The outcome of these interactions is that a single clone may eventually competitively exclude other clones, potentially decreasing future sexual reproduction by decreasing outcrossing potential.
Both processes can decrease outcrossing rates and genetic variation in remnant stands.
As we increased the spatial scale of analysis (Fig. 1), we expected R2 to increase if the added area helped to explain outcrossing, but to decrease once the scale exceeded the distance to which outcrossing occurred.
While some studies have found increases in self-fertilization with elevation [13], [14], there is also evidence of increased outcrossing [15] and decreased selfing rates with elevation [16].
These results indicate that the selfing rate decreased and outcrossing increased over time.
However, we expect that in cases where Brassica hybrid fecundity is restored in backcross generations (see, for example, Jørgensen et al., 2009; Snow et al., 2010) the dependence on the parental species would decrease, whereas higher outcrossing rates would further increase dependence on the parental seed bank dynamics.
The fragmentation of plant populations may decrease seed production and outcrossing rates due to limitations of mates and pollinators in the remaining, fragmented populations, potentially reducing reproductive success [ 1, 2].
For instance, self-fertilization is associated with a reduction in the effective population size [ 13] and Caenorhabditis species which have experienced a transition from obligately outcrossing to selfing show a concomitant decrease in codon bias [ 14].
Consequently, if repeated mating of hermaphrodites did occur in the experimental populations, then the higher costs (i.e. offspring loss) of copulations with multiple males for N2 should decrease male frequencies and thus outcrossing rates to a larger extent in N2 than CB4856.
Fragments also had a slight but statistically significant decrease in the proportion of self-incompatible and overall obligatory outcrossing species (self-incompatible+dioecious; Table 2).
