Illustration above taken from Geometric Designs for Artists and Craftspeople by Dover Publications, which is nice enough to give away free samples of its clip art.
A POPULAR SAYING BACK IN MY COLLEGE DAYS, when we were first breaking free of the moral absolutes our parents had tried to teach us, was "It's all relative." Much later in life, when I began to learn about ecology and such, I changed what by then had become a cliche into a phrase that I can still live by. And so today I often announce, "It's all relatives."
In other words, everything is connected to everything else. This is hardly news to anyone the least bit familiar with ecology or natural history, but the specific examples never cease to inspire interest--and, in me at least, something akin to awe.
The paradox of protection
One such example came up recently in a study published in Science magazine. In this research, scientists working in Kenya fenced off whistling thorn trees (a type of Acacia) so that the trees could no longer be eaten by elephants and giraffes.
Now, it might seem that protecting the trees from huge plant-eating mammals would be a good thing to do. But after about 10 years of this, the trees were all dying off.
It turns out that the Acacias ordinarily provide good habitat for a particular type of ant. The trees provides food and shelter, in return for which the ants attack any animal that tries to eat the trees' leaves.
Once they were fenced off, however, eventually the trees got lazy and stopped providing the right habitat for the friendly ants. As a result, these ants were replaced by other ants, which had no interest in defending the trees. On the contrary, these new ants have a mutually beneficial relationship with a type of wood-boring insect, which soon took up residence in the Acacias.
Eventually the health of the Acacias began to be undermined by the wood-boring beetles and other insects that were able to invade now that the friendly ants were gone. And so the Acacias started to die.
For want of an ant ...
The trees were, quite literally, being killed by kindness.
Fencing off large predators caused the loss of their tiny defending army, leaving the trees exposed to far worse dangers than the occasional elephant or giraffe. Invisibly to human eyes, relationships that had evolved over thousands of years had been preserving the health of the trees. Yet as scientist Todd Palmer pointed out to writer Cornelia Dean in an article for the New York Times, it took only 10 years for this protective net to fall apart after humans intervened.
As Dean's article notes, scientists are finding similarly complicated relationships all over the planet. In North America, for example, research conducted in Yellowstone National Park found that wolves protect aspen trees by frightening off elk that otherwise would over-browse them. In its article on mutualism, the Wikipedia points out that gardeners sometimes try to create mutually interdependent relationships, as when we plant beans next to corn so that the beans can provide nitrogen for the corn while using the corn stalks as trellises.
It's (also) all relative
For wildlife-friendly gardeners and natural landscapers, stories such as these are reminders that we must not be too hasty to identify any creature as an enemy. One of my favorite examples, which I've talked about before, is aphids. Most gardeners kill them on sight, but they are one of the best bird foods in the garden, and if you want to attract birds, usually it's best to let those aphids live.
At one time most people in the West assumed that wolves were "bad" because they killed elk; now we know that the relationship between predator and prey, a., is more complicated than that and, b., affects many living things, not just the most visible participants.
Likewise, preventing a plant from being eaten might seem like the obvious thing for a plant-lover to do. But is it? Can we be sure?
Perhaps the best attitude to take toward any fellow creature is to acknowledge that, like all creatures, it has a role to play. Unless we know what that role is, best to proceed cautiously.
My own rule of thumb is that native species, having evolved together, are presumed to have relationships that are worth preserving. Non-natives, being new introductions, are less likely to be important in some larger drama that is currently invisible to me.