GUANACASTE, COSTA RICA — New research from Costa Rica’s Área de Conservación Guanacaste (ACG) suggests that tropical insects may be vulnerable to rising temperatures.
The study, published in the Proceedings of the National Academy of Sciences (PNAS), examined the heat and cold tolerance of more than 100 species of rove beetles living between the lowland dry forest and the cloud forest of Volcán Cacao.
The researchers found that high-elevation species are adapted to cooler and more stable conditions and have limited capacity to cope as hotter temperatures move upslope, while low-elevation beetles may already be exposed to temperatures that meet or exceed their thermal limits.
“This diverse group of small insects has a big message for us about their environment,” said Dr. M. Alex Smith of the University of Guelph, the study’s corresponding author and a member of the GDFCF Board of Directors. “If we want to understand what climate change is doing to tropical biodiversity, we have to listen to the little things.”
The findings also provide new support for one of tropical ecology’s most influential ideas.
In 1967, ecologist Daniel Janzen published his seminal paper, “Why Mountain Passes Are Higher in the Tropics.” Janzen argued that tropical species living in relatively stable climates may evolve narrower thermal tolerances than species exposed to greater temperature variation. As a result, even relatively modest changes in elevation (and so temperature) can create significant barriers for tropical species.
Nearly 60 years later, the new study tests those ideas.
The results closely matched Janzen’s predictions. The cloud-forest beetles at the top of the mountain, in the (historically) most stable climatic environment, had the narrowest window of thermal tolerance. This calls attention to how some of ACG’s most diverse insect communities are particularly vulnerable to warmer temperatures moving upslope.
“Dan’s paper changed the way ecologists think about tropical mountains,” said Smith. “Nearly 60 years later, we can test those predictions with a diverse community of tropical insects. What we found is that the same adaptations that helped create and maintain this remarkable diversity may also make it especially vulnerable to rapid climate change.”
The study took place across a 1,500-meter elevational gradient within ACG, a UNESCO World Heritage Site in northwestern Costa Rica. Over a relatively short distance, the landscape rises from hot tropical dry forest through rain forest to cool cloud forest. This creates an extraordinary location for understanding how species respond to temperature.
Researchers collected live rove beetles from eight elevations along Volcán Cacao. To measure heat tolerance, they gradually warmed individual beetles until they reached their critical thermal maximum. To measure cold tolerance, they placed a different set of beetles into a chill coma and recorded how long it took them to recover. Since only about 1% of the rove beetle species known from Volcán Cacao currently have scientific names, the researchers used DNA barcoding to distinguish species.
The results revealed different risks at different elevations.
Heat tolerance declined strongly as elevation increased. Beetles from the cloud forest were less able to withstand high temperatures than their lowland counterparts. It is not just the cloud forest insects that are in the hot seat, as while low-elevation beetles are more heat tolerant, they live in forests where temperatures already reach close to their upper thermal limits.
“The insects at lower elevations may already be living very close to their limits,” said Smith, “while the insects higher on the mountain are not built for the temperatures that are coming toward them. Moving upslope may help some species temporarily beat the heat. But most of these species do not move much; and eventually, there will be nowhere higher to go.”
The study is the latest product of decades of biodiversity research in ACG.
None of this work would be possible without the long-term protection of ACG, the decades of biodiversity inventory established by Janzen and Dr. Winnie Hallwachs, and the work of ACG’s parataxonomists and staff.
Since 2013, Smith and colleagues, including the parataxonomists, have recorded temperature every 15 minutes at sites from sea level to 1,500 meters, creating a long-term record of how climate on the volcano is changing.
The new research also builds on nearly two decades of rove beetle collections in ACG and previous work showing that rove beetle diversity increases dramatically with elevation. Most species occupy very limited elevational ranges, and many of the most diverse communities are found in the cool, high-elevation forests now experiencing warmer temperatures. Rove beetles are among the most diverse groups of animals on Earth, with more than 60,000 described species worldwide, and many more still unnamed.
Any work we are able to complete was possible because many people have protected forests, maintained monitored sites, recorded data, and collected insects all to better understand the biodiversity living here.” said Smith
The researchers compared their findings with the world’s largest database of thermal tolerance data and found a very different pattern. Previous analyses suggested that heat tolerance in terrestrial insects does not change with elevation. In ACG’s diverse rove beetle community, it declined sharply.
The difference underscores how little is known about the enormous diversity of tropical insects and how they will respond to a changing climate. In ACG (and around the world), the overwhelming majority of the species do not yet have scientific names, and little is known about their individual biology.
“Trying to predict the future of biodiversity, using only a fraction of the species that actually exist, is like trying to assemble your new furniture without all the pieces, or the Allen key,” said Smith. “ACG gives us an extraordinary opportunity to begin filling in these pieces; not just by discovering what lives here, but by allowing a better understanding of how these species experience a world that is changing around them.”
The study, “Heat tolerance decreases and cold tolerance increases with elevation for a species-rich insect family on a tropical volcano,” was authored by Alexandre M. M. C. Loureiro, Winnie Hallwachs, Daniel H. Janzen and M. Alex Smith.
The research was supported by the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, the Government of Costa Rica, the Guanacaste Dry Forest Conservation Fund and its private donors, with special support from the Wege Foundation.
DOI: 10.1073/pnas.2533455123
Área de Conservación Guanacaste (ACG), a UNESCO World Heritage Site in northwestern Costa Rica, protects more than 172,000 hectares of connected marine and terrestrial ecosystems, stretching from Pacific coastal waters through tropical dry forest, rain forest and cloud forest. ACG is one of the most biologically diverse protected areas on Earth and a globally important center for long-term biodiversity research.
The Guanacaste Dry Forest Conservation Fund (GDFCF) is the international nonprofit partner of Área de Conservación Guanacaste. Since 1997, GDFCF has helped mobilize the science, philanthropy and long-term support needed to conserve, understand and restore one of the most biologically important places on Earth.
Media Contact:
Monique Gilbert
Chief Operating Officer
Guanacaste Dry Forest Conservation Fund
monique@gdfcf.org
www.gdfcf.org
Experimental study
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Heat tolerance decreases and cold tolerance increases with elevation for a species-rich insect family on a tropical volcano
27-Jul-2026