Underground species of army ants are much less tolerant of high
temperatures than their aboveground relatives -- and that difference in
thermal tolerance could mean that many climate change models lack a key
element of how animal physiology could affect responses to changing
environments.
According to a new study from Drexel University, underground species
of army ants are much less tolerant of high temperatures than their
aboveground relatives--and that difference in thermal tolerance could
mean that many climate change models lack a key element of how animal
physiology could affect responses to changing environments.
At face value, this is not surprising, noted Sean O'Donnell, PhD, a
professor in Drexel's College of Arts and Sciences and senior author of
the study published in the
Journal of Animal Ecology. Ants that
live above ground are exposed to higher temperatures than subterranean
ants, so they should be expected to tolerate hotter conditions--but the
relationship between microhabitat and heat tolerance simply hadn't been
tested before. No one knew whether the subterranean ant species might
have been capable of handling high temperatures, even if they prefer
cooler ones.
Current models of climate change are built on predictions that animal
species may shift their geographic ranges to new latitudes or
elevations when the temperature rises. But these models typically use
temperature averages taken at a macro resolution--commonly measured 1
meter above ground, and encompassing areas of a square kilometer or
more--and they don't generally take into account that different species
have varied levels of heat tolerance.
"A few inches of soil can make a big difference in temperature," said
Kaitlin Baudier, a doctoral student in O'Donnell's lab and lead author
of the study.
To look at whether factors like microhabitat preference--living above
ground vs. below ground--affected an animal's thermal range, Baudier,
O'Donnell and colleagues looked at nine closely related species of army
ants that lived in the same general area in Costa Rica's tropical
forests. They sampled ants from each of the species and experimentally
tested their maximum heat tolerance in the lab.
They found that the best predictor of heat tolerance was how active
the ant species was in above-ground environments. Above-ground army ants
were most tolerant of higher temperatures, while species that lived
mostly below-ground had much lower tolerance to heat, and species that
used a combination of above- and below-ground environments had
intermediate levels of tolerance.
Body size and habitat type also interacted, so that in comparisons of
same-size individuals from different species, the species that are
active above-ground were more heat tolerant--another indicator that
habitat use signals the species' tolerance to heat. Within each species,
smaller ants were more sensitive to rising temperatures than the larger
ants of the same type.
"The takeaway message is that an animal's adaptation to its microhabitat is relevant to its thermal physiology," said Baudier.
"This shows us that the ways these species respond to a changing
climate will be different depending on habitat type, and it's important
to know that microhabitat could be an indicator of heat tolerance,"
O'Donnell said.
