or the logistic response function, 



E(p) = logitscl (6) 



1 . e (alpha+betaEGGS) 



The advantage of the logistic function is that it allows greater flexibility 

 in defining the shape of the relationship between egg density and survival 

 (fig. 3). With the Beverton-Holt and Ricker models, the greatest decline in 

 survival always occurs at the lowest densities. With the logistic function, 

 we can establish threshold levels where the density-dependent effects are 

 most acute and survival decreases most rapidly. Note that the logistic 

 model produces a dome-shaped egg-to-presmolt relationship similar to the 

 Ricker model. 



(A) 



Eggs 



(B) 



Eggs 



Figure 3 — General shape of the 

 relationship between initial egg 

 density and egg-to-smolt survival 

 generated using the Beverton-Holt 

 and Ricker models (A) and various 

 parameter combinations with the 

 logistic response function (B). 



9 



