The largest bears in the world use small streams to fatten up on salmon

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It's a familiar scene to anyone who's watched footage of brown bears catching sockeye salmon in Alaska: They're standing knee-deep in a rushing river, usually near a waterfall, and grabbing passing fish with their paws or jaws.

But a new study published in the journal Conservation Letters reveals a different picture of how and when bears eat salmon. Most of these bears, also known as grizzlies, are dipping into small streams to capture their iconic prey.
Using a foraging model based on the Wood River basin in southwest Alaska, a study team led by Oregon State University determined that while small-stream habitats have only about 20% of the available salmon in the watershed, they provide 50% of bear consumption of salmon.
"This tells us that populations of sockeye salmon that spawn in little streams are disproportionately important to bears," said study lead author Jonny Armstrong, an ecologist at Oregon State University. "Bears profit from these small streams because they offer salmon at unique times of the season. To capitalize on plentiful salmon runs, bears need them to be spread across time."
Small streams typically have cold water, which leads to populations of salmon that spawn much earlier in the season when no other populations are available to predators such as bears.
These results have potential consequences for how environmental impact assessments are conducted and evaluated for large projects such as the proposed Pebble Mine in Alaska's Bristol Bay.
These reports typically focus on how the project will affect the abundance of salmon in lakes and rivers, but they usually overlook smaller habitats, Armstrong said.
"When people want to build a large mine, they think these streams don't matter because they represent a small fraction a watershed, in terms of area or salmon abundance. In conservation and management, we generally place value on the largest runs of salmon at the expense of the smallest ones," Armstrong said. "If we pose a different question and ask which habitats are important for the ecosystem, then small streams become particularly relevant."
The researchers developed a mathematical model that explores how watershed development and commercial fisheries affect how many sockeye salmon are available to grizzlies. The model simulated different patterns of development and explored how they affected the number of salmon bears consumed.
Protecting large salmon runs at the expense of smaller ones turned out to be bad for bears.
"This causes the bears' total salmon consumption to drop off faster compared to strategies that protected small salmon runs and the early feeding opportunities they offer to bears," Armstrong said. "If you impair these areas, you may only reduce the total number of salmon by a little, but the number of salmon that end up in bear's stomachs -- you could reduce that a lot."
According to the study authors, there are two significant reasons why the largest bears in the world are drawn to small streams to eat salmon.
First, the fish in these streams are easy to catch for adult and juvenile grizzlies. And second, because the water is colder than in lakes and rivers, salmon spawn in them earlier -- probably to give their eggs more time to incubate, the authors said. So, the fish are plentiful by the first week of July -- making them the first places bears fish after they emerge from hibernation.
"When they come out of hibernation, the bears are just scraping by and barely making it," Armstrong said. "Having these streams means they can start eating salmon in early July, which is about six weeks before the river- and lake-salmon populations start spawning and become available to bears. It's an incredible foraging opportunity for bears."
Armstrong added, "I'm sure that native Alaskans who subsisted on salmon were keenly aware of this, too."

Habitat restoration alone not enough to support threatened caribou

Other conservation methods may also be needed until restored sites are more established

University of British Columbia

IMAGE: New UBC research suggests restoring habitat may not be enough to save threatened woodland caribou--an iconic animal that's a major part of boreal forests in North America and a key... view more 

Credit: UBC Faculty of Forestry

New UBC research suggests restoring habitat may not be enough to save threatened woodland caribou--an iconic animal that's a major part of boreal forests in North America and a key part of the culture and economy of many Indigenous peoples in Canada.
Caribou populations have declined rapidly in recent decades across much of western Canada, including the oil sands region of northeastern Alberta. The researchers placed hidden cameras, known as "camera traps", in the area to see if replanting seismic lines has helped protect caribou by separating them from predators and fellow prey moving through the area.
Seismic lines, which are narrow strips of land cleared to make way for oil and gas exploration, are thought to disturb caribou habitat and promote faster travel for predators and food competitors. These lines do not recover quickly naturally, but are now being restored through replanting with native trees and natural features like mounds and tree debris.
"In theory, restoration should have made it much more difficult for predators to travel across the caribou range, but our cameras showed us a different picture," said lead author Erin Tattersall, who did the work as a master's student in forest sciences at UBC.
Predators like black bears and wolves, and prey like moose, used the restored seismic lines about as much as they used unrestored lines. Only white-tailed deer--a key caribou competitor --showed less use of the restored lines. Caribou preferred to use lines located in low-lying wetland areas, as well as more isolated lines--whether they'd been restored or not.
"In other words, restoration did not do much to keep caribou apart from their predators and competitors, at least not in the short term," Tattersall said.
The work, published last week in Biological Conservation, is one of the first to challenge the assumed impacts of a caribou recovery strategy, and researchers say it makes the case for more rigorous analysis of conservation methods.
"It's possible caribou will eventually recover in the area we studied, and other restoration approaches in other regions could also prove more immediately effective for caribou recovery," said senior author Cole Burton, a professor of forestry who leads the Wildlife Coexistence Lab at UBC. "But our results clearly show that we can't simply assume the best--it's necessary to closely monitor the actual results of restoration."
And while the study focuses on Alberta caribou, it can also be important for discussions on saving B.C. caribou, Burton added.
"We are seeing steep declines in many of B.C.'s caribou populations, and even total losses of some," he said. "Effective restoration of already degraded habitats will ultimately be critical to recovering our caribou."

What wolves' teeth reveal about their lives

IMAGE: Biologist Blaire Van Valkenburgh has spent more than three decades studying the skulls of large carnivores. Here she displays a replica of a saber-toothed cat skull. At left are the... view more 

Credit: Christelle Snow/UCLA

UCLA evolutionary biologist Blaire Van Valkenburgh has spent more than three decades studying the skulls of many species of large carnivores -- including wolves, lions and tigers -- that lived from 50,000 years ago to the present. She reports today in the journal eLife the answer to a puzzling question.
Essential to the survival of these carnivores is their teeth, which are used for securing their prey and chewing it, yet large numbers of these animals have broken teeth. Why is that, and what can we learn from it?
In the research, Van Valkenburgh reports a strong link between an increase in broken teeth and a decline in the amount of available food, as large carnivores work harder to catch dwindling numbers of prey, and eat more of it, down to the bones.
"Broken teeth cannot heal, so most of the time, carnivores are not going to chew on bones and risk breaking their teeth unless they have to," said Van Valkenburgh, a UCLA distinguished professor of ecology and evolutionary biology, who holds the Donald R. Dickey Chair in Vertebrate Biology.
For the new research, Van Valkenburgh studied the skulls of gray wolves -- 160 skulls of adult wolves housed in the Yellowstone Heritage and Research Center in Montana; 64 adult wolf skulls from Isle Royale National Park in Lake Superior that are housed at Michigan Technological University; and 94 skulls from Scandinavia, collected between 1998 and 2010, housed in the Swedish Royal Museum of Natural History in Stockholm. She compared these with the skulls of 223 wolves that died between 1874 and 1952, from Alaska, Texas, New Mexico, Idaho and Canada.
Yellowstone had no wolves, Van Valkenburgh said, between the 1920s and 1995, when 31 gray wolves were brought to the national park from British Columbia. About 100 wolves have lived in Yellowstone for more than a decade, she said.
In Yellowstone, more than 90% of the wolves' prey are elk. The ratio of elk to wolves has declined sharply, from more than 600-to-1 when wolves were brought back to the national park to about 100-to-1 more recently.
In the first 10 years after the reintroduction, the wolves did not break their teeth much and did not eat the elk completely, Van Valkenburgh reports. In the following 10 years, as the number of elk declined, the wolves ate more of the elk's body, and the number of broken teeth doubled, including the larger teeth wolves use when hunting and chewing.
The pattern was similar in the island park of Isle Royale. There, the wolves' prey are primarily adult moose, but moose numbers are low and their large size makes them difficult to capture and kill. Isle Royale wolves had high frequencies of broken and heavily worn teeth, reflecting the fact that they consumed about 90% of the bodies of the moose they killed.
Scandinavian wolves presented a different story. The ratio of moose to wolves is nearly 500-to-1 in Scandinavia and only 55-to-1 in Isle Royale, and, consistent with Van Valkenburgh's hypothesis, Scandinavian wolves consumed less of the moose they killed (about 70%) than Isle Royale wolves. Van Valkenburgh did not find many broken teeth among the Scandinavian wolves. "The wolves could find moose easily, not eat the bones, and move on," she said.
Van Valkenburgh believes her findings apply beyond gray wolves, which are well-studied, to other large carnivores, such as lions, tigers and bears.
Extremely high rates of broken teeth have been recorded for large carnivores -- such as lions, dire wolves and saber-toothed cats -- from the Pleistocene epoch, dating back tens of thousands of years, compared with their modern counterparts, Van Valkenburgh said. Rates of broken teeth from animals at the La Brea Tar Pits were two to four times higher than in modern animals, she and colleagues reported in the journal Science in the 1990s.
"Our new study suggests that the cause of this tooth fracture may have been more intense competition for food in the past than in present large carnivore communities," Van Valkenburgh said.
She and colleagues reported in 2015 that violent attacks by packs of some of the world's largest carnivores -- including lions much larger than those of today and saber-toothed cats -- went a long way toward shaping ecosystems during the Pleistocene.
In a 2016 article in the journal BioScience, Van Valkenburgh and more than 40 other wildlife experts wrote that preventing the extinction of lions, tigers, wolves, bears, elephants and the world's other largest mammals will require bold political action and financial commitments from nations worldwide.
Discussing the new study, she said, "We want to understand the factors that increase mortality in large carnivores that, in many cases, are near extinction. Getting good information on that is difficult. Studying tooth fracture is one way to do so, and can reveal changing levels of food stress in big carnivores."

Poo's clues: Moose droppings indicate Isle Royale ecosystem health

Michigan Technological University

IMAGE: An adult moose must eat approximately 40 pounds of vegetation per day just to keep itself going. Yet despite their need to consume large volumes of food every day, moose... view more 

Credit: Sarah Hoy/Michigan Tech

Given the choice between ice cream and vegetables, for many people it'll be the ice cream. But sometimes it depends on the situation. If you'd eaten ice cream every day for a week, you might prefer the salad. Human preferences for different foods often depend on what's common fare and what's rare.
For non-human animals, like moose, the situation is equally complicated. An adult moose must eat approximately 40 pounds of vegetation per day just to keep itself going. Yet despite their need to consume large volumes of food every day, moose do not eat everything they come across. Instead, moose are considerably more selective than is obvious when deciding which plant species to eat.
Sarah Hoy, assistant research professor, and John Vucetich, distinguished professor, in the School of Forest Resources and Environmental Science at Michigan Technological University, in collaboration with scientists from the United States Geological Survey (USGS) and the University of Wyoming, have developed a method to analyze why moose choose to eat what they do, how their choices change in the presence of predation and how moose diets actually affect the stability of entire ecosystems.
The results appear in "Negative frequency-dependent foraging behaviour in a generalist herbivore (Alces alces) and its stabilizing influence on food web dynamics" published in the Journal of Animal Ecology.
"The research shows how what you would think is a simple decision -- what to eat -- is a complex process that depends on many environmental factors, such as how common food types are, how likely a moose is to be killed by a predator and how difficult deep snow makes it to move around and find food," Hoy said. "The moose eat upwards of 40 pounds each day. You'd think if you had such dietary requirements you'd stuff your face with anything you can find, but that doesn't appear to be the case."
"Something one might consider small, even trivial -- what a moose chooses to eat -- appears to have a stabilizing effect on the whole food web." -- Sarah Hoy, assistant research professor
The advantage to moose of taking the time to seek out and eat plant species that are relatively rare is a well-balanced diet, which requires nutrients that might be found only in those rarer plants. Many plants also contain chemicals that are toxic to moose in large quantities, which means that moose can ingest them only in limited amounts. However, a moose whose palate is too discerning pays a price; a cost of focusing too much on the rare plants is the time spent on the search. Additionally, a moose in search of a delicacy might be a more likely target for a wolf.
"Moose have a choice: eat the rare stuff at risk of not eating enough food overall, or eat what is most common in the forest at risk of missing out on a well-balanced diet," Hoy said. "We hadn't really known how moose manage that choice until now."
Polarized Poop and Mathematics By analyzing a decade's worth of moose droppings under a polarized light microscope -- a technique known as microhistology, which is further explored on Michigan Tech's Unscripted science and research blog -- to determine what exactly moose are eating on Isle Royale, the researchers concluded that moose preferred to eat what was relatively rare in their home range. If balsam fir is rare, they prefer it; if balsam fir is common, they show less preference -- even passing it up in many cases to find a less common plant. However, moose appeared to become less fussy eaters in years when the risk of being killed by wolves was high and in years when deep snow likely made it more difficult for moose to move around and find food.
By combining the evidence of years of meticulous fieldwork with a mathematical model representing the Isle Royale system, Hoy and her fellow scientists were able to draw conclusions about why it's important that moose are choosy eaters in the context of the ecosystem.
Enter Rongsong Liu, associate professor of mathematics at the University of Wyoming. Liu built a mathematical food chain model that she said, "demonstrates that the selective foraging strategies of moose can have an important stabilizing effect on community dynamics and provide a useful framework for assessing the influence of the other aspects of foraging behavior on community stability."
The model further illuminates the strength of the connections across three trophic levels of the Isle Royale landscape: vegetation, herbivore, carnivore.
"The mathematical model is a way to test how important the patterns in moose behavior we observed are for the community as a whole," Hoy said. "Moose may change their diet in response to a harsh winter or a high risk of being killed by wolves, but how important is that to the ecosystem?"
Don DeAngelis, a research ecologist for the USGS, has worked with Liu to develop and analyze models of herbivores of the boreal forest, including moose. One factor influencing what a moose prefers to eat is the aforementioned toxins in certain plants and how those toxins can effectively skew moose diets toward better overall balance.
"The data implied the moose were deliberately limiting their intake of coniferous vegetation, and also that this effect was related to the level of other environmental conditions, probably the level of predation by wolves," DeAngelis said. "My role was to work with Liu to translate the way that we think wolves, moose and forest vegetation all interact with each other into mathematical equations, and then use these equations to build a model that reflects the way that the Isle Royale ecosystem works."
Ecological theory indicates that simple food chains, such as that of Isle Royale National Park, are prone to extinction. Where there is a single predator -- wolves -- and a single herbivore -- moose, which eats two basic kinds of plants: deciduous and conifer trees -- there can be erratic population fluxes. However, Hoy, Vucetich and colleagues discovered that the foraging behavior of the moose might be one factor that favors the persistence of wolves, moose and the different tree species in the food chain.
This distinctive combination of theoretical models and field observations from the predator-prey study on Isle Royale provides ecologists with more insight about how and why populations tend to persist where basic theories of ecology otherwise suggest that they should not.

Fearing cougars more than wolves, Yellowstone elk manage threats from both predators

IMAGE: Wolves are often implicated as the top predator affecting prey populations. New research from Utah State University indicates that cougars are actually the main predator influencing the movement of elk... view more 

Credit: National Park Service

Wolves are charismatic, conspicuous, and easy to single out as the top predator affecting populations of elk, deer, and other prey animals. However, a new study has found that the secretive cougar is actually the main predator influencing the movement of elk across the winter range of northern Yellowstone National Park.
The study highlights that where prey live with more than one predator species, attention to one predator that ignores the role of another may lead to misunderstandings about the impact of predators on prey populations and ecosystems. It also offers new insight into how prey can use differences in hunting behavior among predators to maintain safety from all predators simultaneously.
Utah State University researchers Michel Kohl and Dan MacNulty co-led the study, published in Ecology Letters, with Toni Ruth (Hornocker Wildlife Institute and Wildlife Conservation Society), Matt Metz (University of Montana), Dan Stahler, Doug Smith, and P.J. White (Yellowstone National Park). Their work was supported, in part, by the National Science Foundation, Ford Foundation, and Utah State University as part of Kohl's doctoral research. The study was based on long-term data from the Park's wolf and elk monitoring programs and Ruth's cougar research, which is detailed in a forthcoming book from the University Press of Colorado.
The team revisited global positioning system (GPS) data from 27 radio-collared elk that had been collected in 2001-2004 when numbers of wolves and cougars were highest. Kohl and MacNulty combined the elk GPS data with information on the daily activity patterns of GPS-collared cougars and wolves and the locations of cougar- and wolf-killed elk to test if elk avoided these predators by selecting for 'vacant hunting domains', places and times where and when neither predator was likely to kill elk.
"Cougars hunted mainly in forested, rugged areas at night, whereas wolves hunted mainly in grassy, flat areas during morning and at dusk" said Kohl, lead author of the paper and now an assistant professor at the Warnell School of Forestry and Natural Resources at the University of Georgia in Athens. "Elk sidestepped both cougars and wolves by selecting for areas outside these high-risk domains, namely forested, rugged areas during daylight when cougars were resting, and grassy, flat areas at night when wolves were snoozing".
Recognizing that cougars and wolves hunted in different places and at different times allowed the researchers to see how elk could simultaneously minimize threats from both predators. "Had we ignored the fact that these predators were on different schedules, we would have concluded, incorrectly, that avoiding one predator necessarily increased exposure to the other," said MacNulty, who is an associate professor in USU's Department of Wildland Resources and Ecology Center. "Movement out of the grassy, flat areas and into the forested, rugged areas to avoid wolves did not result in greater risk from cougars and vice versa because these predators were active at different times of the day".
Despite the compatibility of elk spatial responses to cougars and wolves, Ruth, who is now executive director of the Salmon Valley Stewardship in Salmon, Idaho, cautioned that "some adult elk still end up on the cougar and wolf menu, with those in poor condition during winter being most at risk".
Nevertheless, "the findings help explain why we observe wolves, cougars, and elk all coexisting and thriving on the Yellowstone landscape" said Stahler, who leads the current study of cougars in the Park. He notes that the ability of elk to coexist with wolves and cougars is consistent with their "long, shared evolutionary history".
More surprising, however, was that cougars, not wolves, exerted the most pressure on elk habitat selection. "Wolves are often the presumed or blamed predator for any change in a prey population, numerical or behavioral," said Smith, who leads the Park's wolf program. "Our research shows that this is not necessarily true, and that other large predators in addition to wolves need to be considered."
"Despite the fact that most prey species live in habitats with multiple predators, the majority of research on predator-prey interactions focuses on a single predator species," added Betsy von Holle, program director for the National Science Foundation's Division of Environmental Biology. "The novelty of this research is the simultaneous study of multiple predator species, revealing the complexity of predator avoidance behavior by the prey."

What drives Yellowstone's massive elk migrations?

Study finds elk have the means to adapt to changing climate cues, but migratory shifts may have unknown ripple effects throughout the region

University of California - Berkeley

IMAGE: Yellowstone's migrating elk use climate cues, like melting snow and greening grasses, to decide when to make the trek from their winter ranges in prairies and valleys to their summer... view more 

Credit: Joe Riis

Every spring, tens of thousands of elk follow a wave of green growth up onto the high plateaus in and around Yellowstone and Grand Teton national parks, where they spend the summer calving and fattening on fresh grass. And every fall, the massive herds migrate back down into the surrounding valleys and plains, where lower elevations provide respite from harsh winters.
These migratory elk rely primarily on environmental cues, including a retreating snowline and the greening grasses of spring, to decide when to make these yearly journeys, shows a new study led by University of California, Berkeley, researchers. The study combined GPS tracking data from more than 400 animals in nine major Yellowstone elk populations with satellite imagery to create a comprehensive model of what drives these animals to move.
"We found that the immediate environment is a very effective predictor of when migration occurs," said Gregory Rickbeil, who conducted the analysis as a postdoctoral researcher in Arthur Middleton's lab at UC Berkeley. This is in contrast with some other species, such as migratory birds, which rely on changing day length to decide when to move, Rickbeil pointed out.
The results, published in the current issue of the journal Global Change Biology, suggest that, as climate change reshapes the weather and environment of the park, elk should have the means to adjust their migratory patterns to match the new conditions.
While this adaptability may benefit the survival of the elk, it may also have unknown ripple effects in local economies and throughout the Greater Yellowstone Ecosystem -- one of the last remaining large, nearly intact ecosystems in Earth's northern temperate zone, which encompasses about 18 million acres of land managed by more than 25 public entities and hundreds of private landowners. Another recent UC Berkeley-led study suggests that climate change is likely to hit National Parks harder than other areas of the country.
"The decisions that these animals make about when to migrate are absolutely dependent on changes in the landscape, changes that are ultimately governed by the climate," said Middleton, an assistant professor of environmental science, policy and management at UC Berkeley and senior author on the study. "And in the future, with climate change, we should expect the timing of these mass movements to be altered, which will affect the other wildlife and the people who depend on them, including predators, scavengers and hunters across the ecosystem."
Though the migration study's period was too short to say whether or not climate change is already affecting migratory timing, the tracking data did reveal a surprising trend: Elk on average arrived on their winter ranges 50 days later in 2015 than in 2001. This change had been noted by wildlife managers in the area, but had yet to be quantified on the ecosystem scale until now.
"This [study] provides great insight into the adaptation strategies of elk to climate change in the Greater Yellowstone Ecosystem," said Jonathan Jarvis, former director of the National Park Service, who now serves as executive director of the Institute for Parks, People, and Biodiversity at UC Berkeley.
Jarvis noted that more broadly, the new picture of the Yellowstone elk migrations provided by the study's comprehensive mapping effort "clearly demonstrate the need to think and operate at the landscape scale." He added, "For the park managers, this kind of research gives them options and incentives, such as protection of migration corridors and seasonal habitats, for ensuring elk and other keystone species in the Greater Yellowstone Ecosystem will persist."
Eating and being eaten
Yellowstone's approximately 20,000 migratory elk are among the most important large mammals in the ecosystem, comprising about 10 million or so pounds of animal biomass pulsing in and out of the parks and adjacent wilderness areas each year -- so where they can be found at any given time matters to both animals and humans alike.
"These elk eat a lot of things, and they are eaten by a lot of things, so wherever these masses of hundreds or thousands of elk are on the landscape determines who gets to eat and who doesn't," Middleton said. "In some cases, this could be sensitive populations of carnivores, like grizzly bears or wolves, and on the human side, it could be hunters, some of whom are making their income as outfitters and guides."
Recent studies have shown that threatened grizzly bears depend heavily on newborn elk calves as a food source in spring -- right when the migration is happening -- and that a Yellowstone wolf kills, on average, 16 elk per year. Meanwhile, each fall, thousands of hunters from around the country pay guides for the chance to harvest an elk in the wilderness near Yellowstone.
While a smattering of studies has investigated the migration of individual herds in the park, none before this study had investigated the phenomenon on an ecosystem scale. To get a more complete picture of migration, Middleton partnered with state and federal wildlife managers in the Yellowstone region to pool information on 414 elk across nine herds that had been fitted with GPS collars between 2001 and 2017.
Rickbeil then analyzed the data to pinpoint when each elk made its trek from winter range to summer range and back again and used satellite images to infer the conditions on the ground during journeys.
He found that elk tended to leave their winter ranges and set out to their summer ranges as soon as the snow had melted and during the "green-up," when fresh, nutritious plant growth began to sprout. Likewise, encroaching snowfall and hunting pressure cued them to make the return journey.
The team was surprised by the extent of the elks' flexibility: One year, a female elk might migrate in early May, but the next year in late July, depending on the timing of snowmelt and green-up.
"They've got a big brain and big eyes, and they can look around and, to a large degree, see changes on the landscape and react to them," Middleton said.
However, Rickbeil notes, the snow cover and vegetation couldn't fully explain why the elk are now arriving so much later at their winter ranges. Variations in snow depth, which cannot be inferred from satellite data, might explain part of the dramatic change, Rickbeil said.
Alyson Courtemanch, who manages the Greater Yellowstone Ecosystem's Jackson elk herd as part of her job as a wildlife biologist with the Wyoming Game and Fish Department, says knowing the whereabouts of the elk is critical to her job setting hunting seasons and managing the spread of diseases among wild elk and domestic cattle.
"We've been observing a lot of really interesting changes over the past decade about the way that elk are moving across the landscape, specifically of the timing of the migrations," said Courtemanch, who supplied GPS data on the Jackson herd for the study. "This analysis helped confirm a lot of things that people on the ground had suspected were happening, but that weren't really quantified."
"It seems like these animals can adapt to changing climates, which is likely a good thing," Rickbeil said. "But there will be a lot of consequences to these changes."

Surprisingly, inbred isle royale wolves dwindle because of fewer harmful genes

Genomic signatures of extensive inbreeding in Isle Royale wolves, a population on the threshold of extinction

American Association for the Advancement of Science

The tiny, isolated gray wolf population on Isle Royale has withered to near-extinction, but not because each animal carries a large number of harmful genes, according to a new genetic analysis. Instead, each one has been more likely to inherit the same harmful recessive alleles from both parents. This pattern enables expression of related genes as physical deformities, including the population's characteristically crooked spines. The findings contradict many previous studies, which suggest the crux of the genetic problem for historically small or sharply reduced populations is an increase in the quantity of harmful alleles. While the Isle Royale wolf population once consisted of 50 wolves, it has dwindled to just two - a father and daughter that are also half siblings. The collapse of the Isle Royale wolf population occurred despite a reported genetic "rescue" in 1997 by a single migrant from the mainland. To better characterize the genome-wide effects of intense inbreeding and isolation on this population, and their role in its decline, Jacqueline A. Robinson and colleagues analyzed mutations within the protein-coding regions of DNA from Isle Royale wolves, compared with genetic data from wolves in nearby mainland Minnesota. The former didn't have a greater number of deleterious genes than the Minnesota group, but the proportion of Isle Royale wolves with paired harmful recessive alleles in their genome was 38.4% higher. When the researchers compared Isle Royale genetic data with that from other wolf genomes from around the world, they found that individuals from historically large populations more frequently contained two different alleles at a gene location, while those from historically small populations more frequently contained short sequences of identical allele pairings, as with the Isle Royale wolves. These findings, supported by further simulations, contain broader implications for conservation efforts to manage fragmented populations at risk for decline due to inbreeding. Individuals brought in from historically small populations, rather than those from larger, more diverse gene pools, may actually prove more beneficial because they carry fewer potentially harmful alleles.