Biology Reference
In-Depth Information
<Dispersal_Distribution>
<functionpoint x=“0” y=“0”/>
<functionpoint x=“6” y=“0.25”/>
<functionpoint x=“13” y=“0.5”/>
<functionpoint x=“22” y=“0.75”/>
<functionpoint x=“301” y=“1”/>
</Dispersal_Distribution>
The fi rst offspring dispersal frame runs from 0 grid points to a maximum 5
grid points (x-1). This means that from the central female, a propagule can be
dispersed from 0 to 5 grid points in either the x or y directions. For example, a
propagule could be dispersed 0, 4, or 5 units in the x or negative x directions,
while being dispersed 0, 2, or 1 units in the + y directions. However, x or
y dispersal distances cannot exceed 5 units. There is a 25% chance that a
particular newly produced offspring will be dispersed to some point chosen
at random within that fi rst frame. The next most distant second frame is
described by the next statement, and the minimum dispersal distance value
for that frame is given by the “x” value of the preceding statement that
describes the termination of that previous frame. In the example above,
the second most distant dispersal distance frame has a minimum value
equal to 6 grid units (the x value of the preceding statement) and includes
grid points out to the borders of the square surrounding a central female,
the borders being at a distance of 12 grid units (x-1, that is, 13-1) in the
vertical (above and below) and in the horizontal (left and right) directions.
Since the indicated
total
probability of dispersal out to 12 grid units is 50%
(y = 0.5), and since the probability of dispersal out to 5 grid points was 25%,
the probability of being dispersed from 6 to 12 grid units is 25%. In other
words, for a given frame, the probability of dispersal to that frame is the y
value given for that frame minus the y value given for the preceding frame.
By these conventions, the most distant frame for offspring dispersal in the
above statement set runs from 22 to 300 grid points, and the probability of
dispersal to somewhere in that frame is 25%.
For a given offspring dispersal distance distribution statement set,
x values and y values in successive statements must be increasing, and in the
last statement for a set, the value of y must = 1 (100%). In the production of
offspring for a new cohort, individual offspring cannot establish at a point
where a living individual already exists (unless that living individual is
scheduled to die after the current bout of reproduction), nor do they persist
if dispersed beyond the grid bounds as defi ned by the user. An offspring
dispersed to such points dies even though the production of the propagule is
tallied as a reproductive event as driven by the reproduction rate statements.
Two or more offspring may be dispersed to the same unoccupied point.
Before the next generation “offi cially” begins (after all matings of the
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