ECOVIEWS: Color means a lot in ecology

December 16, 2018

Christmas is red and green. Halloween is orange and black; Thanksgiving is green and brown (in my mind), for reasons I am unsure of, and everyone knows Valentine’s Day is pink or red. Color is an important component of our lives and plays a key role in the lives of many plants and animals. Color can also become a teacher’s tool for encouraging students to think about nature by questioning why one color is prevalent and another is not. Outside of the classroom, color offers all of us opportunities to ponder ecological questions about wildlife.

A basic question when looking at any plant or animal is why is it this color and not another? Some explanations for color seem obvious; others have not yet been answered. Why most plants are green is not especially intriguing. Chlorophyll is the green pigment essential for most plants to survive, although one might ask why chlorophyll is green and not yellow or purple? Simply thinking about how important color is in the outdoor world can be an entertaining exercise. Plants use color to great advantage, the various forms of color advertising being the most apparent. In some species brightly colored flowers attract insects essential for pollination. These plants make overt advertising pitches by using flower color to attract insects, which are treated to nectar and serve as pollinators for the plant. Bright red or yellow berries that attract birds such as cedar waxwings offer a meal for the bird and assure that the enclosed seed will later be deposited in another area.

A backyard color mystery for me is why the red berries of our holly tree disappear within days when migrating birds pass through, yet the equally bright red berries of the horticultural plant nandina will be on the bushes till they fall off in summer. How do the birds know that nandina berries contain a form of cyanide that makes them poisonous to wildlife? Is the bright red berry a slightly different shade of red than a holly berry? In China and Japan where it originated does the nandina berry attract a native bird that is immune to the poison and helps spread the seeds?

Color is also used as a lure in some species of animals. Baby copperheads and cottonmouths have bright yellow tails that are waved enticingly in the presence of small frogs or lizards. Because the rest of the snake is well camouflaged in dead leaves, the frog or lizard becomes prey when focusing its attention on the tail and mistaking it for something to eat. Flash colors are a special use of color for defense among some animals. The gray treefrog is a perfectly camouflaged creature when sitting on an oak tree or other drab background. When a gray treefrog is pursued by a bird that intends to make a meal of it, the frog jumps and displays bright yellow underparts. Upon landing on a tree and tucking in its legs, the frog once again blends into the background. The bird, meanwhile, is searching for something yellow that cannot now be found.

Endless examples can be given for how color is used to advantage by both plants and animals and for how natural selection could readily result in certain colors being key to the survival and propagation of a species. One color phenomenon, albinism, is not a product of the natural environment of plants and animals. Albinism is the expression of an inherited genetic condition, although neither parent need be an albino. An albino is incapable of producing the pigments that normally give color to hair, skin, feathers and other surface tissues. Because of this abnormal condition, survival in the wild is a difficult struggle. Ironically, laboratory white rats are the most successful and plentiful albinos in the world, demonstrating how human intervention in the natural world can have an enormous impact on what constitutes success in certain environments.

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