Sandrine Fanfard (2013-2016)

How ecogeochemical feedback shapes benthic metacommunities in shallow marine ecosystems

Director : François Charles

Co-Director : Jean-Marc Guarini

Subject description

The input of large detrital particles derived from terrestrial plants constitutes a significant and recurrent source of organic matter available for benthic fauna in Mediterranean coastal ecosystems. This input is closely related with high rainfall events through the flooding of rivers of which the frequency and intensity are likely to be affected by global warming. This general perspective provides the opportunity to explicitly address the relationship between resource and biodiversity by building a theoretical framework specific to marine ecosystems.        
The current issue in Ecology is not anymore the loss of biodiversity but the consequences of this decline on ecosystem functioning ( Loreau et al. , 2001) and beyond on services provided by ecological systems (Gray, 1997). Because species may play similar roles within an assembly, there is a need to consider the effects of species interactions on the dynamics of communities for understanding the consequences of the biodiversity loss major eco -geochemical equilibrium (McCann , 2007) and determining the fundamental relationships linking the networks of species interactions and the stability of the systems they support (Fonseca and Ganade , 2001).

In general, biological communities are not isolated but rather organized in sets of local communities spatially connected through the exchange of individuals on a regional scale. In the context of communities organized in metacommunities, the goal of this Ph D thesis is to formalize the link between the dynamics of a resource, competitive interaction between consumers for the use of this resource and the control of the consumer dynamics through predation presure. This requires: (1) the identification of the species involved in the conversion of the primary food source, (2) the quantification of the interactions that shape the community organization around that resource, and (3) experimental works for testing the properties of the community structure on the functioning of the interacting system that includes both resources and consumers.

To describe and to quantify the dynamics of the resource and the interactions between that dynamics and the one of the animal community feeding on the resource, the approach is to consider the assembly of species that can tear nutrient and energy from an easily characterizable resource in an environment which is otherwise rather heterogeneous and complex. For this prupose, communities of marine invertebrates which are organized around macro detritus derived from terrestrial plants are a good model. The achievement of the PhD should thus provide information on: (1) the effects of the biodiversity on the cycling of terrestrial organic matter in coastal marine environment; (2) the biotic interactions involved in the degradation of this matter; and (3) maintaining communities‘function and diversity when resources and consumers both have their own dynamics.

The proposal is based on observation, experimentation and theoretical formalization of the dynamics of the resource and the capacity for marine benthic macrofauna to use and alter the state of their resource, two aspects that are routinely treated in isolation.