Patterns of insect biodiversity are less well understood than those of vertebrates and flowering plants, according to researchers from the University of Florida.
Exploring the genetic diversity of North American butterflies (Papilionoidea), they discovered that the variety of evolutionary distinct groups is surprisingly high in the sunny deserts of southwestern US and Mexico.
This is despite a dearth of different flowering plants in those regions, which share an evolutionary history with the captivating critters.
“When you think of desert, you don’t automatically jump to butterflies, but our results showed that this area is actually a really important hotspot for butterflies, even if it isn’t for plants,” says Chandra Earl, co-first author on the study.
The researchers suggest that several factors could explain the phenomenon.
“Most butterflies are generalists that don’t utilise just one host plant,” says Michael Belitz, the other co-first author on the study. “This makes butterflies less likely to clump into groups of tightly related species like plants do.”
Their mobility could also be a factor – unlike desert plants, with limited scope for spreading their seeds, butterflies fly freely. “These factors all add noise to the data,” says Belitz, “where you won’t see as strong a relationship between plants and butterflies as you might expect.”
The colourful appeal of butterflies has attracted a wealth of attention. Natural history and genetic data are available for nearly 1500 of the 1900 North American species, providing an ideal resource.
“This abundance of data positions butterflies as one of the best insect groups for asking broad-scale questions about the structure and drivers of diversity,” write the authors in their paper. The data reveals insights into the insects’ evolutionary history that is not apparent by simply counting species.
And while “some hotspots have been long recognised, understanding where diversity is highest, rarest and most threatened is still a work in progress,” they note.
To conduct their analysis, the team scoured several genetic repositories including Genbank, Barcode of Life Data System (BOLD) and Map of Life, and explored links between butterfly and plant phylogenetic diversity and historical climate patterns across the continent.
Overall, their findings align with well-known areas of rich biodiversity: the California Floristic Province, North American Coastal Plain, Madrean Pine-Oak Woodlands and Mesoamerica.
They found biodiversity patterns were even higher than expected in those areas, while revealing the desert regions with “significant endemism, relatively old lineages and high phylogenetic diversity”.
“Our results make a strong case for habitat conservation across warm deserts in particular,” they write, “especially because they are not already documented biodiversity hotspots.”