where U is another normalized variable and Σ is the component of the environmental variance that cannot be explained by fluctuations in the covariates. This leads to the relation:
σ e2 = var(∑ai yi,t ) + σ2, eqn 5
so that the covariates together explain a fraction:
p = var(∑ ai yi,t )/[var(∑ ai yi,t ) + σ2], eqn 6
of the total environmental variance