Effective population size

Two recent blog posts by Carol Beuchat at http://www.instituteofcaninebiology.org/blog/ entitled "Vulnerable breeds: how small is too small? and "The trouble with Terriers" are worth a read. (Her April Fools post is also good.) In general I agree with her analysis and conclusions.

To double-check her calculations, I used version 1.94 of my Norwich pedigree database. For dogs in my database born in a particular year, I counted the number of distinct sires (Nm) and the number of distinct dams (Nf), and calculated the effective population size (Ne). The results since 1990 are as follows:

year	Nm	Nf	Ne
1990	119	224	310.9
1991	124	209	311.3
1992	115	214	299.2
1993	130	240	337.3
1994	137	231	344.0
1995	140	257	362.5
1996	135	262	356.4
1997	121	214	309.2
1998	128	228	327.9
1999	143	243	360.1
2000	157	275	399.8
2001	150	239	368.6
2002	153	279	395.2
2003	156	260	390.0
2004	170	265	414.3
2005	170	266	414.9
2006	159	261	395.2
2007	159	241	383.2
2008	164	255	399.2
2009	153	227	365.6
2010	146	222	352.3
2011	121	201	302.1
2012	113	173	273.4
2013	68	124	175.7
2014	23	48	62.2

So the numbers are roughly in line with what Carol Beuchat claims for Norwich.

However I have three reservations about this calculation.

1. The American Kennel Club (AKC) only lists dogs in its studbooks when they *first* sire or whelp a litter. (Every other registry of which I am aware lists all dogs registered.) Since the vast majority of information in my database comes from studbooks, my database does not list all AKC registered Norwich. Thus the number of sires and dams for any given year is an underestimate.

2. My database is only complete for Norwich from the UK, Canada, Germany, and Switzerland. There are several other European countries that I would like to add that would make the database more complete. So again the number of sires and dams for any given year is an underestimate.

3. While the definition of effective population size is easy to understand, the derivation of the formula of effective population size is not easy. So most people must take the formula on faith. I dislike such formulas.

In spite of my reservations, I believe her conclusions are correct - Norwich are a small gene pool ... perhaps too small to survive without some infusion of new genes.

For an interesting contrary viewpoint, see http://rufflyspeaking.net/is-opening-the-akc-stud-book-a-good-idea/