, Volume 22, Issue 10, pp 2375-2400
Date: 26 Jul 2013

Meta-analysis reveals microevolution in grassland plant species under contrasting management

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Grassland species might be under differential selection pressure due to management regimes by man or unmanaged grazers. To investigate microevolutionary changes in plants, I used a meta-analysis and a comparative approach. This analysis incorporates 28 studies on 19 species in 3 paired management regimes with a total of 152 reported trait values resulting in 40 pooled Hedge’s d effect sizes on genetic, vegetative and reproductive traits as well as 83 Hedge’s ds of 14 specific traits. Of the pooled and specific traits, 60 and 72 % indicated divergent selection pressures within a management regime. The pooled Hedge’s ds did not differ among the management regimes. Within mown versus grazed sites, trait groups were affected differently with increased reproductive traits in plants originating from grazed sites. In the other management regimes, the trait groups were affected similarly, except of some specific traits. Longevity, palatability, clonality and biome origin did not explain differences in pooled effect sizes, but tended to explain differences in some specific traits. Overall, general selection patterns were rare probably due to a high heterogeneity of among and within species responses, which might level each other out. Moreover, the number of data points per group of interest is often low and thus, for a final conclusion more studies are needed. Nonetheless, the divergent plant reactions indicate that selection pressures within paired management regimes might be large enough to induce microevolutionary changes in grasslands. Subsequently, the increased variation within species under different management techniques might buffer species persistence in the long term.