Friday, April 29, 2005

Thinking About Species Loss


Eskimo Curlew, which may be extinct.


We often hear about wildlife species loss, but only rarely is such species loss quantified, defined, or given proper causation.

Whenever I hear about species loss, I naturally ask five key questions --and I often find the answers surprising.


1. Do the animals exist at all?

This may sound like an odd question, but it's a pretty important one because a lot of what is written about species extinction is totally unsupported by observed data.

Here's the scoop: Over the course of the last 400 years, only about 820 species of vascular plants and vertebrate animals are listed as having gone extinct by the IUCN Red List. In addition, the IUCN reports several species being "rediscovered" every year after having previously listed them as "lost".

Though the IUCN cannot report on what has not been discovered, we have clearly discovered most of the mammals, birds, fish, snakes, frogs, shrubs, vines, grasses and trees in the world. While new species of wildlife are being discovered every day, there is no evidence to support the notion that even 50 vertebrates and vascular plants are going extinct every year, much less the 20,000 number commonly cited (invertebrates and fungi are very difficult to push into extinction as any farmer can tell you).

As odd as it may sound, even physical evidence of the existence of a species does not necessarily mean that this species has ever existed. Here, I am specifically talking about birds, where it turns out some "extinct" species are based on single skins collected in the 19th or early 20th Century. The cone-billed tanager is a good example (to read more about the hunt for this "extinct species" read "The Ghost With Trembling Wings" by Scott Weidensaul).

The problem with birds is that they hybridize a lot, and bird species are not always very distinct from each other. Along with the cone-billed tanager, for example, there are several species of hummingbirds that we know of only due to single examples collected for the millenary trade. These so-called "Bogotá Skins" (for their central shipping point out of South America to Europe) may in fact represent evidence of a new species of now extinct hummingbirds -- or they could simply represent hybrids of other hummingbirds. With about 10 percent of all bird species known to cross the "species barrier," it's hard to know.


2. Is the animal being described really a species?

In fact a lot of stories about species decline are NOT about the decline of a species, but about the decline of a SUB-species in a very specific area.

A sub-species is, by definition, NOT a species. In fact most subspecies are nothing more than slightly different colored animals that exhibit no other behavior differences and that freely breed with populations of other animals in their species (animals whose populations may in fact be quite large and growing).


Sub-species are an interesting thing. I have always found it ironic that many environmentalists place little value on the prolific creation of thousands of new subspecies of apples, potatoes, pigs, cattle, and chickens, but assign tremendous value to subspecies of cougars, lions and pronghorns (to give just three examples). In fact, many sub-species of wild animals are little more than political artifices designed to boost the careers or egos of the people naming them.


In some cases there is another less vanity-centered reason to name a subspecies -- you can "up list" an animal (and its habitat) for protection by simply singling it out. The Sonoran pronghorn appears to be an example -- an animal made "rare" despite the fact it appears to be little more than a light-colored variant of an animal that actually numbers in the million.


3. Was the species ever very common?

Some threatened and endangered species are animals that were always rare and not very successful to begin with. Take the Whooping Crane, for example. DNA analysis suggests Whoopers never numbered more than about 5,000 individuals. The 1850 population of the bird (when most of the American West was still unsettled and very wild) is estimated to have been just 1,500 individuals. There are now 500 Whoopers in the world, with about 350 of them in the wild. I am very glad the Whooper was pulled back from the edge of extinction, but the fact that the bird was never common or genetically successful is not an inconsequential part of its story (though it is rarely told).


The Florida Manatee is another animal that was probably never terribly common. The Manatee population of Florida before there were outboard motors is estimated to have been around 10,000 or so. By the 1980s, the manatee population had declined to about 800, but it has since risen to over 3,000.
Again, bringing the American manatee (Trichechus manatus) back from extirpation in the U.S. is excellent, but we should not expect the population to ever get really huge. Note that the American manatee also exists in many other Caribbean countries south to Brazil, but it is a rare animal there due to hunting by indigenous people .


4. What is the population of the species now?

The point here is that numbers are only meaningful within context. Do I wish there were more pronghorn in America? Sure! But one million pronghorn -- up from just 13,000 individuals at the turn of the 20th Century -- is pretty good news and one we should be celebrating!


5. What has really caused the decline (or increase) of this species?

The death of any species is important, but I also want to know the circumstances of the decline or extinction. I consider the loss of the Passenger Pigeon and the Eskimo Curlew (there were once millions of these birds flying over vast areas of this continent) a much more significant tale than the loss of a species of flightless rail on a small island in the Pacific. One extinction signals the total loss of a once very common species that was successful over a very large area. The other signals the total loss of a very rare species that was NOT successful over a very large area. There are very different lessons to be learned from these very different stories.


Most people are surprised to learn that most extinctions are of the latter type (fairly unsuccessful species in very isolated locations) and not the former (fairly successful species in fairly common locations). They are further amazed to discover that habitat loss is a much rarer cause of species extinction than the introduction of rats, cats, goats and pigs -- or of indiscriminate hunting. If you go through the IUCN Redlist of extinct species, for example, you find zeros for most countries (no known endemic species pushed into extinction), but incredible numbers of extinctions for such tiny islands as Mauritius (41 extinct species), Réunion (16 extinct species), Saint Helena (29 extinct species), French Polynesia (67 extinct species), and the Cook Islands (15 extinct species). In fact, these little spots of land, along with Hawaii, account for about 200 of the 812 species pushed into extinction over the course of the last 400 years.

Is the loss of an "unsuccessful species" a bad thing? I think so. But it may not be quite as horrible or as unprecedented as it is commonly made out to be. In fact it may be part of the order of things. After all, instead of a living at a time when there is a "biodiversity bottleneck," as some texts would have you believe, we are actually living at a time of incredible genetic diversity. As the folks at the World Resources Institute note, "Global biological diversity is now close to its all time high. Floral diversity, for example, reached its highest level ever several tens of thousands of years ago. Similarly, the diversity of marine fauna has risen to a peak in the last few million years." In short, we live in a very bio-diverse time, and with diversity will come a lot of failure which is every bit as much a part of Darwin's evolutionary equation as success (if not more so).


It's also worth remembering that even as we are losing species, we are also gaining them -- new types of chickens, pigs, apples, corn, and trees. New hybrids of canaries, geese, ducks, pigeons, cattle, horses, falcons, eagles, dogs and cats. And we are doing it with wild birds too.


The last time I flipped through a Sibley's Audubon guide to birds, I counted one extinct species of parrot (the Carolina parakeet, since rediscovered in the Caribbean), but 27 new species of introduced parrots that are found in wild flocks in the U.S. (65 species have been encountered in Florida alone). In California and Florida these wild-flocking parrots are already creating new hybrids. Wild parrot colonies are not just found in warm climates by the way -- they are found near my home in suburban Virginia, and in downtown parks in Seattle and Chicago. One hundred and fifty years from now my great grandchildren may find hybridized variations of these same birds listed as entirely new "American" species of parrots (the Sibley guide already notes the presence of many Amazon hybrids in Florida and California).

Food for thought.

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1 comment:

Anonymous said...

This is something that I have argued as well. I do not think that we should give up on animals like the California Condor. It would be interesting, however, to see a fraction of the media covereage of and reasources allocated to the disappearace of a vulture (evolved to feed on long extinct pleistocene animals) commands when the emergence of a new species to fill the niche of the carolina parakeet takes place right in front of us in Florida. It seems that there would be more for us to learn in watching the adapting parrots rather than the Condor that failed to adapt.

It does show that when the reasources are present, nature will find a way to fill the hole.