Netting entire islands in The Bahamas to manipulate the agents of selection
A central theme underlying studies of adaptive radiation is that ecologically mediated selection drives diversification. However, demonstrating the ecological basis of natural selection and linking this process to patterns of morphological diversity represents a formidable challenge. This is because selection experiments that test correlations between an organism’s phenotype and its ecology are difficult to perform in the wild. In natural populations, performance-related traits such as limb length are subject to correlational and disruptive selection driven by differences in habitat use. Selection is dynamic and our work illustrates the importance of inter-annual environmental variation in shaping adaptive variation. Thus, we try to take a long-view of the problem and use experiments and multi-year data sets to address how selection actually shapes
adaptation. For example, we are in the midst of a long-term manipulation of bird and snake predators on small islands (above). Netting islands removes predation pressure by birds whereas adding or removing snakes from islands (in conjunction with our net additions) will allow us to understand the different roles of alternative avian and terrestrial predators. The figure on the left shows one of our experimental designs. Solid circles represent islands covered by bird netting, dashed circles indicate open-net control islands. The four treatments are: (A) no predators, (B) only bird predators, (C) only snake predators, and (D) both bird and snake predators.
Related Publications
Logan, M.L., Cox, R.M. and Calsbeek, R. Natural selection on thermal performance in a novel thermal environment. Proc. Natl. Acad. Sci. U.S.A. in press.
PDF Calsbeek, R., and Cox, R.M. Experimentally assessing the relative importance of predation and competition as agents of natural selection. Nature 465: 613-616. Supplementary Information Nature PodCast (5/13) Nature News
PDF Calsbeek R., and Smith, T.B. Probing the adaptive landscape using experimental islands: density dependent natural selection on lizard body size. Evolution 61: 1052-1061.
PDF Calsbeek, R., and Irschick, D.J. The quick and the dead: Correlational selection on morphology performance, and habitat use in island lizards. Evolution 61-11: 2493–2503.
PDF Calsbeek R. Experimental evidence that competition and habitat use shape the individual fitness surface. J. Evolutionary Biology 22: 97-108.
PDF Calsbeek R., Beurmann W., and Smith T.B. Parallel shifts in ecology and Natural selection. BMC Evolutionary Biology 9:3 (open access available here: http://www.biomedcentral.com/1471-2148/9/3)