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Mellor, P. S. (1993). African horse sickness: transmission and epidemiology. Vet Res, 24(2), 199–212.
Abstract: African horse sickness (AHS) virus causes a non-contagious, infectious, arthropod-borne disease of equines and occasionally of dogs. The virus is widely distributed across sub-Saharan African where it is transmitted between susceptible vertebrate hosts by the vectors. These are usually considered to be species of Culicoides biting midges but mosquitoes and/or ticks may also be involved to a greater or lesser extent. Periodically the virus makes excursions beyond its sub-Saharan enzootic zones but until recently does not appear to have been able to maintain itself outside these areas for more than 2-3 consecutive years at most. This is probably due to a number of factors including the apparent absence of a long term vertebrate reservoir, the prevalence and seasonal incidence of the vectors and the efficiency of control measures (vaccination and vector abatement). The recent AHS epizootics in Iberia and N Africa spanning as they do, 5 or more yr, seem to have established a new pattern in AHS virus persistence. This is probably linked to the continuous presence of adult C imicola in the area. Culicoides imicola is basically an Afro-Asiatic insect and prefers warm climates. Therefore its continuous adult presence in parts of Iberia and N Africa may be due to some recent moderations of the climate in these areas.
Keywords: Africa, Northern/epidemiology; African Horse Sickness/epidemiology/*transmission; African horse sickness virus/*physiology; Animals; Arachnid Vectors/microbiology; Ceratopogonidae/*microbiology; Culicidae/microbiology; Horses; Insect Vectors/*microbiology; Portugal/epidemiology; Spain/epidemiology; Ticks/microbiology
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Heyes, C. M. (1993). Imitation, culture and cognition. Anim. Behav., 46(5), 999–1010.
Abstract: Abstract. This paper examines the significance of imitation in non-human animals with respect to the phylogenetic origins of culture and cognitive complexity. It is argued that both imitation (learning about behaviour through nonspecific observation) and social learning (learning about the environment through conspecific observation) can mediate social transmission of information, and that neither is likely to play an important role in supporting behavioural traditions or culture. Current evidence suggests that imitation is unlikely to do this because it does not insulate information from modification through individual learning in the retention period between acquisition and re-transmission. Although insignificant in relation to culture, imitation apparently involves complex and little-understood cognitive operations. It is unique in requiring animals spontaneously to equate extrinsic visual input with proprioceptive and/or kinaesthetic feedback from their own actions, but not in requiring or implicating self-consciousness, representation, metarepresentation or a capacity for goal-directed action.
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Todd, I. A., & Kacelnik, A. (1993). Psychological mechanisms and the Marginal Value Theorem: dynamics of scalar memory for travel time. Anim. Behav., 46(4), 765–775.
Abstract: Abstract. The relation between memory for travel time and foraging decisions was studied experimentally. The temporal properties of two environments with patchily distributed food were simulated in the laboratory using pigeons, Columba livia, as subjects. The two environments differed in mean travel time, while the coefficient of variation of travel time and the decelerated function relating cumulative food gain to time in the patch were held constant within and between environments. Each environment contained a uniform mixture of five travel times experienced in a random order. Two of the five travel times were common in both environments. Effects of travel time were studied by comparing prey collected per patch visit (PPV) after various travel times within each environment, and by comparing patch exploitation after equal travel times between environments. Within the environment with long mean travel time (LMT) PPV was positively correlated with the last and the penultimate travel times but not with travel times before that. The increase in PPV per second of last travel time was six times greater than the increase per second of penultimate travel time, implying very steep memory discounting. In the environment with short mean travel time (SMT), there was no correlation between PPV and previous travel times. However, comparisons between environments of visits following travel times common to both environments (thus removing the effect of the last travel time) showed that substantially more prey were taken after equal travel times in the LMT than in the SMT environment. This difference cannot be accounted for by the within-environment effect of penultimate travel time, implying that there is a different, less steeply devalued, effect of the mixture of travel times. A model of information processing based on combining Scalar Expectancy Theory with the predictions of rate maximization under the Marginal Value Theorem is presented. The model can approximate the results obtained in this and previous experiments and provides a framework for further analysis of memory mechanisms of foraging behaviour.
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Barton, R. A. (1993). Sociospatial mechanisms of feeding competition in female olive baboons, Papio anubis. Anim. Behav., 46(4), 791–802.
Abstract: Abstract. Social and spatial mechanisms of feeding competition among adult female olive baboons were studied in two free-ranging groups, one foraging for natural foods, and one that was being provisioned. Similar behavioural processes were found to underlie rank-related differences in food intake in the two situations. Dominance rank of females in the naturally foraging group was positively correlated with the rate at which other animals were supplanted from feeding sites, the ratio of supplants of others to supplants received, and the number of near neighbours while feeding on clumped foods. It is unlikely that the latter result was due to rank-related differences in matriline size, because no significant correlations between rank and neighbour density were found for non-feeding activities. Step-wise regression analysis indicated that both number of neighbours and the supplant ratio explained significant proportions of inter-individual variance in daily food intake, though only the supplant ratio contributed significantly to feeding rate. High-ranking females also had priority of access to feeding sites within trees, and competition was most intense for foods that were spatially clumped. Similarly, in the provisioned group, rank was correlated with the rate at which supplants were received, and with spatial indices estimating centrality and the area of unoccupied space around an individual. Over 99% of the inter-individual variance in feeding rate was explained in a step-wise regression with supplant rates and spatial indices as independent variables. It is concluded that both active supplanting and individuals' spatial positions within the group mediate rank-related differences in food intake.
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Feh, C., & de Mazières, J. (1993). Grooming at a preferred site reduces heart rate in horses. Anim. Behav., 46(6), 1191–1194.
Abstract: Abstract. It is commonly suggested that the principal function of allogrooming is to reduce social tension between group members, but direct evidence of the physiological consequences of grooming at particular sites is lacking. By filming allogrooming sequences in a herd of Camargue horses, Equus caballus , their preferred grooming site, which lies on the lower neck, was identified. Experimental imitation of grooming at this site reduced the heart rate of the recipient while grooming on a non-preferred area did not, in both adults and foals. This preferred site lies close to a major ganglion of the autonomic nervous system.
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Rutberg, A. T., & Keiper, R. R. (1993). Proximate causes of natal dispersal in feral ponies: some sex differences. Anim. Behav., 46(5), 969–975.
Abstract: Abstract. Fifteen years of data on natal dispersal age and the context of dispersal for the feral ponies of Assateague Island, Maryland are presented. Ninety-seven per cent of males and 81% of females dispersed from their natal groups by 5 years of age. For animals that left their natal group, average age of dispersal was 20[middle dot]8 months for males and 24[middle dot]6 months for females. Male dispersal age was strongly and significantly correlated with number of peers in the natal group, and males dispersing with peers were significantly older than males dispersing without peers, suggesting that males delayed dispersal when peers were available for interaction. Female dispersal age was not influenced by number of peers, but was correlated with age of first reproduction. Factors not influencing dispersal age in either sex were presence of a younger sibling, maternal band transfers, and maternal age and dominance rank. The relatively high frequency of females failing to disperse from their natal groups is puzzling in light of data showing diminished fecundity in non-dispersing pony mares.
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Barton, R. A., & Whiten, A. (1993). Feeding competition among female olive baboons, Papio anubis. Anim. Behav., 46(4), 777–789.
Abstract: Abstract. Competition for food is thought to play a key role in the social organization of group-living female primates, leading to the prediction that individual foraging success will be partly regulated by dominance relationships. Among adult females in a group of free-ranging olive baboons, dominance rank was significantly correlated with nutrient acquisition rates (feeding rates and daily intakes), but not with dietary diversity or quality, nor with activity budgets. The mean daily food intake of the three highest-ranking females was 30% greater than that of the three lowest-ranking females, providing an explanation for relationships between female rank and fertility found in a number of other studies of group-living primates. The intensity of feeding competition, as measured by supplant rates and spatial clustering of individuals, increased during the dry season, a period of low food availability, seemingly because foods eaten then were more clumped in distribution than those eaten in the wet season. Implications for models of female social structure and maximum group size are discussed.
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Chalmeau, R., & Gallo, A. (1993). Social constraints determine what is learned in the chimpanzee. Behav. Process., 28(3), 173–179.
Abstract: A group of six chimpanzees was placed in a social learning situation, without training. The learning task was an operant conditioning situation; that is, a subject had to pull two handles simultaneously to cause a piece of fruit to fall into the cage. Only three individuals acquired the operant behaviour. For the operant individuals, social influences on the expression of the learning task were then examined; the dominant chimpanzee during feeding had an inhibiting effect when close to the operant subjects. Depending on the subject, social factors may influence not only the specific expression of what is learnt, but also the nature of what is learnt. Chimpanzees appear to experience situations differently: they develop an individual problem-solving strategy according to their social relationships even if the experimental procedure is the same for all.
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Herbert, T. B., & Cohen, S. (1993). Stress and immunity in humans: a meta-analytic review. Psychosomatic Medicine, 55(4).
Abstract: : This article presents a meta-analysis of the literature on stress and immunity in humans. The primary analyses include all relevant studies irrespective of the measure or manipulation of stress. The results of these analyses show substantial evidence for a relation between stress and decreases in functional immune measures (proliferative response to mitogens and natural killer cell activity). Stress is also related to numbers and percent of circulating white blood cells, immunoglobulin levels, and antibody titers to herpesviruses. Subsequent analyses suggest that objective stressful events are related to larger immune changes than subjective self-reports of stress, that immune response varies with stressor duration, and that interpersonal events are related to different immune outcomes than nonsocial events. We discuss the way neuroendocrine mechanisms and health practices might explain immune alteration following stress, and outline issues that need to be investigated in this area. Copyright (C) 1993 by American Psychosomatic Society
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Murray, M. G., & Brown, D. (1993). Niche Separation of Grazing Ungulates in the Serengeti: An Experimental Test. T. J. Anim. Ecol., 62(2), 380–389.
Abstract: 1. The niche separation of three species of alcelaphine antelope (wildebeest, topi and hartebeest) with similar body size was compared by measuring bite weight, bite rate, intake rate and selectivity of tame animals in plots containing grass at different growth stages. 2. On growing swards, hartebeest had a smaller bite weight and lower intake rate, and were also less selective of green leaf, than either topi or wildebeest. On senescent swards, hartebeest were more selective of leaf than the other two species. 3. Wildebeest had a faster bite rate than either topi or hartebeest on swards with low biomass and high protein content of green leaf (green flush). Bite weight and intake rate of wildebeest and topi were similar despite the difference in breadth of their incisor rows. 4. Topi were significantly more selective of green leaf than the other two species and were the only species to maintain a rapid bite rate on swards with high green leaf biomass. 5. The feeding experiments did not reveal significant cross-overs between species in the rate of food intake on different grass types, but each species was most proficient either in leaf selection or bite rate when feeding on grass swards in a particular growth stage. We suggest that growth stage is a primary determinant of niche separation. 6. In Serengeti, grazing ungulates which migrate are specialists of the earlier growth stages of grass which tend to be transient, while those that are residential specialize on late growth stages which are more enduring. The mobility of species, and the spatial and temporal dynamics of pastures containing different growth stages of grass, contribute to niche separation.
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