Table 2.

Season-specific density dependence in the gray-sided vole

Seasonal R	Model parameters (SE)			R2, %
Winter R = Scr(t) − Fcr(t − 1) =	−0.60Fcr(t − 1)	−0.56Scr(t − 2)	−0.76Fov(t − 1)	62.3
	(0.09)	(0.10)	(0.21)
Summer R = Fcr(t) − Scr(t) =	−0.29Fcr(t − 1)	−0.26Fcr(t − 2)		78.5
	(0.07)	(0.07)

Let F_cr(t) and S_cr(t) denote the fall and spring densities of gray-sided voles in year t, and let F_ov(t) and S_ov(t) be the fall and spring densities of other voles. Joint estimates of density effects on the population growth during winter and during summer are given. Only effects included in the statistically optimal model are shown. The estimated residual variance of the winter and summer are 0.35 and 0.22, respectively, and their covariance is −0.08. The R² column gives the amount of variation explained by the model in spring and fall densities, respectively. Elimination of the F_ov(t − 1) effect leads to a model worse by 9.08 AIC units. Hence, the fit is much better than in a model without any effects of other voles. However, inclusion of an S_ov(t − 2) effect on the winter growth (the second-best model) is worse by only 0.88 AIC units. SE values are given in parentheses.