Normandeau's Julia Willmott co-authors study on butterfly diversity
|Gainesville, FL — Julia Robinson Willmott, a Normandeau Associates Senior Scientist and ornithologist, co-authored a study about how microhabitats, or small areas of highly localized environmental conditions, may contribute to the wide variety of colours and patterns butterflies use to deter predators.
The research was undertaken by an international team of researchers including Robinson Willmott and her husband, butterfly researcher Keith Willmott from the University of Florida, as well as other academics from the University of Cambridge, UK, and the National Museum of Natural History/National Centre for Scientific Research in France. The study is unusual in that the scientists examined both predator species and prey, which is often practically and logistically difficult to achieve.
The study focused on an area of Ecuadorian rainforest close to the Napo River, a tributary of the Amazon, where a range of low hills provided two distinctive microhabitats: small valleys with streams, and areas with low ridges. These have slightly different natural features, such as subtle changes in light and temperature, and variations in plant life. The birds in these areas have learned that butterflies exhibiting certain markings are toxic, and butterflies have evolved to copy, or mimic, each other's markings to deter the insect-eating birds. Rather than converging on the same defensive markings, however, butterflies in these areas exhibit a wide spectrum of diverse colours and patterns.
The team studied four areas, each located in either a valley or a ridge, and documented the relationship between 64 species of butterflies (including 58 species of ithomiines, commonly known as clearwing butterflies), and 127 species of local insectivorous birds, including tyrant flycatchers, jacamars and antbirds. Ithomiine butterflies have evolved a number of contrasting mimicry rings, often using bright colours such as orange and yellow to warn the birds about their toxicity.
The researchers found that although the microhabitats do not seem dramatically dissimilar from one another, they expose the butterflies to different predators. As a result, the pattern that is the most effective signal to predators may differ from one part of the forest to another. Microhabitats are probably only one of several causes of diversity in butterfly mimicry rings. Other factors, such as seasonal variations in predators, or the fact that different species are active at different times of day, may also be significant.
This paradox applies not just to butterflies, but to a wide range of species, and addresses broader questions about how multiple different defensive strategies can be optimal in one place. Although many species have evolved warning colour patterns that signal to predators that they are bad to eat, there is still a remarkable diversity of these patterns. Scientists predict that all species should converge on the same pattern, but this has clearly not happened. The study adds to a developing picture of the very complex interrelationships between plants, herbivores and predators in which even small ecological changes can have an effect for multiple species and, it would seem, their diversity.
The study, Maintaining mimicry diversity: optimal warning colour patterns differ among microhabitats in Amazonian clearwing butterflies, was published in Proceedings of the Royal Society B http://rspb.royalsocietypublishing.org/content/284/1855/20170744
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Julia Robinson Willmott
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