Seed dispersal and environmental heterogeneity in a neotropical herb: a model of population and patch dynamics

Abstract

We examined the effects of three kinds of seed dispersal on mean fitness in the ant-dispersed perennial herb Calathea ovandensis (Marantaceae): (1) local dispersal to safe sites, (2) longdistance dispersal, and (3) dispersal through time, i.e., dormancy. Because, persistence of this species depends upon periodic disturbance by treefalls, we propose a matrix model of population dynamics that combines the successional dynamics of the forest with the habitat-specific demographic dynamics of the plant. Using empirically determined values for the demographic parameters for Calathea ovandensis in a new gap, and three different models of how stage-specific growth and survival change as succession proceeds, we characterize the overall population dynamics of our study species. For the model best representing the demographic response of Calathea ovandensis to succession, the results of our computer simulations predict strong selection for local dispersal to safe sites, and selection against long-distance dispersal. These predictions are consistent with observed patterns of seed dispersal in Calathea ovandensis. In addition, the model predicts very weak selection for long-term seed dormancy, a life-history stage currently under investigation. Models combining patch dynamics with population dynamics provide a method of quantifying the demographic consequences of lifehistory variation for plants occupying variable environments.