Territorial dynamics and stable home range formation for central place foragers

Uncovering the mechanisms behind territory formation is a fundamental problem in behavioural ecology. The broad nature of the underlying conspecific avoidance processes are well documented across a wide range of taxa. Scent marking in particular is common to a large range of terrestrial mammals and is known to be fundamental for communication. However, despite its importance, exact quantification of the time-scales over which scent cues and messages persist remains elusive. Recent work by the present authors has begun to shed light on this problem by modelling animals as random walkers with scent-mediated interaction processes. Territories emerge as dynamic objects that continually change shape and slowly move without settling to a fixed location. As a consequence, the utilisation distribution of such an animal results in a slowly increasing home range, as shown for urban foxes (Vulpes vulpes). For certain other species, however, home ranges reach a stable state. The present work shows that stable home ranges arise when, in addition to scent-mediated conspecific avoidance, each animal moves as a central place forager. That is, the animal's movement has a random aspect but is also biased towards a fixed location, such as a den or nest site. Dynamic territories emerge but the probability distribution of the territory border locations reaches a steady state, causing stable home ranges to emerge from the territorial dynamics. Approximate analytic expressions for the animal's probability density function are derived. A programme is given for using these expressions to quantify both the strength of the animal's movement bias towards the central place and the time-scale over which scent messages persist. Comparisons are made with previous theoretical work modelling central place foragers with conspecific avoidance. Some insights into the mechanisms behind allometric scaling laws of animal space use are also given.     

Flight speeds of central place foragers: female Lapland longspurs feeding nestlings

According to a recent model (Norberg 1981), birds feeding nestlings should fly faster than V_mr, the speed which minimizes the cost of transport over the ground. The flight speeds of female Lapland longspurs (Calcarius lapponicus) feeding nestlings were not significantly different from the predicted V_mr under various wind conditions. They were, however, significantly higher than the speed that minimizes the rate of energy expenditure (i.e. minimum power speed, V_mp) and significantly lower than the optimal speed (V_opt) predicted from Norberg's model. Thus, maximizing the distance travelled per unit energy expenditure appears to be the most important energetic factor affecting their flight speeds. We suggest that there may be no benefit to increasing air speed above V_mr when brood size is smaller than the maximum number that parents can successfully nourish, or when travel time makes up a small proportion of the total foraging time.     

An economic model of the limits to foraging range in central place foragers with numerical solutions for bumblebees

1. A model is described that evaluates the maximum economic foraging range in central place foragers by using optimality criteria to discriminate between foraging sites at different distances from the forager's central place. 2. The basic model can be varied to suit foragers that optimise either their rate of net energy uptake or their foraging efficiency. 3. The model requires specification of the time and energy budgets of travel and foraging, and of the rewards obtainable at potential foraging sites. 4. The specific case of bumblebees, whose foraging ranges are poorly known, is considered. 5. Numerical solutions of the model for parameter values that represent bumblebees and their forage predict economic foraging ranges exceeding several kilometres. The model demonstrates that economics alone can explain extensive flight ranges in bees.     

Weaning and the nature of early childhood interactions among bofi foragers in central Africa

Western scholarly literature suggests that (1) weaning is initiated by mothers; (2) weaning takes place within a few days once mothers decide to stop nursing; (3) mothers employ specific techniques to terminate nursing; (4) semi-solid foods (gruels and mashed foods) are essential when weaning; (5) weaning is traumatic for children (it leads to temper tantrums, aggression, etc.); (6) developmental stages in relationships with mothers and others can be demarcated by weaning; and (7) weaning is a process that involves mothers and children exclusively, with weaned children moving from close relationships with their mothers to strengthened relationships with other children. In many respects, these presumptions are consistent with contemporary Euroamerican practices: nursing stops early (usually before six months) relative to other cultures and takes place over a few days or weeks with the help of bottles and baby foods. Because bottles are available, weaning seldom appears traumatic, but it is seen as an important step in the establishment of independence between mothers and infants. By contrast, weaning from the bottle is often perceived as traumatic. Despite considerable academic and popular interest, weaning has seldom been studied systematically, especially in small-scale cultures. Qualitative and quantitative data from a study of Bofi foragers in Central Africa are used here to evaluate the cross-cultural applicability of the assumptions summarized above. Hillary N. Fouts is a Ph.D. student in cultural anthropology at Washington State University, Pullman. Her research interests include breastfeeding, weaning, childfeeding, parenting and alloparenting, cross-cultural child development, and life-history theory. Barry S. Hewlett is a professor of anthropology at Washington State University, Vancouver (Washington). His research interests include paternal involvement, cross-cultural child development, and dual transmission models. Michael E. Lamb is the Head of the Section on Social and Emotional Development at the National Institute of Child Health and Human Development. He has written extensively on parent-child relations in a variety of contexts and cultures.     

Prey processing in the Siamese fighting fish (Betta splendens)

We studied prey processing in the Siamese fighting fish (Betta splendens), involving slow, easily observed head-bobbing movements, which were compared with prey processing in other aquatic feeding vertebrates. We hypothesized that head-bobbing is a unique prey-processing behaviour, which alternatively could be structurally and functionally analogous with raking in basal teleosts, or with pharyngognathy in neoteleosts. Modulation of head-bobbing was elicited by prey with different motility and toughness. Head-bobbing involved sustained mouth occlusion and pronounced cranial elevation, similar to raking. However, the hyoid and pectoral girdle were protracted, and not retracted as in both raking and pharyngognathy. High-speed videofluoroscopy of hyoid movements confirmed that head-bobbing differs from other known aquatic prey-processing behaviours. Nevertheless, head-bobbing and other prey-processing behaviours converge on a recurrent functional theme in the trophic ecology of aquatic feeding vertebrates; the use of intraoral and oropharyngeal dentition surfaces to immobilize, reduce and process relatively large, tough or motile prey. Prey processing outside the pharyngeal region has not been described for neoteleosts previously, but morphological evidence suggests that relatives of Betta might use similar processing behaviours. Thus, our results suggest that pharyngognathy did not out-compete ancestral prey-processing mechanisms completely during the evolution of neoteleosts.     

A guide to central place effects in foraging

We develop a general patch-use model of central place foraging, which subsumes and extends several previous models. The model produces a catalog of central place effects predicting how distance from a central place influences the costs and benefits of foraging, load-size, quitting harvest rates, and giving-up densities. In the model, we separate between costs that are load-size dependent, i.e. a direct effect of the size of the load, and load-size independent effects, such as correlations between distance and patch qualities. We also distinguish between predictions of between- and within-environment comparisons. Foraging costs, giving-up densities and quitting harvest rates should almost always increase with distance with these effects amplified by increases in metabolic costs, predation risk and load-costs. With respect to load-size: when comparing foraging in patches within an environment, we should often expect smaller loads to be taken from distant patches (negative distance–load correlation). However, when comparing between environments, there should be a positive correlation between average distance and load-size.     

Dispersed central place foraging in Australian meat ants

Summary Australian meat ants often inhabit colonies with widely dispersed nest holes, and this study examines how resource is harvested and distributed in a colony ofIridomyrmex sanguineus Smith (Formicidae: Dolichoderinae). The three principal types of foragers (tenders, honeydew transporters, scavengers) exhibited nest hole fidelity, where harvested resource was consistently delivered to the same nest hole by each foraging individual. Australian meat ants thus use a harvesting system based on dispersed central place foraging. Evidence of frequent larval transport among nest holes, age polyethism developing in the direction of foraging, and the tendency for nest-associated workers to accept new nest holes more readily than foragers, suggests that workers develop fidelity to the particular nest hole in which they eclose. Coupled with larval transport, nest hole fidelity may allow a colony with widely dispersed nest holes to adjust its structure to more efficiently harvest a resource distributed unevenly in space or time.     

Prey processing in amniotes: biomechanical and behavioral patterns of food reduction

In this paper we examine the biomechanics of prey processing behavior in the amniotes. Whether amniotes swallow prey items whole or swallow highly processed slurries or boluses of food, they share a common biomechanical system where hard surfaces (teeth or beaks) are brought together on articulated jaws by the actions of adductor muscles to grasp and process food. How have amniotes modified this basic system to increase the chewing efficiency of the system? To address this question we first examine the primitive condition for prey processing representative of many of the past and present predatory amniotes. Because herbivory is expected to be related to improved prey processing in the jaws we review patterns of food processing mechanics in past and present herbivores. Herbivory has appeared numerous times in amniotes and several solutions to the task of chewing plant matter have appeared. Birds have abandoned jaw chewing in favor of a new way to chew--with the gut--so we will detour from the jaws to examine the appearance of gut chewing in the archosaurs. We will then fill in the gaps among amniote taxa with a look at some new data on patterns of prey processing behavior and jaw mechanics in lizards. Finally, we examine evolutionary patterns of amniote feeding mechanism and how correlates of chewing relate to the need to increase the efficiency of prey processing in order to facilitate increased metabolic rate and activity.     

Know your place: neural processing of social hierarchy in humans

Social hierarchies guide behavior in many species, including humans, where status also has an enormous impact on motivation and health. However, little is known about the underlying neural representation of social hierarchies in humans. In the present study, we identify dissociable neural responses to perceived social rank using functional magnetic resonance imaging (fMRI) in an interactive, simulated social context. In both stable and unstable social hierarchies, viewing a superior individual differentially engaged perceptual-attentional, saliency, and cognitive systems, notably dorsolateral prefrontal cortex. In the unstable hierarchy setting, additional regions related to emotional processing (amygdala), social cognition (medial prefrontal cortex), and behavioral readiness were recruited. Furthermore, social hierarchical consequences of performance were neurally dissociable and of comparable salience to monetary reward, providing a neural basis for the high motivational value of status. Our results identify neural mechanisms that may mediate the enormous influence of social status on human behavior and health.     

Life-history strategies of optimal foragers

The optimal life histories are examined for models in which the average life-history strategy adopted by the population affects the costs and benefits of any individual's strategy. The situation modeled is one in which organisms can gain energy to be used in reproduction by foraging, but in doing so, they expose themselves to increased mortality; thus the proportion of time spent foraging can be used to measure reproductive effort. Simple models of a demographically homogeneous population are used to reexamine questions which have been studied previously using other models. The effects upon optimal reproductive effort of the following factors are examined: increased births per unit effort, increased mortality, and variability in population parameters. In addition, the questions of whether optimal reproductive effort maximizes population size and whether there can be multiple alternative life histories are examined. Results in most cases differ significantly from those of previous studies. No generalizations emerge regarding the effects of the three factors listed above. Optimal life histories in this model generally do not maximize population size. It is possible to have globally stable alternative life histories. It is concluded that frequency dependence will often be important in determining optimal life histories.     

A general theory of central place foraging for single-prey loaders

This paper analyses the problem of prey choice for a forager that can collect only one item per foraging trip. In the terminology of Orians and Pearson (1979) this is central-place foraging by single-prey loaders. Our analysis goes beyond that of Orians and Pearson by including a cost of time away from the central place that can be a constant per unit time or can increase. Two new effects emerge: (i) It can be optimal to abandon the foraging trip without having collected an item, (ii) The minimum acceptable item depends on the time spent foraging. We show how our framework encompasses cases not usually thought of as central place foraging, such as diving animals that must surface for air.     

Competition in a group of equal foragers

Abstract Using techniques from renewal process theory, we build a stochastic model for gain accumulation in a group of equal competitors foraging in a patchy environment. The model for gain of the individuals is based on the waiting times between subsequent prey encounters by the group. These waiting times depend on the number of foragers in the group. A single parameter of this dependency encompasses a variety of foraging scenarios, from co-operation to scramble. With constant patch size, correlations between gains of any pair of foragers are negative. This dependency is most intense in small groups. Increased variation in patch size makes correlations in gains between group members positive irrespective of the group size. For a solitary forager, variance in gain approaches zero with increasing time in the patch. For an individual member in a group, variance grows monotonically. Thus, depending on the patch departure rule controlling the time to be spent in the patch, solitary foragers may have a smaller variance in gain than members in a group. As solitary foragers also potentially harvest all prey in the patch, it is hard to believe that grouping behavior would evolve solely on the basis of foraging.     

Erythropoietin processing in erythropoietic system and central nervous system

We describe possible functions of carbohydrates attached to growth factors and strategies to examine the functions, concentrating on erythropoietin, a major regulator of erythropoiesis. Erythropoietin in erythropoiesis functions as an endocrine hormone; it is produced by kidney cells and transferred into the circulation to hemopoietic sites. In the brain, erythropoietin acts on neurons in a paracrine fashion. Comparison of glycosylation has been made between kidney and brain erythropoietins.Abbreviations BHK Baby Hamster Kidney - Epo Erythropoietin - Epo-R erythropoietin receptor     

Sex differences in spatial cognition among Hadza foragers

This paper describes sex differences in spatial competencies among the Hadza, a mobile hunter–gatherer population in Tanzania. It addresses the following questions: (a) Is the usual male advantage in Euclidean spatial abilities found in this population, where both women and men are highly mobile? (b) Do Hadza women have better object location memory than men, as the gathering hypothesis predicts? (c) Do women who are nominated by others as being good at finding bushfoods excel at the object location memory task? We tested object location memory with a version of the memory game using cards of local plants and animals. This allowed us to also ask whether women and men would have better spatial memory for the plant and animal cards, respectively. We found that Hadza men were significantly better than women in three tests of spatial ability: the water-level test, targeting, and the ability to point accurately to distant locations (the latter only in the less mobile groups). There was a trend toward a male advantage at the object location memory task, in contrast to results found previously in nonforaging populations, and women's performance at the task deteriorated with age, while that of men did not. The women who were nominated by peers as being good at finding bushfoods were consistently older women. We discuss the probable hormonal causes and functional consequences of age changes in the spatial competencies of female foragers.     

The allocation of foragers in red wood ants

Abstract. 1. We studied how colonies of the red wood ant, Formica polyctena , adjust the numbers of foragers allocated to different foraging trails. In a series of field experiments, foragers were marked and transferred from one nest to another, related nest, where they joined the foraging force. Transferred workers acted as a reserve of uncommitted, available foragers.
2. Previous work shows that each individual forager habitually uses one trail. We found that for an uncommitted forager, the influence of recruitment initially is stronger than that of directional fidelity. Transferred workers were likely to use trails leading to new food sources. When transferred to a new nest, foragers were not likely to use a trail in the same direction as their original trail in the donor nest.
3. After a week, transferred foragers tended to develop route fidelity. Even after bait was no longer present, they continued to use the trail that had formerly led to a bait source.
4. We examined how colonies adjust numbers on a trail by experimentally depleting some trails. Colonies usually did not compensate for depletion: foragers were not recruited to depleted trails.
5. In general, the dynamics of foraging in this species facilitate a consistent foraging effort rather than rapid adjustments of forager allocation.     

Adult Prey Neutralizes Predator Nonconsumptive Limitation of Prey Recruitment

Recent studies have shown that predator chemical cues can limit prey demographic rates such as recruitment. For instance, barnacle pelagic larvae reduce settlement where predatory dogwhelk cues are detected, thereby limiting benthic recruitment. However, adult barnacles attract conspecific larvae through chemical and visual cues, aiding larvae to find suitable habitat for development. Thus, we tested the hypothesis that the presence of adult barnacles (Semibalanus balanoides) can neutralize dogwhelk (Nucella lapillus) nonconsumptive effects on barnacle recruitment. We did a field experiment in Atlantic Canada during the 2012 and 2013 barnacle recruitment seasons (May–June). We manipulated the presence of dogwhelks (without allowing them to physically contact barnacles) and adult barnacles in cages established in rocky intertidal habitats. At the end of both recruitment seasons, we measured barnacle recruit density on tiles kept inside the cages. Without adult barnacles, the nearby presence of dogwhelks limited barnacle recruitment by 51%. However, the presence of adult barnacles increased barnacle recruitment by 44% and neutralized dogwhelk nonconsumptive effects on barnacle recruitment, as recruit density was unaffected by dogwhelk presence. For species from several invertebrate phyla, benthic adult organisms attract conspecific pelagic larvae. Thus, adult prey might commonly constitute a key factor preventing negative predator nonconsumptive effects on prey recruitment.