What’s in a Niche?

Well-adapted species could be more vulnerable to the impacts of climate change

Have you ever wondered why some species, like deer and rats and gray squirrels, seem to thrive everywhere, and others, like the polar bear, seem to need a very specific type of habitat? It has to do with a concept that ecologists call the “niche” (rhymes with “ditch”), a word that summarizes how a given species makes its way in the world. A species’ niche is the aggregation of all the things that it does: what it eats and how it finds its food, where it makes its den, how it finds a mate and how it avoids predators.

Species become adapted to certain niches that differ from that of other species – such as feeding on the ground vs. high up in a tree—as a way of reducing competition. The more specialized a species is, the more it can exploit a niche that no one else is using. A good example is the hummingbird, whose long bill allows it to reach deep into flowers to drink nectar, but isn’t good for eating much else.

Having a specialized niche can be a great thing for a species — at least until conditions start changing too quickly for them to keep up. At that point, the once-useable niche begins to shrink, and the very thing a species once relied on to survive can become a danger to its survival. We are already seeing this happening as the climate warms, and species that have a specialized niche – of habitat, diet, or other requirements – are on the front lines of vulnerability.

Polar bear: Habitat Specialist

Polar bears are among the largest carnivores on the planet, and uniquely adapted to a life on a very specialized habitat: sea ice. Far from being a frozen wasteland, sea ice is actually the basis for an important habitat in the spring and summer months, when long trains of algae grow fastened to its edges and in shallow surface melt pools. This algae forms the base of a food chain. Krill eat the algae, fish eat the krill, and seals (polar bears’ favorite prey) eat the fish. Polar bears’ specialization to this harsh habitat is evident in the ways they differ from their closest relative, the brown bear: polar bears’ bodies have a shape built for swimming, and fur and blubber to help them withstand a life in the cold.

Polar bears’ reliance on sea ice has made them the poster child of climate change. Since the late 1990s, Arctic sea ice extent has been below the long-term average in nearly every year, and had a record low in 2012. Less ice means less algae to feed that food chain, and fewer places where the bears can hunt for seals. Although they are excellent swimmers, they have trouble catching and eating seals in open water, so they need the ice. Female polar bears also frequently give birth in snow dens on thick, stable ice.

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In recent years, harrowing stories have emerged of bears drowning in the open ocean miles from the ice edge, or starving to death while trying to subsist on land, eating birds and carrion. The extremes of Arctic habitat make it difficult to track exactly how polar bear populations are responding to climate change, but declines have been observed in many of the better-studied populations. For instance, Canada’s Western Hudson Bay population has dropped 22% since the 1980s, and cub survival is down on the north coast of Alaska. The polar bear was listed under the Endangered Species Act in 2008 as a result of the threat that climate change poses to this specially-adapted species.

Atlantic Puffin: Diet Specialist

With their brightly colored bills and penguin-like appearance, Atlantic puffins are one of the most readily recognized and beloved of birds. These seabirds breed in colonies along the coasts of Maine and Canada, Scandinavia, Iceland and Greenland. Pairs lay a single egg in a burrow or crevice, and both parents share incubation and feeding duties.

In the Gulf of Maine, where puffins reach their southern breeding extent, puffins rely on a food web based on phytoplankton that are specialized to live in the very cold, nutrient-rich water in the basin. In turn, these plankton feed an array of small, slender fish that thrive in cold water, including herring, hake, capelin and sand lance. Puffin chicks are specialized to eat only these types of fish; other local species have a rounder body shape that is too wide for them to swallow.

In 2012, an exceptionally warm spring heated the Gulf early in the breeding season, and most of the usual fish that puffins feed their chicks shifted their ranges northward, leaving only round butterfish. The warm water conditions also gave the butterfish a head start at growth, so they were larger than usual by the time the puffins hatched. As a result, the puffins were forced to try to feed their chicks fish that were too wide for them to swallow. That year, only 31% of puffin pairs successfully raised a chick. In cooler years the rate is closer to 77%. 2013 was almost as warm, and the numbers were even worse: only 10% of chicks survived, and the puffin population in the Gulf of Maine dropped by a third.

Pika: Temperature Specialist

Related to rabbits but looking more like oversized hamsters, pikas live on rocky slopes of high mountains in the West. Instead of hibernating or digging burrows, pikas spend all summer harvesting grasses and other plants and storing them under piles of rock so they have food to get them through the winter. Because they keep their warm winter coats year-round, pikas are very sensitive to high air temperatures; long exposure to excessive warmth kills them outright. As a result, pikas can only thrive where the temperature reaches above 95°F fewer than 30 days per year.

Climate warming is already having an effect on pikas, particularly in the southern part of their range – New Mexico, Nevada, California and Utah. Researchers have found that pikas there are heading to higher ground, moving upslope an average of 450 feet per decade. As climate change continues to heat up their mountain strongholds, pika will be squeezed further and further upslope, and those that run out of room will die off. In some places, this is already happening: forty percent of populations in the Great Basin region have vanished in recent years.

Wildlife is already feeling the effects of a warming climate, especially those species that are adapted to a specialized niche. These are the species on the front lines of climate change – and others will be feeling the heat soon enough. Changes in temperature, rainfall, severe storms and more are projected to happen so quickly that even species that can usually thrive in a variety of conditions may have a hard time keeping up. That makes it all the more important both to reduce emission of greenhouse gases, to reduce other threats to species, and to continue to protect the habitats they rely on.