Dispersal - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 200

come from each of zone 1 (0-5 grid point units), zone 2 (6-12 units), zone
3 (13-21 units), and zone 4 (22-300 grid point units). While all these trials
have this same pattern of microgamete dispersal, they differ in that 100% of
the offspring are dispersed to within 5 grid point units for population g, 10
units for h, 15 units for i, and 22 units for j. Only this one zone of maximum
offspring dispersal distance is specifi ed for these four trials.
Type 3: In trials o, s, t, and u, probability of dispersal of offspring is equally
likely to each of four zones surrounding a randomly selected offspring
producer in each particular mating. In other words, 25% of the dispersed
offspring across all of the matings for a given trial will be dispersed to
either zone 1 (0-5 grid point units), zone 2 (6-12 units), zone 3 (13-21 units),
or zone 4 (22-300 grid point units). While all these trials have this same
pattern of offspring dispersal, they differ in that 100% of the successful
microgametes in a mating must come from an eligible mate within 5 grid
point units for population o, 10 units for s, 15 units for t, and 22 units for p.
Only this one zone of maximum microgamete dispersal distance is specifi ed
for these four trials.
Results for these trials (averages of 30 runs per trial) are shown in
Figs. 12.15 and 12.16. Population growth increased for trials with increased
dispersal of either offspring (g, h, i, j), or microgametes (o, s, t, u), although
greatest growth occurred when offspring dispersal was increased.
Populations o, s, and t (pollen dispersed to 5, 10, or 15 units) exhibited
population growth rates below population N, which had 100% of both
microgametes and offspring dispersed within 5 grid units. All populations
exhibited a lower rate of loss of observed heterozygosity compared to
population N, except for population o as it declines towards 0 individuals. F
values for all populations were below N, indicating that the more even and
distant dispersal of one of the dispersules acted to reduce inbreeding and/or
Wahlund effect subdivision. As for unique alleles retained, all populations
for which distribution of offspring to the four distance categories was held
constant retained fewer alleles than population N, this effect being rather
substantial at least for populations o, s, and t, while all populations where
pollen dispersal was equal to each category always exceeded population
N, the greatest retention of alleles by population j being approximately 8%
greater. As long as microgamete dispersal is at least as distant as offspring
dispersal, unique allele loss is minimized, as opposed to cases in which
microgamete dispersal is increasingly less than offspring dispersal.
These results reveal an asymmetry of the effects of evolutionary forces
that might act to increase microgamete dispersal versus those acting to
increase offspring dispersal under certain average conditions such as
those in the above trials. To the extent that increased rates of population
growth and/or increased retention of genetic diversity (which may include