Relative Effects of Habitat Amount and Fragmentation Per Se on the Genetic Diversity of The Glanville Fritillary Butterfly

Abstract

Habitat loss and fragmentation are considered the key drivers of biodiversity loss. Understanding their relative roles is difficult as habitat loss and fragmentation tend to co-occur. It has been proposed that the total habitat amount available in the local landscape mainly drives species richness while fragmentation per se - the breaking apart of habitat independent of habitat amount - has negligible or even a positive effect on biodiversity. Several studies support this at the species richness level. Yet, the potential effects of fragmentation per se on genetic diversity at the landscape scale are understudied. Using the Glanville fritillary butterfly metapopulation in the [A]land islands, we tested the effects of fragmentation per se on genetic diversity using a landscape-based approach and 2,610 individuals genotyped at 40 neutral SNP markers. We assessed the independent effect of habitat amount and fragmentation (i.e. number of patches) within the local landscape on the focal patch genetic diversity. The amount of habitat in the local landscape had a positive effect on genetic diversity, while fragmentation per se had a more negligible impact on the genetic diversity. Our results thus highlight that all fragments, even the small ones, likely contribute to the maintenance of genetic diversity of the focal population.