BODY SIZE OF INSULAR LIZARDS: A PATTERN OF HOLOCENE DWARFISM

Until recently there have been scant historical data available to test and supplement studies on the evolution of body size within insular lizards. However, there is now an accumulating fossil record from islands which shows that numerous species have declined in average maximum body size since the beginning of the Holocene, regardless of phylogenetic afffinities, habits, or even size of the species itself. Coincident with decline in body size, human colonization of islands has permanently altered insular environments, with the consequence that native flora and fauna have been depleted. Indeed, the fossil record documents high extinction rates among insular vertebrates during the past few thousand years. It follows that resource deterioration may have led to the reduction of lizard body size, as expressed genotypically in selection for corresponding smaller dimensions, and phenotypically through arrested growth and development leading to compression of the age-class structure. The effect of human settlement on small islands has been underestimated, and although the consequences do not render completely in vain the attempts to understand ecological processes on them, they are of sufficient magnitude to stress caution in any assessment of a modern insular biota.