Contributors

Jeremy England remembers learning about proteins and protein folding in high school and being struck by how biology works at the molecular level , where biology , chemistry , and physics intersect .
England graduated from Harvard University with a degree in biochemical sciences in 2003 , then received a Rhodes Scholarship and studied physics at the University of Oxford .
He then completed a PhD in physics at Stanford University in 2009 and worked as a postdoc at Princeton University before joining the faculty at MIT .
There , he set his mind on studying self-copying and self-replication of @ @ @ @ @ @ @ rules that constrain when those processes can or should happen .
From this research , he pieced together a theory to explain the spontaneous emergence of life based on how collections of molecules learn to obtain and use energy more efficiently—a process he calls dissipative adaptation .
“ Once you study life as a physicist and you see , from the perspective of physics , how impressive life is at accomplishing very complicated functional tasks using just a combination of the right physical principles and how they interact in some particular architecture , @ @ @ @ @ @ @ ” England says .
In 2019 , he left MIT to work at GlaxoSmithKline as one of the company ’ s senior directors in artificial intelligence and machine learning .
England also maintains a research position in physics at the Georgia Institute of Technology .
In this issue , England takes a deep dive into dissipative adaptation and reconsiders life ’ s origin .
Matan Shelomi was in the third grade when he learned the word “ entomologist.
” “ I decided I needed to memorize it , ” he says , “ @ @ @ @ @ @ @ to be.
” As a child growing up in Queens , New York , Shelomi didn ’ t have the opportunity to see many wild animals—besides the ants in his family ’ s apartment , he jokes—but he did have access to Pokémon , the multimedia franchise that allows players to collect and evolve fictional creatures , some of which resemble real insects .
In 2014 , after receiving his bachelor ’ s degree in organismic and evolutionary biology at Harvard University , Shelomi completed a PhD at the University of California , @ @ @ @ @ @ @ stick insects .
Shelomi next moved to Germany for a postdoc at the Max Planck Institute for Chemical Ecology before accepting a professorship at National Taiwan University in 2017 .
Like most academics , Shelomi frequently receives emails from predatory journals asking to publish his work .
Eventually , he became so frustrated that he decided to submit a fabricated , Pokémon-themed article to Plant Biochemistry and Physiology in 2019 .
Shelomi has since had almost a dozen papers accepted in nine predatory journals , each manuscript containing fictitious references to pop culture @ @ @ @ @ @ @ bad practices .
In March of this year , Shelomi published a piece claiming that SARS-CoV-2 stemmed from a bat-like Pokémon ( see “ Opinion : Using Pokémon to Detect Scientific Misinformation ” ) to demonstrate how damaging such misinformation can be , and to teach others how to spot it .
“ What these journals are doing is fraud , ” Shelomi tells The Scientist .
“ If anyone can publish anything and call it a scientific paper , the door is wide open for anyone to make false claims.
” From @ @ @ @ @ @ @ to draw , but she also loved science .
Her mother was an art teacher and three of her sisters graduated from art school .
Winslow took a slightly different path , majoring in biological sciences at Mount Holyoke College in Massachusetts .
Upon graduating , she worked in a lab at Duke University researching muscular dystrophy , and then at the Massachusetts Mental Health Center ’ s Neuropsychopharmacology Lab ( while employed by Harvard University ) .
Ultimately , she was able to combine her interests by enrolling in Johns Hopkins School @ @ @ @ @ @ @ to Medicine program , where she received a master ’ s in medical and biological illustration in 1984 .
Since then , Winslow has maintained a medical and scientific illustration business , and her art has appeared in textbooks , journals , magazines , and electronic media .
Winslow says she is particularly proud of her work for the National Cancer Institute , where her illustrations can be found on the webpage summaries for most cancers .
Both of Winslow ’ s parents , three of her siblings , and ten other relatives @ @ @ @ @ @ @ “ I have a personal interest in helping people with cancer.
” She admits that she often uses her family members as models for her illustrations .
She ’ s used her son as a model in illustrations of head and neck cancers , for example , and her daughter for a drawing of thyroid cancer .
“ My poor husband is in colonoscopy illustrations , ” Winslow says .
In this issue , she illustrates how vaccines train innate immunity ; for this infographic , she used her daughter ’ s neighbor @ @ @ @

KATHERINE TAYLOR
Jeremy England remembers learning about proteins and protein folding in high school and being struck by how biology works at the molecular level, where biology, chemistry, and physics intersect. England graduated from Harvard University with a degree in biochemical sciences in 2003, then received a Rhodes Scholarship and studied physics at the University of Oxford. He then completed a PhD in physics at Stanford University in 2009 and worked as a postdoc at Princeton University before joining the faculty at MIT. There, he set his mind on studying self-copying and self-replication of cells and organisms, aiming to derive rules that constrain when those processes can or should happen. From this research, he pieced together a theory to explain the spontaneous emergence of life based on how collections of molecules learn to obtain and use energy more efficiently—a process he calls dissipative adaptation.
“Once you study life as a physicist and you see, from the perspective of physics, how impressive life is at accomplishing very complicated functional tasks using just a combination of the right physical principles and how they interact in some particular architecture, it’s really quite marvelous,” England says. In 2019, he left MIT to work at GlaxoSmithKline as one of the company’s senior directors in artificial intelligence and machine learning. England also maintains a research position in physics at the Georgia Institute of Technology. In this issue, England takes a deep dive into dissipative adaptation and reconsiders life’s origin.
MATAN SHELOMI, MPI-CE
Matan Shelomi was in the third grade when he learned the word “entomologist.” “I decided I needed to memorize it,” he says, “because that’s what I wanted to be.” As a child growing up in Queens, New York, Shelomi didn’t have the opportunity to see many wild animals—besides the ants in his family’s apartment, he jokes—but he did have access to Pokémon, the multimedia franchise that allows players to collect and evolve fictional creatures, some of which resemble real insects. In 2014, after receiving his bachelor’s degree in organismic and evolutionary biology at Harvard University, Shelomi completed a PhD at the University of California, Davis, studying the digestive physiology of stick insects. Shelomi next moved to Germany for a postdoc at the Max Planck Institute for Chemical Ecology before accepting a professorship at National Taiwan University in 2017.
Like most academics, Shelomi frequently receives emails from predatory journals asking to publish his work. Eventually, he became so frustrated that he decided to submit a fabricated, Pokémon-themed article to Plant Biochemistry and Physiology in 2019. Shelomi has since had almost a dozen papers accepted in nine predatory journals, each manuscript containing fictitious references to pop culture and directly calling out the journals’ bad practices. In March of this year, Shelomi published a piece claiming that SARS-CoV-2 stemmed from a bat-like Pokémon (see “Opinion: Using Pokémon to Detect Scientific Misinformation”) to demonstrate how damaging such misinformation can be, and to teach others how to spot it. “What these journals are doing is fraud,” Shelomi tells The Scientist. “If anyone can publish anything and call it a scientific paper, the door is wide open for anyone to make false claims.”
JANE WINSLOW
From a young age, Terese Winslow loved to draw, but she also loved science. Her mother was an art teacher and three of her sisters graduated from art school. Winslow took a slightly different path, majoring in biological sciences at Mount Holyoke College in Massachusetts. Upon graduating, she worked in a lab at Duke University researching muscular dystrophy, and then at the Massachusetts Mental Health Center’s Neuropsychopharmacology Lab (while employed by Harvard University). Ultimately, she was able to combine her interests by enrolling in Johns Hopkins School of Medicine’s Art as Applied to Medicine program, where she received a master’s in medical and biological illustration in 1984. Since then, Winslow has maintained a medical and scientific illustration business, and her art has appeared in textbooks, journals, magazines, and electronic media. Winslow says she is particularly proud of her work for the National Cancer Institute, where her illustrations can be found on the webpage summaries for most cancers. Both of Winslow’s parents, three of her siblings, and ten other relatives all had cancer, she says. “I have a personal interest in helping people with cancer.”
She admits that she often uses her family members as models for her illustrations. She’s used her son as a model in illustrations of head and neck cancers, for example, and her daughter for a drawing of thyroid cancer. “My poor husband is in colonoscopy illustrations,” Winslow says. In this issue, she illustrates how vaccines train innate immunity; for this infographic, she used her daughter’s neighbor as a model.


thescientist--2020-11-01--Herbivore Body Size Influences Grazing Behavior, Poop Quality

The paper E. le Roux et al.
, “ Animal body size distribution influences the ratios of nutrients supplied to plants , ” PNAS , doi:10.1073/pnas.2003269117 , 2020 .
Animals eat plants .
Animals poop .
Poop nourishes plants .
It may sound simple , but it ’ s not .
Elizabeth le Roux , an ecologist and Newton International Fellow at the University of Oxford , studies this complex cycle in the South African savanna , particularly as it relates to larger animals and how they differ from small species in their effects on ecosystems .
As a graduate @ @ @ @ @ @ @ Africa , le Roux began investigating how animal dung varies across the grassy plains of Hluhluwe-iMfolozi Park and whether that variation influences the local plant life .
At 15 sites , she and her colleagues assessed the density of the vegetation , used camera traps to record how many of each animal species frequented a particular area and how long they stayed , surveyed the amount of dung and noted what species it came from , and sampled dung , soil , and plants to assess nitrogen and phosphorus levels .
The team @ @ @ @ @ @ @ be frequented by large animals , which are less likely to be targets for lions and other predators that sneak up in the foliage .
Indeed , camera traps showed that smaller grazers such as impala stick mainly to open areas , while elephants and rhinos often graze at denser sites .
When it came to the animals ’ dung , the team predicted that larger animals would excrete proportionally less phosphorus .
That ’ s because larger animals have relatively larger skeletons , le Roux says , and thus may require more @ @ @ @ @ @ @ , too , was supported by the data—phosphorus was scarcer in larger animals ’ dung , both as a proportion of dung mass and relative to nitrogen content .
The researchers also analyzed the grasses at their sites to see if dung nutrient differences were reflected in plant tissue .
Here , the data hinted that phosphorus : nitrogen ratios may be lower in grasses in vegetation-dense areas frequented by large herbivores , but the effect was weak .
That ’ s not surprising , le Roux says , as plant nutrient ratios @ @ @ @ @ @ @ , such as soil microbes and fire .
Ecologist Harry Olde Venterink of Vrije Universiteit Brussel praises the study for its innovative use of camera traps to collect quantitative data on animal behavior , and says it provides good evidence that larger animals are using sites differently than smaller ones and may be influencing nutrient availability via their dung .
His team recently showed that herbivore dung quality in Europe influences plant community diversity ( Sci Rep , 9:5675 , 2019 ) , and he says the new study is a further step @ @ @ @ @ @ @ .
However , Venterink questions some of the study ’ s assertions—in particular , the idea that species with larger skeletons need more phosphorus , a connection le Roux agrees isn ’ t well established .
Venterink suggests that differences in dung nutrients could simply reflect differences in animals ’ diets .
Le Roux says the findings could help researchers understand the effects of adding or removing larger species from ecosystems .
As humans influence wild animal populations , often “ we ’ re changing the average [ body ] size of the @ @ @ @ @ @ @ “ We need to understand : What are the consequences ?
”

ABOVE: © ISTOCK.COM, NICOLAMARGARET
EDITOR’S CHOICE IN ECOLOGY & ENVIRONMENT
The paper
E. le Roux et al., “Animal body size distribution influences the ratios of nutrients supplied to plants,” PNAS, doi:10.1073/pnas.2003269117, 2020.
Animals eat plants. Animals poop. Poop nourishes plants. It may sound simple, but it’s not. Elizabeth le Roux, an ecologist and Newton International Fellow at the University of Oxford, studies this complex cycle in the South African savanna, particularly as it relates to larger animals and how they differ from small species in their effects on ecosystems.
As a graduate student at Nelson Mandela University in South Africa, le Roux began investigating how animal dung varies across the grassy plains of Hluhluwe-iMfolozi Park and whether that variation influences the local plant life. At 15 sites, she and her colleagues assessed the density of the vegetation, used camera traps to record how many of each animal species frequented a particular area and how long they stayed, surveyed the amount of dung and noted what species it came from, and sampled dung, soil, and plants to assess nitrogen and phosphorus levels.
PDF BIG DUNG: Areas with denser vegetation and thus lower visibility (left) are more likely to be frequented by larger animals—which have less to fear from predators—than by smaller animals, according to a recent study. Compared with smaller herbivores such as impala, large herbivores such as elephants and rhinos produce dung with relatively lower phosphorus content. These differences in dung are associated with variable availability of nutrients for plants growing in the savanna, the researchers found, suggesting that the animals’ body sizes could influence ecosystem functioning. WEB © Melanie Lee
The team hypothesized that vegetation-dense, low-visibility areas would be frequented by large animals, which are less likely to be targets for lions and other predators that sneak up in the foliage. Indeed, camera traps showed that smaller grazers such as impala stick mainly to open areas, while elephants and rhinos often graze at denser sites.
When it came to the animals’ dung, the team predicted that larger animals would excrete proportionally less phosphorus. That’s because larger animals have relatively larger skeletons, le Roux says, and thus may require more phosphorus from their food. This hypothesis, too, was supported by the data—phosphorus was scarcer in larger animals’ dung, both as a proportion of dung mass and relative to nitrogen content.
The researchers also analyzed the grasses at their sites to see if dung nutrient differences were reflected in plant tissue. Here, the data hinted that phosphorus:nitrogen ratios may be lower in grasses in vegetation-dense areas frequented by large herbivores, but the effect was weak. That’s not surprising, le Roux says, as plant nutrient ratios are influenced by factors other than dung, such as soil microbes and fire.
Ecologist Harry Olde Venterink of Vrije Universiteit Brussel praises the study for its innovative use of camera traps to collect quantitative data on animal behavior, and says it provides good evidence that larger animals are using sites differently than smaller ones and may be influencing nutrient availability via their dung. His team recently showed that herbivore dung quality in Europe influences plant community diversity (Sci Rep, 9:5675, 2019), and he says the new study is a further step toward deciphering how animals influence nutrient cycles.
However, Venterink questions some of the study’s assertions—in particular, the idea that species with larger skeletons need more phosphorus, a connection le Roux agrees isn’t well established. Venterink suggests that differences in dung nutrients could simply reflect differences in animals’ diets.
Le Roux says the findings could help researchers understand the effects of adding or removing larger species from ecosystems. As humans influence wild animal populations, often “we’re changing the average [body] size of the herbivore community,” she says. “We need to understand: What are the consequences?”


thescientist--2020-11-01--Infographic: How Vaccines Train Innate Immunity

While researchers have observed for decades that certain vaccines seem to help recipients ward off more than just the target pathogen , only in recent years have they identified possible mechanisms for these bonus benefits .
For example , in a study published this year ( depicted here ) , researchers examined immune cells from the blood and bone marrow of healthy adults before and after they received a live tuberculosis vaccine known as bacille Calmette-Guérin , or BCG .
In the bone marrow post-vaccination , genes are expressed that trigger hematopoietic stem and progenitor cells to differentiate into monocytes @ @ @ @ @ @ @ cells .
In a separate analysis of the effects of BCG in newborns , the researchers found that the vaccine ramped up the number of neutrophils in babies ’ blood compared with unvaccinated infants .
Monocytes from the blood displayed epigenetic changes after vaccination that opened chromatin harboring multiple genes involved in driving an inflammatory response , making them more accessible for transcription .
Meanwhile , chromatin closed around genes associated with immune tolerance .
When exposed to the fungal pathogen Candida albicans in vitro , immune cells sampled from patients ’ blood @ @ @ @ @ @ @ the cytokine interleukin 1β , which mediates inflammation , than did cells from blood drawn from the same individuals before vaccination .

ABOVE: © TERESE WINSLOW
While researchers have observed for decades that certain vaccines seem to help recipients ward off more than just the target pathogen, only in recent years have they identified possible mechanisms for these bonus benefits. For example, in a study published this year (depicted here), researchers examined immune cells from the blood and bone marrow of healthy adults before and after they received a live tuberculosis vaccine known as bacille Calmette-Guérin, or BCG.
© TERESE WINSLOW
In the bone marrow post-vaccination, genes are expressed that trigger hematopoietic stem and progenitor cells to differentiate into monocytes, neutrophils, and other so-called myeloid cells. In a separate analysis of the effects of BCG in newborns, the researchers found that the vaccine ramped up the number of neutrophils in babies’ blood compared with unvaccinated infants.
© TERESE WINSLOW
Monocytes from the blood displayed epigenetic changes after vaccination that opened chromatin harboring multiple genes involved in driving an inflammatory response, making them more accessible for transcription. Meanwhile, chromatin closed around genes associated with immune tolerance.
When exposed to the fungal pathogen Candida albicans in vitro, immune cells sampled from patients’ blood 90 days after vaccination released more of the cytokine interleukin 1β, which mediates inflammation, than did cells from blood drawn from the same individuals before vaccination.
Read the full story.
Correction (November 13): Incorrect labels of the open and closed chromatin in the graphic have been corrected. The Scientist regrets the error.


thescientist--2020-11-01--Slideshow: How Ecologists Study the World’s Apex Predators

ABOVE : The female jaguar Isis is part of a breeding project in the Iberá wetlands in Argentina .
Her offspring will be reintroduced into the wild .
MATÍAS REBAK Around the world , predators have powerful , yet diverse and nuanced effects on the living world around them .
These effects often manifest as trophic cascades , whereby predators indirectly influence the abundance of plants or other organisms at the bottom of the food web , either by killing their herbivore prey or changing prey behavior .
So far , much knowledge about the role of apex predators is @ @ @ @ @ @ @ on the effects of their population declines .
But researchers around the world are using a number of experimental approaches to produce stronger evidence , and in some cases , are actively tracking the effects of predator reintroductions to secure a better understanding of the animals ’ ecological roles .
Scientists are poised to monitor changes both in abundance and behavior of large rodents known as capybaras ( Hydrochoerus hydrochaeris ) after the jaguars return .
If capybaras spend more time on the lookout for their predators , they could spend less time @ @ @ @ @ @ @ grasses .
Ecologists were able to demonstrate the trophic cascade by constructing exclosures to experimentally exclude vicuñas from particular patches of ground .
In the relatively flat , sparsely vegetated areas of the park where pumas are easily spotted by vicuñas and less likely to hunt there , grass flourished inside the exclosures , demonstrating that those areas were subject to heavy grazing .
This was not the case in meadows with tall grass and rocky canyons where pumas could hunt more efficiently .
Fishing for trophic cascades in the ocean One study @ @ @ @ @ @ @ of barking dogs , they foraged fewer crabs and other seafood , showing that trophic cascades can be triggered through fear of predators alone .

ABOVE: The female jaguar Isis is part of a breeding project in the Iberá wetlands in Argentina. Her offspring will be reintroduced into the wild.
MATÍAS REBAK
Around the world, predators have powerful, yet diverse and nuanced effects on the living world around them. These effects often manifest as trophic cascades, whereby predators indirectly influence the abundance of plants or other organisms at the bottom of the food web, either by killing their herbivore prey or changing prey behavior.
So far, much knowledge about the role of apex predators is based on correlational evidence, often based on the effects of their population declines. But researchers around the world are using a number of experimental approaches to produce stronger evidence, and in some cases, are actively tracking the effects of predator reintroductions to secure a better understanding of the animals’ ecological roles.
How wolves changed Yellowstone
The reintroduction of more than 40 gray wolves (Canis lupus) to Yellowstone National Park in the 1990s has become the best-known predator reintroduction, yet researchers still debate the wild canid’s precise ecological role. FLICKR , JACOB W. FRANK, NATIONAL PARK SERVICE
Early studies from Yellowstone spearheaded by Oregon State University ecologists William Ripple (pictured) and Robert Beschta show that aspen trees are taller in streamside areas frequented by wolves, suggesting that the predators are indirectly boosting tree growth by deterring vegetation-munching elk from visiting those areas. FLICKR , ROBERT BESCHTA, OREGON STATE UNIVERSITY
More-recent research by Colorado State University and others involving measurements and experimentally constructed dams suggests that some tree species in Yellowstone, such as willows that grow on streambanks, haven’t regenerated following wolf reintroduction. DAVID COOPER, COLORADO STATE UNIVERSITY
TOM HOBBS, COLORADO STATE UNIVERSITY
Returning jaguars to the world’s second-largest wetland
In the next couple of months, conservationists at Argentina’s Iberá wetlands hope to release five jaguars, including the two-year old Mbareté (pictured). MATÍAS REBAK
Scientists are poised to monitor changes both in abundance and behavior of large rodents known as capybaras (Hydrochoerus hydrochaeris) after the jaguars return. If capybaras spend more time on the lookout for their predators, they could spend less time eating, affecting the growth of local grasses. RAFAEL ABUíN
CONSTANZA PASIAN
Tracking wild dogs in Gorongosa
In Mozambique, ecologists are monitoring the ecological impact of reintroducing wild dogs (Lycaon pictus) into Gorongosa National Park in an extensive project involving GPS collars and scat analyses for predator and prey, as well as satellite imagery. © JEN GUYTON
In studies involving GPS-collared antelopes such as bushbuck (Tragelaphus sylvaticus), ecologists have found that the loss of wild dogs and other apex carnivores during Mozambique’s civil war have altered the herbivores’ behavior, making them less vigilant of their predators. © JEN GUYTON
Pumas prowl the high Andes
In Argentina’s San Guillermo National Park in the Andean mountains, ecologists have found that vicuña (Vicugna vicugna), a relative of the llama, are more vigilant in areas where pumas (Felis concolor) are a greater threat, affecting the local vegetation. MARCO ESCUDERO
JOE RIIS
Ecologists were able to demonstrate the trophic cascade by constructing exclosures to experimentally exclude vicuñas from particular patches of ground. In the relatively flat, sparsely vegetated areas of the park where pumas are easily spotted by vicuñas and less likely to hunt there, grass flourished inside the exclosures, demonstrating that those areas were subject to heavy grazing. This was not the case in meadows with tall grass and rocky canyons where pumas could hunt more efficiently. EMILIANO DONADIO
Fishing for trophic cascades in the ocean
In Shark Bay, Australia, researchers used exclosures to help demonstrate that dugongs (Dugong dugon) and sea turtles (Chelonia mydas) graze heavily in areas that aren’t patrolled by tiger sharks (Galeocerdo cuvier). SHARK BAY ECOSYSTEM RESEARCH PROJECT
Research is also underway to characterize a long-held hypothesis that “grazing halos,” white barren rings such as these spots visible in the Red Sea, result from the eating activity of reef fish, which don’t venture far from their rocky refuge due to the risk of predation. CNES/AIRBUS; DIGITALGLOBE
Using sound to scare prey
Some ecologists study the behavioral influence of predators on their prey by playing the carnivores’ vocalizations. Automated behavioral response systems such as the one pictured couple playback devices with a camera trap to document the prey animal’s response to hearing a predator. LIANA ZANETTE, WESTERN UNIVERSITY
One study demonstrated that when racoons heard the sounds of barking dogs, they foraged fewer crabs and other seafood, showing that trophic cascades can be triggered through fear of predators alone.
LIANA ZANETTE AND JUSTIN SURACI
Not only do large apex predators, such as mountain lions (another name for pumas, (Felis concolor) instill fear in others, they themselves are afraid of humans, suggesting that Homo sapiens is the ultimate predator. LIANA ZANETTE, WESTERN UNIVERSITY
Read the full story.


thescientist--2020-11-01--Can Rewilding Large Predators Regenerate Ecosystems?

The jaguars don ’ t know it yet , but soon they ’ ll be free to roam Argentina ’ s Iberá wetlands , becoming the first apex predators to do so in a century .
Three adults and the two-year-olds Amarí and Mbareté currently live in an enclosure on San Alonso , a patch of high ground in Iberá ’ s patchwork of flooded wilderness , lagoons , jungle , and grasslands .
Once a pristine habitat , the region has lost much of its wildlife since the early 20th century , when ranchers moved into the area .
@ @ @ @ @ @ @ livestock , and many species were decimated to satisfy a burgeoning market for fur , leather , and feathers .
Now , wildlife is making a comeback in Iberá , thanks to an ecological restoration effort spearheaded by the nonprofit Rewilding Argentina Foundation .
Because of the region ’ s now-protected status and the reintroduction of locally extirpated species to reconstruct ecological communities , the area is thriving with pampas deer and marsh deer , capybaras , caimans , and diverse bird and insect life .
Yellow anacondas have also been spotted .
@ @ @ @ @ @ @ conservationists hope to install one of the final missing ecological pieces—an apex predator—with the release of the jaguars .
To Emiliano Donadio , the foundation ’ s scientific director , the release not only is crucial to rebuilding Iberá ’ s ancient ecosystem , but is a scientific experiment that will provide a rare glimpse of how the return of one of the world ’ s largest carnivores could transform an ecosystem .
Scientists know that losing large predators can have far-reaching , disruptive effects on ecosystems through cascading forces that reverberate from @ @ @ @ @ @ @ the food web—to their prey and beyond , even sculpting the abundance and structure of plant life .
The loss of jaguars ( Panthera onca ) , pumas ( Felis concolor ) , and other predators from fragments of the Venezuelan rainforest after the construction of a hydro-electric dam , for instance , is thought to be a key factor in triggering an explosive proliferation of herbivores including monkeys , which ravaged the vegetation and caused what researchers described as an “ ecological meltdown.
” But seldom do ecologists get to investigate whether @ @ @ @ @ @ @ restoring predators .
“ We think that an ecosystem devoid of predators will be in better shape when the predators come back , ” Donadio says , but that supposition remains largely untested .
Part of the problem is , while it ’ s well accepted that large carnivores play vital ecological roles , just how they shape ecosystems through cascading effects in different environments isn ’ t well understood .
In addition , predator reintroductions such as the ongoing project in Iberá are extremely rare and have lagged greatly behind herbivore rewilding @ @ @ @ @ @ @ animals capable of killing people and livestock is so controversial .
“ We only have so many natural experiments , ” notes wildlife ecologist Justine Smith of the University of California , Davis .
In the absence of firm evidence , conservationists have been eager to interpret early predator reintroduction studies—largely based on the purported regenerative ecological effects of returning gray wolves ( Canis lupus ) to Yellowstone National Park in the mid-1990s—as a rationale for bringing predators back to many parts of the globe .
In Colorado , for instance , conservation @ @ @ @ @ @ @ push for the approval of a bill on the November ballot that would effectively mandate wolf reintroduction in the state to restore the ecosystem ’ s “ natural balance.
” But some ecologists caution that the ecological outcomes of such projects are unclear .
In search of answers , scientists are employing novel approaches to study the ecological roles of large carnivores , from the African savannah and the Andean plateau to the ocean , and to understand how ecosystems change as they are lost or reintroduced .
What they ’ re finding @ @ @ @ @ @ @ nuanced and complex effects that ripple through food webs in what are known as trophic cascades—effects that depend not only on the nature of the hunter itself , but also on characteristics of its prey and the habitat the animals share .
“ There ’ s still good reason to believe that trophic cascades will .
.
.
occur in many systems , ” Smith says .
“ It ’ s just that we don ’ t really have all the data yet to understand exactly when , where , and why.
” @ @ @ @ @ @ @ a simple question : “ Why is the world green ?
” In the late 1950s , when ecologists Nelson Hairston , Frederick Smith , and Lawrence Slobodkin were pondering this question , the prevailing notion was that the abundances of animals that inhabit ecosystems depend solely on the amount of plants and nutrients at the bottom of the food web .
Herbivore numbers were determined by the abundance of vegetation , and predator numbers by herbivore abundance .
But the three University of Michigan scientists suggested in a 1960 paper in The @ @ @ @ @ @ @ t controlled by the availability of plants alone , because predators were also playing a key role , and that by managing herbivore populations , predators indirectly protected vegetation .
This idea was quickly met with fierce criticism , and to be fair , there wasn ’ t any robust evidence for their hypothesis at the time .
That was a gap that one of Smith ’ s students , Robert Paine , was determined to fill .
In the early 1960s , Paine regularly ventured out to Washington State ’ s Makah @ @ @ @ @ @ @ , mussels , limpets , and the predatory starfish Pisaster ochraceus to conduct an experiment that would become one of ecology ’ s most famous .
From a 25-foot-long stretch of rock , he pried off the starfish and flung them into the ocean , while leaving another stretch unaltered .
Over the course of a year , Paine noticed that life on the starfish-less rock transformed .
The starfish ’ s main prey , the barnacle Balanus glandula , began to take over , followed by fast-growing mussel species , crowding out @ @ @ @ @ @ @ 15 invertebrate species dwindled to 8 .
Paine concluded that by keeping its prey in check , the Pisaster starfish was helping to maintain biodiversity .
Despite being small in number , the five-legged predator was performing a crucial ecological function that earned its recognition as the first ever “ keystone species.
” Paine ’ s belief that predators are ecologically important , and his recognition that their roles are best understood by studying animal communities that have been perturbed , inspired ecologist Jim Estes , then a PhD student at the University @ @ @ @ @ @ @ Enhydra lutris ) inhabiting the lush kelp forests around the Alaskan island of Amchitka .
After a brief meeting with Paine in 1971 , Estes decided to visit nearby islands where otters had been wiped out during the fur trade and immediately noticed a difference .
“ When I looked down at the seafloor , I was stunned by the vast numbers of urchins and absence of kelp , ” Estes , who is now at the University of California , Santa Cruz , wrote in a 2016 memoir about his work .
@ @ @ @ @ @ @ were playing a key ecological role , he observed : by keeping urchins in check , the marine mammals limited the invertebrates ’ consumption of kelp , thereby regulating the abundance of life-giving plants at the bottom of the food web .
In a 1979 lecture , Paine coined the term trophic cascades to describe these indirect effects .
Estes ’ s observations were quickly followed by a series of observations from other researchers that pointed to the existence of trophic cascades in other aquatic ecosystems , such as those in lakes and @ @ @ @ @ @ @ Schmitz , an ecologist at Yale School of the Environment , discovered that a terrestrial predator , the nursery web spider Pisaurina mira , could similarly create a trophic cascade , although in this case he uncovered an entirely different mechanism .
It turns out that the spiders didn ’ t have to kill their prey to affect the ecosystem ; they just had to scare them into skipping a meal .
Schmitz placed leaf-chewing grasshoppers , specifically Melanoplus femurrubrum , in a small , grass- and herb-filled enclosure , and observed that @ @ @ @ @ @ @ web hunting spiders , even without any immediate change in grasshopper numbers .
Then , in a series of experiments in which Schmitz glued the spiders ’ mouthparts shut so they could still instill fear but not consume their prey , he demonstrated that their mere presence was enough to allow grasses to flourish , as grasshoppers would forgo a meal to avoid becoming one .
Biologists now call such fear-driven effects behaviorally mediated trophic cascades , distinguishing them from density-mediated ones that involve the predators ’ consumption of their prey .
See @ @ @ @ @ @ @ Us About Fear ” These behavioral effects come at a long-term cost to prey that can ultimately lead to declines in population densities .
Avoiding the spiders caused some of Schmitz ’ s grasshoppers to starve , and their populations eventually dwindled .
In a menagerie of animals , the sheer fear of predation can affect prey species ’ metabolism , stress hormone levels , neurophysiology , and reproduction .
In the forests of the southern Gulf Islands off the coast of British Columbia , Canada , for instance , Western University ecologist @ @ @ @ @ @ @ that hearing the sounds of predatory birds and raccoons throughout a breeding season can cause song sparrows ( Melospiza melodia ) to reduce the number of young they produce by 40 percent .
“ The role of predators is way greater than we ever previously imagined , ” she says .
What remains unclear is how common such trophic cascades are in nature , Estes notes .
“ What I think is probably one of the biggest outstanding questions in this part of ecology [ is ] just how repeatable , how generalizable @ @ @ @ @ @ @ challenge in studying the ecological role of large terrestrial carnivores is that the vast majority of them are in decline .
Much knowledge of their influence comes from studies of local extinctions .
One remarkably common effect is that smaller predators—which are often held in check by apex predators—take over and wreak havoc .
As coyote populations ( Canis latrans ) declined in Southern California with the increasing expansion of human settlements in the 1990s , for example , the number of raccoons , skunks , and cats decimated reptile , bird , @ @ @ @ @ @ @ also experience population booms when a predator is lost .
In Yellowstone National Park , after federal officials had killed off most of the park ’ s wolves by 1926 as part of a national wolf control program , elk numbers surged , with particularly destructive effects on woody vegetation around the park ’ s streams .
Then , in the winters of 1994 , ’ 95 , and ’ 96 , Yellowstone officials released 41 wolves into the park ’ s interior and northern range .
It was one of the first @ @ @ @ @ @ @ reintroductions of a large carnivore to part of its historical distribution , and researchers were eager to study the effects .
Six years later , ecologists William Ripple and Robert Beschta of Oregon State University and others reported that aspen trees were taller and elk droppings less abundant in streamside areas frequented by wolves compared with places where wolves were seldom seen .
The researchers have since gathered a wealth of correlative evidence that the wolves created a “ landscape of fear ” for elk ( Cervus elaphus ) that prevented them from @ @ @ @ @ @ @ s northern creeks and rivers .
This supported the growth of aspen , cottonwood , and willow on their banks , and even improved the structure and function of particular waterways , Beschta and Ripple proposed last year .
In no small part due to an immensely popular 2014 YouTube video narrated by The Guardian columnist George Monbiot titled “ How Wolves Change Rivers , ” Yellowstone ’ s canine predators became internationally famous for single-handedly repairing Yellowstone ’ s broken landscape .
Yet the video ’ s narrative conceals a stark disagreement @ @ @ @ @ @ @ wolves to the decline in elk , as well as the role of fear in the ecological changes observed .
Utah State University ecologist Dan MacNulty questions whether adult elk , which are large and thus difficult for wolves to kill , would be so afraid of wolves as to miss out on a good meal , he says .
Indeed , he and his colleagues have tracked wolves and elk with radio collars and found that elk often don ’ t avoid areas frequented by the predators , and that the ungulates @ @ @ @ @ @ @ cougars ( another name for pumas , Felis concolor ) .
To Schmitz , this makes sense , given pumas ’ sit-and-wait hunting strategy .
As he ’ s learned from comparing spiders with different hunting styles , predators that tend to ambush their prey are more likely to create behaviorally mediated cascades .
The wolves at Yellowstone typically hunt by chasing elk across the landscape .
Because the elk can often see them coming from a distance , Schmitz explains , there ’ s no point avoiding certain areas .
Ecologist Tom @ @ @ @ @ @ @ doubts that the reintroduction of wolves was enough to repair some of the damages caused by wiping them out decades ago .
In their absence , an expanding elk population decimated streamside willows ( Salix spp . )
, prime dam-building material for beavers .
With fewer dams , the streams flowed faster , cutting deeper into the ground .
That caused the water table to drop , making it harder for willows to drink and grow , experiments by Hobbs and colleagues in the park ’ s northern range have shown .
@ @ @ @ @ @ @ such changes to the physical landscape anytime soon , he says .
“ Predators are so important , their removal has such long-lasting effects , that it ’ s naive to think that you can quickly reverse the effects of their absence by restoration.
” Doug Smith , a senior wildlife biologist in Yellowstone who has collaborated with all three research teams , says there ’ s an element of truth to the trophic cascade , although the effect was probably more density-mediated than fear-driven .
In addition , the cause of Yellowstone @ @ @ @ @ @ @ just wolves but rather a suite of factors , including the fact that cougars and bears increased in abundance around the same time that the wolves were introduced .
And while collectively these predators helped to regenerate parts of Yellowstone , Smith agrees with Hobbs that the park is “ not restored to what it [ once ] was .
That might never happen.
” Outside Yellowstone , Iberá will soon be one of a few locations where a predator has been intentionally reintroduced and its ecological effects intensively studied .
This time @ @ @ @ @ @ @ the challenges in deciphering cause and effect by collecting baseline data before the predators arrive .
In several locations within Iberá ’ s 1.3 million–hectare protected area , biologists with specialties in entomology , ornithology , predator ecology , and animal behavior are busy characterizing various facets of the ecosystem that they suspect the jaguars might influence .
Populations of oversized rodents called capybaras ( Hydrochoerus hydrochaeris ) might plummet after the predators ’ arrival , and their behavior may radically change , PhD student Belén Avila of Argentina ’ s Institute of @ @ @ @ @ @ @ the capybaras are acting fearlessly , Donadio says , even dozing on the paths cutting through the area .
But once they realize there are killers lurking about , individuals are likely to become more cautious and vigilant , which means they ’ ll spend less time eating , possibly affecting grass abundance .
The jaguars could also reduce the number of smaller predators such as pampas and crab-eating foxes , which are abundant at the moment , and in doing so protect the endangered birds that the foxes sometimes eat .
As @ @ @ @ @ @ @ over the coming years , Donadio says , “ it ’ s going to provide really , really good information when it comes to the importance of large predators on landscapes and biodiversity.
” Even without reintroducing predators into the wild , researchers elsewhere are using experimental approaches to detect trophic cascades already in action .
In 2008 , in the rugged Andean terrain of San Guillermo National Park in Argentina , Donadio wanted to understand how pumas influenced their prey , llama relatives known as vicuñas ( Vicugna vicugna ) .
He @ @ @ @ @ @ @ they ’ d easily see a predator approaching , the vicuñas ’ heads were usually buried in the grass eating , only occasionally popping up to look around .
In meadows with taller grasses and canyon areas where pumas could lurk behind rocky outcroppings , on the other hand , the vicuñas spent less time eating and more time on watch .
To test the effects of these behavioral differences on vegetation , Donadio constructed a number of 20-meter-by-20-meter exclosures—fenced areas intended to keep the vicuñas out , though the herbivores ( as @ @ @ @ @ @ @ frequent the general area .
Sure enough , he observed that the growth of grass inside the exclosures in the grasslands shot up compared with grass in surrounding control plots , while grass growth in the canyon and meadow exclosures did not , suggesting that vicuñas were indeed sacrificing grazing opportunities there to avoid an ambush .
This behaviorally mediated cascade is created by the complexity of the animals ’ habitat , Donadio says , and in turn , it helps shape the environment .
If the pumas weren ’ t there , @ @ @ @ @ @ @ and meadows ] would look exactly like the vegetation in the plains.
” By enhancing the diversity of habitats in San Guillermo , pumas may be creating new niches for other species , he explains , and in doing so , enhancing biodiversity .
Princeton University ecologist Robert Pringle and his colleagues have also used exclosures in their search for trophic cascades in Kenya ’ s Laikipia Plateau , which was recolonized by African wild dogs ( Lycaon pictus ) in the 1990s .
The researchers didn ’ t find any difference in @ @ @ @ @ @ @ the dogs ’ prey—small antelopes known as dik-diks ( Madoqua guentheri ) —before and after the arrival of wild dogs , even though the antelopes declined in abundance .
Pringle suggests that , among other factors , perhaps the timeframe of the study wasn ’ t long enough to detect a trophic cascade , given that trees take a long time to grow .
Pringle did , however , find evidence of cascading interactions between other species in the same ecosystem .
In clearings where impala ( Aepyceros melampus ) gather to avoid @ @ @ @ @ @ @ ) , the researchers noticed an abundance of acacia trees ( Acacia etbaica ) , which carry thorns to defend against intense herbivory .
In other areas where the bush was thicker—areas less frequented by the impala , probably due to fear of predation— “ there were a bunch of plants that actually tend to be much more palatable , ” Pringle says .
Similar approaches have also revealed such behavior-driven dynamics in marine ecosystems .
In seagrass meadows in Shark Bay in Western Australia , for example , researchers have found that @ @ @ @ @ @ @ patrolled by tiger sharks ( Galeocerdo cuvier ) —risky areas for grazers such as dugongs ( Dugong dugon ) and sea turtles ( Chelonia mydas ) —doesn ’ t have much of an effect , because the grazers were already kept away from these areas by the sharks .
In low-risk areas , on the other hand , when “ you put the cages out , it goes from this very sparse seagrass to just a giant salad bowl ” of marine vegetation , says Florida International University marine ecologist Mike Heithaus .
@ @ @ @ @ @ @ land are the same because animals are making the same kind of trade-offs—they ’ re trying to optimize food versus risk.
” Broadcasting predator vocalizations is another approach to interrogate predator trophic cascades , one that can more directly assess the effects of fear on prey .
Upon playing recordings of barking dogs in the intertidal zone on Canada ’ s west coast beaches , for instance , Zanette ’ s team found that raccoons ( Procyon lotor ) spent less time foraging , allowing crabs and fishes to increase in abundance—a behaviorally @ @ @ @ @ @ @ terrestrial habitat into the ocean .
Similar studies have reported that underwater playbacks of mammal-eating killer whales ( Orcinus orca ) , but not of local fish-eating killer whales , trigger harbor seals ( Phoca vitulina ) to dive to safer depths .
In Mozambique ’ s Gorongosa National Park , researchers have sought to understand the historic impacts of losing nearly an entire guild of top carnivores .
Decades ago , the area had become a battlefield during the country ’ s civil war , decimating populations of large animals , including @ @ @ @ @ @ @ .
In 2019 , Pringle , Princeton postdoc Justine Atkins , and their colleagues reported that in the absence of these carnivores , the typically forest-dwelling bushbuck ( Tragelaphus sylvaticus ) had spilled out into the open floodplains , where they appear to be suppressing certain plant species .
But when Pringle ’ s team played recordings of leopards , the bushbucks retreated into the forest .
Pringle is now studying how the recent return of wild dogs to the park will reconfigure the ecosystem , and Gorongosa officials just obtained permission to @ @ @ @ @ @ @ Bouley , who directs the park ’ s carnivore introduction program .
“ I think Gorongosa is going to be a classic case of rewilding.
” With these experiments only just now getting underway , it ’ s not clear how exactly such rewilding projects will play out .
MacNulty is unconvinced that Pringle ’ s data on bushbuck behavior are strong enough to demonstrate a trophic cascade in Gorongosa .
“ Evidence [ for such phenomena ] can be hard to produce in some of these complicated systems , ” he says @ @ @ @ @ @ @ have on ecosystems can be unpredictable .
For example , in another study of Pringle ’ s in which he released predatory curly-tailed lizards ( Leiocephalus carinatus ) onto Bahamian islands , the reptilian predators appeared to intensify competition between prey species and limit their ability to coexist , rather than maintain biodiversity .
Without a clearer understanding of the species interactions at play , the ecological benefits of rewilding predators remain unresolved .
While several researchers argue that restoring an environment ’ s lost predatory dynamics will generally be a positive thing @ @ @ @ @ @ @ t be a “ quick fix ” for degraded ecosystems .
And “ when it has been in this new predator-free equilibrium for a long time , ” says marine ecologist Boris Worm of Dalhousie University in Canada , “ we really don ’ t know what the outcome will be once we add predators back in.
” Outcomes of rewilding are even more uncertain in areas that are populated by people , not least because predators are often aggressively persecuted in those areas .
Large carnivores can also be fearful of humans @ @ @ @ @ @ @ Zanette and Justine Smith have observed that cougars stop eating and even abandon entire kills when they hear the sound of people talking .
Such findings raise the question of whether predators can influence their environment through trophic cascades in landscapes dominated by people , remarks University of Washington wildlife biologist Laura Prugh .
This problem also preoccupied Paine of the famous starfish experiments toward the end of his career .
In an opinion article he wrote with Worm that was coincidentally published online the day Paine died , June 13 , 2016 @ @ @ @ @ @ @ such pervasive ecological influencers that they should be considered a “ hyperkeystone ” species , with an even bigger influence than apex carnivores .
Rather than treating humans as external to the natural world , ecologists should integrate studies of human behavior into food-web theory , they argued .
In other words , understanding ecosystems in their entirety , and the ability of predators to restore them , will require understanding people .
“ It ’ s not just about other species , ” Worm says .
“ It ’ s first and @ @ @ @ @

ABOVE: © SHUTTERSTOCK.COM, BARANOV E
The jaguars don’t know it yet, but soon they’ll be free to roam Argentina’s Iberá wetlands, becoming the first apex predators to do so in a century. Three adults and the two-year-olds Amarí and Mbareté currently live in an enclosure on San Alonso, a patch of high ground in Iberá’s patchwork of flooded wilderness, lagoons, jungle, and grasslands. Once a pristine habitat, the region has lost much of its wildlife since the early 20th century, when ranchers moved into the area. People killed off native predators to protect livestock, and many species were decimated to satisfy a burgeoning market for fur, leather, and feathers.
Now, wildlife is making a comeback in Iberá, thanks to an ecological restoration effort spearheaded by the nonprofit Rewilding Argentina Foundation. Because of the region’s now-protected status and the reintroduction of locally extirpated species to reconstruct ecological communities, the area is thriving with pampas deer and marsh deer, capybaras, caimans, and diverse bird and insect life. Yellow anacondas have also been spotted. By the end of this year, conservationists hope to install one of the final missing ecological pieces—an apex predator—with the release of the jaguars.
To Emiliano Donadio, the foundation’s scientific director, the release not only is crucial to rebuilding Iberá’s ancient ecosystem, but is a scientific experiment that will provide a rare glimpse of how the return of one of the world’s largest carnivores could transform an ecosystem. Scientists know that losing large predators can have far-reaching, disruptive effects on ecosystems through cascading forces that reverberate from predators at high trophic levels—the top of the food web—to their prey and beyond, even sculpting the abundance and structure of plant life. The loss of jaguars (Panthera onca), pumas (cervu concolor), and other predators from fragments of the Venezuelan rainforest after the construction of a hydro-electric dam, for instance, is thought to be a key factor in triggering an explosive proliferation of herbivores including monkeys, which ravaged the vegetation and caused what researchers described as an “ecological meltdown.” But seldom do ecologists get to investigate whether those negative effects can be reversed by restoring predators. “We think that an ecosystem devoid of predators will be in better shape when the predators come back,” Donadio says, but that supposition remains largely untested.
RETURN OF THE JAGUAR: Key to restoring the second-largest wetland in the world is the reintroduction of its ancient predator. To that end, a jaguar breeding program is underway. The resulting cubs will be released along with three adults into the wild. MATÍAS REBAK; REWILDING ARGENTINA FOUNDATION
Part of the problem is, while it’s well accepted that large carnivores play vital ecological roles, just how they shape ecosystems through cascading effects in different environments isn’t well understood. In addition, predator reintroductions such as the ongoing project in Iberá are extremely rare and have lagged greatly behind herbivore rewilding projects, in large part because releasing animals capable of killing people and livestock is so controversial. “We only have so many natural experiments,” notes wildlife ecologist Justine Smith of the University of California, Davis.
In the absence of firm evidence, conservationists have been eager to interpret early predator reintroduction studies—largely based on the purported regenerative ecological effects of returning gray wolves (Canis lupus) to Yellowstone National Park in the mid-1990s—as a rationale for bringing predators back to many parts of the globe. In Colorado, for instance, conservation organizations have been using such findings to push for the approval of a bill on the November ballot that would effectively mandate wolf reintroduction in the state to restore the ecosystem’s “natural balance.” But some ecologists caution that the ecological outcomes of such projects are unclear.
See “Where the Wild Things Were”
In search of answers, scientists are employing novel approaches to study the ecological roles of large carnivores, from the African savannah and the Andean plateau to the ocean, and to understand how ecosystems change as they are lost or reintroduced. What they’re finding is that predators have powerful, yet nuanced and complex effects that ripple through food webs in what are known as trophic cascades—effects that depend not only on the nature of the hunter itself, but also on characteristics of its prey and the habitat the animals share.
“There’s still good reason to believe that trophic cascades will . . . occur in many systems,” Smith says. “It’s just that we don’t really have all the data yet to understand exactly when, where, and why.”
A green new world
Modern predator ecology began in principle with a simple question: “Why is the world green?” In the late 1950s, when ecologists Nelson Hairston, Frederick Smith, and Lawrence Slobodkin were pondering this question, the prevailing notion was that the abundances of animals that inhabit ecosystems depend solely on the amount of plants and nutrients at the bottom of the food web. Herbivore numbers were determined by the abundance of vegetation, and predator numbers by herbivore abundance. But the three University of Michigan scientists suggested in a 1960 paper in The American Naturalist that herbivore numbers weren’t controlled by the availability of plants alone, because predators were also playing a key role, and that by managing herbivore populations, predators indirectly protected vegetation. This idea was quickly met with fierce criticism, and to be fair, there wasn’t any robust evidence for their hypothesis at the time.
That was a gap that one of Smith’s students, Robert Paine, was determined to fill. In the early 1960s, Paine regularly ventured out to Washington State’s Makah Bay and its vibrant community of barnacles, mussels, limpets, and the predatory starfish Pisaster ochraceus to conduct an experiment that would become one of ecology’s most famous. From a 25-foot-long stretch of rock, he pried off the starfish and flung them into the ocean, while leaving another stretch unaltered. Over the course of a year, Paine noticed that life on the starfish-less rock transformed. The starfish’s main prey, the barnacle Balanus glandula, began to take over, followed by fast-growing mussel species, crowding out other organisms. The intertidal community of 15 invertebrate species dwindled to 8. Paine concluded that by keeping its prey in check, the Pisaster starfish was helping to maintain biodiversity. Despite being small in number, the five-legged predator was performing a crucial ecological function that earned its recognition as the first ever “keystone species.”
Predators are so important, their removal has such long-lasting effects, that it’s naive to think that you can quickly reverse the effects of their absence by restoration. —Tom Hobbs, Colorado State University
Paine’s belief that predators are ecologically important, and his recognition that their roles are best understood by studying animal communities that have been perturbed, inspired ecologist Jim Estes, then a PhD student at the University of Arizona observing the sea otters (Enhydra lutris) inhabiting the lush kelp forests around the Alaskan island of Amchitka. After a brief meeting with Paine in 1971, Estes decided to visit nearby islands where otters had been wiped out during the fur trade and immediately noticed a difference. “When I looked down at the seafloor, I was stunned by the vast numbers of urchins and absence of kelp,” Estes, who is now at the University of California, Santa Cruz, wrote in a 2016 memoir about his work. Like Pisaster starfish, otters around Amchitka were playing a key ecological role, he observed: by keeping urchins in check, the marine mammals limited the invertebrates’ consumption of kelp, thereby regulating the abundance of life-giving plants at the bottom of the food web. In a 1979 lecture, Paine coined the term trophic cascades to describe these indirect effects.
Estes’s observations were quickly followed by a series of observations from other researchers that pointed to the existence of trophic cascades in other aquatic ecosystems, such as those in lakes and rivers. In the 1990s, Os Schmitz, an ecologist at Yale School of the Environment, discovered that a terrestrial predator, the nursery web spider Pisaurina mira, could similarly create a trophic cascade, although in this case he uncovered an entirely different mechanism. It turns out that the spiders didn’t have to kill their prey to affect the ecosystem; they just had to scare them into skipping a meal.
Schmitz placed leaf-chewing grasshoppers, specifically Melanoplus femurrubrum, in a small, grass- and herb-filled enclosure, and observed that the vegetation flourished after he added nursery web hunting spiders, even without any immediate change in grasshopper numbers. Then, in a series of experiments in which Schmitz glued the spiders’ mouthparts shut so they could still instill fear but not consume their prey, he demonstrated that their mere presence was enough to allow grasses to flourish, as grasshoppers would forgo a meal to avoid becoming one. Biologists now call such fear-driven effects behaviorally mediated trophic cascades, distinguishing them from density-mediated ones that involve the predators’ consumption of their prey.
These behavioral effects come at a long-term cost to prey that can ultimately lead to declines in population densities. Avoiding the spiders caused some of Schmitz’s grasshoppers to starve, and their populations eventually dwindled. In a menagerie of animals, the sheer fear of predation can affect prey species’ metabolism, stress hormone levels, neurophysiology, and reproduction. In the forests of the southern Gulf Islands off the coast of British Columbia, Canada, for instance, Western University ecologist Liana Zanette and her colleagues have shown that hearing the sounds of predatory birds and raccoons throughout a breeding season can cause song sparrows (Melospiza melodia) to reduce the number of young they produce by 40 percent. “The role of predators is way greater than we ever previously imagined,” she says.
What remains unclear is how common such trophic cascades are in nature, Estes notes. “What I think is probably one of the biggest outstanding questions in this part of ecology [is] just how repeatable, how generalizable, these phenomena are.”
The gray wolf: An American hero?
A major challenge in studying the ecological role of large terrestrial carnivores is that the vast majority of them are in decline. Much knowledge of their influence comes from studies of local extinctions. One remarkably common effect is that smaller predators—which are often held in check by apex predators—take over and wreak havoc. As coyote populations (Canis latrans) declined in Southern California with the increasing expansion of human settlements in the 1990s, for example, the number of raccoons, skunks, and cats decimated reptile, bird, and small mammal populations.
Herbivores can also experience population booms when a predator is lost. In Yellowstone National Park, after federal officials had killed off most of the park’s wolves by 1926 as part of a national wolf control program, elk numbers surged, with particularly destructive effects on woody vegetation around the park’s streams. Then, in the winters of 1994, ’95, and ’96, Yellowstone officials released 41 wolves into the park’s interior and northern range. It was one of the first and remains one of the few intentional reintroductions of a large carnivore to part of its historical distribution, and researchers were eager to study the effects.
While it’s well accepted that large carnivores play vital ecological roles, just how they shape ecosystems isn’t well understood.
Six years later, ecologists William Ripple and Robert Beschta of Oregon State University and others reported that aspen trees were taller and elk droppings less abundant in streamside areas frequented by wolves compared with places where wolves were seldom seen. The researchers have since gathered a wealth of correlative evidence that the wolves created a “landscape of fear” for elk (Cervus canadensis) that prevented them from browsing the foliage along the park’s northern creeks and rivers. This supported the growth of aspen, cottonwood, and willow on their banks, and even improved the structure and function of particular waterways, Beschta and Ripple proposed last year.
In no small part due to an immensely popular 2014 YouTube video narrated by The Guardian columnist George Monbiot titled “How Wolves Change Rivers,” Yellowstone’s canine predators became internationally famous for single-handedly repairing Yellowstone’s broken landscape. Yet the video’s narrative conceals a stark disagreement among ecologists about the relative contribution of wolves to the decline in elk, as well as the role of fear in the ecological changes observed.
Utah State University ecologist Dan MacNulty questions whether adult elk, which are large and thus difficult for wolves to kill, would be so afraid of wolves as to miss out on a good meal, he says. Indeed, he and his colleagues have tracked wolves and elk with radio collars and found that elk often don’t avoid areas frequented by the predators, and that the ungulates seem to be more concerned with avoiding cougars (another name for pumas, Felis concolor). To Schmitz, this makes sense, given pumas’ sit-and-wait hunting strategy. As he’s learned from comparing spiders with different hunting styles, predators that tend to ambush their prey are more likely to create behaviorally mediated cascades. The wolves at Yellowstone typically hunt by chasing elk across the landscape. Because the elk can often see them coming from a distance, Schmitz explains, there’s no point avoiding certain areas.
Ecologist Tom Hobbs of Colorado State University says he doubts that the reintroduction of wolves was enough to repair some of the damages caused by wiping them out decades ago. In their absence, an expanding elk population decimated streamside willows (Salix spp.), prime dam-building material for beavers. With fewer dams, the streams flowed faster, cutting deeper into the ground. That caused the water table to drop, making it harder for willows to drink and grow, experiments by Hobbs and colleagues in the park’s northern range have shown. Reintroducing wolves alone is unlikely to reverse such changes to the physical landscape anytime soon, he says. “Predators are so important, their removal has such long-lasting effects, that it’s naive to think that you can quickly reverse the effects of their absence by restoration.”
Doug Smith, a senior wildlife biologist in Yellowstone who has collaborated with all three research teams, says there’s an element of truth to the trophic cascade, although the effect was probably more density-mediated than fear-driven. In addition, the cause of Yellowstone’s elk declines wasn’t just wolves but rather a suite of factors, including the fact that cougars and bears increased in abundance around the same time that the wolves were introduced. And while collectively these predators helped to regenerate parts of Yellowstone, Smith agrees with Hobbs that the park is “not restored to what it [once] was. That might never happen.”
LESSONS FROM PAST REINTRODUCTIONS In the mid-1990s, officials at Yellowstone National Park released gray wolves from areas in Canada and Montana into the park; it had been more than half a century since the predators last roamed the park. Researchers tracking the revolutionary experiment published results that they say point to the reintroduction’s role in revitalizing the once-degraded ecosystem, with the wolves’ predatory behavior indirectly supporting the growth of vegetation and even improving the health of the park’s waterways. But a heated debate rages on concerning the effects the wolves had on their environment, especially relative to roles of other members of Yellowstone’s rich carnivore community. Yellowstone, Wyoming, US
41 gray wolves reintroduced in the mid-1990s © LUCY CONKLIN Following wolf reintroduction, elk numbers dropped dramatically—from nearly 20,000 in 1994 to just 8,300 in 2000—but wolves are likely not the only carnivore that contributed to that decline; black bear, grizzly, and cougar populations surged around the time of the wolf reintroduction. Ecologists first posited that by keeping elk away from streams, wolves were indirectly allowing aspen trees to flourish. Although the trees increased in height in certain areas, their overall abundance changed little. Although they suffer less browsing pressure since the predator increases in the 1990s, willows have not fully recovered, according to some researchers. And without willows, the recovery of streams has been limited. Initial studies proposed that elk stay away from streamside areas where they could more easily fall prey to wolves, but new research suggests that elk only avoid these regions in the morning and at dusk. The herbivores also appear to have altered their behavior to avoid cougar-patrolled forested areas at night.
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Beyond Yellowstone
Outside Yellowstone, Iberá will soon be one of a few locations where a predator has been intentionally reintroduced and its ecological effects intensively studied. This time, researchers hope to overcome some of the challenges in deciphering cause and effect by collecting baseline data before the predators arrive. In several locations within Iberá’s 1.3 million–hectare protected area, biologists with specialties in entomology, ornithology, predator ecology, and animal behavior are busy characterizing various facets of the ecosystem that they suspect the jaguars might influence.
Populations of oversized rodents called capybaras (Hydrochoerus hydrochaeris) might plummet after the predators’ arrival, and their behavior may radically change, PhD student Belén Avila of Argentina’s Institute of Subtropical Biology hypothesizes. Right now, the capybaras are acting fearlessly, Donadio says, even dozing on the paths cutting through the area. But once they realize there are killers lurking about, individuals are likely to become more cautious and vigilant, which means they’ll spend less time eating, possibly affecting grass abundance. The jaguars could also reduce the number of smaller predators such as pampas and crab-eating foxes, which are abundant at the moment, and in doing so protect the endangered birds that the foxes sometimes eat. As the researchers track these and other outcomes over the coming years, Donadio says, “it’s going to provide really, really good information when it comes to the importance of large predators on landscapes and biodiversity.”
PLANNING FOR FUTURE REINTRODUCTIONS The release of predators into the wild is controversial, and for years Yellowstone remained one of the only sites of such a bold reintroduction. But now, similar efforts are in the works around the world. In the Iberá wetlands of Argentina, for example, conservationists will soon release their first jaguars, and hypothesize that a variety of ecological changes will occur across the landscape. Iberá, Argentina
Five jaguars to be reintroduced in 2020/2021 © LUCY CONKLIN Researchers expect numbers of deer and capybaras, the jaguars’ prey, to drop once the cats are reintroduced. By reconfiguring capybara population structure, the jaguars might reduce the spread of mange between the rodents. Ecologists suspect that the capybaras’ behavior will change in response to the presence of the jaguars, becoming more vigilant and cautious. If the capybaras spend more time watching for predators than eating, that could allow grassy vegeta-tion to flourish in certain areas. Jaguars could kill or change the behavior of local foxes and in doing so indirectly boost numbers of the endangered birds that the foxes are known to eat. Ecologists hypothesize that the jaguars’ presence could increase the abundance of certain scavenger species such as vultures and enhance the diversity of beetles that live off carcasses left behind by the predators.
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Even without reintroducing predators into the wild, researchers elsewhere are using experimental approaches to detect trophic cascades already in action. In 2008, in the rugged Andean terrain of San Guillermo National Park in Argentina, Donadio wanted to understand how pumas influenced their prey, llama relatives known as vicuñas (Vicugna vicugna). He noticed that, in open grasslands where they’d easily see a predator approaching, the vicuñas’ heads were usually buried in the grass eating, only occasionally popping up to look around. In meadows with taller grasses and canyon areas where pumas could lurk behind rocky outcroppings, on the other hand, the vicuñas spent less time eating and more time on watch. To test the effects of these behavioral differences on vegetation, Donadio constructed a number of 20-meter-by-20-meter exclosures—fenced areas intended to keep the vicuñas out, though the herbivores (as well as the pumas) could still frequent the general area. Sure enough, he observed that the growth of grass inside the exclosures in the grasslands shot up compared with grass in surrounding control plots, while grass growth in the canyon and meadow exclosures did not, suggesting that vicuñas were indeed sacrificing grazing opportunities there to avoid an ambush.
Understanding ecosystems in their entirety, and the ability of predators to restore them, will require understanding people.
This behaviorally mediated cascade is created by the complexity of the animals’ habitat, Donadio says, and in turn, it helps shape the environment. If the pumas weren’t there, “the vegetation in the canyons [and meadows] would look exactly like the vegetation in the plains.” By enhancing the diversity of habitats in San Guillermo, pumas may be creating new niches for other species, he explains, and in doing so, enhancing biodiversity.
Princeton University ecologist Robert Pringle and his colleagues have also used exclosures in their search for trophic cascades in Kenya’s Laikipia Plateau, which was recolonized by African wild dogs (Lycaon pictus) in the 1990s. The researchers didn’t find any difference in grazing pressure exerted on local plants by the dogs’ prey—small antelopes known as dik-diks (Madoqua guentheri)—before and after the arrival of wild dogs, even though the antelopes declined in abundance. Pringle suggests that, among other factors, perhaps the timeframe of the study wasn’t long enough to detect a trophic cascade, given that trees take a long time to grow. Pringle did, however, find evidence of cascading interactions between other species in the same ecosystem. In clearings where impala (Aepyceros melampus) gather to avoid being ambushed by leopards (Panthera pardus), the researchers noticed an abundance of acacia trees (Acacia etbaica), which carry thorns to defend against intense herbivory. In other areas where the bush was thicker—areas less frequented by the impala, probably due to fear of predation—“there were a bunch of plants that actually tend to be much more palatable,” Pringle says.
Similar approaches have also revealed such behavior-driven dynamics in marine ecosystems. In seagrass meadows in Shark Bay in Western Australia, for example, researchers have found that setting up small exclosures in areas frequently patrolled by tiger sharks (Galeocerdo cuvier)—risky areas for grazers such as dugongs (Dugong dugon) and sea turtles (Chelonia mydas)—doesn’t have much of an effect, because the grazers were already kept away from these areas by the sharks. In low-risk areas, on the other hand, when “you put the cages out, it goes from this very sparse seagrass to just a giant salad bowl” of marine vegetation, says Florida International University marine ecologist Mike Heithaus. “At its core, oceans and land are the same because animals are making the same kind of trade-offs—they’re trying to optimize food versus risk.”
Broadcasting predator vocalizations is another approach to interrogate predator trophic cascades, one that can more directly assess the effects of fear on prey. Upon playing recordings of barking dogs in the intertidal zone on Canada’s west coast beaches, for instance, Zanette’s team found that raccoons (Procyon lotor) spent less time foraging, allowing crabs and fishes to increase in abundance—a behaviorally mediated trophic cascade that extended from a terrestrial habitat into the ocean. Similar studies have reported that underwater playbacks of mammal-eating killer whales (Orcinus orca), but not of local fish-eating killer whales, trigger harbor seals (Phoca vitulina) to dive to safer depths.
In Mozambique’s Gorongosa National Park, researchers have sought to understand the historic impacts of losing nearly an entire guild of top carnivores. Decades ago, the area had become a battlefield during the country’s civil war, decimating populations of large animals, including leopards, wild dogs, and lions. In 2019, Pringle, Princeton postdoc Justine Atkins, and their colleagues reported that in the absence of these carnivores, the typically forest-dwelling bushbuck (Tragelaphus sylvaticus) had spilled out into the open floodplains, where they appear to be suppressing certain plant species. But when Pringle’s team played recordings of leopards, the bushbucks retreated into the forest. Pringle is now studying how the recent return of wild dogs to the park will reconfigure the ecosystem, and Gorongosa officials just obtained permission to bring in several leopards, says Paola Bouley, who directs the park’s carnivore introduction program. “I think Gorongosa is going to be a classic case of rewilding.”
PLANNING FOR FUTURE REINTRODUCTIONS, PART 2 In Mozambique’s Gorongosa National Park, where a reintroduction project involving wild dogs and leopards is ongoing, a study is underway using state-of-the-art tools to track the predators’ ecological effects. Gorongosa National Park, Mozambique
Dozens of African wild dogs introduced in 2018/2019; leopard reintroductions slated for 2021 © LUCY CONKLIN Scientists plan to use high-resolution satellite imagery—including LiDAR, which captures the height of trees and grasses—to assess changes in vegetation structure. Researchers will be analyzing antelope scat using fecal DNA barcoding, alongside studies of the predators’ feces, to track the animals’ diets. Ecologists are using GPS collars and camera-trap data to monitor the behavior of different antelope species.
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Learning from rewilding
With these experiments only just now getting underway, it’s not clear how exactly such rewilding projects will play out. MacNulty is unconvinced that Pringle’s data on bushbuck behavior are strong enough to demonstrate a trophic cascade in Gorongosa. “Evidence [for such phenomena] can be hard to produce in some of these complicated systems,” he says. Moreover, the effects that predators have on ecosystems can be unpredictable. For example, in another study of Pringle’s in which he released predatory curly-tailed lizards (Leiocephalus carinatus) onto Bahamian islands, the reptilian predators appeared to intensify competition between prey species and limit their ability to coexist, rather than maintain biodiversity.
Without a clearer understanding of the species interactions at play, the ecological benefits of rewilding predators remain unresolved. While several researchers argue that restoring an environment’s lost predatory dynamics will generally be a positive thing, others caution that it won’t be a “quick fix” for degraded ecosystems. And “when it has been in this new predator-free equilibrium for a long time,” says marine ecologist Boris Worm of Dalhousie University in Canada, “we really don’t know what the outcome will be once we add predators back in.”
ECOSYSTEM EFFECTS: The Iberá wetlands in Argentina lost most of their wildlife during the 19th century as people moved into the remote area, but the region’s native species, including capybaras (top), maned wolves (bottom left), and pampas deer (bottom right), are now recovering, thanks in part to an ambitious ecological restoration effort. DEER AND CAPYBARA: MATÍAS REBAK; MANED WOLF: RAFAEL ABUIN
Outcomes of rewilding are even more uncertain in areas that are populated by people, not least because predators are often aggressively persecuted in those areas. Large carnivores can also be fearful of humans. In California, for instance, Zanette and Justine Smith have observed that cougars stop eating and even abandon entire kills when they hear the sound of people talking. Such findings raise the question of whether predators can influence their environment through trophic cascades in landscapes dominated by people, remarks University of Washington wildlife biologist Laura Prugh.
This problem also preoccupied Paine of the famous starfish experiments toward the end of his career. In an opinion article he wrote with Worm that was coincidentally published online the day Paine died, June 13, 2016, the two argued that humans are such pervasive ecological influencers that they should be considered a “hyperkeystone” species, with an even bigger influence than apex carnivores. Rather than treating humans as external to the natural world, ecologists should integrate studies of human behavior into food-web theory, they argued. In other words, understanding ecosystems in their entirety, and the ability of predators to restore them, will require understanding people. “It’s not just about other species,” Worm says. “It’s first and foremost about ourselves.”
Correction (November 27, 2020): A previous version of this story misidentified pumas as Felis concolor and the elk species described as Cervus elaphus. The article has been updated to reflect the fact that pumas are in fact classified as Puma concolor, and the elk as Cervus canadensis. The Scientist regrets the errors.


thescientist--2020-11-01--Tropical Birds Differ in Their Responses to Drought

ABOVE : Long-lived tropical bird species such as the indigo flycatcher ( Eumyias indigo ) reduce their reproduction rate during a drought and up their chances of survival , a study finds .
© THOMAS MARTIN T.E .
Martin , J.C. Mouton , “ Longer-lived tropical songbirds reduce breeding activity as they buffer impacts of drought , ” Nat Clim Change , doi:10.1038/s41558-020-0864-3 , 2020 .
Thomas Martin was studying parenting behavior among wild birds in Venezuela when a drought hit in 2008 .
In one species , the gray-breasted wood wren ( Henicorhina leucophrys ) , the number of @ @ @ @ @ @ @ study area declined from 65 in 2007 to just 7 during the drought , the University of Montana wildlife biologist says .
Reproduction comes at a cost , because animals must expend energy producing and caring for their young , so Martin wondered what effect this temporary drop in reproduction might have on the adult birds ’ survival rates .
To find out , he set up another experiment in 2009 , this one in the forests of Borneo .
With then–graduate student James Mouton and their field assistants , Martin caught and @ @ @ @ @ @ @ nest locations and bird sightings .
Seven years later , a drought hit .
It wasn ’ t as severe as the one in Venezuela in 2008 , where there was a more than 50 percent average reduction in nests across 18 species , and Martin suspects that ’ s why the effects he and his team saw in Borneo weren ’ t as extreme .
Still , the 20 bird species studied in Borneo reduced the number of nests in which they laid eggs by an average of 36 percent compared with @ @ @ @ @ @ @ reduction varied among species , with long-lived birds—those with average lifespans of about 10 or more years—reducing their reproduction the most .
And in contrast to past studies that indicated that birds ’ survival drops during droughts , survival rates increased in the species that were most inclined to hold off on having offspring .
“ The contrast between long-lived and short-lived species in how they cope with a stressful environment is striking , ” writes Rosemary Grant , an emeritus biologist at Princeton University who was not involved in the study , @ @ @ @ @ @ @ The research , she says , “ provides a good example of the value of long-term studies .
”

ABOVE: Long-lived tropical bird species such as the indigo flycatcher (Eumyias indigo) reduce their reproduction rate during a drought and up their chances of survival, a study finds.
THOMAS MARTIN
EDITOR’S CHOICE IN ECOLOGY & ENVIRONMENT
The paper
T.E. Martin, J.C. Mouton, “Longer-lived tropical songbirds reduce breeding activity as they buffer impacts of drought,” Nat Clim Change, doi:10.1038/s41558-020-0864-3, 2020.
Thomas Martin was studying parenting behavior among wild birds in Venezuela when a drought hit in 2008. In one species, the gray-breasted wood wren (Henicorhina leucophrys), the number of active nests in his team’s study area declined from 65 in 2007 to just 7 during the drought, the University of Montana wildlife biologist says.
Reproduction comes at a cost, because animals must expend energy producing and caring for their young, so Martin wondered what effect this temporary drop in reproduction might have on the adult birds’ survival rates. To find out, he set up another experiment in 2009, this one in the forests of Borneo. With then–graduate student James Mouton and their field assistants, Martin caught and banded birds, and began to record nest locations and bird sightings. Seven years later, a drought hit.
It wasn’t as severe as the one in Venezuela in 2008, where there was a more than 50 percent average reduction in nests across 18 species, and Martin suspects that’s why the effects he and his team saw in Borneo weren’t as extreme. Still, the 20 bird species studied in Borneo reduced the number of nests in which they laid eggs by an average of 36 percent compared with the year before. The level of reduction varied among species, with long-lived birds—those with average lifespans of about 10 or more years—reducing their reproduction the most. And in contrast to past studies that indicated that birds’ survival drops during droughts, survival rates increased in the species that were most inclined to hold off on having offspring.
“The contrast between long-lived and short-lived species in how they cope with a stressful environment is striking,” writes Rosemary Grant, an emeritus biologist at Princeton University who was not involved in the study, in an email to The Scientist. The research, she says, “provides a good example of the value of long-term studies.”


thescientist--2020-11-01--Infographic: Herbivore Dung Nutrients Vary Across the Savanna

Areas with denser vegetation and thus lower visibility ( left ) are more likely to be frequented by larger animals—which @ @ @ @ @ predators—than by smaller animals , according to a recent study .
Compared with smaller herbivores @ @ @ @ @ herbivores such as elephants and rhinos produce dung with relatively lower phosphorus content .
These @ @ @ @ @ with variable availability of nutrients for plants growing in the savanna , the researchers found @ @ @ @ @ ’ body sizes could influence ecosystem functioning .

Areas with denser vegetation and thus lower visibility (left) are more likely to be frequented by larger animals—which have less to fear from predators—than by smaller animals, according to a recent study. Compared with smaller herbivores such as impala, large herbivores such as elephants and rhinos produce dung with relatively lower phosphorus content. These differences in dung are associated with variable availability of nutrients for plants growing in the savanna, the researchers found, suggesting that the animals’ body sizes could influence ecosystem functioning.
© Melanie Lee
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thescientist--2020-11-01--Infographic: Investigating Whale Strandings Along the North American Coast

Over the past two years , hundreds of gray whales have washed ashore along North America ’ s west coast .
Researchers are learning that the answer to the question of why these whales are dying is complex , but likely involves warming ocean waters and melting Arctic sea ice brought on by climate change .
So far , the evidence is circumstantial , and scientists are still seeking more-definitive data about what ’ s killing the marine giants .
To investigate the deaths of gray whales , researchers have been tracking where they wash ashore along their migration route @ @ @ @ @ @ @ spend summers in the Arctic , where they dine on crustaceans called amphipods that live at the seafloor .
Each whale can consume more than 2,000 pounds of food a day , amassing fat to fuel their yearly migration down to warmer waters off the Baja Peninsula , where they spend winters breeding and giving birth .
During their 24,000-mile roundtrip journey , the whales eat almost nothing .
Only occasionally along the way will they stop at snacking stations , skimming surface sea waters for squid , krill , crab larvae , @ @ @ @ @ @ @ often be enough for a whale to survive its yearlong fast , but may “ not be enough for a pregnant female to bring a calf to term , ” Moore says , or produce enough nutritious milk to support the growth of the baby ’ s blubber before making the trek back north .
Sure enough , yearlings and adolescents accounted for most of the 2019 strandings .

Over the past two years, hundreds of gray whales have washed ashore along North America’s west coast. Researchers are learning that the answer to the question of why these whales are dying is complex, but likely involves warming ocean waters and melting Arctic sea ice brought on by climate change. So far, the evidence is circumstantial, and scientists are still seeking more-definitive data about what’s killing the marine giants.
© LOGAN PARSONS ILLUSTRATION
Malnourished whales are probably not as good at fending off orca attacks, toxins, and maladies that make them more vulnerable to death. Without sea ice to collect algae, which would normally fall to the seafloor when the ice melts seasonally, shrimp-like crustaceans called amphipods
that use the algae as a source of carbon become less nutritious food for gray whales, affecting mammals’ ability to pack on blubber for the winter. Having less ice opens more-northern territories for whales to feed. Reduced ice also leads to an increase in commercial shipping along the Northern Sea Route, raising chances for ships to collide with whales. The whales may ingest toxins, such as the neurotoxin domoic acid, from the sediment as they filter feed, which could be damaging to animals that are unhealthy as a result of warming waters.
Death Map
To investigate the deaths of gray whales, researchers have been tracking where they wash ashore along their migration route from Mexico to Alaska. The whales spend summers in the Arctic, where they dine on crustaceans called amphipods that live at the seafloor. Each whale can consume more than 2,000 pounds of food a day, amassing fat to fuel their yearly migration down to warmer waters off the Baja Peninsula, where they spend winters breeding and giving birth. During their 24,000-mile roundtrip journey, the whales eat almost nothing. Only occasionally along the way will they stop at snacking stations, skimming surface sea waters for squid, krill, crab larvae, and herring roe. Those snacks can often be enough for a whale to survive its yearlong fast, but may “not be enough for a pregnant female to bring a calf to term,” Moore says, or produce enough nutritious milk to support the growth of the baby’s blubber before making the trek back north. Sure enough, yearlings and adolescents accounted for most of the 2019 strandings.
NOAA FISHERIES/MARINE MAMMAL HEALTH AND STRANDING RESPONSE PROGRAM
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