Founder Number and Allelic Diversity - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 70

When specifi cally discussing ex situ conservation of plant genetic diversity
(p. 155), Frankham et al. suggest, “Representation is a greater concern
for plants than for animals, especially for selfi ng species, where a higher
proportion of genetic diversity is distributed among populations.” Here
they recommend the sampling of 1-20 seeds from each of 10-50 individuals
from each of fi ve separate populations.
Adding to the complexity of these issues, attempts to reintroduce species
typically have relatively low survival rates (e.g., see Primack and Miao 1992;
Primack 1996; examples given in Part Four of Falk et al. 1996). For example,
restoration projects involving oaks often result in only 10-25% seedling
survival rates after 10 years (Allen et al. 2001). A planting of 2000 individuals
may result in 200 or fewer reproductive individuals. Introducing many more
individuals than the ultimate target number may thus promote the chances
for successful establishment (e.g., see Wolf et al. 1996). In summarizing
studies of reintroductions of animals, Frankham et al. (2002: 464) note that
releases generally were in the hundreds, with successful projects releasing
an average of 726 versus 336 animals for unsuccessful introductions. Even
for species that are already well represented at a given introduction site,
introduction of additional conspecifi cs often results in low numbers of
establishing new individuals (e.g., Primack and Miao 1992; Primack 1996).
Several of these studies also note that the genetic diversity consequences
of such introductions are largely unknown, since genetic factors were not
initially considered in decisions involving reintroduction.
Given the above, it seems that reintroduction and founding of ex situ
populations will take many different forms, and that more information is
needed on assessment of genetic consequences of these different situations.
NEWGARDEN provides a means for examining potential or realized
population genetic effects stemming from different types of founding
events.
One way of investigating founder effects with regard to the retention of
unique alleles in founding populations is to ask: How many founders would
you need to randomly collect from a source population to ensure that at least
one copy of each unique allele in the source population has been “captured”
among the founders? While there are different approaches to examining
this problem, examples include Lawrence et al. (1995), who address this
problem specifi cally, and, more inclusively, Chakraborty (1993). Lawrence
et al. note that the mating system history of a source population affects its
balance of heterozygous to homozygous loci. They estimate that drawing
86 founders from a randomly mating source population, or 172 founders
from a completely selfi ng source population, is suffi cient to capture, at a
very high probability, all of the unique source alleles with frequency not less
than 0.05 in the source population. Since the mating pattern of most species
is not known, they recommend selecting at least 172 founders (e.g., seeds,