PARENT SESSION
Oral Session #51: Invasions: Population and community interactions.
Presiding: T. Stohlgren
Wednesday, August 7. 8:00 AM to 11:30 AM. Graham Meeting Room, TCC.
The role of density-dependent mortality in weed patch persistence.
MORTENSEN, DAVID*,1, NEESER, CHRISTOPHE2, DILLE, JOHANNA3, 1 The Pennsylvania State University, University Park, PA2 Alberta Agriculture Food and Rural Developent Crop Diversification Centre, Brooks, Canada3 Kansas State University, Manhattan, KS
ABSTRACT- Detailed mapping of agricultural weeds over several years revealed patches that remain in the same location, that vary in size from year to year and that did not show the geometric growth that has often been postulated on theoretical grounds. From past research we suspected negative density dependent mortality during early seedling growth played an important role in constraining low-density patch edges while protecting plants in patch centers. A spatially explicit population dynamics model was used to explore mechanisms regulating Abutilon theophrasti plant patch stability. To parameterize the model artificial patches were created by planting A. theophrasti seed at the rate of 10, 50, 90, 150, 500, 1000, and 2000 seeds per patch. Emerging cohorts of seedlings were subjected to a range of mortality events. A Weibull function provided the best fit, where mortality was near 100% at low seedling densities and dropped to 60% at densities of 200 plants m-2. In most cases mortality declined at densities above 100 plants m-2 and reached a lower asymptote, at densities in excess of 200 plants m-2. The difference in mortality rates between high and low densities ranged from 22 % to 36 % when under high mortality pressure and from 36 % to 41 % at lower mortality intensity. Simulation results indicated patch growth was sensitive to dispersal distance and to the density dependent response described herein. Internal dynamics shaping patch extent and rate of spread is strongly influenced.
KEY WORDS: invasive weeds, spatially explicit population dynamics, density dependent mortality, Abutilon theophrasti