Biology Reference
In-Depth Information
8
CHAPTER
Population Genetics Edge
Effects
Edge effects are the effects of an abrupt boundary between community
types (ecotone) on community ecology and dynamics in the region of
the boundary (e.g., see Primack 2006). Factors that change at boundaries
include insolation, temperature, wind, rates of organism ingress or egress,
organisms on either side of an edge, and edge-specialist organisms. Such
effects dissipate with increasing distances from the boundary until an
equilibrium state more characteristic of a more widely uniform community
is achieved. For the preserve manager, edge effects take on increasing
importance in smaller preserves (higher edge to area ratio), or preserves
where human activity has increased disturbance and thus edges between
community types. The effects of edges on population genetics have rarely
been studied. We start with a very simple example: do edges affect the
genetic diversity of establishing populations if all other initial conditions
are held constant?
One way to examine this issue is to introduce the same number of
founders, always in the same geometric pattern, into a series of different
NEWGARDEN virtual preserves, with all factors kept constant except that
the border increasingly recedes from the founders across the series. After
allowing the different populations of each preserve type to develop through
the same number of generations, we can examine whether a receding reserve
boundary affects subsequent population genetic diversity by comparing
NEWGARDEN results from these different virtual preserve trials.
For the series of edge effect trials to be examined here, the initial
conditions for the basic fi rst trial input are as follows:
10 loci, each with two alleles of equal frequency = 0.5.
Individuals are bisexual.
An average (Poisson distribution) of two fruit per individual per
generation.
All individuals within pollen dispersal distance have an equal chance of
contributing pollen.
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