暖化操控對不同海拔的本土種紋白蝶、外來種紋白蝶及其蜜源植物的影響

Abstract

授粉者可提供重要的生態系統服務。鑑於暖化可能改變授粉者及/或植物的生長與發育，進而影響不同環境梯度下的授粉者與植物之關係，本研究想探討1)暖化會如何影響授粉者與蜜源植物的生長與發育，2)暖化是否會影響授粉者與蜜源植物的授粉關係，3)暖化對授粉者和蜜源植物的影響是否會隨著海拔或本土種和外來種授粉者而變化，4)野外的授粉關係如何隨季節和海拔變化。本研究的物種包含大花咸豐草及兩種紋白蝶。大花咸豐草(Bidens pilosa var. radiata )是台灣近年來重要的外來入侵物種，已成為許多授粉者重要的蜜源植物，其中常見的授粉者包含了本土種的台灣紋白蝶(Pieris canidia)與外來種的紋白蝶(P. rapae)。為探討暖化對不同海拔的兩種紋白蝶與大花咸豐草的影響，本研究包含了實驗室暖化操控實驗以及野外調查。實驗室暖化操控實驗收集來自中海拔(~1000 m a.s.l.)和低海拔(~100 m a.s.l.)各三個地點的大花咸豐草種子和兩種紋白蝶雌蝶(使用F1做實驗)，分別利用三個生長箱調控溫度來記錄暖化對其生長與發育的影響(控制組、3℃暖化與6℃暖化)。根據野外平均溫度資料，設置控制組溫度為16.8℃(中海拔)或22.8℃(低海拔)。野外調查則檢測紋白蝶的密度及大花咸豐草花朵的形質，是否會隨海拔及月分而改變。 研究結果顯示，暖化可對授粉者、植物、及兩者之交互關係造成影響，且此影響會隨海拔改變。首先，暖化可影響兩種授粉者(紋白蝶)的表現，然其結果受物種及海拔的影響 - 暖化會減少低海拔外來種紋白蝶的壽命與前翅長度，而暖化會對中海拔之本土種紋白蝶造成類似的影響。其次，暖化對蜜源植物(大花咸豐草)的影響亦隨海拔改變 – 暖化使中海拔大花咸豐草的開花時間提前、增加其開花數量，但減少其花朵的反射率。最後，暖化亦會影響授粉行為，然其結果受物種及海拔的影響 - 暖化增加了低海拔外來種紋白蝶的訪花頻率與覓食時間。野外調查顯示，紋白蝶的密度及大花咸豐草花朵的形質會隨海拔與月份改變。低海拔有較高的授粉者密度，而低海拔大花咸豐草(花蜜總糖量及反射率)和中海拔大花咸豐草(花蜜蔗糖量)在吸引力形質的表現上則各有優勢，而這些形質會隨月份而變化。以上的研究結果顯示，暖化可對這兩種紋白蝶(本土種vs.外來種)造成不同的影響，而此影響及暖化對大花咸豐草的影響，皆會隨海拔改變。鑒於暖化對各授粉者物種(兩種紋白蝶)及海拔族群(中低海拔紋白蝶或大花咸豐草)的影響程度不同，暖化不但可能會改變現有本土種與外來種的生態系統服務，也可能會改變各海拔的授粉者與蜜源植物之間的交互關係，進而影響當地的動植物群聚。

Pollination is an important ecosystem service. Given that climate warming has reportedly affected the growth and development of pollinators and/ or plants, likely shifting current plant-pollinator interactions (e.g. mismatches) across spatial gradients (e.g. altitude or latitude), this study examines 1) how warming may affect the growth and development of pollinators and nectar plants (flowers), 2) whether warming will affect the interactions between pollinators and nectar plants, 3) whether the effects above, if any, will vary across altitude (spatially) and between native and invasive pollinators, and 4) how plant-pollinator interactions vary temporally across altitude in the field. This study examined a nectar plant and its two 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 butterflies and their nectar plants across altitude, this study included a laboratory experiment and field survey. The laboratory experiment collected the seeds of B. pilosa var. radiata and females of the two Pieris species (F1 for study) from three sites each at medium (~1000 m a.s.l.) and low altitude (~100 m a.s.l.). Species from medium or low altitude were each raised in three growth chambers (control temperature, 3oC, and 6 oC warming); the control temperature for medium and low altitude was set at 16.8 oC and 22.8 oC, respectively, based on field data. The field survey examined the population density of both Pieris and the flower traits of B. pilosa across altitude over months. The results showed that warming impact on pollinators, plants, and their interactions varied with altitude. First, warming affected the native and invasive Pieris butterflies differently across altitude. In specific, warming reduced the adult longevity and forewing length of low-altitude invasive P. rapae, but of medium-altitude native P. canidia. Second, warming affected nectar plants (B. pilosa) 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. Third, warming also affected pollination activity differently between the two pollinators across altitude. For instance, warming increased the frequency and duration of flower visits by low-altitude P. rapae. In addition, the field survey showed that both Pieris and flower traits varied spatially (altitude) and temporally (months). Low altitude had a higher Pieris density; low-altitude B. pilosa plants (total sugar weight in flowers, flower reflection) and medium-altitude B. pilosa plants (sucrose concentration in flowers) might have a different strength in attracting pollinators. Many of these traits also varied with months. 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, potentially shaping local plant-animal communities.