Chitty cycles–at last!

Abstract

Forty years ago, Dennis Chitty took a brave and pioneering step in population biology, when he proposed that the so-called ecological and evolutionary timescales might be less different than was traditionally assumed. He made this proposal in the context of linking rodent cycles to cyclic selection among different phenotypes. The core of Chitty's argument is that competition between two morphs, one a superior competitor (and inferior reproducer) and the other an inferior competitor (and superior reproducer), might generate cycles in abundance if evolution is very rapid. Two objections can been raised against the ‘Chitty hypothesis’ for population cycles. The first is whether selection can be strong enough to act on an ecological timescale. The second is whether there is enough heritability in such tightly fitness-linked traits as survival and fecundity. The answer to the second will clearly depend on many things. However, as for the first, evidence is mounting that evolution can be very rapid. The time might, therefore, have come for a new appreciation of this idea, in general, but in particular with respect to oscillations in the abundance of the Side-blotched Lizard (Uta stansburiana) of southwestern USA.