders do not necessarily subdue larger prey items than orthognath (=mygalmorph) spiders and (b) that webbuilding spiders are superior to non-webbuilding spiders in respect of catching large prey. A modified model of the generalized pattern of the length relations of predator and prey is given with special reference to spiders and compared to other polyphagous predator groups.     

Food and feeding habits of pearly razorfish, <Emphasis Type="Italic">Xyrichtys novacula </Emphasis>(Linnaeus, 1758), in the southern Tyrrhenian Sea: variation by sex and size

We collected pearly razorfish, Xyrichtys novacula (Labridae), from a sandy bottom of Capo dOrlando (Tyrrhenian Sea) to study their feeding habits. We caught fish by hand-lines and seine nets and identified, counted and weighed food items in their stomachs. We evaluated the importance of the different prey types by calculating the frequency of occurrence, abundance and mass. We used these values to calculate the index of relative importance (IRI) for each taxonomic category and a modified index (MI) which did not incorporate %N into the formula. Gammarideans were dominant food items in terms of %F but showed a very low MI value; the bivalve Acanthocardia tubercolata was the dominant species in terms of %W and MI value. The prey items were mostly benthic organisms belonging to the assemblage of fine, well-sorted sands showing that X. novacula is a benthic feeder. Despite the large number of prey taxa found, few species accounted for most of the prey consumed, indicating specialist feeding, as confirmed by the low value of the Levins standardised index. We found significant differences in prey distribution among size classes, with the highest prey diversity recorded in 120–140 mm TL size classes. Correspondence analysis showed a trend of increasing predator size classes among prey items, with small prey, such as copepods and amphipods, in the smallest predator size classes and bigger prey in the larger ones. Prey caught by larger predators differed significantly in weight from those taken by smaller specimens. There was a significant positive correlation of fish length with bivalves, decapods and echinoids, and a negative one with copepods, ostracods, caprellids, gammarideans. There were no significant differences between males and females of overlapping sizes. Juveniles are able to exploit only small, vulnerable prey, while adults take few, large prey, thereby avoiding competition with juveniles.     

Diet and foraging opportunism of the Guiana dolphin (Sotalia guianensis) in the Abrolhos Bank,Brazil

Diet analysis allows exploring how coastal dolphins interact with the environment and their role in the marine food webs. We studied the diet and feeding ecology of the Guiana dolphin, Sotalia guianensis, through analysis of stomach content from 42 animals stranded on the eastern coast of Brazil. A total of 1,336 semidigested prey items (fish, otoliths, cephalopod beaks, and crustaceans) were identified. Teleost fish comprised the most frequent food item (92% of the total), followed by cephalopods, and crustaceans. Prey belonged to 34 taxa and richness in individual stomachs varied from 1 to 15 prey taxa. Prey were generally small, but showed a significant trend to increase in size with dolphin length. The main prey of Guiana dolphins were demersal, estuarine, and sound-making fish such as catfish and sciaenids. No sex-related differences in diet were found. Diet composition varied seasonally and occurrence of prey items was coherent with breeding or high abundance periods of some fish species and squids. Our study shows the importance of demersal prey from estuarine and soft-sediment habitats to Guiana dolphin in the Abrolhos Bank and reveals that feeding habits are generalist and opportunistic, with diet reflecting the seasonal abundance and availability of prey.     

Prey preferences ofPortia fimbriata,an araneophagic,web-building jumping spider (Araneae: Salticidae) from Queensland

Portia fimbriata from Queensland, a previously studied jumping spider (Salticidae), routinely includes web-building spiders and cursorial salticids in its diet, both of these types of prey being dangerous and unusual prey for a salticid. The present paper is the first detailed study ofP. fimbriata's prey preferences. Three basic types of tests of prey preference were used, providing evidence that (1)P. fimbriata males and females prefer spiders (both web-building spiders in webs and salticids away from webs) to insects; (2)P. fimbriata males and females prefer salticids to web-building spiders; (3)P. fimbriata males and females prefer larger spiders to smaller spiders; (4) there are intersexual differences in the preferences ofP. fimbriata for prey size, females preferring larger prey and males preferring smaller prey; and (5)P. fimbriata's prey preferences are not affected by a prior period without food of 2 weeks. When preferences were tested for by using both living, active prey and dead, motionless lures, the same preferences were expressed, indicating thatP. fimbriata can distinguish among different types of prey independent of the different movement patterns of different prey.     

The feeding behaviour of New Zealand Dolomedes species (Araneae: Pisauridae)

Abstract

The prey spectrum and predatory behaviour of Dolomedes sp. (‘D. III’), D. aquaticus, and D. minor are described from a series of field and laboratory investigations, the former made around Nelson and on Banks Peninsula, Canterbury, during summer months. All species are large, robust spiders that capture prey by directly seizing it in their mouthparts, not using silk at any stage of predation. Adult aquatic insects are their main prey, but these are available only irregularly during their activity period (night-time), and the spiders are opportunistic in their feeding habits. They will eat virtually any available small animal, and at least the largest species, D. III, is able to capture and ingest small fishes. Dead as well as live organisms are taken. Furthermore, the spiders are capable of feeding infrequently; when feeding on small prey organisms they may capture several sequentially, to increase the size of the meal. Live prey is caught while it is in flight, or on the ground, or at the water surface (rarely submerged), and is detected primarily by touch and airborne sound; vision is unnecessary for normal predation. Prey is captured very rapidly, even though this may initially involve a dash of up to 40 cm across the water surface to locate the organism. Stages in the behaviour of an active spider, from waiting for prey to grooming after ingestion, are described.     

Food consumption and diet composition of the web-building spider Agelena limbata in two habitats

Summary Prey capture rate, food consumption, and diet composition of all developmental stages of the funnelweb spider Agelena limbata were estimated in woody and open habitats by a sight-count method. Prey availability was evaluated on the basis of two indices, i.e. the ratios of daily food consumption to dry weight of predator and to daily standard metabolic rate. These indices varied seasonally and between instars in this spider. Comparison of these indices between arthropod predators suggests that A. limbata live under conditions of relatively limited food supply. In the open habitat, the spiders reduced foraging activities to avoid heat stress at midday in summer because the sheet web was exposed to the direct rays of the sun and its temperature exceeded 40°C. The daily food consumption of adult spiders in the open habitat was about half of that in the woody habitat. The lower rate of energy intake of spiders in the open habitat may cause the observed smaller size of adults and lower fecundity. A. limbata captured a great range of prey comprising ten orders of arthropods and ate chemically defended insects, e.g. stink bugs, lady beetles, and ants which were rejected by many spiders. This generalistic foraging may be associated with limited and heterogeneous food supply in this spider.     

The food of the Nile perch, Lates niloticus (L.), after the disappearance of the haplochromine cichlids in the Nyanza Gulf of Lake Victoria (Kenya)

After the disappearance of the haplochromine species in the Nyanza Gulf of Lake Victoria as a result of predation by Lates niloticus , the latter has turned its attention to aquatic invertebrates and other fish. Changes in the diet of the Nile perch with increase in its size have been observed: young L. niloticus preyed mostly on invertebrates, including crustaceans and various small aquatic insects; large, immature L. niloticus supplemented the invertebrate diet with both young and small fish; adults above 80 cm total length were mainly piscivorous. L. niloticus feeds on fish prey of about one third its own length.
The tendency of L. niloticus to switch from one prey item to another, depending on availability, is reported; e.g., in the Nyanza Gulf, the prey diet has shifted from the haplochromine to Caridina nilotica and L. niloticus juveniles.