Perennials - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 218

15

CHAPTER

Perennials

All of the examples given previously in this topic have involved annuals.
NEWGARDEN also permits input data regarding age-specifi ed schedules of
mortality and rates of reproduction to model population growth and genetic
diversity retention for a wide variety of perennials. For example, some
species may have low mortality (say, 3%) in the fi rst 4 years of establishment
followed by steeper losses for older individuals. In another species (or
at another location for the same species), early mortality may be much
higher. These differing mortality schedules will generate different rates
and spatial patterns of population establishment that can have associated
effects on population growth and genetic diversity. Likewise, the number
of surviving offspring generated, as well as the chances of being a pollen
donor, change with age for most perennials. Individuals that are 5 years old
may contribute only 2% of the seed or pollen contributed by individuals that
are 30 years old. As outlined in Chapter 4 (Input), these parameters can be
specifi ed for developing populations via the NEWGARDEN input fi le. In
the following sections, we examine, for perennials, some of the population
genetic consequences that can stem from different patterns of introduction
for populations or species that differ in life history characteristics such as
mating system, seed or pollen dispersal patterns, age-specifi c production,
or different schedules of age-specifi c rates of mortality.

Restoration of a Dioecious Shrub

In the next series of trials, the introduction of a dioecious perennial shrub
to a preserve is modeled. Dioecy has been found to be associated with bird
dispersal (e.g., Bawa 1980; Givnish 1980; Lloyd 1982), giving the potential
for occasional to common long-distance fruit dispersal, the consequences
of which are explored to some degree below. Many shrubs are denizens of
early to middle stages of successional series. Lifespans for such species may
be limited by eventual increasing canopy closure, and thus many shrubs are
not extremely long-lived compared to late successional species. Shrubby
species are also often found in frequently stressed (e.g., drought, cold) or
periodically disturbed (e.g., by fi re) environments, and again, some of these
shrubs may have shorter lifespans. Below we model various scenarios for