Populations on the edge

ResearchBlogging.org Are populations on the edge of the geographic range of a species not so important to conserve as more central ones? That’s the provocative question tackled by a recent meta-analysis. (( ECKERT, C.G., SAMIS, K.E., LOUGHEED, S.C. (2008). Genetic variation across species’ geographical ranges: the central-marginal hypothesis and beyond. Molecular Ecology, 17 (5), 1170-1188. DOI: 10.1111/j.1365-294X.2007.03659.x)) Theory would suggest that marginal populations should be less diverse, and therefore possibly of less conservation value. But the theory has never really been properly tested, so the common assumption that marginal populations are less diverse is just that — an assumption.

Its theoretical underpinning is that individuals and populations are likely to be fewer and more widely spaced on the periphery compared to the centre of the range of a species. That means that effective population sizes are likely to be lower and isolation more pronounced, which suggests that genetic diversity within populations should be lower and among populations (differentiation) higher in marginal areas.

That turns out to be more or less the case for the 134 population genetic studies (of both plants and animals) reviewed by the authors: “any given species is more than twice as likely to show the predicted pattern as not, and usually a change in diversity is accompanied by a parallel change in differentiation.”

There are some caveats, however. The differences were generally pretty small. The actual mechanisms producing them not clear (were the differences the legacy of historical environmental changes or the result of ongoing evolution?). The sampling of species was biased taxonomically and geographically. Plus all of the studies looked at (supposedly) neutral variation rather than traits which might actually have adaptive importance.

But the results are nevertheless intriguing. Especially when you think about how they might be different for crops (I don’t think any of the 134 studies reviewed were of domesticated species). If anything, one would predict geneflow from the center to the periphery, and indeed among peripheral populations, to be stronger in crops than in wild species. That means that differences in genetic diversity and differentiation between centre and periphery are likely to be even smaller, maybe non-existent. Sounds like something worth checking.

Sorghum to Swaziland; coals to Newcastle?

I’m having a little trouble getting my head round this one. The “Republic of China on Taiwan” funded a successful project to teach Swazi farmers how to grow sorghum in areas with little rainfall. You might have thought that at least a few local farmers would have known how to grow this staple, but apparently all had been forgotten in the rush to cotton and maize. The Swazi Minister of Agriculture also said that education assisted the move away from sorghum:

Sorghum needed someone in the fields to chase away birds and because most children now go to school, maize then became popular.

The farmers who took part in the project were happy enough with the result. I just hope they don’t keep their children away from school to work as scarecrows.

A chef on seed saving

Chef’s Corner seems like a great idea: a blog by an experienced chef interested in American food traditions and the agrobiodiversity that underpins them. A recent post waxed lyrical about seed saving. Problem is, prior to this month’s six posts, the only previous ones were in May 2007. So I’m not sure how serious Chef Robert is about this venture. But I hope he sticks with it.

American Gothic, 21st century style

Somewhat related to Jeremy’s post just below, there’s an article in the New York Times about young Americans going back to the farm. Or rather, going to the farm for the first time: we’re talking Upper East Siders clambering onto tractors. Would be interesting to see whether the percentage of organic farmers among them turns out to be above the average, and whether they will tend to eschew biofuels and favour weird niche crops, heirloom varieties, and agricultural biodiversity in general. Via Metafilter.

Local to where?

One of the great dangers of the internet is that it makes everywhere seem like next door. So when I stumbled across Local Harvest my first thought was, “Not to here it isn’t”. But that’s needless nitpickery. The fact is, southern Europe is still sufficiently diverse that one doesn’t really need a service such as this to locate a decent source of locally grown food. I can go to my local market and ask where the produce was grown and get an answer. But I also know that this is becoming more and more of a luxury. So perhaps it would be nice for the many and varied farmers and farmers’ market schemes across Europe to come up with something similar. There’s something in London, but it isn’t nearly as inclusive as it makes out. May as well get started with it now, before we really need it. Or maybe there’s already something similar out there?