Climate-only models likely underestimate species extinction

Date:
December 9, 2021
Source:
University of Arizona
Summary:
To accurately predict species' distributions and risk of extinction,
models must include more than just climate, according to new
research.



FULL STORY ========================================================================== Ecologists estimate that 15 to 37% of plant and animal species will go
extinct as a direct result of the rapidly changing climate. But new
University of Arizona-led research published in the journal Ecology
Letters shows that current models don't account for the complexities of ecosystems as they are impacted by climate change. As a result, these extinction rates are likely underestimated.


==========================================================================
As the climate continues to rapidly change, the area in which a given
species can live often shrinks. Researchers wondered what factors beyond climate must be considered when trying to determine species abundance, distribution and risk of extinction.

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

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

"If we want to make predictions, we have to know what causes species to
be in an area in the first place," said lead study author Emily Schultz,
who was a postdoctoral researcher at UArizona when this research was
conducted and is now a postdoctoral 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 to where we
find species, but climate seemed to be more important." Anyone can
observe the direct effects of climate on plant species by driving up the
Santa Catalina Mountains north of Tucson, where pin~on pines grow, Evans
said. As you ascend, the landscape cools and the ecosystem changes from
desert to shrubland to pine forests. As the climate in the southwestern
U.S. warms and dries, species retreat to areas with cooler temperatures
farther up the mountain. At the very top, some species have nowhere left
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-only perspective, Evans said.

"Climate change is having cascading effects on ecosystems. Climate stress
makes individuals physiologically weak and more susceptible to disease,"
Evans said.

"Understanding species distribution is much more complicated than
climate models alone will capture because they don't capture that level
of complexity.

The predictions from climate-only models represent the end point you would expect if nothing complicated happened, but that isn't the real world."
The researchers chose to look at pin~on pines because the species has
undergone dramatic population changes in recent decades, due to drought
and subsequent insect outbreaks.

"In the early 2000s, there was a strong, regional drought," Schultz said.

"Those unhappy conditions stressed the trees and made them vulnerable to
attack by their natural enemy, the bark beetle." Climate also indirectly affects pin~ons in other ways. Wet conditions alone can have a direct and positive impact on pin~ons, but such conditions can also have indirect
negative effects. More rain means more vegetation, which can be fuel
for wildfires.



========================================================================== "Pin~on pines are not at all resistant to fires," Schultz said. "We
want to next include fire in our models." Evans said she had her
"aha!" moment when she was talking over lunch with a friend on campus.

"He told me about a paper of his about the extinction of Monte Verde
golden toad," she recalled. "Was it climate or was it the invasive
chytrid fungus that caused frogs worldwide to go through massive
die-offs? The bottom line, for the Monte Verde golden toad, was that it
was an interaction between the two. The extreme drought year they had then reduced the size and number of the pools the frogs were found in. Because
they were crowded into smaller pools, they transmitted the fungus
more rapidly." Evans said the scenario made her realize how climate
and other factors could interact to cause a sudden decline and extinction.

Similar patterns of climate-driven stress, disease and mass mortality
events are popping up in species around the world. For example, a disease
known as sea star wasting syndrome struck sea star populations in 2013
and 2014, sword fern plants died off in droves in 2013 and saiga -- a
kind of antelope -- were decimated in 2015. Evans and her collaborators
say similar patterns will continue as species struggle to cope with a
rapidly changing world.

They say an increase in uncharacteristic weather events, which they
refer to as the "global weirding" of Earth's climate system, will be accompanied by a "weirding" of Earth's ecology.

========================================================================== Story Source: Materials provided by University_of_Arizona. Original
written by Mikayla Mace Kelley. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Emily L. Schultz, Lisa Hu"lsmann, Michiel D. Pillet, Florian Hartig,
David D. Breshears, Sydne Record, John D. Shaw, R. Justin DeRose,
Pieter A. Zuidema, Margaret E. K. Evans. Climate‐driven, but
dynamic and complex? A reconciliation of competing hypotheses
for species' distributions. Ecology Letters, 2021; DOI:
10.1111/ele.13902 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211209133924.htm

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