I have run a nMDS analysis in vegan and I have a few questions on the stress values of the analysis as well as the p-values associated with utilizing the ordisurf() function (also in vegan).
First of all, what is a good stress value? I know that getting closer to zero is ideal. Depending on how many dimensions I add this value changes. For example at k=2 my stress value is around 0.12, and k=3 it goes down to 0.08. I've looked around the web and have found different opinions. Some say 0.05 is a good cutoff while others say anything below 0.15 is considered "great". Any ideas?
Next, I've also started utilizing the ordisurf function to includes surfaces of my environmental data. As I understand it ordisurf essentially runs a general additive model using the environmental data as a response and using the nMDS axes as predictors. There is a p-value associated with this model. However, I am wondering whether or not to take these p-values with a grain of salt. For example if I have a p-value of 0.07 does that automatically throw out the usage of that model/surface?