Climate Change Poses Challenges to Plants and Animals
In the Rocky Mountains, climate change has raised summer temperatures 0.72˚ F each decade over the last 30 years, while snows are melting three to five days earlier in spring. Wildflowers bloom several days earlier, with peak flowering also occurring earlier. No one knows what this might eventually mean for pollinators. In Australia, warmer winters are forcing mountain pygmy possums out of hibernation earlier than their prey, the bogong moth, so many are starving to death. In Europe, roe deer, whose fertility is triggered by the length of days, are giving birth after the first flowers, which are blooming earlier than in the past. The mismatch of 36 days between birthing times and food availability is resulting in a decline in the deer population’s fitness.
According to one study, spring, summer, fall and winter in the temperate zones are all arriving on average 1.7 days earlier than they did before 1950. The U.S. Environmental Protection Agency reports that average temperatures in the U.S. have increased 0.14˚F per decade, and worldwide, the decade from 2001 to 2010 was the warmest on record since measurements began. The changing climate with its more extreme weather is already affecting many plant and animal species and disrupting ecosystem functioning.
The Intergovernmental Panel on Climate Change estimates that 20 to 30 percent of assessed plants and animals could be at risk of extinction if average global temperatures reach the projected levels by 2100. Evolution would have to occur 10,000 times faster than it typically does in order for most species to adapt and avoid extinction.
A 2011 study found that in response to warming temperatures, species are moving to higher elevations at an average rate of 36 feet per decade and to higher latitudes approximately 10 miles per decade, though individual species vary in their rates.
The National Wildlife Federation reports that 177 of 305 North American bird species shifted their range further north by 35 miles in the last 40 years; and over the last century, 14 species of small mammals extended their range 1,640 feet higher in the Sierra Nevada region. But many scientists say climate change is occurring too rapidly for the majority of species to outrun it. And even if some species are able to migrate northward or upward, they could enter territory where there is increased competition for food or unprecedented interactions with species they have never encountered before. Those that are already at their northern limits have no place left to go. For example, as forests move north into the tundra, many Arctic creatures such as caribou, arctic fox and snowy owl are losing their habitat. Other species may not be able to migrate due to geographical obstructions or man-made barriers such as cities or highways.
In addition to driving species to cooler regions, warming temperatures affect the timing of seasonal life cycle events of plants and animals such as mating, blooming or migration. One population of pink salmon in Auke Creek, Alaska, and sockeye salmon in the Columbia River are migrating to spawn earlier than they did 40 years ago in response to warmer water temperatures. The changing conditions can lead to mismatches of life cycle events, making growth or survival more difficult when babies are born or migrating animals arrive before or after their food is available. In one Dutch park, as spring arrives earlier, caterpillars are appearing earlier, but their predators, the great tits, are not always laying their eggs earlier, so the bird population is declining.
Pests and pathogens, however, benefit from warmer temperatures, which enable them to expand their territory and survive through the winter; their populations are on the increase.
From 1997 to 2010, mountain pine beetles destroyed trees on 26.8 million acres in the American West. Warmer winters have helped an oyster parasite extend its range from Chesapeake Bay north to Maine, with the potential to cause large oyster die-offs. The Aedes aegypti mosquito that carries dengue and yellow fever and that is usually found in Texas or the southeastern United States appeared as far north as San Francisco in 2013.
With less winter snowfall to insulate the soil and keep it warm, frozen soils result in more root death and nutrient runoff, which can produce algal blooms and dead zones where nothing can survive. Decreasing snow pack in the mountains can create a greater risk of winter and spring flooding, and means there will be less snowmelt runoff to cool streams in summer and fall. Changes in stream flow and temperature can damage habitat and stress fish and wildlife, disrupting their life cycle events. And as rivers and streams become warmer, warm-water fish are crowding cold-water fish out of their habitat.
Warming oceans become increasingly acidified, stressing corals and causing bleaching and die-offs. Warmer waters also cause the rapid melting of Arctic sea ice, which has ramifications all along the food chain: The decline of sea ice results in the loss of ice algae, which are eaten by zooplankton. Arctic cod, which feed on zooplankton, are the prey of seals, which in turn are the main food of polar bears.
Global warming is also intensifying rainfall, flooding, hurricanes and droughts. Changing precipitation patterns can affect plant growth, the amount of moisture in soils, nutrient runoff, water retention and insect prevalence. In California, drier conditions have meant less food for desert bighorn sheep. The drying up of ponds in Yellowstone National Park has led to the decline of four amphibian species. And in the Sonoran Desert in the southwest, some bird species stop breeding altogether during extreme drought conditions.
Over the last 50 years, the Arctic has warmed two to three times faster than the rest of the planet. The tundra is a treeless expanse with only low-lying growth where the subsoil is permanently frozen. Because of global warming, however, more and more woody deciduous shrubs are appearing. Natalie Boelman, assistant research professor at Lamont-Doherty Earth Observatory, is studying the impacts of the changing conditions here on some of the millions of songbirds from all over the world that migrate to the Arctic in spring and summer to breed because of abundant food sources and fewer predators and parasites.
The increasing shrubbiness of the Arctic means that the habitat and food supply are changing. The Lapland longspurs that Boelman and her team are studying prefer to nest on the open tundra, while the Gambel’s white-crowned sparrows favor shrubs. On the open tundra, spiders, beetles and more predator insects are prevalent. The shrubbier areas have many types of flies and grasshoppers, so all the birds are eating more flies which is their preferred food source.
Relative to 30 years ago, the sparrows’ range limit has moved north by dozens of miles, tracking the shrubs they like to nest under as the shrubs move north. “Because of changing food availability and environmental conditions, the birds on the northern range are more stressed,” said Boelman. “But they are doing it so far.” Looking ahead, Boelman predicts there will be an increase in sparrow habitat and a decrease in longspur habitat. “It seems clear that shrub nesters will be happy, but open nesters will have a harder time. … Maybe the longspurs can move further north, but it’s a very waterlogged area, so they may be out of luck unless they can adapt to these shrubbier habitats.”
Boelman’s team is also researching the impacts of changing seasonality. The birds, which migrate based on day length cues unaffected by climate change, will likely continue to arrive in the Arctic at the same time each year. Their reproduction is timed to dovetail with the availability of insects, so that when chicks are born, there is plenty of food. With spring now beginning earlier, fall arriving later and a resulting longer growing season, Boelman is investigating whether the chicks will be hatching after the period of greatest insect availability and thus have a harder time surviving.
The Arctic generally has very unpredictable spring weather conditions, with huge swings between years. As it turned out, the growing season started 12 days late in 2013. The birds also showed up later, had their babies later, found enough insects to eat and did fine dealing with the delayed snowmelt. The delays had no significant effect on their reproduction. Boelman explained. “Animals living and migrating up there are well adapted to big swings and extremes. Perhaps they will react less to climate change because they are already well adapted. We are looking at if we are starting to exceed the range of conditions they can cope with.”
While organisms that adapt evolve through natural selection over many generations, some individual organisms can change their features (developmental, behavioral and physical) during their lifetime in response to the environment through phenotypic plasticity. Plasticity enables organisms with identical genes to exhibit different traits in reaction to climate conditions through altering gene expression. For example, a Rocky Mountain wild mustard plant’s traits normally vary according to whether it is growing at a low elevation with a hot, dry climate or at higher elevations under cold, wet conditions. Researchers found that when they simulated climate change by reducing the snowpack at an intermediate elevation, the plants flowered earlier and took on the appearance of the lower elevation plants.
Having phenotypic plasticity could allow some species to remain in place and give others time to migrate and adapt. Having more plasticity could also help some species migrating to new areas better adapt to unfamiliar conditions. How plastic a species is can also potentially evolve over time, as species with genes that allow for plasticity might survive better in changing climate conditions. It’s also possible, however, that climate change could cause some organisms to change in ways that make them less able to adapt.
Factors other than plasticity also affect how well a species can adapt to climate change. The shorter the generation time (the time it takes for a species to go from one generation to another), the faster the evolutionary rate. The size of a particular population, the amount of genetic variability it has and the fitness of its individuals are also important variables. Adaptation could conceivably keep pace with climate change in situations where there is less environmental disruption, a good-sized population with genetic variation, short generation times and fit individuals.
For example, the Quino checkerspot butterfly, once common in Southern California, was thought to be at risk of extinction because of climate change and habitat loss. To the surprise of scientists, it adapted by shifting its range to higher ground and finding a completely new plant on which to lay its eggs.
Some corals in Samoa have also shown unexpected resilience in response to higher water temperatures. Scientists believe that natural selection may have favored the most heat-tolerant corals, allowing them to survive and produce more offspring.
While there are numerous examples of nature’s resilience, today species also face the human-induced stresses of pollution, invasive species and habitat fragmentation or degradation, which can decrease or isolate populations and inhibit migration, all of which make adaptation more difficult.
Organisms that do not have the phenotypic plasticity or genetic variation that enable them to adapt to changing conditions may well face extinction. For example, the endangered red-cockaded woodpecker, which depends on the longleaf pine forests in the southeast U.S., has not shifted its range north at all. As its habitat changes, scientists do not know if the bird will survive.
Polar bears are at risk because of their long generation times and small populations. According to the National Wildlife Federation, the amount of Arctic sea ice observed in 2012 was 49 percent less than in the 1980s and 1990s. Polar bears need thick near-shore ice on which to hunt seals, but with the sea ice dwindling so rapidly, polar bears must now swim, sometimes as long as 12 days, to reach offshore ice floes, and they often drown. The U. S. Geological Survey projects that two-thirds of the world’s polar bear sub-populations will be extinct by 2050.
A National Wildlife Federation report offers a range of recommendations to safeguard wildlife including:
- Provide funding to federal and state programs that promote climate science and adaptation.
- Make sure that steps taken to reduce carbon emissions minimize impacts on wildlife and their habitats.
- Promote climate adaptation plans that enhance natural ecosystems and habitats while providing natural protection against extreme weather events.
- Discourage development and infrastructure building in environmentally sensitive areas.
- Make room for wildlife to shift their ranges in response to changing climate conditions by expanding parks and refuges and providing connectivity between them.
There are now a number of efforts to preserve larger expanses of land that allow for species to move. Landscapes that run north-south like the Yellowstone-to-Yukon project, a joint U.S. and Canada initiative seeking to preserve wild lands from Yellowstone to the Yukon, would allow organisms to move north to cooler temperatures. East-west landscapes would enable species to move away from the increasingly hot, dry West. The Wildlands Network aims to create four Continental Wildways, large protected areas for wildlife movement across North America.
The Nokuse Plantation in Florida, the largest private conservation project east of the Mississippi, is a strategic link between various tracts of existing protected lands. The Quabbin-to-Cardigan partnership’s mission is to preserve 2 million acres of one of the largest areas of intact, ecologically important forest in central New England. And Regional Conservation Partnerships are helping private owners, public organizations and agencies in New England work together to preserve larger and connected areas of land.
Renowned evolutionary biologist E.O. Wilson believes the only way to prevent the sixth mass extinction of life on earth is to set aside half the planet for all the other species. He described his vision this way: “I see a chain of uninterrupted corridors forming, with twists and turns, some of them opening up to become wide enough to accommodate national biodiversity parks, a new kind of park that won’t let species vanish.”