We reviewed the literature on sexual segregation in polygynous ungulates in an effort to clarify terms and concepts, summarize recent information that supports or discredits three broadly defined hypotheses, and suggest directions for future research that should help resolve when and why the sexes segregate in these large mammals. The hypotheses discussed include those based on intersexual differences in energetics and security (reproductive-strategy hypothesis), body size dimorphism and dietary requirements (sexual dimorphism-body size hypothesis), and social mechanisms (social-factors hypothesis). These hypotheses represent ecological, physiological, and social perspectives and are not mutually exclusive. Most evidence reviewed supported the reproductive-strategy hypothesis. Less support was available for either the sexual dimorphism-body size hypothesis or the socialfactors hypothesis. Nonetheless, most available evidence is provided by field studies that contend with many confounding variables. We suggest several areas of future study that may serve as critical tests and are likely to be productive in resolving why sexual segregation occurs in polygynous ungulates.

Subsistence hunting and commercial exploitation directly influence wildlife populations in many regions of Central and South America. Where prey populations are exploited, the foraging ecology of top-level predators can be effected negatively. This study assessed the food habits and prey selection of jaguar Panthera onca and puma Puma concolor within hunted and non-hunted segments of the Maya Biosphere Reserve (MBR), Guatemala. Food habits were determined from analysis of 76 jaguar and 145 puma scats collected within hunted and non-hunted areas of the MBR from February 2000 to August 2001. Diets of jaguar and puma were compared (1) within species between areas with and without hunting to evaluate effects of subsistence hunting, and (2) between species to evaluate resource partitioning between these sympatric carnivores. Origin of predator scats was determined from mitochondrial DNA, diets were determined from prey remnants found within scats, and frequency of prey in scats was compared to expected values based on prey density estimates to test the hypothesis that diets of jaguar and puma were selective. Densities of major prey species were estimated using line-transect sampling. White-lipped peccary Tayassu pecari, collared peccary Tayassu tajacu and brocket deer Mazama sp. were less abundant, and coatis Nasua nasua more abundant, in the hunted area than in the non-hunted area. Jaguar and puma in both hunted and non-hunted sites obtained similar dietary contributions from large prey to their respective diets despite differences in the abundance of these prey species. Diets of jaguar and puma, as measured by percentage biomass occurrence of prey species, did not differ between hunted and non-hunted areas. Jaguar diets were dominated by medium-sized prey, particularly armadillos Dasypus novemcinctus and coatis, in both hunted and non-hunted areas. Medium-sized mammals also were prominent in puma diets, but large mammals constituted approximately 50% of prey biomass in both hunted and non-hunted areas. Deer Odocoileus virginianus and Mazama sp. and large rodents Agouti paca and Dasyprocta punctata were the most important prey of puma. Dietary overlap between jaguar and puma in both hunted and non-hunted areas was low.

Sexual segregation in ungulates has important conservation and theoretical implications, but despite numerous studies, the impetus for this behavioral pattern remains a topic of debate. Sexual segregation hypotheses can be broadly grouped into social and ecological explanations, but only ecological explanations can adequately describe why sexes use different areas and habitats. The reproductive strategy hypothesis (RSH) and forage selection hypothesis (FSH) are leading ecological explanations, and although both have received support in the literature, neither the collective basis for that support nor overlap between these hypotheses has been adequately evaluated. This review analyzed seasonal sex comparisons of habitat forage quantity (n=66), quality (n=67), and diet (n=63) from peer-reviewed studies of north temperate ruminants to test predictions of each hypothesis. Empirical data supported predictions of the RSH, but did not support two of three key predictions of the FSH. Males used habitats with greater forage quantity significantly more than females. But, contrary to predictions of the FSH, females did not use habitats with superior forage quality nor consume higher-quality diets more than males. Sexes typically used habitats and consumed diets of similar quality, and when differences were reported, males used higher-quality habitats significantly more than females. Results refute FSH arguments that differences in dietary requirements associated with sexual dimorphism are a universal explanation for sexual segregation in ungulates, but the physiological mechanism on which the FSH is predicated may explain why males consume poorer-quality diets when high-quality forage is scarce. The FSH, therefore, operates at a proximate level because it explains diet and habitat selection by males under certain environmental conditions, but multiple environmental factors may influence sexual segregation, and no single proximate explanation adequately describes this behavioral pattern. The RSH explains sexual segregation as the evolutionary response to differences in reproductive strategies: males choose habitats to maximize energy gains in preparation for rut, and females select habitats with combinations of resources that contribute to offspring survival. Consequently, the RSH provides an ultimate explanation that can be used to explain and interpret studies of sexual segregation in ungulates.

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