What makes birds of a feather flock together?
The co-existence of hundreds of bird species is still a mystery to evolutionary biology. A new study led by Daniel Kissling of the Institute for Biodiversity and Ecosystem Dynamics (IBED) and his French colleague Jean-Yves Barnagaud of the University Bordeaux now shows how diet, mobility, body size and climatic preference of birds influence their co-occurrence with close relatives worldwide. These findings have recently been published in the top-journal 'Ecology Letters'.
In the footsteps of Darwin
Since the seminal work by Charles Darwin, the study of bird diversity has been of central interest to evolutionary biology. Darwin’s well-known observations on beak sizes of Galapagos finches revealed that morphological differences among species allow coexistence on islands, yet little is known about the co-existence of bird species within larger regions or continents .
The researchers compiled a comprehensive dataset of almost 10,000 bird species worldwide, with their geographic distributions, ecological characteristics and phylogenetic relationships; the latter indicating how closely related they are. Using advanced computational analyses, they showed that the regions in which many closely-related species co-occur are those dominated by birds of prey, migratory birds and birds adapted to a cold climate. This probably reflects that only a few bird families have been able to colonise and diversify in extra-tropical regions, a phenomenon called ‘tropical niche conservatism’ (i.e. tropical species are unable to expand outside the tropics).
Perspective on the future
The new analyses also show that specific ecological characteristics (e.g. body size and dietary adaptations) are particularly important for the co-existence of related birds at a regional scale. This suggests that the species distributions along environmental gradients are not only influenced by the climatic preferences of species but also by their ecological characteristics . Some of these characteristics are deeply rooted in the bird tree of life, meaning that they are strongly influenced by previous evolutionary adaptations of birds. This poses a great challenge to scientists who want to predict the impact of global change on biodiversity, because the distributional responses of species to global environmental change is not only driven by climate but also by the various ecological characteristics of species. ‘In this context, a deeper understanding of the interactions among multiple species and their ecological characteristics is particularly important, and this forms the basis of my ongoing research at the University of Amsterdam’, says Kissling.
Barnagaud, J.-Y., Kissling, W.D., Sandel, B., Eiserhardt, W.L., Sekercioglu, C.H., Enquist, B.J., Tsirogiannis, C. & Svenning, J.-C. Ecological traits influence the phylogenetic structure of bird species co-occurrences worldwide. In: Ecology Letters (2014), doi:10.1111/ele.12285