Futurity, by Jeff
Mullhollem -Penn State 8/2/17
Precipitation may be nearly as
important as temperature in figuring out which animals are in the most danger
of decline or disappearance. That’s especially true for moisture-sensitive
frogs and other amphibians, a new study suggests.
Researchers looked at long-term
monitoring data from 746 wood frog populations in 27 study areas, from
Tennessee to Canada. The data focused on how climatic variation affected
population growth rates and how these relationships varied with respect to
long-term climate.
Northward shifts in wildlife
ranges may be expected in coming years or decades, says lead researcher Staci
Amburgey, a doctoral student in ecology at Penn State, but that trend may
depend nearly as much on demographic weather patterns as warming temperatures.
And in the case of wood frogs, other factors are also at play.
As reported in Global Change Biology,
sensitivity to changes in climate cannot be predicted simply by knowing
locations within the species’ climate envelope. Many climate processes don’t
affect population growth rates as expected, based on range position. Processes
such as species interactions, local adaptation, and interactions with the
physical landscape likely have an effect on the frogs’ responses.
“Wood frogs are really broadly
distributed, so I don’t think the species is going to be declining anytime
soon,” Amburgey says. “But having said that, it appears that populations in the
southern portion of the wood frog’s range are vulnerable if we have more hot,
dry summers. Certainly frogs in the southern part of their range are more
sensitive to hot years than frogs farther north, where the conditions will not
push their physiological tolerances.”
For the study, researchers did
more than just document where wood frogs exist and where they don’t. Instead,
they analyzed reproduction rates by counting egg masses in spring pools to
determine where the amphibian’s populations were growing or declining—trying to
determine how each population was responding to year-to-year differences in
climate.
(Credit: Staci Amburgey/Penn
State)
Wood frogs are an ideal species
to study to develop predictions about how animals will respond to warming
conditions, says David Miller, assistant professor of wildlife population
ecology.
They are cold-weather frogs with
a range that extends farther north than other amphibians. As such, they have
evolved with some amazing adaptations, not the least of which is the ability to
survive freezing solid in winters.
“In a warming world, wood frogs
at the southern end of their range may be in trouble. By freezing solid, they
thrive as far north as Alaska. They spend winters near the surface, and they
are one of the first species to come out when things thaw.
“Then they head immediately to
small wetlands in the forest that tend to dry out during the summer to breed,
and their tadpoles develop really quickly and get out into the woods early.
They are an important part of our forested ecosystems in the Northeast and a
truly unique species.”
The Amphibian Decline Working
Group supported by the US Geological Survey’s John Wesley Powell Center for
Analysis and Synthesis supported the work.
Source: Penn
State
Original Study DOI:
10.1111/gcb.13817
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