Effect of Rotational Shepherding on Demographic and Genetic Connectivity of Calcareous Grassland Plants

Abstract

Response to habitat fragmentation may not be generalized among species, in particular for plant communities with a variety of dispersal traits. Calcareous grasslands are one of the most species-rich habitats in Central Europe, but abandonment of traditional management has caused a dramatic decline of calcareous grassland species. In the Southern Franconian Alb in Germany, reintroduction of rotational shepherding in previously abandoned grasslands has restored species diversity, and it has been suggested that sheep support seed dispersal among grasslands. We tested the effect of rotational shepherding on demographic and genetic connectivity of calcareous grassland specialist plants and whether the response of plant populations to shepherding was limited to species dispersed by animals (zoochory). Specifically, we tested competing dispersal models and source and focal patch properties to explain landscape connectivity with patch-occupancy data of 31 species. We fitted the same connectivity models to patch occupancy and nuclear microsatellite data for the herb Dianthus carthusianorum (Carthusian pink). For 27 species, patch connectivity was explained by dispersal by rotational shepherding regardless of adaptations to zoochory, whereas population size (16% species) and patch area (0% species) of source patches were not important predictors of patch occupancy in most species. [Correction made after online publication, February 25, 2014: Population size and patch area percentages were mistakenly inverted, and have now been fixed.] Microsite diversity of focal patches significantly increased the model variance explained by patch occupancy in 90% of the species. For D. carthusianorum, patch connectivity through rotational shepherding explained both patch occupancy and population genetic diversity. Our results suggest shepherding provides dispersal for multiple plant species regardless of their dispersal adaptations and thus offers a useful approach to restore plant diversity in fragmented calcareous grasslands.

Directed dispersal by rotational shepherding supports landscape genetic connectivity in a calcareous grassland plant

“…Population genetic diversity in patches grazed by sheep exhibits higher levels of genetic diversity compared with ungrazed patches (Rico et al . ). Average inbreeding F IS in D. carthusianorum was rather low ( F IS = 0.095), but contrary to our expectation, small ungrazed populations showed lowest F IS coefficients, which were significantly lower than those of small populations of grazed patches.…”

“…A previous analysis in D. carthusianorum in this study area suggested that both patch occupancy and genetic diversity are associated with rotational shepherding (Rico et al . ).…”

“…On the basis of previous plant species surveys of calcareous grasslands in our study system, we categorized the size of populations using four ordinal classes: 1 = 1–4 individuals, 2 = 5–39 individuals, 3 = 40–99 individuals and 4 = ≥100 individuals (Rico et al . ). In populations with <40 plants, we collected leaf material from all flowering individuals, whereas for larger populations, we sampled 30–40 flowering individuals evenly across each patch.…”

“…Analysis of patch occupancy data showed that dispersal along shepherding routes and the diversity of microsites promoting establishment in focal patches were important predictors of patch occupancy for multiple species regardless of adaptations to zoochory (Rico et al . ). However, whether rotational shepherding connecting geographically fragmented calcareous grasslands also influences spatial genetic structure has not yet been shown.…”

Genetic diversity of calcareous grassland plant species depends on historical landscape configuration

“…However, it has recently been reported that the genetic diversity of the grassland species Succisa pratensis depends on the historical landscape structure of the habitat [15], which supports the results of our study. Moreover, it has been shown that the genetic diversity of Dianthus carthusianorum depends on patch connectivity by shepherding [61] and that population disconnection can create a genetic bottleneck, even in the absence of a demographic collapse [62], which underlines the importance of historical gene flow for the level of current genetic diversity.…”