THE ELEMENTS OF CONNECTIVITY WHERE CORRIDOR QUALITY IS VARIABLE

Small mammals in heterogeneous environments have been found to disperse along corridors connecting habitat patches. Corridors may have different survivability values depending on their size and the degree of cover they provide. This deterministic model tests the effects of varying corridor quality on the demographics of a metapopulation of Peromyscus leucopus. Two types of corridors are defined based on the probability of survival during a dispersal event. Results indicate that mortality during movement through corridors influences metapopulation demographics. We found that: 1. Any connection between two isolated patches is better than no connection at all in terms of persistence and population size at equilibrium. 2. Metapopulations with exclusively high quality corridors between patches have a larger population size at equilibrium than do those with one or more low quality corridors. 3. Increasing the number of high quality corridors between patches has a positive effect on the size of the metapopulation while increasing the number of low quality corridors has a negative effect. 4. The addition to a metapopulation of a patch connected by low quality corridors has a negative effect on the metapopulation size. This suggest the need for caution in planning corridors in a managed landscape. 5. There is no relationship between the number of corridors and the metapopulation size at equilibrium when the number of connected patches is held constant. 6. Geometrically isolated patches connected by low quality corridors are most vulnerable to local extinctions. We conclude that corridor quality is an important element of connectivity. It contributes substantially to the effects of fragmentation and should be carefully considered by landscape planners.