Species and genetic diversity patterns show different responses to land use intensity in central European grasslands
Abstract
Aim: Empirical studies have often reported parallel patterns of genetic and species diversity, but the strength and generality of this association, as well as its origin, are still debated. Particularly in human‐dominated landscapes with complex histories of land use histories, more complicated and partly diverging patterns have been observed. In this study, we examine whether species and genetic diversity correlate across grasslands with different levels of land use pressure and spatial differentiation in habitat quality and heterogeneity. Location: We selected eight extensively used (grazed, unfertilized) dry grasslands and eight intensively used (mown, fertilized) hay meadows in southeastern Germany. Methods: We used vegetation surveys and molecular markers of six widespread dry grassland and six hay meadow plant species to compare species and genetic alpha and beta diversity between the two grassland types. Results: Species diversity patterns expectedly showed higher alpha diversity, stronger spatial structure and less turnover in dry grasslands than in hay meadows. Neither of the corresponding genetic diversity patterns showed the same significant trends. Main conclusion: Our results question the idea that species and genetic diversity patterns will always show similar patterns. Likely, genetic and species diversity emerge partly from shared, partly from different processes, including the regional species pool, environmental heterogeneity, fragmentation and land use history. The practical conservation implication is that species and genetic diversity are not generally interchangeable. Looking at species and genetic patterns together, however, may eventually lead to a better understanding of the complex processes that shape the structure and dynamics of ecological communities.
What the paper shows and why it matters
(AI-generated)
Genetic diversity within species is a conservation goal in its own right and is sometimes used as an indicator of species diversity. Many studies found the two to go together, and Vellend (2005) and Vellend et al. (2014) offer a reasonable explanation: if both are shaped mainly by habitat patch size and isolation, as island biogeography and the island model of population genetics assume, they should run in parallel. This rests on equilibrium conditions, which are often the exception, particularly in human-dominated cultural landscapes. Other studies found no or even negative relationships; most studies of either kind examined a single species. The open question is whether the two still run in parallel in such landscapes.
The paper suggests that, in human-dominated landscapes, species diversity and genetic diversity are driven partly by the same processes and partly by different ones, so their patterns need not run in parallel. It tests this near Regensburg, comparing eight grazed dry grasslands with eight mown, fertilised hay meadows, using vegetation surveys and AFLP fingerprints of six common plant species per habitat. Species diversity differed: dry grasslands had more species per site, their communities were more strongly structured in space, and they differed less between sites. Genetic diversity within populations did not differ significantly between grassland types after allowing for species differences, nor did genetic differentiation between populations. Power is low with six species per habitat, but the paper reads the smaller estimated effects as suggesting that any genetic differences are likely smaller than the species differences. It conjectures that species patterns follow habitat differences, whereas genetic patterns are evened out by gene flow and by history, for example that dry grasslands were once the more widespread type and hay meadows now are.
Parallel patterns of species and genetic diversity cannot be taken for granted in human-dominated landscapes. Protecting species diversity may not automatically protect genetic diversity, and the genetic diversity of common species may not be a reliable stand-in for species diversity (or for endangered species), although the paper cautions that rare or self-compatible species could behave differently; it recommends considering both levels explicitly in conservation. The paper still favours studying the two together, as their differences carry complementary information, and calls for a landscape-scale theory of communities with models predicting both from the same processes.
References
- Vellend (2005). Species Diversity and Genetic Diversity: Parallel Processes and Correlated Patterns. The American Naturalist 166, 199–215. doi:10.1086/431318
- Vellend et al. (2014). Drawing ecological inferences from coincident patterns of population‐ and community‐level biodiversity. Molecular Ecology 23, 2890–2901. doi:10.1111/mec.12756