analysis of the population dynamics of an endangered lizard (xenosaurus grandis) through the use of projection matrices

Abstract

We conducted a demographic analysis from 2000 to 2004 of a population of the crevice-dwelling lizard, Xenosaurus grandis, in Veracruz, Mexico. We used population projection matrices to model its population dynamics. Three of the four annual matrices projected an actively growing population, whereas the matrix corresponding to 2003-2004 projected a declining population, apparently associated with a higher-than-average environmental temperature during this period. Observed population structure differed from that expected at equilibrium, according to the four matrices. Highest reproductive values corresponded to adult categories. The transition of newborns and juveniles to larger categories, as well as adult stasis, were the vital rates that made the largest contribution to population growth rate (lambda). Growth from one size class to the next was the demographic process that contributed the most to lambda, and all size classes had similar elasticities in all years. Stochastic simulations integrating interannual demographic variability projected population growth rates above unity, even under an ecological scenario that consisted of 50% of unfavorable years. Despite this trend toward positive population growth, this X. grandis population faces an imminent threat due to the growing industrial development in the region in which it is endemic. Thus, we suggest this population as a primary target for conservation efforts, as well as a change in the conservation category of this species from "special protection" to "threatened."