Spatial Arrangement of Founders - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 130

unique alleles (Fig. 9.8B), most likely due to increased population growth
rate originating from lowered offspring competition for usable safe sites
when founders are introduced at lower density. Introduction pattern of
trial i produces a greater than 21% increase in the number of unique alleles
retained compared to the introduction pattern of trial v.
To give another example of the principle of the effects of increased
spacing among founders, consider Figs. 9.9 and 9.10, in which two
populations are compared that have identical input conditions (the same
used in the examples just discussed) except there are 25 founders, and in
one population (population r) the founders are placed in a 5 by 5 square
with closest spacing, while the 25 founders for the second population
(population o) are placed in a 5 by 5 individual square with 4 average
density grid units between individuals (offspring and pollen are dispersed
a maximum of 5 units).
Population growth rate (Fig. 9.9A) is accelerated when the 25 founders,
placed in a central square, are introduced with 4 average density units for
the species between them (population o) compared to when the founders are
placed in a square at the average density for the species (population r). Trial
population o experiences a 43% increase in growth over population r. In the
latter case, there is much greater likelihood that offspring will be dispersed
to the same grid point, and thus fewer offspring establish, leading to the
persistently lower population growth rate. However, the greater distance
between individuals yields a more rapid decline in observed heterozygosity
(Fig. 9.9B). This more rapid decline in observed heterozygosity is related
to the consequent more localized breeding with less mixing given the
offspring and microgamete dispersal distances of 5 grid units (F is higher
for population o; Fig. 9.10A). While inbreeding is thus higher in population
o with more distant spacing of founders, that population also retains more
unique alleles (Fig. 9.10B), probably because of the higher population growth
rate with more localized inbreeding.
In an earlier example ( Figs. 9.6 and 9.7) , there was an approximately
2.5% increase in unique allele retention when 20 founders were placed in
line versus a hollow square. In the current example (Fig. 9.10B), in which 25
founders are placed in a square with closest spacing versus with 4 grid points
between individuals, there is a 13.8% increase in unique alleles retained
when founders are placed in the latter confi guration. These results confi rm
the trend found in Fig. 9.8 where increased spacing between founding
individuals increased allele retention, although the degree of retention is
even higher when the number of grid points between individuals, and thus
the number of grid points available for individual propagules, is higher (4
grid units in Fig. 9.10).