Corridors - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 281

L (172 founders in one preserve), the former 12 th generation including 10%
more individuals. This pattern is reversed under long-distance conditions.
For example, when the corridor is 10% high, placing the founders in a large
square in one preserve (V) increases growth by 12.7% compared to placing
founders in two smaller groups, one in each preserve (W). The same trend
appears to occur when the corridor is 40% high (trial R versus S), but the
difference is not signifi cant (p = 0.16). These results suggest that knowing
dispersal patterns for a species is critical in designing optimal plans for
introducing founders. Natural populations will respond differently to the
same number of founders depending on their dispersal schedules and
founding patterns. Such considerations are reinforced by noting that, of
all the alternatives in Figs. 17.3 and 17.4, the most successful population in
the former fi gure (I) is 9.2% greater than that in the latter fi gure (R), even
though dispersal is shorter in trial I. Reasons for the more rapid growth of
trial I most likely include the fact that fewer offspring are dispersed off the
preserve-corridor-preserve grid when dispersal distances are short.
With long-distance dispersal, although unique allele retention (Fig.
17.4B) in R differs from S (corridors 40%), and V differs from W (corridors
10%), they differ by only 2.5-3%. When founders are placed in one large
square in one preserve, the population retains the most unique alleles
in both cases. After 12 generations, the greatest difference in observed
heterozygosity is approximately 1% among all trials (approximately 0.967
to 0.977; data not shown). With short-distance dispersal (Fig. 17.3) versus
long-distance dispersal (Fig. 17.4), the highest unique allele retention occurs
in trial I versus trial R, the former exceeding the latter by 9.6%. This increase
with short-distance dispersal occurs even though R has a 40% corridor,
while I has a 20% high corridor. The latter has the founders divided into
two groups, while the former has founders in one group. Again, these
results demonstrate that different dispersal patterns interact with different
founding patterns of the same number of founders to produce different
degrees of genetic diversity retention. These results also suggest that in
restoring some species in corridor situations, manipulation of offspring
and/or pollen dispersal resulting in lower dispersal distances would be
advantageous.
Varying offspring and pollen dispersal distances can produce complex
effects in relation to placement of founders. Results from four trials with
almost identical input conditions (e.g., 40% high corridors; r = 1.6) are
depicted in Fig. 17.5. The only differences among these trials are that all
172 founders are placed in a square in the left preserve only (trials L and
R) versus the 172 split into two groups, one placed in each preserve (M
and S); and trials L and M have short-distance dispersal for pollen and
offspring, while R and S have dispersal categories that are four times as
great (long-distance dispersal; maximum dispersal = 2,804 units). First,