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ItemSexual segregation in kangaroos : testing alternative evolutionary hypotheses(University of Melbourne, 2006)Males and females of many animal species live apart for most of the year, coming together only for mating. The causes of this sexual segregation are still debated, with most research being focused on ungulates. However, if we are to develop robust and inclusive explanations for this phenomenon we need better coverage of other vertebrate taxa. In this thesis, I investigate the occurrence of sexual segregation in Australian marsupials, and describe and quantify this phenomenon in western grey kangaroos, Macropus fuliginosus, and red kangaroos, M rufus, at Hattah-Kulkyne National Park in north-western Victoria, Australia. Exploiting some of the unique life-history characteristics of kangaroos, which are ecological analogues of ungulates, I test a number of hypotheses that have been proposed to account for the evolution of sexual segregation in ungulates. A literature review revealed that sexual segregation occurs in some Australian marsupials, as it does in some eutherians, but is most pronounced among the larger macropods, as it amongst their eutherian counterparts, the ungulates. Sexual segregation appears to be associated with body size dimorphism and birth synchrony in marsupials, as it is in ungulates: all species that exhibited sexual segregation were either dimorphic in body size, highly synchronous in breeding, or both. Species that were monomorphic, and gave birth year-round or only moderately synchronously, did not exhibit segregation. Sexual segregation occurs at the social, spatial and habitat level in western grey and red kangaroos, and the degree of social and spatial segregation is greater than that of habitat segregation in both species. The magnitude and timing of sexual segregation in these species is influenced by the synchrony and timing of their mating activity. In the synchronously breeding western grey kangaroo, segregation peaks during autumn, when females are in lactational anoestrus. In red kangaroos, which mate year round, segregation is weaker but occurs throughout the year. Intraspecific variation in body size in kangaroos, particularly amongst males, allows predictions of the four main hypotheses for sexual segregation (predation risk, forage selection, activity budget and social factors) to be tested independently of each other. I found that, in accordance with the predation risk hypothesis, female western grey kangaroos made greater use of secure habitats, large males made greater use of nutrient-rich, open habitat, while small males were intermediate between females and large males in their habitat use. Consistent with the social factors hypothesis, same-sex groups composed of females only, and males of both small and large body size, predominated. The activity budget hypothesis is an unlikely explanation for social segregation in western grey kangaroos since two assumptions of this hypothesis were not supported by my results. First, differences in body size did not result in activity budget differences, and consequently activity asynchrony: individuals of different body size did not have different transition times between resting and feeding, sex- size classes were not least synchronized when in mixed-body size groups, and synchrony was not lower in mixed-body size than same-body size groups. Second, activity asynchrony did not cause mixed-body size groups to be less cohesive than same-body size groups. Although mixed-body size groups were fused for less time than same-body size groups, synchrony was not correlated with group stability. An examination of the fission/fusion dynamics of groups of western grey kangaroos confirmed that the social factors hypothesis, and more specifically, social affinity among males, best explains social segregation in western grey kangaroos. As predicted by the male social affinity hypothesis, large males joined groups composed of other males more frequently than expected. This study contributes significantly to our understanding of the behavioural ecology of kangaroos, and more generally, identifies key factors involved in the evolution of sexual segregation in vertebrates.
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ItemSexual segregation in kangaroos : testing alternative evolutionary hypotheses(University of Melbourne, 2006)Males and females of many animal species live apart for most of the year, coming together only for mating. The causes of this sexual segregation are still debated, with most research being focused on ungulates. However, if we are to develop robust and inclusive explanations for this phenomenon we need better coverage of other vertebrate taxa. In this thesis, I investigate the occurrence of sexual segregation in Australian marsupials, and describe and quantify this phenomenon in western grey kangaroos, Macropus fuliginosus, and red kangaroos, M rufus, at Hattah-Kulkyne National Park in north-western Victoria, Australia. Exploiting some of the unique life-history characteristics of kangaroos, which are ecological analogues of ungulates, I test a number of hypotheses that have been proposed to account for the evolution of sexual segregation in ungulates. A literature review revealed that sexual segregation occurs in some Australian marsupials, as it does in some eutherians, but is most pronounced among the larger macropods, as it amongst their eutherian counterparts, the ungulates. Sexual segregation appears to be associated with body size dimorphism and birth synchrony in marsupials, as it is in ungulates: all species that exhibited sexual segregation were either dimorphic in body size, highly synchronous in breeding, or both. Species that were monomorphic, and gave birth year-round or only moderately synchronously, did not exhibit segregation. Sexual segregation occurs at the social, spatial and habitat level in western grey and red kangaroos, and the degree of social and spatial segregation is greater than that of habitat segregation in both species. The magnitude and timing of sexual segregation in these species is influenced by the synchrony and timing of their mating activity. In the synchronously breeding western grey kangaroo, segregation peaks during autumn, when females are in lactational anoestrus. In red kangaroos, which mate year round, segregation is weaker but occurs throughout the year. Intraspecific variation in body size in kangaroos, particularly amongst males, allows predictions of the four main hypotheses for sexual segregation (predation risk, forage selection, activity budget and social factors) to be tested independently of each other. I found that, in accordance with the predation risk hypothesis, female western grey kangaroos made greater use of secure habitats, large males made greater use of nutrient-rich, open habitat, while small males were intermediate between females and large males in their habitat use. Consistent with the social factors hypothesis, same-sex groups composed of females only, and males of both small and large body size, predominated. The activity budget hypothesis is an unlikely explanation for social segregation in western grey kangaroos since two assumptions of this hypothesis were not supported by my results. First, differences in body size did not result in activity budget differences, and consequently activity asynchrony: individuals of different body size did not have different transition times between resting and feeding, sex- size classes were not least synchronized when in mixed-body size groups, and synchrony was not lower in mixed-body size than same-body size groups. Second, activity asynchrony did not cause mixed-body size groups to be less cohesive than same-body size groups. Although mixed-body size groups were fused for less time than same-body size groups, synchrony was not correlated with group stability. An examination of the fission/fusion dynamics of groups of western grey kangaroos confirmed that the social factors hypothesis, and more specifically, social affinity among males, best explains social segregation in western grey kangaroos. As predicted by the male social affinity hypothesis, large males joined groups composed of other males more frequently than expected. This study contributes significantly to our understanding of the behavioural ecology of kangaroos, and more generally, identifies key factors involved in the evolution of sexual segregation in vertebrates.