On December 11th, 2017 we learned about

Florida raptors show surprising resilience in their rapid recovery against invasive snails

The arrival of an invasive species is usually terrible news for an ecosystem. History can offer plenty of examples of plants or animals arriving in a new place, only to out-consume everything that had previously lived there, as no predators are prepared to help keep populations in check. Humans have tried curbing these conflicts by introducing new creatures meant to go after the invaders, but our efforts don’t have the best track record either. All this makes the story of North American snail kites rather surprising, as the native birds have apparently been able to survive, and even take advantage of, snails that would otherwise be wrecking havoc across the Florida Everglades.

Snacking on apple snails

North American snail kites (Rostrhamus sociabilis) live in various locations around the Gulf of Mexico, including parts of Florida. With sharp talons, a long, hooked beak, dark plumage and crimson eyes, these raptors look ready to take on anything. In reality, they’re only interested in one thing, which is the small apple snails they find in wetlands. While they’re capable of feeding on small turtles and rodents in a pinch, the kite’s usual tactic is to hold a snail in one claw while using their long beak to pick flesh out of the mollusk’s shell. As their name implies, snail kites are specialists, which is why ecologists were so worried when their narrow menu options became threatened by…other snails?

Oddly, the invasive species that was encroaching on the apple snails and thus threatening the snail kites was another species of apple snail. However, the South American apple snail grows much larger, making them harder to prey on. This left them more or less unchecked, allowing them to quickly cause billions of dollars worth of damage to the ecosystem, from hurting bird populations to eating plants that normally helped prevent algae blooms. Predictions were grim for the kites and the ecosystem in general.

Getting bigger, faster

Amazingly, the snail kites have found a way to rebound. Their population has grown, as have their bodies and beaks. The birds are now growing eight percent larger than they used to, with some growth spikes reaching as high as 12 percent. They seem to be benefiting from eating the larger snails as prey, but bigger meals alone don’t explain all the changes researchers have witnessed. In less than two generations time, the surviving kites are already showing a bias towards genes that grow larger beaks. It’s easy to see how bigger beaks allows the kites to scoop food out of bigger snail shells, but the rate that these changes are taking place are startling.

Natural selection is continuous process, but it usually operates on longer time-scale in larger animals. It’s easy to witness change in something like bacteria, which can propagate beneficial mutations across multiple generations in 24 hours. The snail kites, on the other hand, live to be eight years old, and so the larger birds with bigger beaks have somehow boosted their real and proportional numbers in less than two life spans. Researchers don’t necessarily think that the snail kites will now reign in Florida’s apple snail problems, but they do feel optimistic for the future of the raptors, which are now estimated to have a population over 2,000 for the first time in ten years.

Source: Things Looked Bleak Until These Birds Rapidly Evolved Bigger Beaks by Douglas Quenqua, New York Times

On November 19th, 2017 we learned about

Lemurs depend on leaves because their local fruit lacks protein

No matter how delightful a good salad may be, most of us can’t live on leafy greens alone. Primates, including humans, definitely consume plants in our diets, but we eat other items like nuts, fruit or meat to round our our nutritional needs. Lemurs break this pattern though, and skip everything but leaves when they go looking for food. As it turns out, the lemurs might just think that the local produce on in Madagascar just isn’t worth eating in the first place.

To be clear, fruit does grow in Madagascar. Studies have named at least 125 native species, and humans have introduced everything from oranges to avocados. With seemingly a number of choices in their habitat, scientists wondered why more lemurs didn’t follow the model of other primates and make these fruits a bigger part of their diets. Scientists wondered if the fruit supply was historically unstable due to events like cyclones, forcing lemurs to shape their diets around more reliable leaves. After all, even the local fruit bats, Eidolon dupreanum, have to switch to eating nectar for portions of the year when their favorite foods are unavailable.

Not enough nitrogen

When scientists started looking closer at what foods were available to lemurs, they started finding that the quality of the fruit was the real issue. While fruit could be found in the lemurs’ habitat, it didn’t seem to provide much protein per bite. To quickly compare the nutritional content of the fruit available to lemurs and other primates around the world, researchers started measuring nitrogen concentrations, since nitrogen is a key ingredient in many proteins. Fruit eaten by various monkeys from around the world was sampled, and all of it had more valuable nitrogen per bite than the fruit available to lemurs in Madagascar.

To make up for this gap in their diets, it seems that lemurs had to learn to skip the fruit and eat more leaves. Leaves don’t always provide a lot of calories per bite though, and so this required further energy-conserving adaptations, like eating leaves around the clock, or hibernating to use less energy in the first place. Now that the importance of leafy-greens is better understood, conservation efforts can be better designed to ensure that critically endangered lemurs have access to the slightly unintuitive foods they’ve come to depend on.

Source: Lemurs are weird because Madagascar's fruit is weird, Phys.org

On November 16th, 2017 we learned about

Composition of coal deposits suggests that plants benefited from dinosaur defecation

Plants love giant herbivores. It’s not that they are dying to be devoured exactly, but big eaters like a modern buffalo or ancient Diplodocus have historically helped disperse resources that plants need throughout an ecosystem. By eating plants and seeds, these unintentional gardeners break down nutrients in their digestive system, pooping them out on fresh soil in a new location. Plants’ dependency on this fecal fertilization is sometimes obvious, such as with the impossibly large pit of an avocado that evolved in conjunction with huge creatures like the giant ground sloth, Megalonyx. Other aspects of this dynamic, like nutrient distribution, are a bit more elusive, since the only direct record of that process in the herbivore’s poop itself. To study how this relationship may have worked long ago, researchers skipped looking for the poop itself, focusing instead on coal.

Coal is largely made up of carbon from ancient plants, compressed over millions of years into the black rocks we know today. It’s not completely homogeneous though, and significant amounts of other materials from the original plants can still be detected when the coal is analyzed. These data are routinely gathered as part of geological surveys, so when Christopher Doughty from the University of Flagstaff wanted to find out how much over-sized herbivores like dinosaurs impacted their ecosystems, the coal was an attractive data source.

Comparing coal collections

Obviously, nobody can be exactly sure where these huge dinosaurs were dropping their dung, but the fossil record does provide evidence about where dinosaurs were spending their time. Doughty focused his study on two batches of coal deposits, with one being primarily samples from the western United States, dated to the Cretaceous period, and the other coming from Appalachia’s Pennsylvanian subperiod, a time that predated any true dinosaurs by over 40 million years. As expected, the coal, and thus the plants, from the Cretaceous had much higher nutritional levels, with an average of 136 percent more calcium, magnesium, phosphorus and sulfur. These nutrients were also more evenly distributed geographically, indicating that the dinosaurs that were depositing them weren’t congregating for extended periods of time in a single location. Based on the bathroom habits of modern herbivores, Doughty estimates that a multi-ton herbivore was likely to walk between four to 10 miles before taking needing a rest stop, making sure that no single plot of land got all the nutritious feces.

As much as these patterns make sense, it’s hard to be conclusive about this activity. To rule out non-fecal explanations for the differences between the western and Appalachian coal, like erosion or precipitation, aluminum levels were used as a kind of control. Aluminum is naturally occurring but toxic to plants, so if it was also more prevalent in the Cretaceous coal, it might suggest that these elements were added independently of plant growth cycles. However, aluminum levels were very similar from both batches of coal, indicating that changes in geology and the weather were not responsible for the enriched coal. While it’s not the same as finding a massive collection of distributed coprolites, it does look like dinosaur poop made a big difference to plants’ health.

Plants deprived of dung

So if plants seemed to do better when there were huge herbivores spreading nutrients near and far, where does that leave our ecosystems today? Unfortunately, it looks like human development has broken this dynamic, as we’ve purged many habitats of their plant-eating megafauna. Those that remain are also unable to roam as freely as their ancestors did, which is likely creating pockets of nutrition in places where the buffalo still roam, while leaving other areas less inviting to plant life.

Source: Signatures of Dinosaur Poop Found in Cretaceous Coal Seams by Katherine Kornei, Eos

On November 15th, 2017 we learned about

Oceanic noise pollution poses serious problems for fish’s reproductive success

When submerged in water, human communication often gets reduced to hand-gestures, like a vague game of slow-motion charades. Without specialized equipment, it’s the best we can do in an environment that doesn’t accommodate our air-based speech. This limitation for our species has led to a lot of ignorance about how other species click, chirp and sing in the water, but new investigations are now discovering the importance of sound to the denizens of the sea. Scientists are now finding that aural communication is much more widespread than headline-grabbing whales and dolphins, extending all the way to the ocean’s floor with mating songs of the humble goby.

Gobies like Pomatoschistus microps are small fish that live usually don’t live more than a year. They live in shallow, coastal areas around Europe, and are mostly preyed up on by larger fish like cod. The sand goby (Pomatoschistus minutus) spends most of its time sitting motionless on the sea floor, waiting to grab passing invertebrates to eat. They perk up a bit in the summer though, when the males will commandeer an empty clam shell, sitting under it while courting local females with song. If the song catches the ear of a female, she’ll spawn her eggs under the male’s shell where he will fertilize and guard them until they hatch.

Sefloor seranade

The goby’s song itself probably won’t sound much like a good Barry White album to a human ear, but experiments have found it to be crucial to reproductive success. To test the role of the male’s song, researchers subjected two female and one male goby to the sound of a motorboat engine, simulating the kind of noise pollution that has become common in today’s oceans. When the humble “purring” (or in case of the common goby, “woodpecker-like”) sounds of the male goby had to compete with sounds of human activity, there was very little interaction between the male and female fish. In the cases where the fish did mate, the eggs seemed to somehow be affected by the noise as well, with half the eggs dying before hatching, and the surviving eggs taking longer to gestate. While slower courtship is likely explained simply by noise drowning out the male’s song, researchers aren’t sure why the eggs also suffered once they’d been fertilized.

This sensitivity to noise is a mounting problem for our oceans, where ships of all sizes, as well as undersea drilling and mining, are making more and more noise each year. However, this study also suggests that noise may be a consideration on small scales as well. The scientists behind this study worry that labs that work with fish need to take greater care to keep noise to a minimum, as fish in aquariums may be reacting to sound and skewing research results more than researchers have commonly been accounting for.

Source: Female fish like males who sing by University of Gothenburg, Science Daily

On October 31st, 2017 we learned about

Guppies manipulate gestation to ensure their offsprings’ maturity matches their environment

From as young as seven weeks old, guppies can start earning their nickname “millionfish,” spawning offspring quickly and frequently. At first glance, birthing as many offspring as possible seems like a simple if crude way to ensure some reproductive success- if many babies are likely to be eaten, have more babies than predators can eat. However, scientists are finding that there’s more nuance to guppy reproduction than this, even to the point that mother fish, who give life birth, can adjust the length of time a brood gestates. Instead of just hoping for the best, it looks like guppies are actually giving birth according to a well-optimized strategy.

Two populations of guppies (Poecilia reticulata) were studied in Trinidad’s Aripo river. Fish living downstream usually had more predators to contend with, while fish living upstream, above a waterfall, had almost no fear of being eaten. Researchers noted that the guppy fry, or babies, weren’t living on the same timescale. No guppy lives much more than two years, but the fry born upstream seemed to be physically mature more quickly after they were born than the fish born downstream. After carefully measuring for differences in skeletal growth rates, or when this growth starts in the guppies’ lifecycles, researchers were able to determine that the big difference was the length of a brood’s gestation.

Challenges posed by predators or peers

Guppies born downstream, where predators are a concern, were basically born earlier. The threat of predation means that mothers are more likely to have surviving offspring if those babies aren’t waiting in their mother’s belly any longer than necessary. The guppies born upstream don’t have this pressure, trading it for another concern. With no predators threatening them, populations rise meaning that food scarcity becomes an issue. By gestating just a bit longer, the fry are born with more developed bone and less cartilage, especially around their mouths. This makes it easier for these offspring to scrape algae and other food off rocks, letting them make the most of what food is available.

This isn’t the only way upstream guppies seem to favor investing more in each offspring than their downstream counterparts. These fish also tend to start reproduction at a later age, and reproduce less often, rounding out the sort of “quality of quantity” strategy. We often frame gestation as being set by the needs of embryonic development, but guppies are showing how small variations in maturity can help a species react to larger environmental pressures.

Source: Where food is limited, guppy mothers gestate their young longer by David Orenstein, News from Brown

On October 30th, 2017 we learned about

Components of farmers’ fertilizers could be promoting the growth of mind-controlling parasites

There’s probably no major cause for alarm, but scientists have been running experiments to create zombies. It’s not that they’re mad- the experiments are actually aimed more at ecological concerns with pollution rather than satisfying some kind of maniacal god complex. The experiments do prominently focus on mind-controlling parasites, but unlike they zombies of popular mythology, these creatures have no interest in eating your brains, because their real goal is to be eaten.

Making themselves into a meal

The zombies in question are actually salt-marsh amphipods called Orchestia grillus. They’re little crustaceans less than an inch long, looking a bit like a shrimp that’s been forced to crawl out of the sea. They normally scurry in the shelter of rotting debris along salt marshes, eating algae and other decaying leftovers in the area. Eating decaying organic material sounds kind of zombie-like, but no more so than your average earthworm. The real horror, at least for the amphipods, starts with the arrival of Levinseniella byrdi, a flatworm-like parasite.

Once the parasite has infected an amphipod, it takes control of it’s behavior, turning it from a spritely, hopping land-shrimp into a slow, mindless creature that barely responds to stimuli. It doesn’t march along cannibalizing it’s friends though, since its real goal is to be eaten by birds. So instead of scurrying to safety when caught in the open, zombified amphipods will wander out of cover, sitting still until a predator finds it. Just in case this mindlessness isn’t enough to get the crustacean eaten, L. byrdi takes the extra step of recoloring its host’s body. Instead of a subtle brown, infected amphipods turn bright orange, making them all the more apparent to passing sparrows, willets or sandpipers. Once eaten, L. byrdi can continue with the next stages of its life cycle, taking up residence in the bird’s intestines.

Watching parasite populations

Scientists didn’t invent any of this relationship, but they are trying to figure out what makes it work. They’ve been adding nitrogen to specific plots in New England salt marshes, simulating the fertilizer-rich runoff that frequently flows downstream from farms. The concern isn’t for the undignified death of infected amphipods, but for the long-term effect of all this extra nitrogen. As suspected, the extra nutrients help more algae grow, providing more food for amphipods and thus, more food for birds that can then spread the parasites further. The nitrogen-rich areas had 13 times more parasites than areas with more natural nitrogen levels. We’re not necessarily going to run out of amphipods, but spikes in parasite populations may be a problem in larger numbers. These results may also provide a model for other parasites’ relationships with environmental pollutants, including those that don’t conveniently turn their hosts bright orange for a quick head-count.

Source: Study warns of pumpkin-colored zombies by Virginia Institute of Marine Science, EurekAlert!

On October 17th, 2017 we learned about

A history of air pollution recorded on preserved bird bellies

History is usually studied in written records, man-made objects, rocks and bones. It’s no surprise that we generally rely on durable materials like this, but more studies of more recent history aren’t so limited. Thanks to careful preservation of biological samples from around 200 years ago, we can use softer, more delicate bits of biology to find out what was happening in the world, including picking up evidence of very indelible events, like air pollution from the industrial revolution. In that case, instead of looking at stone or tools, researched dug into museum collections to survey thousands of dead, but preserved, birds.

By the 1870s, parts of the United States were being overwhelmed by smoke from furnaces and steam engines. These early combustion engines opened up a lot of new possibilities in technology, but they also dumped a lot of soot on their surrounding neighborhoods. By 1874, places like Chicago were so choked with smoke that it obscured the Sun on a daily basis, a scenario we usually associate with natural disasters. These smokey years have been documented in some forms, but biologists wanted to find data on air pollution across a wider territory and time span. The record they then turned to was the accumulated soot that was still stuck to the feathers of birds collected from the 1800s to the present day.

Documenting accumulated dirt

The researchers traveled to museums around America’s so-called Rust Belt to compare as birds across different decades and locales. Instead of taking samples of soot for chemical analysis, they measured the overall level of contamination on a bird’s body by taking photos, then quantifying exactly how dark its white feathers had become. To make sure varying light levels or human error didn’t throw off these measurements, each bird was placed next to a paint strip called a reflectance that allowed each photo to be properly calibrated, ensuring that the gray on a woodpecker or horned lark’s belly was the result of smoke and not a shadow. Once the data was gathered, it was plotted by location and time frame, revealing the history of America’s air quality with impressive specificity.

The dirtiest birds were dated from the beginning of the 20th century, when industrial air pollution was at its peak. Feathers were cleaner when manufacturing declined during the Great Depression, and were then dirtier again during World War II. Birds after the 1955 Air Pollution Control Act looked cleaner than their predecessors, and those that had lived after 1963’s Clean Air Act were cleaner still. When he birds were laid next to each other, the gradation was obvious enough that my four- and eight-year-old immediately picked up on it. My eight-year-old also commented that the dirtier birds were generally smaller as well. Unfortunately, the effects this soot might have had on the birds (ruling out age or other nutritional differences) wasn’t in the study’s scope.

Bird breathing problems

Other studies, however, have looked at the effects on air pollution on our feathered friends, even before they’re covered in soot. Beyond canaries in coal mines, birds’ health has been found to decline from air pollutants faster than humans, as pollutants often lead to thinner egg shells and lower birth rates. Relative body sizes probably play a role, but scientists suspect that bird respiration also contributes to their sensitivity to particulate in the air. While humans breath in and out in two distinct steps, birds breath in a more continuous cycle, essentially inhaling and exhaling in one step. This allows them to fuel the metabolism needed for high-energy tasks like flying without pumping their lungs as a ridiculous rate. It unfortunately also means that they’re more efficient at sucking in soot and other toxins that can cause health problems. So if the birds are suffering in an area, there’s a chance that human health is being attacked as well. Or to put it in a more positive light, you can breath easy if your avian neighbors are clean and in good health.

Source: Sooty Feathers Tell the History of Pollution in American Cities by Alex Furuya, Audubon

On October 17th, 2017 we learned about

Optimistic findings about preventing fires by reducing the amount of flammable fuel in forests

With yet another wildfire filling our skies with smoke, it’s starting to feel like California will never stop burning. The state experienced an unusually rainy winter that thankfully helped fend off a multi-year drought, spurring new plant growth at the same time. Unfortunately, all that vegetation was dried out in record-setting summer heat. From that perspective these fires feel somewhat inevitable, since we can’t stop the rain and many people in power seem intent on avoiding doing much to curb climate emissions that help make more extreme temperatures. However, there’s still opportunities to reduce our fire risks by thinning out the forests themselves, either mechanically or with controlled burns. These aren’t easy tasks to take on, but studies suggest that strategic thinning may reduce some of the costs and logistics associated with wildfire prevention.

For millions of years, forests have occasionally caught fire. In this time, they’ve adapted to make the most of blazes naturally caused by things like lightning strikes, in some cases even evolving pine cones that only open in a fire’s extreme heat. Humans have thrown this balancing act off a bit though, as we both help start fires more often with sparking cars, campfires and cigarettes, but also rush to put those fires out as soon as possible. The result is that forests are now denser than before, not just with living plants but also dry, dead branches, pine needles and more. This means that when a fire does start up, it’s got a lot more fuel to burn, and can get out of control much more quickly.

Small burns aren’t bad

A controlled burn certainly works, because it’s intended to be a safer version of a good lightning strike. Burning a small area ideally clears out dry tinder, but can then be contained before it becomes a problem. Detractors to this method have worried about the fires getting out of control, but also about unintended damage to the environment. To see if prescribed burns were harming plants or animals, the U.S. Forest Service and six universities embarked on detailed studies of the flames’ effects on the affected environment. While there’s obviously smoke and soot after a burn, a smaller fire caused no measurable harm. If anything, plant diversity increased and trees seemed more resilient to things like bark beetles after a small fire. This makes sense, because the more frequent fires of the past would have been smaller on average, and thus something these ecosystems have been able to adapt to.

Mechanical thinning, for less money

Mechanical thinning doesn’t risk running out of control like a fire, and aside from some diesel exhaust, shouldn’t introduce widespread threats to the environment. Instead, detractors bring up the prices and logistics of sending in personnel to clear brush and remove trees, as it can become a huge task in a large forest. Real world experiments were, appropriately, cost prohibitive, so biologists from the University of New Mexico ran simulations of two approaches to mechanical thinning. One option tested the effectiveness thinning vast ranges of land, while the other looked at scenarios where only areas that were considered to be higher risk were dealt with. With all other things being equal, both strategies reduced the severity of simulated fires by as much as 60 percent. This may sound inconclusive until you compare the difficulty of either approach, and realize that the much simpler, cheaper option of thinning only high-risk areas of a forest offers the same benefits for a much smaller price. This means that well-planned mechanical thinning may be more affordable than people previously understood.

If these last two weeks are anything to go by, it looks like we’ll unfortunately have ample opportunities to put these prevention methods to work in the coming years.

Source: Fighting Fires Before They Spark, Scienmag

On October 16th, 2017 we learned about

Currency made from fruit bat teeth offers an opportunity for conservation

How much is a tooth worth? It probably depends on who you ask. A tooth that needs saving at the dentist can get pretty pricey, while a baby tooth that falls out might net around a dollar from the tooth fairy. For mammals like giant fruit bats living in the Solomon Islands, a mouth full of teeth may cost them their lives. Traditional practices on various islands use bat teeth as a form of currency, primarily for ceremonial events like weddings. This, along with the large bats’ meat, has led to increased hunting which is now threatening the safety of various bat species. The good news is that the demand for bat teeth may also turn out to be a way to help keep these same species alive.

Hunting bats for protein and profit

As their name implies, giant fruit bats eat fruit and are big. The Pacific flying fox (Pteropus tonganus), for example, can have a three-foot wingspan while weighing a under two pounds. That may be smaller than your average chicken, but it’s big enough to make these bats a target for islanders looking for scarce sources of protein. It also means that the bats grow teeth large enough to trade and even drill holes in for use in jewelry. While P. tonganus aren’t technically endangered yet, they’re one of many species of bat that are hunted on the Solomon Islands without much care for population management or conservation.

Dietary needs are of course hard to ignore, but trading in teeth has certainly raised a few eyebrows throughout history. Solomon Islanders have been using teeth as currency for centuries, with the practice temporarily dropping off in the 19th century, around the arrival of Christian missionaries. The teeth haven’t only come from bats either, as dolphins have also been hunted for their teeth and meat in a similar manner to the bats. These practices saw a revival around 1948, and while younger islanders feel like these traditions are once again on the decline, they’re still significant enough to make an impact on local ecology. Since these bats are key seed dispersers for the islands, any shift in their populations can spell trouble for the plants, and other animals, that depend on them.

Using culture to motivate conservation

Conservationists focusing on fruit bats suggest that the continuing use of teeth may actually be an opportunity. The fruit bats need better protections from hunting, but also from indirect threats like habitat loss where their deaths are simply an unfortunate byproduct of other goals. However, if the bats’ teeth retain their cultural value, than the bats’ lives will too. The hope is that educating people about the bats’ vulnerability will inspire people to protect them as part of preserving their people’s traditions. Banning hunting outright might help in the short term, but it probably won’t make people feel invested in the bats’ continued success on the islands either, exposing them to further habitat degradation. Promoting teeth as tender as a way to save bat lives may seem counterintuitive, but it’s not a terribly far-fetched idea. Other animals, from sharks to pigs, may also stand a better chance at survival if humans maintain our reason to kill some (but not all) of them.

Source: How to save giant tropical fruit bats: Work with local hunters who use bat teeth as money

On October 9th, 2017 we learned about

White-tailed deer’s dietary preferences inadvertently encourage invasive plant species

White-tailed deer are picky eaters, which poses bigger problems than your usual worries about dietary health. The North American ruminants now live in such dense populations that they make a big impact on whatever plants they choose to eat. Those preferences do shift seasonally, but with millions of deer now living in the United States, that basically means that almost every plant gets a turn to be over-foraged. Experiments have found a key exception to this pattern though, and it’s one conservationists wish the deer didn’t make.

Making space for the wrong species

White-tailed deer (Odocoileus virginianus) have long been known to devour whatever they can reach, but ecologists noticed a possible preference for native species of plants. To test just how choosy deer were, 23 plots of land in various white-tail habitats were fenced off so that the plants living there could be measured and compared. Some plots allowed deer to enter and eat, while others kept the deer out. Scientists were then able to quantify just how much of an impact the deer made on each plant species in a plot, revealing which plants they preferred and which they passed over.

Somewhat unsurprisingly, the deer liked what their ancestors liked. Probably thanks to a genetic predisposition for certain plants that were safe and healthy to eat, the deer ate more native plants than species that were imported or invasive. Importantly, this didn’t change the overall amount of plant growth in a plot, just the composition of those plants. So while a plot may have started out with 50 percent native plants and 50 percent invasive plants, the deer were essentially clearing out the native plants allowing the invasive species to claim the rest of the space. This isn’t just a problem for the native plant species, since the deer were inadvertently promoting the spread of plants that they don’t want to eat, possibly upending their dietary preferences in the future.

Population problems

While the white-tailed deer seem to be making bad situations worse, it’s not entirely their fault. Invasive garlic mustard (Alliaria petiolata), for example, was imported to North America by people as an herb in cooking, but now dominates eastern forests without many natural predators. The deer themselves followed a similar pattern. While they were once hunted to dangerously low levels, conservation laws have helped white-tailed deer populations rebound in the 20th century. However, the deer’s predators like wolves and bears haven’t been so lucky, leaving the deer to multiply unchecked. People now hunt and try to curb deer populations to a degree, but we’re not quite as good at managing their numbers as balanced food-web would be. Since the deer are on course to eat their favorite foods out from under themselves, it appears that the deer aren’t good at managing their populations either.

Source: Deer prefer native plants leaving lasting damage on forests by Lindsey Hadlock, Cornell University Media Relations