The Rate of Reproduction - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 152

the loss of some unique alleles after the fi rst round of mating. When r is 4
or greater, there is little or no initial loss of unique alleles. In other words,
for populations initiated under the given conditions with 10 through 100
founders, an r of 4 or greater for the fi rst round of reproduction must be
maintained to prevent pronounced unique allele loss. This “rule” appears
to hold through fi ve generations ( Fig. 10.9B) . However, when 400 founders
are drawn, there is only a very minimal or no loss of unique alleles even
at lower r values (e.g., for population w, r = 1.5). The latter occurs since in
drawing 400 founders (800 draws per locus across 10 loci = 8,000 draws),
there is a high likelihood that not only all unique alleles are drawn, but
also a high proportion of the 100 unique alleles at a locus are drawn more
than once in the 800 draws for that locus, these duplicate alleles reducing
the loss of unique alleles to drift. These results suggest that, under the
given conditions, establishing populations with 400 founders will not only
capture most or all of the unique alleles found in the source population,
but also prevent extensive loss of unique alleles to drift at r values as low
as 1.5. Note, however, that after fi ve rounds of mating for populations
initiated with 400 founders (Fig. 10.9B; trial populations w through z and
W through Z), some unique allele loss due to drift is more apparent at the
lowest r values.
Although these results suggest that planting about 400 founders is
preferred to prevent unique allele loss, that number of founders may not
be available for many endangered species, or loss of founders before they
reproduce may reduce their number to well below 400. NEWGARDEN
analyses can be used in such cases to provide establishment and population
growth goals aimed at reducing loss of unique alleles. Plant populations
initiated with differences in initial conditions other than those examined
above might exhibit different patterns of ways in which unique allele loss is
related to changing r values. Although various approaches to estimating the
rate of loss of alleles via drift are available, some involve prior knowledge
of Ne. NEWGARDEN analyses can be used to investigate allelic loss when
differing initial conditions combine with complex population dynamics,
making it diffi cult to determine Ne.
Changing perspective, let us suppose a restoration manager has a
limited number of propagules and is primarily interested in introducing
founders in a fashion that will maximize population growth rate. Or perhaps
a manager has limited resources for a restoration project. This manager
wants to produce the maximum number of descendants per founder
planted. To examine these issues, we will defi ne the population-to-founder
“growth factor” here as:
the number of descendants living in generation 5/the number of
founders.