Browsing by Subject "Chimpanzee"

Now showing 1 - 4 of 4
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    Cooperation, Competition, and Killing: Reproductive strategies of chimpanzees (Pan troglodytes)
    (2023-08) Massaro, Anthony
    Group-living commonly involves tensions between conflict and cooperation. Group members need one another to survive, but also compete for access to key resources such as food and mates. To better understand reproductive strategies in group-territorial species with sex-biased dispersal, I used decades of data from Gombe National Park, Tanzania to test hypotheses regarding how and why chimpanzees (Pan troglodytes) cooperate, compete, and fight. First, I found that male chimpanzees exhibit a consistently high degree of participation in boundary patrols (mean=75%) and that the best predictors of participation in patrols were sighting frequency and participation in hunting bouts, indicating a mutualistic payoff structure for male territorial effort. Second, I found that female chimpanzees produced copulation calls more frequently when they were nulliparous, and in the early days of their swelling. Thus, these calls likely function as an anti-infanticide strategy, inducing otherwise uninterested males to mate and maximizing the pool of potential sires. Females also called less frequently in the presence of higher-ranking females, indicating that intrasexual competition plays a role in call production. Third, I found that males killed by other chimpanzees suffered a higher-than-expected rate of genital wounding, but during non-fatal fighting, only in one of four communities (Kasekela) did males experience a higher-than-expected rate of genital wounds. Females in all four study communities experienced a higher-than-expected rate of genital wounds, indicating that genital wounding is an unlikely alternative to lethal aggression. Finally, I found that lethal aggression was more common in Mitumba than Kasekela. As a smaller community, Mitumba has fewer females and thus less overlap between reproductively active females and a greater opportunity to monopolize mating opportunities. Overall, this work emphasizes the importance of within-group reproductive competition.
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    Dynamics of intergroup competition in two neighboring chimpanzee communities.
    (2010-07) Mjungu, Deus Cyprian
    Among group-living animals, larger groups tend to win intergroup fights. In chimpanzees, larger groups are likewise believed to win most intergroup interactions. Because intergroup fights in chimpanzees sometimes lead to the death of individuals, larger groups are expected to eliminate smaller groups - as observers witnessed in Gombe, in the 1970s, when the Kasekela group exterminated the smaller Kahama group. However, in some cases, smaller groups continue to persist alongside larger groups. How smaller groups are able to do this is poorly known. Gombe National Park provides a unique natural settings for examining how smaller groups of chimpanzee manage to survive against difficult odds. Currently the park contains two neighboring habituated groups: the large Kasekela group and the much smaller Mitumba group. Despite the Mitumba group being sandwiched by the Kasekela group and cultivated lands, the Mitumba group has not only survived but also increased in size over the past 10 years. I explored how the smaller Mitumba group managed to survive alongside the larger group. First, I investigated the factors that caused changes in range size and population of the Mitumba group over the past 25 years. I found that, both anthropogenic habitat destruction and intergroup competition influenced the range size of the Mitumba chimpanzee group. Then, I examined whether large group size conferred competitive advantage by examining the range size and range use of two neighboring groups and outcome of territorial contests. I found that, group size influenced the range use of neighbors. Each group used more contested area when numerical strength was in its favor. Furthermore, I found that, the number of males in a party and not the location of the range determined whether the Mitumba chimpanzees would counter-call. Mitumba chimpanzees were less likely to call when in a party contained zero or one male. However, the probability of counter-calling increased when number of males in a party increased. My study suggests that, anthropogenic habitat destruction and intergroup competition could interact in a complex way to influence the survival and reproduction of individuals in this population. Furthermore, my study also suggests on the importance of numerical strength in intergroup competition in chimpanzees.
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    Male reproductive strategies in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes)
    (2023-05) Mouginot, Maud
    Bonobos are often portrayed as peaceful while chimpanzees are described as aggressive. This contrast has greatly influenced efforts to explain the evolution of war and peace in human societies. However, studies reported that males have higher reproductive skew — the stage in which some males obtain a disproportionate share of paternities — in bonobos than chimpanzees. Because reproductive skew is usually associated with intense contest competition among males for mates, how male bonobos manage to achieve such high reproductive skew despite having what seemed to be less aggressive relations with other males is intriguing. Nevertheless, while researchers have conducted extensive studies in male reproductive strategies in chimpanzees, less is known about bonobos, and how they compare to chimpanzees. Because the current literature does not provide a direct comparison of rates of aggression with similar sampling methods, we still do not know the extent to which these rates differ between these two species. One study directly compared reproductive skew in bonobos and chimpanzees, however, while they included data from five chimpanzee communities, they had data from only one bonobo community. Thus, we need more data to better understand patterns of reproductive skew within bonobos and between bonobos and chimpanzees. Finally, reproductive success can also depend on non-aggressive reproductive strategies. Male-immature interactions have been observed in promiscuous species, such as female-bonded cercopithecoid monkeys (such as rhesus macaques and olive baboons) and chimpanzees. Few studies reported male-immature interactions in bonobos, and none explored how those interactions might affect male reproductive success. In my dissertation, I aimed to fill those gaps by first directly comparing bonobos from the Kokolopori Bonobo Reserve, Democratic Republic of Congo, and chimpanzees from Gombe National Park, Tanzania, conducting generalized linear mixed models (GLMM) within an information theoretic model selection approaches. I found that despite the popular image of bonobos as being more peaceful than chimpanzees, while male chimpanzees had a higher rate of male to female aggression, male bonobos received higher rates of female aggression and, surprisingly, exhibited higher rates of aggression among males than chimpanzees. Moreover, I found that the best predictor of male bonobo copulation rate was the rate of aggression towards females, even though such aggression occurred infrequently (16 interactions out of 2,047 hours of observation). I then re-examined skew patterns using paternity data from published work and new data from Kokolopori and Gombe and reviewed the different mechanisms underlying patterns of reproductive skew. Using the multinomial index (M), I found considerable overlap in skew between the species, but the highest skew occurred among bonobos. My detailed comparison of data from Pan highlights that reproductive skew models should consider male-male dynamics including the effect of between-group competition on incentives for reproductive concessions, but also female grouping patterns and factors related to male-female dynamics including the expression of female choice. Finally, comparing male-immature interactions in bonobos at Kokolopori and chimpanzees at Gombe, I found that male bonobos play more with immatures than male chimpanzees, but I did not find any consistent difference in grooming duration among males and immatures between the two species of Pan. I did not find strong evidence that male bonobos interact with immatures as a mating or paternal effort. However, I found that males were more inclined to copulate with their closer associates and to play and groom with their close associates’ offspring.
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    Paternity and father-offspring relationships in wild chimpanzees, Pan troglodytes schweinfurthii.
    (2010-03) Wroblewski, Emily Elizabeth
    Hamilton's seminal theory of kin selection asserts that because relatives share a certain proportion of genes, individuals can increase their inclusive fitness by helping and/or not harming kin, as long as the benefits to kin outweigh the costs to the individual. We would expect animals to attain maximal inclusive fitness by discriminating both the available maternal and paternal kin from non-kin in their social groups. The primate order is a useful taxon in which to study kin selection and kin discrimination because most primates live in permanent social groups with both kin and non-kin between which to discriminate, and their complex social interactions provide many opportunities to both hurt and aid others. However, the prevailing view has been that the discrimination of paternal kin does not occur in most species. Despite emerging studies that suggest otherwise, study of paternal kin discrimination thus far has been limited in primates. Furthermore, study has been restricted to matrilineal species with male-biased dispersal. Paternal kinship could also be important in a patrilineal species such as chimpanzees as males will remain with fathers and other paternal kin for life, as will females until they disperse. Thus, this study aimed to further our understanding of importance of paternal kinship in social behavior by examining the most direct paternal relationship, that of fathers and offspring, in the chimpanzees of Gombe National Park, Tanzania. Identifying fathers and offspring and characterizing their relationship is a necessary first step on the way to testing for kin discrimination amongst non-descendent paternal kin. Thus, in Chapter 1, I first determined paternal relationships and explored patterns of male reproductive success relative to dominance rank and the priority of access model, as well as fathers' mating strategy and age. Then in Chapter 2, I examined whether fathers showed parental investment in their juvenile and adolescent sons. Finally, in Chapter 3, I investigated whether there was inbreeding avoidance between fathers and daughters.