I am calculating indices for the importance of competition based on a competition experiment involving different genotypes of two species grown in competition and alone in two different soil environment. I would like to use the Cimp of Brooker et al (OIKOS 2005) where Cimp = (Pt+n – Pt-n)/(MaxPt-n – y), Where MaxPt-n refers to the maximum value (here biomass) of P when grown alone among the environments, and y is the smallest of either Pt+n or Pt-n. I am running into the problem that I have genotypes in some combinations for which the MaxPt-n and y are the same and hence the index cannot be calculated (division by zero). It occurs for some genotypes which perform better when growing with a neighbor relative to without. Guess than means that calculating the relative importance of facilitation is more appropriate? Have anyone had similar “problems” and/or does anyone know of a similar index to Cimp which can calculate the importance of competition relative to the impact of the environment?
I think there are a range of indices that can quantify the importance of competition, i.e. the importance of competition relative to the environment. See the opinion paper by Kikvidze et al. (2011) Importance versus intensity of ecological effects: why context matters. TREE, 26, 383-388. I think, the most commonly used importance index to date is the Iimp index by Seifan et al. (2010) Facilitating an importance index. Journal of Ecology, 98, 356-361 (http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2009.01621.x/abstract).
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