When management might backfire: Density-dependent population dynamics of the invasive biennial Alliaria petiolata (Garlic Mustard).
Drake, John*,, Knight, Tiffany, Chase, Jon,
ABSTRACT- Most theory in biological invasions has focused on growth and spread of naturalized, invasive populations, whereas the greatest opportunities for control occur early in the invasion process before population dynamics are well understood. How much information on population biology is required to effectively manage species invasions is controversial. Here we present evidence of density-dependence in seed production and rosette survival in the invasive biennial Alliaria petiolata (Garlic Mustard) from populations in a second-growth oak and hickory forest near St. Louis, Missouri. The coupling of density-dependent vital rates, a three stage life cycle, and an annual time scale for population growth creates the potential for complex dynamics including two-cycles, four-cycles, and chaos. Intervention in such nonlinear dynamical systems can lead to unexpected consequences. Thus, we introduce a model for garlic mustard population dynamics with two kinds of control: (i) removal of rosettes by herbicide or manual pulling, and (ii) removal of adults (by the same methods). In our model, population abundance is sensitive to these controls. In particular, partial control releases individuals from intra-specific competition resulting in negligible gains from intervention or even increased abundance. Generally, incomplete controls (<90% effectiveness) fail to cause the population to stabilize. These results suggest that to prevent management interventions from backfiring, control efforts for garlic mustard must be highly efficient, removing most individuals in a population. A spatial version of this model shows how population cycles can result in repeating waves of invasion. Thus, we conclude that information about population biology may be important for controlling some invasive species and we suggest that high quality information about population dynamics might often be obtained through experimental control. Delaying management because information is lacking is unwarranted.
Key words: Garlic mustard, population dynamics, invasive species, complex dynamics and chaos
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