Empirical studies of sexual selection typically focus on one of the two mechanisms of sexual selection without integrating these into a description of total sexual selection, or study total sexual selection without quantifying the contributions of all of the mechanisms of sexual selection. However, this can provide an incomplete or misleading view of how sexually selected traits evolve if the mechanisms of sexual selection are opposing or differ in form. Here, we take a two‐fold approach to advocate a direction for future studies of sexual selection. We first show how a quantitative partitioning and examination of sexual selection mechanisms can inform by identifying illustrative studies that describe both male–male competition and female mate choice acting on the same trait. In our sample, the most common trait where this occurred was body size, and selection was typically linear. We found that male–male competition and female mate choice can be reinforcing or opposing, although the former is most common in the literature. The mechanisms of sexual selection can occur simultaneously or sequentially, and we found they were more likely to be opposing when the mechanisms operated sequentially. The degree and timing that these mechanisms interact have important implications for the operation of sexual selection and needs to be considered in designing studies. Our examples highlight where empirical data are needed. We especially lack standardized measures of the form and strength of selection imposed by each mechanism of sexual selection and how they combine to determine total sexual selection. Secondly, using quantitative genetic principles, we outline how the selection imposed by individual mechanisms can be measured and combined to estimate the total strength and form of sexual selection. We discuss the evolutionary consequences of combining the mechanisms of sexual selection and interpreting total sexual selection. We suggest how this approach may result in empirical progress in the field of sexual selection.

The avian community of montane coniferous forests changed substantially over 21 years in response to the introduction of the balsam woolly adelgid insect ( Adelges piceae ) and the resulting death of endemic Fraser fir trees ( Abies fraseri ). These relict forests are at the southern limit of their distribution on the highest ridges of the southern Appalachian Mountains. We combined a historical study at Mount Collins in the Great Smoky Mountains with a geographic comparison of sites within five southern Appalachian mountain ranges variably affected by the adelgid. At Mount Collins, fir was virtually eliminated and canopy cover reduced to half its previous level. Long-term data from Mount Collins showed that the combined density for all breeding birds also declined by half. Of the common territorial species present in 1974, 10 of 11 declined, 6 by more than 50%. Some species are near local extinction. Canopy-and subcanopy-foraging species declined more than near-ground and trunk-foraging species. In addition, invasions of birds characteristic of open and disturbed forests have diluted the boreal character of the avifauna. These changes are consistent with two other long-term studies and are not explained by regional population trends. In the other southern Appalachian mountain ranges, where habitat is not as extensive, the adelgid invasion resulted in greater declines in avian abundance, stronger effects on sensitive species, and more pronounced invasions by successional species. Sensitive species in the southern Appalachian studies were also strongly affected in other studies of forest disturbance by fire and logging. The extent of relatively pristine spruce-fir forest and the population pools in other forest types in the Great Smoky Mountains appear to have buffered the effects of forest decline on the bird community. Respuesta de Comunidades de Aves a Perturbaciones de un Insecto Exótico en Bosques de Abeto en el Sur de los Apalaches Resumen: La comunidad de aves de bosques coníferos de montaña cambió sustancialmente a lo largo de 21 años en respuesta a la introducción del insecto adélgido lanudo Aldeges piceae y a la resultante muerte de árboles de Abetos Fraser ( Abies fraseri ). Estos vestigios de bosques se encuentran al limite sureño de su distribución en las montañas mas altas de los Apalaches. Combinamos un estudio histórico del monte Collins en las montañas Great Smoky con una comparación geográfica de sitios entre cinco cordilleras de los Apalaches afectados en forma variable por el adélgido. En el monte Collins, los abetos fueron virtualmente eliminados y la covertura del dosel reducida a la mitad de su nivel previo. Datos de largo plazo del monte Collins mostraron que la densidad combinada para todas las especies de aves anidando también disminuyó a la mitad.De las especies comunes en el territorio en 1974, 10 de 11 disminuyeron, seis en mas de un 50%. Algunas especies se encuentran cerca de su extinción local. Especies forrajeras de dosel y sub-dosel disminuyeron mas que aquellas especies forrajera...

No abstract

The avian community of montane coniferous forests changed substantially over 21 years in response to the introduction of the balsam woolly adelgid insect ( Adelges piceae ) and the resulting death of endemic Fraser fir trees ( Abies fraseri ). These relict forests are at the southern limit of their distribution on the highest ridges of the southern Appalachian Mountains. We combined a historical study at Mount Collins in the Great Smoky Mountains with a geographic comparison of sites within five southern Appalachian mountain ranges variably affected by the adelgid. At Mount Collins, fir was virtually eliminated and canopy cover reduced to half its previous level. Long-term data from Mount Collins showed that the combined density for all breeding birds also declined by half. Of the common territorial species present in 1974, 10 of 11 declined, 6 by more than 50%. Some species are near local extinction. Canopy-and subcanopy-foraging species declined more than near-ground and trunk-foraging species. In addition, invasions of birds characteristic of open and disturbed forests have diluted the boreal character of the avifauna. These changes are consistent with two other long-term studies and are not explained by regional population trends. In the other southern Appalachian mountain ranges, where habitat is not as extensive, the adelgid invasion resulted in greater declines in avian abundance, stronger effects on sensitive species, and more pronounced invasions by successional species. Sensitive species in the southern Appalachian studies were also strongly affected in other studies of forest disturbance by fire and logging. The extent of relatively pristine spruce-fir forest and the population pools in other forest types in the Great Smoky Mountains appear to have buffered the effects of forest decline on the bird community. Respuesta de Comunidades de Aves a Perturbaciones de un Insecto Exótico en Bosques de Abeto en el Sur de los Apalaches Resumen: La comunidad de aves de bosques coníferos de montaña cambió sustancialmente a lo largo de 21 años en respuesta a la introducción del insecto adélgido lanudo Aldeges piceae y a la resultante muerte de ár-boles de Abetos Fraser ( Abies fraseri ). Estos vestigios de bosques se encuentran al limite sureño de su distribución en las montañas mas altas de los Apalaches. Combinamos un estudio histórico del monte Collins en las montañas Great Smoky con una comparación geográfica de sitios entre cinco cordilleras de los Apalaches afectados en forma variable por el adélgido. En el monte Collins, los abetos fueron virtualmente eliminados y la covertura del dosel reducida a la mitad de su nivel previo. Datos de largo plazo del monte Collins mostraron que la densidad combinada para todas las especies de aves anidando también disminuyó a la mitad.De las especies comunes en el territorio en 1974, 10 de 11 disminuyeron, seis en mas de un 50%. Algunas especies se encuentran cerca de su extinción local. Especies forrajeras de dosel y sub-dosel disminuyeron mas que aquellas especies forrajer...

In nature, social groups of animals are typically nonrandom associations of individuals. Such group associations may in part be based on social familiarity among individuals, acquired through repeated past encounters and behavioural experiences with each other. The factors that potentially affect the tendency to associate with familiar individuals remain poorly understood. Here, we investigated whether shoaling preferences based on presumed familiarity occur in wild adult guppies (Poecilia reticulata) originating from a Trinidadian population that experiences relatively low predation intensity from fishes and whether any such preferences differ between the sexes. When tested shortly after being collected in the field, neither males nor females clearly preferred to shoal with familiar same-sex conspecifics (collected from the same pool in the river) over unfamiliar ones (from different pools). Importantly, our results differ from those previously reported for guppies originating from the same population as ours and for a high predation risk population in Trinidad, suggesting that the development of social familiarity and its role in the formation of shoals in nature vary both within and among populations in the guppy. We provide plausible explanations for these observed populational differences in shoaling preferences in the guppy and discuss certain ecological factors that may affect the development and expression of shoaling preferences based on familiarity in nature.Résumé : En nature, les groupes sociaux d'animaux sont typiquement des associations non aléatoires d'individus. Ces associations de groupe peuvent en partie se baser sur la familiarité sociale entre les individus acquise au cours de rencontres répétées dans le passé et d'expériences comportementales mutuelles. Les facteurs qui peuvent influencer cette tendance à s'associer à des animaux familiers restent mal compris. Notre étude examine s'il y a des préférences basées sur une familiarité présumée dans la formation de bancs chez des guppys (Poecilia reticulata) adultes sauvages provenant d'une population au Trinidad qui ne subit qu'une faible pression de prédation de la part des poissons; elle évalue aussi s'il y a des différences dans les préférences entre les mâles et les femelles. Dans des tests de formation de bancs, peu après leur récolte sur le terrain, ni les mâles, ni les femelles ne montrent de tendances claires à s'associer plus à des guppys familiers de même sexe (issus de la même fosse dans la rivière) qu'à des guppys étrangers (provenant de fosses différentes). Ce qui est intéressant, c'est que nos résultats diffèrent de résultats publiés sur des guppys provenant de la même population et sur une autre population de Trinidad, mais à fort risque de prédation; il semble donc que le développement de la familiarité sociale et son rôle dans la formation des bancs chez le guppy en nature peut varier au sein d'une même population et d'une population à une autre. Nous avançons des explications plausibles de ces diffé-rences de préférence entre le...