Does nutritional status constrain adoption of more costly and less risky foraging behaviour in an Amazonian shelter-building spider?

Individual nutritional status may increase marginal foraging costs and potentially drive animal foraging strategies. Here, we investigated how it might affect foraging strategies of the shelter-building spider Hingstepeira folisecens (Hingston 1932) (Araneidae). This spider can catch prey using two strategies with different relative costs: ‘pulling’ (higher energy expenditure) and ‘pursuing’ (lower energy expenditure). We conducted experiments by offering prey at a fixed distance from the shelter entrance to investigate if spiders with lower nutritional status would exhibit riskier but less costly foraging behaviours more frequently than spiders with better status. The nutritional status did not affect the foraging behaviours adopted by H. folisecens. Additionally, the frequency of both foraging behaviours was similar. Therefore, our results did not provide any evidence that individual nutritional status is a factor driving the selection of foraging behaviours in H. folisecens. We suggest that the malnourished spiders should adopt additional strategies to compensate for the costs of pulling behaviour, especially when prey is far from the shelter. Furthermore, it is possible that other factors, like relative prey size in relation to web size, can help us to understand the threshold that determines when such individuals must adopt one of two possible behaviours.     

Feeding ecology of the common sun skink,Eutropis multifasciata (Reptilia: Squamata: Scincidae), in the plains of central Vietnam

We studied the feeding ecology of Eutropis multifasciata in the tropical plains of central Vietnam to understand better the foraging mode, spatiotemporal and sexual variation in dietary composition, and rarefaction curves of prey-taxon richness for males and females. Stomach contents (n = 161) were collected from October 2013 to May 2014 using a nonlethal stomach-flushing technique. A total of 680 food items (624 animal items and 56 plant items) was found in 161 stomachs of skinks, representing 19 unique animal categories. We found that the diet of E. multifasciata is composed mainly of small, sedentary and clumped prey and that this skink specialises on spiders, insect larvae, snails, grasshoppers and crickets (with a combined importance index of 60%). Dietary composition, prey size and total prey volume in E. multifasciata changed between dry and rainy seasons and among regions. The total volume of food items consumed by males was larger than that of females, and the diversity and evenness index of prey categories were larger in males than in females. However, using rarefaction curves revealed that females have the higher prey-taxon richness after points between 130 and 140 prey items for frequency, and between 160 and 170 prey items for number of items, and the differences were not statistically significant. The foraging behaviour of E. multifasciata best fits a ‘widely foraging’ model.     

Natural history of Peucetia flava (Araneae,Oxyopidae): seasonal density fluctuation,phenology and sex ratio on the glandular plant Rhyncanthera dichotoma (Melastomataceae)

The seasonal density fluctuation, phenology and sex ratio of Peucetia flava (Oxyopidae) on Rhyncanthera dichotoma (Melastomataceae) were investigated during a year in a swamp in southeastern Brazil. Peucetia flava displayed an unusual non‐seasonal life cycle and the population size varied little over the year. The density of Peucetia spiders increased with the increase in abundance of leaves and number of arthropods adhered to glandular trichomes on R. dichotoma leaves. Our findings suggest that seasonal density fluctuation of Peucetia may be influenced by foraging site availability (i.e. leaves) and prey supply (i.e. arthropods adhering to glandular trichomes). The unusual seasonal stability of P. flava may be related to the type of habitat in which this spider occurs (swamp), because of the constant input of allochthonous resources from the water source, i.e. aquatic insects that migrate to the terrestrial environment.     

Orb‐web spiders (Araneae: Araneomorphae; Orbiculariae) captured by hunting‐wasps (Hymenoptera: Sphecidae) in an area of Atlantic Forest in south‐eastern Brazil

Members of two hunting‐wasp families, Pompilidae and Sphecidae, are among the major predators of orb‐web spiders. In this study, we collected paralysed spiders from natural nests and trap‐nests provisioned by sphecids in an area of Brazilian Atlantic Forest, and compared these data with the composition of species collected by visual searching during one year. Prey preferences were analysed based on the relative abundance of spider species, their size and web characteristics. We also compiled a list of orb‐weavers captured by four sphecid genera reported in 40 other studies. A large number of prey was obtained from natural nests of Trypoxylon (Trypargilum) albonigrum in Parque Estadual Intervales, especially species of Eustala, Parawixia, and Araneus (Araneidae). Other prey, stored in trap‐nests by T. lactitarse and unidentified hunting‐wasp species, included Nephila (Tetragnathidae), Parawixia, Ocrepeira, Mecynogea, Acacesia (Araneidae), and other spider species that were less abundant. All the species that were heavily preyed upon had a relatively lower abundance in our samples of prey availability. The range of body sizes of spiders captured by Trypoxylon in our study area include the size of some abundant orb‐weavers always absent in their nests. These results indicate that factors other than abundance in the field and the spider's size influence prey selection or susceptibility to attack.     

Natural prey of the crab spider Thomisus onustus (Araneae: Thomisidae), an extremely powerful predator of insects

The natural prey of the crab spider Thomisus onustus inhabiting Eryngium plants was studied in the Absheron Peninsula, Azerbaijan. The total percentage of specimens of T. onustus found while feeding was low (9.1%). However, solitary late instar and adult females exhibited a very high feeding percentage (29.9%). Other sex–age groups of T. onustus, including small juveniles, adult males, and females guarding egg sacs, were found feeding significantly less frequently. Investigation has shown that T. onustus is a polyphagous predator, with representatives of four arthropod orders found in its diet. The primary food of T. onustus was Diptera and Hymenoptera, which collectively accounted for 94.2% of total prey. Worker ants constituted about one‐fifth of the prey, suggesting that T. onustus is a myrmecophagic spider. The length of prey killed by T. onustus ranged between 1.25 and 16.00 mm (mean 6.21 mm) and constituted from 34.4 to 587.9% (mean 194.9%) of length of their captors. The most frequently captured were large arthropods, exceeding the size of the spiders (83.1%). Small and medium‐sized juveniles captured considerably larger prey (in terms of prey–predator length ratio) than late instar and adult females. Over half of their prey constituted arthropods more than two‐fold larger than the spiders.     

Population dynamics of the bark-dwelling spider Eustala perfida Mello-Leitão, 1947 (Araneidae)

Population dynamics of spiders may vary according to biotic and abiotic factors. We studied the phenology of the bark-dwelling spider Eustala perfida over a two-year period and investigated how temperature, precipitation, and prey availability were associated with the population of this species. The population of E. perfida presented a well-defined fluctuation, with one reproductive cycle per year. The recruitment of spiders occurred in summer, followed by successive phenological peaks at all stages of development. The species is protogynic, and the population of adult males peaks in the cold/dry season, indicating a winter mature phenological pattern. The diet of E. perfida is composed mainly of medium-sized homopterans, complemented by small dipterans and hymenopterans. We found that the higher abundance of spiders occurred two months after the highest values of precipitation and temperature, and three months after the higher abundance of potential prey items. These results indicate that spiders require time to respond to changes in environmental conditions. The species’ natural history and the structure of the trunks in which it lives may also affect the number of individuals in a particular area and over time.     

Foraging mode of Australolacerta rupicola (FitzSimons, 1933) (Sauria: Lacertidae): evidence of seasonal variation in an extremely active predator?

Foraging mode of the endemic Soutpansberg rock lizard (Australolacerta rupicola) was determined by (1) measuring the number of movements per minute (MPM) and the percentage time spent moving (PTM); and (2) analysing faecal samples. Furthermore, these criteria were related to diet composition, proportion of attacks initiated while moving and foraging substrate. The results are discussed in comparison to the foraging modes of 20 other lacertid species. Values for MPM and PTM as well as faecal analysis indicate an active foraging strategy for A. rupicola. Although rock living, this species mostly forages in leaf litter where it is well camouflaged while actively searching for sedentary prey. Even in comparison to other active foragers of the family Lacertidae, A. rupicola displays the prototypic behaviour of a widely foraging lizard with very high PTM and very low MPM.     

Bauble spiders: a new species of Achaearanea (Araneae: Theridiidae) with ingenious spiral retreats

A new species of Achaearanea (Theridiidae) is described from the Cedarberg in South Africa. Its unusual morphological features include the position of the spinnerets directly behind the epigastric fold. The male palp is a modification of the palpal conformation of other Achaearanea. This spider lives in a spherical retreat comprizing silk, sand and pebbles. This structure typically dangles from only one thread and has a tiny opening at the bottom that leads into a spirally-coiled tunnel. Males and females build spirals in opposite directions. This enables the male to construct his retreat against that of the female in such a way as to form a brood chamber. Retreats are situated in cool places under low overhanging rocks or branches. The configuration of the narrow, suspended retreat may decrease the spider's vulnerability to enemies while foraging for ants in a typical theridiid fashion.     

Prey choice and raiding behaviour of the Ponerine ant Pachycondyla analis (Hymenoptera: Formicidae)

Termite raiding behaviour of the African poneromorph ant Pachycondyla analis was studied at Mpala, Kenya. In all, 330 raids were observed with the raiding activity showing peaks in the morning and evening. Time spent at the termite source was positively correlated with the numbers of termites taken. The sizes of foraging parties, number of termites taken, distance travelled and time spent at termite sources also showed a positive correlation. Pachycondyla analis preyed significantly more on Microtermes spp. than they did on Odontotermes spp. but no significant differences were found in terms of predator efficiency even though many ants were injured in raids on Odontotermes spp. compared with those on Microtermes spp. Our results indicate that P. analis seems to forage optimally, balancing the costs of energy with prey reward and prey choices were not only influenced by prey abundance, but also by the costs of foraging, as influenced by prey defences, size and foraging behaviour.     

Disentangling prey-handling efficiency of larval newts through multivariate prey trait analysis

Multivariate prey trait analysis is a functional approach to understand predator–prey relationships. In the present study, six prey macroinvertebrate ecological traits were used to identify several key factors in the handling efficiency of seven predatory larval newt species. The results revealed a remarkable similarity in the feeding behaviour among species, suggesting a foraging behaviour convergence among species in the prey-handling efficiency of larval newts. Nevertheless, larvae of some newt species showed clear preferences for particular categories of ecological trait; for example, Lissotriton vulgaris tended to feed on macroinvertebrate taxa with random trajectory, and Calotriton asper fed on macroinvertebrate taxa with high agility. In contrast, Mesotriton alpestris showed a clear ability to feed on prey with movable accessories (cases/tubes) and patterned concealment. This study shows how multivariate approaches can complement traditional diet analyses, and the method has wide applicability across life-stages and species.     

The evolution of nest building and communal nesting in Ageniellini (Insecta: Hymenoptera: Pompilidae)

Pompilid wasps prey upon spiders and use a single spider per nest cell. The majority of species dig simple burrows in the soil in which to cache their spider, on which an egg is laid. The nest is not revisited, but another nest is prepared elsewhere. However, members of the tribe Ageniellini show much diversity in nesting behaviour. Species of the genus Ageniella nest in pre-existing cavities in the soil, closing off their cells with bits of debris. Most other Ageniellini that have been studied carry water to make mud pellets, from which ovoid nest cells are made. Usually a series of such cells is made in close proximity, often under loose bark or stones or in hollow stems. A few species make free nests above ground, usually in protected places or with thick mud walls. In some cases nest sites are known to be re-occupied by members of successive generations. Several species are known to nest communally, co-operating in nest defense and in cell building. In many ways the evolution of nesting behaviour in this group parallels that in the mud-using Vespidae, but the use of a single prey per cell precludes development of progressive provisioning and of eusociality similar to that of many Vespidae.     

Trolling for water striders: active searching for prey and the evolution of reduced webs in the spider Wendilgarda sp. (Araneae,Theridiosomatidae)

Wendilgarda sp. builds unusually simple webs attached to the surface of water. The simplest design consists of a single vertical line with sticky material near the bottom that is attached at the top to a single horizontal line and at the bottom to the water surface. The spider usually sits immobile waiting for prey as the sticky line skates erratically across the surface of the water, but some spiders actively dragged their webs back and forth across the water. The web's simplicity is apparently derived with respect to the webs of other Wendilgarda species, as spiders sometimes made more complex webs similar to typical Wendilgarda webs. The simplicity of W. sp. webs may be causally related to two other unusual traits: extreme variability in web design and construction behaviour and web manipulation behaviour; and construction of prey capture webs with sticky lines by mature males, confirmed here for the first time in a confirmed member of an orb-weaving family. Some behavioural innovations in Wendilgarda, such as the attachment of a short segment of non-sticky silk to the water surface just prior to laying each segment of sticky line, may represent blocks of behaviour that have been shifted temporally in the web construction sequence.     

Prey selection by the critically endangered Asiatic cheetah in central Iran

The presence of the critically endangered Asiatic cheetah (Acinonyx jubatus venaticus) has been verified in several protected areas in central Iran. Prey selection by the Asiatic cheetah was studied in Dare-Anjir Wildlife Refuge, one of its typical habitats in central Iran where there are no carnivorous competitors. The frequency of cheetah kills was compared with the relative abundance of each of its primary prey species obtained through two independent surveys. Jebeer gazelle (Gazella bennettii) was least abundant, but was the preferred prey of cheetah, whereas wild sheep (Ovis orientalis) followed by Persian ibex (Capra aegagrus) were the most frequently killed prey. Cheetahs selectively preyed on males of the three prey species. Our data suggest that Asiatic cheetahs prey mainly on mountain ungulates (wild sheep and Persian ibex), which has management implications for effective conservation of this taxon in Iran.     

Pattern of shell occupation by the hermit crab Pagurus exilis (Anomura,Paguridae) on the northern coast of São Paulo State,Brazil

The purpose of this study was to determine the shell occupation pattern of Pagurus exilis using the percentage of shell types that were occupied and the morphometric relationship between hermits and occupied shells. Specimens were collected monthly from July 2001 to June 2003. A total of 1737 individuals were collected, occupying 19 gastropod shell species. Buccinanops gradatum (82%) was the most occupied shell, followed by Natica isabelleana (6.4%), Stramonita haemastoma (3.2%), and Cymatium parthenopeum (2.2%). There was a differential shell utilization pattern between sexes; males occupied larger and heavier shells while the non‐ovigerous females occupied the lightest ones. Pagurus exilis occupied more bare shells instead of incrusted ones. Buccinanops gradatum was the most occupied shell species as a function of its availability in the survey, and this occupation is strongly associated with the higher internal volume presented by these shells.     

Diet of tropical insectivorous birds in lowland Malaysian rainforest

ABSTRACT

Despite the importance of diet in avian ecology, knowledge of bird diet in tropical regions, particularly South-East Asia, is limited. Assessing predator–prey relationships of how energy flows across ecosystems provides insight into niche segregation of sympatric species. We examined induced-regurgitation samples from 15 species of insectivorous birds – 12 babblers and three flycatcher-like species – from the Krau Wildlife Reserve, central Peninsular Malaysia. The main objective of this study was to compare and characterise the diet of similar trophically insectivorous birds so as to examine the occurrence of dietary overlap or segregation. The majority of identified prey items belong to the following arthropod taxa: Coleoptera (53%), Hymenoptera (19%), Blattodea (11%), and Araneae (11%). The diet of all bird species slightly overlapped (p = 0.070) but network analysis yielded a relatively low value (R_o = 0.53), indicating dietary divergence may have occurred among the studied bird species, possibly reflected by the variation in proportion of arthropod groups. A high proportion of Coleoptera and three other arthropod groups (i.e. Hymenoptera, Blattodea and Araneae) in the diet of studied birds could be related to their richness and abundance in aerial leaf-litter, the substrate preferred by most babblers. Dietary differences may further be explained by variations in bill shapes and sizes, likely corresponding to prey size. Unique foraging strategies (utilising different vertical strata, microhabitats, and attack manoeuvres) could also lead to dietary separation among sympatric species. Flycatcher-like species were expected to flycatch different prey items (families or lower taxa) versus the gleaning birds (most babblers). This study successfully discerned more details on the diets of insectivorous birds inhabiting Malaysian forests, providing a foundation for future studies on the ecology and biology of understorey birds.     

The parasitoid complex and parasitoid‐induced mortality of spiders (Araneae) in a Central European woodland

The parasitoid complex of spiders was studied in three different sites of a forest and, for comparison, in open habitats in north‐western Lower Saxony (Germany). Qualitative data and, for four spider species, detailed quantitative rearing data were obtained. At least 25 parasitoids of spiders were recorded (23 species of Hymenoptera and two species of Diptera). External parasitoids of spiders were rare in the woodlands; only up to 1% of the spiders collected by hand searching and sweep netting had ectoparasitoids. During the investigation 23 parasitoid species were reared from spider egg masses, 10 of them occurring in woodlands. Two species were secondary parasitoids. Several parasitoid–host relationships were recorded for the first time. Egg masses of Floronia bucculenta were parasitized up to 5% by two species of the genus Gelis. Up to 10% of the egg masses of Linyphia hortensis were parasitized by Aclastus species. Egg masses of the spider genus Ero were parasitized by three species, causing an overall mortality of 40%. For egg masses of Agroeca spp. parasitization at some locations was up to 60%. An overview of the Central European parasitoid complex of spiders is provided.     

Host selection by a kleptoparasitic spider

Argyrodes globosus (Keyserling, 1884) is a small kleptoparasite spider that steals prey from the web of web-building spiders. In coffee plantations in the south of Mexico it was observed to parasitize five species: Gasteracantha cancriformis (Linnaeus, 1785) and Verrucosa arenata (Walckenaer, 1841) (Araneidae), Leucauge mariana (Keyserling, 1881) and Leucauge venusta (Walckenaer, 1841) (morphologically indistinguishable species) and Leucauge argyra (White, 1841) (Tetragnathidae). G. cancriformis was more frequently parasitized than the other hosts. An analysis of web diameter for each host species indicated that for L. mariana/venusta, L. argyra and V. arenata the kleptoparasite was associated with webs of a certain size range (23-33cm diameter) although a far larger range of web sizes was available (17-50cm diameter). The average size of the web of G. cancriformis (~23cm) appeared to be close to the preferred size for the kleptoparasite and this, together with an apparent absence of host aggression, may explain the prevalence of A. globosus with this host. For the parasite, web size choice may involve a tradeoff among diverse factors including prey capture rate, ease of access to the web and aggressive behaviour by the host.     

Foraging ecology and behaviour of the ponerine ant Ectatomma opaciventre Roger in a Brazilian savannah

This study provides a detailed account of the foraging behaviour of the ponerine ant Ectatomma opaciventre in a ‘cerrado’ savannah in south-east Brazil. Our observations suggest that this species has an exclusively diurnal foraging pattern. Feeding habits included both predation and scavenging, with termite workers and leaf-cutting ants as the most important food items. Contrary to all other Ectatomma species studied to date, no liquid food such as hemipteran honeydew or plant nectar was collected. Foragers showed clear individual foraging area fidelity.Workers of E. opaciventre employed a typical individual foraging strategy, i.e. there was no co-operation between foragers in the search for or retrieval of food, neither by tandem running nor by trail laying. Nest density was considerably lower than in other Ectatomma (0.015 nests per m²). The observed mean distance to the nearest neighbouring nest was 5.85 m, with a significant tendency toward over-dispersion. Nests were more frequently found in specific microhabitats, which may suggest active choice of nesting site by founding queens.     

Foraging ecology of the giant Amazonian ant Dinoponera gigantea (Hymenoptera,Formicidae, Ponerinae): activity schedule,diet and spatial foraging patterns

This study provides a detailed account of the natural history and foraging biology of the ponerine ant Dinoponera gigantea in a rainforest in north Brazil. The species nests on the ground and the colonies contain 70–96 workers. Ant activity is negatively correlated with temperature, and is more intense at dawn and dusk. Foragers leave the nest independently and search for food individually on the leaf litter, within ca 10 m around the nest. Workers are opportunistic feeders that collect seeds and fruits, and hunt for live prey as well as scavenge for dead animal matter. The dry weight of food items ranges from <10 mg (spiders, insect parts) to >400 mg (seeds, fruits). There is no nestmate recruitment during the search for or retrieval of food, irrespective of food type and size. Foragers have a high directional fidelity, and ants from neighbouring colonies may engage in ritualized territorial contests at the border of their foraging areas. The foraging ecology of D. gigantea is compared with other ponerine species living in tropical forests, as well as with other ant groups showing similar behavioural patterns.     

Two heads are better than one: false head allows Calycopis cecrops (Lycaenidae) to escape predation by a Jumping Spider,Phidippus pulcherrimus (Salticidae)

The deflection of attack from vital organs to the wing margin is regarded as an important adaptation in hairstreak butterflies. However, this “lose-little-to-save-much” strategy akin to the detachable lizard's tail had never been tested experimentally. The present study tests the “false head” hypothesis by exposing a hairstreak butterfly, Calycopis cecrops, as well as many other Lepidoptera species as controls, to the attacks of the jumping spider, Phidippus pulcherrimus. The results unambiguously indicate that the “false head” is a very efficient strategy in deflecting attacks from the vital centres of the hairstreak butterfly whereas other similar-sized Lepidoptera fall easy prey. Predator fatigue resulting from unsuccessful attacks was also observed, suggesting that jumping spiders can learn to avoid attacking prey they cannot capture, which would increase the efficiency of the “false head” as a defensive mechanism.