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Search Results: 1 - 10 of 354299 matches for " S. Peter Henzi "
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Formalising the multidimensional nature of social networks
David Lusseau,Louise Barrett,S. Peter Henzi
Computer Science , 2011, DOI: 10.1098/rstb.2012.0113
Abstract: Individuals interact with conspecifics in a number of behavioural contexts or dimensions. Here, we formalise this by considering a social network between n individuals interacting in b behavioural dimensions as a nxnxb multidimensional object. In addition, we propose that the topology of this object is driven by individual needs to reduce uncertainty about the outcomes of interactions in one or more dimension. The proposal grounds social network dynamics and evolution in individual selection processes and allows us to define the uncertainty of the social network as the joint entropy of its constituent interaction networks. In support of these propositions we use simulations and natural 'knock-outs' in a free-ranging baboon troop to show (i) that such an object can display a small-world state and (ii) that, as predicted, changes in interactions after social perturbations lead to a more certain social network, in which the outcomes of interactions are easier for members to predict. This new formalisation of social networks provides a framework within which to predict network dynamics and evolution under the assumption that it is driven by individuals seeking to reduce the uncertainty of their social environment.
A floristic description and utilisation of two home ranges by vervet monkeys in Loskop Dam Nature Reserve, South Africa
Alan S. Barrett,Leslie R. Brown,Louise Barrett,Peter Henzi
Koedoe : African Protected Area Conservation and Science , 2010, DOI: 10.4102/koedoe.v52i1.990
Abstract: The plant communities occurring in the home ranges of two vervet monkey (Chlorocebus aethiops) troops (referred to as the Donga and Picnic troops) were investigated as part of a comprehensive research project on the spatial and temporal patterns in resource dispersion or distribution and range use. From two-way indicator species analysis (TWINSPAN) multivariate classifications refined by Braun-Blanquet procedures, seven plant communities that can be placed into three major groups were identified in the home range of the Donga troop, and eight plant communities that can be placed into four major groups were identified in the home range of the Picnic troop. Classifications and descriptions of the major groups, including vegetation maps, are presented. Diagnostic as well as prominent species of tree, shrub, forb and grass strata are outlined. Ordinations and floristic analyses were undertaken for the two home ranges to highlight vegetative differences between the areas. The phenology of vervet resources and the available resource energy were determined as a basis for the comprehensive study. Conservation implications: This vegetation description and phenology provide valuable information on the utilisation of home ranges by vervets and demonstrate how various management applications can affect the home range dependence of troops. How to cite this article: Barrett, A.S., Brown, L.R., Barrett, L. & Henzi, P., 2010, ‘A floristic description and utilisation of two home ranges by vervet monkeys at the Loskop Dam Nature Reserve, South Africa’, Koedoe 52(1), Art. #990, 12 pages. DOI: 10.4102/koedoe.v52i1.990
Sparse movement data can reveal social influences on individual travel decisions
Tyler R. Bonnell,S. Peter Henzi,Louise Barrett
Statistics , 2015,
Abstract: The monitoring of animal movement patterns provides insights into animals decision-making behaviour. It is generally assumed that high-resolution data are needed to extract meaningful behavioural patterns, which potentially limits the application of this approach. Obtaining high-resolution movement data continues to be an economic and technical challenge, particularly for animals that live in social groups. Here, we test whether accurate movement behaviour can be extracted from data that possesses increasingly lower temporal resolution. To do so, we use a modified version of force matching, in which simulated forces acting on a focal animal are compared to observed movement data. We show that useful information can be extracted from sparse data. We apply this approach to a sparse movement dataset collected on the adult members of a troop of baboons in the DeHoop Nature Reserve, South Africa. We use these data to test the hypothesis that individuals are sensitive to isolation from the group as a whole or, alternatively, whether they are sensitive to the location of specific individuals within the group. Using data from a focal animal, our data provide support for both hypothesis, with stronger support for the latter. Although the focal animal was found to be sensitive to the group, this occurred only on a small number of occasions when the group as a whole was highly clustered as a single entity away from the focal animal. We suggest that specific social interactions may thus drive overall group cohesion. Given that sparse movement data is informative about individual movement behaviour, we suggest that both high (~seconds) and relatively low (~minutes) resolution datasets are valuable for the study of how individuals react to and manipulate their local social and ecological environments.
Common HLA Alleles Associated with Health, but Not with Facial Attractiveness
Vinet Coetzee, Louise Barrett, Jaco M. Greeff, S. Peter Henzi, David I. Perrett, Ahmed A. Wadee
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000640
Abstract: Three adaptive hypotheses have been proposed to explain the link between the human leucocyte antigen (HLA) genes, health measures and facial attractiveness: inbreeding avoidance, heterozygote advantage and frequency-dependent selection. This paper reports findings that support a new hypothesis relating HLA to health. We suggest a new method to quantify the level of heterozygosity. HLA heterozygosity did not significantly predict health measures in women, but allele frequency did. Women with more common HLA alleles reported fewer cold and flu bouts per year, fewer illnesses in the previous year and rated themselves healthier than women with rare alleles. To our knowledge, this is the first study to show a positive correlation between HLA allele frequency and general health measures. We propose that certain common HLA alleles confer resistance to prevalent pathogens. Nevertheless, neither HLA heterozygosity nor allele frequency significantly predicted how healthy or attractive men rated the female volunteers. Three non-mutually exclusive explanations are put forward to explain this finding.
Ontogenetic Scaling of Fore- and Hind Limb Posture in Wild Chacma Baboons (Papio hamadryas ursinus)
Biren A. Patel, Angela M. Horner, Nathan E. Thompson, Louise Barrett, S. Peter Henzi
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0071020
Abstract: Large-scale interspecific studies of mammals ranging between 0.04–280 kg have shown that larger animals walk with more extended limb joints. Within a taxon or clade, however, the relationship between body size and joint posture is less straightforward. Factors that may affect the lack of congruence between broad and narrow phylogenetic analyses of limb kinematics include limited sampling of (1) ranges of body size, and/or (2) numbers of individuals. Unfortunately, both issues are inherent in laboratory-based or zoo locomotion research. In this study, we examined the relationship between body mass and elbow and knee joint angles (our proxies of fore- and hind limb posture, respectively) in a cross-sectional ontogenetic sample of wild chacma baboons (Papio hamadryas ursinus) habituated in the De Hoop Nature Reserve, South Africa. Videos were obtained from 33 individuals of known age (12 to ≥108 months) and body mass (2–29.5 kg) during walking trials. Results show that older, heavier baboons walk with significantly more extended knee joints but not elbow joints. This pattern is consistent when examining only males, but not within the female sample. Heavier, older baboons also display significantly less variation in their hind limb posture compared to lighter, young animals. Thus, within this ontogenetic sample of a single primate species spanning an order of magnitude in body mass, hind limb posture exhibited a postural scaling phenomenon while the forelimbs did not. These findings may further help explain 1) why younger mammals (including baboons) tend to have relatively stronger bones than adults, and 2) why humeri appear relatively weaker than femora (in at least baboons). Finally, this study demonstrates how field-acquired kinematics can help answer fundamental biomechanical questions usually addressed only in animal gait laboratories.
Facial-based ethnic recognition: insights from two closely related but ethnically distinct groups
V. Coetzee,J. M. Greeff,L. Barrett,S. P. Henzi
South African Journal of Science , 2010, DOI: 10.4102/sajs.v105i11/12.127
Abstract: Previous studies on facial recognition have considered widely separated populations, both geographically and culturally, making it hard to disentangle effects of familiarity with an ability to identify ethnic groups per se.We used data from a highly intermixed population of African peoples from South Africa to test whether individuals from nine different ethnic groups could correctly differentiate between facial images of two of these, the Tswana and Pedi. Individuals could not assign ethnicity better than expected by chance, and there was no significant difference between genders in accuracy of assignment. Interestingly, we observed a trend that individuals of mixed ethnic origin were better at assigning ethnicity to Pedi and Tswanas, than individuals from less mixed backgrounds. This result supports the hypothesis that ethnic recognition is based on the visual
Phytosociology and plant community utilisation by vervet monkeys of the Blydeberg Conservancy, Limpopo Province
A.S. Barret,L.R. Brown,L. Barret,S.P. Henzi
Koedoe : African Protected Area Conservation and Science , 2006, DOI: 10.4102/koedoe.v49i1.88
Abstract: The plant communities of the Blydeberg Conservancy were investigated as part of a research project on the foraging ecology of vervet monkeys Cercopithecus aethiops pygerythrus (senso lato) in mixed lowveld bushveld and sour lowveld bushveld areas. To date there are no formal management plans for vervet monkeys. This is attributed to the limited knowledge of vervets and their utilisation of and impacts on ecosystems. From a TWINSPAN classification refined by Braun-Blanquet procedures, ten plant communities that can be placed into four major groups were identified. A classification and description of these communities, including a vegetation map are presented. Diagnostic species as well as prominent and less conspicuous species of tree, shrub, herb and grass strata are outlined. Of the ten available plant communities, the vervets utilised only six during the study period. There was an abundant supply of various food sources throughout the year, with movement patterns mostly coinciding with the fruiting times of several tree and other plant species.
Vegetation classification as the basis for baboon management in the Bourke’s Luck Section of the Blyde Canyon Nature Reserve, Mpumalanga
L.R. Brown,H. Marais,S.P. Henzi,L. Barrett
Koedoe : African Protected Area Conservation and Science , 2005, DOI: 10.4102/koedoe.v48i2.90
Abstract: The Blyde Canyon Nature Reserve (BCNR) was identified as an important conservation area due to of its extraordinary diversity of plant species. Plant communities represent ecosystems and form the basis of any management plan for natural areas. If these ecosystems and their different potentials are unknown, they cannot be managed successfully. Baboons exploit diverse habitats including human environments where they often cause damage to crops and forest plantations. Baboons are regarded as particularly problematic residents of protected areas as conventional fences do not readily enclose them, their eclectic diets allow them to benefit from a range of agricultural endeavours, and they are behaviourally opportunistic. Thus as a first step to implementing a conservation policy to manage chacma baboons in the BCNR, it was necessary to have some understanding of their exploitation of natural habitats adjacent to areas where they do cause problems. Although a broad vegetation map of the BCNR exists, no detailed vegetation studies have been conducted on the largest part of the reserve. It was therefore decided to ndertake a detailed vegetation study of the home range of a single baboon troop within the Bourke’s Luck section of the BCNR. From a TWINSPAN classification, refined by Braun-Blanquet procedures, 13 plant communities, which can be grouped into seven major groups, were identified. A classification and description of these communities, as well as a vegetation map are presented. Data collected as part of this study also revealed that the baboons show preference to certain communities whilst avoiding others. These have important consequences in terms of the management strategies followed on the reserve.
Population structure and habitat use of baboons (Papio hamadryas ursinus) in the Blyde Canyon Nature Reserve
A.J. Marais,L.R. Brown,L. Barrett,S.P. Henzi
Koedoe : African Protected Area Conservation and Science , 2006, DOI: 10.4102/koedoe.v49i2.117
Abstract: Baboons are highly intelligent and ecologically flexible animals with attributes that allow them to exploit diverse habitats. As a result of their dietary flexibility they often exploit human habitats, causing damage to crops and forest plantations as well as to human dwellings. In the South African context this has led to baboons being regarded as problem animals and attempted extirpation is the most common approach to the damage they cause. This perception of and attitude toward baboons gives many conservationists cause for concern since all southern African cercopithecine primates are CITES listed and it has not been proven that this strategy is the best long-term solution. As part of a research programme focusing on the damage done by chacma baboons in pine plantations along the Drakensberg escarpment in Mpumalanga, a single troop in the Blyde Canyon Nature Reserve was studied to describe their patterns of habitat use. Vegetation and habitat surveys were conducted within the home range of the troop. The troop was habituated and each member’s activity, location and food items utilised were recorded over a 12 month period. The results of this study indicate that baboons utilised plant communities based on food production and availability rather than size in hectares. The results also indicate that the group size, foraging and food search strategies of this troop resembles that of the Drakensberg troops previously studied. The study troop employs two different forage modes of engagement depending on where they choose to forage while they avoid utilising an easily accessible pine plantation. Due to the troop’s long inter-birth intervals it is likely that the current forestry practice of extirpation may have a negative influence on baboon population viability in these areas.
Entwicklung und Evaluation eines Diskussionsforums für Studierende mit Handicaps der Sozialberatung der Universit t Basel
Caroline Cornelius,Gaudenz Henzi
E-Beratungsjournal , 2009,
Abstract: Seit Februar 2007 bietet die Sozialberatung der Universit t Basel in Zusammenarbeit mit dem Portal Uniability ein moderiertes, barrierefreies und passwortgeschützes Internetforum mit begleitender Mailing-Liste für Studierende mit Behinderungen und chronischen Erkrankungen und für ihre KommilitonInen an, welche in einem vertraulichen Rahmen nach Informationen, Hilfestellungen und Austauschm glichkeiten rund um Studium, Accessibility, Laufbahnplanung und Behinderung suchen. Die vorangegangene Bedarfsanalyse zeigte, dass sich die Studierenden von einem solchen Forum vor allem eine gegenseitige Beratung (Peer-Mentoring), aber auch niederschwellige Beratungsangebote durch die Sozialberatung erhoffen. In der fortlaufenden Evaluation wurde deutlich, dass diese Erwartungen an das Forum weitgehend erfüllt werden konnten. Der erwünschte Ausstrahlungs-Effekt, die Teilnahme an Pr senzveranstaltungen der Sozialberatung und den Bekanntheitsgradder Angebote der Sozialberatung zu steigern, trat ein, so dass insgesamt eine flexible Kombination von Einzel- und Gruppenberatung Face-to-Face, per E-Mail, Mailingliste und in einem geschützten Forum für die Zielgruppe der Studierenden mit Handicaps an Schweizer Universit ten empfohlen werden kann.
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