Conclusions and Discussion - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 313

population genetic idiosyncrasies because in establishing populations,
founders get one chance to contribute their genes to the next generation.
If a founder is lost without successfully reproducing in the only bout of
mating in which it can participate, then its unique alleles (or those of its
early cohort members) are lost from the population, unless there are copies
in other founders or early cohort members that do successfully reproduce.
Such idiosyncratic allele losses will lead to more variation among small,
isolated populations. In contrast, when founders are perennial, they have
numerous opportunities to pass their genes to several different cohorts
before they perish, and thus unique allele retention through time will be
higher.
NEWGARDEN can be used in analyzing the effectiveness of preserve-
corridor systems with different shapes in promoting population growth
and genetic diversity conservation. The effects of islands or barriers can
likewise be investigated.
Corridors, even with different heights and lengths, do not always have
much effect on diversity maintenance under a broad range of conditions
for newly founded populations. Thus, splitting founders on two sides of
a corridor, while not having a large effect on overall population genetics,
can increase the safety of an introduction project by protecting against an
almost total loss of individuals at one location (e.g., by fi re or disease).
The preserve-corridor system trials presented in this topic demonstrate
that, in some cases, knowing offspring and pollen dispersal distance patterns
for a species is critical in designing optimal plans for introducing founders.
Not all species will respond the same way to a given founder-preserve-
corridor system.
In several NEWGARDEN trials presented in this topic, although there
was an initial rapid decline of low-frequency unique alleles, rates of loss
often declined to the point where only a few unique alleles were being lost
across generations as the population expanded in size. Despite the early
loss of unique alleles, a signifi cant number of low-frequency alleles could
be retained in such populations. Losses of heterozygosity often showed
a similar pattern. This suggests that even in populations founded from
relatively few founders (e.g., 172 or fewer), many alleles can be maintained
at very low frequencies for many generations, and thus, many such alleles
may be resident in source populations for newly founded populations.
NEWGARDEN trials can be used to compare the risk of lower
population growth or lower retention of population genetic diversity
associated with different trial conditions. When two trials with different
input conditions have similar rates of population growth and/or genetic
diversity retention, the trial with the greatest standard deviation value may
be considered more unpredictable or risky in that more extreme rates may
occasionally occur.