The Rate of Reproduction - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 140

10

CHAPTER

The Rate of Reproduction

One of the primary means of controlling the rate of reproduction via
offspring production is expressed using statements such as the following:

<Reproduction_Rate>
<functionpoint x=“0” y=“1.3”/>
<functionpoint x=“1” y=“0”/>
</Reproduction_Rate>
<Offspring_Distribution method=“poisson”/>

In the example above, offspring are produced by parents in their fi rst
year only with an average r = 1.3 offspring per reproducing individual,
but the actual offspring production is randomly determined according
to a Poisson distribution. Obviously, populations grow more rapidly
when the value of r is increased (Fig. 10.1A) . Despite the differences in
growth rate for populations i and g, they lose observed heterozygosity at
the same rate, while heterozygosity loss is much greater for the slowest-
growing population a (Fig. 10.1B). Suppose that, in restoring a population,
maintaining high heterozygosity is the foremost goal. If intervention is
required to promote population growth rate, such comparative trials can
provide targets for degree of effort needed. For example, a population
exhibiting growth rates similar to trial population c would require less
effort to maintain its growth rate than populations g or i in order to preserve
heterozygosity to a similar degree. Or, if maintaining lower population F
values is the crucial target, then growing populations with growth rates
similar to population c would suffi ce as well ( Fig. 10.2A) .
However, if the primary concern of a restoration ecologist, or of an
evolutionary biologist tracking the effects of demography on genetic
diversity, is retention of unique alleles in a population, a population
growing at a rate similar to trial population c will lose approximately 27%
more of those alleles than population g at generation 17 (Fig. 10.2B). Even
at generation 14, trial i exhibits a 9% increase in unique alleles retained
compared to trial g. Intervention to increase population growth under
the given population conditions can clearly have a major impact on
maintaining genetic diversity in terms of unique rare alleles preserved.
NEWGARDEN thus allows researchers a means of comparing the effects
of different scenarios of introduction and reproduction on conservation of
genetic diversity.