Effects of body mass,age, dominance and parasite load on foraging time of bighorn rams,<Emphasis Type="Italic"> Ovis canadensis</Emphasis>

In sexually dimorphic ungulates, males generally spend less time foraging than females, possibly because of difference in body mass or because of the energetic requirements of lactation. The relationship between body size and foraging time has received little attention at the intra-specific level, because few studies have documented activity budgets for individuals of known size. Bighorn rams are a good model to explore how body mass affects foraging time, because they range in mass from 55 to 140 kg. We examined how the foraging time of bighorn rams varied according to individual characteristics. We observed rams in a marked population and constructed time budgets during the 3 months preceding the rut. We determined ram social rank based on agonistic encounters and collected fecal samples to count lungworm larvae. Time spent foraging was negatively correlated with body mass. After accounting for age differences, larger rams spent less time foraging and more time lying than smaller rams. Among rams aged 6–12 years, dominants spent less time feeding than subordinates, while fecal output of lungworm larvae was negatively correlated with foraging time for rams of all ages. Body mass accounts for much of the individual variation in foraging time, suggesting that sexual dimorphism is important in explaining differences in feeding time between males and females.Communicated by P. Heeb     

Influence of male harassment and female competition on female feeding behaviour in a sexual–asexual mating complex of mollies (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>, <Emphasis Type="Italic">P. formosa</Emphasis>)

Differential interests between the sexes regarding the number of copulations can result in sexual harassment. Hence, females may have less time available for foraging. Male sexual harassment often leads to fitness reduction in females. We used the mating complex of the bisexual fish Poecilia mexicana and the co-occurring all-female Poecilia formosa to study sexual harassment and its incurred cost on female feeding efficiency. P. formosa is a sperm-dependent parthenogen that requires mating with host males to induce embryogenesis, but the male genes are not used. We therefore predicted P. mexicana males to prefer conspecific females. Hence, costs of male sexual harassment should not occur in unisexuals. While P. formosa are at a disadvantage compared to P. mexicana females due to male mate choice (leading to sperm limitation), this could be traded-off by suffering less from sexual harassment. In our experiment, we found males to direct significantly more pre-copulatory mating behaviour towards conspecific females, whereas actual mating attempts did not differ between species. Contrary to our prediction, both types of females started feeding later and spent less time feeding in the presence of a male partner compared to the time spent feeding with another female, suggesting that females of both species suffer from male harassment. The focal females' feeding time declined with increasing body size of the female competitor, and the same pattern was found when a male was present. We discuss that—besides sexual harassment—other factors such as food competition and female mate choice may affect female feeding efficiency.     

Energy expenditure and food consumption of foraging Imperial cormorants in Patagonia, Argentina

Energy management during the breeding season is crucial for central place foragers since parents need to feed themselves and their offspring while being spatially and temporally constrained. In this work, we used overall dynamic body acceleration as a measure of activity and also to allude to the foraging energy expenditure of breeding Imperial cormorants Phalacrocorax atriceps. We also analyzed how changes in the time or energy allocated to different activities affected the foraging trip energy expenditure and estimated the daily food requirements of the species. Birds spent 42 % of the total energy flying to and from the feeding areas and 16 % floating at sea. The level of activity underwater was almost 1.5 times higher for females than for males. The most expensive diving phase in terms of rate of energy expenditure was descending though the water column. The total foraging trip energy expenditure was particularly sensitive to variation in the amount of time spent flying. During the breeding season, adult cormorants breeding along the Patagonian coast would consume approximately 10,000 tons of food.     

Sex differences in the foraging behavior of squirrel monkeys in a seasonal habitat

Summary The effects of sex and seasonal changes in food abundance on foraging behavior was studied in squirrel monkeys (Saimiri oerstedi) in Costa Rica over an eleven-month period. Females searched for and ate food at significantly greater frequencies than did males throughout the study. The frequency of the specific foraging techniques used occasionally differed significantly within seasons, but not across the study period. Few differences were found in the foraging behaviors of nonreproductive sexually mature females compared to females that were pregnant or lactating. The major exception was that during the month following parturition reproductive females foraged for flowers and fruits more frequently than did non-reproductive females. The reduction of time spent by males in foraging activities gives them more time for other activities, especially anti-predator vigilance. Foraging techniques and the proportions of different food types in the diet changed seasonally. Foraging for arthropods was most frequent in the season when arthropod abundance was lowest, resulting in the amount of time spent eating arthropods to vary less across the seasons. Fruits and flowers were not eaten in a direct relationship to availability, but were used more than expected relative to availability when arthropod abundance was reduced. Individuals were more dispersed when foraging compared to other activities. Overall, there was little evidence of any direct foraging benefits for a squirrel monkey from being social.     

The development of sex differences in ring-tailed lemur feeding ecology

Sex differences in feeding ecology may develop in response to fluctuations in physiological costs to females over their reproductive cycles, or to sexual size dimorphism, or function to minimize feeding competition within a group via resource partitioning. For most mammal species, it is unknown how these factors contribute to sex differences in feeding, or how the development of males and females reflects these intraspecific feeding differences. We show changes in dietary composition, diversity, overlap, and foraging behavior throughout development in ring-tailed lemurs (Lemur catta) and test how the development of sex differences in feeding is related to female costs of reproduction and year-round resource partitioning. Sex differences in dietary composition were only present when females were lactating, but sex differences in other aspects of feeding, including dietary diversity, and relative time spent feeding and foraging, developed at or near the time of weaning. Sex difference in juveniles and subadults, when present, were similar to the differences found in adults. The low year-round dietary overlap and early differences in dietary diversity indicate that some resource partitioning may begin with young individuals and fluctuate throughout development. The major differences between males and females in dietary composition suggest that these larger changes in diet are closely tied to female reproductive state when females must shift their diet to meet energetic and nutritional requirements.     

Intra-sexual variability in feeding behaviour of a mountain ungulate: size matters

Many studies comparing the behaviour of individuals of different genders or species showed that animal body mass and forage quality/quantity are key elements of the foraging ecology of herbivores. Since body mass could also influence the animal’s sensitivity to predation risk, its vigilance behaviour should consequently be affected. Alpine ibex (Capra ibex) is characterised by a strong dimorphism among males of different ages, thus representing an ideal case study for testing the Jarman-Bell principle, avoiding possibly misleading effects resulting from the comparison between different species or genders. We analysed the fine-scale foraging behaviour of male ibex in order to assess the effect of body mass and the effects of vegetation quality/quantity on both foraging and vigilance behaviour. Our results showed that smaller males were more selective than larger ones, on account of their lower capability of digesting plant. Smaller males scanned the environment more frequently than larger ones. Male ibex grazed more selectively in sites with high quality forage and their bite rate increased as forage biomass decreased. Vigilance frequency increased with increasing forage biomass as, under these circumstances, ibex are able to prolong anti-predator vigilance while chewing bites that have already been cropped. Our findings highlight the effects of body mass per se on both foraging and anti-predator behaviours in herbivores, thus supporting the Jarman-Bell principle. Foraging can arguably be considered a very flexible behaviour with high evolutionary relevance as it enables herbivores to optimally adjust their total energy intake under varying conditions of food resources.     

Effects of sex-associated competitive asymmetries on foraging group structure and despotic distribution in Andean condors

Phenotype-limited interference models assume competitive asymmetries among conspecifics and unequal sharing of resources. Their main prediction is a correlation between dominance status and patch quality: dominant individuals should preferentially exploit better-quality habitats. We tested assumptions and predictions of the phenotype-limited interference model in Andean condors (Vultur gryphus), a New World vulture with strong sexual size dimorphism (males are 30–40% heavier than females). We recorded searching birds in habitats differing in quality: mountains and plains. We also observed scavenging behaviour at 20 sheep carcasses, and videotaped 5 of them. Intraspecific hierarchy at carcasses was based on size: males dominated females and, within each sex, older birds dominated younger ones. Adult males and juvenile females occupied extreme positions in the feeding hierarchy. Aggression was directed at those individuals belonging to lower hierarchical levels. In high-quality areas (mountains), more condors arrived at carcasses. Juvenile females were more often observed searching in low-quality areas (plains), far from breeding areas and main roost sites. GLM analyses of individual behaviour showed that the hierarchy did not influence time of arrival, but low-ranking individuals spent more time at carcasses, especially if the number of condors at arrival was high. Additionally, low-ranking condors spent less time feeding at carcasses when individuals of higher hierarchical levels were present. On the other hand, the number of condors present had a positive effect on feeding rates of dominant individuals, probably because of a reduction in individual vigilance. These results support most of the assumptions and predictions of the phenotype-limited distribution model, although a spatial truncated distribution between phenotypes was not observed. Asymmetric feeding pay-off, unequal parental roles and sexual selection constraints could favour sexual divergence in body size in Andean condors. Received: 6 April 1998 / Accepted after revision: 11 July 1998     

Bite rates in Rocky Mountain bighorn sheep (<Emphasis Type="Italic">Ovis canadensis</Emphasis>): effects of season,age, sex and reproductive status

We investigated the effects of vegetation biomass, crude protein content of consumed forage, age, sex and reproductive status on bite rates in Rocky Mountain bighorn sheep. We expected higher bite rates and vigilance in lactating females with young and higher bite rates in young growing individuals, than in non-reproducing females or rams. Lactating ewes had higher bite rates than yeld ewes and than subadult or adult rams. Subadult rams had higher bite rates than adult rams or yeld ewes. On recently burned grassland in spring, however, rams had a higher bite rate than adult females, while the contrary was true on control plots and on the burned plots in autumn. Bite rates declined for both ewes and rams from April to September and varied from year to year. While rams of different ages had significantly different bite rates, there was no effect of age on bite rates for ewes. There was no correlation between bite rates and available total biomass or biomass of live vegetation, or the numbers of steps taken while foraging for either ewes or rams. Adult rams had a lower vigilance rate than adult ewes, and vigilance decreased with increasing bite rates for all sheep. Bite rates in bighorn sheep vary greatly according to age, season and vegetation structure. An increase in bite rates during the forage growing season may compensate for higher energy demands during lactation and growth. There is a potential trade-off between foraging and vigilance as vigilance decreased with increasing bite rates.     

Differences in diet composition and foraging patterns between sexes of the Magellanic penguin (Spheniscus magellanicus) during the non-breeding period as revealed by δ13C and δ15N values in feathers and bone

In diving seabirds, sexual dimorphism in size often results in sex-related differences of foraging patterns. Previous research on Magellanic penguins, conducted during the breeding season, failed to reveal consistent differences between the sexes on foraging behavior, despite sexual dimorphism. In this paper, we tested the hypothesis that male and female Magellanic penguins differ in diet and foraging patterns during the non-breeding period when the constraints imposed by chick rearing activities vanish. We used stable isotope ratios of carbon and nitrogen in feather and bone to characterize the diet and foraging patterns of male and female penguins in the South Atlantic at the beginning of the 2009–2010 and 2010–2011 post-breeding seasons (feathers) and over several consecutive breeding and migratory seasons (bone). The mean δ¹³C and δ¹⁵N values of feathers showed no differences between the sexes in any of the three regions considered or in the diet composition between the sexes from identical breeding regions; however, Bayesian ellipses showed a higher isotopic niche width in males at the beginning of the post-breeding season. Stable isotope ratios in bone revealed the enrichment of males with δ¹³C compared with females across the three regions considered. Furthermore, the Bayesian ellipses were larger for males and encompassed those of females in two of the three regions analyzed. These results suggest a differential use of winter resources between the sexes, with males typically showing a larger diversity of foraging/migratory strategies. The results also show that dietary differences between male and female Magellanic penguins may occur once the constraints imposed by chick rearing activities cease at the beginning of the post-breeding season.     

Food abundance affects energy intake and reproduction in frugivorous female Assamese macaques

In most mammals, female fertility and reproduction are strongly influenced by nutritional status and, therefore, by foraging conditions. Here, we investigate the relationship between food resources, feeding competition, energy intake and reproduction in a group of wild female Assamese macaques (Macaca assamensis) in northeastern Thailand. Over 2,100 h of data on feeding behaviour, energy intake and activity budgets were combined with data on resource characteristics, female reproduction and physical condition. We found that an increase in food availability had a positive effect on female energy intake and conception rates. In addition, it appeared that females incurred energetic costs during lactation and that females with a better physical condition during the mating season were more likely to conceive. The annual birth season occurred a few months before the annual peak in food availability, causing peak lactation to coincide with a period of high food availability. This suggests that females use the increased food abundance to compensate for the energetic costs of lactation. Neither energy intake rates nor activity budgets were influenced by female dominance rank, even during periods when the levels of contest competition were predicted to be high. In line with this, we found no evidence for rank-related differences in reproduction. The apparently limited influence of feeding competition in female Assamese macaques adds to the debate on the extent to which patterns in feeding competition and fitness can reliably be predicted based on ecological conditions. We suggest that this may partially be resolved by including potential competition-reducing mechanisms into the predictive framework.     

Food or sex—males and females in a sex role reversed pipefish have different interests

In a sex role reversed pipefish, Syngnathus typhle, we found that basic life history allocations were directly influenced by sexual selection. We investigated time allocation to foraging and mating, respectively, in a choice experiment, giving males and females, of small or large body size, a choice between food and a potential partner. We found that males were more interested in foraging than mating, i.e., were more frequently observed in front of the food than in front of the partner, whereas females were more interested in the potential partner. This reflects sexual selection operating differently on the two sexes, as males and females are relatively similar in other life history traits, such as growth, mortality, age of maturity, dispersal, and parental expenditure. Moreover, large individuals allocated more time to mating activities, small to feeding. Individuals more interested in mating compared to food were subsequently more critical when given a choice between a large (high-quality) and a small (low-quality) partner, whereas individuals more interested in food were not selective. These findings are consistent with our predictions: sex-role reversed males can be relatively sure of achieving one or more matings, and should allocate more time to feeding and, hence, to parental investment, growth and/or future reproduction. Females, on the other hand, have more uncertain mating prospects and should allocate time to imminent reproductive activities, thereby foregoing other life history traits such as growth and future egg production. By this, they also sacrifice future fecundity and attractiveness.     

Feeding and reproductive behaviour and their effect on catchability of the spanner crab Ranina ranina

The behaviour of 16 adult (8 male and 8 female) spanner crabs (Ranina ranina), collected off southern Queensland, Australia, was monitored continuously in captivity by closed-circuit television for fifteen months from September 1982. Spanner crabs spent most of the time buried in the substrate, emerging mainly only when food became available. They remained emerged for twice as long on feeding days as on days without food. Females responded significantly faster than males to the presence of food. Response was slowest in October and November. There was no correlation between temperature and response time. The average feeding time was 2.0 min (SE=0.12), with no significant difference between males and females. Crabs without food were aggressive towards crabs with food, which sometimes led to fighting and wounding. These interactions also could result in food being transferred from one individual to another. When males interacted, food was transferred more often than when either females, or males and females interacted. Around moulting, male crabs did not feed for 52 d (SE=9.0) and females for 22 d (SE=2.2). This habit would reduce the frequency with which newly moulted crabs are caught in the baited tangle nets used by commercial fishermen. In mating interactions, copulation was always initiated by the males. Males dug up other crabs but, apparently unable to distinguish the sex of these individuals, attempted copulation with either sex. The majority of copulations occurred between midday and midnight and in the period August to December. The frequency of copulations with a female increased 10 d before she extruded eggs, after which it dropped to zero for the following 41 to 50 d. Eggs were carried for 39 to 44 d in the period September to November. The females remained emerged for long periods before extruding their eggs, but the period shortened immediately afterwards. This behaviour would lead to low catchability of ovigerous females. Because females respond more rapidly than males to a food stimulus, they may be more catchable in baited nets than are males. It is concluded that seasonal changes in the behaviour of spanner crabs could affect the number caught by baited tangle nets and may influence the sex ratio in catches.     

Foraging behaviour and habitat use by brown skuas Stercorarius lonnbergi breeding at South Georgia

Top predators are critical to ecosystem function, exerting a stabilising effect on the food web. Brown skuas are opportunistic predators and scavengers. Although skuas are often the dominant land-based predator at seabird colonies, this is the first detailed study of their movements and activity during breeding. The study was carried out at Bird Island, South Georgia (54°00′S, 38°03′W), in the austral summer of 2011/2012 and included GPS data from 33 breeding adults tracked during the late incubation and early chick-rearing periods. Brown skuas spent on average more than 80 % of time in the territory, and it was extremely rare for both partners to leave the territory simultaneously. Much more time was spent foraging at the coast than in penguin colonies and, based on saltwater immersion data, adults never foraged at sea. None of the tracked birds appeared to specialise in catching small petrels at night. Fewer foraging trips were made per day, and hence, more time was spent in the territory, during incubation than chick-rearing. Despite the pronounced sexual size dimorphism, there were no effects of sex on territorial attendance, foraging time or habitat use. Skuas at Bird Island show higher territorial attendance and are less likely to leave the territory unattended than those breeding elsewhere, suggesting closer proximity to more diverse or abundant food resources than at other colonies. The results tie in with previous diet studies, indicating that brown skuas at this site feed mostly on seal placentae and carrion and that birds may rely on a broader range of food resources as the season progresses.     

Evaluating the relative importance of intrinsic and extrinsic factors on the foraging activity of top predators: a case study on female little penguins

A complex interaction of biotic and abiotic factors influences animal foraging activity. It is often difficult to understand which factors may affect animals’ foraging and how it is affected. For instance, whereas the effect of sexual dimorphism on foraging activity has been reported in several species, little is known of the complex interactions between variables acting at a finer scale, e.g. the variability of body mass within a sex. Evaluating the importance of these finer scale factors is also essential to the understanding of foraging behaviour. We propose here a simple approach by applying principal component analysis (PCA) in a novel way to examine relationships between biotic and abiotic factors affecting foraging behaviour of top predators. We studied female little penguins (Eudyptula minor) of known age, carrying miniature accelerometers during the guard stage of breeding. Surprisingly, the body mass of the females did not influence any of the foraging parameters, but females foraging later in the breeding season dived shallower and more often, showing a strong correlation with laying date. Similarly, the diving effort of females was greater with increasing chick age within the same breeding stage. These results indicate that for female little penguin, the relationship between changes in prey availability and hunting effort can change at a fine scale, within a breeding stage. Therefore, any analysis of little penguin foraging behaviour during breeding should consider the timing in relation to the breeding season. We encourage researchers to develop the use of this PCA approach as it could help clarify the complexity of the underlying mechanisms determining foraging activity and we propose that it should be used as a first step of foraging behaviour analysis, before examining a particular relationship.     

Fluctuating sexual dimorphism and differential hibernation by sex in a primate, the gray mouse lemur (Microcebus murinus)

The aim of this study was to investigate reproductive strategies and their consequences in gray mouse lemurs (Microcebus murinus), small solitary nocturnal primates endemic to Madagascar. Previous reports of sexual dimorphism in favor of males and females, respectively, a high potential for sperm competition and pheromonal suppression of mating activity among captive males, led us to investigate mechanisms of intrasexual competition in a wild population. Based on 3 years of mark-recapture data, we demonstrate that sexual dimorphism in this species fluctuated annually as a result of independent changes in male and female body mass. Male body mass increased significantly prior to the short annual mating season. Because their testes increased by 100% in the same period and because their canines are not larger than those of females, we suggest that large male size may be advantageous in searching for estrous females and in enabling them to sustain periods of short-term torpor. In contrast to reports from captive colonies, we found no evidence for two morphologically distinct classes of males. Finally, we also show that most adult males are active throughout the cool dry season that precedes the mating season, whereas most adult females hibernate for several months. This is in contrast to other solitary hibernating mammals, where males typically emerge 1–2 weeks before females. Thus, this first extended field study of M.␣murinus clarified previous conflicting reports on sexual dimorphism and male reproductive strategies in this primitive primate by showing that their apparent deviation from predictions of sexual selection theory is brought about by specific environmental conditions which result in sex-specific life history tactics not previously described for mammals. A general conclusion is that sexual selection can operate more strongly on males without resulting in sexual dimorphism because of independent selection on the same traits in females. Received: 6 July 1997 / Accepted after revision: 28 March 1998     

Nutritional constraints on mountain baboons (Papio ursinus): Implications for baboon socioecology

Summary Populations of baboon (Papio sp.) at geographic and climatic extremes for the genus show a tendency to one-male organization, whereas most baboons live in multimale social groups; this effect has been attributed largely to limitation of food supply, but baboons' complex diet has hindered proper nutritional analyses. To test these optimal-diet explanations of social variation, we quantified intake and used phytochemical analysis of foods to compare the nutrition, during seasonal changes, of two groups of mountain baboons (P. ursinus) living at different altitudes of a continuous grassland habitat. The majority of plant foods were eaten uniquely by one or other group, though their altitudinal separation was only 400 m, and the time budget of feeding choices varied with age-sex class as well as season. Converting to a common currency of nutrients reveals that baboons gained the same yield from a unit time spent foraging (whether this is measured in edible dry weight, or simply protein) in both groups, despite their differing mean altitude, whereas seasonal variation was large and statistically significant. Increased feeding time at the winter bottleneck made no effective compensation for the poorer food yields: in late winter there was a minimum for daily nutrient gain at both altitudes. Apparently this population is already at an extreme for the time animals devote to foraging in winter, when they rely on inconspicuous and slow-to-harvest swollen shoot bases and underground plant storage organs. Since an individual's nutrient yield does not vary with altitude, we conclude that socioecological parameters are effectively optimized for feeding. Since contest competition is absent, this adjustment of foraging efficiency is largely through the effect of differential density on scramble competition. Differences in social structure are considered to be a secondray consequence of optimal foraging, mediated through altitudinal variation in either population density or in day range limits.     

Effects of male removal on female foraging behavior in the Eurasian treecreeper

In old, spruce-dominated forests of central Finland, Eurasian treecreepers Certhia familiaris divide their territories spatially during the breeding season. Females forage primarily on the upper parts of the tree trunks, while males use the lower parts of the tree trunks. In this study we removed males from eight territories in the early nestling period to see if the mate's absence would change the foraging patterns of the resident female. Widowed females foraged at lower heights, thus behaving more like paired males. These females also spent less time on each tree and on each foraging bout than did paired females. We conclude that male removal facilitated the change in a female's foraging niche and foraging time at the trees. Females may re-optimize their foraging site selection owing to the absence of dominant males and a consequent need to increase their parental care. Behavioral plasticity may be the mechanism of niche partitioning between the sexes in this species. Received: 28 June 1996 / Accepted after revision: 27 March 1997     

Seasonal variation in male-female competition,cooperation and selfish hoarding in a monogamous songbird

Both cooperation and conflict between the sexes are commonplace in monogamous mating systems. However, little is known about how cooperation and competition varies seasonally in monogamous species that maintain permanent territories. We presented territorial pairs of male and female New Zealand robins (Petroica australis) with a large supply of insect prey at monthly intervals for 2 years. Behavioural observations after food presentation were then made to quantify seasonal and sexual differences in aggressive interactions over prey, prey acquisition rates, mate provisioning, offspring provisioning, selfish food hoarding and cache retrieval. Data were used to evaluate sex-specific behavioural strategies of mediating competition for food. Results showed that males aggressively excluded females from experimental food sources year-round. Females only accessed food sources when males left them unattended. Consequently, females acquired fewer prey than males. After controlling for differences in prey acquisition, both sexes consumed similar amounts of prey in the non-breeding season. Even though males aggressively excluded females from accessing food sources directly, males fed large amounts of prey to females during the breeding season. Both sexes provisioned young at similar rates. Males cached less prey than females in the breeding season but more prey than females in the non-breeding season. Females showed similar caching intensities year-round. Although males tried to defend their hoards, females frequently retrieved male-made caches. Overall, results showed that although New Zealand robins cooperate to raise offspring during the breeding season, conflict between the sexes occurs year-round. Males and females display different behavioural strategies to gain access to experimental food sources, which appear to lessen male–female competition for food and evenly distribute food resources between the sexes.     

The special role of male Cebus monkeys in predation avoidance and its effect on group composition

Summary Vigilance behavior, predator detection abilities, and responses to real and model predators were studied in two species of capuchin monkeys (Cebus albifrons and C. apella) in a Peruvian lowland rain forest. Adult males were more vigilant than adult females in both species, mainly because the males spent less time feeding and foraging and partly because they were at the periphery more often than the females. The increased vigilance of adult males is reflected in their superior performance in the detection of (model) predators. Adult and subadult males were also far more likely to approach and mob real and model predators. Adults that were outside the center of the group increased foraging activities but cut back an feeding, much of which was done in exposed tree crowns. Current theory suggests that primate groups are multi-male when a single male is unable to defend sexual access to the group of females. In these small capuchin groups, which are multimale, the enhanced safety of females and young provided by extra adult males furnishes a more plausible explanation. A comparison of the two capuchins with the ecologically similar Southeast Asian Macaca fascicularis suggests that the high predation risk outside the group may also have caused the unusual male career profile in capuchins, which have a long tenure of dominants and a very long potential lifespan. Further predictions of this hypothesis are developed.     

Fitness consequences of sexual cannibalism in female<Emphasis Type="Italic"> Argiope bruennichi</Emphasis>

The evolution of sexual cannibalism as the most extreme form of nuptial feeding is still poorly understood. Although increasing evidence suggests that female aggressiveness is related to other aspects of foraging behaviour, it is not clear whether the nutritional value of a male is sufficient to provide an adaptive significance for sexual cannibalism. A widely cited though rarely tested explanation is based on a paternal investment model, and predicts that consumption of a male results in increased female fecundity. The available evidence is either correlational or restricted to species with relatively large and potentially nutritious males, and different studies have come to different conclusions. Here we present a test of the paternal investment hypothesis using the very cannibalistic and highly size-dimorphic spider Argiope bruennichi. After a preset schedule, we had females consume none, one or two males independent of the female's cannibalistic behaviour. Consumption of male bodies did not result in any detectable fitness benefit for the female: neither the number of clutches, nor clutch size or hatching success were affected by consumption of males. The frequency of cannibalism was around 80%, independent of the female mating status. We did not observe male complicity, but cannibalism was associated with prolonged copulation. This suggests a sexually selected benefit of cannibalism for males. We conclude that the paternal investment hypothesis does not explain the existence of sexual cannibalism in A. bruennichi and probably not in other spider species with a pronounced sexual size dimorphism.Communicated by L. Simmons