Note: Two questions combined.

Q: "Please enlighten this person of very little brain. Just WHAT is a
"Founders Effect?"
"Ok, exactly how can a founders effect show how ferrets can't go feral?"

A: I know the flounder's effect can leave you feeling a bit flat, but
the idea is just a bit fishy.

"Founder's effect" is a term that comes from population genetics where
there is a noticeable loss of genetic variation within the descendents
of a new colony because of a limited number of breeding individuals.
This could mean that there were a limited number of breeding
individuals, or that there were a large number of individuals, but most
did not breed. In either case, there are fewer genetic differences
within the descendants (offspring) compared to the founders
(ancestors).

Sometimes a founder's effect is called a bottleneck (they are sometimes
used interchangeably), although a bottleneck is generally defined as
being caused by a large die off of animals (at least 50%), such as with
the black-footed ferret, while the founder's effect is usually applied
to colonization events, such as with feral animals in New Zealand.
Black-footed ferrets, cheetahs, golden hamsters, American bison, and
northern elephant seals all display the effects of a bottleneck. While
the reason for the loss of genetic information is different between
the two, the results are similar. However, the loss of genes in a
bottleneck can be permanent, while the loss from a founder's effect
can be reversed by the introduction of breeding individuals from the
unaffected population.

This loss of genetic information can occur with line breeding,
in-breeding, the breeding of endangered species, or a small number
of animals establishing a feral population.

There are some genetics studies that have concluded all modern polecats
descended from a single small founding population between 250,000 and
100,000 years ago. This would imply that the founding population of
modern polecats suffered a bottleneck as ancestral polecats survived,
but the other polecats went extinct. After surviving polecats
repopulated Europe and Asia, the steppe polecats crossed into North
America. As their offspring became landlocked, they underwent a
founder's effect, resulting in the black-footed ferret. Later,
black-footed ferrets suffered a bottleneck when the population
crashed. Got all that?

Well, the end result is that polecats are very closely related. Yep,
all of 'em. So closely related that there is some argument that --
based on genetic studies -- all polecats are a single species
(including the black-footed ferret). The other implication is that
the animal domesticated from these closely related polecats -- our
domesticated ferret -- would also be closely related. I am sure you can
intuitively understand why it is so difficult to identify the ancestor
(or progenitor) of the domesticated ferret; it is easier to, um, ferret
out genetic relationships when there is more genetic variation present.

Ok, but what about the feral ferrets in New Zealand? The history of the
introductions of ferrets in New Zealand has two separate histories:
the official government history, and the unofficial actual history.
Understanding both is very important.

In the official story, ferrets were bred and released by acclimation
societies and government agencies beginning in the 1870s. New Zealand
law protected ferrets until the 1920s. The introduction was to control
the rabbits that had been released earlier, and it failed to such an
extent that weasels and stoats were later released to accomplish what
ferrets couldn't do. There are now sizable populations of feral ferrets
on both North and South Islands. Estimates of the number of ferrets
released during the initial introduction vary, and some government
agencies seem to be purposely disingenuous in reporting the numbers.
For example, some reports like to say something along the lines of
"five ferrets were released in 1879 and now New Zealand has the largest
wild ferret population in the world." This implies that a small number
of ferrets can populate a large geographic area, when in fact, the
introduction took decades, large numbers were initially released, the
ferrets were protected, and current populations are due to a century
of breeding, as well as additional releases.

The unofficial story, much harder to document, is that not just
government agencies and acclimation societies were involved in the
ferret releases, but also scores of private individuals. I have several
sources that say cattle and sheep ranches would breed ferrets purposely
to release them in an effort to control rabbits. I have documents in
hand that prove American ferrets were being shipped to New Zealand
during the introduction period. Obviously, more ferrets were being
released than the government suggests, but I don't think a realistic
estimate of additional numbers can be made.

Both histories are true (well, not the disingenuous part), but it shows
how difficult it can be to document the numbers of ferrets initially
released. When you add to the mix the numbers of ferrets accidentally
and purposely released by fur farms, it is probably not possible to
determine ANY number with accuracy. Nonetheless, the numbers must have
exceeded 20,000 breeding animals released during the introduction years
(1880-1900), and it could have reached to as many as 100,000.

Even if the number released were only 20,000 ferrets capable of
breeding, how does that fit with a founder's effect? Conservationists
are not in agreement with a minimum number of breeding individuals that
would prevent a founder's effect, but conservatively, that number could
be as small as 25 to 400 breeding individuals. Obviously, the numbers
of ferrets released in New Zealand significantly exceeds that number,
so a founder's effect should not be a factor.

Of course, there is the question of genetic drift, which suggests the
genetic composition of a population can randomly shift for no apparent
reason (assuming the shift is not under selective pressure). However,
with the decades-long release of ferrets, as well as the large number
of ferrets released from fur farms, there would have to be a lot of
corroborative evidence before genetic drift could be accepted.

So, why is this important in the California feral ferret issue? There
are three major attributes of ferrets that have been historically used
to maintain their illegal status (or in attempts to make them illegal).
The danger of ferrets biting young children is one, another is the risk
of rabies, and the last is the danger of feral ferrets. Since ferrets
have been shown to be as safe or safer than cats or dogs, the first
argument is void. An effective rabies vaccine and virus shedding
studies have voided the second argument. The remaining argument is
the feral ferret issue.

There are two types of feral ferret reports: those that can actually
document ferrets living in the wild (such as the feral ferrets in New
Zealand), and those that cannot document feral ferrets but suggest
they are there (such as "reports" of ferrets in New Mexico). The
vast majority of feral ferret reports are of the second type, where
uncorroborated reports are offered as evidence, and any found ferret
(even a lost pet) is defined as feral. Except for those biologists with
a clear anti-ferret bias, these reports can't fool a single biologist.
But, you still have the feral ferrets that live on some British
islands, and -- of course -- the New Zealand feral ferrets.

Thus, the New Zealand feral ferrets have become quite important to the
California Fish & Game; for them it is clear evidence that ferrets
could actually become feral. This is the remaining evidence; the
cornerstone of their existing argument at ferrets should be kept
illegal in that state. To strengthen the argument, the CF&G tries
to make California as "New Zealand-Like" as possible.

So, how does finding a founder's effect/bottleneck in the remains of
88 New Zealand feral ferrets fit into the equation? Simple. Remember
that the genetic variation in a species is conserved if the number of
breeding individuals is between 25-400? Well, if only 20,000 ferrets
were released in New Zealand between 1880 and 1900, that means an
average of 1000 breeding ferrets were released each year. Even if
ALL ferrets died between the yearly releases, the number of ferrets
released still well exceeds the number required to maintain genetic
variation. In short, there shouldn't be a founder's effect. When you
add in all the private releases, fur farm releases, and survivors and
offspring, there clearly should not be a founder's effect.

Are you beginning to see the implication? Why would I find clear
evidence of a founder's effect in the New Zealand feral ferret
population if such an event should not have occurred? The possible
explanations are that only a few ferrets were able to breed, most of
the ferrets died, or a combination of the two. These explanations
suggest that despite the efforts of the New Zealand government,
acclimation societies, and private individuals to stack the deck and
insure the initial survival of the released ferrets, the ferrets did
very poorly.

This undermines the CF&G position that pet ferrets are a danger for
being able to go feral. If a founder's effect/bottleneck exists in the
New Zealand feral ferret population, it means most of the released
ferrets never reproduced or did not survive to reproduce. Ready for the
curve ball? It could also mean the initial releases of ferrets were
successful, but something later caused a huge population crash. So,
the two (most likely) possible scenarios are that the initial releases
were a failure, or that something later caused a huge decline in feral
ferret numbers (or some degree of both, I suppose).

What could have caused such a crash? It is hypothesized that rabbit
control measures caused a huge ferret crash in New Zealand. This is
actually a very attractive hypothesis because in every place where
ferrets once were or are feral, there are also feral European rabbits.
Recent studies in New Zealand suggest feral ferret numbers are directly
tied to feral rabbit numbers.

Luckily for us, both scenarios are really cool. For example, if it is
discovered that ferrets have a hard time going feral, then it shows pet
ferrets are low risk animals for going feral. However, if it discovered
that ferrets could only go feral where there are large numbers of feral
rabbits, well, the risk is likewise as low if there are no large feral
European rabbit populations. In either case, the CF&G argument is
undermined.

There is one last piece of the puzzle. In Europe, the American mink was
released, mostly accidentally, starting in the late 1950s. Barely 50
years later, American mink are naturalized throughout Europe. Compare
that to the ferret in North American, where I can first document them
being here between the 1780s (indirect evidence) to 1820s (direct
evidence). They were most likely here before then, but there is a
difference between thinking they were here and proving they were here.
In 200 years, there are no feral ferret populations in North America
(and I can document both intentional and accidental releases during
that time). Mink? 50 years to spread over Europe. Ferrets? 200 years
to hide under a china cabinet. My working hypothesis is that ferrets
have not been able to go feral in North America because 1) there are
no large populations of feral European rabbits, and 2) they cannot
out-compete the American mink.

Part of the trip is to get supportive evidence that ferrets in New
Zealand had a founder's effect/bottleneck, and part is to document the
ability of the American mink to out-compete the local polecats. If I
can get the empirical evidence, then it can go a long way to undermine
the last argument of the CF&G for outlawing ferrets. I think that could
be a good thing.

I could discuss this for hours and I am creating a Powerpoint
presentation on the subject. While important to California ferret
owners, it deserves national exposure because the feral issue can crop
up at any time. Like my dental findings, it will also get published in
appropriate publications and presented at zoological meetings. I could
even have a preliminary report ready for the ferret symposium if
invited. The point is that this is an important issue and it needs
to be discussed in as many formats as possible. It takes a lot of
shot-gunning to get some people to listen, so if that is what it
takes, then that is what I will do.

Bob C [log in to unmask]

[Posted in FML 5855]