Why are swal­low­tails so re­stricted in the UK?

BBC Wildlife Magazine - - Q&A - Richard Jones

AThe Bri­tish swal­low­tail Papilio machaon, sub­species bri­tan­ni­cus, is limited to the fens of the Nor­folk Broads. Its cater­pil­lars feed solely on milk pars­ley Peu­ci­danum palus­tre, which only grows in the East Anglian wet­lands. Yet in France and the Low Coun­tries, the sub­species gor­ganus is com­mon and wide­spread, avail­ing it­self to a range of host plants.

Like many or­gan­isms at the edge of a range, our swal­low­tail has a nar­row set of very pre­cise habi­tat re­quire­ments. Ge­netic di­ver­sity is the key fac­tor: in south­ern Europe, in­ter­min­gling pop­u­la­tions keep ge­netic vari­abil­ity high, re­sult­ing in a greater di­ver­sity of habits, host plants and ranges. Out­lier pop­u­la­tions, such as those in Nor­folk, were founded by a small num­ber of in­di­vid­u­als – pos­si­bly just one – fol­low­ing the last Ice Age. With a shal­lower gene pool, their mem­bers are more seden­tary, less ex­per­i­men­tal when it comes to egg-lay­ing and less ca­pa­ble of colonis­ing new eco­log­i­cal niches. There are fears that ris­ing num­bers of gor­ganus mi­grants into Bri­tain may well es­tab­lish colonies here and in­ter­breed with the Fen­land race, di­lut­ing it to the point of nonex­is­tence.

See swal­low­tails at RSPB Strump­shaw Fen, Nor­folk. 101

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.