A matrix model for the population dynamics of Hyptis suaveolens, an annual weed

Abstract

Hyptis suaveolens is a neotropical annual weed that invades savanna agricultural systems. Although fire, grazing and soil disturbances have been proposed to cause its local dominance, these factors have not been experimentally tested. A field experiment was carried out in a savanna in the Venezuelan Llanos. Six treatments were meant to simulate proposed disturbances and explore underlying causes of the species’ local dominance. A matrix population model was developed and for each treatment demographic and perturbation analyses were performed. Results indicate that population growth rate is promoted by all simulated disturbances but fire and nearby vegetation removal, increasing with disturbance intensity, especially under plowing. Demographic analyses show that the increase in population growth rate is mainly due to fecundity. However, germination is the most sensitive parameter. Fire and digging produced a strong reduction in germination, although this negative contribution is smaller than the positive contribution made by fecundity in the digging treatment. Matrix population model analyses allowed a better understanding of the processes leading to increases in the weed’s growth rate, and allow development of more effective control measures. Some of them include avoiding soil disturbance and increasing control over germination. We also discuss the constraints of the developed model.