PARENT SESSION
Poster Session 9: Arid Lands and Deserts
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Interaction between the invasive grass Schismus barbatus (Poaceae) and the native perennial Ambrosia dumosa (Asteraceae) in the Colorado Desert, California.
Rodriguez-Buritica, Susana1, Miriti, Maria1, 1 Department of Evolution, Ecology, and Organismal Biology, Columbus, OHIO, U.S.A
ABSTRACT- Arid regions in the U.S. have strongly experienced the impact of invasive grasses. In arid communities, perennial shrubs may enhance the performance of annuals, a dynamic that may boost the invasiveness of exotics. We investigated the interactions between the widely distributed native shrub Ambrosia dumosa and Schismus barbatus , an exotic annual grass, in the Colorado Desert. During 2003-2004, we experimentally examined Schismus performance at three distances (50, 150, 200 cm) from 20 focal Ambrosia adults. At each distance we buried treatment and control pots that contained seeds of both species. Performance was evaluated at the end of one growing season. This field experiment was supplemented by a surface response experiment conducted in the greenhouse to explore the interaction between Schismus and Ambrosia seedlings at three total densities, and at five proportions of Ambrosia seeds (0, 25, 50, 75, 100%). Each of the 15 treatments had 4 replicates. Growth of both species was evaluated three times during the experiment. Field results showed that growth of Schismus is greater close to shrubs although germination is higher at inter-shrub spaces. Ambrosia did not germinate in the field. Final Schismus biomass, height, and reproductive effort were negatively correlated with density (r2=23.9; 31.3; 13.3 respectively, p<0.005, n=116) and with distance when density was controlled. Thus, although germination is higher in open areas, performance improves close to Ambrosia adults. In the greenhouse, Ambrosia biomass decreased more than growth with density of both species (r2=13, p<0.001 n=279), while for Schismus growth decreased with density (r2=37, p<0.01, n=1072). Interestingly, the reproductive effort of Schismus was higher at intermediate Ambrosia densities, which suggests facilitation (r2=10 p<0.03, n=300). Results suggest that long term population dynamics of both species may be shaped by 1) the reduction of Ambrosia establishment caused by high density of Schismus, and 2) facilitation of Schismus by Ambrosia adults and seedlings. These processes are endorsed by physical characteristics that promote high densities of seeds around shrub canopies.
Key words: Invasive species, Facilitation, Deserts, Schismus barbatus