South Sister St. Marys, Tasmania

South Sister

line of parapatry

- Alastair Richardson

 

Sorry for the delay in getting this to you, I have been writing lectures and everything else is on hold, which means that the paper just piles up on my desk.

As I said, my only real claim to any knowledge about the South Sister area is that I supervised an Honours program of a student named David Horner, who was looking at the parapatric boundary between the two large endemic velvet worms, the blind velvet worm Tasmanipetus anophthalmus and the giant velvet worm T. barretti. The general form of the boundary had been identified by Bob Mesibov, but what David did was to map it quite precisely, at least over short distances, and try to establish what mechanism keeps the two species so neatly adjacent to each other.

I can let you have his mapping data if that is of interest (I guess you need to establish exactly where the boundary runs relative to the proposed forestry activity), but as far as a mechanism is concerned, David was only partly successful. The most likely thing seems to be that the females of T. anophthalmus are more attracted to the males of T. barretti than to their own males. This sort of reproductive disruption might be enough to maintain the boundary between the two species.

In more general terms, parapatric boundaries of this type are rarely identified and are landscape features that should be treated in the same way as a threatened species distribution, but it hard to convince people of that when there is nothing to see on the ground. But the boundary between the two is a real phenomenon and may be as sharp as a complete turnover from one species to the next in less than 200m. David Horner noted that in one of his intensive sites at the Nicholas Range the boundary had been disrupted and he suggested that this might be due to changes in land use.

I hope this helps a bit.

Assoc. Prof. Alastair Richardson
Head, School of Zoology

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