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Can Colombia’s rich biodiversity escape to cooler altitudes?

By Stuart Pimm

Chingaza National Park, Colombia–Colombia didn’t qualify for the World Cup this year. You’d never know from the throngs of people around TVs everywhere I went in Bogota last week. (If you are not a football follower: Fans have to cheer for more than one team given the odds and the vagaries of the refereeing.)

For biodiversity, however, Colombia’s position at the top is easy to defend, with only a few countries–Brazil, Kenya, Indonesia–challenging

The obvious question is: Why? The important question is: What next?

Two days of meetings at the Humboldt Institute–Colombia’s center for biodiversity research–and I’m ready to spend time in the field. We’re on our way by 5 a.m.–at this latitude the sun comes straight up and it’s bright by 6 a.m.

Mountains make biodiversity

Mountains make biodiversity. Some species live at their base, others at the top and, if the mountains are tall enough, there’s room for some species to live in the middle.

Colombia’s mountains are tall enough. One can travel from the steamy heat of the Amazon lowlands to snow-covered mountains and pass an extraordinary spectrum of habitats. Bogota itself is cool, rainy, feels a little like England. My hosts worry that I’m not wearing a coat.

And Colombia has an excess of mountains. In the north, the Sierra Nevada de Santa Marta rises out of the Caribbean as one of the largest, isolated mountains in the Americas. It’s about 10,000 square kilometers (4,000 square miles) at its base. Eighteen species of birds, a dozen species of amphibians–and many other species that I haven’t had chance to look up–live only here.

If that weren’t enough, the Andes run along the length of the country from north to south. Two rivers–the Cauca and the Magdalena–split the mountains into three ranges.

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Photo of Colombia’s wet forest by Stuart L. Pimm

As the sun comes up, we’re crossing the Magdalena valley to the west, climbing into the middle range. The eastern side is sheltered from the rains blowing in from the Pacific. The vegetation is scrubby and dry. Within five minutes, we cross the ridge and are in wet forest. Beyond is the Cauca Valley, beyond that the Western Andes, and beyond it the very wet lowland rainforest forest of the Chocó. I wrote about that last year.

Out come the binoculars. We accumulate a steadily increasing list of bird species–75 by day’s end.

Prominent are the tanagers–small fruit-eating species that move rapidly from tree to tree in search of food, often in flocks of several species. We end up with a dozen species of them. They are glorious jewels, with different combinations of reds, yellows, greens, blues, and black. It’s hard to remember which combination is which. If it is red and green and blue, it must be …. I check my book to remember. There are two species with that combination.

We’re after two key targets. Both live in just this mountain range.

The first is the turquoise tanager-dacnis. Late in the afternoon, we glimpse one in a flock with other tanagers.

The other is the black inca–a lovely black hummingbird with patches of white and iridescent pale blue. We find a cluster of large, red, pendulant flowers–just the kind that large hummingbirds love. In time, we’re rewarded.

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Photo of black inca by Stuart L. Pimm

These birds are both threatened with extinction. First, their geographical ranges are small. Second, their habitats are being destroyed. We find the birds in small patches of native forest in a mosaic of cattle pastures.

We see other species with small ranges as the day progresses–a striking moustached brush-finch poses for my camera amid some cobwebs.

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Moustached brush-finch photo by Stuart L. Pimm

Colombia has so many species with small ranges, in part, because of its mountains. The other reason is that Colombia “double dips.” Until 3.5 million years ago, North and South America were separate continents. Hummingbirds evolved in South America. Tanagers, including the dacnis, evolved in North America.

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The numbers of species of birds with small geographical ranges–those smaller than the median  (or 50 percentile) concentrate in the mountains of Colombia, Ecuador, and Peru.

Courtesy of Dr. Clinton Jenkins from data supplied by NatureServe.

When the isthmus of Panama connected the continents, South American species oozed northwards. That’s why we have a few hummingbird species in North America. Northern species came south. To a greater degree than elsewhere, Colombia got species from both north and south. And, of course, they further speciated in its rich mix of mountains and lowlands.

“This is an oak tree!” Luis Miguel Renjifo, a Colombian conservation biologist (and my guide) tells me. Even to someone as botanically challenged as I am, the acorns are pretty obvious. “It’s an example of a familiar northern hemisphere plant that just gets into South America here in Colombia.”

Another few hundred yards on and even I can recognize the papaya tree–a native species here, different from the domestic ones. I just love papayas–and a long list of tropical fruits from which the Colombians delight in making into juices.

Video by Stuart L. Pimm

The darker side

There’s a darker side to these biological riches. The climate is warming. There’s not a lot of “north” into which species could move from Colombia to find cooler climes. Panama is a narrow strip of land and low. Moving uphill will be the only solution.

A basic fact: Mountains always have less “up” than there is “down.” They are, roughly, conical. One of the reasons why the floating mountains in the movie Avatar are so striking. They have more “up” than “down”!

The dacnis lives from about 1,000 to 2,200 metres above sea level (3,300 to 7,200 feet) and the inca 1,650 to 2,600 meters above sea level (5,400 to 8,500 feet). As the climate warms, these already threatened species will see the area suitable for their survival shrink substantially.

“Colombia could be number one in climate-caused extinctions.”

Just what fractions of species are at risk in Colombia–and the northern Andes more generally? That’s what I was discussing with Colombian colleagues. If my guess is right, Colombia could be number one in climate-caused extinctions.

To make matters worse, species can only move uphill through their natural habitats–cattle pastures form barriers to forest-dependent species. Luis was doing something about that. Working with local landowners, he was planting strips of trees to connect the forest patches.

The ultimate solution will be to stop global warming or at least minimize it. In the meantime, connecting the forest patches would be giving the species the best possible chance of survival.

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Professor Stuart L. Pimm is a conservation biologist at Duke University, North Carolina. A former member of the National Geographic Committee for Research and Exploration, Pimm is the author of dozens of books and research papers, including the book “The World According to Pimm: A Scientist Audits the Earth.”

 

 Earlier blog posts by Stuart Pimm>>