Population Genetics Edge Effects - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 96

occur. Initiating populations at much greater distances may waste travel
time, transport effort and other resources and make them more diffi cult to
monitor, maintain and protect.
0,0
-a,-a
-b,-b
Fig. 8.4 Fewer grid points are available for establishment and more offspring are dispersed
(arrows) out of the preserve when borders are closer to the founders (the two lines) and the
initial developing population.
Edge Effects and Heterozygosity
Do genetic edge effects affect levels of heterozygosity? Figure 8.5 shows
that losses of observed heterozygosity decrease as distance from the border
increases. The results suggest that placing founders even relatively short
distances from borders reduces losses of observed heterozygosity. Is this
increased loss of observed heterozygosity in the population initiated
with founders at the origin due to increased inbreeding? Perhaps the
increased loss of individuals leads to more localized mating among related
individuals. What mechanisms drive these differences? If inbreeding were
the main cause, then F values for the “2” population initiated at the lower left
preserve corner should be highest. Figure 8.6 shows how F changes through
generations for these populations. The degree of inbreeding, as indicated
by F, was not highest when the founders were placed at the origin, or inset
by 10 grid units (trials 2 and 3, respectively), but rather was higher when
the founders were inset by 40 units or 2,560 units (trials 4 and 5) from the
border. Figure 8.7 demonstrates that observed heterozygosity can drop most
rapidly for population 2 (founders on origin) but F increases relatively more
rapidly for cases where the founders are 40 or 2,560 units from the origin.