- 學位論文
食物品質與化學計量不匹配對橈足類生長速率之影響
Effects of food quality and stoichiometric mismatch on copepod growth rates
摘要
生產者和消費者之間的互動是決定群落結構和生態功能的重要因素。許多研究已指出在這兩個食階間能量和物質的傳遞效率主要受到食物品質影響。然而這些研究大部份都是以淡水物種作為對象的實驗，目前尚未有研究探討食物供應和消費需求之間化學計量不匹配在自然海洋系統中之影響。因此本篇研究在東海海域進行野外調查，以定量的方式去測試食物品質和化學計量不匹配是否能影響到橈足類的生長速率。我們分別利用顆粒有機物 (POM) 與兩個浮游動物群落的碳氮元素比值 (C:N) 代表浮游植物和橈足類的化學計量，再採用人造年級群測量橈足無節幼蟲和橈足幼生的單位重量生長速率，並在分析前利用生態代謝理論去除溫度及體型大小的影響。結果顯示POM的C:N (5.94 ± 0.77) 只有很小的變異，而且低於Redfield ratio。相反地，橈足無節幼蟲的C:N (7.55 ± 1.20) 和橈足幼生 (6.83 ± 1.34) 變異較大並高於Redfield ratio，兩者也未跟POM的C:N有關係。我們同時發現橈足無節幼蟲的C:N比橈足幼生的C:N高，證實橈足類C:N在個體發育過程中會產生變化，因此本篇研究結果與普遍接受的浮游動物體內化學計量恆定性概念抵觸。橈足類的生長速率也沒有像預期般受到食物品質的影響，但橈足幼生的生長速率與化學計量不匹配 (C:Ncopepod - C:NPOM) 卻有明顯的正比關係。根據結果我們可以推論較大程度的不匹配是較高生長速率的誘因：當橈足幼生比食物有較大的C:N時，橈足幼生以提高攝食率來達到Redfield ratio。儘管如此，橈足幼生的攝食率也有可能因為高碳生長和脂肪積存而提高，繼而引致這正比關係。
並列摘要
Trophic interactions between producers and consumers determine community structure and ecological function. The efficiency of energy and materials transfer at this interface through grazing critically depends on the quality of producers as food for consumers. Existing evidences showing the effect of food quality on consumers were mainly gained from controlled experiments and studies on freshwater species. However, the effect of stoichiometric mismatch between food supply and consumer demand has not been examined quantitatively in natural marine systems. Here, we investigate whether food quality and stoichiometric mismatch can impact on growth rates of copepods, using field data in the East China Sea. We use C:N ratios of particulate organic matter (POM) and two zooplankton community size fractions (nauplii and copepodites) to represent stoichiometry of phytoplankton and copepods respectively, and measure copepod in situ weight-specific growth rates using the artificial cohort method. We remove temperature and body size effects on growth rates a priori according to the Metabolic Theory of Ecology to test the effect of stoichiometry. The C:N ratios of POM (5.94 ± 0.77) were lower than the Redfield ratio with small variation. In contrast, the C:N ratios of nauplii (7.55 ± 1.20) and copepodites (6.83 ± 1.34) vary substantially and are on average higher than the Redfield ratio, and are not correlated with the C:N ratios of POM. In addition, the C:N ratios of nauplii are generally higher than those of copepodites, indicating ontogenetic change. Our results contradict the generally accepted perception of stoichiometric homeostasis of zooplankton. Surprisingly, growth rates of both size fractions were not affected by food quality. Rather, growth rates of copepodites increased significantly with the increasing stoichiometric mismatch (C:Ncopepod - C:NPOM). We propose a hypothesis to explain this observation: higher stoichiometric mismatch triggered higher copepodite growth rates. That is, for the copepodites having high C:N relative to the C:N of their food, they would increase their consumption rates in order to reach the Redfield ratio; as such, their growth rate elevated. Nevertheless, we cannot rule out the possibility that the positive correlation between growth rates and C:N of copepodites could simply occur when higher consumption rates (and thus higher growth rate) are associated with high carbon growth and lipid accumulation.
參考文獻
延伸閱讀
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