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"Ring-tailed lemurs (Lemur catta) are an excellent species to study when sex differences in feeding ecology develop, if differences in immatures mirror those in adults, and how sex differences are related to reproductive costs and resource partitioning. The ring-tailed lemur is a monomorphic primate endemic to southwestern Madagascar that lives in multi-male multi-female social groups where females dominate males in all contexts (Jolly 1984; Kappeler 1990). They feed from a diverse diet composed primarily of ripe fruit and leaves, and the inconsistent rainfall of southwestern Madagascar is correlated with unpredictability in resource availability (Dewar and Richard 2007). "
[Show abstract][Hide abstract] ABSTRACT: Sex differences in feeding ecology may develop in response to fluctuations in physiological costs to females over their reproductive cycles, or to sexual size dimorphism, or function to minimize feeding competition within a group via resource partitioning. For most mammal species, it is unknown how these factors contribute to sex differences in feeding, or how the development of males and females reflects these intraspecific feeding differences. We show changes in dietary composition, diversity, overlap, and foraging behavior throughout development in ring-tailed lemurs (Lemur catta) and test how the development of sex differences in feeding is related to female costs of reproduction and year-round resource partitioning. Sex differences in dietary composition were only present when females were lactating, but sex differences in other aspects of feeding, including dietary diversity, and relative time spent feeding and foraging, developed at or near the time of weaning. Sex difference in juveniles and subadults, when present, were similar to the differences found in adults. The low year-round dietary overlap and early differences in dietary diversity indicate that some resource partitioning may begin with young individuals and fluctuate throughout development. The major differences between males and females in dietary composition suggest that these larger changes in diet are closely tied to female reproductive state when females must shift their diet to meet energetic and nutritional requirements.
"Female aggression in spotted hyenas is adaptive in the context of intense feeding competition and has also been explained as an extreme form of maternal investment due to the exceptionally long time that the specialized bone-crushing feeding apparatus takes to develop in this species, and thus the need of maternal aggressive support during feeding (Watts, Tanner, Lundrigan, and Holekamp, 2009). Like spotted hyenas, females in many lemur species tend to be dominant over males and, at least in some cases, this dominance is achieved through or associated with higher rates of female aggression (Kappeler, 1990; Meredith, 2012). Female dominance in lemurs may be associated with a high benefit/cost ratio for aggression relative to males: Females may gain more from competitive aggression over food than males because of low food availability in Madagascar and the constraints it poses on female reproduction (Dunham, 2008); in addition, the costs of female aggression may be lower in lemurs than in other primates because most lemurs are sexually monomorphic. "
[Show abstract][Hide abstract] ABSTRACT: An optimization analysis of human behavior from a comparative perspective can improve our understanding of the adaptiveness of human nature. Intra-specific competition for resources provides the main selective pressure for the evolution of violent aggression toward conspecifics, and variation in the fitness benefits and costs of aggression can account for inter-specific and inter-individual differences in aggressiveness. When aggression reflects competition for resources, its benefits vary in relation to the characteristics of the resources (their intrinsic value, abundance, spatial distribution, and controllability) while its costs vary in relation to the characteristics of organisms and how they fight (which, in turn, affects the extent to which aggression entails risk of physical injury or death, energetic depletion, exposure to predation, psychological and physiological stress, or damage to social relationships). Humans are a highly aggressive species in comparison to other animals, probably as a result of an unusually high benefit-to-cost ratio for intra-specific aggression. This conclusion is supported by frequent and widespread occurrence of male-male coalitionary killing and by male-female sexual coercion. Sex differences in violent aggression in humans and other species probably evolved by sexual selection and reflect different optimal competitive strategies for males and females.
"Since the rate of aggression in this species is low, however, there could be other behaviors, more complex and difficult to identify, that indicate dominance; two possibilities would be scent-marking and submission (Kraus et al. 1999; Lewis 2006; Pochron et al. 2005). Our analysis of the contexts in which aggressions were initiated by female crowned sifakas, with most observed aggressions happening outside the feeding phases, confirms that female dominance in lemurs is not related only to priority access to resources (Kappeler 1990). Despite the limited number of observation days, the low intergroup encounter rate we report is consistent with observations in other sifaka species (Irwin 2006; Benadi et al. 2008). "
[Show abstract][Hide abstract] ABSTRACT: We carried out a study of the social behavior and dominance hierarchy in three groups of crowned sifaka (Propithecus coronatus) in the Antrema Forest Station in north-west Madagascar. Data were collected from April to June 2009 and October to November 2009 using all-occurrence sampling. During 273 hours of observation, the majority of social behaviors observed were grooming interactions (39%), followed by agonistic behavior (25%), play (19%), scent-marking (9%), call-localization (5%) and approach (3%). A social hierarchy was maintained in the groups of P. coronatus, with females dominating the males. Although different groups of P. coronatus defended their territories against other neighboring groups of the same species, the most frequently observed outcome of intergroup encounters was tolerance. In addition, we detected no significant change of sifaka behavior during interspecific encounters with rufous brown lemur (Eulemur rufus) or with mongoose lemur (Eulemur mongoz), suggesting these two species live in total sympatry with P. coronatus.