Input - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 29

for example, may affect propagule success to reproduction differently at
different sites. The population genetic effects of such differences in rate of
offspring establishment can be examined by varying offspring production
rates for individuals of given age classes while holding other user-defi ned
conditions constant.
Ultimately, one hopes to make comparative trials as realistic as
possible. In using NEWGARDEN, this will take some experimentation.
For example, if a population is generating 30,000 offspring in the seventh
generation of what is meant to be the introduction of a K-selected tree
into an established community, the user will have to assess the likelihood
of such rapid population growth. For most species that are endangered,
population growth rates will often be very low, especially when introduced
into a community that is already well established. Some studies indicate
that likelihood of establishment in an undisturbed habitat from introduced
propagules is very low indeed, even for species that are already well
represented at the introduction site (e.g., Primack and Miao 1992; Primack
1996).
Rather than considering NEWGARDEN as a tool to obtain precise
predictions of what will happen in a particular reproductive scenario, the
theorist and practitioner can better use the program to compare variations
in reproductive schedules to judge their effect on the population genetics
of future establishing populations. Although many details of reproduction
are not known for most species, by varying the reproductive conditions,
NEWGARDEN can be informative as to when and where efforts are best
applied to improve reproduction. For example, if early decrease in distance
of dispersal greatly increases retention of genetic diversity, then efforts
can be more effi ciently focused early on to promote the establishment of
more clustered individuals, relaxing such efforts to allow the population
to grow spontaneously in later stages. In such cases, NEWGARDEN may
help determine target goals for assisted reproduction (e.g., assisted matings,
plantings or placing, provisioning, protecting), and thereby reduce the
likelihood of investing assistance efforts that are far greater than required
to maintain genetic diversity levels.
One way to perhaps establish a “realistic” estimate of the rate of
reproduction is to observe or create situations in which a few individuals of
the target species have been introduced into a habitat where the species was
previously lacking, and determine the rates of establishment, reproductive
maturation, and successful generation of new individuals. While this will
generally be a thesis in itself, even preliminary observations regarding the
natural demographics of populations of a species may give valuable clues
as to whether NEWGARDEN trial output is completely off base.