Mixed model with nested random effect and repeated measures
Dear list, I have an issue with the design of an experiment. I am to analyze the data from this experiment that manipulated three levels of species richness and wanted to see the effects of it on several freshwater ecosystem functioning (productivity, decomposition, respiration). The author also nested 7 different species composition within each treatment. Each of these 7 was replicated twice (see figure attached) by randomly taking species from a species pool with a total 21 species. I want to use phylogenetic diversity (a continuous variable) as a predictor of each ecosystem functioning, instead of species richness. However, since there are 7 different species compositition nested within each species richness treatment, this yields 7 different values od phylogenetic diversities for each treatment. Additionally, the author also took 6 measurements of each ecosystem functioning throughout the experiment. I've tried to run a mixed model and specify the nested design for the random effect (phylogenetic diversity) in lme4, but I'm getting an error. My data is like (see whole dada attached): *tank* *treat* *comp* * PD* *div* time *prod* 1 18 1 1 2141.15 1 1 0.259 2 60 1 1 2141.15 1 1 0.269 3 20 4 1 2141.15 1 1 0.299 4 58 4 1 2141.15 1 1 0.294 5 18 1 1 2141.15 1 2 0.244 6 60 1 1 2141.15 1 2 0.295 Where PD = phylogenetic diversity; div=diversity; prod=productivity; tank= the cattle tank (sampling unit); treat=treatments The model I've tried to run with the nested factors is: m1 <- lmer(prod ~ factor(div)*factor(time) + factor(div)+ factor(time) + (1|comp) + (factor(PD)/factor(tank)/factor(time)), data = dados) The error is: Error in mer_finalize(ans) : Downdated X'X is not positive definite, 21. I really appreciate with anyone could help me with this. I have also attached a cartoon explaining the experimental design.
Atenciosamente, *Diogo Borges Provete* ============================== Bi?logo Mestre em Biologia Animal (UNESP <http://www.ibilce.unesp.br>) Doutorando PPG Ecologia e Evolu??o <http://www.ecoevol.ufg.br> Laborat?rio de Ecologia de Insetos (sl. 222) Departamento de Ecologia <http://www.icb.ufg.br/pages/18570> Instituto de Ci?ncias Biol?gicas <http://www.icb.ufg.br> - ICB 1 Universidade Federal de Goi?s <http://www.ufg.br>, campus II Goi?nia-GO 74001-970 Brazil Tel. Lab. +55 62 3521-1732 *Cel. +55 *62 8231-5775 * *: diogoprovete *Personal web page <http://diogoprovete.weebly.com>* Editor Herpetology Notes<http://www.herpetologynotes.seh-herpetology.org/index.html> NorthWestern Journal of Zoology<http://biozoojournals.3x.ro/nwjz/index.html> ==============================