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。     

甘肃石羊河流域干旱荒漠区花棒蒸腾耗水量

研究了甘肃石羊河流域干旱荒漠区天然生长条件下花棒的蒸腾耗水规律．结果表明：花棒木质部液流速率随探针插入深度的加大呈“高-低”变化趋势;主根直径较小的花棒各位点的平均液流速率上升速度较快,变幅较大;不同主根直径花棒的液流量相差较大,但变化趋势较为一致,即昼夜变幅较大,夜间液流量较小,白天液流量较大,呈多峰曲线;日液流量与蒸发蒸腾量ET0呈线性相关,蒸腾耗水主要在6-9月,占生长季总蒸腾量的79．04％;花棒生长后期日液流量与0—50cm深沙层含水量呈显著相关,与其它层含水量无明显相关性;气象因素对花棒树干液流量影响的大小表现为日均气温〉空气水汽压差〉风速．     

种子特征和结实量对啮齿动物取食和扩散种子行为的影响

为了深入了解啮齿动物在不同种子丰富度条件下对不同大小和单宁含量种子的觅食行为策略及其与植物种群更新的关系,在宁夏六盘山区的华北落叶松人工林,研究了不同大小和单宁含量[0%Tannin(T)、2%T、8%T和15%T]的人工种子在模拟结实小年和结实大年对啮齿动物取食和扩散行为的影响.结果表明: 啮齿动物消耗种子速度在结实小年更快,结实大年的种子消耗速度相对缓慢. 种子就地取食率(ISPR)在不同结实年份间无显著差异,扩散后取食率(PRAD)在结实小年显著高于结实大年,但前者的扩散后贮藏率(HRAD)显著低于后者;种子扩散后的取食距离(PDAD)和贮藏距离(HDAD)在结实小年均显著大于结实大年.在结实小年,大种子的PDAD和HDAD均大于小种子,前者在不同大小种子间均差异显著,而后者仅在2%T和15%T的不同大小种子间差异显著;在结实大年,除0%T外的其他单宁含量种子的PDAD和HDAD在不同大小种子间均差异显著.ISPR在中等单宁含量种子最大,高单宁含量种子最小;PRAD分别在结实小年的高单宁含量种子和结实大年的无单宁种子最大;不论在结实大年还是结实小年,HRAD均在高单宁含量种子最大,中等单宁含量种子最小.这说明结实大年可延缓啮齿动物对种子的消耗速率,提高种子的HRAD,但种子扩散距离减小;啮齿动物在结实大年和小年均表现出对大种子的扩散偏好,且大种子被扩散的距离更远;啮齿动物在不同结实年份均偏好于就地取食中等单宁含量种子,而扩散高单宁含量种子.     

凋落物和土壤覆盖对动物取食和搬运辽东栎种子的影响

在六盘山区的华北落叶松人工林,研究了清除凋落物、凋落物覆盖和土壤覆盖(以不清除凋落物直接将种子投放于森林地表为对照)等处理对动物取食和搬运辽东栎种子的影响.结果表明:种子释放3d后,凋落物和土壤覆盖处理种子均具有较高的留存率(分别为10.7％和7.0％);释放14 d后,土壤覆盖处理种子的留存率仍最高(0.7％),但凋落物覆盖处理种子的留存率为0.凋落物和土壤覆盖处理种子的就地取食率很高(分别为45.9％和41.5％);清除凋落物处理种子的就地取食率最低(27.0％),但其被搬运后的取食率最高(49.8％);凋落物覆盖、清除凋落物和土壤覆盖处理种子被动物搬运后的埋藏率均显著高于对照(P＜0.01).种子被动物搬运后集中分布于5 m以内,尤其在＜1 m和l～2m两个距离组的分布频率更高;种子被搬运后取食的平均距离大干埋藏的平均距离,以土壤覆盖和凋落物覆盖处理最大,分别为2.38 m±0.55 m和1.44m±0.26 m.     

华山松种子大小对啮齿动物贮藏行为的影响及其时空变化

华山松(Pinus armandii)是广泛分布在中国中西部海拔1000～3300m的山地、种子较大(约300mg)的松属植物。为探究华山松种子大小对啮齿动物贮藏行为的影响,于2006年和2007年在滇西北3个不同地点进行种子标记和追踪实验。结果表明,在所有年份和地点,啮齿动物都倾向于贮藏更多的大种子和取食更多的小种子;啮齿动物贮藏大种子的数量,以及平均距离和最大距离均显著高于小种子。3个地点具有不同的啮齿动物群落结构,从而对种子命运产生显著影响。种子命运在两个年份间也存在显著差异。     

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。     

啮齿动物对不同林木种子的搬运和取食微生境选择机制

不同植物种子依靠不同的方式实现扩散,啮齿动物对林木种子搬运后在取食点微生境和贮藏方式的选择存在偏好,研究其贮藏行为与微生境的关系是探究幼苗建成的关键。在秦岭中段火地塘林区,采用标签标记法,以锐齿槲栎、华山松和油松种子为材料,探究了小型啮齿动物对松栎混交林建群种种子扩散过程的影响。结果表明:1)油松种子原地取食率显著高于锐齿槲栎和华山松种子,且啮齿动物更倾向于搬运后取食(60%)和埋藏(4.33%)华山松种子,搬运后取食距离也为华山松最大(2.49 m);锐齿槲栎小种子被搬运后埋藏的距离最大(4.92 m)。2)除华山松种子外,其他类型种子被搬运后单个取食的比例均在85%以上;油松种子不存在埋藏点,而其他类型种子90%以上均以单个形式被埋藏。3)大部分种子被啮齿动物搬运后选择在裸地丢弃;锐齿槲栎大种子(87.5%)、小种子(78.57%)和华山松种子(53.33%)较大比例被啮齿动物埋藏在灌丛下方,埋藏在裸地的种子较少。4)大部分种子在灌丛下方被取食,仅华山松种子被啮齿动物搬运到洞穴取食;除油松种子被大量原地取食外,其他类型种子被搬运到取食点的种子比例基本呈现由微生境植被复杂到简单(灌丛—草丛—灌丛边缘—裸地)而逐渐减小的趋势。种子的营养价值及取食和搬运过程中啮齿动物付出的成本是影响种子命运的关键性因子,且啮齿动物对种子埋藏和取食地点的微生境存在较明显的选择性。     

种子大小对小泡巨鼠贮藏行为的影响

以小泡巨鼠为研究对象,在围栏条件下,测定小泡巨鼠对大小两种栓皮栎种子的贮藏行为差异,以检验最优贮藏空间模型的两个预测:(1)大种子(高价值食物)的贮藏率大于小种子(低价值食物);(2)大种子的贮藏距离远于小种子.结果表明:大种子的搬运比例(39%)多于小种子(21.5%),多数的小种子(53%)被取食,大种子的贮藏比率(16%)远大于小种子(7%),上述结果支持模型的预测(1).但是,不同大小种子在贮藏距离上没有显著差异,因而预测(2)没有被支持.实验结果表明种子价值对鼠类的取食和贮藏行为有十分重要的影响,但围栏空间可能影响对模型预测(2)的检验.     

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.     

Role of small rodents in the seed dispersal process: Microcavia australis consuming Prosopis flexuosa fruits

Understanding the functional role of animal species in seed dispersal is central to determining how biotic interactions could be affected by anthropogenic drivers. In the Monte Desert, mammals play different functional roles in Prosopis flexuosa seed dispersal, acting as opportunistic frugivores (endozoochorous medium‐sized and large mammals) or seed hoarders (some small sigmodontine rodents). Our objective was assessing the functional role of Microcavia australis, a small hystricognathi rodent, in the fruit removal and seed deposition stages of P. flexuosa seed dispersal, compared to sympatric sigmodontine rodents. In situ, we quantified fruit removal by small rodents during non‐fruiting and fruiting periods, and determined the distance seeds were transported, particularly by M. australis. In laboratory experiments, we analysed how M. australis stores seeds (through scatter‐ or larder‐hoarding) and how many seeds are left in caches as living seeds, relative to previous data on sigmodontine rodents. To conduct field studies, we established sampling stations under randomly chosen P. flexuosa trees at the Ñacuñán Man and Biosphere Reserve. We analysed fruit removal by small rodents and seed dispersal distance by M. australis using camera traps focused on P. flexuosa fruits covered with wire screen, which only allowed entry of small animals. In laboratory trials, we provided animals with a known number of fruits and assessed seed conditions after removal. Small rodents removed 75.7% of fruit supplied during the non‐fruiting period and 53.2% during the fruiting period. Microcavia australis and Graomys griseoflavus were the main fruit removers. Microcavia australis transported seeds to a mean distance of 462 cm and cached seeds mainly in scatter‐hoards, similarly as Eligmodontia typus. All transported seeds were left in fruit segments or covered only by the endocarp, never as predated seeds. Microcavia australis disperses P. flexuosa seeds by carrying fruits away from a source to consume them and then by scatter‐hoarding fruits and seeds.     

秦岭南北坡森林鼠类对板栗和锐齿栎种子扩散的影响

森林鼠类的种子贮藏行为对植物的扩散及更新会产生积极的影响。2012和2013年秋季,分别在秦岭北坡的周至国家级自然保护区和南坡的佛坪国家级自然保护区内,调查了森林鼠类对板栗(Castanea mollissima)和锐齿栎(Quercus aliena)种子的取食和扩散差异。结果显示:1)秦岭南北坡的环境因素,特别是植被因素,对鼠类扩散板栗和锐齿栎种子具有重要的影响。南坡较为丰富的壳斗科植被种类,导致2种种子在南坡存留时间均长于北坡,而北坡的扩散取食和丢失率均高于南坡。2)种子特征影响鼠类的取食或贮藏偏好。由于较高的蛋白、脂肪等营养含量,鼠类更喜好取食或搬运贮藏板栗种子。然而,低营养但高丹宁含量的锐齿栎种子仍然被鼠类大量贮藏。3)2种种子在南北坡的扩散历程在两个年份间有很大差异,在食物相对匮乏的年份(2012年),种子被扩散的速度更快且丢失的比率更高。这种差异反映了种子大小年现象对森林鼠类取食和贮藏策略的影响。4)无论在秦岭南坡还是北坡,营养价值含量(如蛋白和脂肪)较高的板栗种子的取食和贮藏距离都明显大于营养价值含量较低的锐齿栎种子,这与最优贮藏空间分布模型的预测一致。     

Selection,caching, and consumption of hardwood seeds by forest rodents: implications for restoration of American chestnut

Recent field trials on blight‐resistant hybrids (BC₃F₃) of American chestnut (Castanea dentata) and Chinese chestnut (C. mollissima) have intensified planning for widespread restoration of Castanea to eastern U.S. forests. Restoration will likely rely on natural seed dispersal from sites planted with chestnut; however, we do not know how dispersal agents such as granivorous rodents will respond to hybrid chestnuts. At one extreme, excessive seed consumption may impede restoration. Alternatively, scatter‐hoarding rodents might facilitate the spread of chestnut by dispersal of seeds from restoration plantings. We conducted trials with five rodent species to quantify foraging preferences and to evaluate the potential role of granivores in chestnut restoration. Specifically, we presented seeds from American and hybrid chestnuts (BC₃F₂) with other common mast species and recorded the proportion of seeds removed and the fates of tagged seeds. Mice, chipmunks, and flying squirrels harvested both chestnut types preferentially over larger, tougher black walnut, hickory, and red oak seeds, but fox squirrels and eastern gray squirrels preferred larger seeds to chestnuts. All rodents consumed a greater proportion of the chestnuts than other seed types. American and hybrid chestnut also differed in important ways: except for fox squirrels, rodents preferentially removed American chestnuts over hybrid chestnuts, but we estimated that fox squirrels carried a greater proportion of hybrid chestnuts beyond our tag search area, suggesting that hybrids may be dispersed farther and cached more often than American chestnut. These differences indicate that hybrid chestnut may not be functionally equivalent to American chestnut with regard to seed–granivore interactions.     

Seed removal,seed dispersers,and the allocation of tissues in Myrtaceae seeds

To avoid seed predation, plants may invest in protective seed tissues. Often related to seed size, allocation in seeds' physical defenses can also be influenced by dispersers. We explore the relationships between seed traits (seed mass and hardness) and seed removal in 22 Myrtaceae species of the Brazilian Atlantic Forest, a dominant and diverse fleshy-fruited taxon dispersed by birds, rodents, and other mammals. Our goal is to understand how seed traits influence seed removal rates, and whether dispersers can affect tissue allocation in the seed coat. Seeds were exposed to field removal experiments. In the laboratory, total seed mass and seed coat mass were obtained. To evaluate the influence of seed traits on removal, we performed Kruskal–Wallis and Simple Linear Regression tests. We assessed seed coat and seed mass covariation through standardized major-axis allometric regressions. Harder seeds were larger than softer ones. Seed traits affect removal rates, as tougher and heavier seeds had lower removal. Seed mass significantly predicts seed coat proportion in seven of the 14 species tested. Bird-dispersed species tend to exhibit lower proportions of seed coat as seed mass increases, whereas rodent-dispersed species apparently present the opposite trend, with seed coat proportion increasing with seed mass. Such difference may be caused by the contrasting seed predation pressure represented by birds and rodents. Energy allocation for defense, expressed in seed coat proportion, is greater in large seeds, as these are mostly dispersed by rodents whose propensity to cache and disperse seeds is greater for large and well-protected seeds.     

Scatter‐hoarding and cache pilfering of rodents in response to seed abundance

Seed caching and reciprocal cache pilferage play an important role in the coexistence of food‐hoarding animals. Understanding what affects seed caching and how cache pilferage occurs is an important question in seed dispersal ecology. However, tracking seed fate and cache pilferage presents substantial practical difficulties. Siberian chipmunks Tamias sibiricus always remove the entire pericarp when scatter‐hoarding acorns of Mongolian oak Quercus mongolica, whereas wood mice Apodemus peninsulae often store whole acorns in their caches. These differences in behavior provide an opportunity to investigate unilateral cache pilferage of T. sibiricus from A. peninsulae in response to seed abundance. In this study, tagged acorns were released at the peak and end periods of seed rain from Q. mongolica. This allowed us to investigate seed caching and unilateral cache pilferage at different seed abundances. We found that a higher proportion of acorns were cached at lower level of seed abundance (toward the end of seed rain), mainly because T. sibiricus rather than A. peninsulae scatter‐hoarded significantly more acorns at this time. Cache distances decreased with increasing seed abundance, indicating that acorns were cached further away and into smaller caches at lower seed abundance. Unexpectedly, unilateral cache pilferage by T. sibiricus was not significantly influenced by seed abundance—remaining at around 28% during both periods of high and low seed abundance.