Park Rangers Use Butterflies to Measure Biodiversity

Insect populations are in trouble. But with so many species, it’s difficult for researchers to study the true extent of their losses.

So scientists have come up with a novel approach. They’ve enlisted the help of park rangers in Ecuador to monitor butterfly abundance in one of the most biodiverse places on Earth. Researchers, students, and park employees have been monitoring butterflies in Yasuni National Park, considered to be a biodiversity hotspot.

A large-scale study between 2008 and 2017 found insects in Germany plummeted. There were 34% fewer species in forests and grasslands. The abundance of insects dropped 78% and the total weight, or biomass, dropped 67%. That followed a 27-year study that also showed substantial declines.

More research has shown similar losses in insect populations across the globe. But with 1 million species of insects discovered and likely millions more that have yet to be found, researchers don’t have the resources to count them all.

So they turned to rangers in Ecuador for help.

“Ecuador has about 20% to 25% of the world’s butterfly species and is one of the three most diverse countries in the world. It’s a natural place to study butterfly diversity and evolution—over the three decades that I’ve been working on Ecuadorian butterflies we’ve described hundreds of new species and got a better understanding of species diversity and identification, so we’re at a point where it’s becoming increasingly possible to address broad ecological questions,” senior author Keith Willmott, curator and director of the Florida Museum’s McGuire Center for Lepidoptera and Biodiversity, tells Treehugger.

“One question that has fascinated me for many years is what explains the remarkable changes in butterfly abundance across seasons and, more intriguingly, across years, and even decades. Also, like many Neotropical butterfly researchers, we have a vague suspicion that overall butterfly abundance may be declining, but we have no solid evidence to test that.”

To understand what drives those changes in abundance over seasons and to see whether those changes are long-term, they came up with a monitoring program.

They chose Ecuador's Yasuni National Park because it is one of the most diverse tropical ecosystems on Earth, including butterfly species. The park has the infrastructure, including rangers and ranger stations, to implement a monitoring program.

“It is a protected area and therefore somewhere one should be able to establish a long-term monitoring program that will hopefully not be directly affected by habitat destruction,” Willmott says. “Also, for the same reason, changes in butterfly populations can be seen as a ‘control’ to measure changes in other regions where habitat alteration may be important. At the same time, any changes in butterfly populations in Yasuni likely reflect large-scale processes, such as climate change, which will impact all natural organisms.”

Why Butterflies?

Butterflies are considered an indicator species, meaning because they are easy to find and so well distributed, they can be used to measure how similar species are doing.

“Butterflies are the best-known insect group in terms of their diversity, identification, relationships, nomenclature, biology, and distribution. They are easy and cheap to sample and easy to identify (relatively, because most species can be identified from their wing patterns once key characters have been found),” Willmott says.

“They are diverse and occur in most microhabitats and habitats, most species are closely tied to particular plant species as caterpillars, and they are linked to parasitoid and predator communities, and so they closely reflect changes in natural habitats.”

They respond quickly to change and researchers have extensive knowledge of the insects which should help them understand changes in abundance.

“For example, if we find that some groups of butterflies are declining and others are increasing, we can look for ecological traits that might help explain what is happening,” Willmott says. “Perhaps species that specialize as caterpillars on understorey plants are declining, which might implicate changes in microhabitat conditions, etc.”

Rangers as Citizen Scientists

For the study, park rangers conduct butterfly monitoring events every two months. They start by preparing bait traps filled with rotting fruit and carrion and refilling the traps every morning for five days.

Rangers patrol the traps each day, removing butterflies with forceps. They use field guides to identify them. They write a number with a permanent marker on the underside of the wing, photograph it, and release it. A few butterflies are photographed and saved for future identification.

They record whether the butterfly was marked and released or collected, the specimen code, the species name, the trap number, where the trap was located, the type of bait in the trap, the date and time, and the image number. They also offer basic information about the weather at the time.

The rangers send their records and images to the researchers to confirm identifications and provide feedback.

Information on the monitoring program and how it works is published In the journal Insect Conservation and Diversity.

Challenges of Tropical Regions

Many studies have been carried out and published over the past five to ten years that show insect population declines, but most of these have been conducted in temperate regions. Most biodiversity, however, is in tropical regions.

“Tropical regions are particularly challenging to study because diversity is about an order of magnitude higher, at least for insects, making sampling and identification more complicated and expensive,” Willmott says.

Because there are fewer seasonal changes in tropical areas, the weather may play less of a role in controlling abundance, making patterns harder to analyze.

Citizen scientists play an important role in documenting changes in temperate regions. But there are fewer amateur researchers like this on hand in tropical regions. That's because they don’t have the field guides and clubs to encourage them and tropical landscapes can be hard to access.

“In short, the work is vastly more complicated and more expensive and there are many fewer people to do it than in temperate regions. Our approach benefits from the existing presence of park rangers, with their general knowledge of biodiversity issues, in remote, undisturbed areas that are otherwise difficult to access,” Willmott says.

“It is thus cost-effective, hopefully sustainable in the long-term, and provides opportunities for park rangers to expand their knowledge, sampling skills, and understanding of the biodiversity that they are charged with protecting.”