Julia Riedel

Lethal aggression in Pan is better explained by adaptive strategies than human impacts

Observations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide valuable comparative data for understanding the significance of conspecific killing. Two kinds of hypothesis have been proposed. Lethal violence is sometimes concluded to be the result of adaptive strategies, such that killers ultimately gain fitness benefits by increasing their access to resources such as food or mates. Alternatively, it could be a non-adaptive result of human impacts, such as habitat change or food provisioning. To discriminate between these hypotheses we compiled information from 18 chimpanzee communities and 4 bonobo communities studied over five decades. Our data include 152 killings (n = 58 observed, 41 inferred, and 53 suspected killings) by chimpanzees in 15 communities and one suspected killing by bonobos. We found that males were the most frequent attackers (92% of participants) and victims (73%); most killings (66%) involved intercommunity attacks; and attackers greatly outnumbered their victims (median 8:1 ratio). Variation in killing rates was unrelated to measures of human impacts. Our results are compatible with previously proposed adaptive explanations for killing by chimpanzees, whereas the human impact hypothesis is not supported.

Domestic dogs (Canis familiaris) use a physical marker to locate hidden food

Dogs can use the placement of an arbitrary marker to locate hidden food in an object-choice situation. We tested domestic dogs (Canis familiaris) in three studies aimed at pinning down the relative contributions of the human’s hand and the marker itself. We baited one of two cups (outside of the dogs’ view) and gave the dog a communicative cue to find the food. Study 1 systematically varied dogs’ perceptual access to the marker placing event, so that dogs saw either the whole human, the hand only, the marker only, or nothing. Follow-up trials investigated the effect of removing the marker before the dog’s choice. Dogs used the marker as a communicative cue even when it had been removed prior to the dog’s choice and attached more importance to this cue than to the hand that placed it although the presence of the hand boosted performance when it appeared together with the marker. Study 2 directly contrasted the importance of the hand and the marker and revealed that the effect of the marker diminished if it had been associated with both cups. In contrast touching both cups with the hand had no effect on performance. Study 3 investigated whether the means of marker placement (intentional or accidental) had an effect on dogs’ choices. Results showed that dogs did not differentiate intentional and accidental placing of the marker. These results suggest that dogs use the marker as a genuine communicative cue quite independently from the experimenter’s actions.

Stable isotope evidence of meat eating and hunting specialization in adult male chimpanzees

Observations of hunting and meat eating in our closest living relatives, chimpanzees (Pan troglodytes), suggest that among primates, regular inclusion of meat in the diet is not a characteristic unique to Homo. Wild chimpanzees are known to consume vertebrate meat, but its actual dietary contribution is, depending on the study population, often either unknown or minimal. Constraints on continual direct observation throughout the entire hunting season mean that behavioral observations are limited in their ability to accurately quantify meat consumption. Here we present direct stable isotope evidence supporting behavioral observations of frequent meat eating among wild adult male chimpanzees (Pan troglodytes verus) in Taï National Park, Côte d’Ivoire. Meat eating among some of the male chimpanzees is significant enough to result in a marked isotope signal detectable on a short-term basis in their hair keratin and long-term in their bone collagen. Although both adult males and females and juveniles derive their dietary protein largely from daily fruit and seasonal nut consumption, our data indicate that some adult males also derive a large amount of dietary protein from hunted meat. Our results reinforce behavioral observations of male-dominated hunting and meat eating in adult Taï chimpanzees, suggesting that sex differences in food acquisition and consumption may have persisted throughout hominin evolution, rather than being a recent development in the human lineage.

How feeding competition determines female chimpanzee gregariousness and ranging in the Taï National Park, Côte d'Ivoire.

Socioecological theory suggests that feeding competition shapes female social relationships. Chimpanzees (Pan troglodytes) live in fission–fusion societies that allow them to react flexibly to increased feeding competition by forming smaller foraging parties when food is scarce. In chimpanzees at Gombe and Kibale, female dominance rank can crucially influence feeding competition and reproductive success as high‐ranking females monopolize core areas of relatively high quality, are more gregarious, and have higher body mass and reproductive success than low‐ranking females. Chimpanzee females in Taï National Park do not monopolize core areas; they use the entire territory as do the males of their community and are highly gregarious. Although female chimpanzees in Taï generally exhibit a linear dominance hierarchy benefits of high rank are currently not well understood. We used a multivariate analysis of long‐term data from two Taï chimpanzee communities to test whether high‐ranking females (1) increase gregariousness and (2) minimize their travel costs. We found that high‐ranking females were more gregarious than low‐rankers only when food was scarce. During periods of food scarcity, high rank allowed females to enjoy benefits of gregariousness, while low‐ranking females strongly decreased their gregariousness. High‐ranking females traveled more than low‐ranking females, suggesting that low‐rankers might follow a strategy to minimize energy expenditure. Our results suggest that, in contrast to other chimpanzee populations and depending on the prevailing ecological conditions, female chimpanzees at Taï respond differently to varying levels of feeding competition. Care needs to be taken before generalizing results found in any one chimpanzee population to the species level. Am. J. Primatol. 73:305–313, 2011.

The role of the hunter: stable isotope evidence of hunting in adult male chimpanzees

The statistics of error and uncertainty are intertwined with ascertaining the admissibility of forensic evidence in a court of law. This issue was especially examined in the 2009 National Academy of Science review of forensic practice. In the analysis of unidentified skeletal remains it is, thus, crucial to formulate a biological profile that gives not only stated errors, but also accuracy and precision of the raw data. In particular, the most accurate biological profile is achieved by using contemporary population-specific standards.S AAPA PRESENTATIONS Crossing disciplines to challenge the adaptationist paradigm. REBECCA R. ACKERMANN. Department of Archaeology, University of Cape Town. In the wake of the Modern Synthesis, Sherwood Washburn’s appeal for a new physical anthropology explicitly called for a shift towards a process-oriented view of evolution. Like others at the time, Washburn overwhelmingly emphasized the role that selection plays in shaping diversity, and biological anthropologists soon began to embrace the idea of interpreting human variation and evolution in terms of underlying selective processes. Today, explanations for phenotypic variation in human evolution remain largely functional/adaptive, despite the strong challenges to the adaptationist paradigm mounted outside of biological anthropology in the past few decades. In this paper, I will discuss our current understanding of the important role that random genetic drift and gene flow have played in shaping phenotypic diversity in hominins. This fuller understanding of the underlying processes responsible for variation has necessitated engaging with other disciplines (e.g. evolutionary biology, quantitative genetics). We have much to gain from modifying the methodological approaches and theoretical developments within those disciplines to our own ends, including a more sophisticated interpretation of the fossil record. As one example, the emerging genomic evidence for gene flow among archaic human populations (e.g. Neanderthals, Denisovans) might have been less surprising (to those for whom it was a surprise) were it not for methodological approaches couched within a lingering adaptationist perspective that has failed to provide a sufficiently nuanced understanding of the evolutionary prevalence and phenotypic consequences of the ‘other’ evolutionary forces. Research funded by the National Research Foundation of South Africa and the University of Cape Town. Effects of predator presence on the behavior of bald-faced saki monkeys (Pithecia irrorata) in the Peruvian Amazon. DARA B. ADAMS, DAWN M. KITCHEN and ASHLEY HURST. Anthropology, The Ohio State University, Anthropology, The University of Texas at San Antonio. Predation is an important selective pressure on prey populations but its influence on primate evolution remains hotly debated. While some researchers argue predation has little effect on group-living in primates, others maintain that constant threats of death strongly impact behavior. Here, we explore the effects of predator presence on saki monkey (Pithecia irrorata) behavior. We hypothesized that saki monkey behavior would differ in high and low use predator areas. Data were collected from June to July 2012 at Centro de Investigación y Capacitación Río Los Amigos in Peru. Over 78 hours of scan and focal sampling were collected on 8 saki monkeys. During 10-minute focal follows, we recorded activity, canopy height, intragroup spacing, vigilance, and number of alarm calls emitted. To determine high and low use predator areas, we conducted a 30-day camera trap survey within the focal group’s home range. During 30 trap nights, we documented four felid species (jaguar, puma, ocelot, and margay) on 11 separate occasions. Camera trap data indicates a pattern of higher predator densities within parts of the sakis’ home range. Analyses of behavioral data suggest that sakis maintain closer associations and engage in less rest and social behavior in high predator areas (Chi-square: P<0.05). However, alarm calling and canopy height are not associated with predator presence (Chi-square: P>0.05). Surprisingly, individuals seem to exhibit less vigilance in high predator areas, which may be related to habitat differences. Our future research will include an assessment of factors such as habitat quality and seasonality on antipredator behavior. Predicting impact stiffness and rate of loading during human walking and heel-strike running. BRIAN J. ADDISON and DANIEL E. LIEBERMAN. Human Evolutionary Biology, Harvard University. Heel-striking during human walking and running generates impacts beneath the foot. These impacts produce large forces over short time periods and occur millions of times per foot per year. In order to understand how the human body evolved to cope with these repetitive impacts, we must first understand how impact force parameters are generated beneath the foot in walking and running. Therefore, we used mass-spring models to predict stiffness and the rate of loading during the impact phase of gait. These models were tested on 20 human subjects walking and running on a rigid surface and four substrates of varying stiffnesses. All subjects walked and ran at Froude numbers of 0.28 and 1.2, respectively. Three-dimensional kinematic and kinetic data were collected using Qualysis motion capture software and an instrumented treadmill. Results indicate that impact stiffness on various substrates can be predicted accurately using knowledge of substrate stiffness and impact stiffness measured a rigid surface. Results also indicate that rate of loading scales predictably with impact stiffness. Importantly, declines in substrate stiffness of 94% produce only 17% declines in impact stiffness during walking compared to 55% declines in impact stiffness during running. This finding suggests that the human foot plays a greater role than substrate in governing impact forces during walking compared to heel-strike running. The performance differences in walking versus running provide a biomechanical context for interpreting morphological changes thought to be related to resisting impact forces, including variations in hominin calcaneal morphology. Funding for this study was provided by Hintze Charitable Foundation and VibramUSA Microfractures in elderly ribs: Contributions to bone quality. AMANDA M. AGNEW, SAM D. STOUT and PAUL W. SCIULLI. Division of Anatomy, The Ohio State University, Department of Anthropology, The Ohio State