Eat or be eaten: Where friends are foes and foes are friends

Most of us are familiar with the term food chain. Generally speaking, a food chain describes a linear sequence of who eats whom in an ecosystem.  

More realistically, though, these chains cross, twist, and overlap, forming webs that can be far from linear. One great example is the food chains, or webs, found in our Daniel Island lakes and ponds. There are so many species here feeding on and being fed on by each other that the concept of a food chain is almost useless. 

Picking just a few animals, there are fish, frogs, snakes, and rodents living in and near all of these bodies of water. Some of them feed on each other, and all of them are fed on by a number of common predators. 

Egrets, herons, and alligators, for example, will all feed on fish, frogs, snakes, and rodents. Ecologists refer to a group of species that need and use common resources in similar ways as a guild. Egrets, herons, and alligators, sharing the same habitat and consuming the same food resources, would belong to such a group. 

But what if some of these predators don’t just feed on their common prey but also on fellow guild members? 

Alligators also eat birds. Intraguild predation is an ecological term for when species that compete for the same food resources also eat their competition. A gator that eats a heron has not only gotten a meal – he has also removed a fellow predator that could have beaten him to the next meal he might catch. 

So, why are we discussing esoteric ecological terms that most of us would never use? 

It’s because of an incredible photo that fellow island resident, friend, and co-worker Susan Schmenk sent me recently. While walking her dog near an island pond not long ago, Susan and a friend were startled by a great blue heron swooping in nearby amid what she described as a lot of noise and thrashing.  

It soon became apparent that the heron had a small alligator in its beak, which was writhing around mightily and squealing but was unable to escape. The heron soon flew to the far end of the pond with his catch, and the squealing stopped.  

We now need a new term: reciprocal or mutual intraguild predation. These species not only compete for common food. They also, at least at certain stages of life, eat each other. 

I recently saw an interview with Michael J. Fox about the 40th anniversary of “Back to the Future.” If you are a young person – to me that means you are under 50 – and you have never seen this movie, borrow your parents’ VHS player and check it out! Much like how Michael J. Fox could have changed the world (and his existence) with his trip to the future, this bird may have changed his own. 

While herons don’t eat adult alligators, adult alligators certainly eat herons. This bird may have, without even needing a DeLorean, reached far into the future and saved its own life or that of its mate or offspring. I don’t know an ecological term for that, but I call it cool!