Dispersal - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 196

More than One Dispersal Distance Zone for Offspring while
Microgamete Dispersal Distance Remains Constant
In the previous set of trials, offspring dispersal distance was constant (5
units), while pollen dispersal varied. In the next set of trials, it is pollen
dispersal distance that is held constant at a maximum of 5 units, while
offspring dispersal distance is varied. These next trials are identical to the
previous trials and to one another except for the following changes. For
population N, offspring and microgamete maximum dispersal distances
are both 5 grid units. This is the same population N as used in the previous
two sections. Populations m, n, and o have only one maximum distance for
microgamete dispersal = 5 grid units, but offspring are dispersed to four
different zones according to the probabilities listed in Table 12.2. Thus,
trials m to o refl ect, respectively, increasing evenness of offspring dispersal
percentages across zones.
The results of these trials are shown in Figs. 12.13 and 12.14. In contrast
to the previous trials in which offspring maximum dispersal was always 5,
when microgamete dispersal is held constant at 5 units, population growth
is less than population N (offspring and microgamete maximum dispersal
equal, being 5 units), this trend increasing as offspring are dispersed on
average to greater distances. In fact, when dispersal to the four different
zones is equal (25% to each; population o), the population declines towards
extinction. In these trials, as offspring average dispersal distance increases,
some offspring become increasingly isolated out of range of any possible
pollinator when pollen dispersal maximum is 5 units (within the closest
121 potential establishment grid points).
When offspring maximum dispersal was constant at 5 units (previous
section), losses of heterozygosity were always less as microgamete
reproductive effort became more and more dispersed. However, when
pollen dispersal is constant at 5 units, loss of heterozygosity may be reduced,
compared to population N, when offspring are dispersed to a relatively
limited degree (population m). There is no difference (population n) with
increasingly distant offspring dispersal, although there is eventual loss of
heterozygosity as the population declines when offspring are more distantly
dispersed evenly to all zones (population o). F values (inbreeding and/
or increased Wahlund effect subdivision) are reduced whenever either
offspring (previous section) or microgametes (this section) are more widely
dispersed relative to population N (Fig. 12.14A; F values become negative for
population o, as sometimes occurs when populations are extremely small).
Whereas increasing microgamete dispersal increased unique allele retention
compared to population N in the previous section, here more unique alleles
are lost as offspring are more widely dispersed (Fig. 12.14B).