Conclusions and Discussion - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 334

be thousands of such newly founded, isolated populations, and thousands
of local subpopulations may be affected by such processes depending on
the degree of subdivision and connectivity with nearby subpopulations.
The alteration of genetic diversity and allele frequency relationships will
follow pathways unique to each population. The resulting idiosyncratic
variation in genetic diversity across such populations may locally bring
about novel gene combinations in higher frequencies than possible for
the species when it is more highly homogenized. The development of
genetically unique subpopulations by these processes may especially hold
for marginal (parapatric) populations. Newly founded, isolated populations,
whether resulting from range expansion, anthropogenic fragmentation or
initiation, or natural disturbance, may be evolutionary playgrounds of the
sort where lineages of unique diversity and selection landscape histories
arise. Indeed, Budd and Pandolfi (2010) found that intraspecifi c evolutionary
novelty is often concentrated in more marginal populations in another set
of sedentary organisms, corals. Invasive species may follow this model to
varying degrees. As noted above, NEWGARDEN analyses demonstrated
that, even when subpopulations have signifi cant levels of realized gene fl ow,
they can remain genetically differentiated across numerous generations,
this also providing different local gene assemblages upon which selection
can act (and see Rauch and Bar-Yam 2004). Such differentiation will likely
increase as the number of distinct alleles per locus increases.
Thus far, our discussion of the effects of spationumeric founding effects
on evolution has focused primarily on loss or change in frequency of
unique alleles. However, in most of the NEWGARDEN analyses presented
earlier, effects on other population genetic measures of diversity dependent
on founder spationumeric effects, such as comparable trial differences
in heterozygosity, F values, and subpopulation differentiation, were
appreciable. Further, spationumeric founding effects on population growth
rates were often pronounced. Differences in population expansion could
have several evolutionary effects, such as the cumulative effects individuals
in populations have on mutualists, competitors, or resource modifi cation.
Obviously, spationumeric founder effects can affect the evolution of
populations in a variety of ways beyond allele frequency fl uctuations and
loss of unique alleles.
Several “meta-analyses” have demonstrated some degree of correlation
across plant species of certain life history characteristics with the degree
of genetic diversity maintained within and among populations (e.g.,
Hamrick 1983; Loveless and Hamrick 1984; Hamrick and Godt 1996).
These correlations are commonly not tight even though they often make
sense a priori . NEWGARDEN analyses above show that variations in local
colonization history (e.g., number of founders, pattern of introduction,
dispersibility in a given environment) can have weak to profound effects on