The ecological causes of evolution

Natural selection is the process that results in adaptive evolution, but it is not the cause of evolution. The cause of natural selection and, therefore, of adaptive evolution, is any environmental factor (agent of selection) that results in differential fitness among phenotypes. Surprisingly little is known about selective agents, how they interact or their relative importance across taxa. Here, I outline three approaches for their investigation: functional analysis, correlational analysis and experimental manipulation. By refocusing attention on the structure and consequences of ecological variation, a better characterisation of selective agents would improve understanding of natural selection and evolution, including adaptive radiation, coevolution, the niche, the evolutionary ecology of the ranges of species and their response to environmental change.