Population Genetics Edge Effects - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 99

0.5

0.4

0.3

0.2

0.1

0.0

p
q

0.0 0.2 0.4 0.6 0.8 1.0

1.0 0.8 0.6 0.4 0.2 0.0

ALLELE FREQUENCY

Fig. 8.8 For populations initiated with heterozygosity = 0.5 (loci have two alleles of equal
frequency = 0.5), as drift changes the frequency of one of the two alleles at a locus, the frequency
of the other allele changes concomitantly but in the opposite direction, changing expected
heterozygosity. Any relative loss of one allele yielding a frequency < 0.5 (or change resulting
in greater discrepancies in frequencies among the alleles at a locus) results in a lower expected
heterozygosity. Inbreeding does not alter gene frequencies directly.

and numbers of alleles, so the measure F is informative as to levels of
inbreeding (higher F is due to a greater difference between expected and
observed heterozygosity). Since the actual level of heterozygosity (observed
heterozygosity) in populations will be the most important assessment for
interpreting changes in average realized homozygosity (1-heterozygosity)
due to different introduction and population management practices, and
thus interpreting whether inbreeding depression may be on the rise, only
observed, rather than estimated, heterozygosity will be reported in many
of the examples below. When F values are also consulted in these examples
as a measure of the degree of inbreeding induced by different founding
scenarios, if observed heterozygosity is lower for one population, and if
F is also higher for that population, then inbreeding accounts for some of
the observed heterozygosity decrease. If F is similar in that population
compared with others with higher observed heterozygosity values, this
implies that its loss of observed heterozygosity is infl uenced by loss of
alleles.
But now we are left with the question, why should inbreeding be highest
in cases where the founders are placed at greater distances from the border
(trials 4 and 5 of Fig. 8.6) ? This effect is most likely due to the geometry of
the production and dispersal of offspring.
In Fig. 8.9, founders placed near the origin (A) have fewer directions
for initial successful dispersal (only up and/or to the right) compared
to an equivalent set of founders placed more internally in a preserve