e-Publications@Marquette

What mechanisms allow some species to attain and maintain high relative abundance in tropical forests, while other species remain at low population densities? This is a key question in ecology. Although there are a number of theoretical explanations, few have been convincingly supported by experimental evidence. We are testing the hypothesis that many plant species attain high abundance in seasonal tropical forests due to the competitive advantage gained from growth during seasonal drought, when solar radiation is high, moisture is limiting, and competing species are dormant. Because most tropical forests are seasonal, the hypothesis has relevance worldwide, and the ideas underlying the hypothesis can be extended to any ecosystem that experiences seasonal fluctuations. We are currently testing this “Dry Season Advantage” hypothesis using a combination of long-term physiological and growth measurements on lianas and trees in experimental gardens and in permanent forest plots along a steep rainfall gradient across the Isthmus of Panama. Lianas are of particular importance because they are integral components of tropical forests and they are more prevalent in areas that have less rainfall, a pattern. The project will provide one of the first tests of a simple mechanism that may control the abundance and distribution of plant species based on seasonality and mean annual rainfall, readily available parameters for forests around the world.