Category Archives: Biodiversity

Video: mountain species, climate change, and the escalator effect

Mountains are especially vulnerable to climate change, so scientists are keeping a close watch on species such as the American pika (Ochotona princeps). This small mammal, which resembles a hamster and is a relative of the rabbit, lives in alpine and subalpine terrain across Western North America.

Although relatively widespread and usually found in protected public lands, the American pika is considered an indicator species for climate change and may face a challenging future. These cute critters are super-sensitive to heat and can die in a matter of hours is exposed to temperatures of 78 degrees or above.

As the mercury continues to rise in the decades ahead, pikas and many other mountain species are expected to ascend in elevation in search of cooler conditions—what’s been dubbed the “escalator effect.” But mountains eventually top out at a summit or ridge, so plants and animals can only climb so high.

“The pika is toast,” is how environmental law expert J.B. Ruhl opened his 2008 Boston University Law Review article on the challenge of administering the Endangered Species Act in an era of climate change.

Although some scientists and conservation groups remain deeply troubled about the pika’s prospects, recent research on the species has suggested it may be more resilient than previously thought.

Because pikas are photogenic and mountains are at the heart of the American West, I thought they would be fitting subjects for our first EcoWest video, which is embedded below (you can also watch on our Vimeo and YouTube channels). This is a new format that we’d like to explore further, so I’d welcome any feedback from viewers.

Escalator effect: climate change and mountains from EcoWest on Vimeo.

Background on boulder bunnies

Pikas live near sea level in parts of Western Canada, but in the United States they’re found much higher up. In places such as Nevada and Southern California, they’re rarely observed below 8,200 feet. In North America, as one moves southward toward warmer climes, pikas live at progressively higher elevations.

Here in Colorado, pikas are a common sight on talus slopes around treeline (roughly 11,000 feet) and above. The five-ounce animals blend in well with the boulders and scree, so you’re likely to hear them chirping first. But they’re not hard to see in summer as they scurry to gather grass and flowers for “hay piles” that will sustain them through the brutal alpine winter.

“Charismatic and conspicuous” is how the National Park Service’s Pikas in Peril project describes the animals, which were called “little chief hares” in the 19th century and are nicknamed “boulder bunnies” today.

American pika in Colorado
American pika in Indian Peaks Wilderness, Colorado. Photo by Mitch Tobin.

Conservation status and climate change

The International Union for the Conservation of Nature’s Red List, which rates the status of species around the world, puts the American pika in its “least concern” category. But the IUCN also notes that “the most pervasive threat affecting the American pika appears to be contemporary climate change.”

The map below (from this presentation by Scott Loarie at Stanford’s Carnegie Institution) shows the probability of pikas going locally extinct in the American West in the 21st century. Areas in red, such as Northern California, Oregon, and the Great Basin, are where pikas face the greatest threats of extirpation. They’re expected to fare better in higher-elevation blue areas, in places like Colorado, Wyoming, and Montana. (This map includes areas with suitable habitat but no pikas; for the outlines of the pika’s current range, see this image.)

Probability of pika extirpation in 21st century

Noted conservation biologist Stuart Pimm, who taught Loarie in graduate school, says that “if Scott’s map is correct, pikas will no longer be charming companions to weary, out-of-breath hikers like me in Nevada, Oregon, and most of California.”

Below is another set of projections from University of Idaho researchers. These maps show the pika’s suitable habitat under three climate change projections: B1 is an optimistic scenario for greenhouse gases, A2 is pessimistic about our ability to contain carbon emissions, and A1B lies in between. According to this study, higher emissions and warmer temperatures will shrink the pika’s range.
Current and projected suitable habitat for pikas

Current and projected suitable habitat for pikas

Steep declines in Great Basin

Besides increasing heat-related stress, global warming could, paradoxically, cause pikas to freeze to death. If warming temperatures thin the snowpack, the animals will have less insulation during the winter, when they retreat beneath the surface but don’t actually hibernate.

In a place like the Great Basin, where climate change is projected to boost summer temperatures and shrink the winter snowpack, pikas face a “perfect storm,” the IPCC says. A 2011 paper in Global Change Biology concluded that the extinction rate for pikas in the Great Basin had increased nearly five-fold over the past decade. Examining 25 sites with historical records of pikas in the 20th century, the researchers found that nearly half of the local extinctions had occurred since 1999. Pikas in the Great Basin have been moving upslope at an average rate of nearly 500 feet per decade since 1999, 11 times faster than before (see this ScienceDaily story for details).

American pika in Indian Peaks Wilderness, Colorado
American pika in Indian Peaks Wilderness, Colorado. Photo by Mitch Tobin.

Resilient species?

While Great Basin pikas appear to be in deep trouble, other research in the American West has found that the species is adapting to the 21st century climate. A 2011 study of 69 historical pika sites in the Southern Rockies, some dating back more than a century, found the animals still present at 65 of the locations.

Since the 1940s, scientists have been observing pikas living in ore dumps near Bodie, California, at about 8,400 feet elevation. “There appears to be no evidence that heat stress in summer at Bodie causes mortality or population decline of pikas on these small habitat islands,” the IUCN said, although warmer temperatures may have inhibited pikas from colonizing unoccupied habitat.

Here’s how the Fish and Wildlife Service describes the situation:

Despite the trends of increasing American pika declines in the Great Basin due to increasing temperatures, there is ample evidence that the species can survive and thrive in some habitats with relatively hot surface temperatures. American pika populations thrive at a lower elevation site in the mountains near Bodie, California and in the hot climates of Craters of the Moon (Idaho) and Lava Beds National Monuments (California). Pika persist at these sites because they reduce activity during hot mid-day temperatures by retreating to significantly cooler conditions under the loose rock areas and perform daily activities during the cooler morning and evening periods. Despite altering their behavior in response to high temperatures, pikas can maintain high birth and low mortality rates.

Feds decline to list pika under ESA

That statement from the Fish and Wildlife Service came in response to a 2007 petition from the Center for Biological Diversity to list the American pika under the Endangered Species Act.

In February 2010, the Fish and Wildlife Service declined to protect the pika under the tough federal law. “Although the American pika could potentially be impacted by climate change, we believe the species as a whole will be able to survive despite higher temperatures in a majority of its range,” the Fish and Wildlife Service said. “We believe the pika will have enough high elevation habitat to ensure its long-term survival.”

Working with the National Oceanic and Atmospheric Administration, the Fish and Wildlife Service developed models to predict if increasing surface temperatures due to climate change would affect the pika (below the surface, in the crevices of a talus slope, temperatures can be as much as 43 degrees cooler).

“New peer-reviewed information and rigorous scientific research demonstrates that the pika is able to survive despite higher temperatures and will have enough suitable high elevation habitat to ensure that it will not face extinction in the forseeable [sic] future,” the agency said. The Center for Biological Diversity called the ruling a “political decision that ignores science and the law.”

The history of the Endangered Species Act certainly has its share of political meddling (see my book Endangered for the full story). But in this case, listing the pika wasn’t a biological slam dunk, in part because the danger lies decades ahead. The Fish and Wildlife Service acknowledged the jeopardy, saying “climate change is a potential threat to the long-term survival of the American pika,” but it concluded that the threat wasn’t urgent enough to warrant regulatory action. About 93 percent of the pika’s habitat is already under federal control and 30 percent is designated as wilderness.

Other species moving uphill

Pikas are just one of many mountain species that are being forced to adapt to climate change by moving uphill.

In August, researchers reported in Ecology and Evolution that plants have been scaling a mountain range near Tucson, Arizona in response to climate change. By re-examining a transect in the Santa Catalina Mountains five decades after a 1963 survey, scientists found “large changes in the elevational ranges of common montane plants” and concluded that “the Southwest is already experiencing a rapid vegetation change.” (See this story from the University of Arizona for more details on the study.)

As shown in the figure below, a Southern Arizona mountain is a layer cake of life zones, ranging from the Sonoran Desert at the bottom to a spruce-fir forest at the top. Enough warming could push the top layers right off these mountains.

Life zones in a typical southern Arizona mountain


Mountains and climate change

Anyone who has climbed to the top of West’s tallest mountains knows that biological diversity tends to decline the higher up you go. Here in Colorado, the tundra above treeline is a harsh environment (it’s already snowing in September), so few species can survive. Yet many mountains are biological gems with large numbers of endemic species found nowhere else. “Although species richness decreases with elevation, mountain regions support many different ecosystems and have among the highest species richness globally,” according to the Intergovernmental Panel on Climate Change.

Here’s how the U.S. Global Change Research Program summed up the situation:

Animal and plant species that live in the mountains are among those particularly sensitive to rapid climate change. They include animal species such as the grizzly bear, bighorn sheep, pika, mountain goat, and wolverine. Major changes have already been observed in the pika as previously reported populations have disappeared entirely as climate has warmed over recent decades. One reason mountain species are so vulnerable is that their suitable habitats are being compressed as climatic zones shift upward in elevation. Some species try to shift uphill with the changing climate, but may face constraints related to food, other species present, and so on. In addition, as species move up the mountains, those near the top simply run out of habitat.

In 2010, the Center for Biological Diversity also petitioned the Fish and Wildlife Service to grant Endangered Species Act protections to four other mountaintop species: the ‘i‘iwi, a Hawaiian songbird; the white-tailed ptarmigan, a grouse-like bird that lives in the Rockies; Bicknell’s thrush, a songbird from the Northeast; and the San Bernardino flying squirrel of Southern California. All of these petitions are currently under review.

Winners and losers

On balance, scientists see global warming as a threat to fragile mountain ecosystems, but some montane species may actually benefit from climate change.

In 2010, scientists reported in Nature that yellow-bellied marmots (Marmota flaviventris) had increased in both size and number in response to warming conditions. Warmer weather means less time hibernating, more time fattening up, and therefore a higher survival rate for this type of ground squirrel. “Earlier emergence from hibernation and earlier weaning of young has led to a longer growing season and larger body masses before hibernation,” the scientists concluded. (See this companion story in Nature and segment on NPR for more on the marmot study.)

Marmot in Holy Cross Wilderness, Colorado
Marmot in Holy Cross Wilderness, Colorado. Photo by Mitch Tobin.

Climate change will create winners and losers, not only among high-country critters but also in human society and the global economy. A resurgent marmot population will have implications for other species in their habitat, while any declines among pikas will affect their own ecological niche. As challenging as it is to predict the future range and behavior of one species, the situation gets even more complicated once you factor in the many interconnections in the web of life.


Download Slides: Escalator EffectDownload Slides: Escalator Effect (9.29 MB pptx)

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EcoWest’s mission is to analyze, visualize, and share data on environmental trends in the North American West. Please subscribe to our RSS feed, opt-in for email updates, follow us on Twitter, or like us on Facebook.

Viewing biodiversity through the ecoregional lens

The Nature Conservancy’s Atlas of Global Conservation is a fabulous resource for understanding biological diversity. Scientists have divided up the world into more than 1,000 ecoregions and analyzed how they compare across dozens of measures.

I’ve used data from TNC’s atlas to create a slide deck that illustrates patterns in species richness and threats to biodiversity, with a focus on the United States and American West. Below is a video of the PowerPoint, which you can download at the bottom of this post.

Visualizing biodiversity through the lens of ecoregions from EcoWest on Vimeo.

Biome basics

Before we get to ecoregions, let me first note a broader way that TNC and others classify the natural world: biomes. An area’s climate more or less determines what types of plants can grow, and at the highest level we can classify the planet’s land masses according to the predominant vegetation, or lack thereof. There are 16 terrestrial biomes, ranging from snow and tundra to tropical forests.

The map below (click to enlarge) shows the biomes found in the United States. Much of the interior West is dominated by desert and xeric (dry) shrublands, but the higher elevations support temperate conifer forests. California has Mediterranean forests along much of its coast and the Sierra Foothills. There’s a bit of subtropical forest in the mountains of Southeast Arizona and temperate broadleaf forest in Oregon’s Coastal Range.

United States biomes

As with temperature, rainfall, and elevation, there is more uniformity in the biomes found in the East than the West. Look, for example, at how many different types of communities are found in California, or how isolated mountains in the Great Basin create little biome islands.

The United States actually leads the world in the number of biomes and smaller ecoregions within its borders, even exceeding countries that are much larger in size, as shown in the graphic below.

United States biomes and ecoregions

So it’s no surprise that the United States also ranks high in species diversity. In the graphic below, blue bars show the number of species by type. Orange diamonds show what percent of the world’s species are found in the United States and the number in parenthesis in the labels indicate the U.S. ranking worldwide. The highest levels of diversity for several groups are found in the United States, including freshwater mussels, freshwater snails, and crayfishes; several other groups, such as freshwater fishes and gymnosperms, are also well represented here.

United States ranks high in species diversity

Analyzing ecoregions

A more fine-grained view than biomes classifies the terrestrial world into 825 unique ecoregions. These areas are sort of like ecological neighborhoods with similar habitat. Below is a close-up of the American West. If you were to drive through several ecoregions on an interstate road trip, you’d notice the differences simply by looking out the window.

Ecoregions of the American West

TNC’s atlas also analyzes the planet according to its 426 freshwater ecoregions. Each of the regions has a unique collection of aquatic species and freshwater habitats. The map below shows the West’s two-dozen or so freshwater ecoregions, which generally correspond to the boundaries of important river basins.

Freshwater ecoregions of the American West

Dozens of biodiversity metrics

TNC’s atlas offers dozens and dozens of layers of geographic information by terrestrial, freshwater, and marine ecoregion. The deck that you can download at the bottom of this post has 71 slides, with views of both the world and United States.

To give you a taste of what’s available, here’s a summary of three slides.

1) Species diversity is greatest around the equator

One way to describe biodiversity is to look at the evolutionary distinctiveness of species in a given location. The map below shows the phylogenetic diversity of terrestrial vertebrate species (animals with a backbone). Phylogenetics is a measure of how closely related a group of species is. An ecoregion with high phylogenetic diversity has species that are more distinct from one another (see this summary and this paper for more on the measure).

In general, measures of species diversity are greater at lower latitudes due to the past effects of Ice Age glaciation at higher latitudes and the configuration of islands and other landforms on the Earth, both past and present. In the West, phylogenetic diversity of vertebrate species tends to be highest in the desert Southwest.

Phylogenetic diversity of species

2) Hotspots for threatened animals 

The analysis and conservation of biodiversity often focuses on those species most at risk of extinction. The map below shows the number of globally threatened animals by terrestrial ecoregion. Threatened species are those listed by the International Union for the Conservation of Nature’s Red List as vulnerable, endangered, or critically endangered. Globally, some of the greatest concentrations of threatened vertebrates are in South America and Southeast Asia. About half of the threatened animals are reptiles and amphibians, one quarter are mammals, and one quarter are birds. In the United States, the Southwest, the foothills around California’s Central Valley, the Southeast, and the Appalachians have the most threatened animals.

Number of globally threatened animals

3) Plenty of plants in arid American West

The map below shows the number of plant species by terrestrial ecoregion. Worldwide, there are more than 420,000 of the so-called higher order plants: trees, vines, grasses, fruits, vegetables, and legumes. Deserts and arid lands typically have fewer plant species, while tropical rainforests have the most. But in North America, some drier parts of the inland West actually have more plant species than wetter climes along the coast. Compare, for example, the Great Basin in Nevada to Washington.

Number of plant species

Those are just a few of the slides that I found most interesting. I’d be curious to hear from readers if they spot other patterns.

Data sources

To create the maps, I downloaded the GIS data from Data Basin (a search query for “Hoekstra,” as in atlas lead author and EcoWest advisor Jon Hoekstra, will return all the layers).

I highly recommend the book form of TNC’s atlas, which taught me a ton about biodiversity around the globe.

See this page for more background on ecoregions from WWF.


Download Slides: TNC Conservation AtlasDownload Slides: TNC Conservation Atlas (54.77 MB pptx)
Download Notes: TNC Conservation AtlasDownload Notes: TNC Conservation Atlas (5.18 MB pdf)

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EcoWest’s mission is to analyze, visualize, and share data on environmental trends in the North American West. Please subscribe to our RSS feed, opt-in for email updates, follow us on Twitter, or like us on Facebook.

Hawaii, West and South have most at-risk species

The United States boasts the greatest diversity of ecosystems of any country and it’s home to more than 200,000 species. But about one-third of U.S. plants and animals are considered at risk by biologists, and at least 500 U.S. species are already extinct or missing.

How do the 50 states compare in terms of number of species—and their imperilment? I’ve created some simple dashboards that illustrate the state-by-state tallies. These graphics, which you can sort, print, and customize, show the number of various types of species found in each state and the fraction of those species that are imperiled.

Percent of species at risk

The data comes from Precious Heritage: The Status of Biodiversity in the United States, a great book produced by The Nature Conservancy and NatureServe in 2000. At-risk species have elevated risks of extinction, according to the system developed by the project, and therefore have the greatest conservation concern.

Here are some of the patterns I noticed in the dashboards:

  • Despite their aridity, many Western states have tons of species. Arizona and New Mexico, neither of which have any coastal habitat, rank third and fourth in total number of species.
  • Hawaii has by far the greatest percent of species at risk. The native biodiversity of this isolated archipelago has been devastated by the introduction of non-native species.
  • States in the West, especially the Southwest, also have many imperiled species. California, Arizona, Utah, and Nevada round out the top 5 states.
  • Freshwater fish are doing very poorly, especially in the West, where Arizona, Utah, Nevada, New Mexico, California, and Oregon all have at least 25 percent at risk.
  • Outside of Hawaii, birds tend to be doing better than many other types of species.

Using the dashboard

A couple of notes about the dashboards:

  • You can sort by state name or by any of the variables at the bottom.
  • Because Hawaii is such an outlier, I can be helpful to examine the dashboard by excluding that state (just click on the name and the option will pop up).
  • The toolbar at the bottom allows you to create an image or PDF, plus download the underlying data.
  • This dashboard reports the percent of a state’s species at risk, not the actual number, but that data is also provided in Precious Heritage.

Learn more in our biodiversity deck

These dashboards focus on the state level, but in our biodiversity slide deck we offer a slew of maps and graphics summarizing the national picture. The one below shows that many freshwater species are in jeopardy, whereas some of the best known types of species, such as birds and mammals, are doing comparatively better.

National species at risk

Data sources

Anyone doing research on U.S biodiversity should definitely check out the Precious Heritage book. It contains a wealth of information on the status of U.S. species and many of the graphics in the book are available for free download on this page.

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[catlist name=biodiversity]

EcoWest’s mission is to analyze, visualize, and share data on environmental trends in the North American West. Please subscribe to our RSS feed, opt-in for email updates, follow us on Twitter, or like us on Facebook.