Dispersal - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 179

Offspring dispersal distances are equal to pollen dispersal distances, with
trials having average density grid unit dispersal distances varying as
follows:
5 (offspring and microgamete dispersal within the nearest 121
individuals)
12 (offspring and microgamete dispersal within nearest 625 grid points)
or
30 (offspring and microgamete dispersal within nearest 3,721
individuals).
The preserve is a square with lower left corner coordinates (-2560, -2560)
and upper right corner coordinates (2559, 2559), which includes 26,214,400
possible grid points that can be occupied.
Most runs are for 15 rounds of reproduction (unless indicated otherwise),
and data points in graphs represent the mean value of 30 replicate runs of
the input conditions for a trial.
Although the founders always number 172 and there are always four grid
points between all adjacent founders, three different patterns of founder
placement were explored:
1. The founders were all placed in a square at the center of the preserve
(populations F, G, and H of Figs. 12.7 and 12.8) .
2. The founders were placed in four subgroup squares of 43 individuals
each, each subgroup placed with founders at least 20 grid units from
the preserve center in the direction of one of the preserve corners (N,
O, and P).
3. The founders were placed in four subgroup squares of 43 individuals
each, the squares placed internally at the four preserve corners with
the shortest distance of any founder from a border being 80 grid units
(R, S, and T).
In Fig. 12.7A, it can be seen that, under the given conditions, increasing
subdivision increases the rate of population growth. For example, compare
populations with dispersal set to 30 grid points: H (no subdivision),
P (founders subdivided with approximately 40 grid units separating the
closest individuals of any two subgroups), and T (founder subgroups
placed at much greater distances from one another being 80 units from
each corner of a preserve that is 5,120 units on a side). Populations G,
O, and S (dispersal 12 units) show a similar pattern of increasing rate
of population growth with increasing subdivision. Placing founders in
smaller, widely separated groups decreases competition for establishing
offspring yielding greater rates of population growth. As shown earlier,
increasing dispersal distance increases population growth, a trend here
confi rmed with the dispersal distances under consideration regardless of