The hypothesis that patterns of sex-biased dispersal are related to social mating system in mammals and birds has gained widespread acceptance over the past 30 years. However, two major complications have obscured the relationship between these two behaviors: 1) dispersal frequency and dispersal distance, which measure different aspects of the dispersal process, have often been confounded, and 2) the relationship between mating system and sex-biased dispersal in these vertebrate groups has not been examined using modern phylogenetic comparative methods. Here, we present a phylogenetic analysis of the relationship between mating system and sex-biased dispersal in mammals and birds. Results indicate that the evolution of female-biased dispersal in mammals may be more likely on monogamous branches of the phylogeny, and that females may disperse farther than males in socially monogamous mammalian species. However, we found no support for a relationship between social mating system and sex-biased dispersal in birds when the effects of phylogeny are taken into consideration. We caution that although there are larger-scale behavioral differences in mating system and sex-biased dispersal between mammals and birds, mating system and sex-biased dispersal are far from perfectly associated within these taxa.

On encountering a predator, many species emit potentially risky vocalizations known as alarm calls. We evaluated the relative importance of two adaptive hypotheses on the evolution of calling: (1) communicating to predators, which may function by deterring pursuit and hence increasing individual survival, and (2) an alternative nepotistic hypothesis for alarm calling whereby callers obtain direct and indirect fitness by warning relatives. Focusing on 209 species of rodents, we found significant associations between diurnality and alarm calling, living socially and alarm calling, and diurnality and sociality. Diurnality, however, accounted for nearly three times as much variation in whether or not a species alarm called than did sociality. Phylogenetic tests revealed that the evolution of diurnality preceded the evolution of alarm calling, and that the evolutions of diurnality and sociality were unrelated. Our results are consistent with the hypothesis that alarm communication evolved to communicate to predators. If so, then nepotistic benefits, although important for the maintenance of alarm calling in some rodents, may be relatively less important in its evolution.

We studied the applicability of Lanchester's laws of combat to explain interspecific dominance in birds. We focused on 10 species of Australian birds in the arid zone of New South Wales that foraged at an established locust trap. Consistent with the “linear law,” larger species usually dominated smaller species in one-on-one encounters. We found no support for the “N-square law,” which predicted that large numbers of smaller species could dominate larger species when more abundant. Further analysis of the most abundant species revealed that it was less likely to visit the locust trap when larger, more dominant heterospecifics were present. Body size, and not numerical superiority, seems to be an important determinant in interspecific foraging decisions in birds.¿Puede la Ley de Lanchester Ayudar a Explicar la Dominancia Interespecífica en Aves?Resumen. Hemos estudiado la aplicabilidad de las leyes del combate de Lanchester en explicar la dominancia interespecífica en aves. Hemos focalizado este estudio en 10 especies de aves australianas de la zona árida de New South Wales, las cuales se alimentaron en trampas de insectos establecidas para tal fin. Consistente con la “ley lineal,” las especies de mayor tamaño usualmente dominaron a las especies más pequeñas en los encuentros uno a uno. No encontramos evidencia que apoye la “ley cuadrática,” la cual predice que un gran número de especies de pequeño tamaño podrían dominar a especies de tamaño mayor cuando las primeras son más abundantes. Posteriores análisis sobre la especie más abundantes revelaron que la probabilidad de visita a las trampas de insectos es menor cuando individuos heteroespecíficos más grandes y más dominantes están presentes. El tamaño corporal, y no la superioridad numérica, parece ser un importante factor en las decisiones de forrajeo en las aves.

No abstract