Perennials - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 248

Compared to trial r, trial s has a lower mortality rate early on, a higher
mortality rate from age classes 7 to 10, with a very much greater successively
interpolating mortality rate from age class 10 on. The increased mortality
for later age classes in trial s produces a lower population growth rate,
a more rapid decrease in heterozygosity, a more rapid rise in F, and an
approximately 19% decrease in unique alleles retained at age 62.
Trial t is very similar to trial s, although in the latter, early mortality is
somewhat increased, with intermediate and late ages having a somewhat
decreased (but not pronounced) difference in rates of mortality ( Fig. 15.12B
and Table 15.2) . These slight changes in mortality for trial t compared to
trial s produce a greatly increased rate of population growth, a lesser degree
of heterozygosity loss, lower F values, and a 12% increase in the amount
of unique alleles retained at age 62. Again, slight differences in mortality
schedules can have a signifi cant impact on population growth and genetic
diversity.
Population u has a constantly increasing rate of mortality. With these
age-class rates of mortality, and under the other given conditions, population
growth is not sustainable. All measures of growth and diversity continue
to drop as this population develops.
Taken together, these results demonstrate that small differences in
mortality schedules can affect population growth and genetic diversity in
major ways in some cases. NEWGARDEN modeling can be used to study
how differing patterns of mortality might affect introduced populations,
or how diversity has already likely been affected by the history of growth
the population has experienced. Further, these results emphasize that
populations establishing with similar numbers of founders but experiencing
sometimes slight differences in mortality can grow and lose diversity at
differing rates. Just planting 172 founders (Lawrence et al. 1995) does not
ensure that all unique alleles introduced from a source population will
persist, even when the subsequent population exhibits constant growth.
Such comparative NEWGARDEN trials can be used to optimize diversity
supplementation in managed populations.
Spicebush Age-specifi c Reproduction
NEWGARDEN allows the user to specify age-specifi c rates of reproduction
via pollen versus offspring for perennials. It is commonly observed that
plants set relatively few fl owers when young, often engaging in “full”
production of pollen or offspring once they have achieved a certain size
(age), this full production sometimes declining as individuals senesce or
become overmature. Users can input values to designate the relative rate
of reproduction (relative to the maximum specifi ed, that is, reproduction
occurs at the relative rate of: age-specifi c rate divided by the maximum