Environmental Engineering Reference
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The discovery opened Janzen's eyes to the notion that alien species can fit in and do a job and that
perhaps they have always done this, colonizing new environments, adopting new feeding habits, and
developing relationships with new neighbors. He called it “ecological fitting” and wondered if these
chance encounters might perhaps be the normal way in which complex ecological communities formed
and developed. Perhaps there was more ecological fitting out there than coevolution.
It would, after all, be easy for ecologists to miss the distinction. They have been trained to assume
that cooperation between species, often called “mutualism,” is the result of coevolution. Janzen wrote in
a 1980 paper titled “When Is It Coevolution?” that “it is commonly assumed that a pair of species whose
traits are mutualistically congruent have co-evolved. . . . For example the fruit traits of a mammal-dis-
persed seed co-evolved with the mammal's dietary needs. However, it is also quite possible that the
mammal entered the plant's habitat with its dietary preference already established and simply began
feeding on the fruits.”
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What looked like co-evolution is very likely just a happy union. Like horses
and the Guanacaste tree in the Santa Rosa park.
Perhaps finding an ecological niche is a bit like falling in love. Romantics may believe they have
found the only person in the world who is “meant” for them, but more likely their partner just happened
to be close by and love grew. For pair bonding, read ecological fitting.
Janzen did not deny that coevolution happened. He simply said ecologists should not treat it as a
default explanation for every relationship between species. Nor should the discovery of such mutuality
be used to justify conservation policies that keep aliens out. That would be bad science and could blind
conservationists to many opportunities to do their work effectively. For aliens may be essential to reviv-
ing ecosystems, as Janzen found in Costa Rica.
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If nature is a kaleidoscope of species, constantly reorganizing and adapting, then newcomers will
come and go, often in largely random ways. They will fit in as they can, with no more likelihood of
doing harm or good than natives. They are not good or bad or at a special advantage or disadvantage.
They just are. This doesn't mean that there isn't any evolution going on. Far from it. There is growing
evidence that the arrival of new species often creates a burst of evolution and hybridization among both
hosts and newcomers as they learn to coexist. But the context is a dynamic, open, and unpredictable en-
vironment, rather than one in which a fixed group of natives is working toward some idealized perfect
state. When necessary, species adapt and evolve very quickly to take advantage of their new environ-
ments. Many of the most successful have different ecosystem functions in different places—fitting in as
necessary.
Stephen Pyne of Arizona State University, a fire specialist, has more opportunity than most to see the
dynamic and temporary face of ecosystems. “Ecologists used to believe nature evolved to create pristine
ecosystems of climax vegetation,” he says. “They saw fire as a ruinous interruption to that evolution.
But we can now see that fire has a major biological role.” It is essential. “It shakes and bakes. It frees
nutrients and restructures biotas—it takes apart what photosynthesis puts together.”
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Nature, like humans, can get stuck in a rut, he says. It needs clearing out in order to renew itself. A
spring cleaning. Disturbance is essential on all scales, from the local and instant to the global and long-
term. Fire is a big part of that, whether in forests or grasslands. It makes space in an individual forest,
incinerating dead wood and allowing new saplings to rise up. The American public saw this in 1988
during the massive fire that burned more than a third of Yellowstone National Park. A superabundance
of fuel—a result of decades of ruthless fire suppression by well-meaning ecologists intent on preserving
their own vision of balanced nature—only required a dry summer and a spark. The result was spectac-
ular but far from disastrous. The spring cleaning happened. Two decades later, when I visited the park,
the forests were recovered. The main change was to the management of fire. Foresters now allow smal-
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