Prey use of the fishing spider Dolomedes triton (Pisauridae,Araneae): an important predator of the neuston community

Summary Prey of feeding juvenile and adult Dolomedes triton (Walckenaer 1837) were sampled over two seasons on three small ponds in central Alberta, Canada. Prey were mainly insects active at the water surface with truly aquatic species making up about 14% of the diet. Throughout the season aquatic and semi-aquatic Heteroptera represented about 30% of the prey. Diptera and adult Odonata were also important prey items but their abundance in the diet was more variable seasonally. Of the 625 prey items recorded nearly 50% were represented by taxa taken no more than once by spiders in one of the five size classes (adult females, adult males, large, intermediate and small juveniles). Large spiders did not take the smallest prey available, although small and intermediate-sized spiders fed on nearly the full size range taken by larger spiders. Cannibalism was common, accounting for 5% of the observations, with females and large juveniles as the most frequently observed cannibals. We hypothesize that intraguild predation (including cannibalism) could be an important coevolutionary force structuring phenology, population dynamics and microhabitat use of the predatory guild of the neuston community.     

Changing handling times during feeding and consequences for prey size selection of 0+ zooplanktivorous fish

The interrelationship of fish size, prey size and handling time within a 15-min feeding period was studied in three size groups of 0 + roach, Rutilus rutilus, and bleak, Alburnus alburnus. Four size classes of cladoceran prey were used to measure changes in feeding rate and handling time from initial rapid feeding to sustained feeding. Observed differences in increase of handling time between prey size classes led to a change in the prey profitability ranking of those size classes within the first 2 min of the experiments. A 1-min feeding period is interpreted as reflecting an intermediate motivational status between extreme hunger and satiation. The use of average handling times for this period revealed a substantial change in prey profitability estimates compared to previous studies which used handling times based on short-term (a few seconds up to 1 min) feeding. It is not the largest prey items a fish can handle and swallow that are most profitable, but prey of intermediate size. By this approach a closer fit between expectations derived from optimal foraging theory and empirical data on prey size selection of 0 + zooplanktivorous fish is qualitatively achieved. Optimal prey size was found to be close the mouth gape width in small fish of 15 mm standard length, decreasing to 50% of mouth gape width in fish of 40 mm standard length.     

The effect of hunger level on predation dynamics in the spider Nesticodes rufipes: a functional response study

It is well known that a predator has the potential to regulate a prey population only if the predator responds to increases in prey density and inflicts greater mortality rates. Predators may cause such density-dependent mortality depending on the nature of the functional and numerical responses. As spiders are usually faced with a shortage of prey, the killing behavior of the spider Nesticodes rufipes at varying densities of Musca domestica was examined here through laboratory functional response experiments where spiders were deprived of food for 5 (well-fed) or 20 days (hungry). An additional laboratory experiment was also carried out to assess handling time of spiders. The number of prey killed by spiders over 24- and 168-h periods of predator–prey interaction was recorded. Logistic regression analyses revealed the type II functional response for both well-fed and hungry spiders. We found that the lower predation of hungry spiders during the first hours of experimentation was offset later by an increase in predation (explained by estimated handling times), resulting in similarity of functional response curves for well-fed and hungry spiders. It was also observed that the higher number of prey killed by well-fed spiders over a 24-h period of spider–prey interaction probably occurred due to their greater weights than hungry spiders. We concluded that hungry spiders may be more voracious than well-fed spiders only over longer time periods, since hungry spiders may spend more time handling their first prey items than well-fed spiders.     

An experimental study of body size and food size relations in crucian carp,Carassius carassius

Synopsis In dense, single-species assemblages of crucian carp, competition is intense and results in populations of stunted fish. To explore mechanisms underlying this competition, we measured handling times, return rates, and prey choice for five sizes of crucian carp feeding on six sizes of a standardized food. Handling times increased with prey size and decreased with fish size. Return rates (dry mass ingested per unit handling time) increased dramatically with fish size, and generally decreased with increasing prey size, especially for small fish. Patterns of return rates among size-classes suggested that one or more size-related shifts in feeding efficiency exist for crucian carp; combined with physiological stresses related to winter anoxia, the inability of fish to make these shifts may contribute to size structures observed in high-density populations. Comparisons of relations among fish size, prey size, and return rates for crucian carp and bluegill, Lepomis macrochirus, suggest that similar intraspecific competitive relations exist between generalist species with size-structured populations. Despite differences in return rates among prey sizes, the extent of food selectivity based on prey size exhibited by crucian carp in two types of choice trials was less than predicted. Crucian carp commonly take in several items before mechanically processing food with their pharyngeal apparatus; this multiple prey processing may contribute to disparities between observed choice patterns and those predicted based on return rates for single prey.     

Diet and Feeding Behavior of Mysore Slender Lorises

We studied the feeding ecology of the Mysore slender loris (Loris lydekkerianus lydekkerianus) for 10.5 mo in a dry scrub forest at Ayyalur Interface Forestry Division, Tamil Nadu, South India. We recorded and analyzed 1240 feeding incidents, which indicate that the lorises were almost exclusively faunivorous, with 96% of all feeding events representing animal prey. Of prey items that could be identified (n = 605), 62.9% were ants and termites. Lorises fed on 9 orders and 17 families of insects, plus spiders, molluscs, and small vertebrates. Lorises infrequently fed on gums and a legume pod. They usually grabbed prey with one hand, while other appendages firmly held the substrate. Many of the identifiable prey items belong to insect taxa likely to contain toxic chemicals. Consumption of insects inferred to be toxic was accompanied by an elaborate behavioral repertoire of sneezing, slobbering and urine-washing. A high proportion of insects eaten by slender lorises (71%) occurred in patches or aggregations. The utilization of aggregated social insects may have implications for understanding the unusually high degree of gregarious behavior exhibited by the lorises.     

Estimating consumable biomass from body length and order in insects and spiders

1. Current models used to estimate insect prey biomass for diet studies use whole weight. However, a large proportion of an arthropod's body is taken up by an indigestible exoskeleton, leading to erroneous estimation of the food intake of insectivorous animals. 2. Linear mixed effect models were used to obtain equations to predict consumable biomass from body length for a variety of Neotropical insects and spiders. These data were obtained by feeding taxa of various orders to groups of 100 social spiders and comparing pre‐ and post‐consumption weights using size‐matched controls. 3. Significant linear relationships were found relating body size to consumed biomass for all orders, with slopes ranging from 1.276 to 4.011 and R² values from 0.476 to 0.929. For orders other than spiders and Orthoptera, the increase in weight with size exhibited negative allometric scaling, suggesting a decrease in tissue density, or an increase in internal air space, with size. 4. Although there were significant differences across taxonomic orders in the proportion of biomass consumed, within most orders the proportion consumed did not differ significantly with body size. The estimated regression coefficients may be used by other workers to estimate consumable biomass of arthropod prey for studies requiring large sample sizes or non‐lethal sampling of rare or endangered species.     

Resource Management in the Orb-Weaving Spider Zygiella x-notata: I. Influence of Spider Behaviour and Available Prey

Management of resource exploitation by the orb-weaving spider Zygiella x-notata was investigated in relation to available prey. Prey capture is studied according to prey type (cricket or fly), and the spider's behaviour (waiting without prey or consuming other prey), at the moment when a prey item was placed onto the web. Characteristics of the spider's exploitation of the previous item (feeding time, and quantities ingested) were analysed according to the type and quantity of prey presented, (1 or 2 items at 1-h intervals). Capture time did not vary in relation to prey type, nor spider activity. However, duration and quantities of certain behavioural components (biting and wrapping) did vary according to prey type and the spider's behaviour, at the moment of presentation of prey. Whatever the type of prey received, if the first item consumed was a cricket, the spiders reduced time spent feeding on this prey without any decrease in the quantities ingested.     

Prey analysis of four species of tropical orb-weaving spiders (Araneae: Araneidae) and a comparison with araneids of the temperate zone

Summary The actual prey in the orb webs of four araneid spiders (Nephila clavipes, Eriophora fuliginea, Argiope argentata, and A. savignyi) and the relative abundance of their potential prey (pitfall traps, yellow traps, and sweep-netting) was investigated over 1 year at different locations in Panama. The relative abundance of insects and spiders depends on seasonal fluctuations (Fig. 2) which are reflected by corresponding variations in the effectiveness of the webs. The main prey groups are Nematocera (50%–68%), winged Formicoidea (6%–15%) and Hymenoptera, Coleoptera, and Brachycera (4%–10% each) (Fig. 4-6). The remaining 10%–17% of the prey comes from up to 26 other groups (Table 2). Differences in prey size and prey composition between the spider species are small (Fig. 7). Most prey items are 1–2 mm long: only a few insects exceed 30 mm body length (Figs. 9–12). Relative to the available prey, some groups (e.g. Nematocera, Aphidoidea, Psocoptera) are caught selectively, while other groups (e.g. Heteroptera, Coleoptera, Brachycera, Orthoptera) are underrepresented in the prey spectrum and obviously avoid orb webs (Table 7). The differences in prey composition between araneids of the tropics and of the temperate zone are discussed (Table 8) and compared to those recorded in other studies (Table 9, 10). Most of these report large numbers of big prey items (Odonata, Lepidoptera, wasps/bees). It is pointed out that those studies do not take into account the total available prey in a spider's web but only that part which the spider selects from the web (mainly according to size). The importance of small prey items even for large spiders is explained and an obvious lack of niche partitioning among coexisting araneids is discussed (Table 11).     

The effects of overwintering and habitat type on body condition and locomotion of the wolf spider Pardosa alacris

Overwintering in temperate regions is a prominent mortality risk for invertebrates and may affect their behaviour and body condition. Pardosa alacris is a common ground dwelling spider in central European native and plantation forests, and habitat type and prey availability may play important roles in their overwintering. The effect of overwintering on body condition and behaviour of spiders in semi natural and exotic habitats is relatively unknown. Here we assess the effects of winter on spiders from native poplar and exotic pine plantations. The locomotory behaviour of P. alacris (distance covered and speed) was assessed by tracking their movement in a white circular plastic arena. We assessed body condition, body size, and total fat content. Forest type and sex had significant effects on body length. Fat content was significantly higher in the spring than in autumn, and spiders covered larger distances and were faster in autumn than in spring. Fat content had a significant negative effect on average speed. Spiders in native forests were smaller but grew more during the winter than in exotic plantations, possibly due to higher prey availability in native forests. Visually-hunting predators may significantly affect spiders. Fat spiders with better body condition moved less, and were thus less detectable by predators. However the low movement rate may result in a low rate of encountering prey items, thus lowering feeding efficiency.     

Age-Related Changes in Nestling Diet of the Cooperatively Breeding Green Woodhoopoe

In many socially monogamous bird species, parents of altricial young respond to the increasing demands of growing nestlings by increasing their feeding rate and the size of prey items delivered and by altering the types of prey provided. In some cooperatively breeding species, similar changes in feeding rate and prey size have been documented. However, potential changes in the types of prey delivered, both as nestlings age and by different group members, remain largely unexplored. Moreover, studies rarely compare the diet fed to nestlings with that eaten by the provisioning adults themselves. Here, I show that green woodhoopoe ( Phoeniculus purpureus ) nestlings receive a smaller proportion of spiders and larger proportions of caterpillars and centipedes as they grow older. Both male and female adults delivered a higher proportion of spiders to young nestlings than they ate while self-feeding, probably in response to particular nutritional requirements of the chicks. However, only males altered the proportions of caterpillars and centipedes delivered, providing smaller proportions to young nestlings than eaten themselves. These prey items may be too large for young nestlings to handle, and males may make a greater adjustment in provisioning diet than females because they collect more caterpillars and centipedes than do females. Although there were sex differences in provisioning diet, there were no differences between same-sex breeders and helpers in terms of the overall proportions of prey delivered or the changes with nestling age. Hence, individuals of different reproductive status may be following the same provisioning rules, at least in terms of prey type.     

Individual diet differences in a molluscivore shorebird are associated with the size of body instruments for internal processing rather than for feeding

Especially in birds, it is widely found that the size of individual prey items follows the size of the instruments of prey capture, handling and processing, i.e. bill size. In fact, this is the natural history basis of major discoveries on adaptive evolution in the face of changing food resources. In some birds, e.g. the molluscivore shorebirds ingesting hard‐shelled prey, most of the prey processing takes place within the digestive tract. This study of a salvaged sample of actively feeding great knots Calidris tenuirostris accidentally drowned in fishing nets in northern China, is the first documentation of diet selection at the level of the individual in previously well‐studied molluscivore shorebirds. Diet composition was not associated with the length of the bill, but with the mass of the muscular gizzard. Gizzard mass, which unlike bill length is a phenotypically flexible trait, enables great knots to adjust to changing food resources as an individual, i.e. instantly responding to the food on offer. For migratory species like great knots which rely on seasonal sequences of interdistant feeding areas offering prey with a variety of characteristics, the capacity to individually adjust appears a key adaptation.     

Foraging behavior of the communal spider,Philoponella republicana (Araneae: Uloboridae)

The communal orb-weaving spider, Philoponella republicana,was observed in the subtropical moist forest of Southeast Peru. These spiders live in colonies of conspecifics whose individual orbs are connected by silk. The wrapping of a prey prior to feeding is a large component of the prey capture process because P. republicanahas no venom with which to kill an insect. Wrapping time was the only aspect of prey capture that was strongly correlated with the size of the insect captured. Occasionally we observed several individuals working together to wrap a prey item. These joint efforts were more frequent on prey larger than the capturing spider. Although group captures accounted for only 5.5% of captures, they represented 14.7% of the biomass obtained. A comparison of the relationship between wrapping time and prey size for solitary and group efforts suggested that, by working together, the spiders reduced their total handling time. In most cases only one spider fed on the captured prey.     

Masquerading predators deceive prey by aggressively mimicking bird droppings in a crab spider

In aggressive mimicry, a predator accesses prey by mimicking the appearance and/or behavior of a harmless or beneficial model in order to avoid being correctly identified by its prey. The crab spider genus Phrynarachne is often cited as a textbook example of masquerading as bird droppings (BDs) in order to avoid predation. However, Phrynarachne spiders may also aggressively mimic BDs in order to deceive potential prey. To date, there is no experimental evidence to support aggressive mimicry in masquerading crab spiders; therefore, we performed a field survey, a manipulative field experiment, and visual modeling to test this hypothesis using Phrynarachne ceylonica. We compared prey-attraction rates among BDs, spiders, and control empty leaves in the field. We found that although all prey combined and agromyzid dipterans, in particular, were attracted to BDs at a higher rate than to spiders, other dipterans and hymenopterans were attracted to BDs at a similar rate as to spiders. Both spiders and BDs attracted insects at a significantly higher rate than did control leaves. As predicted, prey was attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders. Finally, visual modeling suggested that spiders and BDs can be detected by dipterans and hymenopterans against background leaves, but they are indistinguishable from each other. Taken together, our results suggest that insects lured by spiders may misidentify them as BDs, and bird-dropping masquerading may serve as aggressive mimicry in addition to predator avoidance in P. ceylonica.     

Diet and foraging behaviour of huntsman spiders in the Namib dunes (Araneae: Heteropodidae)

Diet and foraging behaviour of three species of burrowing huntsman spiders, Leucorchestris arenicola, L. steyni and Carparachne aureoflava , from the Namib dunes were investigated over a three-year period. These nocturnal spiders are polyphagous predators that prey on more than 97 species of insects, arachnids and reptiles. Most prey were nocturnal or crepuscular tenebrionid beetles, moths and weevils. Diet varied regionally owing to faunal differences, but was relatively constant over seasons. Although spiders occasionally captured prey greater than themselves, average prey length was about two-thirds their own length. Prey size was not strongly related to spider size. Larger spiders were both cannibals and intraguild predators. Foraging pattern of L. arenicola was variable with several nights of activity followed by one or several nights of rest. Spiders foraged within 3 m of the burrow, but occasionally pursued prey or neighbouring conspecifics further. Large prey (> 3 mm) were captured approximately every five weeks in summer and every seven weeks in winter, producing an average annual consumption of ≅ 10 prey/spider. Namib huntsmen are sit-and-wait predators within narrow territories waiting for the fortuitous arrival of prey and are thus unlikely to limit prey populations. They compensate for food shortages by cannibalism, thus restricting their own population.     

Web damage and feeding experience influence web site tenacity in the orb-web spider Argiope keyserlingi Karsch

For orb-web spiders, the decision to remain at a particular site or to relocate elsewhere will ultimately depend on the quality of the site. In the past, the quality of the site has been measured in terms of prey availability; spiders experiencing large numbers of prey items are less likely to relocate. However, regular web damage caused by larger nonprey animals may also contribute to the quality of a particular site. Laboratory experiments revealed that the frequency and extent of web relocation by the orb-web spider Argiope keyserlingi was influenced by the feeding regime and the rate of nonprey web damage. Daily movement patterns were influenced by web damage, and these movements were in the direction away from the source of damage. However, the cumulative distance moved during the 7 days of the experiment was influenced by the frequency with which spiders were fed. Spiders that were not given prey moved further than spiders that obtained prey. These data indicate that spiders respond to web damage on a daily basis, but the cumulative movement of spiders over a longer period is influenced mostly by the history of prey ingestion rate. Copyright 2000 The Association for the Study of Animal Behaviour.     

Prey size,prey perishability and group foraging in a social spider

Summary Selection might favor group foraging and social feeding when prey are distributed in patches that do not last long enough for a solitary individual to consume more than a small fraction of them (Pulliam and Millikan 1982; Pulliam and Caraco 1984). Here we considered the foraging behavior of a social spider, Anelosimus eximius, in light of this ephemeral resource hypothesis. This species builds large webs in which members cooperate to capture a wide variety of different sizes and types of prey, many of which are very large. The capture success of this species was very high across all prey sizes, presumably due to the fact that they foraged in groups. Group consumption times in natural colonies for all prey larger than five mm were less than the time that dead insects remained on the plastic sheets that we used as artificial webs. Solitary consumption estimates, calculated from the rate at which laboratory individuals extracted insect biomass while feeding, were the same as the residence times of insects on artificial webs in the field for insects between 6 and 15 mm in length and were significantly longer than the persistence of insects on plastic sheets for all larger insects. Large prey, that contribute substantially to colony energy supplies, appeared to be ephemeral resources for these spiders that could not be consumed by a single spider in the time they were available. These factors made the food intake of one spider in a group less sensitive to scavenging by others and could act to reinforce the social system of this species.     

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.      

A specialized araneophagic predator's short‐term nutrient utilization depends on the macronutrient content of prey rather than on prey taxonomic affiliation

A specialist predator that has a specialized diet, prey‐specific prey‐capture behaviour and a preference for a particular type of prey may or may not be specialized metabolically. Previous studies have shown that jumping spiders of the genus Portia prey on other spiders using prey‐specific prey‐capture behaviour, prefer spiders as prey to insects and gain long‐term benefits in terms of higher survival and growth rates on spider diets than on insect diets. However, it is unclear whether there are substances uniquely present in spiders on which Portia depends, or, alternatively, spiders and insects all contain more or less the same nutrients but the relative amounts of these substances are such that Portia perform better on a spider diet. These questions are addressed by testing the hypothesis that prey specialization includes metabolic adaptations that allow Portia an enhanced nutrient extraction or nutrient utilization efficiency when feeding on spider prey compared with insect prey. Three groups of Portia quei Zabka are fed either their preferred spider prey or one of two types of flies (Drosophila melanogaster Meigen) that differ in nitrogen and lipid content. Portia quei shows a higher feeding rate of high‐protein flies than of high‐lipid flies and spiders but, after 5 days of feeding, there is no significant difference in growth between treatments, and the diets lead to significant changes in the macronutrient composition of P. quei as a result of variable extraction and utilization of the prey. The short‐term utilization of spider prey is similar to that of high‐lipid flies and both differ in several respects from the utilization of high‐protein flies. Thus, the short‐term nutrient utilization is better explained by prey macronutrient content than by whether the prey is a spider or not. The results suggest that spider prey may have a more optimal macronutrient composition for P. quei and that P. quei does not depend on spider‐specific substances.     

Variable dependence on detrital and grazing food webs by generalist predators: aerial insects and web spiders

Recent studies have shown that organisms from the detritus food web subsidize generalist predators in aboveground food webs, but its significance in space and time is largely unknown. Here we report seasonal dynamics of aerial insects from grazing and detritus food webs in both forest and grassland habitats, and show how these patterns influence the dependence of web spiders on the detritus food web. Detrital insects were more abundant in spring, decreased in summer, and then increased slightly in autumn. This pattern was most conspicuous in Nematocera. Due to different seasonal activity patterns of grazing and detrital insects, the proportion of detrital insects was greater in spring and autumn. Detrital insects were relatively more abundant in the forest than in the grassland. Prey captured by web spiders generally reflected seasonal and spatial patterns of aerial insect abundance. In particular, Leucauge spiders reversed their dependence on the two food webs seasonally. Body size of spiders was negatively correlated with the proportion of detrital prey, suggesting that the detrital subsidy is essential for relatively small predators. This size effect probably resulted from interaction of the following two factors: 1) the maximum body size of prey that can be caught increased with spider body size, 2) larger body size classes of aerial insects included a higher proportion of insects from the grazing food web.     

Distinct feeding strategies of generalist and specialist spiders

1. Feeding behaviour of generalist and specialist predators is determined by a variety of trophic adaptations. Specialised prey‐capture adaptations allow specialists to catch relatively large prey on a regular basis. As a result, specialists might be adapted to exploit each item of prey more thoroughly than do generalists. 2. It was expected that obligatory specialist cursorial spiders would feed less frequently than generalists but for a longer time and, thus, that their foraging pause would be longer. First, the feeding frequencies of three generalist spider species (Cybaeodamus taim, Harpactea hombergi, Hersiliola sternbergsi) were compared with those three phylogenetically related specialist species: myrmecophagous Zodarion rubidum, and araneophagous Nops aff. variabilis and Palpimanus orientalis. 3. Generalists captured more prey, exploited each item of prey for a significantly shorter time, and had a shorter foraging pause than was the case for specialists. Generalists also gained significantly less relative amount of prey mass than did specialists. 4. Second, the study compared the prey DNA degradation rate in the gut of generalists and specialists by means of PCR. The degradation rate was not significantly different between specialists and generalists: the detectability half‐life was estimated to exist for 14.3 days after feeding. 5. This study shows that the feeding strategies of cursorial generalist and obligatory specialist spiders are different. Obligatory specialists have evolved a feeding strategy that is based on thorough exploitation of a few large prey, whereas generalists have evolved a strategy that is based on short exploitation of multiple small items of prey.