Field ecology of freeze tolerance: interannual variation in cooling rates, freeze‐thaw and thermal stress in the microhabitat of the alpine cockroach Celatoblatta quinquemaculata

Abstract

Microclimate recordings were made over four years on the Rock and Pillar Range, New Zealand. These are used in conjunction with mortality and freezing data derived in the laboratory to make inferences about the winter thermal ecology of the freeze‐tolerant alpine cockroach Celatoblatta quinquemaculata (Dictyoptera: Blattidae). Threshold temperatures are identified through laboratory experiments at ecologically relevant cooling rates: 0°C; −3.1°C (FP5: the temperature at which 5% of cockroaches are expected to be frozen); and −4.5°C (FP50). The maximum cooling rate in the microhabitat across any of the thresholds was 0.06°C min−1, considerably slower than the 1°C min−1 normally used in laboratory studies. Freeze‐thaw events occurred regularly in the field, and temperature minima occasionally fell to temperatures lethal to C. quinquemaculata. Variability in snow cover contributed to interannual variation in microclimate temperatures. Decreased snow cover is predicted with climate change scenarios, and this will probably result in more freeze‐thaw cycles and more extreme minimum temperatures in this environment. It is concluded that the limited environmental tolerances of the animals living in this habitat make the few degrees of interannual variation ecologically relevant.