Oscillatory Dynamics in Populations of an Annual Weed Species Abutilon Theophrasti

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Abstract
Calibrated neighbourhood population dynamic models had predicted that monocultures of Abutilon theophrasti (velvet leaf) can exhibit oscillatory and chaotic dynamics. This hypothesis was tested both in field experiments and under controlled-environment conditions. The effect of soil nutrient levels on the population dynamics was observed in glasshouse experiments. Seed-set-density relations have negative slopes for a wide range of plant densities, both in the field and under controlled conditions, indicating that oscillatory dynamics are possble. The negative slope occurs because the fecundity of an Abutilon individual is not directly proportional to its biomass but is actually proportional to its biomass minus a constant. Field populations are in a state of damped rather than persistent oscillations solely due to the effect of delayed germination of seeds. Oscillatory responses are likely to be found in populations of annuals that lack seed dormancy, have high seed survivorship, grow in locations with high soil fertility, and have minimum plant-size thresholds for seed production. Populations of adult perennials may be less likely to fluctuate in response to changes in seed numbers.