Presentation Detail

Evolutionary Ecology

Oswald, Jessica A. [1], Burleigh, J. Gordon [2].

The evolution of ecological specialization in birds.

Specialization is a common theme in the literature of adaptation and diversification, but the origin of specialization and its evolutionary implications often are not clear. A persistent problem is the difficulty of defining and quantifying specialization. We first define a novel measure of specialization, the species co-occurrence index (C.I.), which measures the extent of a species’ range, defined by the number of co-occurring species, relative to the range size of the other species it encounters. We built an avian species co-occurrence network from over 82 million records in the Avian Knowledge Network and used these data to calculate the C.I. for over 6,000 bird species. Species restricted to limited habitats, for example island endemics all have extremely low C.I. scores. In contrast, species with nearly worldwide distributions, which co-occur with many, if not most, other species, have the highest C.I. scores. The bird species overall are highly interconnected, with a maximum path length of two between any pair of species in the co-occurrence network, but the great majority of species appear to be specialists, meaning that they are connected to relatively few other species. This apparent discrepancy is due to the presence of some extreme generalists, or species with extraordinarily high C.I. values. The large proportion of specialists may be due to a biased transition rate favoring specialists and/or higher diversification rates for specialists. We mapped the C.I. values onto a phylogenetic tree containing over half the extant bird species, and used the BiSSE model to estimate transition rates between generalists and specialists as well as extinction and speciation rates associated with specialists and generalists. We found evidence for a strong bias favoring the transition from generalist to specialist states. Also, specialists have significantly higher speciation and extinction rates than generalists. These results provide strong empirical support for idea that specialists arise from generalists much more often than generalists arise from specialists. They also emphasize the importance of specialization in generating avian biodiversity, as well as the elevated extinction risk often associated with specialists.

1 - University of Florida , Biology, Florida Museum of Natural History , 1659 Museum Road, Gaineville, FL, 32611, United States
2 - University of Florida , Biology, Gainesville, FL, 32611, USA

Keywords:
Specialization 
Macroecology
Evolutionary Ecology 
birds.

Presentation Type: Regular Oral Presentation
Session: 30
Location: Alpine C/Snowbird Center
Date: Saturday, June 22nd, 2013
Time: 2:15 PM
Number: 30004
Abstract ID:298
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation