Biology Reference
In-Depth Information
effect. This tendency for populations to grow faster when the founders are
placed diagonally, be it at the corner or at the center of the preserve, is due
to differences in the number of inhabitable spaces available to diagonal
versus horizontal founders (Fig. 9.2).
5000
V
v
V
v
4000
V
v
V
v
3000
V
v
V
v
V
v
2000
V
v
V
L
v
L
V
L
v
l
L
l
V
L
1000
v
l
L
l
V
v
L
l
L
l
V
v
L
l
L
l
V
v
L
l
L
V
v
l
L
l
V
v
L
l
V
V V
V
V
v
L
l
L
l
v
L
l
l
0
v
L
v
L
l
l
L
v
l
L
l
l
0
7
14
21
GENERATION
Fig. 9.1
Mean values (30 replicate runs per trial here and in the following graphs on spatial
arrangement of founders) for population growth of four NEWGARDEN populations generated
with identical input conditions (see text) except placement of 20 founders (in two lines of
10 with closest spacing). l, lines of founders begin at the lower left corner of the preserve
running horizontal to the lowest border; L, lines of founders begin at the lower left corner
but run at a 45
o
angle up and into the preserve; founders lines for v and V are identical to l
and L, respectively, except they are placed at the very center of the preserve. The means of l
versus L are statistically different at the p < 0.0001 level. The means of v versus V differ with
a confi dence level of 92.2 (p < 0.08), supporting the notion that founders placed diagonally
in the square grid system of the preserve will tend to produce more offspring than those
placed horizontally.
This increase in available establishment sites for a diagonally placed
set of founders is due to NEWGARDEN grid system conventions. When a
maximum dispersal distance of 1 is user specifi ed, this means that, from a
parent occurring at one (x,y) grid point = (0,0), dispersal can occur to the
(1,0), (1,1), (0,1), (-1,1), (-1,0), (-1,-1), (0,-1), or (1,-1) grid points. When
founders are placed diagonally, the absolute distance between founders
increases (square root of 2
(1/2)
= 1.4 grid units). Since most closely spaced
diagonal founders have a greater distance between them than horizontal
founders, more establishment grid sites become available to the former
under the dispersal rules
(
Fig. 9.2).
The use of these grid system conventions thus in some ways diminishes
the realism of NEWGARDEN dispersal patterns, which under ideal
conditions would be circular. However, the NEWGARDEN populations
depicted in Fig. 9.1 grow differently according to geometric expectations:
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