1,721,152 research outputs found
When to choose which tool: Multidimensional and conditional selection of nut-cracking hammers in wild chimpanzees
No full textInvestigating cognitively complex behaviours in their natural ecological context provides essential insights into the adaptive value of animal cognition. In this study, we investigated the selection of hammers used for cracking Coula nuts by wild chimpanzees, Pan troglodytes verus, in the Taï National Park, CÔte d'Ivoire, taking account of the availability of potential tools at the site and time of tool selection. Using GLMMs and focal follows of five adult females, we estimated the probability of an object being selected as a hammer according to its physical properties, transport distance and the location of the anvil on the ground or in trees. We found that chimpanzees took account of several variables at the same time (multidimensionality) when selecting nut-cracking tools and that their selection for hammer weight was adjusted to the state/value of other variables (conditionality). In particular, chimpanzees (1) preferred stones over wooden clubs and hard woods over soft woods; (2) selected heavy stones, but relatively lighter wooden hammers; (3) selected increasingly heavier hammers the closer they were to the anvil; and (4) selected lighter hammers when they were going to crack nuts on a tree. The latter two results represent instances of conditional tool selection based on the next steps in an operational sequence (transport and/or use of the tool in a stable or unstable location) and suggest that chimpanzees anticipated future events when they chose a tool. This large set of conditional rules suggests a high level of cognitive sophistication in a tool use task. Our results represent a compelling example of how powerful cognitive skills allow the optimization of an ecologically relevant foraging activity, supporting a food extraction hypothesis for the evolution of complex cognition in our closest relatives
Accounting for pseudoreplication is not possible when the source of nonindependence is unknown
No full textRepeated observations of the same individuals or other units, which can lead to clustered observations, are common in animal behaviour research, and mixed models are commonly employed to model and account for such clustering in the data and avoid pseudoreplication. However, in some cases, while the data might comprise repeated samples from the same individuals, the precise identity of the individuals from which samples originated is unknown. In a recent paper Garamszegi (2016, Animal Behaviour, 120, 223–234) suggested an approach to account for pseudoreplication which is based on repeatedly assigning random subject identities to the samples and then analysing the data using a mixed model or averaged values for each randomly assigned identity. Here we tested this approach using a simulation study. We found that the approach suggested by Garamszegi leads to clearly inflated type I error rates that were essentially the same as those obtained from a naïve linear model simply ignoring individual identity and that only a model based on the correct subject identities roughly produced the nominal type I error rate. We conclude that, currently, there is no method available that allows pseudoreplication to be controlled when subject identities are unknown
Do chimpanzees anticipate an object’s weight? A field experiment on the kinematics of hammer-lifting movements in the nut-cracking Taï chimpanzees
Full text linkWhen humans are about to manipulate an object, our brains use visual cues to recall an internal representation to predict its weight and scale the lifting force accordingly. Such a long-term force profile, formed through repeated experiences with similar objects, has been proposed to improve manipulative performance. Skillful object manipulation is crucial for many animals, particularly those that rely on tools for foraging. However, despite enduring interest in tool use in non-human animals, there has been very little investigation of their ability to form an expectation about an object's weight. In this study, we tested whether wild chimpanzees use long-term force profiles to anticipate the weight of a nut-cracking hammer from its size. To this end, we conducted a field experiment presenting chimpanzees with natural wooden hammers and artificially hollowed, lighter hammers of the same size and external appearance. We used calibrated videos from camera traps to extract kinematic parameters of lifting movements. We found that, when lacking previous experience, chimpanzees lifted hollowed hammers with a higher acceleration than natural hammers (overshoot effect). After using a hammer to crack open one nut, chimpanzees tuned down the lifting acceleration for the hollowed hammers, but continued lifting natural hammers with the same acceleration. Our results show that chimpanzees anticipate the weight of an object using long-term force profiles and suggest that, similarly to humans, they use internal representations of weight to plan their lifting movements
Costly culture: Differences in nut-cracking efficiency between wild chimpanzee groups
No full textCultural diversity among social groups has recently been documented in multiple animal species. Investigations of the origin and spread of diverse behaviour at group level in wild-ranging animals have added valuable information on social learning mechanisms under natural conditions. Behavioural diversity has been especially informative in the case of dispersal, where the transfer of individuals between groups leads to a sudden exposure to unfamiliar behaviour. Little is known, however, about the underlying costs and benefits of cultural transmission in animals and humans alike, as efficiency of cultural variants is often difficult to measure. The chimpanzees, Pan troglodytes, of the Taï National Park in Ivory Coast are known to exhibit a number of cultural differences between social groups, including hammer selection for nut cracking. This provides the unique opportunity to quantify the efficiency of cultural variants. We compared foraging speed and number of hits applied during nut-cracking events between three neighbouring chimpanzee groups. Our results showed significant differences in nut-cracking efficiency, caused by hammer material selection and differences in the applied power of impact per nut. Persistent behavioural coherence within the respective groups implies that immigrants adjust their behaviour to local nut-cracking techniques, even when individual foraging success might be compromised. This suggests that the benefit of belonging to a social group might outweigh the benefits of maximizing individual foraging efficiency. The differences in nut-cracking efficiency between chimpanzee groups add to the ever-growing body of cultural variants in wild chimpanzees and expand our knowledge of the importance of group belonging and conformity in wild chimpanzees
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Modelling primate abundance in complex landscapes: a case study from the Udzungwa mountains of Tanzania
No full textWith persistent degradation of tropical forests creating fragmented landscapes, the study of patterns of primate responses to habitat changes is of increasing conservation relevance. We modeled primate abundance in the Udzungwa Mountains of Tanzania through a landscape approach, i.e., one that includes a representative range of discrete forest blocks. The area is internationally recognized for biological endemism and is a primate hotspot in Africa. We targeted three predominantly arboreal monkeys: Udzungwa red colobus (Procolobus gordonorum), Peters’ Angola colobus (Colobus angolensis palliatus), and the Tanzania Sykes’ monkey (Cercopithecus mitis monoides). In each of the four forests (12–522 km2 in size), we counted primate groups along a grid of line transects (267 km walked) and sampled canopy trees in vegetation plots along the same transects (N = 408) to derive structural and floristic forest parameters and proxies of human impact. We found that elevation and the percentage of climber coverage on trees consistently emerged as significant predictors of primate abundance for all three species in spite of their differences in feeding habits, with a negative effect of elevation and a positive effect of climber coverage. This pattern held despite large variations in elevation, forest habitat, and human disturbance across the four forests surveyed. We conclude that arboreal primates in the Udzungwas are dependent on lowland and medium-elevation forests (ca. 300–1200 m a.s.l.) and show considerable resilience to moderate forest disturbance. However, agricultural intensification causes rapid forest degradation, with detrimental effects on primates that need to be prevented through increased protection and community conservatio
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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