我国草地资源丰富, 总面积约为293万km2 (方精云等, 2018)。其中, 内蒙古温带典型草原是我国北方草原的主体和重要生态屏障, 以放牧作为主要管理利用方式。大量研究表明, 轻度或中度放牧能够维持或增加草原植物多样性, 而长期过度放牧导致植物多样性丧失、生态系统功能和稳定性降低, 从而危及人类生存与发展(李博, 1997; Tilman et al., 2014; 杨婧等, 2014; Li et al., 2015; Zhang et al., 2022)。毫无疑问, 设置合理的放牧强度对于草原植物多样性保护具有重要意义。但是, 选择性采食现象是放牧过程中十分常见的现象(Ren et al., 2015; Li et al., 2021), 大多数研究没有考虑家畜选择性采食对植物多样性的潜在影响。然而, 最近在欧洲草地的研究发现, 放牧选择性采食产生的斑块效应可能比放牧强度本身对于植物多样性的改变有更重要的作用(Tonn et al., 2019)。因此, 即使草地放牧强度相同, 放牧家畜类型及其采食行为的差异也可能会对植物多样性和物种组成产生截然不同的影响。
目前关于放牧对植物多样性影响的研究已有很多。通常认为食草动物通过直接采食竞争力强的优势物种, 间接地弱化竞争排斥作用从而能够提高植物多样性(Olff & Ritchie, 1998)。但是这种关系会随着食草动物种类、环境条件以及空间尺度的改变而发生变化。例如, 在北美和欧洲草地的研究中发现体型较大(>30 kg)的食草动物(牛、羊、鹿等)在高生产力草地中能够增加植物多样性, 在低生产力草地中会降低植物多样性, 而体型较小(<10 kg)的食草动物(野兔、啮齿类等)对植物多样性的影响则无明显规律(Bakker et al., 2006)。不过, 该研究中每个样地均是多种食草动物的混合放牧效应, 尚未区分牛羊等各自的影响。房健(2013)在松嫩草地的研究进一步表明, 尽管牛和羊均属于大型食草动物, 体尺较大的牛放牧提高了植物多样性, 而体尺较小的羊放牧却降低了植物多样性。此外, 放牧对植物多样性的影响具有尺度效应。研究表明, 放牧绵羊在较大空间尺度上比较小空间尺度上引起的物种丧失比例更高(Li et al., 2015)。因此, 不同放牧家畜如何在多个尺度上影响植物多样性仍需要深入研究。
放牧选择性采食是不同家畜影响植物多样性的关键过程和重要机制(王德利和王岭, 2011)。不同放牧家畜对植物的选择性与其消化系统功能、唇齿结构、体型大小、空间活动行为等多种因素密切相关(Vallentine, 1990; Rook et al., 2004)。内蒙古典型草原常见的放牧家畜包括牛、马、羊等。其中, 牛和羊的消化系统均能够进行反刍活动, 但是马的消化系统没有反刍功能, 所以马主要通过快速且大量采食来满足其能量需求, 对植物的选择性相对更低(Hanley, 1982)。然而, 尽管牛和羊均属于反刍动物, 但是不同的唇齿结构导致它们对植物的选择性存在差异。牛的嘴部较大且主要通过舌头卷起植物个体进行采食, 通常选择距离地面5 cm以上的植物; 而绵羊和山羊的嘴部较小且能够通过开裂的上唇对植物不同部位进行更多的选择采食, 还可以更加贴近地面采食下层植物(Vallentine, 1990; 房健, 2013)。此外, 牛和羊之间的体型大小存在差异, 对食物的摄入量不同也会影响它们对植物的选择(Clauss et al., 2013)。体型相对较大的食草动物需要采食较高的上层植物来满足其能量需求, 而体型相对较小的食草动物更加易于依靠低矮的植物维持生存(Illius & Gordon, 1987)。另外, 牛和羊在空间上的活动范围不同。牛在较大斑块采食且空间异质性较低, 而羊在较小斑块采食且空间异质性较高(李静, 2014)。放牧家畜对不同高度植物的采食及其空间采食聚集程度如何影响植物多样性仍需进一步研究。
为此, 本研究依托内蒙古大学典型草原放牧实验平台, 通过野外植物群落调查与家畜放牧轨迹定位相结合的方法, 旨在探索中等放牧强度下: (1)放牧家畜类型(牛、山羊、绵羊)如何影响不同空间尺度植物多样性指数(α、β、γ多样性)和群落结构? (2)放牧家畜对植物的选择性采食和聚集性采食如何影响α、β和γ多样性?
1 材料和方法
1.1 研究区概况
研究区位于内蒙古自治区锡林浩特市朝克乌拉苏木内蒙古大学典型草原示范牧场(116.52°- 116.54° E, 44.26°-44.27° N, 海拔1 146 m)。研究区属于温带大陆性气候, 夏季炎热多雨, 冬季寒冷干燥, 年平均气温2.4 ℃, 年降水量281 mm, 主要集中在生长季(5-9月), 约占全年降水量80%以上(张景慧等, 2021)。土壤为栗钙土。植物群落主要优势种包括羊草(Leymus chinensis)、糙隐子草(Cleistogenes squarrosa)、大针茅(Stipa grandis)和黄囊薹草(Carex korshinskyi), 其地上生物量分别占群落地上生物量的36%、20%、17%、8%, 总计81% (李艳龙等, 2018)。
1.2 实验设计及取样方法
研究区域于2012年围封禁牧, 2016年在地势平坦、土壤和植物群落均匀的区域建立放牧实验平台。本研究涉及4个实验处理, 即中等强度放牧牛、山羊、绵羊以及不放牧对照, 每个处理4个重复, 共计16个实验小区。实验小区采用完全随机区组设计, 各小区面积为50 m × 50 m。每个小区在每年6、7、8月放牧3次, 保持相同放牧强度。具体地, 当优势种留茬高度约6 cm时将家畜移出小区, 此时每个放牧小区的“羊单位×放牧天数”一致, 达到中等放牧强度。
2020年7月对不同处理下植物群落组成和地上生物量进行调查取样。首先, 每个小区内间隔5 m均匀布设7条样线, 样线上间隔5 m设置7个1 m × 0.25 m的样方。其次, 记录样方内出现的植物物种名称、每个物种的个体数, 同一物种随机选取3个个体测量植株高度。最后, 每个小区在放牧后随机设置8个1 m × 0.25 m的样方, 采用齐地刈割法收集地上剩余植物, 样品经65 ℃烘干48 h后称质量, 获得地上生物量干质量数据。此外, 7月放牧期间, 在不影响家畜日常行为的前提下, 每个小区选取3只家畜佩戴高精度定位跟踪项圈(UbiTraq UT100-TB, 北京全迹科技有限公司, 北京), 项圈每秒记录一次位置信息, 连续定位3天, 定位空间精度可达10 cm (Li et al., 2021)。
1.3 数据计算和统计分析
通过生物量比值法计算家畜对4个优势植物的选择性采食指数(SI), $SI=\frac{(i-o)\text{/}(Ti-To)}{i\text{/}Ti}$。其中, i和o分别为围封处理和放牧处理中该植物平均生物量, Ti和To分别为围封处理和放牧处理中样方平均生物量(汪诗平, 2000)。根据SI将家畜对植物的偏食程度划为4个等级: 嗜食(SI > 1.5)、喜食(1–1.5)、可食(0.5–1)和少食(SI ≤ 0.5)。通过群落中植物平均高度将4个优势种进一步划分为上层优势种大针茅(株高33.3 cm)和羊草(株高26.7 cm)、下层优势种糙隐子草(株高10.3 cm)和黄囊薹草(株高14.1 cm)。比较不同高度和偏食程度的物种地上生物量变化及其对植物多样性和群落结构的影响。
通过轨迹定位数据分析家畜采食的空间聚集行为。首先, 选取单日内家畜定位点记录时间较为连续且相邻定位点时间间隔小于30 s的数值。其次, 根据坐标位置信息, 计算相邻两次记录的家畜位移距离(D), $D=\sqrt{{{({{x}_{1}}-{{x}_{2}})}^{2}}+{{({{y}_{1}}-{{y}_{2}})}^{2}}}$。其中$({{x}_{1}},{{y}_{1}})$和$({{x}_{2}},{{y}_{2}})$分别为相邻两个定位点的坐标。位移距离除以时间间隔得到家畜运动速度V = D/Δt, Δt为相邻两点间的时间间隔。之后, 将同种家畜所有速度数据整合后进行k-means迭代分类(侯路路, 2020)。根据前人研究中划分家畜行为特征的方法(Kilgour et al., 2012; Augustine & Derner, 2013), 将家畜行为模式划分为休息、采食和游走, 并考虑离群值对迭代分类结果的影响(González et al., 2015), 计算不同行为中休息、采食和游走分类结果的百分位数, 取各分组数据的上四分位数(75%)作为家畜行为模式划分的速度阈值(表1)。最后, 利用网格法将整个研究区用1 m × 1 m的网格覆盖, 统计每个网格内采食点数量, 通过计算网格内家畜采食点数量的全局莫兰指数(Global Moran’s I)(Griffith, 1987)分析家畜采食行为在空间上的聚集程度。比较不同采食聚集性对植物多样性的影响。
表1 根据速度阈值对内蒙古典型草原不同放牧家畜行为的划分
Table 1
| 家畜类型 Livestock type | 休息 Resting (m·s-1) | 采食 Feeding (m·s-1) | 游走 Wandering (m·s-1) |
|---|---|---|---|
| 牛 Cattle | 0-0.05 | 0.05-0.26 | >0.26 |
| 山羊 Goat | 0-0.03 | 0.03-0.16 | >0.16 |
| 绵羊 Sheep | 0-0.05 | 0.05-0.20 | >0.20 |
数据统计分析均在R 4.0.5中完成。数据符合正态分布且各变量不存在空间自相关。利用“stats”包进行单因素方差分析、使用“multcomp”包进行Dunnett多重比较和p值校正, 对比放牧家畜与对照之间植物多样性和地上生物量的响应变化。通过“vegan”包进行多元方差分析, 反映放牧家畜对群落物种组成的影响。通过“stats”包进行Pearson相关性分析, 探索植物多样性对家畜选择性采食和聚集性采食的响应。家畜轨迹数据处理和采食聚集性分析在ArcGIS 10.2软件中完成。数据绘图在GraphPad Prism 8软件中完成。
2 结果
2.1 植物α、β和γ多样性对不同放牧家畜的响应
图1
图1
不同家畜中等强度放牧下内蒙古典型草原植物多样性(平均值±标准误)。*, p < 0.05; **, p < 0.01。
Fig. 1
Plant species diversity under moderate grazing of different livestock species in a typical steppe in Nei Mongol (mean ± SE). *, p < 0.05; **, p < 0.01.
2.2 群落结构对不同放牧家畜的响应
图2
图2
不同家畜放牧下内蒙古典型草原植物群落组成非度量多维尺(NMDS)度排序, 椭圆置信区间为95%。图中所列植物相对多度与其在横轴和纵轴的数值显著相关(p < 0.05), 括号内的数字表示相关系数。
Fig. 2
Ordination of plant communities in a typical steppe in Nei Mongol under different livestock grazing treatments by non-metric multidimensional scaling (NMDS), with an elliptical confidence interval of 95%. The relative abundance of different species is significantly related to the axis 1 and axis 2 scores (p < 0.05). The numbers in parentheses indicate the correlation coefficients.
2.3 放牧家畜对优势种的选择性采食及其对多样性影响
表2 不同放牧家畜对内蒙古典型草原4个优势种的选择性采食指数
Table 2
| 家畜类型 Livestock type | 上层优势种 Tall dominant species | 下层优势种 Short dominant species | 羊草 Leymus chinensis | 大针茅 Stipa grandis | 糙隐子草 Cleistogenes squarrosa | 黄囊薹草 Carex korshinskyi |
|---|---|---|---|---|---|---|
| 牛 Cattle | 1.148 | 0.713 | 1.113 | 1.253 | 0.918 | 1.673 |
| 山羊 Goat | 1.224 | 0.652 | 0.881 | 1.592 | 0.950 | 2.585 |
| 绵羊 Sheep | 0.277 | 3.029 | 1.072 | 0.576 | 3.583 | 3.309 |
图3
图3
不同家畜中等放牧强度下植物地上生物量(平均值±标准误)。A,上层优势种。B, 羊草。C, 大针茅。D, 下层优势种。E, 糙隐子草。F, 黄囊薹草。*, p < 0.05; **, p < 0.01; ***, p < 0.001。
Fig. 3
Plant aboveground biomass under the grazing of different livestock types at moderate intensity (mean ± SE). A, Tall dominant species. B,Leymus chinensis. C,Stipa grandis. D, Short dominant species. E,Cleistogenes squarrosa. F, Carex korshinskyi. *, p < 0.05; **, p < 0.01; ***, p < 0.001.
图4
图4
不同家畜中等放牧强度下内蒙古典型草原上层和下层优势种地上生物量与植物多样性关系。
Fig. 4
Relationship between the aboveground biomass of tall and short dominant species in typical steppe in Nei Mongol and plant diversity under the grazing of different livestock types at moderate intensity.
2.4 放牧家畜采食空间聚集性及其对多样性的影响
图5
图5
家畜采食聚集性(平均值±标准误)及其与植物多样性关系。**, p < 0.01。
Fig. 5
Aggregation degrees of the feeding behavior of different livestock species (mean ± SE) and their relationships with plant diversity. **, p < 0.01.
3 讨论
3.1 放牧家畜类型对植物多样性和群落结构的影响
本研究中, 我们使用了多种放牧家畜来检验植物多样性在中度放牧时的响应。一方面, 我们发现不同放牧家畜在中等放牧强度下均能够提高植物α、β和γ多样性, 与中度干扰假说的预测(Connell, 1978)一致, 表明适度放牧有利于维持草原植物多样性。国内外开展的草地放牧实验研究大多数也支持该结果, 当然, 不同放牧实验所处的气候条件、植被类型、放牧历史等多种因素的差异都可能导致多样性产生不同甚至相反的响应(Herrero-Jáuregui & Oesterheld, 2018; Gao & Carmel, 2020), 本研究不再展开进行探讨。本研究中, 除放牧强度之外, 多样性的增加还与放牧家畜类型有关。例如, Bakker等(2006)研究指出, 大型食草动物(>30 kg)对多样性通常具有促进作用, 而小型食草动物(<10 kg)对多样性的影响无明显规律。另一方面, 我们发现虽然牛和羊均属于大型食草动物, 但是体尺更大的牛对多样性有更大的提升, 表明不同家畜种类对草原植物多样性的影响不一致。例如, 苏日古嘎(2020)基于相同研究区域不同年份的实验也发现放牧牛比放牧山羊和绵羊能够显著提高植物物种丰富度和Shannon- Wiener多样性指数。此外, 不同家畜对多样性的影响还受到植物群落初始多样性的影响。例如, 基于东北松嫩草地中度放牧实验发现体尺较小的山羊和绵羊在低植物多样性群落放牧甚至会降低植物群落多样性(房健, 2013; Liu et al., 2015)。
本研究中, 放牧家畜不仅改变了植物多样性, 同时也对群落结构产生显著影响。其中, 绵羊放牧后的群落结构与牛放牧后的群落结构表现出相反的变化趋势。导致这种差异的主要原因可能是绵羊比牛有更高的选择性采食作用(Grant et al., 1985; Laca et al., 2010; Cuchillo-Hilario et al., 2018)。一方面, 绵羊放牧后的群落中糙隐子草的相对生物量较低(9.2%)。尽管绵羊对优势种糙隐子草和黄囊薹草的选择性都达到了嗜食程度(SI > 1.5), 但是本研究中糙隐子草相对多度的高低在更大程度上影响了群落结构的变化方向。这主要是由于我们的研究区域内糙隐子草在未放牧群落中占到下层优势种地上生物量的93.4%。因此, 绵羊为了满足自身能量需求会优先采食地上生物量更高的糙隐子草, 使其相对多度发生显著降低。另一方面, 绵羊放牧后的群落中稀有种矮韭的相对多度较低(0.3%)。研究表明, 我们的实验区域内大多数稀有种是杂类草, 其叶片柔软多汁、氮含量高(Li et al., 2015), 绵羊在中度放牧时对矮韭的选择性可达到嗜食程度(Wan et al., 2015)。
3.2 放牧家畜选择性和聚集性采食对植物多样性的影响
本研究表明, 不同家畜对植物多样性的影响与其选择性采食行为密切相关, 与王德利和王岭(2011)的研究结果一致。一方面, 放牧家畜对优势种的采食作用有利于多样性增加。导致这种结果的原因可能是本研究中的优势种适口性较高, 家畜优先采食, 降低了对其他物种的竞争排斥作用。例如, Koerner等(2018)基于全球多个放牧实验meta分析表明, 大型食草动物通过抑制优势种的优势度, 释放的资源可以被新的物种利用从而增加植物多样性。另一方面, 虽然3种家畜对多样性都是促进作用, 但是它们形成的机制有所不同。牛和山羊通过采食抑制上层优势种羊草、大针茅和下层优势种糙隐子草形成促进作用, 而绵羊则主要是通过采食抑制下层优势种糙隐子草产生促进作用。植物选择性采食指数也表明, 绵羊对上层优势种大针茅的选择性接近少食类型。与本研究中7月下旬所得到的结果不同, 苏日古嘎(2020)在8月下旬开展的研究发现绵羊放牧不仅显著降低了糙隐子草地上生物量, 还显著降低了大针茅地上生物量。导致结果不同的原因可能主要是绵羊的食性存在明显的季节性变化(汪诗平, 2000)。此外, 我们发现家畜可能通过对上层或下层优势种的影响进而改变不同尺度的植物多样性。例如, α和γ多样性分别随下层优势种和上层优势种生物量增加而显著降低。这可能是由于上层优势种在群落中的生物量占50%以上, 其生物量减少更加有利于其他物种获得释放的养分和光资源(Borer et al., 2014)。
近年来, 随着全球定位技术的发展, 越来越多的研究将其应用于放牧家畜行为研究(侯路路, 2020; Li et al., 2021)。本研究表明, 不同家畜对植物多样性的影响还与其聚集性采食行为密切相关。一方面, 放牧家畜的采食空间聚集性增加会导致植物多样性降低。这主要是由于食物充足时放牧家畜会优先采食适口性高的植物所在的区域, 并且重复对该区域内再生形成的营养价值高的幼嫩植物进行采食(Coughenour, 1991; Briske et al., 2008), 进而形成重度采食斑块。只有当食物严重短缺时, 家畜才会对之前避开的区域进行采食(Putfarken et al., 2008)。因此, 重度采食斑块内的植物需要承受比中度放牧更高的放牧压力, 从而更加容易丧失物种, 导致多样性降低(Li et al., 2021)。另一方面, 本研究中牛的空间采食聚集程度显著低于绵羊和山羊, 这可能是因为动物活动范围的选择与体型有关(Fisher et al., 2011), 而牛的活动范围相对较大。山羊和绵羊之间的聚集性并无显著差异, 可能是山羊和绵羊体型相近所致, 也可能是本实验中相对较小的小区面积(0.25 hm2)在一定程度上弱化了它们聚集性之间的差异, 需要后续在较大区域内进行比较来验证。此外, 本研究并未开展混合家畜放牧及其空间聚集性实验。已有研究表明, 牛羊混合放牧的采食互补效应更加有利于草甸草原植物多样性维持(Liu et al., 2015; 钟志伟等, 2021)。同时, 这也可能是由于牛和羊在草地资源的空间利用上有很大的空间互补性(Putfarken et al., 2008; 李静, 2014; Cuchillo-Hilario et al., 2017), 需要后续通过同时定位跟踪多种放牧家畜来进一步验证。
放牧是草原不可缺少的生产方式, 适度放牧有利于维持草原生物多样性和生态系统功能。本研究表明, 尽管中等放牧强度能够增加草原植物α、β和γ多样性, 但由于不同放牧家畜选择性和聚集性采食行为存在差异, 其对植物多样性和群落结构的影响不同。因此, 我们在制定草地长期放牧管理体系时既要设置适宜的放牧强度, 也要配置合理的放牧家畜种类, 才能使草地资源得以有效利用。
致谢
本研究得到内蒙古大学人才引进项目(12000-15031907)的资助。感谢内蒙古大学草地生态学研究基地所有老师和工作人员在野外实验中给予的帮助。
参考文献
Assessing herbivore foraging behavior with GPS collars in a semiarid grassland
DOI:10.3390/s130303711
PMID:23503296
[本文引用: 1]
Advances in global positioning system (GPS) technology have dramatically enhanced the ability to track and study distributions of free-ranging livestock. Understanding factors controlling the distribution of free-ranging livestock requires the ability to assess when and where they are foraging. For four years (2008-2011), we periodically collected GPS and activity sensor data together with direct observations of collared cattle grazing semiarid rangeland in eastern Colorado. From these data, we developed classification tree models that allowed us to discriminate between grazing and non-grazing activities. We evaluated: (1) which activity sensor measurements from the GPS collars were most valuable in predicting cattle foraging behavior, (2) the accuracy of binary (grazing, non-grazing) activity models vs. models with multiple activity categories (grazing, resting, traveling, mixed), and (3) the accuracy of models that are robust across years vs. models specific to a given year. A binary classification tree correctly removed 86.5% of the non-grazing locations, while correctly retaining 87.8% of the locations where the animal was grazing, for an overall misclassification rate of 12.9%. A classification tree that separated activity into four different categories yielded a greater misclassification rate of 16.0%. Distance travelled in a 5 minute interval and the proportion of the interval with the sensor indicating a head down position were the two most important variables predicting grazing activity. Fitting annual models of cattle foraging activity did not improve model accuracy compared to a single model based on all four years combined. This suggests that increased sample size was more valuable than accounting for interannual variation in foraging behavior associated with variation in forage production. Our models differ from previous assessments in semiarid rangeland of Israel and mesic pastures in the United States in terms of the value of different activity sensor measurements for identifying grazing activity, suggesting that the use of GPS collars to classify cattle grazing behavior will require calibrations specific to the environment and vegetation being studied.
Herbivore impact on grassland plant diversity depends on habitat productivity and herbivore size
Mammalian herbivores can have pronounced effects on plant diversity but are currently declining in many productive ecosystems through direct extirpation, habitat loss and fragmentation, while being simultaneously introduced as livestock in other, often unproductive, ecosystems that lacked such species during recent evolutionary times. The biodiversity consequences of these changes are still poorly understood. We experimentally separated the effects of primary productivity and herbivores of different body size on plant species richness across a 10-fold productivity gradient using a 7-year field experiment at seven grassland sites in North America and Europe. We show that assemblages including large herbivores increased plant diversity at higher productivity but decreased diversity at low productivity, while small herbivores did not have consistent effects along the productivity gradient. The recognition of these large-scale, cross-site patterns in herbivore effects is important for the development of appropriate biodiversity conservation strategies.
Herbivores and nutrients control grassland plant diversity via light limitation
DOI:10.1038/nature13144 URL [本文引用: 1]
Rotational grazing on rangelands: reconciliation of perception and experimental evidence
DOI:10.2111/06-159R.1 URL [本文引用: 1]
Herbivory and body size: allometries of diet quality and gastrointestinal physiology, and implications for herbivore ecology and dinosaur gigantism
DOI:10.1371/journal.pone.0068714 URL [本文引用: 1]
Diversity in tropical rain forests and coral reefs
DOI:10.1126/science.199.4335.1302
PMID:17840770
[本文引用: 1]
The commonly observed high diversity of trees in tropical rain forests and corals on tropical reefs is a nonequilibrium state which, if not disturbed further, will progress toward a low-diversity equilibrium community. This may not happen if gradual changes in climate favor different species. If equilibrium is reached, a lesser degree of diversity may be sustained by niche diversification or by a compensatory mortality that favors inferior competitors. However, tropical forests and reefs are subject to severe disturbances often enough that equilibrium may never be attained.
Spatial components of plant-herbivore interactions in pastoral, ranching, and native ungulate ecosystems
DOI:10.2307/4003033 URL [本文引用: 1]
Behavioral patterns of (co-)grazing cattle and sheep on swards differing in plant diversity
DOI:10.1016/j.applanim.2017.02.009 URL [本文引用: 1]
Forage selectivity by cattle and sheep co-grazing swards differing in plant species diversity
DOI:10.1111/gfs.12339 URL [本文引用: 1]
How many areas of grasslands are there in China?
我国草地面积有多大?
Body mass explains characteristic scales of habitat selection in terrestrial mammals
DOI:10.1002/ece3.45
PMID:22393519
[本文引用: 1]
Niche theory in its various forms is based on those environmental factors that permit species persistence, but less work has focused on defining the extent, or size, of a species' environment: the area that explains a species' presence at a point in space. We proposed that this habitat extent is identifiable from a characteristic scale of habitat selection, the spatial scale at which habitat best explains species' occurrence. We hypothesized that this scale is predicted by body size. We tested this hypothesis on 12 sympatric terrestrial mammal species in the Canadian Rocky Mountains. For each species, habitat models varied across the 20 spatial scales tested. For six species, we found a characteristic scale; this scale was explained by species' body mass in a quadratic relationship. Habitat measured at large scales best-predicted habitat selection in both large and small species, and small scales predict habitat extent in medium-sized species. The relationship between body size and habitat selection scale implies evolutionary adaptation to landscape heterogeneity as the driver of scale-dependent habitat selection.
A global meta-analysis of grazing effects on plant richness
DOI:10.1016/j.agee.2020.107072 URL [本文引用: 1]
Behavioral classification of data from collars containing motion sensors in grazing cattle
DOI:10.1016/j.compag.2014.10.018 URL [本文引用: 1]
Comparative studies of diet selection by sheep and cattle: the hill grasslands
DOI:10.2307/2260163 URL [本文引用: 1]
The nutritional basis for food selection by ungulates
DOI:10.2307/3898379 URL [本文引用: 1]
Effects of grazing intensity on plant richness and diversity: a meta-analysis
DOI:10.1111/oik.04893 URL [本文引用: 1]
The allometry of food intake in grazing ruminants
DOI:10.2307/4961 URL [本文引用: 1]
The behaviour of beef cattle at pasture
DOI:10.1016/j.applanim.2011.12.001 URL [本文引用: 1]
Change in dominance determines herbivore effects on plant biodiversity
Disentangling the drivers of β diversity along latitudinal and elevational gradients
DOI:10.1126/science.1208584
PMID:21940897
[本文引用: 1]
Understanding spatial variation in biodiversity along environmental gradients is a central theme in ecology. Differences in species compositional turnover among sites (β diversity) occurring along gradients are often used to infer variation in the processes structuring communities. Here, we show that sampling alone predicts changes in β diversity caused simply by changes in the sizes of species pools. For example, forest inventories sampled along latitudinal and elevational gradients show the well-documented pattern that β diversity is higher in the tropics and at low elevations. However, after correcting for variation in pooled species richness (γ diversity), these differences in β diversity disappear. Therefore, there is no need to invoke differences in the mechanisms of community assembly in temperate versus tropical systems to explain these global-scale patterns of β diversity.
Allometry and spatial scales of foraging in mammalian herbivores
DOI:10.1111/j.1461-0248.2009.01423.x
PMID:20100240
[本文引用: 1]
Herbivores forage in spatially complex habitats. Due to allometry and scale-dependent foraging, herbivores are hypothesized to perceive and respond to heterogeneity of resources at scales relative to their body sizes. This hypothesis has not been manipulatively tested for animals with only moderate differences in body size and similar food niches. We compared short-term spatial foraging behavior of two herbivores (sheep and cattle) with similar dietary niche but differing body size. Although intake rates scaled allometrically with body mass (mass(0.75)), spatial foraging strategies substantially differed, with cattle exhibiting a coarser-grained use of the 'foodscape.' Selectivity by cattle (and not sheep) for their preferred food was more restricted when patches were smaller (< 10 m(2)). We conclude that differences in spatial scales of selection offers a plausible mechanism by which species can coexist on shared resources that exhibit multiple scales of spatial heterogeneity.
The rangeland degradation in North China and its preventive strategy
中国北方草地退化及其防治对策
Applying a high-precision tracking system to distinguish the spatiotemporal patterns of animal movement in grassland ecology
DOI:10.1016/j.biocon.2021.109016 URL [本文引用: 2]
Grazing regime alters plant community structure via patch-scale diversity in semiarid grasslands
DOI:10.1002/ecs2.3547 [本文引用: 2]
Scale-dependent patterns and mechanisms of grazing- induced biodiversity loss: evidence from a field manipulation experiment in semiarid steppe
DOI:10.1007/s10980-014-0146-4 URL [本文引用: 3]
The daily intake and forage species selection of three types of grazing livestocks on a typical steppe in Inner Mongolia
内蒙古典型草原三种家畜采食量和食性选择的研究
Impacts of grazing by different large herbivores in grassland depend on plant species diversity
DOI:10.1111/1365-2664.12456 URL [本文引用: 2]
Effects of herbivores on grassland plant diversity
DOI:10.1016/S0169-5347(98)01364-0 URL [本文引用: 1]
Site use of grazing cattle and sheep in a large-scale pasture landscape: a GPS/GIS assessment
DOI:10.1016/j.applanim.2007.05.012 URL [本文引用: 2]
Do sheep grazing patterns affect ecosystem functioning in steppe grassland ecosystems in Inner Mongolia?
DOI:10.1016/j.agee.2015.07.015 URL [本文引用: 1]
Matching type of livestock to desired biodiversity outcomes in pastures-A review
DOI:10.1016/j.biocon.2003.11.010 URL [本文引用: 1]
Biodiversity and ecosystem functioning
DOI:10.1146/annurev-ecolsys-120213-091917 URL [本文引用: 1]
Grazing-induced patchiness, not grazing intensity, drives plant diversity in European low-input pastures
DOI:10.1111/1365-2664.13416 URL [本文引用: 1]
Selective grazing and seasonal precipitation play key roles in shaping plant community structure of semi-arid grasslands
DOI:10.1007/s10980-015-0252-y URL [本文引用: 1]
Interactions between herbivores and plant diversity
草食动物与草地植物多样性的互作关系研究进展
The dietary composition of fine wool sheep and plant diversity in Inner Mongolia steppe
不同放牧季节绵羊的食性及食物多样性与草地植物多样性间的关系
Vegetation of the Siskiyou mountains, Oregon and California
DOI:10.2307/1943563 URL [本文引用: 1]
Mechanisms underlying the impacts of grazing on plant α, β and γ diversity in a typical steppe of the Inner Mongolia grassland
DOI:10.3724/SP.J.1258.2014.00017
[本文引用: 1]
Aims Human disturbance, such as overgrazing have resulted in widespread declines in biodiversity and ecosystem functioning and services in arid and semiarid grasslands worldwide. This study is aimed to examine the effects of grazing intensity, topography and precipitation fluctuation on plant diversity across three levels of organization (i.e., plant species, functional group, and community) in a typical steppe of the Inner Mongolia grassland.Methods Based on a long-term grazing experiment maintained for eight years with seven levels of grazing intensity and two topographic systems in a typical steppe of the Inner Mongolia grassland, the effects of grazing intensity, topography (flat vs. slope), and precipitation fluctuations (wet vs. normal years) on plant diversity (i.e. α, β and γ diversity) and their controlling mechanisms were examined.Important findings Our results showed that: (1) The diversity-grazing intensity relationship differed between two topographic systems and over two years (wet vs. normal years). The α, β, and γ diversity in the wet year (2012) were higher than those in the normal year (2011). The effect of topography on plant diversity was dependent on precipitation, with higher α diversity in the slope system and normal year and higher α and γ diversity in the flat system and wet year. There was no significant effect of topography on β diversity. (2) The α diversity decreased with increasing grazing intensity in both the flat and slope systems. The α diversity response to grazing differed substantially among the dominant species, common species, and rare species in the two topographic systems, with the highest negative response for rare species, intermediate negative response for common species, and the weakest response for dominant species. (3) In the flat system, γ diversity declined with increasing grazing intensity, while it firstly decreased and then increased at the intermediate level of grazing intensity in the slope system. (4) The β diversity decreased with increasing grazing intensity in the flat system due to grazing-induced species convergence, while it did not show any tendency in the slope system. Our results suggest that the topography and precipitation are two key factors governing the relationship between plant biodiversity and grazing intensity in the arid and semiarid grasslands. The loss of species in the dry year was greater in the flat system than in the slope system, while the opposite result was found in the wet year. The rare species plays an important role in maintaining species diversity. These findings provide a better understanding of the biodiversity-grazing intensity relationship in the context of different precipitation and topographic conditions in the semiarid steppe and beyond.
放牧对内蒙古典型草原α、β和γ多样性的影响机制
DOI:10.3724/SP.J.1258.2014.00017
[本文引用: 1]
人类活动干扰对生物多样性和生态系统功能的影响机制是近年来生态学研究的一个热点问题。该研究以内蒙古锡林郭勒草原生态系统国家野外科学观测研究站的大型放牧控制实验为平台, 系统地研究了不同降水(丰水年份和平水年份)和地形(平地和坡地)条件下, 放牧对典型草原不同空间尺度植物多样性(α、β和γ多样性)的影响。研究发现: (1)降水和地形条件及其交互效应对植物多样性有明显的影响, 丰水年份的α、β和γ多样性均高于平水年份; 降水和地形条件存在交互效应, 平水年份坡地系统的α多样性高于平地系统, 丰水年份平地系统的α和γ多样性高于坡地系统, 而地形对β多样性并没有显著影响; (2)随着放牧强度的增加, 平地和坡地的α多样性均呈逐渐下降的趋势, 不同植物群落成员型(优势种、常见种和稀有种)对放牧的响应及其对α多样性的贡献不同, 其中稀有种对α多样性的贡献最大, 常见种次之, 优势种最小; (3) γ多样性对放牧强度的响应受地形条件的影响, 随着放牧强度的增加, 平地γ多样性呈逐渐下降的趋势, 而坡地γ多样性呈现先减少后增加的趋势; (4)平地β多样性随放牧强度的增加而逐渐减小, 而坡地并没有明显的规律。该研究表明, 植物多样性对放牧的响应受降水和地形因素的调控, 平地对放牧的缓冲能力强于坡地, 干旱会加剧过度放牧对生物多样性的影响; 稀有种对于草地生态系统的多样性维持具有重要意义。因此, 在确定合理的放牧强度时, 应结合降水和地形条件。在平水年份需加强平地系统植物多样性的保护, 而在丰水年份需加强坡地系统植物多样性的保护, 从而实现草地资源的可持续性利用。
Biodiversity alleviates the decrease of grassland multifunctionality under grazing disturbance: a global meta-analysis
DOI:10.1111/geb.13408 URL [本文引用: 1]
Effects of grassland utilization on the functional traits of dominant plants in a temperate typical steppe
DOI:10.17521/cjpe.2020.0373 URL [本文引用: 1]
草地利用方式对温性典型草原优势种植物功能性状的影响
DOI:10.17521/cjpe.2020.0373
[本文引用: 1]
当外界环境发生变化后植物能够改变自身功能性状及时调整适应策略, 因此植物功能性状能够有效地反映植物对草地利用变化的响应, 然而在内蒙古草原从植物功能性状角度开展草地利用方式影响的研究略少。该研究以内蒙古典型草原大针茅(Stipa grandis)、羊草(Leymus chinensis)、糙隐子草(Cleistogenes squarrosa)和冷蒿(Artemisia frigida) 4种主要优势种为研究对象, 探讨在长期自由放牧、割草、短期围封和长期无干扰的影响下优势种植物功能性状的差异, 以期从功能性状视角, 揭示植物在受到外界干扰后的适应策略, 旨为天然草地的可持续管理提供基础数据支持和科学依据。结果表明: 1)除糙隐子草外, 在长期放牧后内蒙古典型草原优势植物植株高度、根长和植物碳氮含量降低, 这些性状的变化能够使植物个体小型化, 适口性降低, 表明植物通过逃避放牧的策略适应长期自由放牧的干扰; 在割草管理方式下, 优势种的高度和比叶面积有增加的趋势, 其中冷蒿的氮含量对割草响应最敏感, 其根、茎、叶中的氮含量均在割草样地最低; 围封和长期无干扰处理下植物的碳氮含量增加, 表明在干扰强度降低后, 植物通过功能性状的改变从资源获取策略向资源储藏策略转变。2)对优势种功能性状集合分析表明, 糙隐子草具有较低的植株高度和较高的比叶面积, 冷蒿具有较高的木质素含量和氮含量, 这些性状能够使两种植物被家畜采食量减少, 并保证其具有较强的再生能力, 这可能是糙隐子草和冷蒿耐牧的原因; 大针茅具有最高的植株高度、最大的叶片干物质含量, 以及最高的茎、叶纤维素含量, 说明大针茅是非常典型的竞争物种, 在干扰较低的条件下, 大针茅采取竞争策略对其他物种产生较大的竞争压力可能是其占优势的重要原因。
Research progresses of plant-herbivore interactions
DOI:10.17521/cjpe.2020.0001 URL [本文引用: 1]
植物-植食性动物相互关系研究进展
DOI:10.17521/cjpe.2020.0001
[本文引用: 1]
植物光合作用固定下来的能量沿食物链首先流向相邻营养级的植食性动物。植物-植食性动物相互关系是自然界中最普遍、最重要的一种种间关系, 是食物网理论的基础与核心。该文从植食性动物对植物个体、种群和群落特征的影响, 以及植物在个体、种群和群落3个水平上对植食性动物的防御机制与策略两方面, 综述了当前植物-植食性动物相互关系的研究进展。植食性动物的采食, 可以显著改变植物个体或种群的生长、繁殖和存活率, 植物种群的变化则进一步反馈于植物群落组成和多样性特征。相应地, 植物在个体、种群和群落水平形成了一系列的防御机制, 其中在个体和种群水平以化学与物理防御为主, 而群落水平则是通过影响动物的行为或天敌而实现的。该文对相关领域的重要假说和理论进行了介绍、比较。最后, 该文提出了植物-植食性动物相互关系研究的未来发展趋势。随着全球变化和人类活动对自然系统干扰的加剧, 在不同的时空尺度上探索这些干扰如何影响动植物关系, 以及这些影响如何反馈于生态系统的结构、功能和稳定性, 不但有重要的理论意义, 也将为未来制定合理的生态系统管理政策提供实际支撑。
