Using three pairs of competitive indices to test for changes in plant competition under different resource and disturbance levels

Abstract

Questions: How do different resource and disturbance levels interact to affect competition? How do different indices of competition change the interpretation of how competition changes under different resource and disturbance conditions? Location: Greenhouse, Thompson Rivers University, Kamloops, British Columbia, Canada. Methods: Three pairs of indices that have been used to differentiate the predictions of Grime (CSR) and Tilman's (R Ã ) theories were used to assess competition on two species of temperate bunchgrass, (Pseudorogeneria spicata and Festuca campestris) grown in a greenhouse on stress and disturbance gradients. Stress was created by manipulating the amount of water (high, low) and concentration of nutrient solution (high, low) added to pots, while disturbance was created by clipping (clipped, unclipped) in a fully factorial design. Plants were grown individually or with a single neighbour. The three pairs of indices were: (1) absolute and relative competition; (2) competitive effect and response; and, (3) competitive importance and intensity. Results: Absolute competition and competitive importance were the only indices responsive to the resource gradient, which supports CSR theory, and also the only ones to record an effect of disturbance on the strength of competition -under high resource conditions. The other indices showed few responses along the gradients, which supports R Ã theory. Measures of competitive effect and response did not differentiate the two theories. Conclusion: We show that some indices of competition show a decline with increased stress and disturbance, while other indices do not. Therefore, it is necessary to choose a competition index appropriate to the question being asked. Competitive importance and absolute competition were responsive to changes in stress and disturbance, while the other indices were not.Keywords: Absolute and relative competition; Clipping; Competitive effect and response; CSR strategy theory; Drought; Festuca campestris; Importance and intensity of competition; Nutrient availability; Pseudoroegneria spicata; R Ã theory. Nomenclature: Douglas et al. (1994).Abbreviations: C ab 5 absolute competition; C int 5 competitive intensity; C imp 5 competitive importance; C e 5 competitive effect; C r 5 competitive response.

Competition, invasion effects versus invasiveness and fuzzy classification

“…For 2010, the Editors' Award goes to Carlyle et al (2010). Competition underlines the whole of vegetation science, and is examined or invoked in many of the papers in the Journal of Vegetation Science.…”

“…It has been suggested that the two protagonists are talking at cross purposes, one about the importance of competition and the other about the intensity of competition (Brooker & Kikvidze 2008), and this has already been addressed in the Journal (Jung et al 2009, working in floodplain meadows in Luxembourg; Liancourt et al 2009 working in grasslands in the French Alps). Carlyle et al (2010) improved on this in three ways. Firstly, much previous work has relied on an implied stress gradient, observed in the field, with ''stress'' assumed from standing crop or some measured environmental factor.…”

Effects of Competition, Salinity and Disturbance on the Growth of Poa pratensis (Kentucky Bluegrass) and Puccinellia nuttalliana (Nuttall’s Alkaligrass)

“…The inclusion of the plant's maximum biomass on the entire gradient in the equation enables the index to show the relative role of competition in different environments (or along the gradient). It must be acknowledged that the competitive importance index is thought to be biased towards supporting Grime's theory on competition along a gradient (Carlyle et al 2010). …”

“…While numerous competition indices have been developed to better understand the role of competition in plant community structure (Weigelt and Jolliffe 2003), this study focuses on competitive importance (Brooker et al 2005). Competitive importance indices have been identified as the best solution to determine the role of competition along a gradient (Brooker at al 2005;Carlyle et al 2010), but not without criticism (Freckleton et al 2009). The inclusion of the plant's maximum biomass on the entire gradient in the equation enables the index to show the relative role of competition in different environments (or along the gradient).…”

“…Absolute competition, relative competition and competitive intensity indices and analysis were conducted on the data, but competitive importance was selected as the best representation of the data due to the presence of significant values and its applicability to gradient analysis (Brooker et al 2005;Brooker and Kikividze 2008;Carlyle et al 2010).…”