Rising Temperatures Shrink Habitat as Tropical Insects Face Space Shortages

Tropical insects may be among the most climate-sensitive creatures we overlook, according to new findings from Costa Rica’s Área de Conservación Guanacaste (ACG). A study published in the Proceedings of the National Academy of Sciences (PNAS) shows that rove beetles living along Volcán Cacao experience sharply different thermal limits across elevations. The work links these differences to how species have adapted to the temperature stability of their habitats over evolutionary time.

Researchers assessed heat and cold tolerance in more than 100 rove beetle species distributed across a 1,500-meter elevational gradient from hot dry forest to cool cloud forest. Elevation in ACG creates steep, predictable shifts in temperature over short distances, offering a natural laboratory for testing how climate change may reorganize insect survival. Because many local rove beetles lack formal names, the team used DNA barcoding to distinguish species.

To quantify thermal performance, scientists warmed individual beetles until they reached a critical thermal maximum. For cold tolerance, they induced a “chill coma” and measured recovery time. This combined approach produced a species-rich, experimentally grounded picture of how close each beetle community sits to both heat stress and cold stress.

The results revealed a clear pattern: as elevation increased, heat tolerance declined strongly. Cloud-forest beetles were less able to withstand high temperatures than their lowland relatives. Meanwhile, low-elevation beetles—though better at resisting heat—inhabit forests that may already run near their upper thermal thresholds.

These findings echo an influential tropical ecology idea proposed by Daniel Janzen in 1967: in stable tropical climates, species may evolve narrower thermal tolerances, making mountain “passages” act as barriers even when elevation changes are modest. Nearly 60 years later, the beetle data matched Janzen’s predictions closely, with the most climatically stable zone showing the tightest thermal window.

In a warming world, upslope movement might temporarily buffer some species from extreme heat. But the study emphasizes that many tropical insects have limited dispersal and may eventually face a hard limit—there is no higher place to go.

Beyond its ecological message, the research demonstrates how long-term field infrastructure enables questions that short studies cannot. Since 2013, temperature has been recorded every 15 minutes at multiple sites on the volcano, while decades of biodiversity inventories and rove beetle collections support context for interpreting physiological data.

If thermal tolerance varies this strongly among closely related insect species, predicting biodiversity futures with incomplete species sampling becomes especially risky. With most tropical insect species still unnamed, the researchers argue that understanding vulnerability requires both discovery and experiments that reveal how living organisms actually experience warming.