Population area but not Nc for moss

[rebecca.cit...@gmail.com]

Hi all

I have an interesting example of a moss that I thought would be great to add. As you could imagine, there is no Nc for the known populations but rather an area of occurrence (ha) for some of these.

My current approach is to select 'unknown Nc' for the population and then in the free text add the known area of occupancy for these populations.

How does that sound?

I know if doesn't help with the actual calculations we're doing but thought it made a nice little example of where alternative Nc options may be needed.

Cheers,
Bec

[rebecca.cit...@gmail.com]

Update: have a study with an estimate of stems / 100 cm2 (from one location) that could be used to approximate population sizes at other locations?

[Joachim Mergeay]

Hi Folks,

Sorry my absence yesterday, I'm on leave for two weeks. 

This kind of situation is where we say Nc is not a useful metric, because it doesn't reflect the actual number of genotypes. 

Similar situations occur with vegetatively reproducing plants or other clonally reproducing organisms, or even with species that are predominantly selfing. Self-fertilizing species purge deleterious alleles every generation by 50%, and hence they are unlikely to suffer from inbreeding depression, and criteria based on drift in outcrossing populations just don't apply. 

In our genetic criteria for species of the Habitats Directive (in Dutch, but you can translate) we consider these in Category 0: genetic criteria not applicable (p. 36). 

In species where the number of ramets doesn't represent the number of genets (like mosses) we don't use proxies for Ne either. The only way to estimate Ne is with direct genetic methods, preferably using temporal methods. Generation overlap can be so immense (moss cushions can live for tens to hundreds of years), so LDNe or sibship Ne is unlikely to provide a useful idea of the true Ne. But also temporal methods require generation time estimates... So what we do is we use the Ne95 criterion: the effective size at which the population maintains 95% of its expected heterozygosity across 100 years. If you use a temporal method, you can estimate how much He changed, and from that calculate how much you'd lose over 100 years. (using the formula Ne=-t/(2Ln(Ht/H0)), with Ht/H0 being 0.95 and t the number of generations in 100 years.) 
For species with generation times of 2 years, this actually corresponds to Ne=500 (actually ), for 1 year it's nearly 1000, for 3 years Ne=325, etc. 

Joachim

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Joachim Mergeay (he/him)

Research Institute for Nature and Forest - Belgium                                  

Associate Professor KULeuven Ecology Evolution and Biodiversity Conservation

Tel: +32 499 942 942

Meldpunt wolven Vlaamse overheid : wo...@inbo.be

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