Browsing by Subject "Habitat loss"

Biodiversity has been declining over the last decades due to land-use changes. Habitat loss and fragmentation are considered the key drivers of biodiversity loss. While evidence indicates that habitat loss has a negative impact on biodiversity, the effect of fragmentation itself is debated. The Habitat Amount Hypothesis proposes that fragmentation per se –more discontinuous habitat distribution but no difference in habitat amount- has no effect or even a positive effect on biodiversity. Studies have looked at its effect on species richness, but its impact on intraspecific genetic diversity is still unknown. In this thesis, I aimed to test this hypothesis using the Glanville fritillary butterfly, which has been extensively monitored in the Åland islands since 1990, as a model system. I studied how fragmentation per se affects genetic diversity of the focal populations, while controlling for the habitat amount within the landscape in the Åland islands. For this, I used an existing dataset for which larvae were sampled during two consecutive years and genotyped for 40 neutral SNPs, and calculated four genetic diversity indices in over 200 habitat patches with relatively high population abundance. Following Martin et al. (2021) protocol, I first defined the scale of effect. Then, to reduce the correlation between total habitat amount and number of habitat fragments, I split my dataset in two sub-datasets. Finally, I assessed for each sub-dataset the differences in genetic diversity between landscapes with different level of fragmentation and total habitat amount. The number of fragments had a neutral effect on the genetic diversity, supporting the habitat amount hypothesis. Moreover, the results suggest that all habitat fragments, even the small ones, are contributing to maintain the genetic diversity of the focal population. The species’ ecology, population dynamics and specific adaptations to a fragmented landscape might have led the Glanville fritillary butterfly to be especially resistant to fragmentation.