As 2016 draws to a close, hundreds of local extinctions have just been announced, suggesting that many plants and animals are on their way to global extinction.
Complete extinction has already happened to at least one species this year. The last-known Rabb's fringe-limbed treefrog from Panama died in a zoo in September. A new study, published in the journal PLOS Biology, shows that more than 450 species, representing 47% of the 976 surveyed no longer inhabit regions where they once lived.
Author John Wiens of the University of Arizona told Seeker that, in the U.S. alone, local extinctions have occurred "in 15 plant species, 18 marine fish species, 14 mammal species and 46 bird species. The plants include Gambel's oak and alligator juniper in southern Arizona. The mammals include the pika, pinyon mouse, jumping mouse and the alpine chipmunk. Marine fish include the Atlantic redfish. Birds include the dark-eyed junco, red-breasted nuthatch, two-barred crossbill and the Nashville warbler."
Wiens determined that the majority of local extinctions are happening in the warmest parts of the ranges of both plants and animals, strongly indicating that climate change is a driver. The result is striking because global warming has increased mean temperatures by less than 1.4 degrees Fahrenheit. Temperatures are predicted to increase by an additional 1 to 5 degrees in the next several decades.
The number of local extinctions varies by region, but the phenomenon is almost twice as common in the tropics versus other parts of the world. The finding lends support to a theory developed by pioneering biologist Daniel Janzen 40 years ago, holding that species in tropical areas are specialized to live in a narrow range of temperatures. Since tropical regions experience warm temperatures all year long, species living there have not had to adapt to very cold or very hot fluctuations.
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"So the idea is that tropical species are not adapted to coping with a broad range of temperatures, and so are more susceptible to a rapidly changing climate," Wiens said.
In other places around the globe, the local die-offs are evident even to untrained eyes.
"In some parts of the Southwestern U.S., you can see entire hillsides covered with dead trees, which are likely to have died because of climate change," he said. "In many places, there have been extinctions of entire frog species caused by interactions between climate change and a fungus, with more than 50 species likely to have gone extinct in the Andes Mountains and South America."
"There have been local extinctions of lizard populations around the world," he continued. "There have recently been massive die-offs of corals, especially in the past year in the Great Barrier Reef."
He and other researchers believe that another major threat to flora and fauna globally is habitat loss, which can act together with climate change. For example, he said that a species might be able to survive climate change if it could move to higher elevations to remain cool, but it could not do so if it lived on a small, isolated preserve surrounded by a chopped-down rainforest.
He and others are particularly concerned about edible grasses, such as wheat, rice and corn. Worldwide, humans on average depend on these plants for about half of all calories that they consume. In many places, the success or failure of crops depends a great deal on climate, rather than just irrigation. Prior research determined that grasses do not evolve fast enough to keep pace with climate change, putting many individuals at potential risk of starvation.
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"People in the U.S. should not simply think about how climate change will affect them," Wiens said. "Instead, they should also think about how the climate change that they helped cause might contribute to the loss of plant and animal species around the world, and to crop failures and the loss of human life in other countries."
Mark Urban, an associate professor and director of the Institute of Biological Risk at the University of Connecticut, told Seeker that "further work is needed to relate observed local extinctions directly to climate change and to differentiate them from the natural ebb and flow of range boundaries. Such work is difficult, but will be necessary to separate signal from noise and create accurate predictions for future responses."
Urban continued, "If many of these local extinctions ultimately can be linked to climate change - and I think that many will - then this research will add to mounting evidence that climate change is altering global biodiversity."
Wiens advises that all of us need to make an effort to reduce our carbon emissions, and not just to curb local extinctions.
"Many of these things will cause people to save money and be healthier, like biking or walking instead of driving, and eating a mostly vegetarian diet instead of lots of meat, especially beef," he explained. "Other things include recycling and getting energy from solar and wind power rather than fossil fuels."
Photo (top): Rabb's fringe-limbed treefrog, which is now extinct. Credit: Brian Gratwicke, Wikimedia Commons WATCH: We're Not The Only Species to Cause a Mass Extinction