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Tuesday, 10 June 2014

Ecology and Evolution: Early View, new article abstracts, Week 1 June 2014

Cover image for Vol. 4 Issue 11

Ecology and Evolution

© 2014 John Wiley & Sons Ltd

Early View (Online Version of Record published before inclusion in an issue)
These Early View articles are now available on Wiley Online Library

Original Research

Selection based on the size of the black tie of the great tit may be reversed in urban habitats
Juan Carlos Senar, Michael J. Conroy, Javier Quesada and Fernando Mateos-Gonzalez
Article first published online: 7 JUN 2014 | DOI: 10.1002/ece3.999

Thumbnail image of graphical abstract Most reported examples of differences between urban and nonurban animals reflect behavioral plasticity. Here, we show that survival prospects in forest great tits increased the larger the size of their black breast band, but the reverse was found for urban birds. Our results therefore show that divergent selection can be also an important mechanism in local adaptation to urban habitats.

A standard approach to model how selection shapes phenotypic traits is the analysis of capture–recapture data relating trait variation to survival. Divergent selection, however, has never been analyzed by the capture–recapture approach. Most reported examples of differences between urban and nonurban animals reflect behavioral plasticity rather than divergent selection. The aim of this paper was to use a capture–recapture approach to test the hypothesis that divergent selection can also drive local adaptation in urban habitats. We focused on the size of the black breast stripe (i.e., tie width) of the great tit (Parus major), a sexual ornament used in mate choice. Urban great tits display smaller tie sizes than forest birds. Because tie size is mostly genetically determined, it could potentially respond to selection. We analyzed capture/recapture data of male great tits in Barcelona city (N = 171) and in a nearby (7 km) forest (N = 324) from 1992 to 2008 using MARK. When modelling recapture rate, we found it to be strongly influenced by tie width, so that both for urban and forest habitats, birds with smaller ties were more trap-shy and more cautious than their larger tied counterparts. When modelling survival, we found that survival prospects in forest great tits increased the larger their tie width (i.e., directional positive selection), but the reverse was found for urban birds, with individuals displaying smaller ties showing higher survival (i.e., directional negative selection). As melanin-based tie size seems to be related to personality, and both are heritable, results may be explained by cautious personalities being favored in urban environments. More importantly, our results show that divergent selection can be an important mechanism in local adaptation to urban habitats and that capture–recapture is a powerful tool to test it.

Partitioning the sources of demographic variation reveals density-dependent nest predation in an island bird population
Helen R. Sofaer, T. Scott Sillett, Kathryn M. Langin, Scott A. Morrison and Cameron K. Ghalambor
Article first published online: 6 JUN 2014 | DOI: 10.1002/ece3.1127
Thumbnail image of graphical abstract Population density can shape demographic rates by affecting both competition and predation, but these effects are rarely partitioned. We found that rainfall and density-dependent nest predation had stronger effects on fecundity than intraspecific competition in an island songbird population where we expected competition to be strong. Our results challenge assumptions about the drivers of demographic variation, while our analytical approach highlights methods that separate the processes affecting reproductive failure from those affecting the number of young produced by successful individuals.

Ecological factors often shape demography through multiple mechanisms, making it difficult to identify the sources of demographic variation. In particular, conspecific density can influence both the strength of competition and the predation rate, but density-dependent competition has received more attention, particularly among terrestrial vertebrates and in island populations. A better understanding of how both competition and predation contribute to density-dependent variation in fecundity can be gained by partitioning the effects of density on offspring number from its effects on reproductive failure, while also evaluating how biotic and abiotic factors jointly shape demography. We examined the effects of population density and precipitation on fecundity, nest survival, and adult survival in an insular population of orange-crowned warblers (Oreothlypis celata) that breeds at high densities and exhibits a suite of traits suggesting strong intraspecific competition. Breeding density had a negative influence on fecundity, but it acted by increasing the probability of reproductive failure through nest predation, rather than through competition, which was predicted to reduce the number of offspring produced by successful individuals. Our results demonstrate that density-dependent nest predation can underlie the relationship between population density and fecundity even in a high-density, insular population where intraspecific competition should be strong. 

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