How may climate warming affect a native Pieris butterfly, an invasive Pieris butterfly, and the pollination of their nectar plants across altitude?
Pollination is an important ecosystem service because two thirds of plants require this service for successful sexual reproduction. Given that climate warming has reportedly affected the growth and development of organisms, likely leading to mismatches of interacting species across spatial gradients (e.g. altitude or latitude), this study aims to examine 1) how warming may affect the growth and development of pollinators and nectar plants, 2) whether warming will affect the interactions between pollinators and nectar plants, and 3) whether the effects above, if any, will vary across altitude and between species (native vs. invasive pollinators). Bidens pilosa var. radiata, a notorious invasive plant in Taiwan, has become an important nectar resource for many pollinators, including two common butterflies, the native Pieris canidia and invasive P. rapae. To understand warming impact on these two butterflies and their nectar plants across altitude, we collected the seeds of B. pilosa var. radiata and eggs of two Pierisspecies from three sites each at medium (1000 m) and low altitude (100 m). Species from medium or low altitude were each raised in three growth chambers (control temperature, 3℃, and 6℃ warming); the control temperature for medium and low altitude was set at 16.8℃ and 22.8℃, respectively, based on field data.
The results showed that warming affected the native and invasive Pieris butterflies differently across altitude. In specific, warming reduced the longevity and forewing length of low-altitude individuals in both Pieris species, but of medium-altitude individuals in P. canidia only. Warming affected nectar plants differently across altitude. For example, warming facilitated flowering (earlier flowering and more flowers) and reduced flower reflectance in medium-altitude plants, but had no such effects on low-altitude plants. As for pollination activity, warming generally increased the frequency and duration of flower visits by P. rapae of low-altitude origin. In summary, warming may differently affect the ecosystem service (a function of pollinator longevity and flower visit) provided by the two Pieris pollinators across altitude, and the different response of medium- and low-altitude plants to warming together suggests an upcoming shift in pollinator-plant interactions across altitude under climate warming.