The Rate of Reproduction - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 143

However, NEWGARDEN can be used to examine not only the effects
of subdivision, but also changes in population genetics parameters when
once separated groups begin sharing alleles. When founders are subdivided
into small groups but placed in close enough proximity that alleles will
be exchanged between groups within a few generations, loss of observed
heterozygosity and F will initially increase, but both of these trends will be
reversed as mixing increases depending on the rate of intermixing of the
subpopulations ( Fig. 10.3: trial population y has founders placed in four
initially distinct groups separated by approximately 15 grid units such
that mixing of alleles will begin to increase in later generations). When
population growth rate is increased by increasing the offspring reproduction
rate (r), then the “recovery” of observed heterozygosity and decrease
in inbreeding is achieved more rapidly ( Fig. 10.4) . The degree to which
increased numbers of unique alleles are retained in subdivided populations
with higher growth rates can be seen in Fig. 10.5. As shown in Figs. 9.11
and 9.12, subdividing founders may increase population growth rates and
unique allele retention at the risk of increasing inbreeding. In planning a
reintroduction strategy for a species, it might be worth comparing trials
in which founders are subdivided into groups that are placed at different
proximities such that intermixing will occur at different rates within the
fi rst few generations (Fig. 10.4). Further, trials might have different rates
of growth to refl ect different amounts of management intervention. Such
exploration may aid in designing a strategy that will “optimize” the
balance of early rapid population growth, unique allele retention, loss
of subdivision, and increased heterozygosity, minimizing F relative to
management costs.
We now examine a slightly more complex set of considerations involving
r. In the trial results depicted in Fig. 10.1 , r varied from 1.3 to 4. Below we
examine changes in population parameters over a broader range of r values
(1.5 to 18) to demonstrate some further issues related to r. All of these trials
will share the following characteristics unless noted otherwise:
Bisexual annual plants.
10 loci, each with 100 unique alleles of equal frequency = 0.01.
No selfi ng (self-incompatible; random mating = false).
Offspring distribution method = Poisson.
All individuals (except self) within pollen dispersal distance have equal
chance of being chosen for a particular offspring production event.
Offspring and pollen can be dispersed up to 10 grid units (within the nearest
441 individuals).
Square preserve (-2560, -2560 = lower left corner; 2559, 2559 = upper right
corner) with 26,214,400 potential establishment grid points.