Limits on the capacity of an ectotherm to buffer temperature extremes through the construction of a central refuge

Competition, lack of space, and prolonged environmental change can lead animals to build refuges in areas that are (or become) exposed or otherwise offer poor protection. This is especially problematic for species that invest heavily in refuge construction and reside in that refuge long-term. We examined the consequences of refuge position in an iconic central place forager, the Australian meat ant (Iridomyrmex purpureus). Colonies excavate massive ground nests out of soil and can remain in those nests for a decade or more. We monitored the external and internal temperature of nests for over two years. These data were combined with a phylogenetic analysis of optimal brood incubation temperatures compiled from the literature to infer the probable incubation temperature for this species. Focussing on summertime extremes, our field data across consecutive years showed the spatial position of meat ant nests had critical impacts on the internal conditions of nests. In most instances, colonies would probably be able to protect broods by actively moving broods to different depths within the nest. However, this thermoregulation would unlikely fully compensate for the extreme temperatures experienced by the most exposed nest in our study. This exposed nest has in turn suffered a sustained decline in colony size over the last decade. Even for a central place forager believed to be resilient to environmental degradation, refuges could not protect against prolonged environmental change, with likely tangible impacts on fitness.