动物对濒危特有种大别山五针松种子的捕食和散布

Seed predation and dispersal by animals of an endangered endemic species Pinus dabeshanensis

大别山五针松(Pinus dabeshanensis)是大别山地区特有树种,对研究松属(Pinus)植物分类、系统发育关系和区系分布具有重要科研价值。当前大别山五针松野生种群自然更新受到严重限制,处于极度濒危状态。为探究大别山五针松野生种群更新受限机制,本研究以大别山五针松及其3种同域分布物种茅栗(Castanea seguinii)、枹栎(Quercus serrata)和华山松(Pinus armandii)为研究对象,通过开展野外调查和种子释放实验,探讨了大别山五针松种子产量以及动物对种子的捕食压力和散布限制对大别山五针松自然更新的影响。结果表明:(1)大别山五针松种子产量较低,在所调查的88株成年母树中,仅有21株产成熟球果(共计312个),且种子败育率高达51.89%±0.07%(平均值±标准误);(2)针对146个球果的鸟类啄食情况调查表明,被鸟类啄食的球果数量为90个,显著高于未被鸟啄食的球果数量(56个),平均啄食强度为8.94%±0.55%;(3)种子掉落地表后,小型啮齿动物和地栖鸟类(主要为松鸦Garrulus glandarius)为主要动物拜访者,其拜访频率在不同物种之间差异显著;其中鸟类对大别山五针松种子的拜访次数(n=77)高于啮齿动物(n=46);(4)种子释放实验结果表明,茅栗种子被收获速率最快,显著高于枹栎和大别山五针松,华山松种子的被收获速率最慢;(5)在释放的2,000粒种子中,共计157粒被成功散布,其中华山松和大别山五针松分别为96粒和57粒,显著多于茅栗(3粒)和枹栎(1粒);(6)茅栗的散布距离最远(13.9±4.0 m),其次是大别山五针松(7.3±0.8 m)、华山松(3.8±0.4 m)和枹栎(1.5 m,仅有1粒被成功散布)。综上所述,啮齿动物和鸟类均为大别山五针松种子的潜在散布者,与同域分布的其他植物物种相比,动物并未表现出更高的捕食强度和更低的散布效率,表明种子的被捕食压力和散布限制并非影响大别山五针松自然更新的主要因素。此外,本研究发现,大别山五针松种子产量较低且种子败育率较高,可能是导致其自然更新受阻的重要原因之一。

Aim:Pinus dabeshanensis,an endemic species in the Dabieshan Mountains,has significant scientific values for studying the taxonomy,phylogenetic relationships,and distribution of the genus Pinus.Currently,the wild population of P.dabeshanensis is severely limited in natural regeneration and is critically endangered.Here,we explored the potential effects of seed predation and dispersal by animals on the regeneration of P.dabeshanensis.Methods:First,we investigated the seed production of P.dabeshanensis by focusing all the adult trees in two 1-ha plots(n=88).Second,by tracking the fate of 2,000 seeds,we compared the seed predation and dispersal by animals between P.dabeshanensis and three sympatric tree species.These included two dominant native species,Castanea seguinii and Quercus serrata,and an introduced species Pinus armandii that is a sister species of P.dabeshanensis,which all mainly depend on scatter-hoarding animals for seed dispersal.Third,we compared the visitation frequency of potential seed predators and dispersers between P.dabeshanensis and its sympatric species by using camera-trap surveys.Results:The results showed that:(1)The seed production of P.dabeshanensis was low,with only 312 cones produced by 21 of the 88 adult trees surveyed,and the seed abortion rate reaching 51.89%±0.07%(mean±SE).(2)A total of 146 cones were collected to assess the seed predation by birds,and 90 of them were pecked by birds which was significantly more than un-pecked cones(n=56),with an average pecking intensity of 8.94%±0.55%.(3)Small rodents and ground-dwelling birds(e.g.,Garrulus glandarius)were the main visitors to the seeds in the forest ground,and visitation frequency varied significantly among different tree species.Specifically,for P.dabeshanensis,birds visited the seeds more frequently(n=77)than rodents(n=46).(4)Seeds of C.seguinii were harvested the fastest,followed by Q.serrata and P.dabeshanensis,while P.armandii were harvested the slowest.(5)Of the 2,000 seeds released in the forest,157 seeds were successfully dispersed,including 96 P.armandii seeds and 57 P.dabeshanensis seeds,which were significantly more than C.seguinii(3 seeds)and Q.serrata(1 seed).(6)The seed dispersal distance of C.seguinii was 13.9±4.0 m(mean±SE),followed by P.dabeshanensis(7.3±0.8 m),P.armandii(3.8±0.4 m)and Q.serrata(1.5 m,only one seed was successfully dispersed).Conclusion:In conclusion,both rodents and birds are potential seed dispersers of P.dabeshanensis.Compared to sympatric tree species,P.dabeshanensis does not suffer heavy seed predation or limited seed dispersal,indicating that seed predation pressure and seed dispersal limitation do not explain the poor natural regeneration of P.dabeshanensis.In addition,our results suggest that the low seed production and high abortion rate may be important factors hindering the natural regeneration of P.dabeshanensis.