DEMOGRAPHIC AND GENETIC MODELS IN CONSERVATION BIOLOGY: Applications and Perspectives for Tropical Rain Forest Tree Species

We review deterministic and stochastic demographic models as well as classical population genetic models that have been applied to tropical rain forest tree species. We discuss their implications for conservation. The main conclusions of deterministic demographic models are the key importance of species' longevity in determining susceptibility of population growth rate to harvesting of individuals at different life-stages, the critical effect of patch dynamics, and the importance of density-dependent mechanisms at least for abundant species. Population viability analysis to predict extinction times of tropical rain forest tree species has only been performed for four tropical rain forest tree species using the simplest Lefkovitch matrix linear model. Results obtained are in accordance with results of simple stochastic models for nonstructured populations that have been solved analytically. Population genetic models have shown that tropical rain forest trees: (a) possess high levels of genetic diversity, (b) maintain greater proportions of genetic variation within than among populations, (c) are predominantly outcrossed, and (d) have high levels of gene flow. These results suggest that tropical tree species may not be in immediate danger of extinction from genetic factors if actual conditions are maintained. However, the impact of forest fragmentation is expected to be particularly strong for most tropical rain forest tree species due mainly to the high genetic load kept by their present population genetic structures. Recent theoretical demographic-genetic models for simple systems suggest that the fixation of new mildly detrimental mutations may be comparable in importance to environmental stochasticity, implying minimum viable populations as large as a few thousands. It is urgent to develop a model that integrates genetic and demographic factors, that enables evaluations of their relative importance in long-term persistence of tropical rain forest tree species.