啮齿动物对秦岭松栎混交林建群种种子扩散格局的影响

森林群落中的啮齿动物对林木种子存在着一定的取食偏好性,这种偏好性会使啮齿动物形成不同的捕食和贮藏策略,从而导致林木种子形成不同的扩散格局。以秦岭中段松栎混交林建群种锐齿槲栎、油松、华山松为研究对象,采用塑料标签标记种子方法,研究啮齿动物对种子传播和扩散格局的影响。结果表明:(1)种子特征是影响啮齿动物对其进行扩散的重要因子,油松种子以其质量小、种皮薄等特点吸引啮齿动物大量捕食,其原地取食率达到83.33%,显著高于华山松和锐齿槲栎种子。(2)锐齿槲栎和华山松种子大部分被搬运一定距离后再被取食和埋藏,其中,扩散距离在1 m以内、1—3 m和5—8 m的锐齿槲栎种子分别占59.12%、18.23%和13.26%,最远扩散距离达12 m处;华山松种子扩散距离主要介于在1—3 m(37.85%)和3—5 m(23.73%),在距离5—8 m(13.56%)、8—10 m(11.86%)和大于10 m(11.30%)区间也有一定的分布,最大扩散距离为12 m。(3)啮齿动物倾向于将锐齿槲栎种子搬运至松林内取食,而将华山松种子搬运至栎林内埋藏,说明不同林分类型及其环境因素对林木种子扩散后的分布格局具有重要影响。(4)3种类型种子被啮齿动物捕食的比例以油松最大(96.90%),锐齿槲栎次之(73.57%),华山松最小(50%);次年调查时,未被捕食的种子大部分已经被取食,仅有极少数锐齿槲栎种子萌发成幼苗(1.67%)。啮齿动物的捕食和贮藏行为对林木种子扩散及其成功更新都至关重要。     

生境对啮齿动物介导下锐齿槲栎种子命运的影响

干扰作为森林演替的驱动力,在改变森林结构和地表植被的同时也对林内动物介导下的种子扩散过程产生影响.本研究采用塑料标签标记法,选取秦岭林区不同人为干扰后形成的3种类型生境(未抚育林分、抚育3年后林分、裸地),研究啮齿动物扩散行为对不同生境类型锐齿槲栎种子命运的响应.结果表明:抚育3年后林分的种子扩散速率最大,裸地扩散速率最小.裸地的种子原地取食率显著低于未抚育(25.0%)和抚育3年后林分(36.3%),而抚育3年后林分的种子搬运后取食率显著高于未抚育林分(17.3%)和裸地(5.0%),且抚育3年后的林分中被啮齿动物分散埋藏的种子比例最高(4.3%).种子扩散距离以抚育3年后林分最大(26 m),且扩散距离显著大于裸地和未抚育林分.锐齿槲栎种子的初次扩散过程在不同生境中表现不同,其种子后期成苗率也存在差异.不同类型生境在一定程度上影响啮齿动物的觅食策略,最终导致不同的种子扩散模式和森林天然更新格局的形成.     

啮齿动物对不同大小和种皮特征种子的取食和搬运

在宁夏六盘山区的辽东栎灌丛,以不同大小的辽东栎种子、野李和华山松种子为材料,研究了种子大小和种皮特征对啮齿动物取食和搬运行为的影响.结果表明:辽东栎小种子和华山松种子的就地取食率均显著高于辽东栎大种子和野李种子;具有厚而坚硬种皮(内果皮)的野李种子被啮齿动物搬运后的取食率和贮藏率均最高.辽东栎大种子被啮齿动物搬运后取食的距离最大(3.10 m),被搬运后贮藏的距离(6.48 m)显著大于其他类型种子.除野李种子外,其他3种类型种子的单个种子取食点都在80％以上,所有种子的单个种子贮藏点都在90％以上,含2个以上种子的取食点和贮藏点较少.较高比例的华山松种子在灌丛基部和洞穴以外的其他环境被取食,其他3种类型种子被啮齿动物搬运后主要集中在灌丛基部和洞穴中取食;种皮(内果皮)厚而坚硬的种子以土壤埋藏方式贮藏的比例偏高.     

灌丛高度对啮齿动物贮藏和扩散辽东栎坚果的影响

本文选择高、矮两类灌丛生境, 于2002 年至2003 年在其中释放标记的辽东栎坚果, 并连续记录释放坚果的命运, 以了解生境差异对啮齿动物搬运、取食和贮藏辽东栎坚果的影响以及啮齿动物对微生境的选择等。研究结果表明, 大林姬鼠等啮齿动物对辽东栎坚果的短期取食非常强烈, 而分散贮藏的量则相对较少; 啮齿动物对辽东栎坚果的搬运距离在矮灌丛生境中显著大于高灌丛生境; 啮齿动物倾向于选择灌丛边缘和灌丛下方取食或贮藏辽东栎坚果, 这类微生境也有利于埋藏坚果的萌发。     

贮藏种子的啮齿动物对油茶种子沉积形式的影响

种子沉积的质量常常涉及种子扩散作用者(如鸟类和小型啮齿动物)对生境和微生境的选择以及种子沉积的形式(如种子埋藏)。然而,很少的研究涉及到种子在离开母树后被这些动物沉积在何处。在四川省都江堰一个实验林场的2个林分(次生林和原生林)内,通过追踪用带编号的金属薄片标记的油茶(CamelliaoleiferaAbel.)种子的命运,研究了贮藏种子的啮齿动物对种子沉积的影响。研究发现在2个林分内,80%以上的种子被很好地埋藏在0~60mm深的土壤中,而小部分种子则被放置在地表(但有少量落叶遮盖)。小型啮齿动物喜好在灌丛下或灌丛边缘贮藏和取食种子,可能是在这样的微生境下它们在觅食时将遭遇较小的捕食风险。研究还发现,贮藏点的微生境分布随贮藏点等级而逐渐变化在两个林分内较高等级的贮藏点(如次贮藏点和三级贮藏点)比初级贮藏点有更多的种子被贮藏在灌丛下或灌丛边缘。这表明,啮齿动物对油茶种子的埋藏可能更有益于种子的存活、萌发以及幼苗的建成。啮齿动物将散落在母树下或其附近的油茶种子扩散到不同的微生境,这可能有利于他们遭遇到更多的适宜环境而萌发,实现幼苗补充。     

贮藏种子的啮齿动物对油茶种子沉积形式的影响

种子沉积的质量常常涉及种子扩散作用者(如鸟类和小型啮齿动物)对生境和微生境的选择以及种子沉积的形式(如种子埋藏).然而,很少的研究涉及到种子在离开母树后被这些动物沉积在何处.在四川省都江堰一个实验林场的2个林分(次生林和原生林)内,通过追踪用带编号的金属薄片标记的油茶(Camellia oleifera Abel.)种子的命运,研究了贮藏种子的啮齿动物对种子沉积的影响.研究发现:在2个林分内,80%以上的种子被很好地埋藏在0～60 mm深的土壤中,而小部分种子则被放置在地表(但有少量落叶遮盖).小型啮齿动物喜好在灌丛下或灌丛边缘贮藏和取食种子,可能是在这样的微生境下它们在觅食时将遭遇较小的捕食风险.研究还发现,贮藏点的微生境分布随贮藏点等级而逐渐变化:在两个林分内较高等级的贮藏点(如次贮藏点和三级贮藏点)比初级贮藏点有更多的种子被贮藏在灌丛下或灌丛边缘.这表明,啮齿动物对油茶种子的埋藏可能更有益于种子的存活、萌发以及幼苗的建成.啮齿动物将散落在母树下或其附近的油茶种子扩散到不同的微生境,这可能有利于他们遭遇到更多的适宜环境而萌发,实现幼苗补充.     

啮齿动物捕食压力下生境类型和覆盖处理对辽东栎种子命运的影响

在六盘山区的退化辽东栎灌丛和辽东栎次生林 (以下分别称“灌丛样地“和“次生林样地”),研究了群落生境和清除凋落物、凋落物覆盖及土壤覆盖等处理对啮齿动物取食和搬运/贮藏辽东栎种子的影响。结果表明：(1) 凋落物和土壤覆盖处理在种子释放的前期阶段有利于种子留存,但释放40天后,种子在释放点的最终留存率在灌丛样地显著高于次生林样地 (Z = -2.333, P = 0.020)。灌丛样地的自然状态的种子最终留存率显著高于凋落物覆盖处理 (Z = -0.674,P = 0.05),但其它处理间无显著差异;次生林样地的凋落物覆盖和清除凋落物处理种子的最终留存率为0%,自然状态和土壤覆盖处理均不足1%,各处理间无显著差异。(2) 种子被啮齿动物的就地取食率在不同群落生境间差异显著 (Z = -2.333,P = 0.020);在灌丛样地,凋落物覆盖处理种子被啮齿动物就地取食率最高 (45.56%),而次生林样地的土壤覆盖处理最高 (64.81%),种子被啮齿动物就地取食率在灌丛样地和次生林样地均为清除凋落物处理最低 (分别为23.70%和40.00%);生境类型和覆盖处理对种子搬运后的取食率均无显著影响。(3) 次生林样地种子被啮齿动物搬运后的埋藏率显著高于灌丛样地 (Z = -2.88,P = 0.004);在灌丛样地,土壤覆盖处理种子搬运后的埋藏率最高仅5.56%,而在次生林样地,清除凋落物处理最高达9.26%。(4) 种子被啮齿动物搬运后取食的距离在灌丛样地和次生林样地分别为3.01 m和2.13 m,差异显著 (Z = -2.080,P = 0.038),而种子搬运后的埋藏距离前者小于后者 (分别为1.35 m和2.10 m),两者间差异不显著。     

啮齿动物对六盘山区辽东栎、野李和华山松种子的取食和搬运

为了阐明不同种子投放方式和覆盖处理对啮齿动物取食和搬运/贮藏种子行为的影响,2010年春季,我们在宁夏六盘山区的辽东栎幼林,用塑料标签标记法研究了不同种子投放方式(单独投放、两两组合投放和混合投放)和覆盖处理(对照、凋落物覆盖和土壤覆盖)下啮齿动物对辽东栎、野李和华山松种子的取食和搬运特点。结果表明:(1)不同物种、不同种子投放方式和覆盖处理对种子的就地取食率、搬运后的取食率和贮藏率均具有显著影响,种子较大或具有厚而坚硬的种皮(内果皮)、组合和混合投放及覆盖处理均不同程度地促进啮齿动物对种子的搬运;(2)3种植物的种子被搬运后取食和贮藏的平均距离范围均在5.5m以内,而且种子被搬运后贮藏的距离均大于搬运后取食的距离,其中华山松种子被搬运后取食的距离显著大于辽东栎和野李种子,但搬运后的贮藏距离显著小于后两者。(3)种子被搬运后单个种子的取食点和贮藏点占多数,其他大小的取食点和贮藏点较少,种子被搬运后以土壤埋藏为主要的贮藏方式。结果表明,种子的种皮特征以及种子在群落中的分布方式和存在状态,可能通过延长啮齿动物处理的时间而增大啮齿动物的被捕食风险,使动物改变对种子的取食和搬运行为,进而决定了种子的命运。     

生境类型对啮齿动物扩散和贮藏栓皮栎坚果的影响

在河南省济源市王屋山地区,研究了次生林、灌丛、退耕地三个生境中啮齿动物对栓皮栎坚果的取食、
扩散与贮藏情况。结果表明:1)在研究地区,取食栓皮栎坚果的啮齿动物主要有大林姬鼠、社鼠和黑线姬鼠;
2)在次生林中,啮齿动物对坚果的搬运速率慢于在灌丛和退耕地生境中的搬运速率;3)次生林生境中,贮藏
坚果占被扩散坚果的比例高于灌丛和退耕地,而灌丛生境中被取食坚果占被扩散种子的比例高于退耕地和次生
林;4)栓皮栎坚果的中位存留时间在三个生境间有显著性差异。研究结果提示,在人工造林时,可通过对栓皮
栎坚果进行埋藏处理,以提高种子萌发率。     

秦岭山地松栎混交林主要木本植物组成及更新特征

采用样方法对秦岭南坡中段松栎混交林主要木本植物组成及天然更新特征进行了研究.结果表明:(1)松栎混交林乔木层物种共计40种,油松、锐齿槲栎和华山松为优势种,重要值分别为35.19％、31.99％和8.12％,漆树、栓皮栎和楝木为亚优势种.(2)更新层木本植物共计87种,其中乔木幼苗34种,占总数的39.08％,灌木物种也有一定优势地位,优势种有锐齿槲栎、悬钩子和菝葜等,高度级较小的更新苗在群落内占有较大比例.(3)优势乔木更新特征不同,锐齿槲栎幼苗和幼树密度显著高于油松和华山松,且锐齿槲栎幼苗密度显著高于其幼树,但油松幼苗与幼树、华山松幼苗与幼树间无明显差异.(4)混交林内锐齿槲栎径级结构呈近似倒“J”形分布,种群稳定;油松和华山松种群均呈近似正态分布,大径级个体群相对稳定,但林下幼树不足.该研究结果提示,松栎混交林下油松和华山松更新不良,这将不利于其长期存留于群落中,虽然锐齿槲栎从幼苗到幼树的发育过程中存在更新障碍,但并未影响其种群整体更新,若无大规模干扰,锐齿槲栎将维持逆“J”型的更新方式并成为松栎混交林群落中的第一优势种.     

昆虫蛀蚀对鼠类介导下的锐齿槲栎种子扩散的影响

森林鼠类的种子贮藏行为对植物的扩散和自然更新有着非常重要的影响。然而,鼠类是否具有鉴别虫蛀种子的能力还存在一定的争议。此外,鼠类的鉴别能力是否受到食物丰富度变化的影响也未见相关报道。采用标签标记法,2011年秋季(9—11月,食物丰富季节)和2012年春季(4—6月,食物匮乏季节)分别在秦岭南坡的佛坪国家级自然保护区内,调查了森林鼠类对完好和虫蛀锐齿槲栎(Quercus aliena)种子的选择差异。结果显示:1)在秋季,尽管2种类型种子的存留动态没有显著差异,但是在后期虫蛀种子的存留时间相对更长;而在春季2种类型种子的存留动态则极为显著,几乎所有的完好种子(99%)在释放后的第3天就被鼠类全部扩散,虫蛀种子的存留时间则相对较长。2)在秋季,鼠类更喜好扩散后取食完好种子;而在春季,鼠类则喜好在原地取食绝大部分的种子,并且优先取食完好种子。3)在秋季,鼠类贮藏了更多的完好种子;而在春季,尽管完好种子在释放后第1天便达到贮藏高峰,然而由于后期的大量被捕食,2种类型种子在贮藏动态上没有显示出显著差异。研究结果表明秦岭地区森林鼠类可以准确区分完好与虫蛀种子,但是食物丰富度会影响鼠类对种子的选择策略。在食物丰富的秋季,鼠类更多地选择贮藏完好种子;而在食物相对匮乏的春季,鼠类更倾向于同时取食2种类型种子。森林鼠类通过对2种类型种子的鉴别和选择,影响不同种子的命运,从而可能对种子的扩散和自然更新产生重要影响。     

Seed predation patterns favor the regeneration of dominant species in forest gaps compared with the understory in an oak-pine mixed forest

Recent studies have demonstrated the higher likelihood of regeneration in forest gaps compared with the understory for the dominant species in pine-oak mixed forest. Here, we tested whether rodent seed predation or dispersal was beneficial for gap regeneration. We tracked the seed predation and dispersal of Quercus aliena var. acuteserrata and Pinus armandii using coded plastic tags in the forest understory close to gaps. Our results demonstrated that the proportions of initial buried seeds of both species were significantly more abundant in the forest understory compared with gaps. After seed caching, however, significantly lower proportions of the seeds of both species survived in the forest understory compared with gaps during the 30-day observation period. The final survival proportions of the seeds cached in the forest understory were lower than those cached in the gaps the next spring, which indicated that small rodents rarely retrieved scatter-hoarded seeds from forest gaps. Our findings suggest that rodent seed predation patterns contribute to the regeneration of the dominant species in gaps compared with the understory in a pine-oak mixed forest. In the study area, reforestation usually involves planting seedlings but direct sowing in forest gaps may be an alternative means of accelerating forest recovery and successional processes.     

Seed dispersal of three sympatric oak species by forest rodents in the Qinling Mountains, Central China

Forest rodents play an essential role as seed dispersal vectors through their caching behaviors. Using seeds of Quercus aliena, Q. glandulifera, and Cyclobalanopsis engleriana (Fagaceae), which are dominant, but poorly studied species, in the Qinling Mountains, Central China, we investigated seed predation and dispersal by forest rodents in 2010 and 2011. There were significant differences in rodent seed-eating and caching strategies among the three tree species. Seeds of Q. aliena and C. engleriana had hard coats, high nutrition contents (e.g., protein, fat, and starch), and long germination schedules (C. engleriana only). They were less frequently eaten in situ, but more likely to be eaten after removal or cached. Seeds of Q. glandulifera had soft coats and low nutrition contents and were more often eaten in situ and less likely to be eaten after removal or cached. Our findings indicated that forest rodents were primarily responsible for seed predation and dispersal of these three tree species in the Qinling Mountains, and seed traits, especially coat hardness, nutrition content, and germination schedule, were important factors influencing rodent eating and caching behaviors. In addition, seed dispersal process of each tree species differed significantly between the 2 years, reflecting the effect of mast seeding on the eating and caching strategies of forest rodents.     

Predating strategy of rodents on acorns of Quercusaliena var. acuteserrata under different predating risks and fate of acorns

The effects of rodents on forest regeneration have been highlighted in many ecological studies. In 2002 and 2003, the acorns of Quercus aliena var. acuteserrata were subjected to 12 different treatments. The daily dynamics and the amount of acorns that were finally left intact, predated in situ, or removed off were examined and documented. The ratios of acorns that were infested by bugs before and after predation by rodents were carefully documented. It was found that: (1) the ratios of acorns infested by bugs before and after predation by rodents showed significant difference (P > 0.05), suggesting that rodents would not prey on acorns during the predating process if acorns had been already infested by bugs. (2) When compared with the controls, the fate of acorns could be roughly classified into four types: acorns that were simply buried or placed on black paper showed no significant differences with the controls in their response to rodents, suggesting that rodents have no sensitivity to the little change of odor resulting from burying and may be more adapted to black background. Acorns attached with strings, dyed with black ink, cut into halves, or placed on white/green/red paper were predated in situ with much lower predation rates and lasted the same duration. Compared with the controls, the acorns were removed away by rodents with the same first day rate and the removal lasted longer. The final removal rate of the acorns by rodents was increased, whereas that of predation in situ was decreased, and none were left in the spot. This may suggest that rodents in this case increased their predation risk expectation and adopted a strategy of “less predation proportion in situ”. Acorns that were burnt were not predated in situ as well as removed in the first day, but the rates were raised to the maximum in the forth and fifth day and then declined to zero. Consequently, the final ratios of predation in situ and removal considerably decreased with many acorns, nearly 50%, being left intact. It can be hypothesized that the rodents responded to the change in odor of acorns by using the strategies of “less predation proportion in situ” and “less predating activities”, thereby resulting in larger number of acorns remained intact. Acorns that were enwrapped were barely predated in situ, removed in the first day with a normal predation rate, which declined to nearly zero in the second day and then increased till it declined again from the fourth day to the final day. The final rate of predation in situ was lower than 5% without acorns remained intact, and the rate of removal of acorns showed a considerable relative increase. This suggests that when there was a change in both odor and status of acorns, rodents also adopted the “spying” and “less predation proportion in situ” strategy, Because the predation risk is critical, the sense of sight would play an important role in rodent's living. (3) Definite amounts of acorns were predated in situ, discarded, removed away, predated ex situ, lost and hoarded separately.     

The intermediate dispersal hypothesis: seed dispersal is maximized in areas with intermediate usage by hoarders

Seed dispersal and predation are paramount for tropical plant diversity. When encountered by scatter-hoarding frugivores, seeds can be either eaten, dispersed or ignored. But even after dispersal, seed caches are still subjected to predation. Many factors are known to influence these dynamics; however, how frequently hoarders use certain patches has seldom been related to cache predation rates. We used the interaction between agoutis (Dasyprocta leporina), a scatter-hoarding rodent, and Joannesia princeps, a tropical tree, as a model to investigate how the number of visits by hoarders in certain areas influences cache predation and seed fate. Camera-traps were used for 30 days in twenty different locations in Tijuca National Park to assess number of visits by agoutis. Thereafter, we placed seed piles on the same areas and determined their fate using the spool-and-line method to track seeds for over one hundred days. We found a non-linear relationship between how often an area is used by hoarders and the final proportion of dispersed seeds. At areas with a low number of visits, proportion of dispersed seeds was low due to low removal. As frequency of visits by hoarders increased, seed removal and the number of dispersal events increased but so did cache predation. Thus, in areas intensively used by hoarders, high cache predation resulted in a low number of dispersed seeds that remained alive in caches. As a result, dispersal was maximized in areas with intermediate use by scatter-hoarders, where there was a balance between primary seed dispersal and cache predation.

     

Tree-to-tree variation in seed size and its consequences for seed dispersal versus predation by rodents

Individual variation in seed size and seed production is high in many plant species. How does this variation affect seed-dispersing animals and, in turn, the fitness of individual plants? In this study, we first surveyed intraspecific variation in seed mass and production in a population of a Chinese white pine, Pinus armandii. For 134 target trees investigated in 2012, there was very high variation in seed size, with mean seed mass varying among trees almost tenfold, from 0.038 to 0.361 g. Furthermore, 30 of the 134 trees produced seeds 2 years later, and for these individuals there was a correlation in seed mass of 0.59 between years, implying consistent differences among individuals. For a subset of 67 trees, we monitored the foraging preferences of scatter-hoarding rodents on a total of 15,301 seeds: 8380 were ignored, 3184 were eaten in situ, 2651 were eaten after being cached, and 395 were successfully dispersed (cached and left intact). At the scale of individual seeds, seed mass affected almost every decision that rodents made to eat, remove, and cache individual seeds. At the level of individual trees, larger seeds had increased probabilities of both predation and successful dispersal: the effects of mean seed size on costs (predation) and benefits (caching) balanced out. Thus, despite seed size affecting rodent decisions, variation among trees in dispersal success associated with mean seed size was small once seeds were harvested. This might explain, at least in part, the maintenance of high variation in mean seed mass among tree individuals.     

Scatter-hoarding rodents use different foraging strategies for seeds from different plant species

Seed predation and dispersal by scatter-hoarding rodents are key processes that determine seed survival, and thus, plant regeneration within forests. For decades, there has been much debate on the important effects of seed size (one of the most important seed traits) on rodent foraging preference. Furthermore, the possible selective forces in the evolution of seed size may be influenced by primary selectivity and how rodents treat seeds after harvesting. In this study, different-sized seeds from four species (Pinus armandii, Pinus densata, Abies sp., and Viburnum sp.) harvested by scatter-hoarding rodents were studied in an alpine forest in Southwestern China for two consecutive years. Our results showed that seed size influenced rodent foraging preferences, with bigger seeds being preferred over smaller seeds, within and across species. Rodents only removed and cached the larger seeds of P. armandii, and ate the seeds of the other three species in situ. Rodents are purely seed predators for these three species. For the cached seeds of P. armandii, significantly positive correlations were observed between seed size and dispersal distance among both primary and secondary cached seeds in 2006, but not in 2005. Our results indicate that among many coexisting species with widely different-sized seeds, scatter-hoarding rodents played important roles in the seed dispersal of the big-seeded species alone. This caching behavior could offset the limited seed dispersal of large-seeded and wingless species (P. armandii), in comparison with that of small winged seed species (P. densata and Abies sp.) and frugivore-dispersed species (Viburnum sp.).     

秦岭森林鼠类对华山松种子捕食及其扩散的影响

森林鼠类的种子贮藏行为对植物的扩散和自然更新有着非常重要的影响。通过塑料片标记法,2008和2009年的9月—11月分别在秦岭南坡的佛坪国家级自然保护区内调查了森林鼠类对华山松(Pinus armandii)种子的捕食和扩散,结果显示:森林鼠类对华山松种子有着非常大的捕食压力。在2008年,几乎所有的种子(96.4%)在第3天后就被全部取食,而在2009年,也有将近一半的种子(49.6%)在第3天后被取食。但与此同时,鼠类对华山松种子的扩散也起着非常重要的作用。尤其在2009年,第3天时鼠类最高分散贮藏了17.75%的种子,而且直到第19天后仍然有12.25%被贮藏的种子存活下来。华山松种子在两个年份间的扩散历程有很大差异。在2008年,几乎所有的种子都被鼠类取食,贮藏量非常小;而在2009年,种子被贮藏的比例显著的增加。这个结果可能与种子大小年现象有着十分紧密的联系。2008年是华山松种子的小年,产量非常低。鼠类为了满足其日常的能量需求,只能大量的取食有限的种子,而减少其贮藏量。而2009年是华山松种子的大年,产量非常高。鼠类在满足其日常能量需求的同时,还有大量剩余的种子供其贮藏。     

Fragmentation modifies seed trait effects on scatter-hoarders’ foraging decisions

Scatter-hoarding animals are crucial in seed dispersal of nut-bearing plants. We used the holm oak Quercus ilex—wood mouse Apodemus sylvaticus mutualism as a model system to evaluate the relative importance of seed size and fat content on scatter-hoarders’ foraging decisions influencing oak dispersal and potential recruitment. We performed a field experiment in which we offered holm oak acorns with contrasting seed size (2 vs 5 g) and fat content (3 vs 11%). Moreover, to test if the strength of these seed trait effects was context-dependent, experimental acorns were placed in small fragments, where natural regeneration is scarce or absent, and forest habitats. In small fragments, rodents had to face increased intraspecific competition for acorns and reduced anti-predator cover during transportation. As a result, they became more selective to ensure rapid acquisition of most valuable food items but, in turn, transported seeds closer to avoid unaffordable predation risks. During harvesting and caching, larger acorns were prioritized and preferentially cached. Fat content only had a minor effect in harvesting preferences. In contrast, in forest sites, where rodent abundance was four times lower and understory cover was well-developed, rodents were not selective but provided enhanced dispersal services to oaks (caching rates were 75% higher). From the plants’ perspective, our results imply that the benefits of producing costly seeds are context-dependent. Seed traits modified harvesting and caching rates only when rodents were forced to forage more efficiently in response to increased intraspecific competition. However, when landscape traits limited cache protection strategies, a more selective foraging behavior by scatter-hoarders did not result in enhanced dispersal services. Overall, our result shows that successful dispersal of acorns depends on how specific traits modulate their value and how landscape properties affect rodents’ ability to safeguard them for later consumption.