Pitcher plants have distinctive adaptations for living in nutrient-poor soils: These carnivorous plants produce a pitcher-shaped structure with a pool of water in it. When insects investigate, they slide into the pitcher and meet a watery demise. The plant then dissolves the insect and uses it for food.
Biologists have long assumed that in addition to their nectar-producing glands that attract prey to a potential food source, the plants' bright colors – mostly shades of red and green – help to attract insects. Like bees that are attracted to flowers there's a general idea that insects like bright colors, especially reds and yellows. But thus far there is little evidence that these colorful patterns attract prey to pitcher plants.
Aaron Ellison of Harvard University and his coauthor Katherine Bennett, a fifth grade teacher working under a National Science Foundation Research Experience for Teachers grant, placed painted tubes mimicking pitcher plants' natural color spectrum of redness into the plants' habitat. They found that red coloration didn't affect the number of ants – the pitchers' primary prey – that were captured.
These results are not surprising, says Ellison. Seventy percent of pitcher plants' prey are ants, which see the color red as grey. Since grey probably only weakly contrasts with the green base color of the pitcher, it's probable that the ants can't differentiate between mostly red and mostly green plants.
Ellison thinks this work is a good example of why biological concepts need to be tested and not simply assumed.
"There's no evidence that the coloration in pitcher plants is of any adaptive value for capturing prey," he says. "We don't need to assume that it has an adaptive value, or that it has anything to do with prey."
Animals and plants communicate with one another in a variety of ways: behavior, body patterns, and even chemistry. In a series of talks at the Ecological Society of America's annual meeting, to be held August 3-7 in Albuquerque, New Mexico, ecologists explore the myriad adaptations for exchanging information among living things.
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