- May 6, 2011
What is an Ecological Trap?
The term ecological trap sounds menacing, but what does it mean? And could you have an ecological trap in your own back yard and not even realize it? With the help of some economics metaphors, we’ll delve into this scary-sounding topic and help bring it to light.
Ecologists have constructed a way of thinking about the value of habitat patches that wildlife inhabit. There are two main categories of habitat quality that ecologists talk about: source habitats and sink habitats. A source habitat is one where more animals are born than die in a season; this source population then becomes a net exporter of birds. Source habitats provide enough resources (food, water, structure, space, safety) to allow for successful reproduction. A sink habitat is one in which the number of deaths exceeds the number of births, so there is a net loss. Unusually high mortality can be caused by excessive predators, destruction by human activity, or insufficient food, among other things.
While it would seem plausible that birds and other animals would learn to avoid low quality habitat, often ecological sinks are attractive enough to animals that they set up residence and try to breed. But buyer beware, because such habitats are called ecological traps, meaning that animals that try to live in them get hoodwinked. An ecological trap may in fact look like great habitat while actually robbing birds of their nest egg. Sometimes the effect is subtle: parent birds that have to work harder to find enough nutritious food for their young face opportunity costs if they miss out on future breeding opportunities. Sometimes the effect is dramatic: newly fledged birds taking their first tentative steps out of the nest might be caught by the neighborhood cats. To you and I, these populations may appear stable, but that’s because they receive a net import of birds produced in so-called “source habitats”.
Staying Out of the Trap
Think about your yard and the birds that choose to make it their home. Are there any barriers to its being a source habitat? If so, can you make some initial investments to increase your bird capital? If you answer yes to one or more of the following, you might just have an ecological trap:
- You have an outside cat
- You feed stray cats in your yard
- You mow your grass after it has grown tall enough to attract nesting birds
- You spray chemicals to control pests
- Your nest boxes lack predator guards or baffles
- Your yard doesn’t provide any seeds or berries for birds