OOS 40-6 - Night warming, insect demography, and predation pressure

Background/Question/Methods
Existing studies concerning warming effects on species interactions mainly focused on changes in temperature means, with increases in both daytime and nighttime temperatures or a rise only in daytime temperatures. However, the rise of global mean temperatures has resulted from daily minimum temperatures increasing at a faster rate than daily maximum temperatures. Importantly, day and night warming may have different thermal effects on organisms, implying that night warming may affect species and interspecific interactions differently from that of day warming. Despite previous studies have reported the ecological consequences of warming in mean temperatures, night warming are often overlooked in climate change studies. In the present study, we used the lady beetle Propylaea japonica and the grain aphid Sitobion avenae as a predator–prey model system to study the effect of night warming on interspecific interactions. We studied the extent to which night warming would alter the demographic parameters, stage structure, population growth and prey consumption and energy efficiency of the lady beetle. We also compared the different effects between night warming and mean temperature increase.

Results/Conclusions
We found that night warming accelerated the growth rate of the lady beetle while reduced the reproduction relative to that under the conditions of mean temperature increase. Lifetime predation and energy efficiency of the lady beetle decreased with temperature under constant conditions while remained unchanged under night warming, which implying a stable energy efficiency under realistic night warming. Both mean temperature increase and night warming modified the population structure of the lady beetle, with an increasing proportion of adults whereas a decreasing proportion of larvae, but the proportion of adults under night warming was higher than that of mean temperature increase. Importantly, the population growth rate of the lady beetle decreased with warming under mean temperature increase while increased with night warming, suggesting an opposite result of warming effects between night warming and mean temperature increase. These results provide some key implications for the studies of warming effects on insects and species interactions in the context of ongoing climate change.