Perennials - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 249

rate specifi ed for a trial) via pollen and, separately, via offspring. As with
age-specifi c mortality, NEWGARDEN interpolates rates of reproduction
between two age classes for which different specifi cations have been
given, and for which no intervening age classes have been specifi ed. One
pattern that has been found for some perennial cosexual species is that
individuals tend to act primarily as pollen providers in the earliest bouts
of mating in which they participate even though both sexes are presented
in fl owers (pollen available but no fruit set). Arguments forwarded to
explain this trend include a lower resource commitment to the maturing
of pollen versus to the maturing of fruit, among others (e.g., Zhang 2006;
if true, pollen production may also occur at higher rates later into the
senescence process as resources dwindle). Therefore, the user may want
to schedule the onset of lower rates, the maximum rate, and declining
rates of pollen presentation at different times compared to those rates for
offspring production. The input specifi cation concerning the Poisson (or
other) distribution of fruit production is applied simultaneously with the
age-specifi c relative rate of production. Examples follow that demonstrate
that changes in relative rates of different age class contributions of pollen or
offspring may or may not have pronounced effects on population growth
and genetic characteristics.
The basic trial for this series of comparisons is trial M, described
above as the basic trial to model Lindera benzoin . In all of these trials, the
172 founders are placed in a central square in a preserve of the same size.
All conditions for all trials are identical except for the age-specifi c rates
of relative pollen and offspring production as shown in Table 15.3 . The
differences in age-specifi c pollen and offspring output detailed in Table
15.3, compared to trial M, can be summarized as follows:
Trial A has identical offspring production, but individuals begin to
contribute pollen, and cease contributing pollen, at earlier ages.
Trial B has identical offspring production, but individuals begin to contribute
pollen, and cease contributing pollen, at later ages.
Trial C has identical pollen production, but individuals begin to contribute
offspring, and cease contributing offspring, at earlier ages.
Trial D has identical pollen production, but individuals begin to contribute
offspring, and cease contributing offspring, at later ages.
Thus, in relation to trial M, trials A and B compare the effects of differences
in the timing of the onset and decline in pollen contributions for any given
cohort, while C and D compare differences in the timing of offspring
production.
The results are shown in Figs. 15.15 and 15.16. Even though more pollen
is available earlier with less later in the aging of cohorts, or vice versa,
these differences in pollen provisioning appear to make little difference