Species loss weakens entire ecosystems | Science Matters | David Suzuki Foundation

By David Suzuki with Faisal Moola

The World Conservation Union recently released its annual Red List of endangered species. For 2007, another 200 species were added to the existing list of over 16,000.

But what many people often don't realize is that the decline of these species isn't just a sad story that's happening "out there" in nature; it's really a story that's happening to us, one that we're doing to ourselves. And it's making all of the ecosystems that we ultimately depend on biologically poorer and more vulnerable.

Living in cities, it's easy to forget how much we depend on the services provided by healthy natural ecosystems — things like cleansing water, filtering air and storing carbon to reduce global warming. Our health and well-being depend on these services, which have also been conservatively estimated at being worth trillions of dollars to the global economy.

However, reading stories about how species are being pushed to the brink of extinction doesn't necessarily trigger alarm bells about our own future. Many of the animals in these types of stories have exotic names from far-away places, like the Yangtze River dolphin and the western lowland gorilla, so it's easy to gloss over it as someone else's problem. But the reality is, in an interconnected world their problem is our problem.

As hard as it may be for some people to believe, the other species of the world don't exist just to look pretty and give tourists something to photograph. They actually fulfill ecological niches. Their mere existence is often vital to the overall health of the ecosystem. Losing a species or having one pushed to the brink of extinction can have what biologists call "cascading" effects on the entire region.

Consider the role of large primates in tropical forests. In these forests, large primates play several important roles, one of which is in seed dispersal. Many tropical primates are frugivores, that is, their diet consists largely of fruit. While small-seeded fruit trees may have a large number of species, including mammals, reptiles and birds, to help them spread their seeds, large-seeded tropical fruit trees rely largely on bigger mammals — especially primates.

When primates, like monkeys, apes and chimps eat fruit, they physically spread the seeds over a wide area of forest floor. So the animals receive sustenance from the fruit, while the trees get their seeds spread across a large area, allowing them to grow elsewhere, which then provides more food for the primates. It's a mutually beneficial relationship.

But when large primates are hunted to greatly reduced numbers, as they increasingly are, it can have a profound impact on the ecosystem. For example, a recent special edition of the journal Biotropica focused on the impact of what's called the "bushmeat" trade — local hunting that often includes primates. In one study, researchers from the University of Illinois looked at two sections of Peruvian forest. One section had been heavily hunted by local people using modern weapons, like shotguns, and had lost more than 80 per cent of its large primates. The other section was protected from hunting. The researchers found that there were 55 per cent fewer species of large-seeded fruit trees in the unprotected forest and 60 per cent less of the fruit trees themselves. In other words, once the large primates were gone, the trees that depended on them started to disappear too.

Of course, as the researchers point out, this has a number of unfortunate consequences. It makes the forest less hospitable to large primates, so they are less likely to be able to ever come back. Having less fruit tree diversity makes remaining primates more vulnerable in times of scarcity. And the trees themselves, which often have economic value to humans for timber, fruit or other uses, start to disappear.

Humans depend on the services provided by healthy ecosystems, so it's in our best interests to conserve the creatures that live in them. Losing one species or having 200 more hunted off to the brink of extinction isn't just sad news for us — it's dangerous.

September 21, 2007
http://www.davidsuzuki.org/blogs/science-matters/2007/09/species-loss-weakens-entire-ecosystems/