Projets tutorés

Tradeoff between minimizing sampling effort and maximizing precision in estimation of French Guianan medium and large sized vertebrates abundance

Robin Le Balle et Hugo Reizine under the supervision of Thomas Denis.

Abundance and density population estimates are based on approximations that bring variability in results. The evaluation of this variability is very useful to process data and to evaluate their relevance. Two methods are in use to know the state of a population. The encounter rate is the number of individuals (or group of individuals) noted on a transect and represent the relative abundance of the species. The distance sampling gives the density estimate b y adding the detection function of the species and represents the number of observation by unit of surface.
When managing an ecosystem or a community, these estimates must be as
accurate as possible while the effort required must be reduced at its minimum. The results presented in this paper show the precision obtained for relative abundance and density estimate for an increasing effort. These results can be used to estimate the minimum effort required to reach a certain level of precision or to evaluate the tradeoff between saving effort and gaining accuracy.
While numerous parameters could be added, this tool can already help biologists, wildlife managers and forester in future studies to plan and conduct their surveys.

Article complet

Prospective study about carbon footprint of forest exploitation in French Guiana from 2015 to 2045

Marianne Jounieaux et Thomas Pezet under the supervision of Camille Piponiot-Laroche, Benjamin Ouliac and Bruno Hérault.

Tropical forests store a large amount of carbon, and they are focused when considering climate change. However, they are currently threated because of anthropogenic activities and deforestation. These threats currently increase because of global population growth and associated increase of needs for materials, energy and space. This project aims to predict the carbon footprint of selective logging in French Guiana from 2015 to 2045. In order to do this we have created different scenarios of management strategy for forest exploitation. Using three levels of scenarios, we estimate (i) the effects of individual variables, (ii) the carbon fluxes for theoretical forest management strategies to date not seriously considered and (iii) the carbon fluxes for forest management strategies that have been seriously considered for the evolution of forest exploitation in French Guiana. After modification of a pre-existing model (Cabon et Piponiot-Laroche, 2014), we have simulated all these scenarios. Based on the results of this simulation, we suggest guidelines for minimizing the 2045 carbon footprint. We recommend a management strategy which increases intensity of logging in limited areas, improves techniques of extraction and transformation of wood lumber, and develops wood lumber and wood fuel plantations.

Article complet

Does habitat size influence decomposition rates in tank-bromeliad ecosystem?

Axel Cerdan and Camille Bonhomme under the supervision of Hector Rodriguez.

It has been well established in the literature that biological diversity influences ecosystem processes. Thus, understanding how changes in biodiversity affect ecosystem functions is a primary focus of ecological research. Moreover habitat size is known to affect several aspects of ecological communities including diversity, both structurally (species number) and functionally (functional structure). Therefore habitat size may influence ecosystem functioning, mediated by biological diversity. In this study we test the hypothesis that ecosystem size affect the decomposition ecosystem process, thus ecosystem functioning. (Here we ask whether habitat size and community richness or functional diversity are correlated. Then, we investigated if we can detect a change in decomposition rates among a size gradient.
Taking advantage of methodological asset that represent tank-bromeliads by their natural size variation and the aquatic communities that they hold inside their wells, we tested how bromeliad size affects leaf-litter decomposition, the main energy input in the ecosystem. We address this question by focusing on Bromeliads, plants providing a natural aquatic mesocosm for entire communities. In these ecosystems, the main function is decomposition. We assessed leaf-litter decomposition rates for 45 plants in the field along a size gradient during 35 days. We have explored the decomposition rate relationship with invertebrate communities, exhaustively sampled for each plant. Additionally, in laboratory, we quantified the consumption rates for two of the most important decomposers species. We have found a positive relationship between diversity, measured as invertebrate richness and functional diversity, and habitat size (measured as plant’s average diameter). However, we did not find significant relationships between plant size and decomposition rates. We concluded from this result that invertebrates do not play a main role in decomposition, and we suggest that microorganisms, both bacteria and fungi, are determinant in decomposition rates variation.

Article complet

DiaryTous les événements

News items Toutes les brèves