How may climate warming affect a native butterfly (Pieris canidia), an invasive butterfly (P. rapae), and their competition on a common host plant (Rorippa indica)?

Background/Question/Methods

While the impact of climate warming on ecological patterns has been explicitly documented, we know relatively little about the ecological mechanisms through which climate warming affects organisms, populations, and community structure.   The goal of this study is to understand the consequence of climate warming for a native species, an invasive species, and their competition, by examining the impact of experimental warming on various ecological mechanisms (e.g. warming effects on growth and development).  In specific, we studied two competing butterfly species of Taiwan (the native Pieris canidia and the invasive P. rapae) on their common host plant (Rorippa indica) in three environmental chambers (18.5, 21.5, 24.5^oC).  The chamber at 18.5 ^oC served as control, reflecting the average monthly temperature when both butterflies became abundant in the field; the one at 21.5 or 24.5 ^oC simulated 3 or 6 ^oC warming, respectively.  Each chamber included four treatments, allowing us to examine the intra- and inter-specific competition: a) 4 P. canidia, b) 2 P. canidia and 2 P. rapae, c) 4 P. rapae larvae on a host plant, and d) a host plant only. 

Results/Conclusions

The results showed that warming facilitated larval development, consequently reducing the larval period before metamorphosis in both butterflies.  P. canidia, facing stronger intraspecific than interspecific competition, had a competitive advantage over P. rapae in terms of larval development, pupal weight, adult weight, and adult size.  However, this advantage (e.g. faster larval development) decreased under warming.  This study suggests that the native P. canidia is a superior competitor than the invasive P. rapae on the native host plant R. indica, but this superiority will likely decrease under climate warming.