Biology Reference
In-Depth Information
Size and Shape of the Grid
The borders of the grid system represent the boundaries of the preserve or
region of the habitat that can support a population. As noted, individuals
dispersed beyond these borders die, and for a mating, a microgamete
contributor or female parent cannot be selected from outside the grid.
In NEWGARDEN, any grid coordinate can be assigned to the lowermost
left grid point. For example, one could specify a grid and preserve that
would function exactly the same way as one specifi ed in the previous section
with the following statements:
<Region XL=“-4960” XH=“6303” YH=“2559” YL=“-2560”>
<Rectangle XL=“0” YL=“0” XH=“5119” YH=“5119”/>
</Region>
yielding a preserve with 5120 grid points on a side, but thereby set the origin
point (0,0) to the lowermost left corner. However, if one wishes to study the
effect of placing founders at differing distances from the habitat boundary
on retention of genetic diversity, it is preferable to set the origin in the center
of the grid. It is easier to move the grid boundaries equally in all directions
with the founders remaining in place than it is to re-enter modifi ed grid
points for each of the founders to place them further and further from a
border. For example, rather than the above, use the following:
<Rectangle XL=“-2560” YL=“-2559” XH=“2559” YH=“2560”>
This convention also facilitates studies of the effects of deviation from a
square preserve shape on diversity retention, since founders can be kept
in place while the border set-points are changed to refl ect squares versus
rectangles. Examples using NEWGARDEN to study such population growth
and genetic edge effects are given later in the topic.
The size of the grid system sets the maximum carrying capacity. If
there is concern that a particular preserve will be large enough to conserve
the genetic diversity of a species over time, then if the average density for
that species in that habitat can be estimated, NEWGARDEN can be used
to examine diversity retention. By shrinking or expanding the scale of the
grid, one can investigate the size preserve, or size of habitat, needed to best
introduce a species to maximize the number of unique alleles preserved. By
using differing sizes and shapes of preserves while altering other conditions
(e.g., dispersal distance, mortality), one can study restoration genetic
diversity preservation with regard to preserve geometry versus differing
estimates of the life history characteristics of the targeted species.
In considering the realism of the size of preserves and their carrying
capacity, some estimate of the average density of the species is needed.
In several of the trial examples explored below, the preserve is a square
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