Ecosystems

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.

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.