Article: Species mix across Panama Canal

From: Robert Karl Stonjek (rstonjek_at_bigpond.net.au)
Date: 08/24/04 

Date: Tue, 24 Aug 2004 04:44:34 +0000 (UTC)

Species mix across Panama Canal
Michael Hopkin
Fish get new neighbours as ecosystems mingle.

When the Panama Canal opened in 1914, it was a tremendous boon to the
shipping industry. But research shows that it is not only boats that have
taken advantage of the shortcut: several of Central America's fish species
have also made the journey.

The canal links the Rio Chagres and Rio Grande rivers, which are on opposite
slopes of the Isthmus of Panama. When the waterway opened, the once-isolated
fish communities of the two rivers were given the chance to intermingle.

Although both rivers are now home to a handful of new fish, no species has
gone extinct as a result, report Scott Smith of McGill University in
Montreal, Canada, and his colleagues. This is at odds with many experts'
belief that intruders upset the delicate balance of ecosystems.

Find your niche

According to the 'niche' theory of ecosystems, every species within a
community, be it river or rainforest, has a well-defined role in life. Every
species interacts with other species in the group, for example by forming a
predator-prey relationship, or forging a mutual bond such as that of corals
with algae.

Some theorists argue that ecosystems do not have the capacity to accommodate
new arrivals. In other words, all possible niches tend to be filled, so any
intruder will be stepping one someone's toes. But the fact that Panama's two
fish communities were able to mingle without any extinction argues against
this idea.

Scott and his colleagues sampled fish from the two rivers and compared the
species living there today with those found in a census taken before the
canal opened. The Rio Grande has gained five freshwater species that
previously lived only in the Rio Chagres, and three species have spread in
the opposite direction. This indicates that the number of species in the Rio
Grande has increased by 28%, and in the Rio Chagres by 11%, the researchers
report in the Proceedings of the Royal Society of London B1.

If any species were to go extinct as a result of increased competition, they
should have done so by now, Scott says. "Our results suggest that the
process has not occurred, within the timescale of 10 to 100 generations that
is envisioned by ecologists," he says. And although Scott concedes that
species may still go extinct over a much larger timescale, he thinks this is
unlikely.

Space invaders

This does not mean that ecosystem invaders are always benign, Scott says. "A
small number of case studies have taught the scientific community that
invasions may have disastrous effects," he says. This is particularly true
when the invader is a top predator such as the Nile perch (Lates niloticus),
which was introduced to Lake Victoria in Africa in the 1950s. The perch
wiped out an estimated 200 native fish species.

Although ships continue to chug up and down the Panama Canal, there is
unlikely to be any more traffic in fish species, the researchers predict.
The reason is the introduction of the predatory pea*** cichlid (Cichla
ocellaris) to Lake Gatun, an artificial lake halfway along the canal's
route, in 1967. With such a dangerous gatekeeper blocking the way, the two
rivers are effectively once again separated.

References
Smith S. A, Bell G. & Bermingham E. Proc. R. Soc. Lond. B,
doi:10.1098/rspb.2004.2796 (2004

>>From Nature
http://www.nature.com/news/2004/040816/full/040816-5.html

Posted by
Robert Karl Stonjek

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