You never know what will happen when you remove one piece of the puzzle.  Can it survive for a little while longer, albeit in a weakened state?  Or will it all come crashing down when that one piece gets removed?

Yes, I could be talking about the game of “Jenga”, something many of us have played.  But in this case I’m talking about nature.  In the journal Science Advances, research was just published that discusses a link between hawk populations in the southwestern U.S. and breeding success of Black-chinned Hummingbirds.  One wouldn’t immediately think there was much of a link between the two species.  Hummingbirds are far too small and quick for most hawk species to deal with.  They likely couldn’t capture them, and even if they did, they wouldn’t be more than a mouthful.  So how are the species linked?

As the paper discusses, there are actually three bird species who interact to affect nesting success of the hummingbird.  In addition to the Black-chinned Hummingbird, the study looked at Cooper’s Hawks and Mexican Jays.  What they found was that nesting success was much higher for the hummingbirds when they nested very close to Cooper’s Hawk nests.  The Cooper’s Hawks don’t feed on the hummingbirds, but they ARE a threat to Mexican Jays, and Mexican Jays will readily eat hummingbird eggs and young if they get a chance.  In one case, after Cooper’s Hawks left one nesting location, the researchers immediately saw Mexican Jays move in and decimate all hummingbird nests in the area.

Jenga…ala Mother Nature.  That’s what so scary when human beings start to interfere in natural systems.  One of the most publicized impacts of the removal of one species from a system is the Yellowstone ecosystem, before and after the reintroduction of wolves.  It was expected that the reintroduction would impact ungulate populations in the area, but it soon became apparent just how far-reaching an impact wolves have on the ecosystem.  Without wolves, elk and deer browsed freely in lowlands, resulting in nearly all young aspen trees to be browsed to the ground.  Aspen habitat all but disappeared in the park, but with the reintroduction of wolves, that habitat is now being reborn.  With increased aspen came more beavers.  With more aspen habitat and beaver ponds came an influx of more songbirds and other species that use those habitat.  With more wolves, there were fewer coyotes, which meant more small mammals and an increase in numbers of red fox, eagles, and ravens.

All due to the removal of one species.

Be it hawks in the Southwest or wolves in Yellowstone, the removal of one key species can have cascading impacts on the entire ecosystem.  The same certainly can be true in the “reverse” case, where a new, exotic species is introduced into the system.  As a scientist, it’s fascinating to see the incredible impacts humans have on ecosystems, both through how they manage the landscape, and in how they manage the wildlife within that landscape. As just a human being…it also can be pretty depressing to see how we negatively impact so many ecosystems.