Human influence lowers plant genetic diversity in communities with extinction debt

Abstract

Summary1. Loss of plant species induced by adverse human influence and habitat fragmentation might be delayed due to a slow response to changed environmental conditions. This phenomenon is known as extinction debt, which can lead to the underestimation of actual threats to biodiversity. To adequately estimate the condition of recently fragmented plant communities and avoid future loss of species, good indicators of forthcoming extinctions are needed. 2. We studied the behaviour of genetic diversity of a relatively common habitat specialist grass Briza media in fragmented calcareous grasslands in which the extinction debt has been previously documented. Species richness in this system is shown to be determined by historical landscape patterns and human population densities prevailing centuries ago. We hypothesize that genetic diversity in this grassland system is related to current landscape patterns and contemporary human impact since genetic diversity might react more quickly to environmental changes than species diversity. 3. In contrast to species diversity, genetic diversity was indeed best described by current connectivity of grasslands. Additionally, genetic diversity was negatively related to current human population density, indicating an adverse effect of contemporary human settlements on studied species. The faster response of genetic diversity to changed environmental conditions compared to species richness was further supported by the absence of an expected correlation between species richness and genetic diversity. 4. Human population density a century ago had a positive effect on genetic diversity. A similar effect has been demonstrated for species richness in these grasslands, indicating that traditional land use in the past has supported the development of both genetic and species diversity. 5. Synthesis. Genetic diversity of Briza media in fragmented communities is reacting quickly to changes in landscape structure and anthropogenic pressure. Our results confirm that plant species can be prone to genetic deterioration due to habitat fragmentation and negative anthropogenic impact even if the decline in species richness has been delayed by extinction debt. Thus, a decrease of population genetic diversity in fragmented communities can be taken as the first indication of future species losses.

The structuring of quantitative genetic variation in a fragmented population of Briza media (Poaceae)

“…Prentice et al 2006Prentice et al , 2007Johansson et al 2008;Reitalu et al 2009), and that changes in long-term adaptive potential may be of lesser concern than the more immediate effects on marker gene variation, population viability or species diversity (Saunders et al 1991;Harrison and Bruna 1999;Kiviniemi and Eriksson 2002;Leimu et al 2006;Aguilar et al 2008;Helm et al 2009). As more studies begin to integrate data on different types of biodiversity (Antonovics 2003;Vellend 2004), it will be possible to make broader generalizations about the biological consequences of habitat fragmentation-and the conservation strategies needed to manage, restore and maintain diversity in fragmented grassland landscapes.…”

“…The loss and fragmentation of grasslands has been accompanied by reductions in species diversity (Kiviniemi and Eriksson 2002) and the local extinction of subspecies or varieties adapted to traditional grazing or mowing practices (e.g., Karlsson 1986). Studies using marker genes reveal that some grassland species show clear evidence of genetic drift as a result of population fragmentation (e.g., van Treuren et al 1994;Luijten et al 2000;van Rossum et al 2004;Helm et al 2009), while other studies show low levels of differentiation between fragmented populations (e.g., Weidema et al 2000;Honnay et al 2006). Prentice et al (2006) used allozyme data from the outcrossing, perennial grass Briza media to explore the association between genetic diversity and various descriptors of landscape structure and land-use history in a fragmented grassland landscape on the Baltic island of Ö land (SE Sweden).…”

The structural and functional connectivity of the grassland plant Lychnis flos-cuculi

“…Second, we examined the effects of landscape elements on gene flow in L. floscuculi using a landscape genetic approach based on transects Angelone et al, 2011;Van Strien et al, 2012). We hypothesised that settlements, agricultural land, forests and topography (that is, elevation change) negatively affect gene flow (Tewksbury et al, 2002;Helm et al, 2009;Keller et al, 2012;Pellissier et al, 2012), whereas the amount of ditch verges being one of the key habitats of this species in contemporary agricultural landscapes facilitate gene flow in L. flos-cuculi.…”

Genetic variation in the moss Homalothecium lutescens in relation to habitat age and structure

“…The impact of past population processes and landscape context and history can be investigated with the help of land-use maps or geological data. For example, some studies have used the height of islands in the Baltic postglacial land-uplift areas as a proxy for habitat age (Giles and Goudet 1997;Cronberg 2002), while other studies have used old maps and aerial photographs to characterize the properties of the historical landscape (Jacquemyn et al 2004;Prentice et al 2006;Helm et al 2009;Münzbergová et al 2013). These studies reveal associations between levels of genetic variation within populations of plants, and habitat age and (or) landscape structure, in both forests and grasslands.…”