Robert MacArthur died at the age of 42, leaving a legacy of brilliant theory and cogent observation of nature. In his book on evolutionary ecology, Laurence Mueller credits MacArthur as being one of the founders of the field, an extraordinary achievement for such a short life. The book is part of a series on conceptual breakthroughs in science. Each book selects the most important articles and books of a discipline, describes their significance in a series of two-page essays and assigns a score reflecting its impact on the field. MacArthur rates three of the sixty-five “conceptual breakthroughs” in Mueller’s volume, more than any other author. You might think of these breakthroughs as mini Nobel Prizes for long-standing impact on the field.
What exactly is evolutionary ecology, since it combines two of the three themes of this blog? In a nutshell, it is the study of the ecological conditions where natural selection can operate. The most important condition is the presence of a wide range of inheritable traits in the population. A population without variation will simply get wiped out by the next big change in the environment. The more variation that is present, the more quickly natural selection can adapt the population to the local environment. This idea is captured in Ronald Fisher’s ”Genetical Theory of Natural Selection” in 1930 . Natural selection can act at any stage of a lifecycle from egg to juvenile to reproducing adult. It is not enough to lay many eggs; one must have offspring that can survive to reproduce themselves. Those that manage both survival and reproduction will get a bigger share of the next generation’s gene pool. Evolutionary ecology uses the relative abundance of genes in a population to keep track of which ones are increasing or declining but is also interested in how the traits of plants and animals , for example the beaks of Darwin’s finches, make those changes possible.
About a third of the papers or books that Mueller reviews are assigned an impact score of 9 or 10 on a scale of 1 to 10. These publications vary quite a lot in the number of times they have been cited by other authors. The best known, of course, is Darwin’s “Origin of Species”, which spawned several scientific disciplines and had a profound cultural impact besides. Three others are worth noting, the already mentioned “Genetical Theory of Natural Selection” , Hamilton’s proposal for Kin selection – the idea that you can pass on your own genes by helping your kin, and MacArthur and Wilson’s “Theory of Island Biogeography“. Each of these has attracted more than 20,000 references in the academic literature.
Mueller is careful to include both theory and observation in his selection of conceptual breakthroughs. Important observations include Peter and Rosemary Grant’s work on Darwin’s finches, Kettlewell’s peppered moths and Schluter’s three-spined sticklebacks. These studies ,respectively, document that drought, pollution and the presence of closely related species can cause selection. Still missing from evolutionary ecology is a Source Law – a means of predicting when natural selection is most likely to act. Recent advances in genetic sequencing will help this discipline track the change in abundance of genes and gene complexes. However, without a means of measuring the correspondence between traits and environment, we may never be able to foresee how and when natural selection is about to change the natural world around us.