An editorial in the July 3rd New York Times under the heading "The Rural Life" is about observing birds. The author, Verlyn Klinkenborg, has begun to notice that birds occupy certain "spacial dimensions" as they live among us. That is, the redwinged blackbird lives in the marsh, the meadowlark hunts from the fencepost, the phoebes hunt bugs low to the ground, the barn swallows higher up, the catbird in the thicket at the edge of the lawn. He (I think the name is masculine) is struggling with the concept of habitat, that a bird can't choose to live a certain place, the way a human chooses to live in a particular city.
I quote: "It takes an act of will on our part to remember how profoundly, and how beautifully, bound to habitat all the other creatures around us really are."
I am struck by more thoughts than I can record. One is that most people indeed, may not understand habitat, and the chain of eaters that make up an ecosystem. I saw a Nature program on KQED Public television a few weeks ago that illustrated the concept beautifully by showing how a fig tree growing in the wild, in Africa, served as a host for many many creatures who depend on it for food. And then some of the creatures on the tree are eating others on the tree. There were the wasps that breed in the figs, pollinating them, the creatures that eat the emerging wasps, the creatures that eat the ripe figs, and the ones that hunt them, ones that eat the leaves of the tree, and so forth. And of course there is all of the life related to other food chains in the same place, and all of the invisible life in the soil and of microorganisms. If this ecosystem is disrupted, some of these creatures will not be able to survive in it. Unlike humans, most creatures are slow to adapt to new conditions and simply die if their accustomed food isn't available.
We think of our gardens as nature, and of course they do contain many of the creatures of nature, but they are highly disrupted nature. They are anthropocentric, human centered, selections from nature. They are not wild ecosystems. Even our native plant gardens are not the same as wild ecosystems. We select what we want in our gardens. We do not invite the poison oak (a major food for the California state bird, the quail) or the rattlesnake. We don't encourage bumblebees to make a nest in our small urban gardens. We want the birds and the butterflies, but not the skunks and the cougars. And humans have also inadvertently brought to our gardens nonnative eaters, like European species of snails, that don't have much in the way of predators native to our gardens.
(If the fig tree of the Nature story were in a garden, along with all of its many eaters, the human would become just one among many eaters, competing for the fruit. And the tree would not be beautiful, but mangy and eaten. Humans would even be in danger of becoming the prey of a larger animal.)
Because we eliminate some of the links in the chain in our gardens, and introduce new creatures, we then have a different proportion of the remaining creatures than would exist in the wild. Because of this disruption, sometimes we have a huge population of eaters that are destroying something we really wanted to enjoy looking at in a perfect state, or that we wanted to eat up ourselves. Here our options are to let the critters have the plants (though if the habitat were completely undisturbed, some other creature might not let them eat as unmolested as they are in our garden), or try to reduce the population of eaters.
Integrated pest management is the best strategy yet devised to deal with the situation. It entails, first, a decision whether the pest damage is intolerable. If not, let it be. If so, you begin a careful logical progression of possible solutions, starting with the ones that are least likely to harm natural predators. If you can't find a way to solve the problem without more harm to natural predators than you want to cause, you can stop short of a solution that might save your plants but might also kill something you want to spare. But often you can find a less draconian solution.
Some people choose to garden following "organic" principles, which means using few or no chemicals.Using IPM logic is a great help to them as well, giving them many many tools that manage pests in ways that improve the balance of the habitat.
Birds are indeed habitat dependent, and a story in the July 4th SF Chronicle by Environment Writer Jane Kay, says that bird extinctions are on the rise. Some birds can use our gardens as habitats, if we plant something that feeds them, like native berried bushes, or use few or no pesticides, so the insects they eat won't poison them, but other birds need marshes or forests, or African fig trees in the wild, so the problem is wider than our gardens.
In the final analysis, we ourselves are not really free of habitat limitations. We have learned to use many different natural habitats, and to ship materials to house, clothe and feed us so we can live in cities and other habitats that don't provide our basic needs on site, but our habitat is the planet earth, and if we make it inhospitable for ourselves, we will not be able to make a living on it.
Not so cheery, eh? But gardening is a way into understanding this stuff, and knowledge, as they say, is power.