Ecosystem dynamics: Clark’s nutcrackers and the white bark pine | Khan Academy

What's that? That sound, that call, sounds like something a crow would make but not quite. That's actually the call of a really interesting bird called Clark's nutcracker.

These birds are cousins of the American crow, which you might see and hear around where you live, except that the Clark's nutcrackers like to live up in the mountains and alpine ecosystems in the western United States, where the winters are pretty harsh with lots of snow. There are lots of evergreen trees, like pine trees, which keep their leaves all throughout the year.

But what would this bird possibly eat in this kind of ecosystem? I'll give you a hint: it's in the bird's name. Turns out that Clark's nutcrackers love eating seeds, and not just any seeds, but mainly the seeds of pine trees, like this one, the whitebark pine.

It's actually good for the trees that nutcrackers eat those seeds.

Wait, what? Let's take a look at the whitebark pine. These trees have cones which hold their seeds. Other pine tree species have cones that will open when the temperature is warm enough, or if the air is especially dry, or when the cone is exposed to fire. But for the whitebark pine, their cones don't open on their own. Instead, the cones have to be pried open, and it's the Clark's nutcracker that does this as it looks for seeds to eat.

But the nutcracker doesn't just eat the seeds; it stores them in what's called a cache, or a safe place where they store the seeds to eat them later. Remember, these birds live in an alpine ecosystem where the spring and summer are pretty warm, and there's lots to eat, but the winters are cold and long, with very little to eat. So the nutcrackers have to stock up.

In fact, the nutcrackers will cache up to 100,000 seeds in a single year. I can't remember where I put my phone half the time, but the nutcrackers don't retrieve all of these seeds. Many of the caches won't be used by the nutcrackers, so those seeds germinate and grow into new whitebark pines, and the cycle continues.

Nutcrackers rely on whitebark pines as an important food source, and the whitebark pines rely on nutcrackers to plant their seeds. On top of that, more than 100 other alpine species of plants and animals benefit from that relationship between the Clark's nutcracker and the whitebark pine.

For example, Douglas squirrels will also eat seeds from whitebark pine cones, and mountain bluebirds and northern flickers may nest in the whitebark pine, too. When you look at it, all of these interactions that occur in this alpine ecosystem are like a web. Each population interacts with many other populations, and each population is affected by non-living parts of the environment, like temperature and snowfall.

So a change in any one part of an ecosystem can lead to changes in many of the ecosystem's populations. For example, if something happens to the nutcrackers and their population starts to decline, that could cause some big problems for the pines that need these birds to plant their seeds.

In turn, if the whitebark pine starts to decline, too, that can have negative impacts on all the other species that rely on this tree, like squirrels, bluebirds, and flickers. Even though it seems like a perfect relationship between the nutcracker and the pine in the alpine ecosystem, every ecosystem is dynamic, meaning that parts of the ecosystem, both living and non-living, can and probably will change over time.

Sometimes ecosystems might experience a negative change, like a disruption. Maybe it's a particularly harsh and cold spring, and there aren't as many cones and seeds for the nutcrackers to cache. Changes like that can make it harder for individual nutcrackers to survive and raise chicks, which can cause nutcracker populations to get smaller.

But on the other hand, other types of changes can help individuals in a population. For example, if the ecosystem experienced a particularly warm spring after a wet winter, there would be lots of available food. These types of changes can cause more individuals to survive, have offspring, and increase their population.

Clark's nutcrackers and their relationship to the hard-to-open cones of the whitebark pine are just one example of the kind of relationships that drive many different ecosystems. Just like how a decrease in nutcracker populations could cause problems for the whitebark pine and other species in the ecosystem, a change to one species in any ecosystem can impact a whole web of interconnected organisms.

So next time you're outside and hear the call of a bird, think about all the interactions that bird has with other parts of its ecosystem. These relationships are all part of the complicated web that is life on Earth.