Nothing simple about nature
Wednesday, February 25, 2004
By David Suzuki
People generally like simple answers. This happened, so this
happened.
Cause and effect. Simple.
But nature doesn't work that way. Just when we think we've
got something figured out, another idea comes along that turns
our preconceived notions upside down. In spite of all our
scientific advances, we are only just beginning to understand
how ecosystems work.
Consider invasive species. Plants and animals
evolve to fill particular roles within a given ecosystem.
The population of each of these species is usually held in
check by other forces, such as climate, predators or food
availability. When we take a species out of its native home
and transport it elsewhere, it may face new challenges and
die off, or it may find itself virtually unencumbered by constraining
forces.
When the latter happens, the species can become
"invasive." That is, it can flourish, become a pest
to human beings and overwhelm native species. In fact, invasive
species are believed to be a major cause of the loss of biodiversity
worldwide. Biologists have long known that the lack of insect
enemies is a key factor in determining if a plant species
becomes invasive, but we are finding out that the situation
is decidedly more complex. We now know that another, surprising
agent may also be involved in the success of an invasive plant
- soil organisms.
Most of us tend to think of soil as inert matter,
but it is very much alive, replete with microscopic organisms
that can either enhance a plant's capacity to grow and flourish,
or hinder it. A recent study published in the journal Nature
has found that spotted knapweed, which was introduced to North
America through imported alfalfa seeds more than a century
ago, has likely been able to spread so profusely, not because
it lacked insect enemies, but because it lacked microscopic
soil enemies. In Europe and Asia, specific soil organisms
help keep the plant from becoming an invasive weed, but these
microbes aren't found in North American soil.
Just as few people would have thought that soil
microbes could have such a profound effect on the success
of a plant species, few would likely think that reducing fishing
to protect fish stocks would actually harm seabird populations.
Yet that is exactly what has happened in Europe's North Sea.
One of the North Sea's top predators, the great
skua, has greatly benefited from the leftovers of commercial
fishing. Over the years, these birds have learned to scavenge
fish guts and undersized fish tossed back by fishing boats.
They've eaten well. As a result, the great skua population
is now 200 times larger than it was a century ago.
However, fish stocks in the North Sea are in
trouble from years of overfishing. New European Union policies
have been designed to allow stocks to recover, but reduced
fishing also means fewer discards for the skuas.
And rather than go hungry, the birds are preying
on other seabirds like puffins and kittiwakes.
The impact on other seabird species is not insignificant.
A recent study found that a five per cent increase of birds
in the skua diet would result in an annual loss of thousands
of other seabirds. In some areas, the level of predation by
skuas is already unsustainable and the authors conclude that
the situation "presents a potentially serious threat
to some seabird communities."
We have to remember that nature does not behave
in a simple, linear fashion. Our natural systems have, over
millions of years, developed complex systems of checks and
balances. Humanity is now powerful enough to meddle with those
systems and the results are unpredictable. That's something
to keep in mind when we consider climate change, genetically
modified food and other
emerging scientific issues. We have to be cautious.
And we can't assume we know how things will
turn out, because with nature, the answer is rarely simple.
Source: David Suzuki Foundation
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