Print PageUnderstanding the importance of top-down consumer and bottom-up resource controls on plant productivity and community structure is a central and longstanding theme in ecology. For non-native invasive plants, research investigating the collective effects of such factors on plant performance may provide important insight into the success and management of these introduced species. Through a combination of observational and experimental field studies, we examined top-down and bottom-up effects on the growth and reproduction of the invasive plant Linaria dalmatica (Plantaginaceae). First, we assessed attack levels and impacts of an introduced biocontrol agent, the stem-mining weevil Mecinus janthinus (Curculionidae), on L. dalmatica plants across multiple years and sites. Then, we conducted a manipulative experiment to examine the effects of weevil attack, soil nitrogen availability, and inter-specific competition on L. dalmatica.
Results/Conclusions
We found substantial variation in weevil attack within populations as well as across sites and years. Observational and experimental data showed that increased weevil attack was associated with a reduction in plant biomass and seed production, but only at the highest levels of attack. Nitrogen addition had a strong positive effect on plant performance, with a two-fold increase in biomass and seed production. Clipping neighboring vegetation resulted in no significant effects on L. dalmatica performance, suggesting that plants remained resource limited or continued to experience belowground competitive effects. Overall, our research indicates that M. janthinus can exert top-down effects on L. dalmatica; however, weevil densities and attack rates observed in this study have not reached sufficient levels to yield effective control. Moreover, bottom-up controls, in particular soil nitrogen availability, may have a large influence on the success and spread of this invasive plant.
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