溫度上升與二氧化碳濃度增加對跨海拔植食性昆蟲的直接與間接影響

Abstract

溫度上升與二氧化碳濃度增加，是近年來全球氣候變遷的兩項重要變化。為了進一步了解它們對生態系統造成的衝擊，本研究探討： (一)溫度上升與二氧化碳濃度增加是否會有交互作用，並且直接地(例如透過生長與發育)、或是間接地(例如:透過影響食草)影響植食性昆蟲的表現。 (二)跨越環境梯度(例如海拔)的生物族群，是否具有種內變異，因而對於氣候變遷產生不同的反應。為了回答前述問題，本研究以緣點白粉蝶(Pieris canidia)幼蟲，及其主要食草葶藶(Rorippa indica)為材料，進行兩組生長箱實驗: 直接與間接效應實驗。每一實驗共有十二種(3*2*2)處理組合: (現今平均溫度[21.8°C]、+3°C、+6°C)*(環境CO2濃度500 ppm、預估本世紀末CO2濃度1000 ppm)*(生物的海拔來源:[低或中海拔])，其中溫度處理具有氣溫日變化。「直接效應」實驗將P. canidia飼養在各個(溫度*二氧化碳)處理之下，並以統一培養於人工氣候室的食草加以餵食。「間接效應」實驗則是將食草培養在各個(溫度*二氧化碳)處理之下，分別餵食培養於控制組環境的幼蟲。結果顯示，溫度上升和二氧化碳濃度增加，會透過單獨以及彼此交互作用的形式，影響P. canidia的表現。而溫度上升單獨影響P. canidia的性狀項目，多於二氧化碳濃度增加所影響的項目。此外，物種的海拔來源會單獨的影響P. canidia表現，並且與溫度及二氧化碳處理產生交互作用。綜合以上的結果，本研究建議氣候變遷的評估 (一)應該考慮氣候變遷因子之間的交互作用，以及它們如何透過直接與間接效應影響生物表現; (二)應考慮隨環境梯度產生的種內差異，以族群而非整個物種作為評估的反應單位。

Temperature and CO2 concentration in the atmosphere are predicted to keep rising during this century. Therefore, it becomes increasingly important to understand 1) whether the elevated temperature and CO2 will interact and influence species performance directly or indirectly (e.g., indirectly via their effects on interacting species, such as herbivores’ host plants), and 2) whether these effects will vary spatially (e.g., populations across altitudes might react differently due to their adaption history). To answer the aforementioned questions, we empirically examined the direct and indirect effects of elevated temperature and CO2 on the performance of Pieris canidia (herbivore; Pieris hereafter) on Rorippa indica (host plant; Rorippa hereafter) across altitudinal gradients by conducting two experiments: direct and indirect effect experiments. Each experiment had a 3x2x2 factorial design including temperature treatment (daily fluctuating about a average of 21.8, 24.8, and 27.8°C, representing control, +3°C, and +6°C, respectively), CO2 treatment (500 and 1000 ppm, representing control and elevation) and altitudinal origin of species (low- and medium-altitude), allowing us to examine the individual and collective effects of temperature and CO2 on populations across altitude. In the direct effect experiment, Pieris larvae were reared under each of six temperature-CO2 treatments but fed with Rorippa plants grown from a common garden. In the indirect effect experiment, Pieris larvae were reared under control treatment (21.8°C on average, 500 ppm CO2) but fed with Rorippa plants grown under each of six temperature-CO2 treatments. Pieris and Rorippa plants were originally collected from three regions each at low (c.a.100 m a. s. l.) and medium (c.a. 1000 m a. s. l.) altitudes, to avoid potential idiosyncrasies. The results showed that in direct or indirect effect experiments, elevated temperature and CO2 individually or interactively affected Pieris performance, while elevated CO2 alone affected fewer performance traits than elevated temperature did. Furthermore, species’ altitudinal origin affected Pieris performance and mediated the temperature and CO2 effects. In conclusion, the results have two implications: 1 ) Climate change impact assessments may need to consider the interplay between climate change components (e.g., elevated temperature and CO2), which can directly and indirectly affect species. 2) These assessments should also consider intraspecific variation across spatial gradients, such as treating a population, instead of an entire species, as a responsive unit.