Spatial Arrangement of Founders - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 133

What is the effect of subdividing the 20 founders placed in the above
example in various closely spaced lines or confi gurations into widely
separated groups? Is it possible, for example, that distributing the 20
founders into four separated groups of fi ve founders each can increase the
number of unique alleles retained? In Fig. 9.11A , populations with fi ve lines
of four founders each (trial q), or four lines with fi ve founders each (trial
k), with founders placed at least 80 grid points from a border, exhibit the
greatest rates of growth. When founders are placed in four lines inset only
10 units from corners (trial j), population growth decreases because of the
increased edge effects of higher loss of offspring to dispersal outside the
preserve. However, population growth is greater even in that population
than when the 20 founders are placed in the center of the preserve in two
lines of 10 with closest spacing (trial v). Distributing the founders into
smaller, widespread groups increases population growth rates under the
given conditions.
Observed heterozygosity decreases more rapidly when the founders
are subdivided (Fig. 9.11B), with the loss being greatest when subdivision
is the greatest, namely, with population q. That population also exhibits
the highest rate of increase in F ( Fig. 9.12B) . These latter two fi ndings are to
be expected since the 20 founders in trial q are subdivided into very small
subpopulations of four each. When gene exchange is restricted among
these four individuals and the fi ve separate groups of their descendants,
more inbreeding will occur. Note that the preserve size is 5,120 units on a
side. For the founders in trial populations k and q, more than 2,470 grid
points separate any one subgroup from the others. In these trials, offspring
dispersal was set to 5 grid units (within the nearest 121 average density grid
points surrounding the dispersing individual), so the maximum dispersal
for the descendants of one individual over 14 generations is 14 * 5 = 70
grid units. The subpopulations in trials j, k, and q thus remain isolated
throughout these trials. Below, an example in which subpopulations merge
will be given.
Even though population q grows the most rapidly (Fig. 9.11A), the more
slowly growing populations k and even j retain similar numbers of unique
alleles (Fig. 9.12B). If it is determined that unique allele preservation, rather
than avoidance of inbreeding, is the most important criterion in developing
a best practices plan for the reintroduction of a species with the life history
characteristics and constraints (e.g., only 20 founders are available) modeled
here, then these results have economic importance. Since population j is
practically indistinguishable from populations q and k in terms of unique
allele retention (Fig. 9.12B), it is much more economical, in a preserve with
5,120 average density units to a side (note that an average density unit for
a tree may be 10 m or more), to hike 10 density units into the preserve at
each corner (assuming the preserve has ready access to corners), making