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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #261947
Title: Do populations of an invasive weed differ greatly in their per-gram competitive effects?

Author
item SOWERWINE, JAMES - Bureau Of Land Management
item Rinella, Matthew - Matt
item CARLSON, MATTHEW - University Of Alaska

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2011
Publication Date: 5/1/2012
Citation: Sowerwine, J.E., Rinella, M.J., Carlson, M.L. 2012. Do populations of an invasive weed differ greatly in their per-gram competitive effects?. Western North American Naturalist 72:43-47.

Interpretive Summary: Quantifying an invasive species’ negative impacts across its introduced range will be quite challenging if the impacts vary unpredictably from site to site or population to population. Little emphasis, however, has been placed on quantifying such inter-population variation in the impacts of individual invasive species. We studied the response of a native grass to competition from four geographically dispersed invasive plant (white sweetclover) populations in order to determine if some populations of this invader have greater competitive impacts than others. Despite our greenhouse study’s relatively large number of pots, we did not see evidence that competitive effects varied by invader population. Therefore, in some cases it should be possible to estimate invasive weed impacts with simple competition models, as long as the models control for invader yield. Invader yield must be controlled for, because it varies dramatically from population to population and invasive weed impacts intensify with increasing yield.

Technical Abstract: Quantifying an invasive species’ negative impacts across its introduced range will be quite challenging if the impacts vary unpredictably from site to site or population to population. Little emphasis, however, has been placed on quantifying such inter-population variation in the impacts of individual invasive species. We studied the response of a native grass (Festuca rubra) to competition from four geographically dispersed invasive plant (Melilotus alba) populations in order to determine if some populations of this invader have greater competitive impacts than others. Despite our greenhouse study’s relatively large number of experimental units, we did not see evidence that per-gram-of-biomass competitive effects varied by invader population. Therefore, in some cases it should be possible to estimate invasive weed impacts with simple competition models that ignore some forms of phenotypic variation, as long as the models control for invader biomass per unit area (i.e. invader yield). Invader yield must be controlled for, because it varies dramatically from population to population and invasive weed impacts intensify with increasing yield.