., et al. 2012. Positive relationships between association strength and phenotypic similarity characterize the assembly of mixed-species bird flocks worldwide. American Naturalist 180: 777-90. AuthorsHari Sridhar, Umesh Srinivasan, Robert A. Askins, Julio Cesar Canales-Delgadillo, Chao-Chieh Chen Submitted February 10, 2012; Accepted August 1, 2012; Electronically published MONTH? xx, 2012 Online enhancement: appendix. Dryad data: http://dx.doi.org/10.5061/dryad.th198.abstract: Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrixes from 24 locations) on the composition of mixed-species bird flocks, which are important subunits of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.

Anthropogenic noise produced by human activities affects acoustic communication in animals living in urban habitats. We recorded the calling songs of the cicada Cryptotympana takasagona in the Kaohsiung metropolitan areas of southern Taiwan to investigate possible acoustic adaptations to anthropogenic noise. C. takasagona did not call more in noise gaps. Acoustic features (peak frequency, quartile 25%, quartile 50%, and quartile 75%) of calling songs significantly increased with ambient noise levels. C. takasagona shifted the energy distribution of calling songs to higher frequencies in the presence of higher noise levels. We suggest that the acoustic adaptation by which song frequencies increase with levels of anthropogenic noise in C. takasagona may result from a size-dependent calling strategy in which small-sized males call more in noise conditions or largesized males adjust their song frequency by changing their abdominal cavities.

Foraging niche overlap between attendant species and the nuclear species of mixed-species flocks may induce competition as well as facilitation. In this study, we hypothesized that canopy species would appear more frequently in flocks where nuclear species foraged in the canopy and that species with greater niche overlap with nuclear species would have lower departure rates. Flocking and foraging behaviors of flocks led by the Grey-cheeked Fulvetta Alcippe morrisonia were studied in northeastern Taiwan for two consecutive non-breeding seasons from 1998 to 2000. The foraging height spectrum increased with increasing group size of fulvettas because more fulvettas were found foraging across different strata. The number of species and number of individuals of canopy attendants in a flock increased more rapidly than understory attendants as the group size of fulvettas increased. The more the foraging height of an attendant species overlapped with that of the nuclear species, the lower its departure rate. Specifically, canopy attendant species that usually had a lower niche overlap with the nuclear species dropped out of the flock more frequently than understory attendant species. These observations indicate that foraging niche overlap between attendant species and the nuclear species may facilitate the formation of mixed-species bird flocks. It is therefore important to incorporate the role of positive interactions when trying to understand the formation and maintenance of biological communities.Zusammenfassung Die Ü berlappung von Nahrungsnischen zwischen vereinzelt anwesenden Arten und den Hauptarten in gemischten Schwärmen könnte sowohl zu Konkurrenz als auch zu Begünstigung führen. In dieser Untersuchung stellen wir die Hypothese auf, dass Arten der Kronenbereiche häufiger in Schwärmen vorkommen, in denen die Hauptarten in der im Kronenbereich Nahrung suchen und dass Arten mit größerer Nischenüberschnei-dung mit der Hauptart des Schwarms geringere Abflugraten zeigen. Zwischen 1998 und 2000 wurde in Nordosttaiwan schwarmbildendes und Nahrungsverhalten in Trupps von Grauwangenalcippen Alcippe morrisonia außerhalb der Brutzeit untersucht. Mit zunehmender Gruppengröße an Alcippen stieg das Höhenspektrum zur Nahrungssuche an, da mehr Alcippen in verschiedenen Baumstraten nach Nahrung suchten. Die Anzahl der Arten und Individuen der Begleitarten im Kronenbereich in einem Schwarm stieg mit zunehmender Gruppengröße der Alcippen mehr an als die der Unterholzarten. Je mehr die Höhe der Nahrungssuche Communicated by T. Friedl. Electronic supplementary materialThe online version of this article (

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

No abstract