Population dynamics of Microtus pennsylvanicus in corridor-linked patches

Corridors have become a key issue in the discussion of conservation plannin g: however, few empirical data exist on the use of corridors and their effe cts on population dynamics. The objective of this replicated, population le vel, capture-re capture experiment on meadow voles was to estimate and comp are population characteristics of voles between (1) corridor-linked fragmen ts, (2) isolated or nonlinked fragments, and (3) unfragmented areas. We con ducted two field experiments involving 22600 captures of 5700 individuals. In the first, the maintained corridor study, corridors were maintained at t he time of fragmentation, and in the second, the constructed corridor study , we constructed corridors between patches that had been fragmented for som e period of time. We applied multistate capture-recapture models with the r obust design to estimate adult movement and survival rates, population size , temporal variation in population size, recruitment, and juvenile survival rates. Movement rates increased to a greater extent on constructed corrido r-linked grids than on the unfragmented or non-linked fragmented grids betw een the pre- and post-treatment periods. We found significant differences i n local survival on the treated (corridor-linked) grids compared to surviva l on the fragmented and unfragmented grids between the pre- and post-treatm ent periods. We found no clear pattern of treatment effects on population s ize or recruitment in either study. However, in both studies, we found that unfragmented grids were more stable than the fragmented grids based on low er temporal variability in population size. To our knowledge, this is the f irst experimental study demonstrating that corridors constructed between ex isting fragmented populations can indeed cause increases in movement and as sociated changes in demography, supporting the use of constructed corridors for this purpose in conservation biology.