Nature’s Colors by Dr. Kara Lefevre, 2014
The Origins of Nature’s Colors
Nature is a riot of color. Typically we’re so used to this simple fact, it’s easy to overlook the splendid nuances of the colors that surround us. Then, when you’re on the verge of becoming indifferent, the sight of a hardwoodforest’s leaves turning in autumn, the bloom of an orchid, or the metallic surface of a beetle can take your breath away.
Color figures prominently in the lives of forest organisms. The color of plants and animals can function in heating and cooling, and many other biological processes. A major one is communication, which frequently involves color. Animals use complex color patterning to impress potential mates, or they may use cryptic patterns in an opposite way, for camouflage. Creatures from plants to insects to frogs have bright warning signals that alert predators to the toxic repercussions of choosing the wrong meal.
Often the particular color of things in nature has no particular purpose, being simply a visual side effect of the way that light plays. (For lack of a better rhetorical question, why is the sky blue?).
That touches on some functions of living colors, but the real aim of this article is to explore the “how”. That is, what causes nature’s palette? Every direction one looks in a tropical rainforest showcases a rich array of objects and materials, in all hues and shades. And the origin of each of those colors can be vastly different.
There are two main ways that the visual effect of color is produced: chemically, or physically.
The chemical production of colors
The chemical route of color production involves pigments. These organic molecules, are found in both plants and animals.They absorb different wavelengths of visible light energy, and can retain it briefly because of their chemical structure.
“Visible light” refers to a portion of the radiation that reaches our planet from the sun, at wavelengths of~380-750 nanometers. When the human eye views that range of radiations at once, “white light” is perceived. When just a narrower range is viewed though, the result is a light beam of a particular color, depending on the wavelength.
Living beings contain various pigments in their biochemical make-up. When incoming light hits an organism, each type of pigment absorbs certain wavelengths and reflects others, creating their characteristic colors.
Pigments play many different roles in plants. Of course green is the prevalent color in forests. This is an effect of the pigment chlorophyll that plays an essential role in making plant food, by converting light energy to chemical energy in the process of photosynthesis.
Colors are also used in signaling, to help plants stand out from the green background. For example, pigments play a central role in creating bright floral displays that attract animal pollinators and seed dispersers. Complex biochemical processes can further control color changes within flowers. Some of the factors that affect petal color are temperature, pH, cell shape, and the presence of co-pigments, metals (which can affect pigment structure), and sugars.
Still other pigments may play roles in activities like heat exchange, defense, or other unknown physiological functions. Some of the most common pigment types are described here:
Birds are also, in fact, a great overall example of animals that use color for signaling and communication. Tropical bird species display a particularly wide range of colors on their plumage. The pigments that color bird feathers are mainly porphyrins, carotenoids and melanins.
The physical production of colors
In addition to chemical pigments, the colors of some animals are produced physically, via the structural make-up of their integument (such as skin, feathers, or exoskeleton). Microscopic features of the tissues can produce colors by scattering or interfering with certain wavelengths of light.
Many animals produce colors in this fashion. The iridescence observed in some insects is a structural effect—think of the jewel-like elytra of some beetles, or the glimmering wings of many butterflies, moths, flies, wasps and bees. In these cases, the color that results depends on the angle of observation. Light is refracted and split into its different component colors, which can produce a changing, dazzling visual display. The throat feathers of many of the hummingbirds you will encounter at Monteverde are a classic example of this stunning phenomenon.
Some structural colors are not iridescent, such as most blue-tinged feathers. Those hues result when light hits feather barbs and scatters, which creates a single color of light. Still other colors in nature result from the combination of a pigment with structural colors. For example, feathers can appear green due to an overlap of structural blue with yellow pigments, such as the greens of many parrot plumages.
Interestingly, some animals can see light in the ultraviolet range, including bees and diurnal bird species. Thus, the color displays that they encounter would look very different than what is perceived by our human eyes.
Whether appreciated solely for aesthetics, or for the intricate functions they perform, the resplendent colors of the cloud forest will surely bewitch you.