Distances, climatic differences, and vegetation similarities of alpine grasslands in Europe

The importance of environmental difference among sites and dispersal
limitations of species to the explanation of diversity differs among
biological systems and geographical regions. We hypothesized that climate
and then dispersal limitation will predominantly explain the similarity of
alpine vegetation at increasing distances between pairs of regions at
sub-continental extent. We computed the similarity of all pairs of 23
European mountain regions below 50°N after dividing the species lists of
each region by calcareous or siliceous substrates. Distance decay in
similarity was better fitted by a cubic polynomial than a negative
exponential function, and the fit was better on calcareous than on
siliceous substrate. Commonality analysis revealed that the proportion of
explanation of beta diversity by climatic difference had unimodal patterns
on a gradient of increasing distance between regions, while explanation by
dispersal limitation had consistently rising patterns on both substrates.
On siliceous substrate, dispersal limitation explained more of the
variation in beta-diversity only at longer distances, but it was
predominant at all distances on calcareous substrate. The steeper response
to distance at <1600 km and >2600 km may indicate dispersal
limitation at different temporal scales, and the uptick in the response to
distance at the longest distances may reflect how isolated some regions
have been before and since the Last Glacial Maximum.