Pizzlies and Other Hybrids Won't Become More Common With Climate Change

Just a dirty polar bear cub! Gladkova Svetlana/Shutterstock.
Janet Fang 07 Jul 2015, 13:55

Climate change is shifting species’ ranges, bringing together animals that otherwise wouldn't normally boop noses. But despite increasing reports of hybrids such as polar-grizzly bear cubs (or pizzlies), interbreeding will happen less often than we expect, according to a new study published in Nature Climate Change this week. 

Hybrids have been popping up over the last couple of decades in the Arctic. In 2006, hunters shot a white bear sporting brown patches, and DNA confirmed that it was a pizzly. Then, a few years later, hunters killed a second generation hybrid: The mother was a hybrid and the father was a grizzly. Various whale, seal, and porpoise mixes have also been discovered in and around these icy seas, leading researchers to suggest the presence of an "Arctic melting pot" that could hit polar biodiversity hard. 

To see how much hybridization will actually happen, a University of Washington team led by Meade Krosby tallied up potential pairings of different species across North and South America. Of the 9,577 pairs of closely-related species of birds, mammals, and amphibians examined, only around half of them have ranges that currently don’t overlap. They then used a computer model that takes into account where these animals would need to move for a suitable habitat in a warming world. The team found that only 6.4% of 4,796 species pairs are likely to come into contact by the end of this century because of climate-induced range changes. 

"People have been concerned that climate change would be bringing all these species into contact, and that this could unleash a wave of interbreeding," Krosby says in a statement. "What we found is, not so much." At least not on a global scale: Overlap will be far more common among birds in the tropics, probably because of their higher biodiversity and wider ranges. The projected rates of overlap for birds is 11.6%, which is more than twice that of mammals (4.4%) and amphibians (3.6%).

These rates of future overlap are far lower than expected because many species will have difficulty tracking shifting climates. What’s more, these numbers are overestimations. Natural and manmade barriers ranging from rivers to highways and farms will likely block their migration to new, more accommodating homes. 

"The number one strategy for helping biodiversity respond to climate change is to increase connectivity, to link up habitats that have been fragmented by human activity, so species can move, and track climate as it shifts to stay comfortable," Krosby adds. "If people are worried that wildlife corridors and other ways to increase connectivity could bring these species into contact, we’re saying: That’s probably not going to happen, and allowing species to move is far more important."

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