传粉昆虫是生物多样性的重要组成部分, 它们为植物提供传粉服务, 在维持遗传多样性、提高结实率等方面具有重要意义(Black et al, 2011)。广义的蜜蜂包括了蜜蜂总科的全部种类, 它们为地球上超过75%的被子植物传粉, 是最重要的传粉昆虫(Ollerton et al, 2011; Khalifa et al, 2021)。相较于其他传粉昆虫, 大部分蜜蜂因具有密集且分叉的体毛, 以及后足的携粉结构而具有更强的携粉能力(Michener, 2007)。据报道, 蜜蜂总科近2万种, 其中被驯养的仅有少数几种, 如西方蜜蜂(Apis melli- fera)、东方蜜蜂(A. cerana)和欧洲熊蜂(Bombus terrestris)等, 而绝大部分种类都是野生蜜蜂(Mich- ener, 2007)。野生蜜蜂通常受生存环境等因素影响而具有不同的生活习性, 并且与蜜(粉)源植物存在长期的协同适应, 提供着不可替代的传粉服务(Fenster et al, 2004)。
随着气候变化、物种入侵, 以及牧业生态系统管理实践活动等加剧, 蜜蜂种类和数量急剧下降(Kluser & Peduzzi, 2007; Stokstad, 2007; Potts et al, 2010; Meeus et al, 2018)。Bartomeus等(2013)对美国近500种蜜蜂的研究发现, 几乎所有蜜蜂种群数量都存在不同程度的降低, 其中熊蜂属(Bombus)物种的种群数量下降最为显著。虽然欧美以外地区的传粉昆虫监测数据较为薄弱, 但全球范围内野生和驯化的传粉昆虫种群数量下降是普遍存在的(Wagner, 2020)。传粉昆虫的减少可能导致传粉服务的丧失, 从而影响粮食安全、生物多样性的维持以及生态系统稳定性(Powney et al, 2019)。
放牧是一种普遍的草地利用方式, 地球上近25%的陆地被用于放牧(Ramankutty et al, 2008; Ma et al, 2019)。畜牧业是牧民最主要的收入来源, 放牧不仅可以为人类提供生活及生产所必备的肉、奶和皮毛制品, 而且还被作为促进生物多样性和维持栖息地稳定的有效管理措施(Pykälä, 2000)。合理放牧施加的干扰对维持一个以草本植物为主的群落有积极作用, 同时也能够维持群落内更多样的传粉者, 并为传粉者提供更多的潜在筑巢资源(Black et al, 2011)。然而, 放牧行为通常仅在较低至中等水平时有益, 过度放牧则对生态系统和畜牧业产生不利影响。牲畜过度取食可导致群落植被高度和生物量降低、植物多样性锐减、植物组成变化和土壤条件变化(如践踏作用、粪便沉积)等一系列的环境和生态问题(Enri et al, 2017), 这些改变会影响蜜蜂的食物(花粉和花蜜)和筑巢资源, 并进而影响传粉者的种群动态和多样性(Moreira et al, 2019; Wagner, 2020)。研究表明, 在北美和中国北方草地, 过度放牧已对生物多样性和生态系统功能产生较大威胁(Kimoto et al, 2012; 高二亮等, 2020)。
1 放牧对蜜蜂的影响途径
1.1 放牧改变植物群落花报酬资源
由于群落中不同植物的生活史特征、营养水平以及对植食者防御能力等不同, 牲畜取食对蜜蜂的影响存在差异。Díaz等(2007)对世界不同牧场植物组成的研究发现, 放牧对多年生、植株高大和直立生长的植物具有更高的不利影响。在大部分牧场中, 放牧可能会导致适口植物多度和多样性降低或局域灭绝, 而物理和化学防御作用较强的非适口植物则逐渐泛滥和扩张(Vázquez & Simberloff, 2003; Mayer et al, 2006; Vavra et al, 2007; Zhao et al, 2021)。群落中植物组成的改变会导致花报酬发生相应的变化。植物花粉和花蜜是蜜蜂成虫和幼虫的能量来源(Kevan & Baker, 1983), 多项研究发现, 花报酬资源与蜜蜂多度和多样性正相关, 是影响蜜蜂在群落中种群变化的重要因素(Sárospataki et al, 2009; Roulston & Goodell, 2011)。研究表明花报酬的多度及组成的改变会影响蜜蜂访花行为(Hatfield & LeBuhn, 2007; Franzén & Nilsson, 2010; Roulston & Goodell, 2011)。当牲畜偏好取食禾本科等非虫媒植物时, 对蜜蜂产生的影响较小(Lázaro et al, 2016a; Tadey, 2016; Odanaka & Rehan, 2019)。而当牲畜偏好取食虫媒植物时, 可对蜜蜂产生多方面的负面影响。首先, 牲畜取食作用可能改变植物的开花物候, 导致植物和传粉者时间错配, 从而影响蜜蜂访花(Tadey, 2020)。其次, 蜜蜂偏向于不访问刚被牲畜取食过的植物的花, 因此牲畜高强度的取食对蜜蜂访花频率产生较强的不利影响(Bronstein et al, 2007)。再次, 牲畜取食可能通过影响植物的植株高度和花报酬多度而影响蜜蜂在单位时间内的报酬获取量(Davidson et al, 2020)。虽然一部分蜜蜂可以访问多种开花植物, 能够通过访问群落内其他植物缓解放牧带来的不利影响, 但如果这些植物花报酬量较低或存在花部特征限制, 则依旧会使蜜蜂取食效率下降(Zhao et al, 2022)。
蜜蜂获取花报酬数量和质量的降低会导致资源受限, 进而影响种群动态。由于专性取食的蜜蜂依靠少数植物提供报酬, 它们受放牧的不利影响可能高于取食多种植物的蜜蜂。据报道, 世界不同地区约有15%-60%的蜜蜂是专性取食者, 放牧可能导致这些蜜蜂多样性快速降低(Minckley & Roulston, 2006)。但也有研究发现, 广食性蜜蜂也会受到食物短缺的不利影响。例如, 壁蜂(Osmia lignaria)受到资源不足的影响会使子代数量降低(Williams & Kremen, 2007)。花资源不足还会导致熊蜂产生更少且更小的工蜂个体(Pelletier & McNeil, 2003; Westphal et al, 2009)。另外, 蜜蜂幼虫营养不足会降低其对真菌、细菌和病毒疾病的抵抗能力, 存活率降低(Di Pasquale et al, 2013)。
1.2 放牧改变巢穴资源
图1
图1
蜜蜂总科主要类群筑巢环境。黑色方格: 蜜蜂可以使用的筑巢地点; 白色方格: 蜜蜂不可以使用的筑巢地点。数据来自Michener (2007)和Harmon-Threatt (2020)。
Fig. 1
The nesting sites of the main groups in Apoidea. Black cells: The nesting sites can be used by the bee genus; white cells: The nesting sites cannot be used by the bee genus. Data from Michener (2007) and Harmon-Threatt (2020).
蜜蜂的巢穴资源是有限的, 放牧可通过影响巢穴资源进而对蜜蜂产生影响。大部分在土壤中挖土筑巢的蜜蜂需要裸露的土地。已有研究发现, 在土壤中筑巢蜜蜂的多度和裸地的面积成正相关(Sardiñas & Kremen, 2014)。放牧活动中动物的啃食和践踏会导致植被盖度降低, 创造出新的裸露土地促进蜜蜂在土中筑巢(Vulliamy et al, 2006; Murray et al, 2012)。但牲畜的践踏作用也会压实土壤或直接破坏巢穴, 对蜜蜂筑巢不利(Murray et al, 2012)。例如, 放牧的践踏导致蜜蜂巢穴受损, 使成虫失去遮蔽所、幼虫直接死亡(Sjödin, 2007; Tadey, 2015; Lázaro et al, 2016a)。据报道, 在德国石灰质的草地上, 壁蜂(Osmia spp.)利用空的蜗牛壳建造巢穴, 但牲畜的踩踏会导致超过1/3的蜂巢受损(Hopfenmüller et al, 2020)。
放牧对利用土壤中已有洞穴筑巢的蜜蜂的不利影响可能更大。熊蜂属大部分物种在兔形目和啮齿目动物废弃的巢穴中筑巢。切叶蜂科的壁蜂属(Osmia)、拟孔蜂属(Hoplitis)、黄斑蜂属(Anthidium)、裂爪蜂属(Chelostoma), 以及分舌蜂科叶舌蜂属(Hylaeus)的部分物种依靠土壤中已有的虫洞筑巢。在对美国加州牧场的研究发现, 蜜蜂的多度和已有洞穴的数目正相关(McFrederick & LeBuhn, 2006), 但羊的踩踏使多数废弃的洞穴不能被蜜蜂用于筑巢(Sugden, 1985)。如果放牧使植物结实率降低, 会导致以植物种子为食的鼠类和昆虫洞穴减少, 从而使蜜蜂潜在可用巢穴资源降低。对于利用植物茎秆或树枝筑巢的蜜蜂, 由于其巢穴相比土中的巢穴更易暴露, 牲畜的踩踏和啃食行为对巢穴产生的影响可能更大(Potts et al, 2009; Roulston & Goodell, 2011)。此外, 一些在土中和植物上筑巢的蜜蜂还需要叶片和树脂等作为筑巢材料, 放牧导致这些资源缺乏进而对蜜蜂产生不利影响(Gess & Gess, 1993)。
2 放牧对蜜蜂的影响在不同研究中存在差异
表1 草地群落中放牧对蜜蜂多度和多样性的影响研究案例。放牧对蜜蜂多度和多样性存在正面(+)、中性(0)或负面影响(-)。
Table 1
| 研究区域 Study area | 牲畜种类 Livestock species | 蜜蜂类群 Functional groups of bees | 放牧对蜜蜂 多度的影响 Effect of grazing on bee abundance | 放牧对蜜蜂物种 丰富度的影响 Effect of grazing on bee richness | 文献 Reference |
|---|---|---|---|---|---|
| 美国西北部 Northwest United States | 牛 Cattle | 熊蜂 Bumblebees | - | - | Kimoto et al, 2012 |
| 美国西北部 Northwest United States | 牛 Cattle | 独栖性蜜蜂 Solitary bees | 0 | 0 | Kimoto et al, 2012 |
| 美国中西部 Midwest United States | 牛 Cattle | 蜜蜂总科物种 Apoidea | 0 | 0 | Stein et al, 2020 |
| 美国西南部 Southwest United States | 牛、羊 Cattle, sheep | 熊蜂 Bumblebees | 0 | - | Hatfield & LeBuhn, 2007 |
| 美国西南部 Southwest United States | 牛 Cattle | 蜜蜂总科物种 Apoidea | - | 0 | Minckley, 2014 |
| 美国西部 Western United States | 牛 Cattle | 蜜蜂总科物种 Apoidea | - | 0 | Kearns & Oliveras, 2009 |
| 英国威尔士 Wales, UK | 牛、马、羊 Cattle, ponies, sheep | 蜜蜂总科物种 Apoidea | - | - | Davidson et al, 2020 |
| 德国北部 Northern Germany | 牛 Cattle | 蜜蜂总科物种 Apoidea | + | - | Kruess & Tscharntke, 2002 |
| 德国西北部 Northwest Germany | 羊 Sheep | 独栖性蜜蜂 Solitary bees | 0 | 0 | Steffan-Dewenter & Leschke, 2003 |
| 匈牙利东南部 Southeast Hungary | 牛 Cattle | 蜜蜂总科物种 Apoidea | 0 | 0 | Batáry et al, 2010 |
| 瑞典中部 Central Sweden | 牛 Cattle | 蜜蜂总科物种 Apoidea | 0 | 0 | Sjödin, 2007 |
| 中国西南部 Southwest China | 牦牛 Yak | 熊蜂 Bumblebees | - | - | Xie et al, 2008 |
2.1 不同生境中放牧对蜜蜂的作用
不同生境中由于降水和土壤等环境因子的差异, 植物多样性、组成和植被有所不同, 对放牧可能存在不同的响应。放牧对植物物种的影响随着群落中降水量(或生产力)的增加而增加(Cingo-lani et al, 2005; Lezama et al, 2014)。干旱地区植物对放牧的抵抗能力更强, 可能与其植株矮小、地下生物量比例高、具基部分生组织和较高的分枝密度等特征相关(Herms & Mattson, 1992)。放牧通过影响植物而间接影响与其发生相互作用的蜜蜂, 这种影响可能在高降水地区更大(Thapa-Magar et al, 2022)。已有研究发现, 湿润生境中放牧对蜜蜂多度和多样性的不利影响高于半干旱的生境(Herrero-Jauregui & Oesterheld, 2018)。在蒙古国东部半干旱地区, 高强度放牧虽然导致植物减少, 但对植物-传粉者物种互作数目没有显著负面影响(Yoshihara et al, 2008)。干旱地区蜜蜂受放牧的影响更小还可能与蜜蜂巢穴资源受到放牧影响较小有关。相比高降水牧场, 干旱地区牧场中较低的土壤含水量使其难以被牲畜践踏而压实, 这对在土壤中筑巢的蜜蜂更加有利(El-Swaify et al, 1985)。
2.2 不同放牧历史草地中放牧对蜜蜂的影响
放牧对蜜蜂的影响程度会受到草地和牲畜局部适应历史的影响。经历了牲畜长期取食的草场适牧性和耐牧性较高, 不会轻易被牲畜破坏。研究发现, 在被用作牧场使用的时间久远的草地, 植物可以通过快速再生的形式提高耐受性, 或以匍匐生长或提高二氧化硅含量的形式进行防御(Díaz et al, 2007)。对牲畜啃食有长期适应的草地, 群落的稳定会确保蜜蜂等种群不会发生剧烈的波动(Newbold et al, 2014)。对美国不同牧场的研究表明, 北美大平原相比其他牧区放牧历史更久, 放牧对传粉者的不利影响较小(Glenny et al, 2022)。如果草地和牲畜的演化史较短, 那么牲畜对草地生态群落是极大的威胁(Debano, 2006; Thapa-Magar et al, 2022)。
2.3 不同牲畜种类放牧对蜜蜂的影响
牛和羊是草地中最常见的反刍动物, 虽然二者消化系统类型相似, 但由于它们在体型大小、瘤胃容积、取食灵活性和取食偏好上存在差异, 会对草地植物群落和蜜蜂产生不同影响(Hanley, 1982)。羊在取食过程中能够更好地区分植物, 并偏好取食虫媒植物, 羊会优先选择植株上最有营养的花、果实和嫩枝(Rook et al, 2004; Redpath et al, 2010; Dumont et al, 2011; Ginane et al, 2015)。而牛对植物的取食偏好性较低, 并会取食更高比例的风媒植物, 如禾草等(Cutter et al, 2021)。另外, 羊在植物很矮的情况下依然可以取食, 而牛难以取食低矮的植物(Rook et al, 2004)。因此, 以牛为主和以羊为主放牧导致植物组成存在差异(Dumont et al, 2011)。多项研究发现, 牧羊对蜜蜂多度、物种丰富度和功能多样性的不利影响均大于牧牛(Dumont et al, 2011; Enri et al, 2017; Glenny et al, 2022)。例如, 对美国西部内华达州和中部北达科他州牧场的研究均发现, 牧羊相比牧牛对花多度、蜜蜂多度和蜜蜂多样性均有更强的负面影响(Hatfield & LeBuhn, 2007; Cutter et al, 2021)。有研究还发现, 在降水合适的年份, 牛可以通过抑制禾草和促进虫媒植物的生长, 使得蜜蜂受益于放牧(Kaminer et al, 2010; Enri et al, 2017)。
2.4 不同放牧强度和放牧季节的影响
同一牧区即使牲畜种类相同, 但如果放牧强度存在差异, 对蜜蜂的影响也可能不同。根据中度干扰假说(intermediate disturbance hypothesis), 在中度放牧压力下, 由于牲畜对优势植物和多年生植物的抑制作用, 给竞争能力较弱植物创造出开放的空间, 可以形成一个物种更丰富的植物群落(Tadey, 2016; Wang & Tang, 2019; Gao & Carmel, 2020)。在对希腊蜜蜂的研究中发现, 蜜蜂多度和物种丰富度随放牧强度呈现先升高再降低的钟状曲线关系, 符合中度干扰假说的推断(Lázaro et al, 2016b)。然而, 更多的研究发现, 放牧强度和蜜蜂多样性存在负相关(Söderström et al, 2001; Xie et al, 2008; Thapa-Magar et al, 2022)或正相关(Vulliamy et al, 2006) (表1)。正相关的结果可能是针对放牧强度低的群落, 而负相关的结果可能是针对放牧强度高的群落。因此, 后续研究应尽可能覆盖较宽的放牧强度, 这样才能准确验证中度干扰假说是否能解释放牧对蜜蜂的影响。
3 如何解决放牧对蜜蜂及其传粉植物产生的不利影响
3.1 加强对牧区蜜蜂群落的野外调查
对于蜜蜂的保护和生态修复工作, 首先应该对目标区域内蜜蜂现阶段的生存状况进行系统调查。这需要对蜜蜂种群开展长期且详尽的观测, 但以往的研究主要以蜜蜂科级水平为调查单元, 较少精确到属种水平(Hatfield & LeBuhn, 2007; Yoshihara et al, 2008; Kearns & Oliveras, 2009)。同属中的蜜蜂可能表现出不同的行为和生活史特征。例如, 熊蜂属物种可以在地面或地下筑巢, 也可以利用自身或其他熊蜂的工蜂哺育后代(盗寄生; Michener, 2007)。这些习性的差异会导致不同物种对放牧的响应不同(Sjödin, 2007)。因此, 后续对蜜蜂的调查研究应以种为单元, 这可以促进对放牧如何影响蜜蜂群落的认识, 并有针对性地制定出不同物种的保护和修复方案。目前, 我国对蜜蜂的分类学研究还较为薄弱, 已经出版的《中国动物志》中仅包括了蜜蜂科、切叶蜂科和准蜂科, 而有关地蜂科、隧蜂科和分舌蜂科的分类学资料还很缺乏(吴燕如, 2000, 2006)。另外, 为了便于生态学工作者使用, 一个地区的蜜蜂分类学信息应尽量包括物种目录、图像数据库和DNA序列库3个部分(Orr et al, 2022)。
3.2 准确评估放牧对蜜蜂多样性和传粉服务的影响
描述蜜蜂群落多样性的指数包括物种丰富度、Shannon多样性、功能多样性和系统发育多样性等, 这些指数是生物多样性不同方面的统计表现(Grab et al, 2019; Banaszak-Cibicka & Dylewski, 2021)。在放牧对蜜蜂影响研究中, 多样性指数的选择直接影响评估的可靠性。以往研究主要探讨放牧对蜜蜂物种丰富度的影响, 即认为物种丰富度和生态系统功能正相关(Davidson et al, 2020)。然而, 研究发现, 只有在物种多样性较低的群落中, 物种多样性才与生态系统功能正相关(Chapin et al, 2000)。在物种丰富度较高的群落中, 由于生态位重叠、功能冗余和种间竞争加剧, 物种丰富度和生态系统功能甚至存在负相关(Tilman et al, 1997)。因此, 仅用物种丰富度判断生态系统功能是否健康具有一定的局限性。
有研究发现, 功能多样性可以综合反映物种形态、生理和生殖等与生态系统功能相关性状的多样性, 这克服了物种丰富度指数同等对待每个物种的不足(Tilman, 2001)。另外, 系统发育多样性可以从进化维度进一步描述一个群落的生物多样性。具有较高系统发育多样性的群落能够促进更高营养级物种的维持(Wimp et al, 2005), 并加强群落对外来物种入侵和极端天气的抵御能力(Vellend et al, 2010; Cadotte et al, 2012)。如果蜜蜂的功能性状具有保守性, 维持较高的系统发育多样性还能保证群落有较高的功能多样性(Mouquet et al, 2012; Srivastava et al, 2012)。已有研究发现, 蜜蜂对环境变化的耐受性与其功能性状和系统发育相关(Williams et al, 2010; Bartomeus et al, 2013)。在健康群落中, 具有不同功能性状远缘物种的共存有利于资源利用和生态系统稳定性。而在退化群落中, 具有相似功能性状的近缘物种可能同时灭绝, 导致功能多样性和系统发育多样性显著降低。虽然功能多样性和系统发育多样性与生态系统功能之间具有更强的相关性(Winfree et al, 2018), 可以作为评估放牧对蜜蜂多样性影响更可靠的指标, 但目前的相关研究还很不足。
由于蜜蜂和植物间的互作蕴含传粉这一关键的生态系统功能, 物种互作也可以作为评估放牧对蜜蜂影响的核心指标之一(Cariveau et al, 2020; Genes & Dirzo, 2022)。近年来一些开创性的研究指出, 传粉网络不仅包含植物和传粉者物种丰富度信息, 还包括物种间的相互作用, 因此可以作为评估生态系统稳定性更可靠的综合性指标(Harvey et al, 2017; Moreno-Mateos et al, 2020)。传粉网络的结构特征会影响其对外部干扰的反应方式。传粉网络中物种间由于常存在弥散性协同进化关系, 而具有较高的嵌套结构(Bascompte & Jordano, 2007)。传粉网络的这一属性赋予了群落抵御干扰的能力, 但在退化生态系统中嵌套结构则变弱或消失(Kaiser-Bunbury & Blüthgen, 2015)。已有实验研究表明, 放牧会使物种相互作用发生重排, 并导致整个传粉网络结构发生改变(Vázquez & Simberloff, 2003; Elwell et al, 2016)。
虽然功能多样性、系统发育多样性和生态网络物种互作多样性研究相比物种丰富度的统计要困难得多, 但应用这些指数可以综合考虑到物种之间的进化、功能性状、生态位重叠和功能冗余, 能够更好地反映蜜蜂多样性随放牧强度增加的变化规律。但值得注意的是, 如果不同群落降雨量、放牧历史和牲畜组成等因素存在较大差异, 那么会存在不同的放牧强度-蜜蜂多样性的变化。在我国, 北方和南方草地在自然环境、群落外貌、用作牧场使用的时间和物种多样性等方面存在明显不同, 因此放牧对蜜蜂的影响可能不同。今后需要加强放牧对我国南北方草地的比较研究, 以期更深刻地认识蜜蜂多样性丧失机制。
3.3 放牧导致退化草地中蜜蜂生态修复策略的制定
对于放牧导致蜜蜂丧失的草地, 生态修复能够顺利实施需要降低高牧压带来的不利影响。草地具有一定的自我修复能力, 植物物种可以通过土壤种子库或附近群落中种子的自然散布进行修复, 蜜蜂也可以从相邻群落扩散实现多样性提升。如果草地退化程度较低, 蜜蜂可在放牧压力减少的情况下实现自我修复。降低放牧压力可以通过一系列放牧管理措施实现, 包括控制牲畜种类(如提高牛而降低羊的比例)、控制放牧时间(如轮牧和季节性休牧)、控制载畜量等措施。围栏封育是降低放牧不利影响最经济且便捷的自然再生措施。研究发现, 花期围封禁牧和轮牧可显著提升群落内的花多度, 为蜜蜂和其他传粉昆虫提供更丰富的花粉和花蜜报酬, 从而促进其种群的修复(Scohier et al, 2013; Enri et al, 2017)。另外, 在一个区域内设置部分中等放牧草地和部分围封禁牧草地可增加生境异质性, 对蜜蜂多样性修复更为有利(Shapira et al, 2020)。
如果放牧对蜜蜂的影响较为严重, 可以在降低放牧干扰的基础上通过辅助再生的人为干预手段进行生态修复(Gann et al, 2019)。大量研究发现, 放牧导致的食物缺乏是限制蜜蜂生态修复的重要因素(Xie et al, 2008; Davidson et al, 2020)。因此, 蜜蜂的生态修复可以通过在局域和地区水平补充食物资源实现(Haaland et al, 2011; Roulston & Goodell, 2011; Pywell et al, 2012; Baldock et al, 2019)。在耕地边界人工种植树篱和野花带以增强蜜蜂和其他传粉昆虫多样性是一种有效措施, 已经在欧洲多个国家农作物种植区实施(Haaland et al, 2011; Scheper et al, 2015)。蜜蜂修复程度和所种植植物的物种组成密切相关。研究发现, 群落中少数几种植物大面积开花就能维持较高的蜜蜂多样性, 因此增加蜜蜂偏好取食的植物的开花多度, 而非单纯增加植物多样性对蜜蜂种群修复更加有利(Carvell et al, 2007)。豆科植物是优质的蜜源和粉源植物, 是欧洲人工播种促进独栖性蜜蜂和熊蜂生态修复的首选物种(Scheper et al, 2015)。然而, 不同群落蜜蜂组成不同, 访花偏好也存在差异, 同一植物种植组合方案很难适用于所有群落。因此, 需要对计划种植的植物进行有针对性的筛选和组合才能实现更高效的修复。需要关注的是对传粉网络中物种担任角色进行分析可以甄别出群落中对蜜蜂多样性维持起关键作用的枢纽植物。枢纽植物的种群动态控制着蜜蜂群落的动态, 因此在修复计划中应优先考虑。由于一个花期内不同种蜜蜂成虫访花时间存在差异, 种植植物的选择还需考虑其开花时间和花期长度, 从而确保蜜蜂在不同花期均能获得足够的食物(Pywell et al, 2005; Pywell et al, 2006; Potts et al, 2009)。
巢穴资源是另一个维持蜜蜂多度和多样性的关键因素, 但相比增加食物资源, 蜜蜂生态修复还未受到足够关注(Harmon-Threatt, 2020)。大多数野生蜜蜂都是在土壤中筑巢(Michener, 2007), 因此其生态修复可以通过为蜜蜂提供更适合的筑巢地点实现, 如提供更多暴露在高温和高光照条件下的干燥土壤。对于在植物上筑巢的蜜蜂, 则可以提供枯木和巢管等“蜜蜂旅馆”提升筑巢资源(Buckles & Harmon-Threatt, 2019; Harmon-Threatt, 2020)。已有研究表明, 为蜜蜂创造这些筑巢生境会促进蜜蜂多度和多样性快速修复(Hernandez et al, 2009; Pawelek et al, 2009)。瑞士实行的农业环境改善计划会在农田附近保留面积不低于7%的生态保护区用于蜜蜂筑巢, 此项措施对独居蜂和蜜蜂的种群修复有积极效果(Albrecht et al, 2007)。
4 结语
过度放牧导致的传粉者丧失在全球范围内普遍发生。近年来, 生态修复因可以缓解和扭转栖息地丧失和生物多样性下降而受到国内外学者的广泛关注(Perring et al, 2015)。我国草地占土地面积的41.7%, 而其中90%由于过度放牧和过度耕种等的影响发生退化(Waldron et al, 2010)。实施全国草地群落保护和修复意义重大。本研究认为蜜蜂是草原生态系统中重要的传粉昆虫, 应作为一个重要的生态修复目标。在过度放牧草地上, 蜜蜂群落修复应该如何设计并实施, 首先要评估放牧对蜜蜂多样性的影响程度。本研究建议优先分析功能多样性、系统发育多样性, 以及传粉网络这些与生态系统功能密切相关的特征, 因为这些特征能够更加准确地研究蜜蜂多样性随放牧强度增加的变化规律。退化程度较低的草地群落可以通过有效的放牧管理, 利用生态系统的自身复原力实现蜜蜂群落的逐步修复。退化严重的草地因其自我修复能力较低, 则需要在实行放牧管理的基础上通过人为干预的辅助再生策略加速生态修复进程。补播草种增加群落中粉源和蜜源植物多度的辅助措施可作为首选。蜜蜂的生态修复还可以通过为其提供更适合的筑巢资源实现: 对于在土壤中筑巢的蜜蜂, 为其提供更多暴露在高温和高光照条件下的干燥土壤; 对于利用植物筑巢的蜜蜂, 提供巢管和枯木等筑巢资源。植物的筛选和组合要综合考虑其在传粉网络中的角色, 花特征、花期物候等因素, 确保蜜蜂在不同花期均能获得足够的食物。我国幅员辽阔, 对不同地区代表性草地类型制定有针对性的蜜蜂修复策略, 对草地群落健康发展将产生积极影响。
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Effects of grazing intensity, habitat area and connectivity on snail-shell nesting bees
DOI:10.1016/j.biocon.2020.108406 URL [本文引用: 1]
Integrating network ecology with applied conservation: A synthesis and guide to implementation
An assessment of short-term cattle grazing effects on honeybee forage potential in Mediterranean rangelands
Environmental factors affecting bee diversity in urban and remote grassland plots in Boulder, Colorado
DOI:10.1007/s10841-009-9215-4 URL [本文引用: 2]
Insects as flower visitors and pollinators
DOI:10.1146/ento.1983.28.issue-1 URL [本文引用: 1]
Overview of bee pollination and its economic value for crop production
DOI:10.3390/insects12080688
URL
[本文引用: 1]
Pollination plays a significant role in the agriculture sector and serves as a basic pillar for crop production. Plants depend on vectors to move pollen, which can include water, wind, and animal pollinators like bats, moths, hoverflies, birds, bees, butterflies, wasps, thrips, and beetles. Cultivated plants are typically pollinated by animals. Animal-based pollination contributes to 30% of global food production, and bee-pollinated crops contribute to approximately one-third of the total human dietary supply. Bees are considered significant pollinators due to their effectiveness and wide availability. Bee pollination provides excellent value to crop quality and quantity, improving global economic and dietary outcomes. This review highlights the role played by bee pollination, which influences the economy, and enlists the different types of bees and other insects associated with pollination.
Short-term responses of native bees to livestock and implications for managing ecosystem services in grasslands
Global Pollinator Decline: A Literature Review
Grazing intensity and the diversity of grasshoppers, butterflies, and trap-nesting bees and wasps
Effects of grazing intensity on pollinator abundance and diversity, and on pollination services
DOI:10.1111/een.2016.41.issue-4 URL [本文引用: 2]
Moderation is best: Effects of grazing intensity on plant-flower visitor networks in Mediterranean communities
DOI:10.1890/15-0202 URL [本文引用: 1]
Variation of grazing-induced vegetation changes across a large-scale productivity gradient
DOI:10.1111/jvs.12053 URL [本文引用: 1]
Quantifying grazing intensity using remote sensing in alpine meadows on Qinghai-Tibetan Plateau
DOI:10.3390/su11020417
URL
[本文引用: 1]
Remote sensing data have been widely used in the study of large-scale vegetation activities, which have important significance in estimating grassland yields, determining grassland carrying capacity, and strengthening the scientific management of grasslands. Remote sensing data are also used for estimating grazing intensity. Unfortunately, the spatial distribution of grazing-induced degradation remains undocumented by field observation, and most previous studies on grazing intensity have been qualitative. In our study, we tried to quantify grazing intensity using remote sensing techniques. To achieve this goal, we conducted field experiments at Gansu Province, China, which included a meadow steppe and a semi-arid region. The correlation between a vegetation index and grazing intensity was simulated, and the results demonstrated that there was a significant negative correlation between NDVI and relative grazing intensity (p < 0.05). The relative grazing intensity increased with a decrease in NDVI, and when the relative grazing intensity reached a certain level, the response of NDVI to relative grazing intensity was no longer sensitive. This study shows that the NDVI model can illustrate the feasibility of using a vegetation index to monitor the grazing intensity of livestock in free-grazing mode. Notably, it is feasible to use the remote sensing vegetation index to obtain the thresholds of livestock grazing intensity.
The importance of monkey beetle (Scarabaeidae: Hopliini) pollination for Aizoaceae and Asteraceae in grazed and ungrazed areas at Paulshoek, Succulent Karoo, South Africa
DOI:10.1007/s10841-006-9006-0 URL [本文引用: 1]
Are urban parks refuges for bumble bees Bombus spp. (Hymenoptera: Apidae)?
DOI:10.1016/j.biocon.2005.11.004 URL [本文引用: 1]
Interaction effects of different drivers of wild bee decline and their influence on host-pathogen dynamics
DOI:S2214-5745(17)30180-3
PMID:29764653
[本文引用: 1]
Wild bee decline is a multi-factorial problem, yet it is crucial to understand the impact of a single driver. Hereto the interaction effects of wild bee decline with multiple natural and anthropogenic stressors need to be clear. This is also true for the driver 'pathogens', as stressor induced disturbances of natural host-pathogen dynamics can unbalance settled virulence equilibria. Invasive species, bee domestication, habitat loss, climate changes and insecticides are recognized drivers of wild bee decline, but all influence host-pathogen dynamics as well. Many wild bee pathogens have multiple hosts, which relaxes the host-density limitation of virulence evolution. In conclusion, disturbances of bee-pathogen dynamics can be compared to a game of Russian roulette.Copyright © 2018. Published by Elsevier Inc.
Maintenance of richness despite reduced abundance of desert bees (Hymenoptera: Apiformes) to persistent grazing
DOI:10.1111/icad.2014.7.issue-3 URL [本文引用: 1]
A meta-analysis of herbivore effects on plant attractiveness to pollinators
The long-term restoration of ecosystem complexity
Ecophylogenetics: Advances and perspectives
Local-scale factors structure wild bee communities in protected areas
DOI:10.1111/jpe.2012.49.issue-5 URL [本文引用: 2]
Community responses of arthropods to a range of traditional and manipulated grazing in shortgrass steppe
DOI:10.1603/EN12333
PMID:24780073
[本文引用: 1]
Responses of plants to grazing are better understood, and more predictable, than those of consumers in North American grasslands. In 2003, we began a large-scale, replicated experiment that examined the effects of grazing on three important arthropod groups-beetles, spiders, and grasshoppers-in shortgrass steppe of north-central Colorado. We investigated whether modifications of the intensity and seasonality of livestock grazing alter the structure and diversity of macroarthropod communities compared with traditional grazing practices. Treatments represented a gradient of grazing intensity by cattle and native herbivores: long-term grazing exclosures; moderate summer grazing (the traditional regime); intensive spring grazing; intensive summer grazing; and moderately summer-grazed pastures also inhabited by black-tailed prairie dogs (Cynomys ludovicianus Ord). Beetles and spiders were the most common groups captured, comprising 60% and 21%, respectively, of 4,378 total pitfall captures. Grasshopper counts were generally low, with 3,799 individuals observed and densities <4 m(-2). Two years after treatments were applied, vegetation structure differed among grazing treatments, responding not only to long-term grazing conditions, but also to the short-term, more-intensive grazing manipulations. In response, arthropods were, in general, relatively insensitive to these grazing-induced structural changes. However, species-level analyses of one group (Tenebrionidae) revealed both positive and negative effects of grazing treatments on beetle richness and activity-density. Importantly, these responses to grazing were more pronounced in a year when spring-summer rainfall was low, suggesting that both grazing and precipitation-which together may create the greatest heterogeneity in vegetation structure-are drivers of consumer responses in this system.
Impact indicators: Effects of land use management on functional trait and phylogenetic diversity of wild bees
DOI:10.1016/j.agee.2019.106663 URL [本文引用: 2]
How many flowering plants are pollinated by animals?
DOI:10.1111/more.2010.120.issue-3 URL [本文引用: 1]
A review of global trends in the study types used to investigate bee nesting biology
DOI:10.1016/j.baae.2022.03.012 URL [本文引用: 1]
Modification of a community garden to attract native bee pollinators in urban San Luis Obispo, California
The effect of food supplementation on reproductive success in bumblebee field colonies
DOI:10.1034/j.1600-0706.2003.12592.x URL [本文引用: 1]
Advances in restoration ecology: Rising to the challenges of the coming decades
Enhancing pollinator biodiversity in intensive grasslands
DOI:10.1111/jpe.2009.46.issue-2 URL [本文引用: 2]
Declines of managed honey bees and beekeepers in Europe
DOI:10.3896/IBRA.1.49.1.02 URL [本文引用: 2]
Widespread losses of pollinating insects in Britain
DOI:10.1038/s41467-019-08974-9
PMID:30914632
[本文引用: 1]
Pollination is a critical ecosystem service underpinning the productivity of agricultural systems across the world. Wild insect populations provide a substantial contribution to the productivity of many crops and seed set of wild flowers. However, large-scale evidence on species-specific trends among wild pollinators are lacking. Here we show substantial inter-specific variation in pollinator trends, based on occupancy models for 353 wild bee and hoverfly species in Great Britain between 1980 and 2013. Furthermore, we estimate a net loss of over 2.7 million occupied 1 km grid cells across all species. Declines in pollinator evenness suggest that losses were concentrated in rare species. In addition, losses linked to specific habitats were identified, with a 55% decline among species associated with uplands. This contrasts with dominant crop pollinators, which increased by 12%, potentially in response agri-environment measures. The general declines highlight a fundamental deterioration in both wider biodiversity and non-crop pollination services.
Mitigating human effects on European biodiversity through traditional animal husbandry
DOI:10.1046/j.1523-1739.2000.99119.x URL [本文引用: 1]
Effectiveness of new agri-environment schemes in providing foraging resources for bumblebees in intensively farmed landscapes
DOI:10.1016/j.biocon.2005.10.034 URL [本文引用: 1]
Wildlife-friendly farming benefits rare birds, bees and plants
DOI:10.1098/rsbl.2012.0367
PMID:22675140
[本文引用: 1]
Agricultural intensification is a leading cause of global biodiversity loss, especially for threatened and near-threatened species. One widely implemented response is 'wildlife-friendly farming', involving the close integration of conservation and extensive farming practices within agricultural landscapes. However, the putative benefits from this controversial policy are currently either unknown or thought unlikely to extend to rare and declining species. Here, we show that new, evidence-based approaches to habitat creation on intensively managed farmland in England can achieve large increases in plant, bee and bird species. In particular, we found that habitat enhancement methods designed to provide the requirements of sensitive target biota consistently increased the richness and abundance of both rare and common species, with 10-fold to greater than 100-fold more rare species per sample area than generalized conventional conservation measures. Furthermore, targeting landscapes of high species richness amplified beneficial effects on the least mobile taxa: plants and bees. Our results provide the first unequivocal support for a national wildlife-friendly farming policy and suggest that this approach should be implemented much more extensively to address global biodiversity loss. However, to be effective, these conservation measures must be evidence-based, and developed using sound knowledge of the ecological requirements of key species.
Providing foraging resources for bumblebees in intensively farmed landscapes
DOI:10.1016/j.biocon.2004.05.020 URL [本文引用: 1]
Farming the planet. 1. Geographic distribution of global agricultural lands in the year 2000
Crofting and bumblebee conservation: The impact of land management practices on bumblebee populations in northwest Scotland
DOI:10.1016/j.biocon.2009.11.019 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: 2]
The role of resources and risks in regulating wild bee populations
DOI:10.1146/annurev-ento-120709-144802
PMID:20822447
[本文引用: 5]
Recent declines of bee species have led to great interest in preserving and promoting bee populations for agricultural and wild plant pollination. Many correlational studies have examined the indirect effects of factors such as landscape context and land management practices and found great variation in bee response. We focus here on the evidence for effects of direct factors (i.e., food resources, nesting resources, and incidental risks) regulating bee populations and then interpret varied responses to indirect factors through their species-specific and habitat-specific effects on direct factors. We find strong evidence for food resource availability regulating bee populations, but little clear evidence that other direct factors are commonly limiting. We recommend manipulative experiments to illuminate the effects of these different factors. We contend that much of the variation in impact from indirect factors, such as grazing, can be explained by the relationships between indirect factors and floral resource availability based on environmental circumstances.
Evaluating nesting microhabitat for ground-nesting bees using emergence traps
DOI:10.1016/j.baae.2014.02.004 URL [本文引用: 1]
Factors affecting the structure of bee assemblages in extensively and intensively grazed grasslands in Hungary
DOI:10.1556/ComEc.10.2009.2.7 URL [本文引用: 1]
Local and landscape-level floral resources explain effects of wildflower strips on wild bees across four European countries
DOI:10.1111/1365-2664.12479 URL [本文引用: 2]
Herbivory and floral signaling: Phenotypic plasticity and tradeoffs between reproduction and indirect defense
DOI:10.1111/nph.12783
PMID:24684288
[本文引用: 1]
Plant defense against herbivores may compromise attraction of mutualists, yet information remains limited about the mechanisms underlying such signaling tradeoffs. Here, we investigated the effects of foliar herbivory by two herbivore species on defense compounds, floral signaling, pollinator and parasitoid attraction, and seed production. Herbivory generally reduced the quantity of many floral volatile organic compounds VOCs) in Brassica rapa. By contrast, floral color, flower diameter, and plant height remained unaffected. The decreased amounts of floral volatiles led to reduced attractiveness of flowers to pollinators, but increased the attractiveness of herbivore-infested plants to parasitoids. Plants infested with the native butterfly Pieris brassicae produced more flowers during early flowering, effectively compensating for the lower olfactory attractiveness. Herbivory by the invasive Spodoptera littoralis increased the amounts of glucobrassicanapin, and led to delayed flowering. These plants tended to attract fewer pollinators and to produce fewer seeds. Our study indicates a tradeoff between pollinator attraction and indirect defense (parasitoid attraction), which can be mitigated by reduced floral VOC emission and production of more early flowers. We suggest that this compensatory mechanism is specific to plant-herbivore associations with a coevolutionary history. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.
Is there a benefit of excluding sheep from pastures at flowering peak on flower-visiting insect diversity?
DOI:10.1007/s10841-012-9509-9 URL [本文引用: 1]
Rangeland sharing by cattle and bees: Moderate grazing does not impair bee communities and resource availability
Pollinator behavioural responses to grazing intensity
DOI:10.1007/s10531-006-9103-0 URL [本文引用: 4]
Plants, insects and birds in semi-natural pastures in relation to local habitat and landscape factors
Phylogenetic diversity and the functioning of ecosystems
DOI:10.1111/j.1461-0248.2012.01795.x
PMID:22583836
[本文引用: 1]
Phylogenetic diversity (PD) describes the total amount of phylogenetic distance among species in a community. Although there has been substantial research on the factors that determine community PD, exploration of the consequences of PD for ecosystem functioning is just beginning. We argue that PD may be useful in predicting ecosystem functions in a range of communities, from single-trophic to complex networks. Many traits show a phylogenetic signal, suggesting that PD can estimate the functional trait space of a community, and thus ecosystem functioning. Phylogeny also determines interactions among species, and so could help predict how extinctions cascade through ecological networks and thus impact ecosystem functions. Although the initial evidence available suggests patterns consistent with these predictions, we caution that the utility of PD depends critically on the strength of phylogenetic signals to both traits and interactions. We advocate for a synthetic approach that incorporates a deeper understanding of how traits and interactions are shaped by evolution, and outline key areas for future research. If these complexities can be incorporated into future studies, relationships between PD and ecosystem function bear promise in conceptually unifying evolutionary biology with ecosystem ecology.© 2012 Blackwell Publishing Ltd/CNRS.
Effects of habitat management on vegetation and above-ground nesting bees and wasps of orchard meadows in Central Europe
Evaluating native bee communities and nutrition in managed grasslands
DOI:10.1093/ee/nvaa009
PMID:32215621
[本文引用: 1]
Native pollinators are important for providing vital services in agroecosystems; however, their numbers are declining globally. Bees are the most efficient and diverse members of the pollinator community; therefore, it is imperative that management strategies be implemented that positively affect bee community composition and health. Here, we test responses of the bee and flowering plant communities to land management treatments in the context of grasslands in the upper Midwestern United States, a critical area with respect to bee declines. Twelve sites were selected to examine floral resources and wild bee communities based on three different types of grasslands: tallgrass prairie remnants, ungrazed restorations, and grazed restorations. Total bee abundance was significantly higher in ungrazed restorations than remnants, but there were no significant differences among grasslands in community composition or Shannon diversity. Across the three grassland types we also examined mass and lipid stores as nutritional health indicators in three sweat bees (Halictidae), Augochlora pura, Agapostemon virescens, and Halictus ligatus. Although there were no differences in lipid content, total average bee mass was significantly higher in Ag. virescens collected from ungrazed restorations as compared to remnants. Floral abundance of native and non-native species combined was significantly higher in grazed restorations compared to remnants and ungrazed restorations. However, ungrazed restorations had higher abundance and richness of native flowering ramets. These data suggest that bee abundance and nutrition are driven by high abundance of native flowering plant species, rather than total flowering plants.© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America.
Pollinators of Astragalus monoensis Barneby (Fabaceae): New host records; potential impact of sheep grazing
Indirect effects of grazing intensity on pollinators and floral visitation
DOI:10.1111/een.12209 URL [本文引用: 1]
Variation in insect assemblage and functional groups along a grazing gradient in an arid environment
Reshaping phenology: Grazing has stronger effects than climate on flowering and fruiting phenology in desert plants
DOI:10.1016/j.ppees.2019.125501 URL [本文引用: 1]
A meta-analysis of the effects of habitat aridity, evolutionary history of grazing and grazing intensity on bee and butterfly communities worldwide
The influence of functional diversity and composition on ecosystem processes
DOI:10.1126/science.277.5330.1300
URL
[本文引用: 1]
Humans are modifying both the identities and numbers of species in ecosystems, but the impacts of such changes on ecosystem processes are controversial. Plant species diversity, functional diversity, and functional composition were experimentally varied in grassland plots. Each factor by itself had significant effects on many ecosystem processes, but functional composition and functional diversity were the principal factors explaining plant productivity, plant percent nitrogen, plant total nitrogen, and light penetration. Thus, habitat modifications and management practices that change functional diversity and functional composition are likely to have large impacts on ecosystem processes.
Biodiversity, exotic plant species, and herbivory: The good, the bad, and the ungulate
DOI:10.1016/j.foreco.2007.03.051 URL [本文引用: 1]
Changes in interaction biodiversity induced by an introduced ungulate
DOI:10.1046/j.1461-0248.2003.00534.x URL [本文引用: 2]
Effects of genotype identity and diversity on the invasiveness and invasibility of plant populations
DOI:10.1007/s00442-009-1480-0
PMID:19865832
[本文引用: 1]
Genetic diversity within species is a potentially important, but poorly studied, determinant of plant community dynamics. Here we report experiments testing the influence of genotype identity and genotypic diversity both on the invasibility of a foundation, matrix-forming species (Kentucky bluegrass, Poa pratensis), and on the invasiveness of a colonizing species (dandelion, Taraxacum officinale). Genotypes of Kentucky bluegrass in monoculture showed significant variation in productivity and resistance to dandelion invasion, but the productivity and invasion resistance of genotypic mixtures were not significantly different from those of genotypic monocultures. Indirect evidence suggested temporal shifts in the genotypic composition of mixtures. Dandelion genotypes in monoculture showed striking and significant variation in productivity and seed production, but there was no significant tendency for these variables in mixtures to deviate from null expectations based on monocultures. However, productivity and seed production of dandelion mixtures were consistently greater than those of the two least productive genotypes, and statistically indistinguishable from those of the three most productive genotypes, suggesting the possibility of greater invasiveness of genotypically diverse populations in the long run due to dominance by highly productive genotypes. In both experiments, the identity of genotypes was far more important than genetic diversity per se.
The effects of cattle grazing on plant-pollinator communities in a fragmented Mediterranean landscape
DOI:10.1111/j.2006.0030-1299.14004.x URL [本文引用: 2]
Insect declines in the Anthropocene
DOI:10.1146/annurev-ento-011019-025151
PMID:31610138
[本文引用: 3]
Insect declines are being reported worldwide for flying, ground, and aquatic lineages. Most reports come from western and northern Europe, where the insect fauna is well-studied and there are considerable demographic data for many taxonomically disparate lineages. Additional cases of faunal losses have been noted from Asia, North America, the Arctic, the Neotropics, and elsewhere. While this review addresses both species loss and population declines, its emphasis is on the latter. Declines of abundant species can be especially worrisome, given that they anchor trophic interactions and shoulder many of the essential ecosystem services of their respective communities. A review of the factors believed to be responsible for observed collapses and those perceived to be especially threatening to insects form the core of this treatment. In addition to widely recognized threats to insect biodiversity, e.g., habitat destruction, agricultural intensification (including pesticide use), climate change, and invasive species, this assessment highlights a few less commonly considered factors such as atmospheric nitrification from the burning of fossil fuels and the effects of droughts and changing precipitation patterns. Because the geographic extent and magnitude of insect declines are largely unknown, there is an urgent need for monitoring efforts, especially across ecological gradients, which will help to identify important causal factors in declines. This review also considers the status of vertebrate insectivores, reporting bias, challenges inherent in collecting and interpreting insect demographic data, and cases of increasing insect abundance.
Grassland degradation and livelihoods in China’s western pastoral region: A framework for understanding and refining China’s recent policy responses
DOI:10.1108/17561371011078435
URL
[本文引用: 1]
China has embarked on a major concerted strategy to arrest grassland degradation and livelihood problems in the western pastoral region. The paper aims to provide a framework through which this strategy can be understood and refined into the future.
A global meta-analyses of the response of multi-taxa diversity to grazing intensity in grasslands
DOI:10.1088/1748-9326/ab4932
[本文引用: 2]
Livestock grazing is an important component and driver of biodiversity in grassland ecosystems. While numerous studies and a few meta-analyses had been conducted on the response of single taxon diversity to grazing in grasslands, a synthesis of how multi-taxa diversity is affected has been largely missing, especially reflecting its changes along a grazing intensity gradient. We performed a comprehensive meta-analyses of 116 published studies on the species richness (SR) and Shannon−Wiener index (H′) of plants, arthropods, and microbes to examine the response of biodiversity to grazing intensity in temperate grasslands globally. This quantitative assessment showed that the response of SR and H′ to grazing intensity agreed with the intermediate disturbance hypothesis in grasslands; SR and H′ increased with light and moderate grazing intensities, while they decreased at heavy intensity. In addition, plant SR increased markedly with light and moderate grazing and declined with heavy grazing intensity; however, H′ increased at light intensity and declined at moderate and heavy intensities. Moreover, the SR and H′ of microbes were enhanced at light and moderate grazing and were significantly reduced with heavy intensity. The SR and H′ of arthropods monotonously declined with increasing grazing intensity. Importantly, structural equation modeling showed that grazing resulted in enhanced plant SR mainly through its negative effects on plant biomass. Grazing had negative effects on plant coverage and arthropod abundance so that arthropod SR declined with increased grazing intensity. Moreover, increased grazing intensity caused an increase in soil pH, decrease in soil moisture, and then a decrease in microbe SR. Our findings confirm that different taxa exhibit diverse responses to changes in grazing intensity, and the way that grazing intensity affects diversity also varied with different taxa. We strongly recommend considering the requirements of multi-taxa diversity when applying grazing management and including arthropods and microbes in monitoring schemes.
Diversifying livestock promotes multidiversity and multifunctionality in managed grasslands
A study of grazing intensity in the Hulunbuir grasslands using remote sensing
基于遥感数据的呼伦贝尔草原放牧强度研究
DOI:10.11686/cyxb2016316
[本文引用: 1]
呼伦贝尔草甸草原是我国主要的畜牧业基地,放牧强度直接影响着该草原生态系统的稳定和可持续发展。本文首先建立了研究区草地地上生物量的遥感估算经验模型,然后结合净初级生产力(NPP),研究了草地放牧强度估算方法;基于该方法,利用2014年6月到7月多期Landsat遥感数据计算谢尔塔拉牧场草地地上生物量变化和放牧强度。研究结果表明:所使用方法可较好用于放牧强度的估算,估算结果与实际情况基本吻合,决定系数R<sup>2</sup>达0.7996;谢尔塔拉牧场的公共放牧区放牧强度范围为1~2.5 Au/hm<sup>2</sup>,属于过度放牧状态,重度放牧区多位于小型湖泊周围和草地面积较少但牛相对较多的生产队,轻度放牧区多位于围封地;将尺度扩展到海拉尔区分析:所使用方法能够准确地将轻度、中度和重度放牧区分开,且海拉尔区东北方向的放牧强度明显高于西南地区。
Effective mutualism between sequentially flowering plant species
DOI:10.1038/281670a0 [本文引用: 1]
Mass flowering oilseed rape improves early colony growth but not sexual reproduction of bumblebees
DOI:10.1111/jpe.2009.46.issue-1 URL [本文引用: 1]
Ecological and life-history traits predict bee species responses to environmental disturbances
DOI:10.1016/j.biocon.2010.03.024 URL [本文引用: 1]
Resource distributions among habitats determine solitary bee offspring production in a mosaic landscape
DOI:10.1890/06-0269 URL [本文引用: 1]
Plant genetic determinants of arthropod community structure and diversity
To test the hypothesis that genes have extended phenotypes on the community, we quantified how genetic differences among cottonwoods affect the diversity, abundance, and composition of the dependent arthropod community. Over two years, five major patterns were observed in both field and common-garden studies that focused on two species of cottonwoods and their naturally occurring F1 and backcross hybrids (collectively referred to as four different cross types). We did not find overall significant differences in arthropod species richness or abundance among cottonwood cross types. We found significant differences in arthropod community composition among all cross types except backcross and narrowleaf cottonwoods. Thus, even though we found similar richness among cross types, the species that composed the community were significantly different. Using vector analysis, we found that the shift in arthropod community composition was correlated with percent Fremont alleles in the host plant, which suggests that the arthropod community responds to the underlying genetic differences among trees. We found 13 arthropod species representing different trophic levels that were significant indicators of the four different cross types. Even though arthropod communities changed in species composition from one year to the next, the overall patterns of community differences remained remarkably stable, suggesting that the genetic differences among cross types exert a strong organizing influence on the arthropod community. Together, these results support the extended phenotype concept. Few studies have observationally and experimentally shown that entire arthropod communities can be structured by genetic differences in their host plants. These findings contribute to the developing field of community genetics and suggest a strategy for conserving arthropod diversity by promoting genetic diversity in their host plants.
Species turnover promotes the importance of bee diversity for crop pollination at regional scales
DOI:10.1126/science.aao2117
PMID:29449491
[本文引用: 1]
Ecologists have shown through hundreds of experiments that ecological communities with more species produce higher levels of essential ecosystem functions such as biomass production, nutrient cycling, and pollination, but whether this finding holds in nature (that is, in large-scale and unmanipulated systems) is controversial. This knowledge gap is troubling because ecosystem services have been widely adopted as a justification for global biodiversity conservation. Here we show that, to provide crop pollination in natural systems, the number of bee species must increase by at least one order of magnitude compared with that in field experiments. This increase is driven by species turnover and its interaction with functional dominance, mechanisms that emerge only at large scales. Our results show that maintaining ecosystem services in nature requires many species, including relatively rare ones.Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
The effect of grazing on bumblebees in the high rangelands of the eastern Tibetan Plateau of Sichuan
DOI:10.1007/s10841-008-9180-3 URL [本文引用: 4]
Effects of livestock grazing on pollination on a steppe in eastern Mongolia
DOI:10.1016/j.biocon.2008.07.004 URL [本文引用: 3]
Morphological trait-matching in plant-Hymenoptera and plant-Diptera mutualisms across an elevational gradient
DOI:10.1111/jane.v91.1 URL [本文引用: 1]
The impact of a native dominant plant, Euphorbia jolkinii, on plant-flower visitor networks and pollen deposition on stigmas of co-flowering species in subalpine meadows of Shangri-La, SW China
DOI:10.1111/jec.v109.5 URL [本文引用: 2]
