台灣黑熊取食果實對於種子萌芽之影響

外文標題: 
Effects of Fruit Consumption by Formosan Black Bears (Ursus thibetanus formosanus) on Seed Germination
校院系所: 
屏東科技大學野生動物保育研究所
指導教授: 
黃美秀
出版年份: 
2008年
主題類別: 
摘要: 

台灣黑熊(Ursus thibetanus formosanus)是雜食性的食肉動物,且植物果實為重要的主食,加上攝食量大且活動範圍廣泛,故為潛在的種子播遷者。本研究旨藉由了觀察台灣黑熊取食野外季節性的果實,以瞭解對其種子萌芽率與萌芽時間之影響。野外季節性採集的果實共七種,包括青剛櫟(Quercus glauca)、山櫻花(Prunus campanulata)、香楠(Machilus zuihoensis)、呂宋莢蒾(Viburnum luzonicum)、台灣蘋果(Malus doumeri)、山枇杷(Eriobotrya deflexa)及山柿(Diospyros japonica),依次餵食圈養的台灣黑熊四隻,紀錄攝食方式,以及收集內含試驗種子的排遺,並檢視種子受損程度,再分別置於生長箱及苗圃觀察種子萌芽數量及時間。

台灣黑熊對不同果實的取食方式有所差異。進食肉質性果實多將整個果實一口吞入(63-100%),然進食堅果類的青剛櫟時,通常會將堅果咬碎或吐出後再吃入(73%),其他則吐出不再吃(27%),而且排遺中除了2顆種子之外,沒有發現完整的種子。消化排出的種子之磨損程度因種類而異,其他非堅果類的果實經黑熊消化排出後,除了山枇杷之外,種子的受損程度皆以無受損居多(40%-99%),其次為輕度受損或外覆果肉的種子,僅有<10%的種子為中度或重度受損。山枇杷則以輕度及無受損種子為多(48%、23%),並有較高比例之中度受損種子(24%)。

不管種子經過黑熊消化與否,外覆果肉的六種種子,萌芽率皆比無受損的種子低。尤其對於具休眠性的種子,山櫻花、香楠、呂宋莢蒾及台灣蘋果,經熊消化的種子,萌芽率皆顯著高於熊未消化的對照組。果肉會妨礙種子萌芽,而熊的攝食具有去除果肉的作用,且能促進種子萌芽。

經熊取食消化所造成的種子不同磨損程度,亦有不同的萌芽率。具有果肉或重度磨損的種子,萌芽情況通常較其他組別差。三種核果種子(山櫻花、香楠、呂宋莢蒾)的外覆果肉對照組種子皆未萌芽,熊消化組萌芽率則有21-70%的比例,平均萌芽時間為1-8個月。兩種仁果(山枇杷與台灣蘋果)之熊消化組,整體平均萌芽率為六種種子中最高的(88%、96%),各為對照組之1.5及1.8倍,且平均萌芽時間不及對照組的一半。經熊消化的山柿種子開始萌芽時間也比對照組提早1.5個月。

相較於野外環境的自然落果(即外覆果肉對照組),台灣黑熊食入非堅果種子,可促使種子提早萌芽或提高萌芽率。如此可減少被種子掠食者取食或病菌感染的機會,進而增加最後成功萌芽的數量。對青剛櫟而言,台灣黑熊為果實掠食者,但對非堅果類種子而言,則為一有效的長距離種子播遷者。

外文摘要: 

Formosan black bears (Ursus thibetanus formosanus) are omnivorous carnivores, and fruit is comprised of their primary diet. Besides, because of their enormous intake volume and extensive home range, bears are believed to be potential seed dispersers. The objective was to observe the consumption of various fruits by bears to understand the effects on seed germination percentage and germination time. I fed 4 captive Formosan black bears with seven hand-picked fruits, including Quercus glauca, Prunus campanulata, Machilus zuihoensis, Viburnum luzonicum, Malus doumeri, Eriobotrya deflexa and Diospyros japonica, which wild bears used seasonally. Bear feces with ingested seeds were collected. After classifying the abrasion level of 100 seeds out of each feces, I planted seeds separately in growth chambers and green houses.

Formosan black bears consumed fruits differently. They often swallowed fleshy-fruits directly (63-100%). However, they often crashed the Q. glauca acorn (73%) or spited out (27%), and no intact seeds were found from feces except 2 seeds. The abrasion level of ingested seeds varied by species. Except for E. deflexa, most seeds of the fleshy -fruits collected from bear feces were intact (40%-99%), followed by slightly-damaged or pulp-wrapped seeds, and <10% were partially-damaged or severely-damaged seeds. However, higher percentages of slightly-damaged and intact seeds were found in E. deflexa (48% and 23%), along with partially-damaged seeds (24%).

No matter seeds were ingested by bears or not, seeds with pericarps removed (i.e., intact seeds) germinated more than pulp-wrapped seeds. For seeds with dormancy behavior such as P. campanulata, M. zuihoensis, V. luzonicum and M. doumeri, the germination percentages of ingested seeds were significantly higher than the control groups. It indicated pulps would inhibit seed germination. Bear consumption could help to remove pulps and enhance germination.

Seeds with diverse ingestion-caused abrasion geminated differently. Pulp-wrapped and severely-damaged seeds often germinated less than other groups. Wrapped seeds of all 3 drupes (P. campanulata, M. zuihoensis and V. luzonicum) in control groups did not germinate, but for those collected from bear feces, the germination percentages were 21-70%, with an average germination time of 1-8 months. Pome seeds of E. deflexa and M. doumeri ingested by bears had the highest germination percentages (88% and 96%) among all species, which was 1.5 and 1.8 times of the control groups, and their average germination time was only half of the control seeds. Ingested seeds of D. japonica also geminated 1.5 months earlier than the control seeds.

Compared with the naturally fallen fleshy-fruit under parent trees (i.e., pulp-wrapped seed in control group), Formosan black bears enhanced the seed germination percentage and shortened the average germination time. This may further decrease the possibility of seed predation or fungal infection, and improve the ultimate germination success. But for acorns like Q. glauca, bears may work as seed predators. Therefore, my study suggested that Formosan black bears are an legitimate long-distance seed disperser for fleshy-fruits.