The polar ice caps are melting, damaging habitats and robbing animals of their basic resources. But polar bears have a decent chance of surviving the upheaval, thanks to snow goose eggs...and a little random good luck.
If an animal moves from one habitat to another - or if their habitat changes around them - there's no guarantee that the new environment will have the resources necessary for the species' continued survival. Successful ecosystems have to pull off a tricky balancing act so that predators can maintain their numbers without ever quite hunting their prey to extinction, and a new predator in an existing ecosystem is just as likely to wipe out their food resources as anything else.
Humans are notoriously hungry predators - most infamously, European settlers in the Americas reduced the numbers of local bison from 50 or 60 million heads to just a few hundred in a matter of decades. But humans aren't the only apex predators who do this. Indeed many researchers feared polar bears would, in their effort to survive the loss of seals (their preferred food), eat everything in sight. And thus they would fatally mismanage their best shot at survival too.
But a couple years ago, researchers discovered that polar bears might have a new food source to sustain them - the eggs of the snow goose, a bird that lives in slightly warmer climates than where the bears currently live. As temperatures increase and the bears' access to seals becomes more limited, goose eggs will become a vital new resource.
In this new model, the polar bears can come ashore and raid the geese nesting grounds, eating as many eggs as they need to stay alive. It's a nutrient-rich, easily acquired resource, which is pretty much ideal. The problem is that the polar bears won't have any sense of how many eggs they can eat without endangering the snow geese.
That's where a fortunate bit of timing can save both species, according to new research by zoologist Robert Rockwell:
There will always be the occasional mismatch in the overlap between the onshore arrival of bears and the incubation period of the geese. Even if the bears eat every egg during each year of complete 'match,' our model shows that periodic years of mismatch will provide windows of successful goose reproduction that will partially offset predation effects. Mismatch is often thought to be bad, but in this case periodic mismatch is good because it keeps geese from going extinct and allows polar bears to eat. Are polar bears adaptable? Of course. This could be a nice stable system. The geese aren't going to go away, and they are a nutrient resource for the bears."
The polar bears appear to have a good shot at survival, but their situation isn't likely to be typical. The bears are lucky, as are the snow geese (admittedly to a somewhat lesser extent). A closer match in the bears' time onshore or the geese's incubation periods could easily have resulted in the bears driving the geese to extinction, which would likely sign spell their species's doom as well.
[Read the full scientific paper via Oikos]