Habitat loss causes non-linear genetic erosion in specialist species

Habitat loss can lead to non-linear declines in species abundance once the amount of landscape-wide habitat is reduced to a critical value. Previous studies have suggested that such non-linear responses to landscape-wide habitat loss might also exist in genetic variation, and an in-depth understanding of non-linear habitat loss effects on all levels of biodiversity levels is vital to take appropriate conservation actions.Using individual-based simulations we evaluated the existence of generic non-linear responses in three different response variables and across different combinations of traits related to dispersal and population density. We simulated habitat loss scenarios by incrementally reducing the landscape-wide habitat amount within a previously undisturbed landscape and monitored population abundance, genetic diversity and differentiation of populations within constant sampling areas over time. We found aside from population abundance, genetic variation also responded non-linearly to habitat loss across all scenarios. Importantly, the populations that persisted in remaining habitat fragments experienced genetic erosion before a noticeable effect on local abundance occurred. The observed increase in genetic differentiation and the decrease in genetic diversity of remaining populations are likely caused by the indirect effects of landscape-wide habitat loss on effective patch isolation. Thus, genetic data might have the potential to detect indirect effects of landscape-wide habitat loss before it directly affects the size of a population. Since indirect effects of habitat loss might go unnoticed when extinction risk is estimated from abundance data alone, we argue that an improved understanding of genetic effects is crucial to anticipate and ultimately prevent the negative effects of habitat loss. Keywords: Biodiversity, Extinction threshold, Habitat fragmentation, Population decline, Genetic diversity, Genetic structur