Group-Living Herbivores Weigh Up Food Availability and Dominance Status when Making Patch-Joining Decisions

Two key factors that influence the foraging behaviour of group-living herbivores are food availability and individual dominance status. Yet, how the combination of these factors influences the patch-joining decisions of individuals foraging within groups has scarcely been explored. To address this, we focused on the patch-joining decisions of group-living domestic goats (Capra hircus). When individuals were tested against the top four ranked goats of the herd, we found that at patches with low food availability they avoided these dominant patch-holders and only joined subordinates (i.e. costs outweighed benefits). However, as the amount of food increased, the avoidance of the top ranked individuals declined. Specifically, goats shifted and joined the patch of an individual one dominance rank higher than the previous dominant patch holder when the initial quantity of food in the new patch was twice that of the lower ranking individual’s patch (i.e. benefits outweighed costs). In contrast, when individuals chose between patches held by dominant goats, other than the top four ranked goats, and subordinate individuals, we found that they equally joined the dominant and subordinate patch-holders. This joining was irrespective of the dominance gap, absolute rank of the dominant patch-holder, sex or food availability (i.e. benefits outweighed costs). Ultimately, our results highlight that herbivores weigh up the costs and benefits of both food availability and patch-holder dominance status when making patch-joining decisions. Furthermore, as the initial quantity of food increases, food availability becomes more important than dominance with regard to influencing patch-joining decisions.     

The influence of social rank in the angelfish,Pterophyllum scalare,on locomotor and feeding activities in a novel environment

To investigate differences in behaviour associated with social rank and environmental conditions, a comparison was made between swimming and feeding activities of dominant and subordinate angelfish, housed in groups of six, with those of angelfish housed singly in identical laboratory aquaria. Subordinate individuals were less active, less ready to feed and consumed less food items than dominants, but their feeding and activity levels were still greater than those displayed by isolated fish used as controls. When fish from each of the above categories were transferred to a novel, identical tank to be tested individually for a 6-day period, little change was observed in previously isolated fish. In contrast, the previous social experience had a marked influence on the behaviour of the other individuals, the effects being related to the social status. The strongest initial response to the new environment was shown by subordinate individuals, with a significant increase in swimming and a significant decrease in feeding compared to the group situation. Subordinates were significantly more active than dominants, who in turn moved more than previously isolated fish. Dominants and subordinates were now similarly reluctant to feed, and their food consumption was less than that of previously isolated fish. With time in the novel environment a significant reduction of swimming activity and a recovery of feeding measures were detected, but levels were still depressed in relation to the group condition, and lower in subordinates than in dominants, indicating the long-lasting effects of the previous social interactions. The results have clear implications for laboratory studies using groups of fish in which social hierarchies may be established prior to individuals being tested singly in a novel environment.     

Feeding Competition in <Emphasis Type="Italic">Macaca fascicularis</Emphasis>: An Assessment of the Early Arrival Tactic

In primate species with unidirectional dominance relationships, rank order restricts the access of nondominant females to clumped resources. However, females might attempt to bypass the rank order by reaching feeding sites before the highest ranking individuals (early arrival tactic) when there are net benefits. We therefore analyzed the order of arrival to the feeding site of the adult members of a captive group of long-tailed macaques. We used 2 experimental conditions that differed in the spatial distribution of a fixed amount of food (large vs. small patch). Though each condition induced contest competition, it was stronger in the small-patch condition. Arrival order does not correlate with dominance rank in either experimental condition. The α-male and α-female reached the feeding site 10–30 s after the beginning of the test. Some females seized on opportunities to reach the feeding site before them, especially in the large-patch condition. They used the early arrival tactic when the risks of aggression were relatively low, which subjects accomplished either by being dominant or by being nondominant but tolerated by the α-male. Social tolerance may provide individuals with an alternative means to obtain resources. In sum, variation in food abundance and distribution may affect the extent to which rank order determines order of arrival to feeding sites. A higher rank may confer priority in the choice of tactics, but not necessarily priority of access to the resources themselves.     

The relative influence of prior residency and dominance on the early feeding behaviour of juvenile Atlantic salmon

In many species where social hierarchy mediates conflict over resources, dominant individuals monopolize food, shelter and reproductive opportunities. The benefits of social dominance, however, can often be offset by a prior residence advantage, whereby individuals arriving first in a new habitat obtain, and subsequently defend, the most profitable sites. We investigated the relative influence of these two factors on the acquisition of feeding territories by juvenile Atlantic salmon,Salmo salar L., by placing groups of six individuals of known dominance rank sequentially into an experimental arena with feeding sites of varying quality. Dominants had an advantage over subordinates in the percentage of time spent in a good-quality feeding site and individual feeding rate. There was also a significant time of arrival effect: those individuals that arrived first in a habitat monopolized the resource. The two effects were of approximately equal strength, so that late-arriving dominant fish had similar success as prior resident subordinates. These results indicate that both dominance and prior residence are important in the feeding behaviour of juvenile Atlantic salmon, and that the two factors can have independent and additive effects.Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Benefits for dominant red deer hinds under a competitive feeding system: food access behavior, diet and nutrient selection

Social dominance is widely known to facilitate access to food resources in many animal species such as deer. However, research has paid little attention to dominance in ad libitum access to food because it was thought not to result in any benefit for dominant individuals. In this study we assessed if, even under ad libitum conditions, social rank may allow dominant hinds to consume the preferred components of food. Forty-four red deer hinds (Cervus elaphus) were allowed to consume ad libitum meal consisting of pellets of sunflower, lucerne and orange, and seeds of cereals, corn, cotton, and carob tree. The meal was placed only in one feeder, which reduced accessibility to a few individuals simultaneously. During seven days, feeding behavior (order of access, time to first feeding bout, total time spent feeding, and time per feeding bout) were assessed during the first hour. The relative abundance of each meal component was assessed at times 0, 1 and 5 h, as well as its nutritional composition. Social rank was positively related to the amount of time spent feeding during the 1(st) h (P = 0.048). Selection indices were positively correlated with energy (P = 0.018 during the 1(st) h and P = 0.047 from 1(st) to 5(th)) and fat (only during the 1(st) h; P = 0.036), but also negatively with certain minerals. Thus, dominant hinds could select high energy meal components for longer time under an ad libitum but restricted food access setting. Selection indices showed a higher selectivity when food availability was higher (1(st) hour respect to 1(st) to 5(th)). Finally, high and low ranking hinds had longer time per feeding bout than mid ones (P = 0.011), suggesting complex behavioral feeding tactics of low ranking social ungulates.     

The role of conformity in foraging when personal and social information conflict

There is currently considerable interest in the interplay betweenpersonal and social information in decision-making processes.Two experiments are presented exploring the relative use ofprior personal information and subsequent social informationin foraging decisions of guppies. Experiment 1 tested the assumptionthat when the use of information acquired through personal experienceis not costly, conflicting social information will be ignored.The assumption was confirmed because, when given a choice betweenfeeding at two food patches, at one of which they had previouslyseen conspecifics feed, individual fish with prior experienceof feeding at the alternative site chose the alternative, whereasfish with no prior experience chose the site at which theirconspecifics had fed. Experiment 2 tested theoretical predictionsthat when the use of information acquired through personal experienceis potentially costly, conflicting social information will beweighed more heavily than will personal information. The predictionwas confirmed because, when given a choice between feeding attwo food patches, one at which they had previously seen conspecificsfeed and one behind a visual barrier, individual fish with priorexperience of feeding behind the barrier chose the site at whichtheir conspecifics had fed. These findings suggest that conformitycan promote social learning in naïve individuals, but priorexperience can insulate individuals from conformity providedthe costs of relying on that experience are small. In addition,the experiments highlight the fact that personal and socialinformation are not always weighed equally.     

How social relationships influence a monkey's choice of feeding sites in the troop of Japanese macaques (Macaca fuscata fuscata) on Koshima islet

When the individual Japanese macaques of the Koshima troop feed on natural food, they usually feed alone. In situations where animals usually feed without other animals, there is a possibility that subordinate animals may avoid feeding sites at which dominant animals are feeding. This paper examines whether social relationships such as kinship or dominance exert any influence on an animal's choice of feeding sites, by analyzing episodes in which an animal approached and climbed into a tree where other animals were. As a result, it was found that social relationships did not influence whether an animal climbed into a tree where other animals were feeding, and that no particular age-sex pair co-fed. Agonistic interactions frequently occurred when the inter-individual distance was less than 1 m. From these findings, the feeding sites were divided into two spaces: (1) a tolerance feeding space, and (2) an intolerance feeding space. It is presumed that animals can feed without entering others' intolerance feeding spaces when food is abundant, as it was in the present study period. Thus social relationships do not influence an animal's choice of feeding sites in such a situation.     

Surface feeding and aggressive behaviour of diploid and triploid brown trout Salmo trutta during allopatric pair‐wise matchings

Diploid and triploid brown trout Salmo trutta were acclimated for 6 weeks on two feeding regimes (floating and sinking). Thereafter, aggression and surface feeding response were compared between pairs of all diploid, all triploid and diploid and triploid S. trutta in an experimental stream. In each pair‐wise matching, fish of similar size were placed in allopatry and rank was determined by the total number of aggressive interactions recorded. Dominant individuals initiated more aggression than subordinates, spent more time defending a territory and positioned themselves closer to the surface food source (Gammarus pulex), whereas subordinates occupied the peripheries. In cross ploidy trials, diploid S. trutta were more aggressive than triploid, and dominated their sibling when placed in pair‐wise matchings. Surface feeding, however, did not differ statistically between ploidy irrespective of feeding regime. Triploids adopted a sneak feeding strategy while diploids expended more time defending a territory. In addition, we also tested whether triploids exhibit a similar social dominance to diploids when placed in allopatry. Although aggression was lower in triploid pairs than in the diploid and triploid pairs, a dominance hierarchy was also observed between individuals of the same ploidy. Dominant triploid fish were more aggressive and consumed more feed items than subordinate individuals. Subordinate fish displayed a darker colour index than dominant fish suggesting increased stress levels. Dominant triploid fish, however, appeared to be more tolerant of subordinate individuals and did not display the same degree of invasive aggression as seen in the diploid and diploid or diploid and triploid matchings. These novel findings suggest that sterile triploid S. trutta feed similarly but are less aggressive than diploid trout. Future studies should determine the habitat choice of triploid S. trutta after release and the interaction between wild fish and triploids during the breeding season prior to utilization of triploids as an alternative management strategy within freshwater fisheries.     

Patch Use in Free‐Ranging Goats: Does a Large Mammalian Herbivore Forage like Other Central Place Foragers?

Classic central place foraging theory does not focus on the foraging of central place herbivores. This is especially true with regard to large mammalian herbivores. To understand the foraging dynamics of these neglected foragers, we measured giving‐up densities (GUDs) in artificial food patches. We did this at different distances away from the central point (i.e. corral) for a herd of free‐ranging domestic goats. To determine temporal changes, we conducted the study over a 3‐mo period during an extended dry season. Throughout our study, goats foraged across a gradient of food availability where forage was more available farther away from the central point. In contrast to the prediction that predation risk and/or increased travel costs were the main drivers of foraging decisions, we found that the goats increased their feeding effort (i.e. achieved lower GUDs) the farther away they moved from the central point. This suggests that either metabolic or missed opportunity costs were the main factors that influenced foraging decisions. In addition, we suggest that social foraging may have also played a role. With increases in foraging opportunities away from the central point, a herd will likely move slowly while foraging. As a result, individuals can feed intensively from patches but remain part of the group. Ironically, owing to the sustained close proximity of other group members, individuals may perceive patches farther from the central point as being safer. Temporally, the goats increased their feeding effort throughout the dry season. This suggests there was a decline in food quality and/or availability across the environment as the study progressed. Despite this increase in feeding effort, the negative relationship with distance did not change. Ultimately, our results provide key insight into how metabolic, missed opportunity and perceived predation costs influence the feeding decisions of large central place herbivores.     

The physiology of rainbow trout in social hierarchies: two ways of looking at the same data

Salmonids form dominance hierarchies in environments, where space or food are limiting. Our first objective was to investigate the physiology of individual rainbow trout in 4-fish hierarchies. Our second was to compare conclusions drawn from grouping physiological data on the basis of social rank with those based on relating individual physiology to individual aggressive behavior. To create a social hierarchy, groups of 4 juvenile trout were fed (1 % ration) using a darkened feeding container, twice daily (morning and evening). Each morning feeding was videotaped to record aggressive behavior, thereby facilitating the assignment of a social status rank to each fish. On days 5 and 10–11, physiological parameters were measured in fish fasted for 24 h. Social hierarchies formed in all tested groups. One fish would become dominant, whereas the three subordinate individuals would each assume a stable social rank. When classified according to this social rank, the three subordinate individuals all displayed similar physiology, different from the physiology of the dominant fish. The latter included higher ammonia excretion rate, greater protein utilization in aerobic metabolism, greater feeding, higher specific growth rate, greater increase in condition factor, and lower routine oxygen consumption rate. However, when individual aggression was taken into account, a continuous gradient was observed between aggression and physiology for most parameters, regardless of social status. These relationships could be improved by normalizing the aggression score to the overall level of aggression in each hierarchy. We argue that individual behavior should be considered instead of just social rank when studying the physiology of trout in social hierarchies.     

Fish don't read textbooks: juvenile salmon prove ignorant of foraging theory

The rules governing the selection of feeding patches by foraging animals is an area of intense interest. Much work has focussed on the development of theoretical models that predict when individuals should switch patches. Tests of these models have often been conducted in laboratory environments, but it is not clear how much influence patch‐switching decisions have on population‐level parameters such as growth and distribution in more complex natural environments. We used juvenile Atlantic salmon as a model species to investigate the effects of randomly fluctuating food levels on growth and site selection. We used PIT technology to monitor in detail individuals' patterns of patch use and activity in an artificial stream, at natural densities. This allowed us experimental control of food supplies and sufficient replication, while retaining many features of a natural system. Only a few individuals of high social rank switched patches as predicted by an appropriate foraging model; otherwise, although frequent, patch‐switching was not related to food availability. Thus, while laboratory experiments indicate that this species has the potential to choose foraging sites on the basis of food availability, it is unlikely that this behavioural mechanism is of great importance in natural systems; further tests of foraging models under natural conditions are essential if we are to understand their effects at the level of populations.     

Sparrows and a brushpile: Foraging responses to different combinations of predation risk and energy cost

Our observations of wintering house sparrows (Passer domesticus) feeding on cracked corn at feeders placed at different distances from a brushpile and in positions differentially exposed to the wind supported the hypothesis that where food patches are equal in net energy return, foragers use the one furnishing the most protection from predation. Results reinforced the hypothesis that when food sources furnish equal protection from predators, homeotherms below their lower critical temperature use the one providing the largest net energy return. When the sparrows had available both a colder, safer feeding site and a warmer, riskier one, they frequented both over the course of the winter and, as predicted, their use of the colder, safer site was negatively correlated with wind velocity and positively related to temperature and solar radiation. In this last case, it appeared the birds decided where to feed on the basis of some threshold difference between metabolic rates at the colder, safer site and the warmer, riskier location.     

Metabolism before,during and after anaesthesia in colic and healthy horses

Background  

Many colic horses are compromised due to the disease state and from hours of starvation and sometimes long trailer rides. This could influence their muscle energy reserves and affect the horses' ability to recover. The principal aim was to follow metabolic parameter before, during, and up to 7 days after anaesthesia in healthy horses and in horses undergoing abdominal surgery due to colic.     

State-dependent feed acquisition among two strains of hatchery-reared Arctic charr

The effects of genetic and environmental factors on aggression and feeding hierarchies were studied using X-radiography to measure food intake by hatchery-reared individuals of two strains (Hammerfest and Svalbard) of Arctic charr Salvelinus alpinus . A reduction in food rations and/or water current speed increased intraspecific aggression, and both factors led to increased interindividual variability in food intake, increasing the coefficient of variation (CV). Following a return to pre-manipulation conditions, CVs decreased to their original level. In control groups, CVs and share of group meals were stable throughout the experiment. The increase in CVs following manipulation was the result of a small number of dominant individuals obtaining a high share of the meal. Restriction in food ration affected share of meals, specific growth rates and the frequencies of non-feeding fish, while reductions in water current speed affected only share of meals. Feeding hierarchies were size-dependent in the control groups. In contrast, no relationships between body weight and feeding rank were evident in groups in which food ration or water current speed were reduced. A small, but consistent, difference was revealed in feeding hierarchy responses between the two strains.     

Communal Roosting of Wintering Red Kites Milvus milvus (Aves,Accipitridae): Social Feeding Strategies for the Exploitation of Food Resources

Social feeding strategies of wintering red kites are analyzed in relation to age, food, roost-sites and differences from kite residents. Whereas young and adult wintering kites gathered at roost sites almost daily, adult residents did not, and immature residents only occasionally. Kites using roost sites feed more often on prey prelocated by others, while lone roosters also forage and discover food alone. After finding food, kites tend to shift to a new roost site and foraging area. Two details of the ‘information centre’ hypothesis are confirmed in our study: carcasses are unpredictably found patches, divisible between several individuals. But carcasses disappeared fast in the study area, and no increase with time in the number of birds consuming a carcass was observed, so that information transmission was unconfirmed. When kites leave the roost in groups no leader is detectable. It seems that other types of social foraging are operating, and the model best matching our results is network foraging.     

Experimental field study of the relative costs and benefits to wild tamarins (Saguinus imperator and S. fuscicollis) of exploiting contestable food patches as single- and mixed-species troops

Several species of tamarins form stable mixed-species troops in which groups of each species feed, forage, rest, and travel together during much of the year. Although the precise set of factors that facilitate this ecological relationship remains unclear, predator detection and foraging benefits are presumed to play a critical role in maintaining troop stability. In this work we present data from an experimental field study designed to examine how factors such as social dominance and within-patch foraging decisions affect the costs and benefits to tamarins of visiting feeding sites as single- and mixed-species troops. Our data indicate that when they exploited contestable food patches (sets of eight feeding platforms, two of which contained a 100-g banana), each tamarin species experienced foraging costs when they arrived as part of a mixed-species troop. These costs were found to be less severe for emperor tamarins because they were socially dominant to saddle-back tamarins and could displace them at feeding sites. We conclude that the foraging benefits to tamarins residing in mixed-species troops are asymmetrical, and that at feeding sites in which the amount of food in a patch is insufficient to satiate all troop members, even minor differences in the timing of return to food patches and changes in troop cohesion have a measurable effect on the costs and benefits to participating tamarin species.     

Food competition in captive female sooty mangabeys (Cercocebus torquatus atys)

We studied the social and foraging behavior of two captive groups of sooty mangabeys under two different spatial food situations. These food conditions were clumped (food was placed in a box) and dispersed (food was dispersed over the entire enclosure). In each group five adult females and two adult males were observed. As a criterion for food competition, individual differences in the relative food intake were used. Adult female mangabeys had a linear, stable, and unidirectional dominance hierarchy. Access to food was rank dependent among females only under clumped food distribution, as current models of the evolution of primate social systems predict. However, feeding success appeared to be mediated not by female but by male agonistic behavior toward females. High-ranking females received relatively less aggression from males and could, therefore, stay and feed longer in the feeding area. Male tolerance of higher-ranking females seems to mediate female feeding success under restricted food resources. The establishment of a special relationship with a high-ranking male might, therefore, be a strategy to get better access to food. This study demonstrates that female competition for access to food should not be analyzed separately from male influences on females and suggests that a more integral role of males in socioecological models of the evolution of primate social systems should be considered.     

HUNGER OVERCOMES FEAR IN NASSARIUS FESTIVUS, A SCAVENGING GASTROPOD ON HONG KONG SHORES

On protected intertidal sand flats, virtually worldwide, nassariidsnails scavenge carrion. Typically, they lie in repose beneaththe sand surface but emerge to feed when chemoreceptors detectcarrion. Distance from the potential food influences whetherthey move towards it and, if they do, whether they obtain ameal before it is consumed by others. This study shows that the rate at which Nassarius festivus movestoward food bait is similar for starved and well-fed individuals.That is, when individuals decide to feed, the rate at whichthey move toward food is always approximately the same. Thisstudy exposes another facet of nassariid nutrition related tothe degree of hunger. Recently fed individuals, i.e., thosewhich have fed for < 14 days, will cease feeding and departpalatable food if crushed conspecifics are added to it. Individualswhich have not fed for > 14 days tend to remain feeding,despite the addition of crushed conspecifics. Another studyhas shown that N. festivus consumes sufficient energy from afed-to-satiation meal to sustain it in repose for 20 days.These experiments clarify the observation. Between 14 to 20days since its last meal, N. festivus will feed when the possibilityarises, despite potentially adverse consequences. That is, hungerovercomes the fear of being consumed at a feeding assemblagebecause, without feeding, the alternative may be death by starvation.Thus, a nassariid makes decisions about whether or not to feed.The fear of predation causes N. festivus to abandon a meal ifthe previous one was obtained within a fortnight but, thereafter,it will risk predation to avoid starvation. (Received 14 March 1994; accepted 7 July 1994)     

Feeding rank and dominance in Tilapia rendalli under defensible and indefensible patterns of food distribution

In four scatter-fed groups of Tilapia rendalli , the distribution of food between individuals was not significantly different from that expected if the food was shared uniformly between all the fish in the group for nine of the 12 radiographic assessments of feeding behaviour. Individual fish maintained the same feeding rank over time, indicating a stable feeding hierarchy, in only one of the four scatter feeding groups. In contrast, in four point source feeding groups, the distribution of food between individuals differed significantly from uniformity in 10 of the 12 radiographic assessments of feeding behaviour and stable feeding hierarchies were maintained over time in three of the four groups. Thus, scatter feeding promoted a more uniform distribution of food between individuals within the group and prevented the formation of feeding hierarchies. There was no significant correlation between individual feeding rank and dominance index in all four scatter feeding groups. In contrast, significant positive correlations were found between individual feeding rank and dominance index in all four point source feeding groups. The results of this study confirm that feeding rank can be used as a correlate of relative social status under defensible feeding conditions.     

Interannual Variation in Nut Abundance Is Related to Agonistic Interactions of Foraging Female Japanese Macaques (Macaca fuscata)

The importance of dominance status to foraging and ultimately survival or reproductive success in wild primates is known; however, few studies have addressed these variables simultaneously. We investigated foraging and social behavior among 17 adult female Japanese macaques (Macaca fuscata) on Kinkazan Island, northern Japan, from September to November in 2 consecutive years (2004 and 2005) to determine whether interannual variation in food availability was related to variation in agonistic interactions over food resources and the feeding behavior of individuals of different dominance rank. We compared energy obtained with daily energy requirements and also examined the effect of variation in feeding behavior on female survival and reproductive success. Fruiting conditions differed considerably between the 2 yr: of four nut-producing species, the nuts of only Torreya nucifera fruited in 2004, whereas all four species, particularly Fagus crenata, produced nuts in abundance in 2005. The abundance and average crown size of trees of Torreya nucifera were smaller than those of Fagus crenata, and there was a higher frequency of agonistic interactions during 2004, when dominant, but not subordinate, individuals were able to satisfy daily energy requirements from nut feeding alone through longer nut feeding bouts. In contrast, all macaques, regardless of their dominance rank, were able to satisfy their energy requirements by feeding on nuts in 2005. Subordinate macaques appeared to counter their disadvantage in 2004 by moving and searching for food more and maintaining larger interindividual distances. Several lower-ranking females died during the food-scarce season of 2004, and only one dominant female gave birth the following birth season. In contrast, none of the adult females died during the food-scarce season of 2005, and 12 females gave birth the following birth season. These findings suggest that an interaction between dominance rank and interannual variation in food availability are related to macaque behavior, survival, and reproduction.