都市化與鄰近植物對紫背草屬植物雌全同株繁殖特徵的影響

Abstract

植物發展出多種性別分化系統利用不同繁殖策略適應環境變異。雌全同株的性別分化系統，提供植物更多繁殖策略上的彈性，因應環境中各種生態因子的變化。雌全同株的植物能夠在同個花序中產生兩性花(雌雄同花)與雌性花，雌性花的比例影響該植物適應環境變化的能力。此研究旨在了解在環境變遷的過程，是否會對雌全同株的紫背草屬(Emilia)植物，其雌性花的比例產生影響。都市化已被證實對生態系統造成諸多影響，包括對生物相組成的改變。生物相的組成亦會受到生物間交互作用的影響。本研究欲探討在大尺度都市化進程，與小尺度鄰近物種組成的影響下，是否會對動植物關係中種子傳播前的種子植食者與授粉者的生物相造成改變，因應環境壓力的變化紫背草屬植物雌性花比例是否會間接地受到影響。本研究在臺北市內選取13個樣點，並對其地景結構進行量化，以不透水面積的佔比作為大尺度都市化的指標，並在每個樣點內利用樣框量化小尺度植物的組成，進行成熟花序的取樣與授粉者調查。本研究使用臺灣原生種紫背草 (E. sonchifolia) 和外來種粉黃纓絨花 (E. praetermissa) 作為研究物種檢驗上述內容。我們的結果支持雌全同株的紫背草屬植物，其雌性花比例有所變化以適應環境，且外來種的粉黃纓絨花相較於原生種紫背草，雌性花的佔比較高。我們發現小尺度植物組成差異會對雌性花的比例與生物相造成改變，但大尺度地景結構的影響並不顯著。異種鄰近植物的存在提高雌性花的佔比，但隨著異種植物花序密度的增加，雌性花的比例會隨之下降，顯示雌全同株植物採取分擔風險(bet-hedging)的繁殖策略。異種鄰近植物的存在提高種子傳播前種子被捕食的情形，且授粉者密度與種子傳播前的植食者數量存在顯著正相關，表示兩者在生態系統中可能受到相同的因子影響，但該因子未被納入我們研究系統。

Plants have developed various sexual system to adapt to environmental variations using different reproductive strategies. The gynomonoecy is a plant sexual system providing plants with greater flexibility in reproductive strategies to response to changes in various ecological factors. Gynomonoecious plants can produce both bisexual flowers (hermaphroditic) and female flowers within the same capitulum, with the female floret ratio influencing the ability of plants to adapt to environmental stresses. This study aims to understand whether changes in ecological conditions affect the female floret ratio in gynomonoecious Emilia plant species. Urbanization has been proven to impact ecosystems in many ways, including changes in biota composition. The composition of biotic communities is also influenced by biotic interactions. This study explores whether large-scale urbanization and fine-scale neighboring plant composition affect the pre-dispersal seed predator and pollinator communities, and indirectly influence the female floret ratio in Emilia. We selected 13 study sites in Taipei City and quantified their landscape structures, using the impervious surface ratio as an indicator of large-scale urbanization gradient. We also quantified fine-scale plant neighborhood composition at each site using quadrats in which mature capitulum collection and pollinator surveys were carried out. This study used the native E. sonchifolia and the exotic E. praetermissa as study species. Our results support the hypothesis that the female floret ratio in gynomonoecious Emilia species varies in response to different ecological conditions. The exotic E. praetermissa had higher female floret ratio compared to the native E. sonchifolia. We found that fine-scale neighborhood composition affected both the female floret ratio and biotic factors, while the influence of large-scale urbanization was not significant. The presence of heterospecific neighbors increased the female floret ratio, but it decreased with increasing density of heterospecific capitulum, indicating a bet-hedging reproductive strategy by gynomonoecious plant species. The presence of heterospecific neighbors also increase pre-dispersal seed predation rate, and there was a significant positive correlation between pollinator density and pre-dispersal seed predators, suggesting that both may be influenced by the same factors not included in our study system.