Drought-induced relocation of ant colonies and its consequences for the long-term spatial ecology of a population under stress

Abstract

Maintaining a central refuge such as a nest or burrow can offer protection against environmental stressors but comes at the expense of the capacity to disperse to new locations. This trade-off with mobility can be detrimental when environmental conditions become adverse for extended periods, necessitating animals to relocate in order to track shifting niche envelopes. Long-lived ant colonies that invest in the construction of large nests are especially susceptible to changing environmental conditions. The Australian meat ant, Iridomyrmex purpureus, build large terrestrial nests at sites that balance shade and solar exposure. Long-term study of a population of meat ants showed low nest turnover and a stable spatial distribution of nests across typical rainfall years. With the onset of drought, a dramatic surge in the production of new nests occurred through a process of budding that far exceeded historic trends. This appears to have allowed colonies to relocate nests into areas with more favourable microclimate conditions in a strategy reminiscent of the production of runners in stressed plants. The consequence has also been the packing of nests into a narrow habitable zone that has resulted in an apparent increase in competition among large rival colonies. Following the break in drought and the thinning of some nests through abandonment, competition has progressively eased in later years. The surge in nest budding triggered by acute environmental stress in this population offers a possible strategy for long-lived colonies to effectively migrate across the landscape. With changes in environmental conditions becoming more frequent and severe with the climate crisis, any strategy available to central place foragers to track windows of preferred conditions is likely to become increasingly important. Read the free Plain Language Summary for this article on the Journal blog.