I grew up near the UBC Endowment Lands in Vancouver.
During the spring and summer, a major activity for our group of kids was catching frogs. Unfortunately, my favourite frog pond is now a housing development where frogs don't swim anymore.
This loss of habitat is devastating for a single animal but in some cases, it can also lead to extinction of a species. Indeed, this is usually what we have in mind when we talk about extinction: an animal species completely wiped out by either human activity or some natural circumstances.
But what about the extinction of plants? After all, they are what we call "habitat." Animals live in a world set against a backdrop of vegetation.
When you look around, you can see plants everywhere. In our part of the world, any view is dominated by mighty trees, small shrubs, flowers and grassland. There are so many varieties and types of plants we forget sometimes they, too, are under attack and can go extinct. The fossil record is littered not only with the bones of dinosaurs but also the leaves, stems, and roots of all sorts of plants which have disappeared over time.
Fossil fuels, such as coal and peat, are mostly made up of dead plant material. However, some of those plants come from species which are no longer found on Earth. Their fate is to be burnt to generate heat and electricity.
What are plants supposed to do? They can't very well get up and move or migrate to a new location as animals can when threatened. They can't adjust their ranges to accommodating changing climate conditions.
To fight extinction by predation or other causes, plants have come up with some unique ways of defending themselves. If you can't run away like an animal, then you have to build other forms of defence.
For plants, the defence is chemical warfare. Plants make and use all sorts of organic compounds called phytochemicals. Simply put, phytochemicals are all the compounds a plant produces to attract friends, repel enemies, or engage in any other daily activity such as "talking" to other members of the species.
Take the northern forest as an example. The trees here produce a class of compounds that are labelled terpenes. They are a class of compounds because they are all composed of the same sort of building blocks, with minor modifications that are dependent both on the species of tree and the purpose of the compound.
When a tree is attacked by insects, it tries to fight them by releasing terpenes. (Maybe this is a little anthropomorphic... the response doesn't appear to be reasoned out. Rather the process of attack, by a beetle for example, usually results in a breech in a tree's bark. This releases the chemicals stored there.)
An interesting feature of this process is trees are continually emitting phytochemicals - either to ward off attack or to warn surrounding trees of predators in the neighbourhood. Trees communicate (or talk) with each other by chemical means and defend themselves in the same fashion.
This indiscriminate release of organic compounds into the atmosphere once prompted former U.S. President Ronald Reagan to comment that 80 per cent of airborne pollution comes from trees! Of course, the amazing thing is that depending upon how you define pollution, he was right!
But it is not just trees that produce phytochemicals designed to defend themselves. All plants do this. And the compounds work with varying degrees of success.
This is why some plants simply taste bad while others can kill. After all, a toxin or poison held in the stem will surely deter any animal, insect, or human from thinking about taking a second bite.
It has been estimated that
99.99 per cent of all of the pesticides that a person consumes on a daily basis are naturally produced compounds, generated by plants to stop animals and insects from consuming them.
Some of the more illicit compounds found on the streets of our cities, such as heroin and cocaine, owe their origins to the phytochemical defences of plants. These compounds belong to a large class of compounds called alkaloids which are bitter tasting and intended to deter predation. The psycho-pharmaceutical effects are just an unintended consequence of their chemical structure.
To eat or be eaten - that is the question. For plants, their only defence against extinction is chemical warfare.
