Dispersal - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 176

is growing more rapidly does not mean it will retain more unique alleles:
compare population growth for populations f versus j ( Fig. 12.2, graphs B
versus C). However, the more rapidly growing population j lost unique
alleles at a greater rate than the slower-growing population f (( Fig. 12.5,
graphs B versus C). These results suggest that in restoration of species with
limited dispersal, manipulation of founder spacing and offspring and pollen
dispersal may be used to improve unique allele retention.
The results in this section also suggest that in addition to spatial
considerations, depending on how a restoration manager wants to
manipulate population growth, levels of heterozygosity and/or inbreeding,
or unique allele retention, the manager may want to alter rates of selfi ng
(for example, increase or decrease the number of pollinators, bagging,
treatments).
The population trials in Figs. 12.2 through 12.8 were all conducted
with random mating, where the rate of selfi ng increases as the number of
eligible microgamete donors decreases (e.g., with short dispersal and widely
spaced founders). What happens when population trials are run exactly as
described just above, but when the species is completely self-incompatible
and no self-matings are allowed? When such replicate trials were conducted,
self-incompatibility generally had little effect, except in the following
ways. First, population growth rates were slightly higher when selfi ng was
permitted since isolated individuals were able to reproduce, while such
individuals would not be able to mate under self-incompatibility. But this
effect appeared to be very minor in most cases. A second and very obvious
difference, however, occurred when the distance between founders was
greater than dispersal distance: since no reproduction was then possible, no
founders could produce offspring and the population went extinct. These
effects can be seen in Fig. 12.6. Observed heterozygosity values are given
for populations identical to the populations with the same, but lowercase,
letter in Fig. 12.3 e xcept that populations in Fig. 12.6 denoted with uppercase
symbols were completely self-incompatible. Complete self-incompatibility
had the effect of slightly reducing the loss of heterozygosity since no self-
matings occurred (e.g., compare graphs A of Figs. 12.3 and 12.6). However,
where spacing between founders exceeded maximum dispersal distance,
such populations immediately went extinct and heterozygosity dropped to
0 (compare graphs B and C of those fi gures). Obviously, spacing between
founders of a species that is highly self-incompatible and with limited
dispersal of both pollen and seeds cannot be introduced at distances greater
than dispersal. This may be of concern especially where only offspring or
microgamete vectors with inappropriate dispersal capabilities are available
(or absent altogether), such as when re-introducing a species that has
been missing from a community for some time. These results support the
conclusion that completely self-incompatible species should in general