Data from: Spatial genetic structure in continuous and fragmented populations of Pinus pinaster Aiton

Habitat fragmentation, i.e., the reduction of populations into small
isolated remnants, is expected to increase spatial genetic structure (SGS)
in plant populations through non-random mating, lower population densities
and potential aggregation of reproductive individuals. We investigated the
effects of population size reduction and genetic isolation on SGS in
maritime pine (Pinus pinaster Aiton) using a combined experimental and
simulation approach. Maritime pine is a wind-pollinated conifer which has
a scattered distribution in the Iberian Peninsula due to forest fires and
habitat fragmentation. Five highly polymorphic nuclear microsatellites
were genotyped in a total of 394 individuals from two population pairs
from the Iberian Peninsula, formed by one continuous and one fragmented
population each. In agreement with predictions, SGS was significant and
stronger in fragments (Sp=0.020 and Sp=0.026) than in continuous
populations, where significant SGS was detected for one population only
(Sp=0.010). Simulations suggested that under fat-tailed dispersal, small
population size is a stronger determinant of SGS than genetic isolation,
while under normal dispersal, genetic isolation has a stronger effect. SGS
was always stronger in real populations than in simulations, except if
unrealistically narrow dispersal and/or high variance of reproductive
success were modelled (even when accounting for potential overestimation
of SGS in real populations due to short-distance sampling). This suggests
that factors such as non-random mating or selection not considered in the
simulations were additionally operating on SGS in Iberian maritime pine
populations.