© 1994 by The Society for Integrative and Comparative Biology
The Interplay Between Life History and Environmental Stochasticity: Implications for the Management of Exploited Lizard Populations1
Biology Department, University of New Mexico Albuquerque, New Mexico 87131
SYNOPSIS. The sustainable use of wild species by local people is emerging as an important conservation strategy. The premise is the economic value of species will justify their own preservation as well as the habitats they occupy. However, the lack of natural history and demographic information for the majority of species being exploited or with potential uses presents challenging problems for implementing sustainable use programs. Each year in Argentina and Paraguay, an average of 1.9 million tegu lizards of the genus Tupinambis are exploited for their skins. In spite of the importance of tegus as a resource, their biology is poorly known and their populations have never been managed. The life history of Tupinambis, like that of other exploited lizards, is characterized by a relatively long life span, a large clutch size, several years of growth before reproduction, and high mortality of hatchlings. Importantly, the mortality of young-of-the-year and the proportion of females reproducing each year are both probably strongly influenced by interannual environmental variation.When these parameters were randomized in life table projections to simulate the effects of environmental stochasticity, the population growth rate was highly sensitive to environmental fluctuations. Monte Carlo simulations of different harvest strategies showed that estimates of population growth rates were overwhelmingly influenced by environmental variation and the number of years included in the growth rate estimate, even in the face of seemingly large changes in adult mortality that would result from population management. These results are both encouraging and cautionary for Tupinambis conservation. On the one hand these patterns can help explain how Tupinambis populations may have persisted in spite of high and variable harvest levels during many years, but conversely, stochastic effects make it difficult to evaluate the effects of conservation measures. Size and sex can be determined from harvested skins, and pilot studies suggest that analyses of the annual harvest can provide valuable information for evaluating long-term population trends.