绵羊采食选择与植物联合防御的初步研究
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摘要
天然草地生态系统中,动物是主要的消费者,与生产者植物共同构成了草地生态系统中的两个层面,这两个层面是产生草地生态系统动植物互作的主要区域。动植物互作的研究,对于发展动物采食理论,恢复或维持生物多样性,维持草地放牧系统的稳定性具有重要意义。因此,植物--动物(如牛、羊等)的相互作用已成为生态学家研究的重要内容。
传统的动植物关系研究仅停留在个体水平上,草食动物通过采食来满足自身对营养物质的需求,植物为了生存和繁衍形成简单的形态学防御(如坚硬的角质层、针、刺等)和化学防御(如次生代谢物、毒素等)。然而,植物--草食动物互作关系的核心内容是草食动物(herbivores)的选择性采食(diet selection),是产生动植物相互作用的首要前提条件和基础。研究中人们忽略了草食动物的采食选择性(foraging selectivity)。当草食动物的采食选择发生在种群或群落采食等级时,植物个体不仅可以通过自身的物理和化学防御方式避免被采食,其邻居植物(neighbor plant)的特性也能影响植物个体受保护的程度,这一理论被称为植物联合防御。
本研究目的在于通过研究不同时空尺度下草食动物对不同采食等级(个体等级和斑块等级)选择性的大小,观察植物联合防御是否受时间和空间尺度变化的影响,及对时空尺度变化的响应。试验选择高、中、低三种质量的牧草苜蓿(Medicago sativa)、芦苇(Phragmites australis)、羊草(Leymus chinensis)作为试验植物,根据三种牧草不同的比例构建高、中、低三种质量的斑块。试验设置三个空间尺度(25m×25m、35m×35m、45m×45m),在每一个空间尺度试验内,包含三种质量的斑块各一个,斑块内牧草采用聚集摆放模式。放牧时间设置三个尺度,分别为30min、60min、90min。
试验结果表明:
1)绵羊对植物个体和斑块两个采食等级均存在选择性。时空尺度的变化显著影响绵羊在斑块内和斑块间的选择性。随时间和空间尺度的放大,绵羊在斑块内选择性显著降低;斑块间选择性在小空间尺度内随时间尺度的增加呈现增大的趋势,而在中、大空间尺度内随时间尺度的增加呈现降低趋势。总体上在任意时空尺度下,绵羊在斑块内的选择性都显著高于斑块间选择性。
2)植物联合防御的结果显著受时空尺度的影响。在大空间尺度下,目标植物芦苇在低质量斑块内的采食量高于在高质量斑块内的采食量,目标植物在低质量斑块内受害,而在高质量斑块内得到保护。中空间尺度实验结果不显著,但趋势相同。小空间尺度下的结果与中、大空间尺度的趋势相反,目标植物芦苇在低质量斑块内的采食量低于在高质量斑块内的采食量但不显著,目标植物在低质量斑块内得到保护,而在高质量斑块内受害。两种结果说明植物联合防御随着空间尺度的变化有发生转化的趋势。
3)总采食量显著受空间尺度的影响。其中优质牧草苜蓿的采食量占绝对优势,说明在时空尺度变化条件下,绵羊主要以选择食物的质量为主,主要采食粗蛋白含量较高的食物。随着空间尺度放大,绵羊通过降低游走时间以及在斑块间的转移频率来提高采食效率,从而降低采食成本。
综上,在本实验条件下,绵羊对个体采食等级的选择性高于对斑块等级的选择性;在中、大空间尺度下植物联合防御表现为邻居对比受害(neighbor contrast susceptibility)和邻居对比防御(neighbor contrast defense),而在小空间尺度下微弱的体现了联合受害(associational susceptibility)和联合防御(associational defense)的趋势。
Animals were the main consumers in the natural grassland systems. The producer plants and animals constitute two ecosystem interface in the natural grassland ecosystems. Biological interactions in grassland ecosystem mainly occurred at plant-animal interfaces. The work on plant-animal interaction is of great importance not only for development of foraging theory, but also for maintaining biodiversity, sustaining the stability of grazing grassland systems. So the plant-animal (such as cattle, sheep, etc.) interaction has become the core of the ecologists’research.
The traditional plant and animal relationship research focused on the individual level. Herbivores meet their nutrient needs through foraging. Plants form the simple morphological defenses (hard cuticle, needle, thorn, etc.) and chemical defenses (secondary metabolites, toxins, etc.) in order to survive and reproduce. However, the diet selection was the core of the plant-herbivore interaction, which was the first prerequisite and foundation of the plants-animals interaction. Foraging selectivity has been overlooked sometimes. When herbivore make decisions at the plant population or community level, plant individuals can gain protection not only by its own physical and chemical defense but also by that the neighboring plants. This theory was known as the plant associational defense.
The aim of this study was to explore herbivore feeding selectivity at different foraging levels (individual and patch) under the different spatial and temporal scales, and determine whether the plant associational defense was affected by change of spatial and temporal scales. We selected three species with different quality of high, medium and low (Medicago sativa, Phragmitis australis, Leymus chinensis) as experimental plants. Three patches with high, medium and low quality, were constituted by three different proportions of forages. Three spatial scales (25m×25m, 35m×35m, 45m×45m) were set. The three species were aggregated distribution in each patch. Three grazing temporal scales (30min, 60min and 90min) were set.
The results of experiment showed as follows:
1) Sheep exhibited selectivity at plant individuals and patch levels. The changing of spatial and temporal scale has a significant impact on sheep’s feeding selectivity in within-patch and between-patch. The within-patch selectivity significantly reduced with the temporal and spatial scale enlarged. At small spatial scale, the between-patch selectivity show an increasing trend with the increase of temporal scales, but at medium and large spatial scales, it was on the contrary. Overall, at any temporal and spatial scales, the within-patch selectivity of sheep was significantly higher than the between-patch selectivity.
2) The results of the plants associational defense were significantly affected by the spatial and temporal scales. At the large spatial scale, sheep intake of the focal plant P. australis within low-quality patch was higher than that within high-quality patch. The focal plant was damaged within low-quality patch and protected within high-quality patch. The result at the medium spatial scale was not significant, but the same trend. The result was on the contrary at small spatial scale. Intake of the focal plant P. australis within low-quality patch was lower than that within high-quality patch, but it was not significant. The focal plant was protected in low-quality patches and damaged in high-quality patches. The two different results indicated that plant associational defense altered with the change of the spatial scale.
3) The total intake was significantly affected by spatial scale. The intake of M. sativa was on the dominant at all scales, which indicated that sheep primarily selected the food with higher crude protein. As the spatial scale become larger, sheep improved feeding efficiency by reducing the traveling time and switching frequency between patches, thus reducing feeding costs.
In conclusion, sheep feeding selectivity was higher at individual level than that at patch level in this experimental. The plant associational defense showed“neighbor contrast susceptibility”and“neighbor contrast defense”at the medium and large spatial scale, while“associational susceptibility”and“associational defense”at the small spatial scale.
传统的动植物关系研究仅停留在个体水平上,草食动物通过采食来满足自身对营养物质的需求,植物为了生存和繁衍形成简单的形态学防御(如坚硬的角质层、针、刺等)和化学防御(如次生代谢物、毒素等)。然而,植物--草食动物互作关系的核心内容是草食动物(herbivores)的选择性采食(diet selection),是产生动植物相互作用的首要前提条件和基础。研究中人们忽略了草食动物的采食选择性(foraging selectivity)。当草食动物的采食选择发生在种群或群落采食等级时,植物个体不仅可以通过自身的物理和化学防御方式避免被采食,其邻居植物(neighbor plant)的特性也能影响植物个体受保护的程度,这一理论被称为植物联合防御。
本研究目的在于通过研究不同时空尺度下草食动物对不同采食等级(个体等级和斑块等级)选择性的大小,观察植物联合防御是否受时间和空间尺度变化的影响,及对时空尺度变化的响应。试验选择高、中、低三种质量的牧草苜蓿(Medicago sativa)、芦苇(Phragmites australis)、羊草(Leymus chinensis)作为试验植物,根据三种牧草不同的比例构建高、中、低三种质量的斑块。试验设置三个空间尺度(25m×25m、35m×35m、45m×45m),在每一个空间尺度试验内,包含三种质量的斑块各一个,斑块内牧草采用聚集摆放模式。放牧时间设置三个尺度,分别为30min、60min、90min。
试验结果表明:
1)绵羊对植物个体和斑块两个采食等级均存在选择性。时空尺度的变化显著影响绵羊在斑块内和斑块间的选择性。随时间和空间尺度的放大,绵羊在斑块内选择性显著降低;斑块间选择性在小空间尺度内随时间尺度的增加呈现增大的趋势,而在中、大空间尺度内随时间尺度的增加呈现降低趋势。总体上在任意时空尺度下,绵羊在斑块内的选择性都显著高于斑块间选择性。
2)植物联合防御的结果显著受时空尺度的影响。在大空间尺度下,目标植物芦苇在低质量斑块内的采食量高于在高质量斑块内的采食量,目标植物在低质量斑块内受害,而在高质量斑块内得到保护。中空间尺度实验结果不显著,但趋势相同。小空间尺度下的结果与中、大空间尺度的趋势相反,目标植物芦苇在低质量斑块内的采食量低于在高质量斑块内的采食量但不显著,目标植物在低质量斑块内得到保护,而在高质量斑块内受害。两种结果说明植物联合防御随着空间尺度的变化有发生转化的趋势。
3)总采食量显著受空间尺度的影响。其中优质牧草苜蓿的采食量占绝对优势,说明在时空尺度变化条件下,绵羊主要以选择食物的质量为主,主要采食粗蛋白含量较高的食物。随着空间尺度放大,绵羊通过降低游走时间以及在斑块间的转移频率来提高采食效率,从而降低采食成本。
综上,在本实验条件下,绵羊对个体采食等级的选择性高于对斑块等级的选择性;在中、大空间尺度下植物联合防御表现为邻居对比受害(neighbor contrast susceptibility)和邻居对比防御(neighbor contrast defense),而在小空间尺度下微弱的体现了联合受害(associational susceptibility)和联合防御(associational defense)的趋势。
Animals were the main consumers in the natural grassland systems. The producer plants and animals constitute two ecosystem interface in the natural grassland ecosystems. Biological interactions in grassland ecosystem mainly occurred at plant-animal interfaces. The work on plant-animal interaction is of great importance not only for development of foraging theory, but also for maintaining biodiversity, sustaining the stability of grazing grassland systems. So the plant-animal (such as cattle, sheep, etc.) interaction has become the core of the ecologists’research.
The traditional plant and animal relationship research focused on the individual level. Herbivores meet their nutrient needs through foraging. Plants form the simple morphological defenses (hard cuticle, needle, thorn, etc.) and chemical defenses (secondary metabolites, toxins, etc.) in order to survive and reproduce. However, the diet selection was the core of the plant-herbivore interaction, which was the first prerequisite and foundation of the plants-animals interaction. Foraging selectivity has been overlooked sometimes. When herbivore make decisions at the plant population or community level, plant individuals can gain protection not only by its own physical and chemical defense but also by that the neighboring plants. This theory was known as the plant associational defense.
The aim of this study was to explore herbivore feeding selectivity at different foraging levels (individual and patch) under the different spatial and temporal scales, and determine whether the plant associational defense was affected by change of spatial and temporal scales. We selected three species with different quality of high, medium and low (Medicago sativa, Phragmitis australis, Leymus chinensis) as experimental plants. Three patches with high, medium and low quality, were constituted by three different proportions of forages. Three spatial scales (25m×25m, 35m×35m, 45m×45m) were set. The three species were aggregated distribution in each patch. Three grazing temporal scales (30min, 60min and 90min) were set.
The results of experiment showed as follows:
1) Sheep exhibited selectivity at plant individuals and patch levels. The changing of spatial and temporal scale has a significant impact on sheep’s feeding selectivity in within-patch and between-patch. The within-patch selectivity significantly reduced with the temporal and spatial scale enlarged. At small spatial scale, the between-patch selectivity show an increasing trend with the increase of temporal scales, but at medium and large spatial scales, it was on the contrary. Overall, at any temporal and spatial scales, the within-patch selectivity of sheep was significantly higher than the between-patch selectivity.
2) The results of the plants associational defense were significantly affected by the spatial and temporal scales. At the large spatial scale, sheep intake of the focal plant P. australis within low-quality patch was higher than that within high-quality patch. The focal plant was damaged within low-quality patch and protected within high-quality patch. The result at the medium spatial scale was not significant, but the same trend. The result was on the contrary at small spatial scale. Intake of the focal plant P. australis within low-quality patch was lower than that within high-quality patch, but it was not significant. The focal plant was protected in low-quality patches and damaged in high-quality patches. The two different results indicated that plant associational defense altered with the change of the spatial scale.
3) The total intake was significantly affected by spatial scale. The intake of M. sativa was on the dominant at all scales, which indicated that sheep primarily selected the food with higher crude protein. As the spatial scale become larger, sheep improved feeding efficiency by reducing the traveling time and switching frequency between patches, thus reducing feeding costs.
In conclusion, sheep feeding selectivity was higher at individual level than that at patch level in this experimental. The plant associational defense showed“neighbor contrast susceptibility”and“neighbor contrast defense”at the medium and large spatial scale, while“associational susceptibility”and“associational defense”at the small spatial scale.
引文
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