Closely related invasive species may be controlled by the same demographic life stages

Authors: MOLOFSKY, JANE - University Of Vermont; THOM, DOMINIK - Technical University Of Munich; KELLER, STEPHAN - University Of Vermont; Milbrath, Lindsey

Submitted to: NeoBiota
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2023
Publication Date: 3/2/2023
Citation: Molofsky, J., Thom, D., Keller, S.R., Milbrath, L.R. 2023. Closely related invasive species may be controlled by the same demographic life stages. NeoBiota. 82:189-207. https://doi.org/10.3897/neobiota.82.95127.
DOI: https://doi.org/10.3897/neobiota.82.95127

Interpretive Summary: Populations of spotted knapweed and meadow knapweed, two invasive plant species of increasing concern in meadows and grasslands of the Northeast, may develop similarly and therefore be controlled by targeting the same life stages. We tracked germination, survival, growth and seed production of the two knapweed species at several sites over three years in New York. Analyses indicated that the two knapweed species did indeed respond similarly to simulated changes in seed production, recruitment of new seedlings into a population, the survival of established seedlings, and the rate at which vegetative individuals began to flower. Based on successful management of knapweeds in other parts of the country, it is likely that northeastern populations of both spotted and meadow knapweed can be controlled by increased mortality of older seedlings and juvenile plants. Chemical, mechanical and biological control tactics should be investigated further to determine how they can specifically contribute to management of these troublesome plants.

Technical Abstract: Invasive species that are closely related to each other may have similar population dynamics and therefore be controlled by targeting similar life stages. We studied two invasive knapweed species, spotted knapweed (Centaurea stoebe subsp. micranthos) and the hybrid meadow knapweed complex (Centaurea × moncktonii) in New York, USA, to determine their individual population growth rates (') across several sites over three years. Both knapweed species had growth rates that were greater than 1 (spotted knapweed ' ranged from 1.005-1.440; meadow knapweed ' ranged from 1.541-2.408) but there was high variability between years and sites. One study population of meadow knapweed was composed primarily of individuals of black knapweed ancestry (C. nigra), a species that while introduced is not invasive. For this population, the projected dynamics were stable (' approximately 1). Elasticity analysis showed that the flowering-to-flowering stage contributed the most to population growth rate for six of seven sites, and three additional transitions were also influential for four of seven sites of spotted and meadow knapweed: the seedling-to-vegetative stage, vegetative-to-flowering stage and flowering-to-seedling stage. We simulated how increasing vital rates would affect population growth and found that both spotted and meadow knapweed followed the same pattern. The vital rate of established seedlings maturing to flowering plants had the greatest effect on population growth, followed by the survival of new and established seedlings. In all cases the responses were non-linear, with small initial changes having a large effect. Increases in the vital rates of later stages also tended to have a positive effect on growth rate but the effects were more modest. Although the sensitivity analysis indicated that early vital rates had the largest effect on population growth, targeting these stages is not practical for management. Rather, reducing older life stage survival or delaying maturation of vegetative individuals are more promising. The similarity between the population dynamics and how each life stage contributes to population growth provides support that protocols developed for one species should be effective for the other species with the caveat that any biological control agent should be directly tested on the target species before being utilized