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

自上而下和自下而上的过程对陆地森林生态系统脊椎动物群落物种丰度的重要性仍然是一个有争议的问题。在自上而下的过程中，捕食者应该限制食草动物，从而减少食草动物对植被的压力。这导致了森林更新的增加。如果自下而上的过程更有效，植物的可用性和质量（初级生产）将限制食草动物的数量，从而限制它们的捕食者。在捕食者存在的情况下，由自上而下的效应主导的生态系统应该结合低种群密度的食草动物和高产量的植物。相反，在自下而上效应为主的生态系统中，草食动物密度与初级生产呈正相关。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和复杂的食物网连接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刺状森林脊椎动物群落物种丰度的影响及其对森林更新的影响。马达加斯加的刺林生态系统包含了所有的营养水平，但每个水平由很少的物种组成，使得分析是可行的。我们将使用两因子研究设计（捕食/高初级产量；无捕食/高初级产量；捕食/低初级产量；无捕食/低初级产量），重点研究顶级捕食者大花椒（Galidictis granddieri）（=自上而下效应）和初级产量（=自下而上效应）对植物材料消费者种群的影响。响应变量为：1。消费者群体特征（密度、结构、动态）；森林更新（幼苗的丰度和种类组成）。这种方法应该能够评估捕食者对猎物种群的影响，以及在整个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.