DENSITY-DEPENDENCE AND PATCH DYNAMICS IN TROPICAL RAIN-FORESTS - MATRIX MODELS AND APPLICATIONS TO A TREE SPECIES

In this article I present four matrix models that incorporate the poss ible combinations of two factors affecting populations in tropical rai n forests: presence or absence of density-dependent demographic rates and presence or absence of density-independent patch dynamics. By mapp ing the contrasting results of population growth rate, size, and struc ture to the assumptions of these four models, the combined and isolate d effect of density dependence and patch dynamics is quantified. The m odels were applied to Cecropia obtusifolia, a tropical pioneer tree sp ecies, for which field evidence on gap and density dependence is prese nted. 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 regulati on in fecundity and adult survival that significantly affects populati on structure. Its growth rate and size are strongly affected by the ga p dynamics regime. The population is sensitive to the quality as well as the quantity of disturbances. Results also showed how the specifica tion of a population model mediates evaluations of the importance of d ensity-dependent mechanisms on population dynamics and structure, inte rpretations of the evolutionary dynamics of life-history traits, and a ssessments of the effects of harvesting regimes on the size and struct ure of populations.