  In his highly influential view of evolution, G. G. Simpson hypothesized that
clades of species evolve in adaptive zones, defined as collections of niches
occupied by species with similar traits and patterns of habitat use. Simpson
hypothesized that species enter new adaptive zones in one of three ways:
extinction of competitor species, dispersal to a new geographic region, or the
evolution of a key trait that allows species to exploit resources in a new way.
However, direct tests of Simpson's hypotheses for the entry into new adaptive
zones remain elusive. Here we evaluate the fit of a Simpsonian model of jumps
between adaptive zones to phylogenetic comparative data. We use a novel
statistical approach to show that anoles, a well-studied adaptive radiation of
Caribbean lizards, have evolved by a series of evolutionary jumps in trait
evolution. Furthermore, as Simpson predicted, trait axes strongly tied to
habitat specialization show jumps that correspond with the evolution of key
traits and/or dispersal between islands in the Greater Antilles. We conclude
that jumps are commonly associated with major adaptive shifts in the
evolutionary radiation of anoles.
