MYTHS OF THE ALIENS - The New Wild: Why Invasive Species will be Natures Salvation - page 72

breakout. The Brazilian pepper tree in the Florida Everglades “remained restricted for a century before
rapidly expanding.” Other examples might include the crazy ants of Christmas Island or the Nile perch
in Lake Victoria. 31
Many natives may hang on in the face of invasions, but they are “the living dead,” says Richardson.
“Many of the positive impacts attributed to non-natives are likely to be transient . . . whereas negative
impacts are typically more permanent and often irreversible.” 32 Some modeling studies suggest that
“extinction debts may take hundreds of years to play out,” says Benjamin Gilbert of the University of
Toronto. 33
These arguments have not been convincingly refuted. That would be hard: only time will tell. But
there is a flipside to extinction debt, say Sax and Stephen Jackson of the University of Wyoming. They
call it “immigration credit.” Just as extinctions may lag, so may new arrivals. Take the example of the
European Alps, where plant diversity has increased on mountain summits during the past century. As
temperatures have warmed, species have moved upslope, but incumbent populations have mostly per-
sisted. The newcomers took time to disperse, set up, grow, and reproduce. This process lagged behind
the warming, but it happened. The colonists to come are as inevitable as any natives that may be lost. 34
Another side of the “immigration credit” is the rush of hybridization often unleashed as the genes of
the old species intermingle with those of the new. With time, new hybrids and eventually new species
will emerge. We will return to these aspects later. Both the debt and the credit create uncertainty about
the eventual impact of the ecological changes. But to count one without the other makes no sense. It
reeks of a bias against aliens.
Behind all the arguments about how ecosystems react to invaders is a more basic issue. The abiding pre-
sumption in invasion biology is that there is something inherently different and bad about aliens. That
they are at best misfits and at worst a destructive presence. That, as the environment group WWF puts it
on its website, they “do not belong,” are “unwelcome,” and have impacts that “are immense, insidious,
and usually irreversible.” 35 Similarly, natives are good. The sentiment feeds the research agenda, which
further strengthens the sentiment. It is the bedrock of policy making. As Matthew Chew of Arizona State
University put it after years of trying to break the irrational hatred of tamarisk in the American West,
“Nativeness is an organizing principle of numerous scientific studies and findings, and the sine qua non
invoked by many management policies, plans, and actions to justify intervening on prevailing ecosys-
tem processes.” 36
The battlefield between those who believe in the dichotomy between aliens and natives and those
who think it is mythmaking fills with anecdotal accounts and one-off case studies. Japanese knotweed
versus bracken; Gough Island super-mice versus Joseph Hooker's Ascension Island imports; acacia as
water-guzzling menace in South Africa or as a greener of deserts to the north. This doesn't get us far.
Where is the truth? Are there any general rules to apply?
A few researchers have attempted meta-studies—sifting through hundreds of research papers to find
where the balance of evidence lies. Esteban Paolucci of the University of Windsor in Canada claimed
to refute the friends of alien species with an analysis of more than fourteen hundred papers published in
2010 and 2011 on the relative impacts of alien and native predators. He found that, taken together, “ali-
en consumers inflict greater damage on prey populations than do native consumers”—2.4 times more
damage. 37