THE GREAT GLOBAL SPECIES SHAKEUP
Climate change is redrawing the boundaries of where plants, animals and other organisms can survive. But what happens if the bees, caribou and black spruce can’t keep up?
GUELPH, ONT.— On a relentlessly sunny afternoon last July, two bumblebee researchers met outside the chain-link fence surrounding Pollinator Park, a flower-filled former landfill in Guelph.
It was late in the day and hot. They had spent hours trudging through tangles of wildflowers and thickets of grass, hauling nets, mini-coolers and specimen jars.
Amanda Liczner’s team had begun in nearby Georgetown, while Victoria MacPhail worked alone in the park. Both are graduate students in the same lab at York University, and both were searching for bumblebees — the rarer the better — in separate but related projects.
They compared notes. It had been a bad day for bumblebees. MacPhail found one Bombus perplexus, acouple of Bombus impatiens and a dozen Bombus bimaculatus, all common species. Liczner’s crew fared the same: a bunch of bimaculatus and not much else. “Affinis?” Liczner asked. “No affinis,” MacPhail said. She unlocked a gate in the fence, letting Liczner’s team inside to continue its work. She bolted it closed again.
“You can’t leave until you find affinis,” MacPhail said, both a joke and a plea.
Bombus affinis, the rusty-patched bumblebee, was once common across eastern North America. Its population has plummeted.
In Canada, nobody has seen one in years. The last known sighting was at Ontario’s Pinery Provincial Park in 2009.
Affinis is listed as endangered in both the U.S. and Canada, the only bumblebee with that dubious distinction in either country. But it is far from the only bumblebee species under pressure.
Bumblebees are one of nature’s climate refugees. Global warming is shifting bumblebees’ and countless other species’ ranges, slowly but forcefully redrawing the boundaries where each lives, feeds and breeds.
Roughly half of all species are on the move. The average rate of poleward shift for land-based species has been pegged by different estimates at between six and 17 kilometres per decade. Marine species are moving more than four times as fast.
But these global averages mask local chaos: ecosystems aren’t plodding predictably forward in lockstep. Two trees in the same forest might respond totally differently. Two animals that typically never meet might suddenly be thrust into contact.
Relationships that have adapted over millennia are rapidly being torn apart. No life forms will be spared the consequences of this global shakeup — including humans.
Human self-interest is perhaps one reason for the public’s fascination with the plight of bees. Three-quarters of our food crops depend to some extent on pollinators. But most attention has centred on honeybees. The honeybee,
Apis mellifera, is a single, domesticated species brought to North America 400 years ago by Europeans. Honeybees, like other livestock, are continuously managed by humans.
Evidence has mounted in recent years that a widely used class of pesticides, neonicotinoids, is damaging honeybee colonies. Negative effects are apparent in bumblebee colonies, too.
But comparing the European honeybee to Canada’s 42 species of wild bumblebees is like comparing the domestic house cat to jaguars, leopards and lions.
“Not all species will behave the same way under the same stressors,” says Sheila Colla, a professor of conservation science at York University who specializes in wild bees. MacPhail and Liczner are PhD students in her lab.
“A lot of our declining species, their ranges are in the boreal forests, or protected areas like the Smoky Mountains,” Colla says. “People aren’t spraying pesticides there so much. So I guess the question really is, why are wild bees in decline?”
In 2015, Colla was part of a team of researchers that tried to answer this question. The team analyzed 67 species of bumblebees, from Bombus frigidus, a tundra-dwelling bee, to Bombus
fraternus, the “southern plains” bumblebee. They gathered more than 400,000 instances when a specific bumblebee was observed in a specific location. Then they compared records of observations gathered between1901and1974 to records collected in recent years. What they found was startling.
Nearly all of the bumblebee species had seen losses along the southern edges of their ranges: they could no longer be found in the warmest reaches of their territory. On average, North American bumblebee species saw the southern edge of their ranges retract by more than 230 kilometres, farther than the distance from Toronto to Huntsville.
But the northern, cooler edges of the bumblebees’ ranges had failed to shift poleward. These northern limits were stuck — and in some cases moving southward.
Species that live in remote areas such as Canada’s Arctic, where there’s little bumblebee survey work, may be under-recorded at their northern limits. But remarkably, the team found the exact same pattern among well-studied European bumblebee species: southern limit losses, northern limit freezes. Bumblebees are being trapped in a climate vice. “There were so many species that were having a hard time,” says Jeremy Kerr, the University Research Chair in Macroecology and Conservation at the University of Ottawa and first author of the study, published in the journal Science. “It’s an awful finding. You just look at this and go, really?”
Bombus affinis, the rusty-patched bumblebee, was the most profoundly affected of the North American species, disappearing from more than half of its range. But even common species not considered at risk, such as Bombus bimaculatus and Bombus
impatiens, saw their ranges subtly eaten away. Why bumblebees are failing to shift poleward is unclear. “It unveils for us a frontier of research that we have to go explore rather urgently,” Kerr says.
It may have something to do with their life cycles. Butterflies can eat, move and eat again somewhere else. But bumblebees are “central place foragers”: a colony is tied to its nest.
Queen bees build their nests in early spring, and for the rest of the summer, worker bees and then new queens and males return to this nest for food.
The only chances to relocate are when the queen emerges from overwintering in rotten logs or mulch to build the nest, and at the season’s end, when new queens mate and find a spot to overwinter. These two opportunities to disperse are brief, and energy is scarce. Queens are starving when they first emerge in spring, and in fall, besides being busy trying to find a mate, the plants they prefer to forage on may be less available.
Whatever the cause, the consequences of this climate change squeeze — and all the threats piled on top of it, including habitat loss, non-native pests, pesticide contamination — are dire.
Bumblebees have a special trick. They can vibrate their thoracic muscles, a move called “sonication” that is the source of their distinctive buzz. Some plants, including tomatoes, peppers, eggplants, blueberries and roses, require “buzz pollination.” The pollen in their flowers is packed in tightly; when a bumblebee grabs on and vibrates, it is shaken loose. Honeybees are extremely inefficient at pollinating these plants.
The vibration trick also allows bumblebees to warm up. While other bees like honeybees need the sun to warm them, bumble- bees can forage at close to 0 C. What’s more, bumblebees are able to navigate via landmarks, rather than relying on the sun.
“Bumblebees can forage when it’s cloudy,” Colla says. “And spring in Canada is very rarely wide-open sunny days. So for most parts of Canada, native bees are probably better for that reason. They’re adapted to our climate.”
Colla and her lab are focused on wild pollinator conservation: retaining native bee species and the pollination services they provide.
Victoria MacPhail studies citizen science. One project, BumbleBeeWatch.org, allows the public to submit pictures of bumblebees from backyards, parks and beyond; the species are later confirmed by experts.
When combined with expert-collected data, like the work MacPhail was doing at Pollinator Park in July, citizen science is helping researchers accumulate vastly more records of bees than previously possible, including from remote locations like Baffin Island.
Amanda Liczner is trying to better understand the habitat requirements of rare bumblebee species. All the sites her team visited that day in July, from Georgetown to Guelph, were locations where a rare species had been spotted in the last 15 years. At each site, Liczner measured vegetation type and density.
Some researchers believe we should begin to consider conservation strategies for bees that are already in use for larger vertebrates: raising endangered species in captivity and then reintroducing them to the wild. But to do that, we need to know what each species’ habitat requirements are, knowledge that’s lacking. “We have records from the late 1990s of
Bombus affinis in downtown Toronto — the rusty-patched bumblebee, from St. George St.,” Colla says. “We know it was in the city. We know it’s in the Pinery. Why would it be in both of those places? What are those places offering it?
“So that’s what Amanda’s trying to figure out.”
We also know that Bombus affinis was in Guelph as recently as1998. But at Pollinator Park in July, neither Liczner nor MacPhail spotted one.
Both teams noticed male bumblebees, which aren’t supposed to emerge until later in the year — possibly a sign of inbreeding or another colony disorder. And both teams remarked that even the common species, like Bombus impatiens and Bombus bimaculatus, seemed less plentiful than usual, despite Ontario’s rainy summer.
The two teams diverged inside the park, trudging through clouds of purple vetch and bush clover. Finally, MacPhail spotted a bee and trapped it with a careful swish of her net. It was Bombus terricola, a species classified as vulnerable on the IUCN red list, an international database of threatened species. She was overjoyed.
“Hello beautiful,” MacPhail cooed to the bee. “I haven’t seen you all year.”
The boreal is the largest intact forest system on the planet, a thick crown of green that rings the Northern Hemisphere just below the Arctic Circle. Roughly a third of the Earth’s forest cover is boreal, and 28 per cent of the boreal is in Canada.
Canada’s boreal — stretching from the Alaskan border to Newfoundland — is culturally, economically and ecologically vital.
All of the Canadian boreal is traditional Indigenous territory; hundreds of First Nations, Inuit and Métis communities are located within it. The boreal’s timber, mineral and energy resources, and its hydroelectric production, prop up our economy. Some of Canada’s most iconic wildlife call the boreal home, and the forest is a major regulator of global climate, storing and releasing huge volumes of carbon.
In Canada, boreal is “lifeblood,” says Dennis Murray, the Canada Research Chair in Integrative Wildlife Conservation, Bioinformatics and Ecological Modeling at Trent University.
That is true above all to “boreal-obligate” species: plants and animals that live primarily within the boreal, and live there year-round.
In a study published this year in the journal PLOS ONE, a group led by Murray and Michael Peers of the University of Alberta examined 12 of these species, including trees such as black spruce, birds such as the grey jay, and mammals such as caribou and moose. The team wanted to know how the species would fare in a forest gerrymandered by climate.
A bird that migrates to the boreal from Mexico might be affected by environmental disturbance anywhere along its route. But these 12 species are at the mercy of changes to the forest.
“Any deterioration in the boreal forest would be reflected in changes to those species,” says Murray.
The team looked at the current environmental suitability of the niches of each species, inputting climatic conditions like the hottest, coldest, wettest and driest months. Then they modelled how those conditions would shift in the coming decades under projected climate change scenarios, creating a forecast for the species’ niches in 2050 and 2080.
A minority of species, such as northern flying squirrel and the jack pine, broadly benefited from the warmer, drier conditions. Their ranges were projected to increase in size.
But most of the 12 species saw their ranges severely contract and shift northward. By 2080, the boreal chickadee and the spruce grouse both lost more than 30 per cent of their climatically suitable boreal habitat. Moose lost nearly 37 per cent. Caribou lost over half. The habitat that remained suitable was more likely to be fragmented, with disjointed pockets spackling the landscape.
“One of the things that really blew me away in the analysis was how largely consistent their responses to climate change were,” Murray says, even though the study spanned three totally different groups: birds, trees and mammals.
Most shocking, Murray says, was what the team forecast in the narrowest band of Canadian boreal, the region of forest that runs below James Bay across the Ontario-Quebec border. In this connective tissue, which links the eastern and western halves of the forest, several species saw all of their suitable habitat lost.
Projecting future climatic conditions for a given habitat does not mean we know exactly how the living, breathing animals within those habitats will respond — the web of interactions between a species and its ecosystem are incredibly complex. But these models are “very worrying,” Murray says.
“If our predictions are upheld, you might expect to have completely isolated east and west moose or caribou populations in the years to come.”
Such constriction is usually bad for animals and their resilience, especially during times of rapid environmental change. The bigger a population, the bigger its reservoir of genetic diversity — the source of new and helpful adaptations.
Of the 12, perhaps the species of greatest concern is the boreal caribou, a subspecies that lives in the forest year-round. Boreal caribou are already listed by Canada’s Species at Risk Act as threatened: they lost half their range in Canada in the last 150 years.
Most of that loss was the result of changes in land use, biologists say. Industries such as oil and gas and logging have carved up the range.
Now climate change is compounding the degradation.
“These systems have built up over millennia,” says Steven Mamet, who researches biogeography and species range limits at the University of Saskatchewan. “It’s not just that the climate is changing, but that it’s changing so fast. It’s outpacing the systems’ ability to adapt.”
In one unusually severe drought year in Alberta and Saskatchewan, between 2001 and 2002, 45 million tonnes of trembling aspen at the southern edge of the boreal died — the equivalent of more than two years’ worth of hardwood tree harvest across Canada. Particularly in the west, warmer air temperatures have not been matched by an increase in precipitation. Drought-induced tree mortality is steadily increasing along the southern boreal treeline.
In the zone of patchy permafrost in the middle of the Canadian boreal, ecologists have found the opposite problem. Plateaus of conifers sit atop land that is thawing and sinking, waterlogging the trees. In other areas, the frost layer is moving deeper, taking precious moisture with it. Either way, permafrost loss is stressing and killing trees. Research shows that parts of this middle swath of the boreal — where massive amounts of
carbon is sequestered — could become a sparsely treed wetland.
“We’re seeing the landscapes sort of disintegrate,” says Jennifer Baltzer, Canada Research Chair in Forests and Global Change at Wilfrid Laurier University.
In the northwest boreal, and increasingly in the north-central, forest fires are burning hotter and wider; fires are expected to increase in frequency across the whole forest. Fires are a natural part of the forest system, and conifer species such as black spruce are adapted to recovering after such disturbances. But these super-intense fires sometimes scour away the entire organic soil layer. At severely burned sites, researchers have seen faster-growing deciduous species such as poplar and birch move in instead of the evergreen spruce returning, creating a totally different ecosystem.
Drought, flooding, fires: almost nowhere in the boreal seems to be immune to climate change’s suite of stressors. (One exception may be northern Quebec, where rainier conditions may form a pocket of refuge for boreal trees.)
Yet as these extreme events pile up, across the northern treeline, the boreal’s big conifers are not reliably expanding into the tundra: in some areas they are, but in others they are not.
One reason is what researchers call ecological inertia.
“Even though the climate is right for the forest to advance into the tundra, the structure and legacy of that tundra vegetation means that it’s resisting the forest from invading,” says Carissa Brown, a biogeographer at Memorial University of Newfoundland and lead of the Global Treeline Range Expansion Experiment.
Tree seeds need the right conditions to germinate. If a conifer seed is blown onto the dry, crunchy lichens of the tundra, it may sit suspended inches above soil, or be eaten by an animal competing in the tundra’s food-poor environment. If the seed does germinate, the tundra’s freeze-thaw churn might heave the seed right out of the ground.
Even in optimal conditions, the advance of big, slow-growing conifer species probably tops out at 10 kilometres a century. Parts of the boreal are likely to see winter warming increases of between eight and 10 degrees by the end of this century: the trees are simply being outpaced.
But on top of climate, Brown says “all of these other factors like food availability and habitat and predators are slowing down species’ ability to respond to climate. What that means is that it’s a really big complicated mess” to predict how and when and where a species will shift.
“You’d expect this united front — I often think of the analogy of pulling up your pants. Your whole pants go up all at once. But in reality, you’re sort of like pulling up a belt loop, and another belt loop is going down, and another one is getting smaller,” Mamet says.
These pressures affect many species of boreal wildlife, but caribou happen to be particularly sensitive. “There are very clear limits to the amount we can mess around in their habitat,” says Justina Ray, a wildlife biologist and the president and senior scientist of Wildlife Conservation Society Canada.
Once more than about a third of their territory is compromised, caribou populations begin to suffer. White-tailed deer move in, carrying a brain parasite that deer tolerate but that kills caribou. Moose move in, too, and predators like wolves follow the deer and moose. Caribou don’t reproduce as quickly as their cousins in the deer family, and the cumulative disturbances become too much.
Caribou may also be particularly sensitive to climate change because they rely on ground lichen as a winter forage. Winters are becoming weaker and less predictable. When snow thaws and freezes over again, or when rain falls on snow, it creates a layer of ice that traps lichen: caribou can’t paw through to their food.
Their sensitivity makes caribou a sentinel, Ray says, for the health of the boreal.
Murray agrees. They are “basically a canary in a coal mine,” he says.
Earth-orbiting satellites provide a continuous record of the planet’s surface going back decades. Twenty years ago, in data from satellite sensors that measure vegetation density, scientists noticed a trend.
Since the early ’80s, the northern latitudes had been getting greener. But the picture was fuzzy: the eight-kilometrewide pixels were too big to show whatwas greening. “That was really a black box,” says Ken Tape, an Arctic ecologist at the University of Alaska Fairbanks. At the time, Tape was a technician in the lab of geophysicist Matthew Sturm. Sturm had learned of a cache of 5,000 old photos gathering dust in a government office in Anchorage. They were about to be thrown out, but Sturm arranged for them to be sent to his office.
The U.S. Navy had taken them from a low-flying plane just after the Second World War. They were looking for oil and other resources, but the photographs turned out to be a scientific gold mine: historical evidence of the northern Alaskan landscape 50 years earlier.
Over the next two summers, Tape set out across Alaska to revisit hundreds of the scenes in the photographs. From a helicopter, he recaptured the original angles as closely as possible. The work was first published in a 2001Nature article.
“It was the first real glimpse into these greening pixels, and suddenly the light bulb kind of went,” Tape says.
The photo pairs showed that Arctic shrubs — low-lying deciduous plants like dwarf birch, willow and alder — had dramatically increased. Shrubs that had been barely visible now towered overhead. Shrubs had thickly filled in areas where there had been a scattering. Sometimes, shrubs had advanced into areas where none had been before.
The vegetation shift has been documented all across the Arctic, and has its own name: shrubification. “All of the other plants and animals in tundra ecosystems are affected by increased shrub abundance,” says Trevor Lantz, an ecologist at the University of Victoria.
A few years ago, Lantz and collaborator Robert Fraser learned of old photos sitting in a Canadian Forest Service warehouse.
In 1980, a PhD student had chartered a plane over the Tuktoyaktuk coastlands in the western Canadian Arctic, taking high-resolution photos to study reindeer herd habitat. Fraser, a research scientist at the Canada Centre for Mapping and Earth Observation at Natural Resources Canada, tracked down the photos.
In August 2013, the researchers mounted digital cameras to a helicopter and flew the same paths as the PhD student had in 1980, creating matching pairs of photos taken 33 years apart.
“It’s pretty unambiguous, the changes you can see,” Fraser says.
Shrub cover had increased in 97 per cent of the photo pairs. When combined with satellite data, their analysis showed that this area of the Northwest Territories is one of the most intensely greening regions of the Arctic.
Shrubs are likely better able to take advantage of warming than boreal conifers because they are already growing in the tundra habitat they prefer. But the photos also revealed a more fine-scaled trend, one suggested by plot studies elsewhere: as shrubs increased, lichens declined.
Tall shrubs are likely overtopping and crowding out lichens in this region. This could be a big problem.
“One of the really alarming potential impacts of shrub encroachment is the effect it will have on regional and global climate,” Lantz says.
Light-coloured lichen reflects more sunlight back to space than dark leaf matter. Shrubs also fracture the white reflective expanse of snow. This change in “albedo” — surface reflectivity — may be an accelerant to climate change.
The decline in lichen might also affect another form of wildlife: barren-ground caribou, a migratory cousin of the boreal caribou. Barren-ground caribou undertake seasonal journeys of hundreds, even thousands of kilometres across the tundra, and their ability to digest lichen — thanks to specific gut microbes — is a key adaptation allowing them to survive the environment.
Most barren-ground caribou herds are in steep decline. A federal panel of scientists classified the herds as threatened last year.
Wildlife biologists aren’t yet certain how climate is affecting these trends; the relationship to caribou ecology is complex.
But shrubs are less nutritious forage for caribou than lichens. Caribou also time their arrival to their calving grounds — the end of their massive migrations — to coincide with a brief pulse of green, highly nutritious vegetation. Climate change may be fraying this careful choreography, causing plants to burst forth earlier and caribou to miss this crucial opportunity.
Shifting species ranges have created a paradox for conservation planning: setting aside protected areas becomes difficult when we don’t know where endangered species will be in 100 years.
Canada, as party to the international Convention on Biological Diversity, has committed to protecting 17 per cent of its terrestrial area and 10 per cent of its marine territory by 2020. We have a long way to go: in 2016, Ottawa reported it had set aside 10.6 per cent terrestrially and 0.96 per cent of oceans. (Some new marine protected areas were added in 2017.)
Creating new protected areas is a slow process. Shifting species ranges add a complication.
Scientists speak of connecting conservation landscapes, and some are discussing a concept known as “dynamic” protected areas: boundaries that shift over time.
When Canadian researchers modelled the effectiveness of static versus dynamic protected areas for conserving American marten habitat in the Quebec boreal, dynamic areas that moved every 50 years created more high-quality habitat. But they also found that was harder to achieve when the forest was fragmented by logging and fires.
Of course, humans are animals, and our range is being profoundly affected by climate change, too. A recent study estimated the number of people displaced by sea level rise at two billion by 2100.
But the indirect impacts of shifting species ranges are just as profound.
Climate change is altering the distribution of Anopheles, the mosquitoes that transmit malaria, and Aedes, which transmit the dengue and Zika viruses. Climate change also affects the range of
Ixodes scapularis, the tick that transmits the bacterium causing Lyme disease.
For years, as concern in the U.S. rose over Lyme, Canada and its winters were considered mostly unsuitable habitat for deer ticks. The colder it is, the longer it takes a tick to develop from egg to larva to nymph to adult. If it is cold enough, many larvae will die before finding a host.
Jianhong Wu, Canada Research Chair in Applied and Industrial Mathematics at York University, and Dongmei Chen, a professor of Geographic Information Science at Queen’s University, were co-authors on a study published in June that modelled the impact of climate change on Ontario tick populations.
They had been following the rise of Lyme disease: in 2010, the federal government reported 143 cases. Last year, it reported 987.
They found that warming in Ontario has created new regions where tick populations can sustain themselves, including parts of the Niagara escarpment and Algonquin Provincial Park.
“Lyme disease has been established and will expand,” Wu says.
The Earth’s surface temperature has increased by one degree Celsius over the past 150 years. It is likely to rise by two to five degrees by this century’s end, with significantly more warming in the Arctic.
The shifts that scientists have observed so far have occurred with just this single degree of change. Even the Paris Agreement, seriously weakened after the U.S. pulled out of it, aims to limit warming to two degrees above pre-industrial levels. That would double the levels of warming — and the climate pressure on species — experienced so far.
As researchers struggle to track these changes, the only certainty is that we’re at the beginning of a great global species shakeup.
“It’s not just that the climate is changing, but that it’s changing so fast. It’s outpacing the systems’ ability to adapt.” STEVEN MAMET WHO RESEARCHES SPECIES RANGE LIMITS AT THE UNIVERSITY OF SASKATCHEWAN