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进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。这将增加森林的再生。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）将限制食草动物的种群，从而限制其捕食者。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将低种群密度的食草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，食草动物密度应与初级生产力呈正相关。这些预测在脊椎动物群落中的分析受到阻碍的困难操纵大型食肉动物实验和复杂的食物网连接，而不是营养水平之间的线性关系。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棘林脊椎动物群落物种丰度的影响及其对森林再生的影响。马达加斯加的多刺森林生态系统包含所有营养级，但每一级由很少的物种组成，使分析可行。我们将集中在一个顶级的捕食者，Galidictis grandidieri，（=自上而下的影响）和初级生产（=自下而上的影响）的消费者的植物材料的人口，使用两个因子的研究设计（捕食/高初级生产;没有捕食/高初级生产;捕食/低初级生产;没有捕食/低初级生产。响应变量将是：1。消费者群体的特征（密度、结构、动态）; 2.森林再生（幼苗的丰度和物种组成）。这种方法应允许评估捕食者对猎物种群的影响，并在整个营养级联，对初级生产和森林再生。

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.