[This story first appeared on BBC Earth, 15 October 2015. This is my version before BBC’s edits.]Where would you go to bask in nature’s dazzling colours? Head to the tropics and most of us would follow.
But we might be going the wrong direction. A new study finds that temperate wildlife are more colourful than those in the tropics. Not all scientists agree, however.
Since the 1800s, explorers and natural historians have waxed lyrical about the colourful tropics. The pioneer of biogeography—the study of species distribution—Alfred Russell Wallace described the tropics as lands where animals whose “extreme richness of colour are manifested in the highest degree.” (REF#1)
Wallace spoke for most of us. From parrots to butterflies to orchids and birds-of-paradise, tropical wildlife easily capture hearts and eyes with bold tapestries of turquoise on red or blue on orange. Everything else looks plain, moreso wildlife in fall and winter.But perception can deceive. When Rhiannon Dalrymple started her Ph.D. at UNSW, Australia, she questioned the adage that wildlife are more colourful closer to the equator. Earlier studies do not agree but each of these tested a narrow set of wildlife and checked only colours that humans see. Using huge public datasets, Dalrymple tested for colour patterns across broad scales of latitude and wildlife. She analysed both human-visible and ultraviolet light.
Dalrymple and team compiled a list of 1,333 species of native birds, butterflies and flowers along the eastern coast of Australia down to Tasmania. Their study spans 34.5° latitudes and includes tropical rainforests, temperate woodlands and shrubs. They analysed museum or live specimens of these species, transformed their colouration into numbers and plotted these numbers onto areas where the species live. Then they averaged the numbers at each site and checked if these numbers change with latitudes.
They found that colouration changes little from north to south (REF#2). But the team found weak signs showing that further away from the tropics, wildlife sport more colours; colours were also more intense with bigger contrasts.
“When we started, I thought I would just be proving an old idea” says Dalrymple. “But now we have flipped people’s views.”
Not every scientist is convinced. Jonathan Adams, Associate Professor of School of Biological Sciences at Seoul National University, believes the study has nailed down colouration patterns in eastern Australia. But he questions if patterns found in a specific region would apply worldwide.
Australia’s unique biodiversity and long isolation complicate the picture. One would need a “big jump” to assume that wildlife colours on other continents would evolve as in Australia, says Adams.
Last year, Adams examined 247 butterfly species and found that those in Ecuador were more colourful than those in Florida and Maine (REF#3). Adams suggests that his study better tested if tropics are colourful because it covered ever-wet tropics and more severe temperate climates; the Australian study “touches mild winters and the fringes of subtropics”.
Both Dalrymple and Adams tap into museum collections to get enough specimens for their studies. However, inherent biases could skew the collections’ palette. Many old collections came from professionals who made a living selling specimens from the tropics. But collectors shipped more colourful specimens than drab ones. Admittedly, a jambu dove—plum-red head and jade-green plumage—brightens up a room more than a plain dove.
“Biases in collections could have affected how Europeans perceived colours of tropical animals,” warns Dalrymple.
So where can we find the most colourful wildlife? A lot more work remains “if we really want to know,” says Adams. For now, Adams would rather “keep an open mind” on the debate of colourful tropics.
4. Dalrymple is now adjunct instructor at Hamline University, Minnesota.