Effects of plant growth rate and leaf lifetime on the amount and type of anti-herbivore defense.

Growth, herbivory and defenses were studied for 41 common tree species in a lowland rainforest in Panama. Species represented a range of shade tolerance, but all individuals were measured in light gaps to control for environmental conditions and the availability of herbivores. Species growth rates and leaf lifetimes differed by almost 50-fold and were related to the degree of shade tolerance. Various measures of plant growth were significantly negatively correlated with an estimate of defense investment, and significantly positively correlated with rates of herbivory. Species with long-lived leaves had significantly higher concentrations of immobile defenses such as tannins and lignins. These data support current hypotheses that the intrinsic growth rate of a species evolutionarily determines the optimal amount and type of defense.