Quantifying the functional importance of ants in savanna ecosystems

蚂蚁(膜翅目：蚁科)是热带地区最主要的无脊椎动物，参与了一系列的生态系统过程，发挥着广泛的功能，但很少有研究量化它们在大范围生态系统中的重要性。在热带稀树草原，蚂蚁可能占地面活动无脊椎动物的70%，但它们在构建这些生态系统中所起的作用在很大程度上是未知的。据认为，蚂蚁在多个层面上影响生态过程。在基本水平上，蚂蚁通过筑巢和觅食行为影响土壤结构和养分。在较高的营养水平，蚂蚁通过捕食对无脊椎动物施加自上而下的控制，包括调节白蚁，这可能间接改变基本过程，如分解速度和土壤生物扰动。通过它们对草食性无脊椎动物的调节，蚂蚁可能会间接限制无脊椎动物的食草性，这可能会对植物的生长和生存产生影响。该项目将利用一种蚂蚁抑制疗法来排除蚂蚁，并测量在它们不存在的情况下生态系统发生的变化。共有四个控制区和四个抑蚁区。抑制疗法针对的是蚂蚁，而不会影响群落中的其他无脊椎动物。这项研究将确定蚂蚁通过直接和间接控制一系列生态系统过程对稀树草原生态系统功能的影响程度。目的：量化蚂蚁在稀树草原生态系统功能调节中的作用。目的：量化蚂蚁对以下生态系统过程的影响：1.土壤养分、碳贮量和异质性我们将通过分析土壤pH以及土壤中与土壤肥力相关的碳和其他有机养分(pH、P、Ca、Mg、K、Na、N)的浓度来衡量蚂蚁对土壤性质的影响。还将分析土壤的结构。2.食物资源分配我们将量化稀树大草原中有多少资源重新分配可以归因于蚂蚁，以及当蚂蚁被排除在生态系统之外时，脊椎动物或非蚂蚁无脊椎动物是否会补偿食物资源的消失。蚂蚁、脊椎动物和非蚂蚁无脊椎动物的诱饵清除将通过蚂蚁抑制处理和脊椎动物排除笼子的组合进行量化。3.白蚁活动、土壤生物扰动和分解我们将通过每4周测量一次所有样地白蚁对纤维素诱饵的消耗来量化蚂蚁对白蚁活动的影响。在一年中的不同时间点，我们将测量白蚁对木块的分解量，我们将测量样带下白蚁土壤的生物扰动。4.无脊椎动物群落调节我们将通过从不同地层(土壤、地面、草地、树木)采集无脊椎动物样本，并比较处理和对照样地的群落组成，来评估蚂蚁调节和构建无脊椎动物群落的程度。5.树木生长和草食我们将在两年的时间里确定蚂蚁对两种本地树种丝虫和相思幼苗的无脊椎动物食草率以及所有试验地的存活率和生长率的影响。通过这些实验，我们旨在阐明蚂蚁在稀树草原生态系统中扮演的多种角色。我们希望强调蚂蚁在构建热带系统中的重要性，并强调蚂蚁多样性是热带生态系统健康运行的关键。

Ants (Hymenoptera: Formicidae) are the dominant invertebrate group in the tropics and mediate a range of ecosystem processes and perform a wide variety of functions, but few studies have quantified their importance in ecosystems at large scales. In savannas, ants may constitute up to 70% of ground-active invertebrates, yet the role they play in structuring these ecosystems is largely unknown. It is thought that ants affect ecological processes on a number of levels. At basal levels, ants affect soil structure and nutrients through their nest-building and scavenging behaviours. At higher trophic levels, ants exert top-down control on invertebrates via predation, including regulating termites which may indirectly alter basal processes such as decomposition rates and soil bioturbation. Through their regulation of herbivorous invertebrates, ants may indirectly limit invertebrate herbivory which may have consequences for plant growth and survivorship. This project will utilise an ant-suppression treatment to exclude ants and measure the changes that occur in the ecosystem in their absence. There are four control plots and four ant-suppression plots. The suppression treatment targets ants without affecting the other invertebrates in the community. This study will determine the extent to which ants affect savanna ecosystem functioning through direct and indirect control of a range of ecosystem processes. Aim: To quantify the roles of ants in mediating ecosystem functioning in savannas.Objectives: To quantify the effect of ants on the following ecosystem processes:1. Soil nutrients, carbon storage and heterogeneity We will measure the impact of ants on soil properties by analysing soil pH, and concentrations of carbon and other organic soil nutrients associated with soil fertility (pH, P, Ca, Mg, K, Na, N). The structure of the soil will also be analysed. 2. Food resource distributionWe will quantify how much resource redistribution in the savanna can be attributed to ants, and whether vertebrates or non-ant invertebrates compensate in the removal of food resources when ants are excluded from the ecosystem. Bait removal by ants, vertebrates and non-ant invertebrates will be quantified through a combination of ant-suppression treatment and vertebrate-exclusion cages. 3. Termite activity, soil bioturbation and decompositionWe will quantify the impact of ants on termite activity by measuring termite consumption of cellulose baits on all plots every 4 weeks. At various time points over the course of a year, we will measure the amount of termite-mediated decomposition of wood blocks, and we will measure termite soil bioturbation under transects, in all experimental plots. 4. Invertebrate community regulationWe will assess the degree to which ants regulate and structure the invertebrate community by sampling invertebrates from different strata (soil, ground, grass, arboreal) and comparing community composition in the treatment and control plots, 5. Tree growth and herbivoryWe will determine the impact of ants on rates invertebrate-mediated herbivory on seedlings of two native tree species, Terminalia sericea and Acacia exuvialis, and on rates of survivorship and growth in all experimental plots over the course of two years. Invertebrate-mediated herbivory on adult T. sericea trees will also be measured.Through these experiments we aim to shed light on the many roles ants play in savanna ecosystems. We hope to highlight the importance of ants in structuring tropical systems and emphasise that ant diversity is key to healthy ecosystem functioning in the tropics.