The incidence Function Model - Part II
2. Rescue effect
By this expression it is meant the situation in which emigrants from near occupied patches can reduce the extinction probability of a patch (Brown & Kodric-Brown 1977). To include the rescue effect in the basic model, Eq. (4.2) should be modified as
| (5.2) |
|
where Ci is as in Eq. (4.5), eventually modified by Eq. (5.1). The incidence Ji modifies accordingly.
Example 8.
We consider again the reference metapopulation of Example 4.1. After the computation of C as in Example 5.1, the extinction probabilities according to (5.2) are obtained by
E<-pmin((1-C)*A0^xhat/A^xhat,1)
# We compare these values to those obtained without rescue effect
Eold<-pmin(A0^xhat/A^xhat,1)
plot(E/Eold, xlab="patch", ylab=" E with Rescue Effect / E")
This picture shows the ratio between the extinction probabilities with and without rescue effect. It can be seen that in most cases the extinction probability reduces considerably (ratio close to 0) due to rescue effect.