Dispersal - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 169

this in turn resulting in an increased investment in pollination-supporting
resources. Populations of organisms well below the dispersal distance
critical point will be at risk of non-maximal growth rates.

5000

4000

3000

2000

1000

R

4

X
O

0 2

0 5 10 15 20 25 30 35

DISTANCE

Fig. 12.1 Population growth after four generations relative to the maximum distance that
offspring can be dispersed. Trials denoted with an “x” had a reproductive rate set to 4 (r = 4),
while those designated with “o” had r = 2. More details concerning these comparative trials
are given in the text.

So, species for which increased rates of population growth are critical
should experience elevated selection for greater dispersal distances up
to a point. That the previous statement is not true for many species (e.g.,
“choking growth” short-distance dispersal reproduction of Impatiens
species, among others) suggests that many other factors affect the evolution
of dispersal distances. Clearly, however, in some cases there will be selection
on the elaboration of features that affect offspring dispersal distance.

Interactions of Offspring and Pollen Dispersal Distances

Offspring and gamete dispersal are highly complex topics differing widely
across species in terms of mechanisms, distances and effi ciency, and thus
the comparative trials that follow are presented only as examples of how
NEWGARDEN can be used to explore the effects of dispersal on genetic
diversity in newly establishing populations. We'll begin with a series of
examples where offspring and pollen dispersal distances are always equal
to each other in any trial. The input conditions for these initial trials include
the following: