溪頭柳杉林昆蟲垂直分層群聚研究

Abstract

在陸域生態系中，森林中的林冠對於生產力、生態系功能、氣候調節、生物多樣性的維持具有絕對性的影響。然而，由於在森林環境中垂直空間移動上的困難，林冠研究倍受阻礙，是最不為人知的生態系統之一。過去的研究發現，森林結構的層化現象影響著森林動物的垂直分布；為瞭解溪頭人工林中昆蟲的垂直分布情形，本研究自 2011 年 3 月 16 日至 2012 年 3 月 16 日 1 年期間，於臺大實驗林溪頭林區中的柳杉 (Cryptomeria japonica D. Don) 人工林中進行昆蟲相調查，利用人工林中的二氧化碳通量觀測塔，分別於地被層、灌木層、林下層、冠層、露出層 (1、5、15、25 和 34 公尺高) 放置四色黏紙陷阱 (黃、藍、綠、白)，以全面收集林冠上下所有飛行昆蟲的豐富度組成及群聚在不同時空的變化，並整合當地氣候資料，以探討氣候因子變化對昆蟲群聚分布的影響。採樣期間共採獲昆蟲 16 目 111,526 個體數。進一步將採獲的雙翅目昆蟲鑑定至科級，並計算豐富度 (abundance)、分類群豐度 (taxa richness)、密度 (density)、均勻度 (Pielou’s evenness)、歧異度 (Shannon diversity index) 及優勢種比例 (dominant taxon ratio) 等群聚參數。應用單變量變異數分析 (one-way ANOVA)、多維空間尺度分析 (multi-dimensional scaling, MDS)、聚類分析 (cluster analysis) 及典型對應分析 (canonical correspondence analysis, CCA) 等方法，解析雙翅目昆蟲群聚及其同功攝食群 (feeding guild) 的時空變化及群聚和氣候因子間的關係。 在昆蟲綱目級 (order) 的比較，採樣期間共收集了 16 目 111,526 隻昆蟲，其中雙翅目共 93,207 隻最為優勢，佔了整體的 83.57 %。空間分布上，半翅目集中於 5 公尺以下，鱗翅目集中於 25 公尺，膜翅目、嚙目集中於 25 公尺以上空間，雙翅目集中於 1、25 公尺，纓翅目集中於 5、34 公尺處，而鞘翅目在各高度分布則較為均勻。整體而言，在 1 公尺處的總豐富度最高 (41,130 隻)，25 公尺處居次 (37,106 隻)，15 公尺處的豐富度最低 (5,883 隻)。單變量變異數分析 (one-way ANOVA) 結果顯示，單變量變異數分析 (one-way ANOVA) 結果顯示，除了鞘翅目豐富度在各高度間無顯著差異外，各目昆蟲在不同時間、高度間的豐富度皆呈顯著差異。 在雙翅目科級 (family) 的比較，調查期間共採集了 50 科 93,207 隻雙翅目昆蟲，前十優勢類群依序為蛾蚋科 (Psychodidae，56.29 %)、黑翅蕈蚋科 (Sciaridae，14.58 %)、蚤蠅科 (Phoridae，9.44 %)、水蠅科 (Ephydridae，5.70 %)、果蠅科 (Drosophilidae，2.37 %)、家蠅科 (Muscidae，2.27 %)、舞虻科 (Empidae，1.75 %)、稈蠅科 (Chloropidae，1.26 %)、蠓科 (Ceratopogonidae，1.24 %)、蕈蚋科 (Mycetophilidae，1.11 %)。單變量分析結果顯示：在不同高度下，分類群豐度、密度、均勻度、歧異度、優勢類群比例皆具顯著差異；在各時期中，只有各科豐富度具有顯著差異。多變量分析結果方面，MDS 排序顯示樣本可分為四群：1 m 群、5-15 m 群、25 m 群、34 m 群；ANOSIM 結果也指出除了 5 m 與 15 m 間無顯著外，其餘各高度配對皆具顯著差異；聚類分析則顯示 1 m、5 m、15 m 為一群，且 5 m、15 m 間相似性最高，25 m 與 34 m 樣本另外各分為一群。此外，在 50 科的雙翅目昆蟲中，舞虻科、稈蠅科、果蠅科、水蠅科、家蠅科、蚤蠅科、大蚊科、蕈蚋科、黑翅蕈蚋科、蛾蚋科、蠓科、蚋科共 12 科為代表物種。 攝食同功群的單變量變異數分析結果則顯示各同功群的豐富度在不同高度上皆呈顯著差異；在各時期間，同功群食真菌—朽木組、植食—蜜食組、捕食—擬寄生組有顯著的豐富度變化。以同功群分布高度進行聚類分析則顯示 1 公尺、5¬-15 公尺、25 公尺、34 公尺各成一群。 昆蟲群聚與氣候關係的部份，相關性結果顯示昆蟲豐富度 (密度) 、均勻度、歧異度、優勢類群比例與平均相對濕度相關性較高；生物因子與環境因子相關分析 (BIO-ENV) 結果則顯示平均溫度、平均相對濕度為影響群聚分布的主要因子；進一步進行典型對應分析 (CCA) 的結果則顯示平均溫度、平均日雨量為第一軸主要相關因子，第二軸的主要相關因子為平均相對濕度；且黑艷蠅科、長足虻科豐富度與相對濕度、平均溫度呈正向關係，癭蚋科、蕈蚋科、水虻科與平均相對濕度、平均溫度呈反向關係，花蠅科、果蠅科、蚊蚋科與平均日雨量呈正向關係，搖蚊科、蛾蚋科、蚋科與平均日雨量呈反向關係，其他各類群與氣候因子的相關程度不明顯。 本研究為國內針對昆蟲群聚垂直分層的全新嘗試，研究方法可作為未來國內冠層生物相調查的參考依據，甚至在國內其他二氧化碳觀測塔推行；研究所得結果不但凸顯了冠層生物多樣性之重要，更指出過去森林生物資源調查的不足，冠層生物相的調查研究是未來值得努力的方向；建議臺大實驗林管理處應參考本研究結果，持續推動林冠生物相的研究，並可結合溪頭自然教育園區內之林冠廊道，豐富解說教育資源，成為國內推動林冠研究發展的重地。

Forest canopy has significant contributions to forest productivity, ecosystem function and global climate condition. However, due to the difficulty of vertical movement in forests, the forest canopy is widely recognized as one of poorly known ecosystems on earth. Previous studies have showed that the differentiation of forest strata affects the vertical distribution of forest animals. In order to study the vertical stratification of insect in artificial plantations at Xitou, the investigation was carried out at the flux tower located in a Cryptomeria japonica forest in Xitou by using sticky traps, which were set up at various layers (1, 5, 15, 25 and 34 meters heights) from 16 March 2011 to 16 March 2012. The information of insect community and microclimate data were collected for the comparison associated with insects collected in various times and heights. During the sampling period, a total of 111,525 insects belonging to 16 orders were collected. Moreover, Diptera was the most dominant order (total 93,207 individuals). Samples of Diptera were identified to family level, and the values of abundance, taxa richness, density, Pielou’s evenness, Shannon diversity index and dominant taxon ratio were calculated. One-way ANOVA, multi-dimensional scaling (MDS), cluster analysis, canonical correspondence analysis (CCA) were conducted to analyze the variations of Diptera community, feeding guilds and climate factors. In order level, Hemipteran insects were most abundant under 5 m; most Lepidoptera were found at 25 m, Hymenoptera and Psocoptera were more abundant above 25 m; Diptera were abundant at 1 and 25 m; most Thysanoptera were collected at 5 and 34 m; the Coleopteran insects showed no preference between five locations. In conclusion, most insects were collected at 1 and 25 m, and few individuals appeared at 15 m. According the results of one-way ANOVA, only the abundance of Coleoptera showed no difference among sampling heights. The abundance of different orders were significantly different in time and height. In diptera, there were 93,207 individuals belonging to 50 families. Top 10 dominant families were Psychodidae (56.29 %), Sciaridae (14.58 %), Phoridae (9.44 %), Ephydridae (5.70 %), Drosophilidae (2.37 %), Muscidae (2.27 %), Empidae (1.75 %), Chloropidae (1.26 %), Ceratopogonidae (1.24 %) and Mycetophilidae (1.11 %). According the results of one-way ANOVA, the taxon richness, density, evenness, diversity and dominant taxon ratios of dipterans were significantly different in sampling height. In addition, only the abundances of families were significantly different in sampling time. In the results of multivariate analysis, The MDS plot showed four groups of samples: 1 m group, 5-15 m group, 25 m group and 34 m group. Likewise, the results of ANOSIM indicated all paired samples of height were significantly different except the 5-15 m pairs. In contrast, the results of cluster analysis showed that samples from 1, 5 and 15 m formed a cluster. Moreover, samples from 5 and 15 m also merged into a cluster. On the other hand, samples from 25 and 34 m could be clustered into another group. In conclusion, the key families of Diptera were Empididae, Chloropidae, Drosophilidae, Ephydridae, Muscidae, Phoridae, Tipulidae, Mycetophilidae, Sciaridae, Psychodidae, Ceratopogonidae, and Simulidae. In the abundances of five feeding guilds, the results of one-way ANOVA showed significant differences in different heights. In addition, the results of one-way ANOVA showed significant differences in sampling time in Fungivore-Saproxylic insect group, Herbivore-Nectarivore group, and Predator-Parasitoid group. Furthermore, the results of cluster analysis in indicated that the samples from 1 m, 5-15 m, 25 m, and 34m formed clusters individually. In the relationship between the community of Diptera and climatic variables, correlation analysis results showed that the dipteran insect’s abundance, evenness index, diversity index and dominant taxon ratio were more related to average relative humidity (R.H.). BIO-ENV analysis indicated that the major climatic factors affecting the distribution of dipteran insects were average temperature and average relative humidity. Moreover. In the CCA diagram, the first axis constrained the maximum value on the variation of taxa and the data indicated that the major climatic factors affecting the distribution of taxa were average temperature and average daily rainfall. The second axis represented the sum of average relative humidity. The abundances of Lonchaeidae and Dolichopodidae were positively related with average relative humidity and average temperature; Cecidomyiidae, Mycetophilidae and Stratiomyidae were negatively related with average relative humidity and average temperature; Anthomyiidae, Drosophilidae and Anisopoididae were positively related with average daily rainfall; Chironomidae, Psychodidae and Simuliidae were negatively related with average daily rainfall; Besides, most families were not significantly related with these climatic factors. This research is the first study about insect vertical distributions in Taiwan, and the sampling method can be promoted to the investigation of canopy biota in other CO2 flux towers in Taiwan. This study has showed the importance of canopy biodiversity and reveals some defects of traditional forest 2survey methods. In addition, based on this research, NTU Experimental Forest should continue to carry out the study of canopy biota. Moreover, NTU Experimental Forest could take advantage of the results to improve the interpretation and education of canopy ecology in the canopy walkway in Xitou. It will make Xitou an important site to develop canopy ecology study in Taiwan.