Density Dependence and Patch Dynamics in Tropical Rain Forests: Matrix Models and Applications to a Tree Species

Abstract

In this article I present four matrix models that incorporate the possible combinations of two factors affecting populations in tropical rain forests: presence or absence of density-dependent demographic rates and presence or absence of density-independent patch dynamics. By mapping the contrasting results of population growth rate, size, and structure to the assumptions of these four models, the combined and isolated effect of density dependence and patch dynamics is quantified. The models were applied to Cecropia obtusifolia, a tropical pioneer tree species, for which field evidence on gap and density dependence is presented Models' parameters were estimated from new, 7-yr population data at Los Tuxtlas and published forest dynamics data The C. obtusifolia population at Los Tuxtlas suffers negative density-dependent regulation in fecundity and adult survival that significantly affects population structure. Its growth rate and size are strongly affected by the gap dynamics regime. The population is sensitive to the quality as well as the quantity of disturbances. Results also showed how the specification of a population model mediates evaluations of the importance of density-dependent mechanisms on population dynamics and structure, interpretations of the evolutionary dynamics of life-history traits, and assessments of the effect of harvesting regimes on the size and structure of populations.