Context. Plant populations in agricultural landscapes are mostly fragmented and their functional connectivity often depends on seed and pollen dispersal by animals. However, little is known about how the interactions of seed and pollen dispersers with the agricultural matrix translate into gene flow among plant populations.

Objectives. We aimed to identify effects of the landscape structure on the genetic diversity within, and the genetic differentiation among, spatially isolated populations of three temperate forest herbs. We asked, whether different arable crops have different effects, and whether the orientation of linear landscape elements relative to the gene dispersal direction matters.

Methods. We analysed the species’ population genetic structures in seven agricultural landscapes across temperate Europe using microsatellite markers. These were modelled as a function of landscape composition and configuration, which we quantified in buffer zones around, and in rectangular landscape strips between, plant populations.

Results. Landscape effects were diverse and often contrasting between species, reflecting their association with different pollen- or seed dispersal vectors. Differentiating crop types rather than lumping them together yielded higher proportions of explained variation. Some linear landscape elements had both a channelling and hampering effect on gene flow, depending on their orientation.

Conclusions. Landscape structure is a more important determinant of the species’ population genetic structure than habitat loss and fragmentation per se. Landscape planning with the aim to enhance the functional connectivity among spatially isolated plant populations should consider that even species of the same ecological guild might show distinct responses to the landscape structure.

The data refer to 42, 34 and 36 populations of the forest herbs Anemone nemorosa, Oxalis acetosella and Polygonatum multiflorum, respectively, sampled in seven 5 x 5 km² landscape windows across Europe (North France, Belgium, West Germany, East Germany, South Sweden, Central Sweden,  Estonia). The location of each population is published in the related dataset https://doi.org/10.5061/dryad.tb2rbp00k .

The dataset comprises

(a) pairwise genetic differentiation among populations within landscape windows

The microsatellite allele data used to calculate pairwise genetic differentiation among populations are available and have been described in the related dataset https://doi.org/10.5061/dryad.tb2rbp00k . We used two measures of genetic differentiation, G''_ST (Meirmans & Hedrick 2011, Mol Ecol Resour 11(1):5-18) and D_PS (= 1 minus the proportion of shared alleles).

(b) landscape metrics calculated for buffer zones around each population

We calculated a set of landscape metrics (see Table 1 of the original article) in buffer zones around each herb population. Several buffer distances were chosen to reflect range sizes and forage distances of potential seed and pollen dispersal vectors (Table 1 of the original article): 125 m, 250 m, 500 m, 1000 m and 2000 m. For each buffer zone, we calculated the percent cover of different area-based land-use types, the relative length of different linear landscape elements (= total length divided by buffer area) and two index measures, i.e. the Shannon diversity of land-use types and the density of all land-use patch edges (Table 1). Since the effect that a linear landscape element exerts on gene dispersal might depend on its orientation relative to the movement direction of vectors (orthogonal vs. parallel), we calculated also the orthogonal and parallel length component of each linear landscape element (see Figure 1c and d in the original article). In buffer zones, the parallel direction corresponds to the direction from the midpoint of the linear element to the population centre. The orthogonal-to-parallel length ratio was then used as conditioning variable in statistical models. Moreover, the effect of settlement areas on gene dispersal vectors might depend on the relative proportion of sealed or built-up area vs. unsealed green areas, such as gardens. The latter might serve as forage habitat for pollinators, particularly, when many fruit trees or ornamental shrubs can be found there. Therefore, we used also the proportion of green settlement area as conditioning variable in statistical models.

(c) landscape metrics calculated for landscape strips connecting populations.

We calculated the same set of landscape metrics also for rectangular landscape strips connecting the centres of each pair of herb populations within landscape windows. We chose several width-to-length ratios for the landscape strips connecting the herb populations to account for the fact that different pollen and seed dispersal vectors have different sight distances for their orientation and thus will move more or less linearly through the landscape: 1:7, 1:5, 1:3, 1:2 and 2:3. As for buffer zones, we also calculated the orthogonal and parallel length component of each linear landscape element. Here, the parallel direction corresponds to the connection line between population centres.

See the README file.