新鮮枝葉掉落物對地表無脊椎動物群集的影響

Abstract

間歇性資源是指短暫、罕見並且高強度的可利用性資源在時間與空間的尺度下增加的事件。對地表的無脊椎動物來說，颱風所造成的新鮮枝葉掉落物就是一種間歇性資源的事件。在這個研究中，我在以臺灣二葉松為主的人工林中，人為製造了一個模擬颱風經過臺灣中部亞熱帶山區森林所產生新鮮枝葉掉落物的間歇性資源事件。我建立了二十個五公尺乘以五公尺的網格，隨機指定其中十個於2013年七月接受十公斤的新鮮二葉松枝葉做為處理組，另外十個則不進行處理，以做為控制組。我利用掉落式陷阱採集地表無脊椎動物樣本做為活動密度與生物量的指標，共採集八個月，其中處理前兩個月，處理後六個月。結果顯示，新鮮枝葉掉落物的處理並沒有對無脊椎動物群集的活動密度與生物量有整體上的影響，對於掠食者與碎屑食者的活動密度與生物量也無影響。然而我發現新鮮枝葉掉落物對於中間消費者有一個由營養階層下方往上傳遞的正向影響，而在中間消費者當中，經由新鮮枝葉掉落物而受益的類群，較可能為植食性動物。上述這個正向的影響同時表現在中間消費者的生物量分析以及其生物量占所有類群總合的比例分析上。這個研究發現了新鮮枝葉掉落物對於地表的消費者有營養階層由下往上的效應，但是這個效應並沒有傳到最上層的掠食者。此外，新鮮枝葉掉落物對於碎屑食性的消費者似乎沒有太大的影響，由於其生活史導致活動密度與生物量有強烈的季節性變動，也限制了新鮮枝葉掉落物對碎屑食性消費者的影響。Resource pulses are rare, brief and intense episodes of increased resource availability in space and time. Greenfalls caused by typhoons is a resource pulse event for ground-dwelling arthropods. In this study, I artificially created a resource pulse of greenfalls in a Pinus taiwanensis plantation to simulate one that is caused by typhoons in a subtropic montane forest in central Taiwan. I set up 20 plots (5 m x 5 m) at the study site, of which 10 were randomly assigned to receive 10 kg of fresh P. taiwanensis greenfalls in the summer of 2013 whereas the other 10 plots were left untouched as controls. I monitored the activity-density and biomass of ground-dwelling arthropods using the pitfall traps for 8 months (2 months of pre-treatment time period and 6 months of post-treatment time period). The results suggest that the greenfalls did not have effects on arthropod active-density and biomass as a whole nor did it affect the predators and detritivores. However, I detected positive, bottom-up effects from the greenfalls to the intermediate consumers (most likely herbivores), both in terms of their actual and proportional biomass. This study demonstrated potential bottom-up effects of the greenfalls on the above-ground consumers, which did not propagate to the top predators. Furthermore, the greenfalls likely have limited influences on the detritivores. The strong seasonal fluctuations in arthropod activity-density and biomass at this subtropical montane forest may have limited the influences of the greenfalls.