Fig. 2: Path models showing causal relationships between the evolution of niche components and species diversity in Nearctic aphids.
From: Geographic isolation drives speciation in Nearctic aphids

Values on edges are standardized mean differences for the combined effects of the first two principal components for variables representing environmental niches and host-use niches. Arrow width indicates relative strength of effect. The p-value provided for each model is for a Chi-squared tests of goodness-of-fit; as a rule of thumb, values >0.5 indicate a good fit to the data. a Best model of the causes of variation in the species richness of aphid genera. b Best model of how host-use evolution and environmental niche evolution affect speciation rate. c Best model of how the host-use evolution, host-use breadth evolution, and environmental niche evolution affect speciation rate.