With over a million known species, insects are by far the most diverse group of organisms on Earth, with conservative estimates indicating that there are millions more to be discovered. But extinction due to human pressures could outstrip the pace of discoveries, with species disappearing before researchers even knew they existed.
To conserve these species, scientists must first know where they are found. While the distributions of certain groups of plants and animals have been widely mapped, relatively little is known about the location of insects in the world.
In a new study, researchers have created the most detailed distribution map to date for butterflies in the American tropics, showing that areas of greatest diversity coincide with areas most threatened by deforestation and development. The study specifically focused on the Ithomiini, or glass-winged butterflies, a large group with nearly 400 species found across much of Central and South America. Their ubiquity can make them a good indicator of the fate of other insects in the region.
“If we want to understand the diversity of insects in general, one approach is to focus on groups that probably reflect the diversity of all insects and that we have a good knowledge of, such as butterflies,” the co-author said. of the study Keith Willmott, curator. and director of the McGuire Center for Lepidoptera and Biodiversity at the Florida Museum of Natural History.
Mimicry both helps and hinders the glass wings
Glasswing butterflies get their name from their unusual transparent wings marked with colorful spots of alternating hues and patterns. As with many other butterfly species, such as monarchs, these marks serve as a warning. Male glasswing butterflies feed on the nectar and tissue of poisonous plants, concentrating toxins in their abdomen and passing them on to females during mating. These toxins, a type of alkaloid, give butterflies and their eggs a bitter taste that makes them unpleasant to taste.
But potential predators weren’t born innately knowing not to eat these butterflies, but by learning by trial and error. As a result, many species of glass wings have developed similar wing patterns that give them strength in numbers.
“Because different species share the same warning color patterns, they share the overall cost per species of educating predators to avoid them,” said Willmott.
This type of resemblance, called Müllerian mimicry, has helped glass-winged butterflies survive and diversify into the varied habitats of the tropics, but it comes at a cost, too. While this strategy is effective when all similar species thrive, the extinction of one species could jeopardize the survival of others, Willmott explained. “This is especially true if one of the more common species goes extinct, as all the others lose the advantage they gained from their involvement in Müllerian mimicry with these butterflies.”
Glasswing butterflies are the most diverse and vulnerable at high altitudes
Willmott and his colleagues have spent the last decades scouring mountains and forests in search of glass wings, describing new species and documenting their natural history along the way. By combining the data they’ve collected over the years with information gleaned from specimens in more than 60 museums and private collections, the researchers have compiled nearly 30,000 distribution records. They used this large dataset to map the diversity of glass wings and interactions between similar species across the American tropics.
Their results indicate that glass wings are very diverse in parts of their range, including the Amazon River basin, where their transparent wings help them blend against the backdrop of the gloomy forest. But the majority of species congregate in mountainous biodiversity hotspots. The eastern slopes of the Andes mountains contained the top 5% of the glass wing diversity, while the secondary hotspots included the Central American highlands and the Atlantic coastal forest of Brazil.
While large swathes of the Amazon rainforest remain relatively untouched, Glasswing’s diversity in the tropical Andes frequently overlaps with areas most at risk of habitat loss due to land conversion for agriculture. This was especially true for species with a restricted distribution, highlighting the urgent need for conservation efforts in these areas.
Mountainous regions create a variety of small, localized environments as they rise in altitude. The relatively young Andes, which are among the tallest mountains in the world, are home to a large number of species. Differences in topography, temperature, and rainfall also make the Andes a great place to grow a variety of crops. “At the moment, habitat loss is the most significant threat,” said Willmott. “It is only an unfortunate coincidence that the areas where it is good to live are also areas which support a great diversity of animals and plants. “
Lead author Maël Doré, a doctoral student at the National Museum of Natural History in Paris, also fears that climate change will further limit the range of species already restricted on the slopes of tropical mountains. As temperatures rise, species may cope by shifting their distribution to higher elevations, but it is uncertain whether glass wing communities will move quickly enough to keep up with climate change.
Far from the Andes, the lower and oldest mountains of Brazil’s Atlantic coast are home to a number of rare and endemic glass wing species, which are also threatened by habitat destruction. “This region has seen nearly five centuries of human occupation, but it is also here that pioneering initiatives to protect neotropical butterflies and their habitats began almost 100 years ago,” said the co -author André Freitas, professor at the University of Campinas in São Paulo, Brazil.
Still, Willmott and his colleagues remain optimistic. With a detailed map of the location of the butterflies, conservation efforts can be directed toward preserving endangered environments and communities, as well as those still unaffected by humans.
“With more accurate maps of butterfly distribution, we can identify species and communities that currently lack protection, in order to more effectively focus scarce resources where they are needed most,” said Willmott.