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.     

Dispersal,kinship and inbreeding in an island population of the Great Tit

We investigated the kinship structure of an island population of the Great Tit (Parus major). Kinship of birds could be inferred by comparing their family trees. Dispersal was also studied to explain the observed pattern of kinship. On the island of Vlieland the tits breed in several wooded areas. Both males and females preferred to breed in their natal area; males did so more strongly than females. Hence gene flow between the areas is restricted. However, within the largest wooded area females showed random dispersal, while males showed a slight tendency to breed near their natal site. The degree of kinship of neighbouring birds is a suitable control group for the relatedness of partners that takes into account the effects of dispersal. In the largest wooded area, birds were on average equally related to their partner and to their neighbours. Moreover, the mean coefficient of kinship between male and female neighbours was equal to the average kinship in this part of the population. We conclude that mating is random with respect to kinship. There is no evidence for avoidance of inbreeding. It is unlikely that kin recognition plays an important role in the process of mate choice in this population of Great Tits. We suggest that ecological factors are the main causes for the observed patterns of dispersal and mating. On the island more female than male immigrants enter the population each year. Incidental data indicate an exchange of birds between the population studied and surrounding populations. Ancestries of immigrants are not known, and indeed a first analysis of all birds, including immigrants, showed that males were more closely related than females. However, differential immigration could not fully explain the observed difference in kinship. The presence of local adaptation in males is suggested as a possible additional cause.     

Evolution of prey holding behaviour and large male body size in Ninox owls (Strigidae)

The hawk owl genus Ninox is unique among raptorial birds in that it includes three species in which males are substantially larger than females. This is a reversal of the normal pattern observed in both diurnal and nocturnal raptorial birds in which females are larger. Interestingly, these three Ninox species also are both the largest of the 22 species in the genus and the only species that exhibit the striking behaviour of ‘prey holding’ in which large (> 600 g) mammalian or avian prey is captured at night and held with body parts intact, and draped below a roost for the entire day without being consumed. Because explanations of the evolution of large male size suggest that it results from competition among males, the adaptive significance of prey holding was studied in a wild population of powerful owl Ninox strenua. Prey holding is largely confined to breeding males and its occurrence varies significantly across the breeding cycle, being most frequent during incubation and brooding. The study did not clearly resolve whether prey holding is a form of food storage or territorial display; however, both functions can select for large male body size and therefore play a significant role in the evolution of nonreversed size dimorphism. Although female‐only incubation and brooding is typical of Ninox owls and other owl species, prey holding appears to occur only in the large Ninox species because of the unique combination of large body size, large prey size, separate sex roles, and obligate cavity nesting. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 284–292.     

Agonistic aiding: Kinship,rank, age,and sex influences

An analysis of 3,774 episodes of agonistic aiding collected during a two-year study of a rhesus monkey group (Macaca, mulatta) indicated the differential influence of kinship and rank relationships on the participation of different age-sex classes in both aid to victims and aid to aggressors. Most aiding favored victims rather than aggressors and was much more likely to occur when matrilineal kin were involved. Females were more likely to aid than were males, and the frequency of their participation increased with age. Females were much more influenced by kinship than were males and defended or aggressively supported kin against any third party regardless of dominance relationships. Adult males seldom aided against animals that were dominant to themselves; the rare exceptions occurred when adult males defended kin. Aiding was far more likely to occur if the victim was squealing, and noisy agonistic episodes often involved multiple aiders on both sides. Aiding patterns had some potential to insure dominance rank inheritance within families, in accordance with the Kawamura hypothesis. In aiding animals outside of their own matrilines, however, group members aided randomly with respect to this model. There was little evidence that aiding functioned to support individuals when they targeted animals to which they should be dominant as adults based on matrilineal dominance relationships. Most defensive aiding seemed to function primarily to defend victims (primarily kin) of aggression. Aggressive support of the attacker, on the other hand, seemed to function primarily to reinforce coalitions with the attacker. The identity of the victim was unimportant as long as it was neither kin to nor dominant to the aider. Aggressive support of attackers did not overturn existing dominance relationships.     

Male rank,reproductive behavior,and reproductive success in free-ranging rhesus macaques

Paternity assessment through DNA fingerprinting by synthetic oligonucleotide probes was applied to one birth cohort in a social group of free-ranging rhesus macaques (Macaca mulatta) on Cayo Santiago. The 11 group males and 9 males from other groups were observed mating with the females. Paternity was determined for 11 of the 15 infants. Male dominance rank was not associated with reproductive success. High-ranking resident males (N=5) sired 27% of the infants born during a one-year study. Four of the 11 infants of known paternity were sired by males of other social groups. The four infants of unknown paternity were sired either by males not observed mating with the females or the low-ranking male who was not fingerprinted. Male dominance rank was not associated with reproductive activity during conception cycles. These results suggest that the effect of rank on male reproductive success is not a predictable correlation, but a conditional probability.     

Sex and age differences in juvenile social priorities in female philopatric,nondespotic blue monkeys

Juveniles should choose social partners on the basis of both current and future utility. Where one sex is philopatric, one expects members of that sex to develop greater and sex‐typical social integration with group‐mates over the juvenile period. Where a partner's position in a dominance hierarchy is not associated with services it can provide, one would not expect juveniles to choose partners based on rank, nor sex differences in rank‐based preferences. We tested these ideas on 39 wild juvenile (3.2–7.4 years) blue monkeys (Cercopithecus mitis stuhlmanni), cercopithecines with strict female philopatry and muted hierarchies. We made focal animal observations over 6 months, and computed observed:expected amounts of proximity time, approaches and grooming given to various social partners. Overall, our results agree with the hypothesis that juvenile blue monkeys target social partners strategically. Spatial proximity, approaches and active grooming showed similar patterns regarding juvenile social preferences. Females were far more sociable than males, groomed more partners, reciprocated grooming more frequently, and preferred—while males avoided—infants as partners. Older juveniles (5–7 years) spent more time than younger juveniles (3–4 years) near others, and older females were especially attracted to infants. Close kin, especially mothers and less consistently adult sisters, were attractive to both male and female juveniles, regardless of age. Both sexes also preferred same‐sex juveniles as social partners while avoiding opposite‐sex peers. Juveniles of both sexes and ages generally neither preferred nor avoided nonmaternal adult females, but all juveniles avoided adult males. Partner's rank had no consistent effect on juveniles' preference, as expected for a species in which dominance plays a weak role. Juveniles' social preferences likely reflect both future and current benefits, including having tolerant adult kin to protect them against predators and conspecifics, same‐sex play partners, and, for females, infants on which to practice mothering skills. Am. J. Primatol. 72:193–205, 2010. © 2009 Wiley‐Liss, Inc.     

Hunting rates and hunting success in the spotted hyena (Crocuta crocuta)

Hunting group size, hunting rates and hunting success were monitored over a seven-year period among members of one large clan of spotted hyenas ( Crocuta crocuta ) inhabiting the Masai Mara National Reserve, in south-west Kenya. Prey availability varied seasonally in this study area, and hyenas tended to hunt whichever prey species were most abundant during each month of the year. Over 75% of 272 hunting attempts were made by lone hyenas, even when they hunted antelope three times their own body mass, such as wildebeest and topi. Of all prey that were commonly hunted, only zebra were usually hunted in groups. Approximately one-third of all hunting attempts resulted in prey capture. Although no significant sex differences were observed in juvenile or adult hunting rates, low-ranking adult females hunted at significantly higher hourly rates than did higher-ranking females. Hunting success was not influenced by the social rank of hunters, but hunting group size and hunter's age strongly influenced success. Young hyenas were poor hunters, and did not achieve adult competency levels until they were 5–6 years old.     

Agonistic Interactions of Juvenile Savanna Baboons

19 juvenile members of known genealogies in two wild baboon groups were studied over a 16-month period to compare the ontogeny of agonistic experience and dominance relations for males and females. Juveniles of all age-sex classes were disproportionately likely to receive aggression from and submit to adult males per unit of time spent in proximity. This pattern intensified with increasing juvenile age. With age, juvenile females more often submitted to unrelated adult females from higher-ranking families, whereas this was not true for juvenile males. All juveniles received aggression from older group members more often during feeding than was expected by chance. High rates of agonistic interaction with unrelated adult females accounted for old juvenile females (3–5.5 years-old) interacting agonistically more frequently than male age peers and young juveniles of either sex (1–2.5 years-old). Adult females were also more aggressive toward females among young juveniles, suggesting that adult females target females among juveniles for aggression and resistance to rank reversal. Within juvenile age groups, males dominated all females and all younger males, irrespective of maternal dominance status. Dominance relations among female age-peers were generally isomorphic with relations among their mothers. No juvenile targeted any older male for rank reversal. Males targeted all older females, whereas females typically targeted only older females from families lower-ranking than their own. The strong sexual dimorphism in adult body size in baboons may explain why juvenile males' dominance relations with peers and adult females are not structured along lines of family membership as is true for the less dimorphic macaques. Acquisition of higher agonistic status probably allows juveniles of both sexes to increase their success in within-group feeding competition during late stages of juvenility, which, in turn, could affect important life-history traits such as age at menarche and adult body size.     

Distribution and feeding behaviour of field populations of the water cricket Velio, caprai (Hemiptera)

1. The distribution of individuals, prey capture success and prey choice were studied in a water cricket (Velia caprai) population in southern Ireland. Groups of different sizes were observed in the field during the summer and all potential prey animals entering the groups were counted. Surface drift samples were collected to assess the proportion of profitable prey items. 2. Two types of Velia groups were observed: mixed groups (adults and juvenile instars 4 and 5) and juvenile groups (instars 1–3), A greater proportion of the available prey was captured by the mixed groups. 3. Individuals in large groups had a lower capture rate than individuals in small groups. 4. No differences in capture rates could be found between males, females and juveniles, but differences in prey choice were apparent. Females captured more large prey than expected. 5. Water cricket distribution in the stream did not follow the ‘ideal free’ model; too few individuals were found at the most profitable sites. Food might not be the limiting factor during summer, and other factors such as intraspecific interference and predator avoidance could be more important.     

Prey Habitat Location by the Cassava Mealybug Predator Exochomus flaviventris: Olfactory Responses to Odor of Plant, Mealybug, Plant–Mealybug Complex, and Plant–Mealybug–Natural Enemy Complex

Exochomus flaviventris Mader is considered to be the most active predator of the cassava mealybug Phenacoccus manihoti Matile–Ferrero in Central Africa. The response of experienced gravid female coccinellids to the odor of cassava plant (var. Zanaga), unparasitized mealybugs, plant–mealybug complex with or without feeding prey (parasitized or not), and plant–mealybug complex with or without conspecific coccinellids was investigated in a Y-tube olfactometer. The odor of uninfested cassava plants was not more attractive than clean air. Dual-choice tests revealed that mealybug-infested plants were preferred to mealybugs alone and mealybug-damaged plants and were the major sources of volatiles that attract females coccinellids to the microhabitat of its prey. The emission of volatile chemicals did not appear to be limited to the infested parts of the plant but did occur systemically throughout the plant. The presence of conspecific coccinellid larvae or adult males did not modify the attractiveness of the mealybug-infested plants. However, when an infested plant with conspecific predator females (alone or with conspecific males) was compared to an infested plant or infested plant with conspecific males, E. flaviventris females showed a preference for the last two sources of odor. The uninfested plant with conspecific males was also preferred to the uninfested plant with conspecific females. In addition, the odor of conspecific males was preferred over that of conspecific females. Female predators preferred the plant infested with unparasitized mealybugs over the plant infested with mealybugs previously parasitized. These results showed that E. flaviventris females use herbivore-induced plant volatiles during foraging and can detect via olfaction the presence of conspecific gravid females and parasitized prey, thus assessing patch suitability from a distance.     

Sex Differential Behavior of Immature Hanuman Langurs (Presbytis entellus) in Ramnagar, South Nepal

We investigated sex differences in the social behavior of immature Hanuman langurs (Presbytis entellus) in the light of sex-specifically different life-courses and Hanuman langur characteristics, such as the individualistic dominance hierarchy and the rarity of intragroup coalitions among adult females. We observed four immature female and four immature male langurs—all members of the same free-ranging multimale multifemale group in Ramnagar, South Nepal—from November 1992 to February 1993 for 288 hr via focal-animal and instantaneous sampling techniques. Immature females spent significantly more time in proximity to other group members than immature males did. They had more physical contact and groomed more. Other immature females were their preferred social partners. Immature males also preferred like-aged females. They restricted their relationships with other immature males to proximity and occasional grooming. Monitoring was directed especially toward adult males. Female behavior can be interpreted as oriented toward integration into the female social network and their age-inverted dominance hierarchy. Males seem to prepare for leaving their natal group and for future strong intrasexual competition.     

A preliminary study of kinship and social organization in a semi-free-ranging group ofLemur catta

From long-term studies of a number of anthropoid species, many investigators have shown that kinship affinities affect social relationships. Factors such as proximity, social grooming, dominance rank, and mating patterns have been shown to be related to kinship. In this paper, we report the results of a preliminary study of the social organization of a group of prosimians (Lemur catta) in which individuals were identified and kinship affinities were known. We found that close matrilineal kin preferred to groom one another and to remain in close proximity more than did nonkin and distantly related animals. Furthermore, no copulations were observed within matrilines. These results are similar to those found in a number of species of anthropoids. This research was conducted on a semi-free-ranging group at the Duke University Primate Facility, Durham, North Carolina.     

Effects of prey quantity and quality on predatory wasps

1. The simultaneous effects of prey quantity and prey quality on fitness correlates of the predatory wasp Polistes fuscatus were examined in a glasshouse study. Prey quantity was manipulated by providing prey in excess (high quantity) or one‐third of that (low quantity). Prey quality was manipulated by providing either palatable (Manduca sexta) caterpillars or unpalatable (Junonia coenia) caterpillars. 2. The effect of prey quality on wasp production depended on prey quantity. Nests given unpalatable prey produced few wasps whereas nests given palatable prey increased wasp production with increased prey. 3. The low production of nests given unpalatable prey reflected the low acceptability of those prey. The wasps preferred the palatable prey and learned to reject the unpalatable prey. With no choice of prey, they took only enough unpalatable prey to develop a small nest or colony. 4. A diet of unpalatable prey also resulted in smaller wasps and reduced the proportion of males produced, from about 40% to just 8–14%, depending on the year.     

Factors Affecting Proximity Among Members of a Wild Group of Moor Macaques During Feeding,Moving, and Resting

We studied the effects of kinship, age, sex, and other factors on patterns of spatial proximity among group members in a wild group of moor macaques (Macaca maurus) in Sulawesi, Indonesia. We assessed the importance of each factor via multiple linear regression analyses. Moor macaques stay close to their matrilineal relatives more frequently when the group moves or rests than when they feed. Subjects of similar age, sex, or rank tended to stay close to each other. Females were in the proximity of females with newborn infants regardless of the phase of activity of the group. Kinship may have less effect on proximity during feeding in moor macaques than in Japanese macaques. Weak effects of kinship during feeding may result from weak contest competition for food within the group.     

Individual and social behavioral responses to injury in wild toque macaques (Macaca Sinica)

Toque macaques (Macaca sinica),inhabiting natural forest at Polonnaruwa, Sri Lanka, are frequently injured in fights with conspecifics. The behavior of known individuals when they were injured was compared to that after they had recovered their health. Thus, injured animals rested and alloand autogroomed more, but they foraged less and initiated fewer aggressive episodes. They spent most time being sedentary in the safety of arboreal refuges and reduced acrobatic movements by locomoting more often terrestrially. Other group members showed no special tolerance (or altruism) toward injury victims during the costly and highly competitive activity of foraging for food. In fact, some injured animals received more aggression, or lost dominance rank, and thereby had their competitive abilities further impaired. Care for the injured was manifest mostly by grooming and wound cleaning. All hair in the area surrounding a wound, as well as dirt, scabs, and fly larvae, were removed, and saliva was applied by licking the wound (wounds so treated healed with no obvious signs of infection). (1) Injured macaques sought and received significantly more grooming (owing to wound care); (2) the amount so received increased with the severity of the injury; and (3) the initiative of other group members often compensated for a victim’s inability to solicit care. Juvenile males were especially attentive to injured adult males, suggesting that they were investing in a social bond with these adults, which might reciprocate altruism toward their juvenile caregivers in the future. Injured juvenile females received most care from their mothers.     

Do predators limit the abundance of alternative prey? Experiments with vole‐eating avian and mammalian predators

Predation has been invoked as a factor synchronizing the population oscillations of sympatric prey species, either because predators kill prey unselectively (the Shared Predation Hypothesis; hereafter SPH), or because predators switch to alternative prey after a density decline in their main prey (the Alternative Prey Hypothesis; APH). A basic assumption of the APH is that the impact of predators on alternative prey depends more on the density of main prey than on the predator/alternative prey ratio. Both SPH and APH assume that the impact of predators on alternative prey is at least periodically strong enough to depress prey populations. To examine these assumptions, we utilized data from replicated field experiments in large areas where we reduced the breeding densities of avian predators during three years and the numbers of least weasels (Mustela nivalis) in two years when vole populations declined. In addition, we reduced the breeding densities of avian predators in two years when vole populations were high. The reduction of least weasels increased the abundance of their alternative prey, small birds breeding on the ground, but did not affect the abundance of common shrews (Sorex araneus). In years when vole populations declined, the reduction of avian predators increased the abundance of their alternative prey, common shrews and small birds. Therefore, vole‐eating predators do at least periodically depress the abundance of their alternative prey. At high vole densities, the reduction of avian predators did not increase the abundance of common shrews, although the ratio of avian predators to alternative prey was similar to years when vole populations declined, which supported APH. In contrast, the abundance of small birds increased after the reduction of avian predators also at high vole densities, which supported SPH. The manipulations had no obvious effect on the number of game birds, which are only occasionally killed by these small‐sized predators. We conclude that in communities where most predators are small or specialize on a single prey type, the synchronizing impact of predation is restricted to a few similar‐sized species.     

Asymmetric interactions in semiaquatic insects

Summary Interspecific interactions were studied in three coexisting species of predatory semiaquatic insects: Gyrinus substriatus Steph. (Coleoptera), Gerris lacustris (L.) and Gerris argentatus Schumm. (Hemiptera). Prey capture success was observed in trials with individuals of two different species. Two prey sizes were used: fruit flies Drosophila melanogaster and Mediterranean flour moths Ephetia kuehniella (Zeller). When the two species were starved for the same period of time, G. substriatus was generally more successful at catching prey than either Gerris species, independent of prey size. However, when individuals from the formerly dominant species of the pair were less hungry (i.e. fed shortly before trials), their prey capture success decreased. Prey sharing and prey stealing were observed in trials with large prey and occurred both intra- and interspecifically. The shift in dominance with differing hunger levels and the existence of prey sharing and prey stealing may make the interspecific competition more symmetric allowing these species to coexist.     

The diet of pygmy sperm whales, Kogia breviceps, stranded in New Zealand: implications for conservation

The stomach contents of 27 pygmy sperm whales, Kogia breviceps, stranded on New Zealand beaches between 1991 and 2003 are reported. These individuals comprise 16 males, 10 females, and one for which no sex information is available. The diet was found to include fish and crustaceans, but is comprised primarily of cephalopods, with 0–526 lower beaks, representing an estimated maximum of c. 60 kg of cephalopod prey consumed by any one whale. Cephalopod prey is attributed to 23 species from 13 families, and is dominated by juvenile individuals of the families Histioteuthididae and Cranchiidae (adults of which usually occur at depths exceeding 400 m). Perceived threats to this whale, particularly those affecting distribution and abundance of prey species, are also discussed. These are the first data reporting the diet of this whale species in New Zealand waters. A comparison of the diet of K. breviceps is made with that of the sperm whale, Physeter macrocephalus from New Zealand waters, and with the diet of Kogia known elsewhere.     

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.