01/20/2015 10:08 AM
BATON ROUGE –In a part of the world that is experiencing the most dramatic increase
in temperature and climate change, two very similar species of animals are responding
very differently. New research published today suggests that how these species have
adapted to co-exist with one another might be to blame.
Chinstrap penguins whose namesake describes the black stripe under their chins are
decreasing in number while Gentoo penguins, recognizable by their bright orange beaks,
are increasing at summer breeding colonies in the Antarctic Peninsula. This research
sheds light on the different strategies these two similar species have carved out
over time to reduce competition for food, and the ramifications these different strategies
are having now during a time of rapid environmental change.
“Our data shows Gentoo penguins have a more diverse and flexible diet than Chinstrap
penguins, which forage farther offshore and preferentially feed on Antarctic krill
during the breeding season,” said LSU Department of Oceanography and Coastal Sciences
Assistant Professor Michael Polito, who is the lead author on a paper published in
Marine Ecology Progress Series.
The potential for these two penguins to compete for food is highest when they are
found breeding near each other on land and the need to feed their chicks daily restricts
the distance they can search the ocean to find food. However, the key differences
in what they eat and where they look for food likely evolved over time to reduce competition
and to help Gentoo and Chinstrap penguins co-exist.
Climate change alters food sources
The Antarctic Peninsula has warmed dramatically over the past 50 years. The annual
air temperature has increased by about 5 degrees Fahrenheit, or 2.8 degrees Celsius,
which makes the Antarctic Peninsula the fastest warming region in the Southern Hemisphere,
according to the British Antarctic Survey.
“For a region that for most of the year hovers around the point of freezing, a few
degrees plus or minus is the difference between freezing and melting, particularly
of sea ice,” Polito said.
Penguins’ main prey, Antarctic krill, which are shrimp-like crustaceans, rely on sea
ice. Young krill in particular use sea ice for protection from predators, and they
feed on algae that grow beneath the sea ice. As temperatures warm, there is less sea
ice and therefore fewer krill for penguins to eat.
While in the past, over evolutionary time scales, Chinstrap penguins’ strategy of
foraging for large, predictable patches of krill offshore made sense. But now as krill
have declined, this specialist strategy may not be best suited for today’s conditions.
In contrast, Gentoo penguins seem to be better adapted to deal with a changing environment.
In addition to their dietary flexibility, they are also more flexible in when and
where they breed. They also likely ease the transition of their chicks into adulthood
by feeding them for a longer period of time.
“These may be the reasons why Gentoo penguins in the Antarctic Peninsula are benefiting
from changes in climate and their populations are increasing, but Chinstrap penguins
are decreasing,” Polito said.
Multiple methods confirm differences in diets
Polito and his colleagues applied three methods of data analysis to substantiate how
these two similar penguin species’ behaviors differ. Over five years at a long-term
field camp that is part of the U.S. Antarctic Marine Living Resources program run
by NOAA National Marine Fisheries Service, researchers examined the stomach contents
of breeding adult penguins. These data provided a snapshot of what an individual penguin
was feeding its chick that day. In addition, by identifying the ear bones of fishes,
or otoliths, consumed by penguins, they were able to determine if penguins were feeding
on nearshore or offshore fish. Lastly, the researchers collected breast feathers from
fully grown chicks and analyzed them using a technique called stable isotope analysis,
which allows them to identify how much krill versus fish an individual chick was fed
by its parents. This step further corroborated the stomach content and fish otolith
analyses.
“Any one of those three methods, such as looking at stomach contents, identifying
otoliths or using stable isotopes, will give you some information. But using all three
combined gives you a much clearer picture of what’s going on,” Polito said.
Next steps
While this research studied the two penguin species during the breeding season when
the potential for competition for food is highest, Polito and his colleagues are pursuing
research outside the breeding season to see if the same patterns exist. LSU graduate
student Rachael Herman is furthering this research by investigating whether Gentoo
penguins all eat a wide range of prey or if each individual specializes in something
slightly different. This will help to determine if all Gentoo penguins are benefiting
equally from climate change, or if only a subset of individuals are pre-adapted to
deal with today’s rapidly changing environment.
This project included collaborators from LSU, NOAA National Marine Fisheries Service, University of North Carolina, Wilmington, University of Saskatchewan and Pomona College and was funded by the National Science Foundation and NOAA’s U.S. Antarctic Marine Living Resources program.
Image caption:
Chinstrap and Gentoo penguins evolved differences in diets over time that reduce competition
for food and help them co-exist. However, recent climate-driven declines in Antarctic
krill, the main prey of Chinstrap penguins, have led to declines in the population.
In contrast, the flexible diets of Gentoo penguins likely are better suited to the
rapidly changing environmental conditions in the Antarctic Peninsula. (Photo by Rachael
Herman, LSU)
Related Links:
• Contrasting specialist and generalist patterns facilitate foraging niche partitioning
in sympatric populations of Pygoscelis penguins
• Michael Polito’s Research Lab Website
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Alison Satake
LSU Media Relations
225-578-3870
asatake@lsu.edu
Posted on Tuesday, January 20, 2015