The density effects on performance of a weed Bidens sulphurea (Asteraceae) were evaluated experimentally. There are very few studies available to improve the process of density-dependent to invasive species. We used an experimental set-up in which the population of this weed species is partitioned into different density groups (1, 2, 4 and eight plants per pot) based on local conspecific density to investigate density-based population strategies. The difference between the greatest and the lowest density (8 and 1 plant per pot) was considerably high, around 41%, regarding the variables measured (stem height and diameter, leaf number and size). Plants at higher densities become taller and thinner as a consequence of intraspecific competition. Results suggest that the responses of B. sulphurea, in dense populations, can affect the persistence of population over time. It may be useful in the future for the biological control of this species.
