Biology Reference
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All unique alleles at loci with lower diversity than the most diverse modeled
will likely be conserved over the near and mid-term among the founders
in most cases if the conditions to preserve alleles at the most diverse loci
have been met. It is worth noting that almost all unique alleles arise as rare
alleles, perhaps not in small populations, but across most species. Berg and
Hamrick (1997) advocated using all alleles in genetic diversity analyses due
to their potentially important effects.
But the number of unique alleles preserved is not the only issue for
establishing populations. While comparison of Fig. 7.5 and Fig. 7.11 shows
that founder effects will be greater in founding events involving few
individuals taken from source populations with larger average numbers of
alleles per locus, these types of founding events will also often bring about
large to extreme changes in allele frequencies in the founding population
compared to the source population (e.g., source population unique alleles
at low frequency may attain higher frequencies in the founding population
or vice versa). Such random alterations of gene frequencies among a low
number of colonizers can modify the evolutionary dynamics of the resulting
population, these effects being in addition to those caused by random
loss of unique alleles. This issue is crucial when considering the effects of
drift on multilocus interactions and the resulting potential evolutionary
landscapes available to two populations with different population genetic
trajectories, as will be emphasized in the concluding chapter (see also
Templeton 2006).
In some cases, the maximum potential genetic diversity at any one locus
for a founding population may be known. For example, suppose founders
are taken from a very limited source population of (or initiated by) 16
individuals. Then the maximum number of alleles at a locus in the newly
established population is 32, and the lowest possible frequency for an allele
would be 1/32. Small source populations are likely to be the only sources
available for extremely endangered species or for restorations initiated with
zoo or arboretum ex situ collections (e.g., see examples in Frankham et al.
2002). Obviously, establishment of new populations from a small number
of founders also occurs by natural processes, perhaps rather commonly
for some species. In a world that is becoming increasingly fragmented, or
in which global climate changes will necessitate assisted colonization to
rescue species, such founding events may be on the increase, and genetic
diversity maintenance under such conditions across a range of loci types can
be investigated with NEWGARDEN. To create a founding population of,
say, 16 individuals with a locus at which each founder has unique alleles for
that locus, the NEWGARDEN user can specify that there are numerous rare
alleles at that locus in the source population (see loci commands above).
When genetic variation is generally low in the source population
because of previous inbreeding or severe founder effects, a descendant
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