Arboreality drives heat tolerance while elevation drives cold tolerance in tropical rainforest ants

Area of Science:

• Ecology
• Climate Change Biology
• Zoology

Background:

• Understanding species thermal limits is key to predicting biogeographic patterns and climate change vulnerability.
• Analyses must integrate thermal gradients across multiple spatial scales, from microclimates to broader geographic regions.

Purpose of the Study:

• To investigate the correlation between rainforest ant thermal traits and microclimate conditions at micro- and mesogeographic scales.
• To assess climate change vulnerability by calculating warming tolerance in Australian Wet Tropics ant species.
• To test thermal adaptation and thermal niche asymmetry hypotheses across different spatial scales.

Main Methods:

• Collected 74 ant colonies (40 species) from terrestrial and arboreal habitats at lowland and upland sites.
• Recorded microclimatic conditions for one year and performed ramping assays to determine cold tolerance (CTmin), heat tolerance (CTmax), and thermal tolerance range (CTrange).
• Related thermal traits to microclimate data across elevation gradients.

Main Results:

• Arboreal ants exhibited higher CTmax (+4.2°C) and broader CTrange (+5.3°C) than ground-dwelling ants, irrespective of elevation.
• Upland ants tolerated significantly colder temperatures (CTmin) than lowland ants; CTmax and CTrange showed less pronounced changes with elevation.
• Differential microclimate exposure influenced CTmax divergence, while elevation-driven temperatures drove CTmin divergence.

Conclusions:

• Both thermal adaptation and thermal niche asymmetry contribute to interspecific thermal tolerance patterns, depending on the spatial scale.
• Local niche preferences drive divergence in heat tolerance, while broader environmental temperatures influence cold tolerance.
• Lowland arboreal ants, despite broad thermal ranges, possess the lowest warming tolerance, indicating heightened vulnerability to climate change.