New England’s fisheries are in such bad shape that the Department of Commerce has now declared them a disaster. It’s not merely the sheer volume of fish we’re catching that explains the woeful state of these fish stocks. Even in places where governments have established strict limits on fishing, some fisheries have been unexpectedly slow to recover. That’s because fish don’t exist in isolation. They’re part of ecological networks. And when we hammer these networks, they can suddenly flip into a new state. Getting them back to their old state can be surprisingly hard.
In the new issue of Scientific American, I’ve written a feature on recent research into how ecological networks flip, along with attempts to detect warning signs of food webs on the brink (subscription required).
P.S. A needless snarky commenter objected to having to pay for the article. As I pointed out to him or her, if you want to read two lengthy scientific reviews on the subject for free, here is a pdf and here’s another one.
The world, it bears reminding, is far more complicated than what we can see. We take a walk in the woods and stop by a rotting log. It is decorated with mushrooms, and we faintly recall that fungus breaks down trees after they die. That’s true as far as it goes. But the truth goes much further. These days scientists do not have to rely on their eyes alone to observe the fungus on a log. They can drill into the wood, put the sawdust in a plastic bag, go to a lab, and fish the DNA out of the wood. A group of scientists did just this in Sweden recently, sequencing DNA from 38 logs in total. They published their results this week in the journal Molecular Ecology. In a single log, they found up to 398 species of fungi. Only a few species of fungi were living in all 38 logs; many species were limited to just one.
Consider that on your next walk in the woods. The one or two types of mushrooms you see on a log are an extroverted minority. The log is also filled with hundreds of other species that don’t make themselves known to you. Their invisible exuberance is a paradox. The fungi that live on rotting logs all make a living by releasing enzymes that break down wood. It’s puzzling that so many species can coexist in a log this way, instead of a single superior fungus.
The forces that drive up the diversity of fungi in a log are similar to the ones that fosterer the thousands of species of microbes in our bodies. For one thing, a log or a human body is not a uniform block of tissue. They both have geography. A microbe adapted to the acid bath of our stomach won’t fare well on the harsh desert of the skin. Likewise, what it takes to succeed as a fungus in a branch is different from what it takes in the heartwood of the trunk.
The human body changes over time, and a rotting log does, too. Babies are colonized by pioneer microbes, which alter the chemistry of their host and make it more welcoming to late-arriving species. The pioneers on a fallen log may include the spores of some species of fungi lurking in trees while they’re still alive. They burst into activity as soon as the tree crashes to the forest floor. Other species, delivered by the wind or snaking up through the soil, find it easier to infiltrate a log that’s already starting to rot. The early fungi may go after the easy sugar in the log, while later species unlock the energy in tougher tissues, like lignin and cellulose. Which particular pioneer starts to feed on a log first can make it inviting to certain species but not others.
Warfare also fosters diversity in a log. The fungi inside a log battle each other for food, spraying out chemicals that kill off their rivals. Each species has to balance the energy it puts into making enzymes to feed and weapons for war. Sometimes the war ends in victory for one species, but very often the result is a deadlock that leaves several species in an uneasy coexistence. There are more peaceful forces at work in a log, too. Many species of fungi in a log depend on each other. One species may feed on the waste produced by another, and supply another species with food in turn.
The world in a log influences the world as a whole. If it wasn’t for wood-rotting fungi, forests would be strewn with the durable remains of dead trees. When the first massive forests spread over the land 350 million years ago, fungi hadn’t yet adapted to decomposing logs. Instead of turning to soil, many trees ended up as coal. The great age of coal ended about 300 million years ago–right around the time that tree-rotting fungi emerged. Their emergence may have brought the age of coal to an end.
Three hundred million years later, that coal is coming back up to the surface of Earth to be burned. Some scientists are investigating fuels that could replace climate-warming ones like coal. One possibility is to pull out the energy-rich sugar locked up in the lignin and cellulose of crop wastes or switchgrass. On our own, we would not be able to perform the necessary alchemy. But fungi know how, and so scientists are sequencing the genomes of wood-rotting fungi to borrow their tricks. This is big-scale science: the genomes of over a dozen species have been sequenced or are in the sequencing pipeline. Yet a single log may contain twenty times more fungus genomes. At the moment, we can say for sure that the few mushrooms we see on a rotting log are far from its full reality. But it will be a long time before we know how all the parts of that reality fit together.
Manta rays spend their lives in the ocean, sweeping up microscopic animals. And yet scientists have found that their well-being depends on forests. Meadows in the northwestern United States are ecologically linked to salmon thousands of miles out at sea. Today, I’ve got a piece in Yale Environment 360 in which I explore the bonds that join land and sea together. Check it out.
Earlier this week, my editor at the New York Times asked if I’d write a story about a pair of new papers in Science detailing experiments on how insecticides affect bees. Bees have been in decline in many places, and scientists have been trying to figure out the cause–or causes–of their fall. These two new experiments represent a new wave of more realistic tests, taking place on farms instead of in labs. They’re also important because they were designed to look at what happens when bees are exposed to more realistic, sublethal doses. My story appears in today’s issue.
I found this story to be especially challenging to sum up in a single nut graph. To begin with, these experiments came after many years of previous experiments and surveys, which often provide conflicting pictures of what’s going on with insecticides and bees. The experiments themselves were not–could not–be perfect replicas of reality, and so I needed to talk to other scientists about how narrow that margin was. As they should, the scientists probed deep, pointing out flaws and ambiguity–in many cases even as they praised the research. At the same time, these two papers did not appear in a vacuum. Other scientists have recently published studies (or have papers in review at other journals) that offer clues of their own to other factors that may be at work. And, biology being the godawful mess that it is, it seems that these factors work together, rather than in isolation.
There’s a lot at stake with all this complexity. The insecticides in question–a class called neonicotinoids–earn well over a billion dollars a year for their manufacturers. These insecticides are everywhere. Virtually all corn in the U.S. is treated with them, for example. Meanwhile, just this month (before the latest studies came out), environmental groups stepped up their calls to get these insecticides off the market.
You can see for yourself how I tried to sketch out all this complexity in my piece. And if you want more information, here’s a list of key papers and other documents:
A new review of previous research: “Dietary traces of neonicotinoid pesticides as a cause of population declines in honey bees: an evaluation by Hill’s epidemiological criteria,” by James E. Cresswell, Nicolas Desneux, Dennis vanEngelsdorp. Pest Management Science
Another new review: “Neonicotinoids in bees: a review on concentrations, side-effects and risk assessment.” Tjeerd Blacquière, Guy Smagghe, Cornelis A. M. van Gestel and Veerle Mommaerts. Ecotoxicology.
An emergency petition from beekeepers and environmental groups to the EPA earlier this month calling for suspension of neonicotinoid insecticides. pdf
Pesticide Risk Assessment for Pollinators: an executive summary of a 2011 meeting organized by
Bayer CropScience and the EPA, the Society of Toxicology and Environmental Chemistry, which will become a book later this year. pdf
In tomorrow’s New York Times, I take a look into nature’s crystal ball. Scientists have long been warning that we may be headed into Earth’s sixth mass extinction. But most projections just carry forward the causes of recent extinctions and population plunges (overfishing, hunting, and the like). Global warming is already starting to have an effect on many species–but it’s a minor one compared with the full brunt that we may experience in the next century.
I’ve written in the past about studies scientists have carried out to project what that impact will be like. I decided to revisit the subject after reading a spate of provocative papers and books recently. While the scientists I talked to all agree that global warming could wreak serious havoc on biodiversity in coming decades, they’re debating the best way to measure that potential harm, and the best way to work against it. We all crave precision in our forecasts, but biology is so complex that in this case we may well have to live without it. Check it out.
[Image: Photo by DJ-Dwayne/Flickr]
Behold the Japanese white-eye, considered an invasive species in its new home in Hawaii. Yet the bird does something that conservation biologists might considered useful for sustaining ecosystems: it spreads the seeds of native Hawaiian plants. Get rid of the Japanese white-eye, and you get rid of its service.
In Yale Environment 360 this morning, I take a look at a controversial proposal that’s making its way into the peer-reviewed biology literature: some introduced species are actually beneficial. I wrote about the complicated relationship between non-native species and biodiversity a couple years ago in the New York Times. In my new article, I focus on two new papers (here and here) in which scientists are advancing these ideas further. Reconsidering exotic species is just one part of a bigger vision they’re offering: in a human-dominated world, we will often have to give up the idea of restoring ecosystems to a pre-human state; instead, we should focus on ensuring the ecosystems are as resilient as possible, because they’re going to be facing even tougher times in years to come.
As one of the scientists say, the idea is now edgy, but not nuts. Not nuts, maybe, but certain one that continues to draw the ire of many critics, some of whom I interview in the article. Check it out.