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.

Wolf-dog 'swarms' threaten Europe's wolves

"Swarms" of wolf-dog crossbreeds could drive Europe's wolves out of existence, according to the lead author of new research.
Such hybridisation - driven by human activities that destroy habitats and mean wolves encounter more and more free-roaming dogs - threatens the "genetic identity" of wolves.
The study compares the views of more than 40 scientists and warns that a lack of engagement and agreement could hamper efforts to tackle wolf-dog hybridisation.
The findings suggest most scientists agree on the nature of the problem, but are divided on how to deal with it.
"We need to address this issue before wolf-dog hybrids backcross with wolves to the extent that wolf populations will be lost to hybrid swarms, and the conservation of wild populations will become unfeasible," said lead author Valerio Donfrancesco, of the Centre for Ecology and Conservation on the University of Exeter's Penryn Campus in Cornwall.
"In this paper, we argue that scientific agreement is crucial to encourage decision-makers to act, and to raise awareness about this conservation issue in society at large.
"The fact that we know so little about the ecology, behaviour and social acceptance of the wolf-dog hybrids adds a layer of concern to the issue."
The study, which allowed scientists to share their views anonymously, revealed agreement that people should be educated about the impact of free-roaming dogs, and that governments should remove wolf-dog hybrids from small and recovering wild wolf populations.
But scientists were divided on issues such as how to remove hybrids and free-roaming dogs, and whether they should be kept captive, sterilised and released or killed.
Donfrancesco said: "The disagreements emerged from diverging ethical values between scientists of different backgrounds, such as ecologists and geneticists, from the lack of data on the effectiveness of different interventions, and from the worry of some scientists that on practical grounds allowing the removal of hybrids would open a legal loophole for the killing of wolves."
Co-author Paolo Ciucci, of the Sapienza University of Rome, said: "The management of hybrids and wolf-dog hybridisation should not be a taboo topic, especially within the scientific community.
"There are margins to develop further consensus among scientists if further research addresses topical issues such as the effectiveness and the feasibility of control measures and their social acceptability.
"Scientists should not avoid the problem just because its management appears overly complex."
Co-author Dr Nibedita Mukherjee, from the University of Exeter, added: "We hope that by highlighting areas of disagreement and why they occur, we will be able to build a more unified scientific opinion, and aid an effective management of this urgent issue."
An estimated 17,000 wolves live in Europe, in populations of varying sizes in countries as far apart as Spain, Greece and Finland.
The paper, published in the journal Frontiers in Ecology and Evolution, is entitled: "Unravelling the scientific debate on how to address wolf-dog hybridization in Europe."

The return of the wolves

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Date:

May 20, 2019

Source:

University of Freiburg

Summary:

Researchers examine global strategies for dealing with predators.

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FULL STORY

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Howling wolves.

Credit: © dine Haase / Adobe Stock

The current return of wolves to human-dominated landscapes poses a major challenge for the protection of this species, says conservation biologist and private lecturer (PD) Dr. Marco Heurich from the University of Freiburg. He emphasizes that conflicts arise around the conservation of wolves in these landscapes due to farm animal slaughter, competition with hunters and human protection. The question of how humans can coexist with predators triggers a strong emotional debate.

Based on these observations, a team of scientists led by Dr. Dries Kuijper from the Mammal Research Institute of the Polish Academy of Sciences in Białowieża, Poland, analyzed the existing knowledge on how to deal with large carnivores living in the wild in Europe and other parts of the world. The aim was to enable an objective, scientifically sound discussion of various scenarios of wolf management. The researchers have presented their results in the current issue of the scientific journal Biological Conservation.
According to the scientists, the control of wolf populations, which is often advocated in other countries outside the European Union, is in clear contradiction to current European legislation. In addition, several studies show that control of populations by hunting does not resolve conflicts and can even lead to problems between humans and animals. Fencing in the areas where wolves live is a common tool in other parts of the world for the containment of predators. But even that, according to the researchers, is not practicable in the highly fragmented European landscapes to the extent necessary to maintain a healthy wolf population. In addition, large-scale fencing has a negative impact on other wildlife, leading to fragmentation of habitats. However, the scientists claim smaller electric fences are effective in excluding wolves from high-conflict areas with a high density of livestock.
From a legal standpoint, the least problematic situation is when no preventive measures are taken against the wolves, but farm animals are protected and compensation is paid for any damage caused. The team around Heurich assumes, however, that the conflicts between humans and wolves will become more frequent as wolf populations grow. In addition to protecting farm animals with electric fences or guard dogs, for example, the researchers recommend strengthening the natural population of ungulates such as deer and red deer in order to prevent conflicts.
In addition, the scientists suggest influencing wolf behavior and working towards proper human behavior. The use of so-called deterrence measures, i.e. negative conditioning, is intended to ensure that animals avoid humans. At the same time, however, people must learn to have respect for animals. In this way a meeting of wolves with farm animals and humans can be avoided. However, the Freiburg scientists explain that so far the only experience gathered for this method stems from the Yellowstone National Park in the US, so that its suitability for Central Europe must first be investigated.
Finally, Heurich and his colleagues stress that an important aspect of wolf management is to provide the public with a balanced view of the wolves: "People must be convinced of the ecological value that the return of the wolves has. It is necessary to show that these animals pose a very low risk to human safety. However, we must not forget that wolves are large predators who demand respect."

Isle Royale winter study: 13 new wolves, 20 radio-collared moose

IMAGE: Two of the newly introduced gray wolves pick their way through deep snow on Isle Royale. view more 

Credit: Rolf Peterson/Michigan Tech

Fifteen wolves. 2,060 moose. Extensive ice and deep, powdery snow. Michigan Tech researchers have released the annual Winter Study report. In its 61st year, the study is the longest running examination of a predator-prey relationship in the world.
The report chronicles the four-week research expedition to the island, where researchers track -- by ski and plane -- wolves and moose, collar moose, and catalogue the cascading effects of an ecosystem that has lacked a healthy population of apex predators for a number of a years.
New Tracks in the Snow Prior to this fall and winter's wolf reintroductions, the wolf population on the remote island had remained at just two -- a strongly bonded, but also highly inbred male-female pair -- for three years. The moose population, lacking predation, expanded by an average of 19% each year during the past eight years since 2011, when the wolf population first dwindled to fewer than 10 individuals. Consequently, primary plant species in moose diets -- balsam fir and watershield -- dropped precipitously.
The National Park Service (NPS), after an extensive review process, decided to introduce new wolves to the island. In September and October 2018, NPS introduced four Minnesota-born wolves (one male and three females) to the island. In late October, the male wolf died and on January 31, 2019, one of the female wolves left the island by crossing the ice bridge that had formed on Lake Superior, which reached nearly 95% ice cover.
In late February, NPS in collaboration with the Ontario Ministry of Natural Resources (OMNRF), introduced four Canadian-born wolves, including a male and female from a pack near Wawa, Ontario, and two males from Michipicoten Island, Ontario. In late March, NPS and OMNRF introduced seven more wolves to the island, including three males and three females from Michipicoten and one male from near Wawa.
For researchers, perhaps equal parts vexing and exciting are the unanswered questions about the future of the wolves on the island.
"Some of the most important questions at this point are: Will there be pups this year? How quickly will the wolves form a pack, and how many packs?" said John Vucetich, professor of ecology at Michigan Tech and report co-author. "As is so often the case with nature, the answer is, nobody knows -- but three packs is the likely answer."
The Michigan Tech School of Forest Resources and Environmental Science researchers speculated that wolf pups could be possible this year, but the new wolves were introduced to the island near the end of the traditional breeding season, so only time will tell.
Vucetich added that there are similar questions pertaining to the moose. "What's going to happen to the moose population? Will it keep increasing from 2,060, or level off, or decline quickly or slowly? The answer is the same, nobody knows."
To seek the answers, researchers fitted the first GPS-enabled radio collars since 1985 to the newly introduced wolves and 20 moose. The collaring efforts are part of a collaboration with University of Minnesota College of Veterinary Medicine, National Park Service and Grand Portage Band of Lake Superior Chippewa.
New Collars, More Data Collaring the moose will also help researchers understand the effects of predation, as well as other factors that influence the moose population, including forage abundance, parasites and climate.
"As soon as you start collaring individuals you learn about them in great detail; they all have interesting stories," said Rolf Peterson.
The researchers are also excited about their collaboration with Jennifer Forbey, an associate professor of biology at Boise State University, who studies the chemical ecology of herbivory.
Scientists are coming to understand that the reason many herbivores eat what they eat is due to subtle chemical differences in the plants. Isle Royale offers a unique environment in which to study herbivory.
"Most people study a herbivore's decision of what to eat when there are no predators involved," Vucetich said. "They've got all day to figure out which plant they want. But when exposed to a predator, they still have a choice of which plant to eat, but the calculus of the decision is more complex."
And what individual moose elect to eat may have a profound impact on their population as a whole. Lacking predators, the growing moose population has ravaged much of the available forage on the island, and that has consequences.
"We expect there might be a slowing down of moose population growth next year, at least at the west end of the island," said Sarah Hoy, assistant research professor. "The moose have severely damaged much of the vegetation they rely on during winter on the western end of the island. And it was such a deep-snow winter, it'll have been more difficult for them to get around and find food."
According to the report, moose browsing is one factor relating to a decline in the number of mature fir trees. In 1988, 473 mature balsam fir trees were tagged on the western end of the island. Only 28 (6%) of those tagged trees remained in 2018.
Watershield, a floating-leafed aquatic plant, has also experienced decline as the moose population grew. In the late 2000s, watershield covered as much as 90% of the water surface in ponds on the eastern side of the island. By 2018, it was not readily found in aquatic areas.
Next Steps
Reintroducing a thriving wolf population to Isle Royale also has an effect on the island's other residents, which include beavers and foxes. Wolves eat beavers as well as moose, and so the beaver population, which has been booming since 2012, may eventually decline to levels of a decade ago, about 20% of current numbers. Foxes, which are scavengers, will likely benefit from the return of the island's apex predator.
Also of interest to the scientists is evidence of yet additional wolves who may have crossed the ice bridge and visited Isle Royale during the winter. Each winter, the Isle Royale wolf-moose project embeds a husband-wife team, Ky Koitzsch and Lisa Osborn, to observe the moose and wolves by skis, and they found evidence of the tracks of an unknown wolf on the island. Aerial survey suggested that perhaps three wolves crossed the ice and circumnavigated the island, but this may have been just a quick visit followed by a return home to the mainland.
Peterson, Hoy and Vucetich are headed back to the island in May to conduct summer research, along with six students who will showcase their progress on the project's social media.
As usual, four to five dozen volunteers will head to the island for the annual Moosewatch Expedition to collect bones at locations where the collared wolves seem to have lingered long enough to presume they were feeding on a dead moose.
"When we're there in the winter, we learn a tremendous amount about the moose population, but this summer we are hoping to learn a lot more detailed information about moose behavior and what they like to eat, depending on how tolerant the collared moose are of being watched," Peterson said. "This summer should likewise prove valuable in determining the trajectory of both wolf and moose populations. This is definitely a notable year."
Indeed, there is a sense of renewal in this year's report. For the first time in 10 years, the researchers spotted fresh wolf tracks at Windigo.