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ARS Home » Pacific West Area » Burns, Oregon » Range and Meadow Forage Management Research » Research » Publications at this Location » Publication #166816



Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2005
Publication Date: 10/1/2005
Citation: Carpinelli, M.F. 2005. The absolute-log method of quantifying relative competitive ability and niche differentiation. Weed Technology. 19:972-978.

Interpretive Summary: Ecologists quantify the effects that different plant species have on each other's growth, or 'relative competitive ability,' to help understand and predict the outcome of management actions. For example, a simple greenhouse study may show that a phosphorus fertilizer helps a crop species gain a competitive edge over a weed species with which it commonly grows. This same type of information can be used to say to what degree plant species differ in niche, which helps revegetation specialists design seeding mixes that minimize competition among desirable species. Until now, quantifying relative competitive ability and 'niche differentiation' has been mathematically limited to only those situations where species negatively interfere, or compete, with one another. However, it is known that some species have no effect, or 'neutral interference,' on each other, while some even enhance the growth of their neighbors, so-called 'positive interference.' The Absolute-Log Method is a new mathematical approach that is capable of quantifying the effects that different plant species have on each other for all types of interference'positive, negative, and neutral. This method will extend the ability of ecologists to increase the success and profitability of farming, restoration, and natural resource preservation.

Technical Abstract: Controlled studies designed to quantify interference between plant species provide valuable information on competitive interactions and on the effects of agronomic practices on those interactions. The effect of each species' density on the growth of itself, and on the growth of the other species, is quantified in a series of regression models. Traditionally, the models' regression coefficients are combined in a series of ratios to quantify relative competitive ability and niche differentiation. Coefficients that are negative (positive interference'facilitation, mutualism) or zero (neutral interference or nonsignificant coefficient) do not lend themselves well to use in ratios because of sign-cancellation or undefined values, respectively. As a result, ratio-based methodology is limited to using only positive coefficients (negative interference'amensalism, competition). Rather than using ratios, the Absolute-Log Method uses addition and subtraction of coefficients converted to a pseudologarithmic scale, thus allowing for use of coefficients whose values are negative or zero. As a result, the Absolute-Log Method can be used to quantify relative competitive ability and niche differentiation involving all types of interference--negative, positive, and neutral.