Added: Alfred Ledford - Date: 17.12.2021 20:19 - Views: 16491 - Clicks: 986
Holly A. MacCormick, Daniel R. MacNulty, Anna L. Aggression is ubiquitous, influencing reproduction through inter- and intraspecific effects in ways that reflect life-history strategies of species.
In many social mammals, females remain in their natal group for life, whereas males emigrate and compete for rank in other social groups. Competition for rank is inherently risky. Therefore, it has long been hypothesized that risks of injury depend on an individual's sex, rank, and age in ways that maximize an individual's reproductive output. However, studies quantifying such risks have been lacking.
We analyzed 20 years of long-term data on wounds among olive baboons Papio anubis in Gombe National Park, Tanzania. Males received ificantly more wounds than female baboons, and both sexes received the most wounds at ages when they competed most intensely for rank.
Immature females received more wounds than immature males in their natal groups, and immature females were more likely to be wounded by females than were immature males. Males in their natal group were wounded less often than immigrant males of the same age.
The risk of wounding did not depend on rank in females but rose with rank in immigrant males. Lastly, females received ificantly more wounds when cycling not pregnant or lactating. This study is among the first to quantify the risk of injury for competitors of different sexes, ages, and ranks in social groups.
Our support the prediction that individuals target aggression toward present and future competitors and suggest that sexual coercion increases the risk of wounding in cycling females. Competition and sex are inextricably linked. This linkage broadly spans taxa and affects the very structure and evolutionary dynamics of species. In social species, the relationship between competition and sex depends on such factors as reproductive strategies of the sexes, age and social rank of individuals, and the life history of the species.
Studies of related phenomena include primates Clutton-Brock and Harvey ; Muller and Wranghambirds Wiley ; Arceserodents Dobson ; Edelmancarnivores Bekoff et al. However, comparatively few studies have directly quantified the risks of competition by linking competition with the incidence of physical wounding. Social mammals, specifically primates, provide an excellent system to explore this question because of differences between the sexes that apply to many social mammalian species; females remain in their natal group for life i. In many female-philopatric species, female rank is largely determined by birth order and maternal rank Kawamura ; Koford ; Koyama ; Cheney ; Holekamp and Smale In contrast, male rank rises or falls according to the outcome of pairwise interactions between males that reflect the competitor's body size and physical condition Hausfater ; Packer b ; van Noordwijk and van Schaik ; Haley et al.
High-ranking males have preferential access to females in many social mammalian species with dominance hierarchies e. However, individuals in their natal group often show reduced sexual attraction toward close kin Packer a ; Pusey ; Bolhuis et al.
Thus, males typically do not engage in intrasexual competition for females until dispersing to new groups Packer a ; Pusey and Packer Thus, direct aggressive competition is often most intense between young, high-ranking immigrant males Packer b ; Yoccoz et al. Competition among females generally involves access to resources rather than mates Trivers Female per capita reproductive success often declines with increasing group size van Noordwijk and van Schaik [macaques]; Packer et al.
Thus, infant females often represent future competition for adult females, whereas infant males will eventually disperse to compete elsewhere. Therefore, adult females are expected to employ behaviors that limit the survival of unrelated juvenile females, though documented examples of adult females selectively harassing immature females remain rare for toque [ Macaca s.
Studies of intersexual aggression suggest that males are the predominant aggressor and disproportionately wound females Muller and Wrangham Smuts found that female olive baboons were the targets of male aggression approximately once every 17 h. Adult male olive baboons are formidable opponents, and males are approximately twice as large as females and have canines about a third longer and wider than females Virgadamo et al. Male olive baboons are also formidable relative to other animals. Male baboons have canine teeth whose relative size can exceed those of felids, and primates in general can have canine teeth that are as long as carnivores, relative to their body size Lucas ; Plavcan and Ruff Females may be at greater risk of wounding during particular times if their reproductive state e.
Olive baboons are one of many species that exhibit sexual dimorphism; therefore, the potential costs of mating are of particular interest given the disparities between male and female body size and weaponry and the potential for males to monopolize and sexually coerce females Clutton-Brock and Parker ; Muller and Wrangham Agonistic interactions between individuals inevitably involve risks of physical injury Clutton-Brock et al. Aggressive encounters are potentially the most costly between young adult males that are fully grown and have not yet worn down their weapons Packer b.
In this paper, we analyze the age- sex- and rank-specific risks of wounding in a long-term field study of olive baboons Papio anubis in Gombe National Park, Tanzania, to test the following hypotheses: 1 If wounding differs between sexes, males should receive more wounds than females.
Note, we do not expect to see a clear Lady looking sex Olive between wounding and rank in females because once a female's rank is established, it remains relatively stable for life, reducing female—female competition, and because injuries from males could potentially obscure any possible effect of rank on risk of wounding.
Gombe National Park, Tanzania, is comprised of a chain of steep valleys flanked by Lake Tanganyika to the west and a rift escarpment to the east van Lawick-Goodall ; Packer a. Data on wounding and dominance rank are available from January to November Tanzanian field assistants collected all data under the supervision of D. Monthly reports provide details on the date and of wounds for each baboon and indicate the cause of wounding when witnessed 93 of cases of wounding.
In addition to monthly reports, daily demographic records also note the of fresh wounds. Analyses where the sex of the attacker is known, and those assessing sexual coercion, are done separately for the of wounding events and the of wounds received in a year. A distinction is drawn between annual wounding events and the annual of wounds because the likelihood of receiving a wounding event versus several wounds at once may vary for individuals of different sexes, ages, and ranks. An individual may receive many wounds in a single aggressive encounter or may receive few wounds in multiple aggressive encounters over the course of several different days.
Injuries typically persisted for weeks or months, although the act of wounding was rarely observed. Contact with humans is minimal at Gombe: all study troops have restricted home ranges in the center of the national park and are completely isolated from local villagers. Human contact was limited to the Jane Goodall Institute research staff, Tanzania National Park staff, tourists, and itinerant local fisherman. All staff were strictly prohibited from harassing the baboons, and tourists must maintain a distance of at least 10 m from wildlife.
Although human-caused injuries were recorded, they were easily identifiable e. Of these 10 wounds, 3 baboons were killed after humans had been attacked, 2 were injured after stealing food and destroying property, 2 were injured after stealing fish from fisherman, 1 was shot by park rangers, and the remaining 2 were injured for unknown reasons. Although, chimpanzee-inflicted wounds can be similar to baboon-inflicted wounds, the Gombe chimpanzees are subject to such intensive observation that chimpanzee attacks on baboons are well documented and could be excluded from the analysis.
Although present in Gombe, leopards are rare: In more than 20 years of daily field observations, there is no definitive evidence of a leopard attack on either olive baboons or chimpanzees Wilson et al. Wounds caused by accidents e. To minimize the inclusion of such injuries, we only included wounds that involve a break in the skin, cut, or puncture in the total data set of wound events. Thus, the vast majority of injuries in our analysis could be inferred Lady looking sex Olive have resulted from bites by conspecifics.
Annual dominance ranks were determined by the outcomes of pairwise interactions involving displacements from food sources or overt aggression. Thus, top-ranked individuals would have relative ranks of 1. These scores were sorted into 5 : 0. To address when females were at greatest risk of injury, we noted both the of injured females and of wounds to females that were cycling, pregnant, or lactating.
Note that the visual assessment of the presence of a sexual swelling when females are sexually receptive could be imperfect, especially during times of transition between reproductive stages. We then calculated an expected ratio of injured females and wounds according to the typical time females spent in each reproductive state: the interbirth interval is about 23 months, including approximately 6 months of cycling, 6 months of gestation, and 11 months of lactation. Female olive baboons reach menarche around 4—5 years of age, and cycle until approximately 23 years of age, when their fertility declines and eventually ceases around 24 years of age Smuts and Nicholson ; Packer et al.
Females included in the female reproductive state analysis were between 3 and 22 years of age. The of Lady looking sex Olive females and the total of wounds recorded for cycling i. Expected ratios for each of the were calculated according to average duration of time females spend in each reproductive state: 6 months of cycling, 6 months of gestation, and 11 months of lactation. Annual wounding rates were scored repeatedly up to 21 consecutive years for some animals for individuals and analyzed using generalized linear mixed models GLMMs with a binomial error distribution and with individual identity fitted as a random effect.
All models included a compound symmetric correlation structure, which assumed that all observations within individuals were equally correlated on average. Models were estimated with adaptive Gaussian quadrature with parameters estimated from maximum likelihood, and ificance of effects was determined by an approximate z -test. We used piecewise linear splines to test for nonlinear effects of age as measured in discrete 1-year increments on the probability that an individual was wounded in a given year.
Piecewise splines consist of a covariate e. Each line segment does not have its own intercept; rather, a spline regression model includes only a single intercept that is adjusted by the spline variable to accommodate a change in slope. This keeps the regression line continuous i. To determine the presence and position of age-specific thresholds in wounding, we evaluated a set of competing GLMMs for each of 3 demographic classes: female, natal male, and immigrant male.
Each set included models with a single knot placed at 6—10 different ages females 3—12 years; natal males 2—7 years; immigrant males 6—15 years and a model with no knot, representing the hypothesis of no threshold in wounding.
We selected knots a priori according to the age distribution of each demographic class, which was consistent with guidelines for the efficient use of knots Wold ; Eubank By definition, knots selected a priori are fixed i. The variables were constructed so that the estimated coefficients measure the slopes for each segment before and after a given knot. Our scope of inference concerned the population, so we performed model selection using marginal likelihoods.
We calculated population-averaged fitted values from best fit GLMMs by deriving marginal expectations of the responses averaged over the random effects but conditional on the observed covariates.Lady looking sex Olive
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