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Intrasexual Competition (intrasexual + competition)
Selected AbstractsSize-Related Advantages for Reproduction in a Slightly Dimorphic Raptor: Opposite Trends between the SexesETHOLOGY, Issue 12 2007Fabrizio Sergio Despite many comparative analyses and more than 20 proposed hypotheses, there is still little consensus over the factors promoting the evolution of reversed sexual dimorphism (RSD) in raptorial species. Furthermore, intrapopulation studies, which may elucidate how RSD is maintained once evolved, have been surprisingly scarce and only focused on a handful of species with medium to high dimorphism. We examined the reproductive advantages associated with body size and condition, measured in the pre-laying period, in a diurnal raptor with low sexual dimorphism, the black kite (Milvus migrans). The study population was essentially monomorphic in size. For females, there was an evidence of reproductive benefits associated with larger size and/or with better body condition. Larger females had also access to higher quality partners and territories, consistent with the ,intrasexual selection' hypothesis, by which members of the larger sex enjoy size-related advantages in intrasexual competition over a scarce resource, the smaller sex. Opposite trends emerged for males: smaller, leaner males had higher breeding output, consistent with the ,small efficient male' hypothesis. Overall, the fact that we observed in an essentially monomorphic population the same selection pressures previously found in species with marked dimorphism suggests that such reproductive advantages may be counterbalanced in our study model by opposite selection pressures during other stages of the life cycle. This casts some doubts on the evolutionary significance of studies focusing exclusively on reproduction and calls for the need of more comprehensive analyses incorporating trait-mediated differentials in survival and recruitment. [source] Interpopulation Variation in the Social Organization of Female Collared Lizards, Crotaphytus collarisETHOLOGY, Issue 11 2003Troy A. Baird We tested the hypotheses that levels of intrasexual aggression and the social structure among neighboring females differed in two central Oklahoma populations of collared lizards, Crotaphytus collaris, and examined the extent to which variation in aggression might be related to differences in the availability of arthropods, elevated perches used by females to scan for prey, and crawlspace refugia. Because both the costs of aggression and access to resources may influence female fitness, we also compared growth and survival rates and the number of clutches produced. At Morningside Farms Ranch (MS), lizards occupied naturally-formed sandstone washes with naturally-sculpted irregular topographies, whereas they inhabited homogenous fields of boulders used to construct flood control spillways at the Arcadia Lake Dam (AL). The frequency of intrasexual aggression was markedly higher at MS, and groups of MS females had social hierarchies structured by size and age with older females defending territories, whereas no such social structure was apparent at AL. Moreover, experimental removal of individuals from female groups resulted in more pronounced changes by the remaining females at MS than at AL. Elevated perches and crawlspace refugia were much less abundant at MS. Arthropod availability was similar at the two sites, but at AL arthropods were clustered near the edges of rock patches where elevated perches overlooking adjacent grassy areas were particularly abundant. MS females showed lower rates of survival, and growth during the first year (when growth is highest) than AL females, whereas the number of clutches produced by females at the two sites was similar. Our results suggest that variation in the availability of perch rocks may have resulted in differences in female social structure at the two sites, and relaxed intrasexual competition for perches may have resulted in higher female fitness at AL. [source] Within-sex density dependence and population dynamics of red squirrels Sciurus vulgarisJOURNAL OF ANIMAL ECOLOGY, Issue 1 2004Luc A. Wauters Summary 1Social organization and dispersal of red squirrels (Sciurus vulgaris L.) differ between sexes, and intrasexual competition is intense. Therefore, we predicted that demographic parameters should be gender-specific: that is density-dependent factors will be more strongly related to density of the same sex than to density of the opposite sex. We studied the relative importance of within- and between-sex density-dependent factors and of density-independent factors (habitat type, food abundance, winter temperature) on different demographic parameters, in two populations in northern Belgium. 2Spring density of males was positively correlated with tree-seed abundance in the previous year, but this was not the case for females. None of the population parameters we measured differed between habitats, indicating that the same density-dependent and density-independent mechanisms prevailed in coniferous and deciduous habitat. 3Within each sex, we found several demographic parameters that were dependent on the densities of the same sex; however, none of these parameters was found to be dependent on the density of the opposite sex. 4Reproductive rate increased with food abundance and decreased with female density. Adult survival of females decreased with female density in autumn,winter, while survival of adult males in spring,summer increased with the size of the previous year's seed crop. 5Immigration rate of males was higher in spring than in autumn, and spring immigration increased with food abundance. Male recruitment rate, in both seasons, increased with food abundance, but was male density dependent. However, spring,summer loss rates also increased when food supplies were good, suggesting that despite high food availability, emigration of juvenile and subadult males increased when intrasexual competition was intense. Recruitment rate of females decreased with increasing female density. After a good seed crop, more subadult females dispersed, but their settlement success (recruitment) was lower at high female density. 6Seed crop size positively affected red squirrel densities through increased reproduction, immigration and adult survival of males, but density-dependent reproduction and within-sex density-dependent recruitment of locally born juveniles and dispersing subadults limit the fluctuations in numbers and regulate densities in winter,early spring, as well as in summer. [source] Sexual selection for male dominance reduces opportunities for female mate choice in the European bitterling (Rhodeus sericeus)MOLECULAR ECOLOGY, Issue 5 2005M. REICHARD Abstract Sexual selection involves two main mechanisms: intrasexual competition for mates and intersexual mate choice. We experimentally separated intrasexual (male,male interference competition) and intersexual (female choice) components of sexual selection in a freshwater fish, the European bitterling (Rhodeus sericeus). We compared the roles of multiple morphological and behavioural traits in male success in both components of sexual competition, and their relation to male reproductive success, measured as paternity of offspring. Body size was important for both female choice and male,male competition, though females also preferred males that courted more vigorously. However, dominant males often monopolized females regardless of female preference. Subordinate males were not excluded from reproduction and sired some offspring, possibly through sneaked ejaculations. Male dominance and a greater intensity of carotenoid-based red colouration in their iris were the best predictors of male reproductive success. The extent of red iris colouration and parasite load did not have significant effects on female choice, male dominance or male reproductive success. No effect of parasite load on the expression of red eye colouration was detected, though this may have been due to low parasite prevalence in males overall. In conclusion, we showed that even though larger body size was favoured in both intersexual and intrasexual selection, male,male interference competition reduced opportunities for female choice. Females, despite being choosy, had limited control over the paternity of their offspring. Our study highlights the need for reliable measures of male reproductive success in studies of sexual selection. [source] Distress about mating rivalsPERSONAL RELATIONSHIPS, Issue 3 2000DAVID M. BUSS This research tested the evolutionary psychological hypothesis that men and women would be most distressed about threats from rivals who surpass them on sex-linked components of mate value. Six predictions were tested in samples from three cultures, the United States (N= 208), the Netherlands (N= 349), and Korea (N= 174). Five predictions were supported in all three cultures. Korean, Dutch, and American men, more than corresponding women, report greater distress when a rival surpasses them on financial prospects, job prospects, and physical strength. Korean, Dutch, and American women, in contrast, report greater distress when a rival surpasses them on facial and bodily attractiveness. The cultures differed on some variables. Korean women and men, for example, differed from Americans and Dutch in reporting more distress over rivals who had better financial prospects, better job prospects, and higher status and prestige. Americans exceeded Koreans in reporting distress when rivals had more attractive faces and bodies, whereas the Dutch exceeded the other cultures in reporting more distress when rivals had a better sense of humor. Discussion focuses on possible proximate psychological mechanisms underlying distress over rivals and the theoretical importance of intrasexual competition. [source] Ritualized combat as an indicator of intrasexual selection effects on male life history evolutionAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 1 2010Brent M. Graves Trade-offs between survival, growth, current reproduction, and future reproduction influence life history evolution, leading to adaptive timing of investment in various strategies. If engagement in costly intrasexual contests to gain better access to mates is an important form of male reproductive investment, then the expression of characters that promote success in this process should be influenced by their fitness effects across the lifespan. To test this prediction, the ages at which human (Homo sapiens) males exhibit the greatest investment in morphological, behavioral, and physiological characters associated with intrasexual competition was estimated by examining the ages at which males succeed in a form of ritualized combat. The average age of international boxing champions was in the latter half of the twenties, and titles were held for about 2 years on average. Thus, peak investment in traits that enhance intrasexual competition abilities appears to coincide with ages at which males have highest reproductive success. Additionally, larger males reached peak probability of success in this ritualized combat at ages about 2.6 years greater than smaller males. Because body size is highly heritable and there is strong positive assortative mating relative to this character among humans, this may indicate a polymorphic set of reproductive strategies produced through maintenance of coadapted gene complexes. Am. J. Hum. Biol., 2010. © 2009 Wiley-Liss, Inc. [source] Finger length ratios (2D:4D) in anthropoids implicate reduced prenatal androgens in social bondingAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2010Emma Nelson Abstract The second-to-fourth digit ratio (2D:4D) has been proposed as a biomarker reflecting prenatal androgen effects (PAE), such that individuals with lower ratios have experienced higher PAE than those with higher ratios. 2D:4D has been correlated with a number of sex-linked traits in humans such as aggression, promiscuity, and competitiveness. In addition, polygynous societies reportedly have lower 2D:4D (higher PAE) than more monogamous populations. This evidence suggests that PAE may be implicated in the development of sexually selected behaviors in humans. To place 2D:4D research into a broader context, we test the relationship between digit ratios and behavior across nonhuman anthropoids; polygynous species, with higher levels of intrasexual competition, should have more pronounced markers of PAE (lower 2D:4D) than pair-bonded species. Our results accord with those found in humans: 2D:4D is lower in polygynous species and higher (lower PAE) in pair-bonded species. Old World monkeys have low, and relatively invariant 2D:4D (high PAE), which is coupled with high levels of intrasexual competition. This contrasts with higher and more variable ratios in both great apes and New World monkeys. In addition, both male and female ratios decrease with increasing levels of intrasexual competition. Human ratios are intermediate between pair-bonded and more promiscuous hominoids. We propose that PAE may be involved in promoting species characteristic social behavior in anthropoids. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source] Sexual selection and animal personalityBIOLOGICAL REVIEWS, Issue 2 2010Wiebke Schuett Consistent individual behavioural tendencies, termed "personalities", have been identified in a wide range of animals. Functional explanations for personality have been proposed, but as yet, very little consideration has been given to a possible role for sexual selection in maintaining differences in personality and its stability within individuals. We provide an overview of the available literature on the role of personality traits in intrasexual competition and mate choice in both human and non-human animals and integrate this into a framework for considering how sexual selection can generate and maintain personality. For this, we consider the evolution and maintenance of both main aspects of animal personality: inter-individual variation and intra-individual consistency. [source] | ||||||||||