Input - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 48

Alteration of the offspring and microgamete dispersal patterns
will allow one to assess the effects of such changes on genetic diversity.
For example, if dispersal is more leptokurtic, then heterozygosity may
decrease because of more localized inbreeding, and rate of loss of genetic
diversity may increase. In contrast, under some models, distant dispersal
is disproportionately favored (e.g., see discussion of the Janzen-Connell
hypothesis in Silvertown and Charlesworth 2001), which might act to
increase outbreeding and reduce the loss of genetic diversity. Both sets of
conditions can be modeled and compared using the frame system.
NEWGARDEN also lacks some degree of realism in that for most
organisms, the zone of dispersal eligibility would be best described by
a circle, except in circumstances where variable ecological factors (e.g.,
prevailing winds, differing densities of establishment safe sites) prevail.
Due to varying resources, dispersal effectiveness is not always equal in all
directions or at all locations. These types of variation can be modeled in
various ways. For example, individuals that are of great age (greater than
the last age designated for 100% mortality) and beyond reproductive age can
be placed as founders at grid points. NEWGARDEN is designed such that
these individuals will remain at a given grid point and make it unavailable
for colonization or microgamete contribution. In natural situations, there
may be large areas where the species cannot grow, such as swamps, rivers,
or upland glades. To model the effects of such larger uninhabitable regions
within a habitat on dispersal and retention of genetic variation, complex
grid patterns of mixed habitable and uninhabitable regions can be specifi ed
in the input fi le to generate such a patchy habitat. The means of generating
such a complex habitat are discussed below, and sample analyses employing
such conventions are explored in later chapters.
Grid Region Specifi cation
Each individual of NEWGARDEN founding and successive generation
populations occupies a unique point of a grid system that can be described as
the virtual habitat, or preserve, for the population. Points of the grid system
can be thought of as representative of the average density of reproductive
individuals of the species within the habitat under consideration. At
carrying capacity for a habitat, each grid point within the preserve would
be occupied by one individual.
To defi ne the preserve, the user specifi es a Cartesian (x,y) coordinate
grid system of a certain size and shape. Once specifi ed, the size and
shape remain constant throughout a trial. In initial input statements after
a preserve has been specifi ed, the user places each founder at a specifi c
unique (x,y) grid point location (see section Initial Population, below). Any
individual initially input by the user or later created by NEWGARDEN to