Millipedes are surprisingly particular about maintaining their own territories. Robert Mesibov of Queen Victoria Museum and Art Gallery discovered that two species of Tasmanian millipedes, Tasmaniosoma compitale and Tasmaniosoma hickmanorum, maintain a border that is about 230 kilometers long. At places, the no-millipede’s land between the two regions is only about 100 meters across.
Caption: These are Tasmaniosoma hickmanorum and Tasmaniosoma compitale, preserved in alchohol.
Credit: Bob Mesibov.
It’s not uncommon for two similar species to maintain non-overlapping territories. However, this practice, known as parapatry, usually involves insurmountable physical barriers. For example, two species may live on opposite sides of a river or cliff face. In contrast, T. compitale and T. hickmanorum don’t appear to have any physical reason for their enforced separation.
Although 100 meters is pretty wide for a creature that’s only a few centimeters long, it’s narrow compared to the size of the entire territory. With no environmental impediments separating the two species, you’d expect them to intermingle. Even Mesibov is not sure why they don’t, as you can see from the report below.
Hi, Kathy.
ReplyDelete100m may be pretty wide for a creature only 15 mm long, but as you can see in the video (shows T. compitale), these animals are fast walkers. 10m a night is certainly possible. Yet on the one 100m transect I ran (not in the published article) through uniform forest, the changeover from T. compitale to T. hickmanorum happened in less than 20 m. It's quite spooky to find such a thing in the field, yet it actually isn't uncommon among millipedes and some other non-flying creatures around the world - and nowhere yet satisfactorily explained. I'm a millipede taxonomist, not a biogeographer, and my main reason for publishing this story was to provoke some interest, by using the longest and most spectacular boundary I know of, and the easiest to study in the field (2-wheel drive road access to most parts). In 2012 an evolutionary biologist from the Australian National University hopes to have a crack at it. He has an hypothesis about what keeps the boundary 'alive' - but not why it's so sharp, or how it originated, or why it lies where it does on the map.
Cheers,
Bob
Bob,
ReplyDeleteThanks for the comment! Your work obviously provoked my interest, and hopefully that of my readers.