The Effect of Habitat Corridors on Rates of Transfer and Interbreeding between Vole Demes

Abstract

It has been proposed that habitat corridors enhance exchange of individuals (transfer) and interbreeding between otherwise isolated demes in fragmented populations. However, due to the paucity of experimental studies this proposition has become controversial. We tested these proposed effects of corridors in 12 experimentally fragmented root vole populations. A 50-m long habitat corridor connected two large habitat patches in each of six treatment populations, while equivalent habitat patches in six control populations had no corridor connection. Each of the two patches in each population was initially colonized by founder demes that were monomorphic with respect to two different marker alleles of a single locus. The rate of transfer of individuals and the resultant degree of interbreeding (heterozygosity) between the two demes were monitored by capture–recapture methodology and genetic analyses over the reproductive season. Females were predominantly philopatric in these populations; more than four-fifths of the founder deme females settled and reproduced in their original patch. However, corridors significantly facilitated the transfer of females. The transfer rate of males was generally very high; approximately four-fifths, independent of the experimental factor (absence or presence of corridors). The sex-specific transfer pattern gave rise to very high rates of interbreeding (heterozygosity). The rate of interbreeding was enhanced by the presence of corridors, and more so than expected from the transfer rate. The lack of concordance between expected and observed heterozygosity in the corridor populations was probably due to short-term mating excursions facilitated by the presence of corridors.