More Mice Meanderings

A little addition to the previous post.

Fishing with a mouse pattern feels somewhat frivolous at the moment (though I suppose it shouldn’t) but as I say it is downright fun. There is some interesting biology to hang off it as well. When looking up a suitable link to illustrate mouse plagues down under I came across a rather nice article from New Zealand. Two biologists have written a popular piece highlighting the possibility of a mouse explosion (and the fishing that results from the upsurge) for the 2009-10 season. Aside from some good basic information on what causes mouse populations to increase to plague proportions there is an interesting divergence into why some trout eat mice and some don’t seem to ever switch onto the food source.

Back in the null hypothesis post I briefly (for me) speculated on the idea of specialisation. Specialisation within a population can be envisaged when fish take up different feeding stations and, if these stations are relatively stable, become exposed to different food items. Learning how to capture the food item in front of them leads to an increasing focus on that sort of item and hence divergent feeding behaviour between individual trout. The article speculates on this too in relation to mouse eating trout. As far as I understand, trout densities in New Zealand back country rivers are not high and so learning from ones neighbour is less likely than it might be in a populous spring creek. The authors do a good job on the issue (though the willow grub feeding example doesn’t work) and go to the extent of highlighting the likely role for learning with a one sentence paragraph all on its own.

I find all this deeply interesting and not least because it may also involve the issue of personalities. One can imagine feeding specialisation as a product of geography, or more appropriately hydrology. Where a fish is in a stream dictates both the quantity and type of food items it experiences and this is one mechanism for specialisation. The other, though not mutually exclusive, is via differing personalities. Bold trout may have quite catholic tastes but shy trout could well be the opposite, having an austere calvinist palate. The outcome is the same observation (some do and some don't eat mice in this example) but for a very different reason and one that may well be independent of the spatial structuring of a population. Whether the New Zealand trout that do feed on mice are the brash outgoing type is not known (and interestingly not speculated on in the article) but it is certainly an alternative to the simple explanation based on the availability of food.

Oh, and if you think the bold-shy stuff is a bit far fetched you really haven’t been doing your reading recently. It’s all the rage darlings.