Niches

“The Nutches have troubles, the biggest of which is/The fact there are many more Nutches than Nitches./Each Nutch in a Nitch knows that some other Nutch/Would like to move into his Nitch very much.â€

Those lines of verse (my daughter’s favorite) from Dr. Seuss’s “On Beyond Zebra†got me thinking about the ecological theory of Nitches — well, actually, niches. The idea is that organisms in nature evolve to occupy all the available niches, be they physical spaces, positions on the food chain, or even “a niche in time.â€

For example, hawks and owls play similar roles to predators, but hawks occupy the daytime niche and owls the nighttime niche. This is an oversimplification, of course, but conveys the basic concept.

Niches are one way that animals can divide up, or partition, available resources such as food, so as to avoid conflict with each other. The classic study of partitioning, from the 1970s, involved five species of insect-eating wood-warblers: the Cape May, yellow-rumped, black-throated green, blackburnian, and bay-breasted warblers. It was found that each species generally feeds on a different part of a tree, such as top, middle, bottom, interior or exterior, thereby getting somewhat different insects and minimizing competition for food.  

These same species also nest at slightly different times, further reducing the interspecies competition for resources. (I should add that all five species could be seen in our area in spring, and two, the black-throated green and blackburnian warblers, nest in our forests.)

Sometimes niches are decided by dominance, or aggression. For instance, in Midwestern marshes, yellow-headed blackbirds tend to occupy the center of the marsh, while smaller red-winged blackbirds are relegated to the suburbs. Marsh wrens play a mischievous role in all this by poking holes in the eggs of both the larger birds.

 Of course, as with Dr. Seuss’s “Nutches,†conflicts do occur, most often within species, since individuals of a species are rivals for the same resources, whether habitats or foods.  That is why so many birds are territorial during breeding season. Each breeding pair is trying to get the best and largest territory with the most food with which to feed their young.

If you watch songbirds such as the yellow warbler while they are singing, you can often visualize the boundaries of their territory, because the very reason they are singing is to announce to others of their kind where the borders are. Why fight when you can sing? (It’s sort of like an invisible fence!)

The next time you go out into nature, see if you can observe the theory of niches at work.  If you go to a pond or lake, which kinds of waterfowl use the shallow water and which patrol the deeper sections? What animals stick to the shoreline?  How many different kinds of animals hawk insects over the pond, and do they all hunt at the same height above the water? Or take a close look at how woodpeckers feed. Do they all use the same part of the tree, and drill to the same depth with their bills?

Fred Baumgarten is a naturalist and writer. He can be reached at fredb58@sbcglobal.net. His blog is at thatbirdblog.blogspot.com.