In this debate we should keep in mind that many migration patterns are not fixed but adapt to conditions. We see this in the marine environment where some migratory species are seen to be changing their feeding and spawning grounds in response to changes in sea temperature and other factors. On land, where there can be obstacles to such shifts (towns, roads, pipelines) it may not always be clear whether facilitating new migration patterns is assisted migration or translocation. In these cases, I do not see much of a difference between migration and range extension. Perhaps from a terrestrial point of view it makes sense to identify migration routes on a strictly geographical basis, but for a marine ecologist if a fish always migrates to water of 6 degrees to spawn, the fact that the 6 degree water may not be in the same place every year does not turn this into "range extension".
Someone observed that translocated species may take centuries to adapt to new environments. This may be true, but unfortunately there are many disastrous exceptions. Mosquitoes in Hawaii, rabbits in Australia, Water Hyacinth and Zebra Mussels in N. America for example. As for adaptation, the clam Macoma baltica is found in both Canada and Europe, but the sizes are very different. The amphipod Corophium volutator is a minor species in Europe but dominates the intertidal zone of the Bay of Fundy and has an essential ecological role as food for migrating birds. The literature of ballast water transport can give you hundreds of examples of species that have survived well in new environments, even ones quite different from their home locations. Bill Silvert ----- Original Message ----- From: "James J. Roper" <[EMAIL PROTECTED]> To: "William Silvert" <[EMAIL PROTECTED]> Cc: <[email protected]> Sent: Friday, July 20, 2007 12:16 PM Subject: Re: assisted "migration" (not) Good point Bill. But, while some things may be labeled "assisted migration" many things that fall under that heading are not. Such as the Florida Torreya, the first example in the Conservation Biology paper on the topic. That would clearly be called something like "Assisted range extension". So, we do not want to classify processes that are fundamentally different under the same heading.
