The Founder Selection Effect
The Founder Effect
The Founder Effect stems from an idea of Ernst Mayr:
Modern interpretations of the founder effect often portray it
as an extreme example of genetic drift - e.g.:
The reduced variability of small populations is not always
due to accidental gene loss, but sometimes to the fact
that the entire population was started by a single pair or
by a single fertilized female. These "founders" of the
population carried with them only a very small proportion
of the variability of the parent population. This
"founder" principle sometimes explains even the uniformity
of rather large populations, particularly if they are well
isolated and near the borders of the range of the species.
The reef heron (Demigretta sacra) occurs in two color
phases over most of its range, a gray one and a white one,
of which the white comprises about 10 to 30 percent of the
individuals. On the Marquesas Islands and in New Zealand,
two outposts of the range, only gray birds occur, while
the white birds comprise 50 percent on the Tuamotu Islands,
another marginal population (Mayr and Amadon 1941). The
differences in the composition of these populations is
very likely due to the genetic composition of the original
founders. The same explanation probably covers most of the
cases in which isolated populations of polymorphic species
have much-reduced variability.
The founder effect is actually an accute occurrence of genetic drift, where
changes in the frequencies of alleles in a population or sub-population occur
for reasons other than natural selection.
- ISCID encyclopedia
However there is another effect which is caused
when a small number of individuals establish a new
population. This effect is not based on sampling
The founder effect is a particular example of the influence of random
- Mark Ridley's Evolution textbook
The Founder Selection Effect
The founders may represent a non-random sample of the
original population. This is very likely to be true when
the founders have succeeded in penetrating a challenging
barrier which normally acts to prevent migration.
In that case the founders may be individuals with
exceptional capabilities - since they penetrated the
barrier before any of the other members of their
species managed to do so.
This effect is known as The Founder Selection Effect.
Examples are commonplace - if considering all species.
Founders are likely to be birds and rodents - since they
have the best migration abilities. However, The
Founder Selection Effect also applies within
In the common case of island speciation, founders may have
better swimming capabilities than randomly selected
members of the population - since they successfully
survived the journey to the island.
They may be fatter, have more fuel reserves and better
They may be more likely to go swimming in the first place.
Founders may tend to be extremely physically fit - and
possess more stamina and strength than most members of the