Climate-only models likely underestimate species extinction – ScienceDaily

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Environmentalists estimate that 15 to 37% of plant and animal species will become extinct as a direct result of rapid climate change. But new research conducted by the University of Arizona and published in the journal Ecology Letters shows that current models do not take into account the complexity of ecosystems as they are affected by climate change. As a result, these extinction rates are probably underestimated.

As the climate continues to change rapidly, the area in which a given species can live often shrinks. The researchers wondered what factors beyond climate need to be taken into account in trying to determine the abundance, distribution and risk of species extinction.

“This is a central question in ecology, and it has become even more important with climate change,” said Margaret Evans, co-author of the study, assistant professor of dendrochronology at the Tree Rings Research Laboratory. Arizona.

Evans and coworkers used data from over 23,000 pines in the southwestern United States to model how climate affects pine species. While the climate directly affects trees through temperature and precipitation, it also affects them indirectly through its influence on insects and fire, the researchers found. These indirect effects can cause rapid changes in the population and distribution of trees in the landscape. The researchers say this nuance cannot be captured using climate-only models, which base their estimates on direct climate impacts.

“If we are to make predictions, we have to know what causes species to be in an area in the first place,” said Emily Schultz, lead author of the study, who was a postdoctoral researcher at Arizona when this research was conducted and is now a postdoctoral fellow. researcher at the University of Nevada, Reno. “We were looking at climate and competition with other species as two possible explanations. What we found is that both factors have some importance for where we find species, but the climate seemed to be. most important.”

Anyone can observe the direct effects of climate on plant species as they travel up the Santa Catalina Mountains north of Tucson, where pine pines grow, Evans said. As you go up, the landscape cools and the ecosystem changes from desert to scrub through pine forests. As the climate of the southwestern United States warms and dries up, the species retreat to areas with cooler temperatures higher up the mountain. At the top, some species have nowhere to go.

The more complex indirect effects of climate on species distribution are likely to cause sudden changes in abundance and distribution that are not predictable from a climate perspective alone, Evans said.

“Climate change has cascading effects on ecosystems. Climate stress makes individuals physiologically weak and more susceptible to disease,” Evans said. “Understanding the distribution of species is much more complicated than climate models alone will, because they don’t capture this level of complexity. The predictions of climate-only models represent the end point you would expect if nothing complicated happened, but that’s not the real world. “

The researchers chose to examine pine pines because the species has undergone dramatic population changes in recent decades, due to drought and ensuing insect outbreaks.

“In the early 2000s, there was a severe regional drought,” Schultz said. “These unfortunate conditions have stressed the trees and made them vulnerable to attack from their natural enemy, the bark beetle.”

Climate indirectly affects piñons in other ways as well. Wet conditions alone can have a direct and positive impact on piñons, but such conditions can also have indirect negative effects. More rain means more vegetation, which can fuel forest fires.

“Pine pines are not fire resistant at all,” Schultz said. “We then want to include fire in our models.”

Evans said she had her “aha!” when she was chatting over lunch with a friend on campus.

“He told me about one of his articles on the extinction of the Monte Verde Golden Toad,” she recalls. “Was it the climate or was it the invading chytrid fungus that caused massive frog deaths around the world? The bottom line for Monte Verde’s Golden Toad was that this was an interaction between the two. The year of extreme drought they had then reduced the size and number of ponds in which the frogs were found. Because they were crowded into smaller ponds, they transmitted the fungus more quickly. “

Evans said the script made him realize how the climate and other factors could interact to cause sudden decline and extinction.

Similar patterns of climate-related stress, disease and mass mortality are appearing in species around the world. For example, a disease known as starfish dieback syndrome hit starfish populations in 2013 and 2014, sword fern plants died en masse in 2013, and saiga – a kind of antelope – was wiped out in 2015. Evans and coworkers say the same. The patterns will continue as species struggle to cope with a rapidly changing world.

They say that an increase in unusual weather events, which they call the “global strangeness” of the Earth’s climate system, will be accompanied by a “weirdness” of the Earth’s ecology.

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