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

• Applicant: Professor Dr. Jörg U. Ganzhorn
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2006 to 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 27480704

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.

• DFG Programme: Research Grants
• International Connection: Madagascar
• Participating Persons: Professor Dr. Daniel S. Rakotondravony; Professorin Dr. Olga Ramilijaona