Monday, July 02, 2007

African elephants live in Africa for a reason

In this month's Scientific American is an article about a topic that gets my blood going whenever I read about it - the concept of Pleistocene Rewilding. For those of you who haven't heard of it, Pleistocene Rewilding is the idea that we should introduce non-native megafauna to North American ecosystems. The basic idea is that up to 10,000 years or so ago, relatives of these animals roamed North America as key cogs in the natural landscape. Then humans arrived and most of the large animals went extinct. The correlation between the extinctions and the arrival of Homo sapiens has lead to the hypothesis that humans hunted the large herbivores to the point where their populations were too low to be sustained. With a lack of large herbivores, large carnivores were also unable to survive. The Pleistocene rewilding is an attempt to reverse this Pleistocene overkill.

Lions, mammoths, camels, horses, cheetahs, and others were all found in various ecosystems throughout North America and helped shape the evolution and ecology of plants and animals still found today. For example, it is hypothesized that the pronghorn's speed evolved to help it evade American cheetahs (why else should it run over 60 mph?), and that the large seeds of the honey locust tree were eaten and dispersed by mammoths (now, the honey locust has no natural seed dispersal). Proponents of Pleistocene rewilding see North American ecosystems as "broken", missing major players. Since the missing fauna are now extinct, the idea is to use extant species as proxies. Re-wilders want to import African elephants, cheetahs, lions, and camels to restore North America to what it was (might have been?) before humans killed off the large mammals.

I first read about Pleistocene rewilding some years ago in the now-defunct journal Wild Earth. More recently, researchers at Cornell have reinvigorated the rewilding push. I think it is a monumentally bad idea. First, it's gimmicky - the article in SciAm talks about the increased tourist revenues it would bring in and even shows an illustration with a monorail in the background. If this is what you want, go to Disney's Animal Kingdom, Six Flags' Wild Safari, or the San Diego Zoo's Wild Animal Park. Second, and most important, these animals don't belong here. I'm all for the conservation and restoration of ecosystems. The reintroduction of wolves to Yellowstone was a phenomenal, watershed event. But Canis lupus used to live there - in historic times nonetheless - and still were living relatively nearby. Before zoos, African elephants NEVER lived in North America. African cheetahs NEVER lived in North America. The Dromedary Camel NEVER lived in North America. And even though the American and African lions are considered subspecies of Panthera leo I wonder how similar they truly were (isolated for at least tens of thousnads of years, living in different environments). Haven't we seen the results time and time again of introducing non-native species to ecosystems?

I might think differently about Pleistocene rewilding if we were able to actually reintroduce the Pleisotcene fauna. How great would it be to see herds of mammoths roaming around? Or the chance to see a cheetah chase down a pronghorn? Alas, unless there's some Jurassic Park technologies out there, this ain't happening.

6 comments:

Kevin Z said...

Perhaps this highlights the lack of education in palaeobiology and evolution that many wildlife ecologists are not subject too.

Perhaps anyone that makes decisions about wildlife should be required to sit in on these such courses as part of their degree program. I know several universities that have separate degree programs for Evolution and Ecology (my B.Sc.) and Wildlife Biology (or variants thereof). The latter typically requires less rigorous science-based courses, but in fairness offers much better problem-solving courses.

Now if only they knew enough science to solve their problems...

John said...

The pleistocene rewilding topic gets my blood going too. But for a little different reason. Those too happy to trash the idea show a real ignorance of the issues really at stake. If a major conservation goal is to preserve and restore 'wild' nature (nature as would exist without man's influence), the restoration of ecosystems to how they existed 200 yrs ago is not a restoration at all. Returning the wolves to Yellowstone is a great start. But an endpoint?

Proboscideans (elephants and co.) have been shaping North America for over 15 million years. Camels evolved here, and are one of the few creatures capable of eating noxious desert shrubs. Horses grazed on plains, ground sloths dispersed seeds, and lions kept these herbivore populations in check.

Many conservationists suffer from a case of ecological myopia when they think about rewilding. "Invasive species" having been crossing land bridges for millions of years, populating every continent except Australia and Antartica. The conservation debacles everyone is familiar with involving invasive species included species whose populations could not be controlled (small animals with high reproductive rates, plants), and whose introductions served no ecological value.

Instead, we are suffering an ecological crisis in which 70-80% of the large genera in N. America have been extirpated since man's arrival. Large herbivores and predators are keystone species that strongly shape the structure and and function of an ecosystem. Biodiversity of large animals has not been so drastically and suddenly depleted since an asteroid wiped out the dinosaurs 65 million years ago.

Sure it would be nice to resurrect the identical organisms that filled their ecologcal roles 13,000 yrs ago. Unfortunately, we do not live in an ideal world. An African elephant plays a much more similar ecological role to a Columbian mammoth (both elephants, in the family Elephantidae) than no elephant at all.

Conservation must be viewed in the context of ecology. Ecology can only be understood in the context of evolution. Evolutionary time occurs over millions or 100s of thousands of years. 13,000 years is only a few days in evolotionary time. 200 yrs ago is 5 minutes. Lets keep things in perspective. In evolutionary time, most animals are invaders, 13,000 yrs ago is last week, and man is the only animal that has ever wreaked havoc on biodiversity.

Genetic purity is great. But lets not miss the big picture (functioning ecosystems) because of our shortsightedness and unexamined biases. Maybe the elephants deserve to come home.

Jim Lemire said...

John -
Trust me, I understand what is at stake here ecologically. I get that large herbivores, including camels, elephants, and sloths shaped the ecosystems of North America and that without them here, being gone for only 13,000 years, N.A. ecosystems are missing major players. I understand that, to use Connie Barlow's term, these extinct critters are ghosts of evolution and that ecosystems are not functioning as they evolved to because of their absence.

I also get you point about the distinction between invasives that are small and reproductively "hyperactive" vs. invasives that are larger and reproductively constrained. I did not mean to suggest that introducing elephants would wreak the same kind of havoc as cane toads. I do not know what kind of impact these critters would have on the ecosystem, but I think it is silly to not think there could be serious (bad) consequences.

You are also right in saying that 13,000 years is a blink of the eye in terms of evolutionary history. However, recent studies have shown that the mammoth clade split off from the Asian elephant clade approximately 6 million years ago: (note: not the African elephant clade as originally thought). This is certainly not a blink of the evolutionary eye. To oversimplify, the Colombian mammoth was as distinct from the African elephant as chimpanzees are from the first human settlers of North America. Apples and oranges perhaps, but the point is that a lot of changes can take place in 6 million years.

The African elephant may occupy the same ecological niche as the Columbian mammoth, but that does not make them ecological equals.

John said...

You mention that Columbian mammoths are as different from African plains elephants as chimps are from man. This may be true in terms of genetic distance, but it is not true in what I consider the most relevant sense - ecological functioning. Nothing is similar ecologically to man. Nothing
matches our capacity to alter ecosytems for our own ends. And even if we were mythical hunter-gatheres living in harmony with everything, we would still be ecologically quite distinct from chimpanzees - we are not arboreal foragers and occasional monkey hunters. For one, we eat everything we want.

This is the conservation issue that I think people are only beginning to seriously consider. How important is ecological functioning? How big of a deal are empty niches? What is the appropriate time frame for which restoration should be considered? Does genetic purity trump ecological niche filling? Can we accept the trophic cascades that follows when keystone species are extirpated with no replacement? Is that better than introduing similar players of different species?

Before anyone can answer that question, I think it is helpful to remember that in evolutionary time species come and go, but extinction typically is followed by replacement. That has been true for proboscideans, artiodactyls, horses, and large predators. What doesn't happen, is most large species going extinct as more land becomes available (from melting ice) and nothing replaces them.

If the goal of returning to the ecological baseline (pre-man) makes any sense, then bringing in a Columbian mammoth (six million years removed from the African elephant) gets us much closer to that goal than no elephant at all.

The conservation status quo has been to reflexively denounce all "non-native" species as bad. But not all non-natives are the same. Introducing predators or rats to islands that evolved without them is far different that the mediteranean gecko showing up in the american southwest and displacing nobody. Replacing bactrian camels for extinct american ones is a far cry from introducing the tree snakes to Guam or rabbits to Australia.

In my mind, the closest possible return to an ecologial baseline is the highest goal of conservation. There is an obvious problem, however: we cause extinctions. Since we can't bring animals back in a time machine, I think its reasonable to consider relatives with similar life histories as replacements. Maybe its feasible, maybe its not, but why are so many so quick to rule it out?

Jim Lemire said...

I agree that ecological niches usually turn over and rarely left open. However I disagree that substituting one organism with another that is ecologically similar is conservationally the answer. In fact, what is the rationale for bringing elephants back? What current species or ecosystems are in danger without them? Are people trying to make amends for our prehistoric ancestors?

Regardless, the crux of my argument against Pleistocene rewilding is that I do not think, given the amount of genetic difference, modern African species are the ecological equivalent to extinct North American species. Yes, both the African elephant and the Colombian mammoth may occupy the same broadly-defined ecological niche, but the specifics of their respective ecosystems and behaviors are different. The devil is always in the details.

John said...

'What is the rationale for bring back elephants?' The rationale is that we are closer to an ecological baseline, and more closely reflect evolutionary history, with elephants than without. 'What current species or ecosystems are in danger without them?'

200 years ago, the northeastern united states had largely exirpated deer, wolves, beavers, moose, cougar, bear, and turkey through hunting and habitat change. Undoubtedly some animals did fine. Robins and squirrels probably were doing quite well. Ecosystems have changed too. Tree composition, animal and plant populations all have shifted. Current rabbit populations are in no danger without wolves, turkeys, or black bears. Everything finds its own equilibrium with time and a little stability. However, I don't think maintanence of current gray squirrel populations is a legitimate conservation concern. Maintaining the current degraded status quo in ecology is not a legitimate conservation philosophy, in my opinion.

African plains elephants are not Columbian mammoths. They are not perfect ecological replacements. They are not the same species, and their introduction would be a real shift in conservation strategies. But they are far more ecologically similar than having no elephants at all. I guess thats where our difference of opinions hinge. To you, if they are not identical replacements they don't belong here. To me, proxy replacement brings us closer to true wilderness than no replacement at all, and restores the evolutionary heritage of this continent. And its not irreversible. Elephants and camels can be monitored and removed if need be.

I'd like to see conservationists revisit the topic of what they are really trying to achieve. Is it about clean drinking water, and sweet smelling air? Game to hunt and trees to camp under? Maybe open space, with the local wildlife we're all comfortable and familiar with? Or the happy vision of 1492, with bison, indians, and lots of salmon to catch?

I personally think the right approach is an ecological one that considers the evolutionary history of the land. I also think that related species that act as ecological replacements are preferable to an ecosystem punctured with holes. At least I wish people would think about it. Analyze it. Talk about the topic reasonably. Its easy to sneer at outlandish ideas like bringing in elephants and lions. Its harder to reflect on why we shouldn't.