December 4, 2013
In 1917, British artist Norman Wilkinson experienced a eureka moment while serving in the Royal Naval Volunteer Reserve. Throughout the month of April, German U-boats had been mercilessly torpedoing British ships, sending around eight of those vessels per day into the watery abyss. Hiding a ship traveling on the open ocean from plain sight was impossible, Wilkinson knew, but a bit of artistic trickery may be able to muddle the Germans’ ability to accurately judge the exact location of that ship, he realized.
From that idea, Wilkinson devised a type of camouflage called “razzle dazzle” (its slightly more serious name is dazzle camouflage). The technique consists of squashing together contrasting geometric patterns, shapes and colors to create a pattern of optics that would confuse enemies by distorting the object’s dimensions and boundaries. All in all, more than 2,000 ships received such a makeover, although the scheme’s effectiveness seemed to produce mixed results.
By World War II, razzle dazzle had largely fallen out of favor, but as it turns out, this technique lives on in the natural world. High contrast patterns–nature’s equivalent to dazzle camouflage–are used by animals ranging from snakes to zebra to fish. Like those hidden World War I ships, many creatures seem to use dazzle patterns to conceal themselves from predators. Until now, however, researchers hadn’t considered the flipside of this relationship: could predators use razzle dazzle to sneak up on prey as they mounted an attack?
To investigate this possibility, biologist Roger Santer of Aberystwyth University in the U.K. turned to locusts. These insects are particularly well suited for vision studies due to something called a single lobula giant movement detector neuron, a unique cell that specializes in detecting looming objects (think of a car speeding towards you, or a hand reaching for your face). Researchers think this neuron works by measuring the shape and movement of patterns of light and dark across the eye. Whatever the mechanism, as looming objects approach a locust, its detector neuron fires away, alerting the insect to imminent potential danger and triggering it to flee.
To see how the locusts responded to dazzle camouflage, Santer created an array of visual patterns using a graphics software. He situated the locusts just in front of the computer monitor, and then projected a simulated approach of those objects from about 10 meters away to about 0.07 meters from the cowering insects. The objects varied in contrast: black, grey or white on a grey background. Around 20 locusts took part in the experiment, and Santer measured their cellular reactions to the various shapes through copper wires inserted into the locusts’ neck.
The locusts’ neurological responses to the looming objects depended on which patterns they saw, Santer reports in Biology Letters. Squares with both a darker-than-background top and bottom half elicited the strongest panic response, followed by squares with a dark upper half, but a bottom half that was the same color as the background. Squares that had an upper half that was dark but a bottom half that was bright (in other words, the razzle dazzle ones) produced a significantly weaker panic response, as did squares that were brighter than the background. Finally, squares that were the same color as the background produced no response at all.
These results are interesting in that they correlate with similar dazzle tests performed on humans, who also had trouble quickly registering dazzle patterns. However, at this point, whether or not locust predators actually use dazzle to catch their unsuspecting insect prey remains a matter of speculation. Though lab tests confirm this strategy might work, Santer did not investigate whether or not a dazzle dance of death is carried out in the real world.
Hypothetically speaking, dazzle camouflage, Santer concludes, would help a predator but would not be the most effective way of snagging a locust lunch. Instead, classic camouflage–blending in with the background rather than creating an optical illusion–seems to be the most effective means of tricking would-be prey. However, in the case that other selection pressures favor high-contrast patterns (such as if females of a predator species prefer bold stripes in males), Santer thinks that predators could indeed evolve to give ‘em the old razzle dazzle.
December 3, 2013
Scientific equipment that’s left unattended in the field can provide all sorts of interesting information. It can, for instance, snap photographs of exotic and shy wild animals, or analyze the noises coming from an ecosystem to identify the species living there.
But often, leaving valuable instruments scattered outside risks interference or destruction from an unavoidable force of nature: humans. Data isn’t regularly collected or published on the topic, but it’s well known among field scientists that leaving equipment in highly-trafficked areas leaves it vulnerable to petty vandalism and theft.
This unfortunate trend was recently on the mind of Holger Goerlitz, a scientist at Germany’s Max Planck Institute for Ornithology who studies animal behavior (specifically, how bats use echolocation within their environment) and leaves his field equipment unattended to do so. “As part of a project, I wanted to deploy automated equipment that would sit in the field for several nights,” he says. “So my colleagues and I were concerned about how to protect this equipment. We considered using chains and video cameras. And then suddenly we had this random idea: Let’s see what would be a good label to attach to the equipment to reduce vandalism.”
His team’s results, based on 60 pieces of fake scientific equipment scattered in four different Munich parks and published last week in Methods in Ecology and Evolution, may surprise you. They found that friendly labels that gave information about the project and the researcher led to about 40 percent fewer instances of equipment interference—either theft, vandalism or park visitors simply moving or trying to open up the equipment—as compared to neutral labels or ones that threatened surveillance and punishment.
They found this out by distributing boxes that looked vaguely like scientific instruments (above)—basically, plastic boxes with car antennas and fake cameras attached—for one week in each park, right next to a footpath, and checking for interference with the objects daily. All of the boxes had a similar warning label identifying it as properly of the Planck Institute and giving Goerlitz’ contact information, but the tone of the messages differed slightly.
A third of the boxes had neutral messages (translated to English, they read “Part of an experiment—Please do not touch”), while another third had threatening warnings (“‘Part of an experiment—Every theft will be reported to the police! GPS monitored!”) and the remaining third had a friendly, personalized note (“Part of my thesis–Please do not touch–Please call me if you have any questions and would like to know more.”) The friendly label also had a picture of a juvenile squirrel, to give passersby an idea of the researcher’s work:
The researchers checked the boxes daily, and had even placed pebbles inside so they could determine if the boxes had been picked up and moved. They also counted how many were pried open, vandalized or stolen.
Apparently, at least in these German city parks, the impulse to steal or vandalize is one that can be dislodged by just a bit of information about the potential victim, presented in a friendly way. Simply knowing that the device was important to one particular researcher—likely a student, given the word “thesis”—led visitors to interfere with the equipment about half as frequently. Over the course of a month, 39 instances of interference occurred with a box with a friendly label, compared to 59 with a neutral label and 67 with a threatening label.
Although the researchers were heartened by the finding, they were surprised, especially due to the fact that the threatening labels were the least successful. They imagine that the friendly label worked primarily by establishing the personal connection, perhaps aided by the squirrel photo, but the threatening label’s ineffectiveness is a mystery. “We don’t know why this was the case,” Goerlitz says. “It could be that people didn’t believe the threatening label, or that they thought, ‘oh, there’s a GPS device inside, this could be valuable.’” The fact that it was the only label that included the word “theft” might indicate that simply implanting the idea in people’s minds influenced them to engage in it.
But, although there’s obviously a lot more work to be done—this was conducted with a small sample of people over a short time period in one particular German city—this finding about friendly labels is a positive and potentially helpful one. If presented with the chance, people can be influenced to help science succeed if they’re treated in a respectful way and informed about what’s going on. Despite the enormous amount of money spent annually on scientific equipment, very little research has actually been done in this area to date, and more work to see how this might apply to people in different cultures, for instance, may aid scientists around the world in their efforts to protect their surveying instruments.
Goerlitz, for one, is ready to start using this finding to better safeguard his own equipment that monitors bat echolocation. “In my labels, I’ll try to be informative and friendly to people,” he says. “I think if you expose people to what you’re doing, they’ll be much more supportive of it.”
December 2, 2013
It’s a platitude that we’ve all heard dozens of times, whether to justify our treatment of other species or simply to celebrate a carnivorous lifestyle: humans are the top of the food chain.
Ecologists, though, have a statistical way of calculating a species’ trophic level—its level, or rank, in a food chain. And interestingly enough, no one ever tried to rigorously apply this method to see exactly where humans fall.
Until, that is, a group of French researchers recently decided to use food supply data from the U.N Food and Agricultural Organization (FAO) to calculate human tropic level (HTL) for the first time. Their findings, published today in the Proceedings of the Natural Academy of Sciences, might be a bit deflating for anyone who’s taken pride in occupying the top position.
On a scale of 1 to 5, with 1 being the score of a primary producer (a plant) and 5 being a pure apex predator (a animal that only eats meat and has few or no predators of its own, like a tiger, crocodile or boa constrictor), they found that based on diet, humans score a 2.21—roughly equal to an anchovy or pig. Their findings confirm common sense: We’re omnivores, eating a mix of plants and animals, rather than top-level predators that only consume meat.
To be clear, this doesn’t imply that we’re middle-level in that we routinely get eaten by higher-level predators—in modern society, at least, that isn’t a common concern—but that to be truly at the “top of the food chain,” in scientific terms, you have to strictly consume the meat of animals that are predators themselves. Obviously, as frequent consumers of rice, salad, bread, broccoli and cranberry sauce, among other plant products, we don’t fit that description.
The researchers, led by Sylvain Bonhommeau of the French Research Institute for Exploitation of the Sea, used FAO data to construct models of peoples’ diets in different countries over time, and used this to calculate HTL in 176 countries from 1961 to 2009. Calculating HTL is fairly straightforward: If a person diet is made up of half plant products and half meat, his or her trophic level will be 2.5. More meat, and the score increases; more plants, and it decreases.
With the FAO data, they found that while the worldwide HTL is 2.21, this varies widely: The country with the lowest score (Burundi) was 2.04, representing a diet that was 96.7 percent plant-based, while the country with the highest (Iceland) was 2.54, reflecting a diet that contained slightly more meats than plants.
On the whole, since 1961, our species’ overall HTL has increased just slightly—from 2.15 to 2.21—but this averaged number obscures several important regional trends.
A group of 30 developing nations in Southeast Asia and Sub-Saharan Africa (shown in red)—including Indonesia, Bangladesh and Nigeria, for example—have had HTLs below 2.1 during the entire period. But a second group of developing countries that includes India and China (shown in blue) has slightly higher HTL measures that have consistently risen over time, going from around 2.18 to over 2.2. The HTLs of a third group, shown in green (including Brazil, Chile, South Africa and several countries in Southern Europe), have risen further, from around 2.28 to 2.33.
By contrast, HTL in the world’s wealthiest countries (shown in purple)—including those in North America, Northern Europe and Australia—was extremely high for most of the study period but decreased slightly starting during the 1990s, going from around 2.42 to 2.4. A fifth group of small, mostly island countries with limited access to agricultural products (shown in yellow, including Iceland and Mauritania) has seen more dramatic declines, from over 2.6 to less than 2.5.
These trends closely correlate, it turns out, with a number of World Bank development indicators, such as gross domestic product, urbanization and education level. The basic trend, in other words, is that as people become wealthier, they eat more meat and fewer vegetable products.
That has translated to massive increases in meat consumption in many developing countries, including China, India, Brazil and South Africa. It also explains why meat consumption has leveled off in the world’s richest countries, as gains in wealth leveled off as well. Interestingly, these trends in meat consumption also correlate with observed and projected trends in trash production—data indicate that more wealth means more meat consumption and more garbage.
But the environmental impacts of eating meat go far beyond the trash thrown away afterward. Because of the quantities of water used, the greenhouse gases emitted and the pollution generated during the meat production process, it’s not a big leap to speculate that the transition of huge proportions of the world’s population from a plant-based diet to a meat-centric one could have dire consequences for the environment.
Unfortunately, like the garbage problem, the meat problem doesn’t hint at an obvious solution. Billions of people getting wealthier and having more choice over the diet they eat, on a basic level, is a good thing. In an ideal world, we’d figure out ways to make that transition less damaging while still feeding huge populations. For example, some researchers have advocated for offbeat food sources like meal worms as a sustainable meat, while others are trying to develop lab-grown cultured meat as an environmentally-friendly alternative. Meanwhile, some in Sweden are proposing a tax on meat to curb its environmental cost while government officials in the UK are urging consumers to cut back on their demand for meat to increase global food security and to improve health. Time will tell which approaches stick.
In the meantime, simply keeping track of the amount of meat we’re eating as a society via HTL could provide a host of useful baseline information. As the authors write, “HTL can be used by educators to illustrate the ecological position of humans in the food web, by policy makers to monitor the nutrition transition at global and national scales and to analyze the effects of development on dietary trends, and by resource managers to assess the impacts of human diets on resource use.”
In other words, monitoring the intricacies of our middling position on the food chain may yield scientific fodder to tackle problems like food security, obesity, malnutrition and environmental costs of the agricultural industry. A heavy caseload for a number that ranks us on the same trophic level as anchovies.
November 26, 2013
Seahorses belong to the genus Hippocampus, which gets its name from the Greek words for “horse” and “sea monster.” With their extreme snouts, weirdly coiled bodies and sluggish movements produced by to two puny little fins, these oddly shaped fish seem like an example of evolution gone terribly awry. And yet, new research published today in Nature Communications shows that it is precisely the seahorse’s uncanny looks and slow motions that allow it to act as one of the most stealthy predators under the sea.
Seahorses, like their close relatives the pipefish and sea dragons, sustain themselves by feasting on elusive, spastic little crustaceans called copepods. To do this, they use a method called pivot feeding: they sneak up on a copepod and then rapidly strike before the animal can escape, much like a person wielding a bug swatter tries to do to take out an irritating but otherwise impossible-to-catch fly. But like that lumbering human, the seahorse will only be successful if it is able to get near enough to its prey to strike at very close range. In the water, however, this is an even greater feat than on land because creatures like copepods are extremely sensitive to any slight hydrodynamic change in the currents around them.
So how do those ungainly little guys manage to feed themselves? As it turns out, the seahorse is a more sophisticated predator than appearance might suggest. In fact, it is precisely its looks that make it an ace in the stealth department. To arrive at this surprising conclusion, researchers from the University of Texas at Austin and the University of Minnesota used holographic and particle image velocimetry–fancy ways of visualizing 3D movements and water flow, respectively–to monitor the hunting patterns of dwarf seahorses in the lab.
In dozens of trials, they found that 84 percent of the seahorses’ approaches successfully managed not to sound the copepod’s retreat alarms. The closer the seahorse could get to its unsuspecting prey and the faster it struck, the greater its odds of success, they observed. Once in range of the copepod, seahorses managed to capture those crustaceans 94 percent of the time. Here, you can see that method of attack, in which the seahorse’s giant head looks like a floating bit of marine sludge drifting toward the blissfully ignorant copepod:
The way the seahorse’s movements and morphology–especially its head–interact with the water particles, the researchers found, likely take the credit for its exceptional hunting skill. The animal’s arched neck acts like a spring for generating an explosive strike, they describe, while the shape of its snout–a thin tube with the mouth positioned at the very end–allows it to drift through the water while creating minimal disturbance.
To emphasize this pinnacle of engineering, the team compared water disruptions caused by seahorses with those of sticklebacks, a relative of the seahorse but with a more traditional fishy look. Thanks to the shape and contours of the seahorse’s head, that predator produced significantly less fluid deformation in the surrounding water than the stickleback. The poor stickleback possesses neither the morphology nor posture to generate “a hydrodynamically quiet zone where strikes occur,” the authors describe. In other words, while the seahorse may appear a bit odd so far as fishes go, evolution was obviously looking out for that funny but deadly animal’s best interests.
November 21, 2013
Over the course of 1700 miles, they sampled the water for small pieces of plastic more than 100 times. Every single time, they found a high concentration of tiny plastic particles. “It doesn’t look like a garbage dump. It looks like beautiful ocean,” Miriam Goldstein, the chief scientist of the vessel sent by Scripps Institution of Oceanography, said afterward. “But then when you put the nets in the water, you see all the little pieces.”
In the years since, a lot of public attention has been justifiably paid to the physical effects of this debris on animals’ bodies. Nearly all of the dead albatrosses sampled on Midway island, for instance, were found to have stomachs filled with plastic objects that likely killed them.
But surprisingly little attention has been paid to the more insidious chemical consequences of this plastic on food webs—including our own. “We’d look over the bow of the boat and try to count how many visible pieces of plastic were there, but eventually, we got to the point that there were so many pieces that we simply couldn’t count them,” says Chelsea Rochman, who was aboard the expedition’s Scripps vessel and is now a PhD student at San Diego State University. “And one time, I was standing there and thinking about how they’re small enough that many organisms can eat them, and the toxins in them, and at that point I suddenly got goosebumps and had to sit down.”
“This problem is completely different from how it’s portrayed,” she remembers thinking. “And, from my perspective, potentially much worse.”
In the years since, Rochman has shown how plastics can absorb dangerous water-borne toxins, such as industrial byproducts like PCB (a coolant) and PBDE (a flame retardant). Consequently, even plastics that contain no toxic substances themselves, such as polyethylene—the most widely used plastic, found in packaging and tons of other products—can serve as a medium for poisons to coalesce from the marine environment.
But what happens to these toxin-saturated plastics when they’re eaten by small fish? In a study published today in Scientific Reports, Rochman and colleagues fill in the picture, showing that the toxins readily transfer to small fish through plastics they ingest and cause liver stress.This is an unsettling development, given that we already know such pollutants concentrate further the more you move up the food chain, from these fish to the larger predatory fish that we eat on a regular basis.
In the study, researchers soaked small pellets of polyethylene in the waters of San Diego Bay for three months, then tested them and discovered that they’d absorbed toxins leached into the water from nearby industrial and military activities. Next, they put the pollution-soaked pellets in tanks (at concentrations lower than those found in the Great Pacific garbage patch) with a small, roughly one-inch-long species called Japanese rice fish. As a control, they also exposed some of the fish to virgin plastic pellets that hadn’t marinated in the Bay, and a third group of fish got no plastic in their tanks at all.
Researchers still aren’t sure why, but many small fish species will eat these sort of small plastic particles—perhaps because, when covered in bacteria, they resemble food, or perhaps because the fish simply aren’t very selective about what they put in their mouths. In either case, over the course of two months, the fish in the experiment consumed many plastic particles, and their health suffered as a result.
“We saw significantly greater concentrations of many toxic chemicals in the fish that were fed the plastic that had been in the ocean, compared to the fish that got either clean plastic or no plastic at all,” Rochman says. “So, is plastic a vector for these chemicals to transfer to fish or to our food chain? We’re now fairly confident that the answer is yes.”
These chemicals, of course, directly affected the fishes’ health. When the researchers examined the tiny creatures’ livers (which filter out toxins in the blood) they found that the animals exposed to the San Diego Bay-soaked plastic had significantly more indications of physiological stress: 74 percent showed severe depletion of glycogen, an energy store (compared to 46 percent of fish who’d eaten virgin plastic and zero percent of those not exposed to plastic), and 11 percent exhibited widespread death of individual liver cells. By contrast, the fish in the other treatments showed no widespread death of liver cells. One particular plastic-fed fish had even developed a liver tumor during the experimental period.
All this is bad news for the entire food webs that rest upon these small fish, which include us. “If these small fish are eating the plastic directly and getting exposed to these chemicals, and then a bigger fish comes up and eat five of them, they’re getting five times the dose, and then the next fish—say, a tuna—eats five of those and they have twenty-five times the dose,” Rochman explains. “This is called biomagnification, and it’s very well-known and well-understood.”
This is the same reason why the EPA advises people to limit their consumption of large predatory fish like tuna. Plastic pollution, whether found in high concentrations in the Great Pacific garbage patch or in the waters surrounding any coastal city, appears to be central to the problem, serving as a vehicle that carries toxins into the food chain in the first place.