VIR01 Effects of invertebate and vertebrate herbivory on tallgrass prairie plant community composition and biomass, Konza Prairie LTER

The effects of herbivores and their interactions with nutrient availability on primary production and plant community composition in grassland systems is expected to vary with herbivore type. Although nutrient additions are known to affect plant species diversity and primary productivity, the role of herbivores in mediating the strength of these effects also remains unclear. Herbivores may alter plant responses to nutrient additions in several ways. First, herbivores can alter the plant community response to nutrient additions by either selectively feeding on particular groups of species (e.g. grasses versus forbs) or by generally opening up space, allowing for species turnover and immigration. Second, feeding by herbivores may reduce the production response to nutrient additions if the plants cannot compensate for tissue lost to herbivory. As the functional effects of vertebrate and invertebrate herbivores on plant community composition and production may vary, the interactive effects of vertebrate versus invertebrate herbivores with nutrient additions may also vary. Here we are experimentally assessing the independent and interactive effects of removing vertebrate and invertebrate herbivores on aboveground biomass and plant community composition in native tallgrass prairie. Further, we are examining whether the removal of vertebrate and invertebrate herbivores interacts with nutrient availability. By doing this, we address three related questions: 1) what is the relative strength of the effects of invertebrate versus vertebrate herbivory in a grassland system; 2) how does herbivory (invertebrate and/or vertebrate) affect the relative abundances of grasses and forbs, the two dominant plant functional types within the ecosystem; and 3) what are the consequences of these changes in composition for aboveground net primary productivity, an important ecosystem function?草原生态系统中，植食动物（herbivore）及其与养分有效性（nutrient availability）的交互作用对初级生产力（primary production）与植物群落组成（plant community composition）的影响，会随植食动物类群的不同而产生差异。尽管已有研究证实养分添加（nutrient additions）会对植物物种多样性与初级生产力造成影响，但植食动物在调控这些效应强度方面所发挥的作用仍未明确。植食动物可通过多种途径改变植物对养分添加的响应：其一，植食动物可通过选择性取食特定类群的植物（如禾草与杂类草），或是通过普遍开辟生存空间来促进物种周转与迁入，进而改变植物群落对养分添加的响应；其二，若植物无法补偿因植食作用损失的组织，植食动物的取食会削弱植物对养分添加的生产力响应。由于脊椎动物植食者（vertebrate herbivores）与无脊椎动物植食者（invertebrate herbivores）对植物群落组成及生产力的功能效应存在差异，二者分别与养分添加的交互效应也可能有所不同。本研究通过实验评估了移除脊椎动物植食者与无脊椎动物植食者对原生高草草原（native tallgrass prairie）地上生物量（aboveground biomass）与植物群落组成的独立及交互效应，并进一步探究移除两类植食动物是否与养分有效性存在交互作用。借此，我们旨在解答三个相关问题：1）草原生态系统中，无脊椎动物与脊椎动物植食作用的效应强度相对大小如何？2）植食作用（无脊椎动物及/或脊椎动物）会如何影响该生态系统内两大优势植物功能类群——禾草与杂类草的相对多度？3）上述群落组成变化对地上净初级生产力（aboveground net primary productivity）这一重要生态系统功能会产生何种影响？