Input - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 28

number of newborns generated by an individual). Instead, a more accurate
term in these discussions would be “realized offspring”, that is, offspring
that are produced and survive to be a part of the next age cohort. The
reproduction rate set by the user and offspring survival are conditioned
by several considerations, including density-dependent mechanisms: as
the population becomes more dense within the propagule dispersal range,
there is increasing likelihood of landing on a space occupied by another
established individual or newly arrived, potential offspring. In the latter
case, one individual from all propagules dispersed to a particular grid point
is chosen at random to join the next cohort, all of the other propagules at
that point then dying immediately.
As another example, reproduction rate may also be conditioned by the
mortality statement (e.g., 30% of individuals of age 0 may be randomly
chosen to be deleted). To refl ect the fact that competition, predation,
pathogens, stochastic events, and other considerations may eliminate
establishing propagules before reproduction, NEWGARDEN allows the
user to set mortality rates for each age. Thus, if reproduction is designated to
commence only after age 5, individuals of earlier ages may perish according
to age-specifi c mortality rates before they can participate in reproduction.
Data concerning the average age-specifi c, realized generation of viable
offspring is not available for the great majority of species. Making that
consideration even more complex, changes from one reproductive episode
to the next in realized offspring production per individual are likely to be
extremely variable in most cases. Thus, the user of NEWGARDEN will most
likely have to make some educated guesses and then vary aspects of those
guesses in comparative NEWGARDEN trials to gain a feel for how such
variation will affect genetic conservation. If some relevant data do exist for
closely related species, or a species that is similar in reproductive life history
characteristics, they might provide the best initial estimates. Making such
estimations is easier for some species than for others for a variety of reasons.
For example, monocarpic (semelparous) annuals, biennials, and triennials
reproduce in their terminal year. Reproductive schedules for short-lived
perennials are perhaps somewhat easier to model than those for long-lived
trees. For both, there are liable to be few to several years in which new
individuals will occupy grid points, but will not be reproductive. Onset of
reproduction is likely to be at a lower rate than reproductive rates achieved
in the mature phase of the organism, with perhaps declining reproduction
in an organism's last years. Species may be considered more at one or the
other end of the r- to K-selected species continuum. Many variations on
these themes can be compared using NEWGARDEN.
For the same species, simultaneous reintroduction at two sites may
produce different rates of reproducing offspring production. Differences
in available habitat, resources, herbivores, predators, or pathogens present,