Effects of abiotic, top-down and bottom-up factors for the vertebrate community composition of a spiny forest ecosystem in Madagascar

在陆地森林生态系统的脊椎动物群落中，自上而下和自下而上的过程对物种丰富度的重要性仍然存在争议。在自上而下的过程中，捕食者应该限制草食动物，从而减少草食动物对植被的压力。这导致了森林再生的增加。如果自下而上的过程更有效，植物的可获得性和质量(初级生产)将限制食草动物的数量，进而限制它们的捕食者。在捕食者存在的情况下，由自上而下效应主导的生态系统应该将低密度的草食动物与高植物产量结合起来。相反，在自下而上效应主导的生态系统中，食草动物密度应该与初级生产量呈正相关。在脊椎动物群落中对这些预测的分析受到实验操作大型食肉动物的困难以及复杂的食物网络联系而不是营养水平之间的线性关系的阻碍。该项目的目标是确定非生物、自上而下和自下而上因素对马达加斯加多刺森林脊椎动物群落物种丰富度的影响及其对森林更新的影响。马达加斯加的多刺森林生态系统包含所有营养级别，但每一级别只有很少的物种，这使得分析变得可行。我们将使用双因素研究设计(捕食/高初级生产；无捕食/高初级生产；捕食/低初级生产；无捕食/低初级生产；无捕食/高初级生产；捕食/低初级生产；无捕食/低初级生产)，重点研究顶级捕食者大银鱼(=自上而下的影响)和初级生产(=自下而上的影响)对植物材料消费者群体的影响。响应变量将是：1.消费群体的特征(密度、结构、动态)和2.森林更新(苗木丰度和物种组成)。这种方法应该能够评估捕食者对猎物种群的影响，以及在营养级联中对初级生产和森林再生的影响。

The importance of top-down and bottom-up processes for the abundance of species in vertebrate communities of terrestrial forest ecosystems remains a matter of debate. In top-down processes predators should limit herbivores, thus reducing herbivore pressure on the vegetation. This results in increased forest regeneration. If bottom-up processes were more effective, the availability and quality of plants (primary production) would limit herbivore populations which in turn limit their predators. In the presence of a predator, ecosystems dominated by top-down effects should combine low population densities of herbivores with high plant production. In contrast, in ecosystems dominated by bottom-up effects herbivore densities should be correlated positively with primary production. Analyses of these predictions in vertebrate communities are hampered by the difficulties of manipulating large carnivores experimentally and by complex food web connections rather than linear relationships between trophic levels. The goal of the project is to identify the effects of abiotic, top-down and bottom-up factors on species abundances in vertebrate communities of Madagascar¿ spiny forest and their impact on forest regeneration. The spiny forest ecosystem of Madagascar contains all trophic levels but each level consists of very few species, making analyses feasible. We will focus on the impact of a top predator, Galidictis grandidieri, (= top-down effects) and primary production (= bottom-up effects) on populations of consumers of plant material, using a two factorial study design (predation / high primary production; no predation / high primary production; predation / low primary production; no predation / low primary production. The response variables will be: 1. characteristics of consumer populations (density, structure, dynamics) and 2. forest regeneration (abundance and species composition of seedlings). This approach should allow to assess the impact of the predator on prey populations and, across the trophic cascade, on the primary production and forest regeneration.