There's so much variability in biological systems that it's hard to find generalities that hold up for large groups of organisms. Recently, evidence was found for the hypothesis that successful, harmful species of plants that were introduced from elsewhere out-competed native species because they averaged fewer parasites than the natives; that the few actual plants originally introduced carried only a limited sample of the kinds of parasites they were subjected to in their homeland.
Now comes a new study that suggests that many introduced plants that
have close relatives in the same region do worse than the natives. The reason seems to
be that the native species have adapted to the local predators, evolving defense
mechanisms lacking in those species meeting these predators for the first time. As it
happens, these studies are not mutually exclusive. After all, most introductions never
do do very well in their new home, and many exotics don't have close relatives
where introduced. What it all comes down to is that we have a long way to go before we
understand the natural world.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.