Cooperation between species may be an overlooked factor in community organization.
Ecologists tend to assume that all of the species within a community are more different from one another than chance would predict, because competition precludes two species from sharing the same ecological niche. So mixed-species bird flocks are a puzzle: these groups, which contain birds of different species that all eat roughly the same food, seem to show species happily co-existing. According to an analysis of a global data set by Kartik Shanker at the Indian Institute of Science in Bangalore and his co-authors, the more similar two birds are by taxonomy, body size and foraging style, the more likely they are to be found together, especially where tropical mixed flocks are concerned.
The team suggests that this happens because cooperative benefits — such as those provided by alarm calls or the discovery of food resources — are best obtained from the most similar individuals.
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Benefits of mixed flocks. Nature 492, 314 (2012). https://doi.org/10.1038/492314a
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DOI: https://doi.org/10.1038/492314a