Why are tropical animals so colorful?

​​From the striking rainbow colors of parrots in the rainforest to the brilliant flashes of yellows, oranges and blues in coral reefs, vibrantly colorful wildlife abounds in tropical ecosystems. But what is it about these environments that has driven their animal inhabitants to evolve such eye-catching hues?

Broadly speaking, animals tend to use color to communicate, said Oscar Puebla, a fish ecologist at the Leibniz Centre for Tropical Marine Research in Germany. "It could be communication with members of your species — for example, to attract a mate," he told Live Science. "It could be communication to predators to make the point that you're venomous. It could be camouflage to escape predators."

The reasons and methods of this color communication vary massively among species and environments. Birds tend to acquire colored pigments — like red, orange and yellow carotenoids — through their diet and use the resulting strong coloration to attract a partner or establish dominance. Meanwhile, fish and mollusks use complex microscopic structures within their cells to bend and diffract light and thus change their color to camouflage them from predators. But whether it's on land or under the sea, tropical conditions have played a huge part in this evolved adaptation.

"There's a correlation between the diversity of a certain community and the amount of color or diversity in color that the different species display," said Roberto Arbore, an evolutionary biologist at the Research Center in Biodiversity and Genetic Resources in Portugal who specializes in parrots. "If you live in a very diverse community, such as a rainforest, you need to recognize individuals of the same species because interacting with individuals of different species can be very costly in terms, for example, of mating."

Birds, in particular, rely on their sense of sight to perceive the world. The sheer number of avian species in the forest environment therefore drives up this competition to stand out, leading to the extraordinary variety of colors and patterns exhibited by parrots, hummingbirds, toucans and other birds that call the tropics home.

However, "we have to be careful always with these colors and color patterns," Puebla cautioned. "The way we perceive colors could be very different from the way other animals perceive it."

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This is especially true in marine systems. Because of the way light travels through water, red is absorbed extremely quickly, counterintuitively making it the ideal color for camouflage. Similarly, bright patterns that appear ostentatious to human eyes help many small fish hide from predators in the clear waters of coral reefs.

"Reef fishes have a lot of blue and yellow, but many fish do not see that," Puebla said. "These are colors with a very strong contrast, so they use that to break their silhouette as a way of camouflaging."

The high diversity and good visibility within tropical environments provide strong evolutionary pressures for colorful appearance, but there's also a physiological explanation for this abundance of color in animals that live near the equator, Arbore said. The production of color, whether through pigments or microstructural features, requires an investment of energy — something in short supply in harsher environments such as the tundra or desert.

"Normally, tropical habitats are more rich," Arbore told Live Science. "The conditions are more generous in terms of energy, the availability of food, a milder climate, which has a strong impact on the physiology of animals in tropical environments. Different species can actually invest more energy in color because there is more abundance and the physiological cost of being very colorful is reduced."

Whatever the evolutionary advantage, animals' color is inextricably intertwined with their environment, be it the bright birds of the rainforest or the dull silver fish of the deep sea. And the complex and diverse tropical ecosystem provides the perfect blend of competition and natural resources to support a fantastic explosion of vibrant color.