Predictions of the loss of animal and plant diversity around
the world are common under models of future climate change. But a new study
shows that because these climate models don’t account for species competition
and movement, they could grossly underestimate future extinctions.
“We have really sophisticated meteorological models for
predicting climate change,” says ecologist Mark Urban, the study’s lead
author. “But in real life, animals move around, they compete, they parasitize
each other, and they eat each other. The majority of our predictions don’t
include these important interactions.”
Plenty of experimental studies have shown that species are
already moving in response to climate change, says Urban, assistant professor of
ecology and evolutionary biology at the University of Connecticut.
For example, as temperatures rise over time, animals and plants that can’t take
the heat are moving to higher altitudes where temperatures are cooler.
But not all species can disperse fast enough to get to these
more suitable places before they die off, Urban says. And if they do make it to
these better habitats, they may be outcompeted by the species that are already
there—or the ones that got there first.
With coauthors Josh Tewksbury and Kimberly Sheldon of the University of Washington, Urban created a mathematical
model that takes into account the varying rates of migration and the different
intensities of competition seen in ecological communities. The goal was to
predict just how successful species within these communities would be at
shifting to completely new habitats.
Their results showed that animals and plants that can adjust
to climate change will have a competitive advantage over those that don’t.
Animals with small geographic ranges, specific habitat needs
and difficulty dispersing are likely to go extinct under climate change, their
model shows. Further, these animals are more likely to be overrun by other
species that can tolerate a wider range of habitats.
“When a species has a small range, it’s more likely to
be outcompeted by others,” Urban says. “It’s not about how fast you
can move, but how fast you move relative to your competitors.”
Urban likens this scenario to a train traveling up a mountain
on a track. If each boxcar—representing a species—travels at the same speed,
they will likely all reach the top eventually. But in reality, each car can
move at a different speed, creating a collision course.
“There’s always a car in front of you and a car
behind,” explains Urban. “When you introduce the ability to move at
different speeds, they’re constantly bumping into one another, even running
each other over. It’s a recipe for disaster.”
Importantly, the authors speculate that current predictions
of biodiversity loss under climate change—many of which are used by
conservations organizations and governments—could be vastly underestimating
Tropical communities, for example, which often have many
species living in small areas, could be among the hardest hit by climate
change. Urban says that this is a first step toward making climate change
predictions of biodiversity more sophisticated.
“This a first step—to include in our models things that
we know are true, like competition and dispersal,” says Urban.
“Knowing these things, can we predict which species might be most at risk?”
SOURCE – University of Connecticut