[Article by the Ecology and environment institute of the CNRS]
Researchers of the CNRS, IRD and universities of Toulouse and Clermont-Ferrand studied the ecosystems based in the water reservoirs of 365 Bromeliads in French Guiana. They identified all of the micro-organisms and insects found in these plants, and modeled the food chain. The goal is to understand how the structure of these networks varies depending on environmental changes.
PLOS ONE published this study on August 14th.
Identifying all the species present in an ecosystem, defining the links which exist between them, and then comparing this system to hundreds of other similar systems in order to measure with statistics the impact of environmental variables: this is the slightly crazy challenge taken up by researchers of the Ecology of Guiana Forests laboratory.
A rare initiative, because most research works focus on a few species or sites. To do so, the researchers decided to focus on one of the smallest ecosystems in the forest of French Guiana: tank-bromeliads. These plants which are typical of South America hold rainwater and host dozens of species of water insects and micro organisms (bacteria, fungi, algae, etc.). The researchers studied 365 bromeliads situated in 5 sites in French Guiana along an east-west gradient (several hundreds of kilometers). “The non-destructive method that we used consisted in taking samples of water from each tank with a micropipette“, tells Olivier Dézerald, young researcher doing a thesis in Kourou and first author of this article published in PLOS ONE on August 14th, 2013. A work of patience, when we know that the contained water can go from various millimeters to almost two liters for the largest plants!
The Bromeliads, typical plants of South America, form water tanks where micro organisms and insects develop, like the dragonfly larva on the picture below.
© Céline Leroy
Dragonfly larva found on a Bromeliad © Bruno Corbara
They described all the species they found, as well as the predation links that bind them. In short, who eats whom!
“To understand this, we studied the stomach contents of all the collected insects“, describes Olivier Dézerald. “Then, we caracterized the stability of each network – the more connections there are between species, the more dense is the network, and the more stable it will be. We also determined some key variables for each network: the habitat size, i.e. the volume of water in each tank, the quantity of light received, the intake of plant litter (plants in decomposition present in the water) and the presence of predators“.
The first results indicate that the habitat size above all determines the ecosystem stability: the larger is the tank, better is the system’s resistance to perturbation. “Light also seems to play a role in the sustainability of the network, notably because it favors the presence of photosynthetic algae on which certain insects feed“, underlines the researcher. He now wants to study the impact of climate change on these microecosystems.
(*) In partnership with the following laboratories: Botany and bioinformatics of plant architecture (Amap), Functional ecology and environment, Micro-organisms, genome and environnement, and with the support of the CEBA.
Two teams of the CEBA contributed to this publication: Ecology of Guiana Forests (Ecofog) and Botany and bioinformatics of plant architecture (Amap). Among the researchers that wrote the publication, two are members of the CEBA: Olivier Dézerald (Ecofog, first author, PhD student whose thesis is financed by the CEBA) and Céline Leroy (Amap).
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Publication references:
Food-web structure in relation to environmental gradients and predator-prey ratios in tank-bromeliad ecosystems
Olivier Dézerald, Céline Leroy, Bruno Corbara, Jean-François Carrias, Laurent Pélozuelo, Alain Dejean et Régis Céréghino.
Revue PLOS ONE, August 14th, 2013.
To access the publication: http://dx.plos.org/10.1371/journal.pone.0071735
Communication contact: Claire Lafleur, CEBA, claire.lafleur@labex-ceba.fr, tel : +594 (0)5 94 38 87 58
