Land-use changes are a significant threat to biodiversity and are known to have tremendous effects on the taxonomic diversity and species composition of plant communities (Sala et al. 2000; Newbold et al. 2015). The degree to which land-use differences may also generate differences between populations in terms of key functional traits is less well understood.
When habitats change, plants within these habitats have to adapt to the new conditions to avoid being threatened by local extinction. If these habitat changes constitute strong selection pressures, adaptation and therefore genetic differentiation can occur rapidly.
Temperate grasslands are such habitats that are important for studying micro-evolutionary changes in response to land use because of their wide distribution and economic importance. Land use in these grasslands involves multiple processes, in particular mowing, grazing and fertilization. All these processes likely exert strong but different selection pressures on plant populations. Consequently, different populations under different land use become genetically differentiated, and this would translate in a change in plant functional traits across the populations.
Our study aims to understand how such evolutionary effects of land use are across species. In addition, we were also interested to know which land use factors contribute the most to genetic differentiation and which plant traits are the most responsive.
We investigated eight common grassland species with 23 to 108 populations per species. As population differentiation may also vary across geographic regions, depending on climatic or edaphic conditions (Joshi et al. 2001), we sampled populations distributed across three regions in Germany.
We collected seeds from grasslands with different land use regimes and intensities and from those we grew plants in a common garden. Here, plants are grown under the same environmental conditions and trait differences therefore reflect genetic differences of plants derived from sites of different land use intensities.
Our study shows that evolutionary responses to land use change are a common phenomenon and widespread across a broad range of grassland species, even though the specific evolutionary changes are to a large degree species-specific. Among the studied land use processes, mowing appeared to have the strongest effect on population differentiation, and flowering phenology was the most responsive trait.
Changes in flowering phenology are particularly striking and may have far-reaching consequences because (1) it can reinforce evolution by preventing gene flow among adjacent populations, and (2) it can have cascading effects on associated biological communities. Moreover, flowering phenology is also expected to be under selection by global climate change (Fitter & Fitter 2002; Franks, Sim & Weis 2007).
Thus, evolutionary changes in response to land use intensity are likely to interact with the effects of other global change processes, may shift niches within a community and feed back on species interactions and ecosystems functioning (Post & Palkovacs 2009; Lavergne et al. 2010).
Eva Völler, University of Lüneburg, Germany
You can read the full paper here; Evolutionary responses to land use in eight common grassland plants