Heat pulse tolerance of butterfly pupae: A model for conditions experienced during fire

Background/Question/Methods

Fire is a ubiquitous feature of ecosystems worldwide. Ignitions can be caused by natural forces such as lightning coupled with dry and/or hot periods, and increasingly to both accidental and intentional ignition by humans. The powerful disturbance effects of fires are both direct and indirect, and organisms living in these ecosystems have evolved many ways of coping with the mortality common to such a disturbance. One strategy is to simply recolonize the area post-fire, but an alternative is to survive the pulse of heat that is generated by the combustion of fuels. Sessile organisms or life stages must be able to cope with such effects in order to survive. The mortality of Eumaeus atala butterfly pupae when exposed to a heat pulse was tested under controlled conditions using a water bath.  Since fire is highly variable, the heat pulse transferred can be variable, and so the temperature and duration of the immersion of the pupae in the water bath was randomly varied from 30 to 65 degrees Celsius and from 1 to 55 minutes.

Results/Conclusions

We fitted a model to emergence as a function of duration and temperature. Exposures under 10 minutes had variable emergence outcomes above 47 C while the probability of emergence from 10-55 minutes decreased linearly over the range from 43-48 C. Results from this heat tolerance experiment on Atala pupae may indicate general trends in pupae survival below the ground for other species. The link between below-ground temperatures and surface temperatures remains unknown and will further improve the survival management of burrowed pupae of conservation concern.