Identifying critical life stage transitions for biological control of long-lived perennial Vincetoxicum species.
Demographic matrix modelling of invasive plant populations can be a powerful tool to identify life stage transitions for targeted disruption, in order to cause population decline. This approach can provide quantitative estimates of reductions in select vital rates needed to reduce population growth rate (λ) below 1 and can inform the prerelease selection of effective biological control agents, as in the case of two invasive Vincetoxicum species in North America. We parameterized a five life stage matrix model using vital rate data from six populations (field and forest) of Vincetoxicum nigrum and Vincetoxicum rossicum. Elasticity analyses were used to identify life stage transitions and associated vital rates for perturbation through the incorporation of per capita impact data of candidate agents. Several survival, growth and fecundity-related transitions were identified that were mostly similar across species, habitats and locations, although two populations showed unique population dynamics. Reductions in associated vital rates needed to prevent population growth varied greatly among populations. Defoliation damage and predispersal seed predation can be effective against slower growing forest and field populations of Vincetoxicum species. A fly and bivoltine moth are recommended as priority agents. However, biological control with these same agents will be ineffective against other field populations as well as some forest populations if the intensity of damage is not severe. Synthesis and applications. Control of long-lived perennial plants, such as species of Vincetoxicum, is projected to occur through disruption of some individual vital rates of survival, growth or fecundity if population increase is low to moderate (λ<1.6). However, without significant and simultaneous reductions in multiple lower level vital rates, faster growing populations will not be contained with biological control or other management tools.