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6. Although the 50/500 rule noted earlier (Avise 1994: 370 or Meffe 1996:
53) refers to effective population sizes, losses of genetic diversity in
terms of decreasing heterozygosity or loss of unique alleles, plus
increasing rates of inbreeding, continue for many of these populations
even when absolute population numbers exceed 500 or more.
7. However, most of the trend trajectories seen for these developing
populations (rate of population growth, loss of heterozygosity, increase
in F, loss of unique alleles) are set early in stand development when
population census sizes are low. These early phases of establishment
are thus most important in terms of study, monitoring, and intervention
for improved practices to prevent diversity loss.
8. Moving founders only slight distances (in terms of offspring or pollen
dispersal distances) from a border can reduce losses of diversity to
levels similar to when founders are placed in the center of a preserve,
at least under the conditions used above.
Previous reviews (e.g., Frankham et al. 1992) have argued that
introduction success rates were higher for releases in preserve cores than
at peripheries. This is often in part due to the amelioration of ecological
edge effects in preserve cores, although deleterious dispersal outside
preserves or crowding generated from reproducing individuals placed near
preserve borders may also play a role. But how far into a preserve need one
travel to found a new population successfully, in terms of both population
increase and genetic diversity maintenance? The above analyses suggest
that placing founders only a short way into a preserve conserves genetic
diversity about as effectively as placing founders in the preserve center.
However, these results consider only one “species” with one set of life
history characteristics. What would happen, for example, if pollen dispersal
distance was increased drastically? Or if founders were placed in a hollow
square? NEWGARDEN analyses can be used to gain a general sense of
effects of changes in distance to a border or other initial input conditions
on genetic conservation issues. Determining the effects of such patterns
may translate into savings. If salient characteristics of the species can be
used in a NEWGARDEN input fi le, then the manager may gain a sense of
minimal distances from a border needed to prevent negative population
genetic edge effects. Determining that a set of founders placed 50 density
units from the border will suffer no more diversity losses than the same set
100 or more units from a boundary will save time and effort in establishing
the species: introduction, provisioning, protection, monitoring, harvest and
transport of propagules, movement of equipment, and other tasks will all
be less costly. Disturbance further into the preserve will be lessened. For
the evolutionary biologist, these issues are of interest since, if distance from
an edge does have genetic diversity consequences, then organisms that
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