By Emma Marris
Could you prevent nine local extinctions by hastening one extinction? It sounds completely counterintuitive, but a pair of ecosystem modelers are proposing that conservationists could sometimes prop up a troubled ecosystem by removing one or more of its species--and using models to determine the timing and order of those removals.
The species that make up an ecosystem are connected in complex "food webs" of eater and eaten. When one species disappears, its predators can no longer eat it and its prey are no longer eaten by it. Changes in these populations affect others. Such impact 'cascades' can be unpredictable and sometimes catastrophic.
Sagar Sahasrabudhe and Adilson Motter of Northwestern University in Evanston, Illinois, have shown that in several model food webs, as well as in two webs modeled with data derived from real ecosystems--the Chesapeake Bay off Maryland and Virginia and the Coachella Valley in Southern California--removing or partially suppressing one or more species at key time points after one member has gone extinct saves other members of the web from local extinction. They publish the results January 25 in Nature Communications.
The idea relies on the fact that ecosystem networks can often shift to a different stable arrangement after losing members. "Ecological systems are quite robust, actually," says Motter. The famous "balance of nature" is perhaps better understood as the "multiple possible balances of nature." But the order of removals matters.
Remove A and then B, for example, and a given web might change shape but retain all its other members; remove B and then A, however, and the cascade of changes drives many of the other members extinct.
Exit strategy
In very simple webs, the impacts can be easy to follow. For example, the removal of a large predator could allow a medium-sized predator to increase in numbers and eat its smaller mammal and bird prey into extinction. In this case, keeping a lid on the numbers of the medium-sized predator would prevent these extinctions.
But even small webs can harbor complexities that can make the order of removals for ecosystem stability challenging to sort out. Motter likes the story of the island foxes (Urocyon littoralis) on the Channel Islands off the coast of California, which is recorded in the study. When feral pigs were introduced to the islands, they attracted golden eagles that preyed on both pigs and foxes. Fox numbers then dropped. Removing the pigs would have left the foxes as the sole diet of the eagles, and likely doomed them. So instead, conservationists captured and relocated the eagles and only then eradicated the pigs. The fox population is now recovering.
"The same actions at different times have very different consequences," says Motter.
In more complex webs, the key species that needs to be removed or suppressed to head off more serious collapse isn't intuitively clear. But, by modeling a variety of food webs using established ecological principles, the researchers were able to find such species and they hope that the algorithms that they created might eventually be able to identify target species in the real world.
Factoring in complexity
However, the results will only be accurate if the real ecosystem is well represented by the model. In their food-web modeling, Sahasrabudhe and Motter have used accepted ecological models of predator-prey relationships, but a more elaborate representation of an ecosystem would also include parasitism, seed dispersal, competition, mutualisms (in which species make life easier for each other), nutrient dynamics and more. And to include such complex detail in a model, scientists will first have to go out and gather that information in the field. Who is eating whom? Who is pollinating whom?
When the algorithms point to an exotic species as a target for removal or suppression, conservationists are likely to have little problem with the idea. But if a native species is the proposed target, that will go against many conservationists' impulses to protect rather than remove.
Neo Martinez, director of the non-profit Pacific Ecoinformatics and Computational Ecology Lab in Berkeley, California, says that Sahasrabudhe and Motter's ideas are exciting, but the conservatism of conservation means that they won't be relied on in isolation, at least not right away. "Because of the lack of realism -- we don't include everything in these models -- no one is going to make an important conservation decision solely on these models. That is a long time in the future."
But a long time in the future isn't never. Martinez says that whereas six or eight years ago ecologists generally considered ecosystems too complex to ever be productively modelled, not unlike the stock market, today modellers are gaining confidence.
Motter agrees. "In the long run, I think we will have people in the field advocating for the suppression of native species." He points out that land managers are already doing so, less systematically, by running regulated hunting of prey species in areas where top predators have been extirpated. Human impacts are just too great on most ecosystems, he says, for us to just hope they will sort themselves out. "In the presence of perturbations, it is reasonable to consider compensatory perturbations," he says.
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8 Comments
Add CommentJust like researchers factored in the release of the cane toad in Australia? The list of failures of researchers especially those working for governments is longer than you can possibly imagine, its not always the researcher, politics demands compliance.
Reply | Report Abuse | Link to thisThe best funded research, targets money spinners. The banks financed research into making more money, it turned out to be fraud.
They also imported rabbits in Australia with disastrous results. When humans decide to improve on Mother nature, it normally results in a disaster.
Reply | Report Abuse | Link to thisThe Dutch put some pigs on land, when the Dodo Bird worked with Mother Nature to grow trees. The seeds had to pass through a Dodo before it would germinate.
They are now trying to use Tom Turkeys, force-fed to get some new trees.
If we get rid of the mosquitos, the Predator that eats mosquitos (the Praying Mantis) will get hungry and have to look for other pray.
When we had homes, the climate did not change much. The only High-Rises were churches.
When Otis invented the elevator that all changed.
The High-Rises in New York, Chicago and Toronto changed the weather and rain pattern.
Since man has disrupted ecosystems with transported symbiotes, we have seen the growth of understanding of ecosystems and disruption.
Reply | Report Abuse | Link to thisThe ecosystem engineering suggested hopefully by the author and referred to by the modellers, has, true, been costly and crude, with constant manipulation required to redevelop ecosystems similar to the once-intact one.
Because the least management consistent with the goal is cheapest and altogether best, lab or computer modelers are only part of the show.
Ecologists and conservation biologists recognize the necessity for expanses of habitat suitable of the survival of related ecosystems. They point out that this requires large-scale linkage of habitat to preserve gene flow of all species. By large-scale, they mean: continental in scale.
The digest-like form of the article does not stress that eradication of native species is never a goal. It only reports on the manipulation process thought necessary to reconstructing viable ecosystems, and does not say that natives are to be eradicated.
Yet the question remains of how far it is felt necessary to manipulate fragmented habitat, rather than questing for the habitat preservaton necessary to allow long-term functioning of ecosystems.
It has been shown that near-coast no-take zones for marine organisms can have immense beneficial effects on surrounding areas for species restoration.
And yet, the only support forthcoming, is from those who stand to make near-term gains.
Intense manipulation has many associated questions, even if complex algorhythms have been developed to monitor effects and suggest practices speeding restoration.
Unfortunately the only species that would have a beneficial effect on eradication is the human race.
Reply | Report Abuse | Link to thisOf course the Researchers do not want to be included in that experiment.
Oh, this is too good: We have two physicists who are going to direct our conservation efforts! The beauty of being physicists is that they blithely ignore the details of complex systems and make up stories to fit the a particular system's changes over time. Have you noticed that their resumes only describe just-so stories decorated with integrals and sigmas about systems which will always remain safely outside any human's direct experience?
Reply | Report Abuse | Link to thisToo, we might ask why they're venturing outside their field: it's because none of them can rationalize general relativity with quantum mechanics? Dark matter and energy? They have no idea how the universe works, including earthly ecosystems.
Apparently nobody has told these armchair ecologists that every ecosystem, and its dynamics, is different, no matter how similar they might appear to the untrained eye.
Motter's take on the channel island fox is imprecise, and ignores the subject's unique simplicity due to, in large part, its isolation.
The reason golden eagles expanded their range to the channel islands (off so. Calif. coast) in the first place is that Motter's hominid ancestors depressed the bald eagle's population through cleverly ridding themselves of mosquitoes with "harmless" DDT.
These people don't know how the universe works, certainly not the local part consisting of entities that figure out new ways of doing things -- what physicists condescendingly refer to as "condensed matter." Ask a physicist what emergent properties are and how does he propose to measure them and he'll walk off mumbling to himself. That's what an ecosystem is.
Physicists should stay with their simple systems and leave the non-newtonian wet stuff to biologists.
As an ecologist, I am thrilled by this study, as it points to very interesting new hypotheses concerning ecosystems management and wildlife population control, particularly in systems where natural predators have been overexploited.
Reply | Report Abuse | Link to thisI have the impression that the message of the paper is somewhat lost in this news article, though. The original paper says “the interventions … should be interpreted as limited to islands, lakes, parks and other local areas, without involving the large-scale eradication of any species. They may be implemented in concert with economical activities, such as fishing and hunting, but may also be carried out by means of non-lethal growth suppression and relocation”. The original paper can be found here:
http://www.nature.com/ncomms/journal/v2/n1/abs/ncomms1163.html
Except, of course, that you mess up with mother nature every time you turn on the engine of your own car. The bottom line is that most, if not all, ecosystems in the planet are already altered by human activity, and it’s now our responsibility to manage the consequences of our actions. And, in the case of this study, they are certainly not advocating for the introduction of non-native species, as your examples seem to suggest.
Reply | Report Abuse | Link to thisI agree with the researchers.
Reply | Report Abuse | Link to thisThose jokingly saying that the solution is to eradicate humans should notice that it’s too late to do that – we have already altered the systems.
And those who have such a problem with physicists should remember that they discovered the DNA, which revolutionized not only molecular biology but also paleontology. I’m no physicist, but it seems some comments in this discussion list are personal and not based on scientific facts. Has anybody at least read the papers of Sahasrabudhe and Motter about which they are commenting on?