Retorts

Triagic Conservation

Ian McLean [Black Robin -- Alive by Accident? Aug] criticises Don Merton's rescue of the Chatham Island robin because it was not "good science". Merton did not set out to do an experiment to find out how robins should be saved. He set out to save the robin. Maybe his work was not necessary. Surely it did not ensure that the robin would survive into eternity, but almost certainly it increased its chances of survival into the foreseeable future.

If Merton's practice was good, how good are McLean's theories.

He tells us that "Small numbers of black robins mean large amounts of inbreeding. Inbreeding reduces genetic diversity ... and decreases the ability of a population to cope with adversity."

True, small numbers result in more inbreeding. So Merton's priority was to increase numbers. Did he do wrong?

But inbreeding does not decrease genetic diversity. In fact it will increase phenotypic variance in a population. Nor does it prevent populations from coping with adversity. Many species which cope adequately with adversity inbreed at a much higher rate than will be imposed on the black robin population by its temporary reduction in numbers.

For example, most annual plant species, the species which colonise new, bare, inhospitable habitats, are normally self-fertilising, a breeding system which leads to a very high rate of inbreeding. Try telling a farmer that barley grass has a tenuous hold on New Zealand. Many animal species are also self-fertilising, and many animal populations are sub-divided into small breeding groups with high inbreeding indices.

There are many New Zealand examples which do not comply with McLean's 50/500 rule. I did a quick check through G. M. Thomson's 1922 Naturalisation of Animals and Plants in New Zealand, to find that the fallow deer herd in Nelson was founded by three individuals, the Otago herd from 15. Red deer in Nelson descended from one stag and two hinds, the Wairarapa herd from three animals, the Rakaia herd from nine, the Manawatu sambur from one female and one male, Fiordland wapiti from 10 animals, and Stewart Island Virginia deer from 16 individuals. There are probably many more species which have been established in New Zealand from similarly low numbers.

What is the predictive value of a theory which fails so dismally to account for the past?

Reduced to essentials, McLean's theories say that conservation measures will be most likely to be successful on the commonest species, least successful on the rare ones. One wonders whether a conservation movement driven by deficient theories might spend its efforts on preserving Stewart Island sandflies while letting the kakapo go extinct so that the theories will not be contradicted by the outcome.

At a deeper level, his 50/500 rule is another expression of Matthew's 25.29 law, and consistent with the Panglossian economic "idiotology" of our times, which interprets Matthew's [biblical] law as prescriptive, when it was meant to be descriptive, and so preaches non-intervention as a god-given policy.

Just as well for the biosphere that Noah was not a convert.

Pat Palmer, Christchurch

Black Robin Team

Editorial oversight meant that Ian McLean's thanks to Don Merton for assistance with the article "Black Robin -- Alive by Accident?" [August] was omitted, as was the comment that the black robin programme was very much a team effort.