School of Earth, Environmental and Biological Sciences, Faculty of Science and Technology, Queensland University of Technology, Brisbane, Queensland, 4001, Australia.
Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903, Birmensdorf, Switzerland.
Ecology. 2017 Jan;98(1):239-252. doi: 10.1002/ecy.1637.
Vertebrate and invertebrate herbivores alter plant communities directly by selectively consuming plant species; and indirectly by inducing morphological and physiological changes to plant traits that provide competitive or survivorship advantages to some life forms over others. Progressively excluding aboveground herbivore communities (ungulates, medium and small sized mammals, invertebrates) over five growing seasons, we explored how leaf morphology (specific leaf area or SLA) and nutrition (nitrogen, carbon, phosphorous, potassium, sodium, and calcium) of different plant life forms (forbs, legumes, grasses, sedges) correlated with their dominance. We experimented in two subalpine grassland types with different land-use histories: (1) heavily grazed, nutrient-rich, short-grass vegetation and (2) lightly grazed, lower nutrient tall-grass vegetation. We found differences in leaf traits between treatments where either all herbivores were excluded or all herbivores were present, showing the importance of considering the impacts of both vertebrates and invertebrates on the leaf traits of plant species. Life forms responses to the progressive exclusion of herbivores were captured by six possible combinations: (1) increased leaf size and resource use efficiency (leaf area/nutrients) where lower nutrient levels are invested in leaf construction, but a reduction in the number of leaves, for example, forbs in both vegetation types, (2) increased leaf size and resource use efficiency, for example, legumes in short grass, (3) increased leaf size but a reduction in the number of leaves, for example, legumes in the tall grass, (4) increased number of leaves produced and increased resource use efficiency, for example, grasses in the short grass, (5) increased resource use efficiency of leaves only, for example, grasses and sedges in the tall grass, and (6) no response in terms of leaf construction or dominance, for example, sedges in the short grass. Although we found multiple possible responses by life forms to progressive exclusion of herbivores, we also found some important generalities. Changes in leaf traits of legumes and grasses correlated with their increasing dominance in the short-grass vegetation and plants were more efficient at constructing photosynthetic tissue when herbivores are present with few exceptions. These results demonstrate that vertebrate and invertebrate herbivores are essential to maintain plant species richness and resource-use efficiency.
脊椎动物和无脊椎草食动物通过选择性地消耗植物物种直接改变植物群落；通过诱导植物特征的形态和生理变化，为某些生命形式提供竞争或生存优势，从而间接地改变植物群落。在五个生长季节中，我们逐渐排除了地上草食动物群落（有蹄类动物、中小型哺乳动物、无脊椎动物），研究了不同植物生活形式（草本植物、豆科植物、禾本科植物、莎草科植物）的叶片形态（比叶面积或 SLA）和营养（氮、碳、磷、钾、钠、钙）如何与它们的优势相关。我们在两种具有不同土地利用历史的亚高山草地类型中进行了实验：（1）重度放牧、营养丰富、短草植被；（2）轻度放牧、低营养高草植被。我们发现，在所有草食动物都被排除或都存在的处理之间，叶片特征存在差异，这表明考虑脊椎动物和无脊椎动物对植物物种叶片特征的影响非常重要。对草食动物逐渐排除的反应，由六种可能的组合来表示：（1）在低营养水平下，投资于叶片构建的资源使用效率（叶片面积/养分）增加，叶片数量减少，例如两种植被类型中的草本植物；（2）在短草中，豆科植物的叶片大小和资源使用效率增加；（3）叶片大小增加，但叶片数量减少，例如高草中的豆科植物；（4）在短草中，叶片数量增加，资源使用效率增加，例如禾本科植物；（5）在高草中，只有叶片的资源使用效率增加，例如禾本科植物和莎草科植物；（6）在短草中，莎草科植物的叶片结构或优势没有反应。尽管我们发现了生活形式对草食动物逐渐排除的多种可能反应，但我们也发现了一些重要的普遍性。豆科植物和禾本科植物叶片特征的变化与它们在短草植被中的优势增加有关，而且在草食动物存在的情况下，植物在构建光合作用组织方面的效率更高，除了少数例外。这些结果表明，脊椎动物和无脊椎草食动物对于维持植物物种丰富度和资源利用效率是必不可少的。
