Diversity effect on plant defenses.

Summary of results from generalized linear mixed models testing for the effects of (a) big-leaf mahogany genotypic diversity and (b) plant species diversity on mahogany chemical defenses (polyphenolics and condensed tannins in the stem and leaves). To test the effect of mahogany genotype diversity we compared genotypic monocultures and genotypic polycultures, whereas to test for a species diversity effect we compared genotypic monocultures and species polycultures. Initial models testing only for an effect of diversity are designed as “Model 0”. For models labelled “Model 1”, we tested for an effect of diversity on defenses via growth-defense trade-offs by including plant height (proxy of growth) as a covariate. Finally, for models labelled “Model 2” we tested an effect of diversity via changes in herbivory by including H. grandella attack as a covariate. F-values and associated significance levels (P) are shown, as well as degrees of freedom (as subscripts in parenthesis). Significant (P<0.05) and marginal (0.05<P<0.10) P values are typed in bold.