23 Responses to ‘Stress’ is shrinking polar bears
The BBC reports:
Polar bears have shrunk over the last century, according to research.
Scientists compared bear skulls from the early 20th Century with those from the latter half of the century.
Their study, in the Journal of Zoology, describes changes in size and shape that could be linked an increase in pollution and the reduction in sea ice.
Physical “stress” caused by pollutants in the bears’ bodies, and the increased effort needed to find food, could limit the animals’ growth, the team said.
Okay, it’s not most important climate story in the world, but it does let me use the above photo again. I should note that the NYT‘s Revkin blogged last month, “More Polar Bear Populations in Decline“:
There is rising concern among polar bear biologists that the big recent summertime retreats of sea ice in the Arctic are already harming some populations of these seal-hunting predators. That was one conclusion of the Polar Bear Specialist Group, a network of bear experts who met last week in Copenhagen to review the latest data (and data gaps) on the 19 discrete populations of polar bears around the Arctic. The group, part of the International Union for Conservation of Nature, includes biologists in academia and government and at nonprofit conservation organizations. Only one bear population is increasing (in the Canadian high Arctic), while eight are declining in numbers, the scientists said. At its last meeting, in 2005, the group concluded that five populations were in decline. Three populations appear to be stable and seven are too poorly monitored to gauge a trend.
As for the new study, here’s the abstract for “Craniometric characteristics of polar bear skulls from two periods with contrasting levels of industrial pollution and sea ice extent” (subs. req’d):
A morphometric study was conducted on six skull traits and seven teeth traits of 282 polar bear Ursus maritimus skulls sampled in East Greenland from 1892 to 2002, the polar bear material originated from two distinct periods: one period covering 1892-1939 and the other from 1961-2002. The first period being before the introduction of organochlorines in the Arctic environment and having more extensive sea ice cover when compared with the later period. Admixture analysis, followed by multivariate analyses provided evidence for morphometric differences in both the size and the shape of individual skulls collected in the two periods. These findings are possibly a consequence of environmental factors, such as exposure of organohalogens and changed extension of sea ice, ultimately affecting the amount of prey available, a general weakening of the immune system and reduced reproductive success, factors that can affect the individual growth and the realized size at maturity. The process of reduced reproductive success due to a high concentration of organochlorine and/or changes in the amount of food resources may also have affected the polar bears’ genetic composition and effective population size. Changes in the genetic composition of the population are suggested to have contributed to the observed morphometric changes with time. The fact that environmental and genetic changes produce different combinations of patterns of morphometric changes allows us to individuate the causes of the morphometrical modifications.
In plain English:
“Because the ice is melting, the bears have to use much more energy to hunt their prey,” explained Cino Pertoldi, professor of biology from Aarhus University and the Polish Academy of Science, and lead scientist in this study.
“Imagine you have two twins – one is well fed during its growth and one is starving. (The starving) one will be much smaller, because it will not have enough energy to allocate to growth.”
The team, which included colleagues from Aarhus University’s Department of Arctic Environment, also found shape differences between the skulls from the different periods.
This development was slightly more mysterious, said Dr Pertoldi.
He explained that it was not possible to determine the cause, but that the changes could be linked to the environment – more specifically to pollutants that have built up in the Arctic, and in the polar bears’ bodies.
The aim of the study was to compare two groups of animals that lived during periods when sea ice extent and pollution levels were very different.
The pollutants that the scientists focused on were compounds containing carbon and halogens – fluorine, chlorine, bromine or iodine.
Some of these compounds have already been phased out, but many still have important uses in industry. These include solvents, pesticides, refrigerants, adhesives and coatings….
Rune Dietz from Aarhus University was another member of the research team.
He explained that he and his colleagues had already determined a link between man-made “persistent organic pollutants” and reduced bone mineral density in polar bears – which could leave the animals vulnerable to injury and to the bone disease osteoporosis….
He said: “Polar bears are one of the most polluted mammals on the globe.”
And you thought Homo “sapiens” sapiens had nothing in common with Ursus maritimus.