ANALYSE EN ISOTOPES STABLES DE LA MACROFAUNE BENTHIQUE ET DE SES SOURCES DE NOURRITURE

Outil isotopique pour l’รฉtude de l ‘architecture des rรฉseaux trophiques

ย  ย L’analyse des contenus stomacaux de mรชme que les mesures de taux d’ingestion par utilisation des isotopes radioactifs sont deux mรฉthodes couramment utilisรฉes pour caractรฉriser les sources de nourriture utilisรฉes par les organismes et donc pour identifier les transferts de la MO au sein des rรฉseaux trophiques. L’une des limitations de ces mรฉthodes tient ร  la relative incertitude de faire la part entre ce qui a รฉtรฉ simplement ingรฉrรฉ et ce qui a รฉtรฉ effectivement assimilรฉ par l’animal. L’une des faรงons d’identifier le type de nourriture assimilรฉe consiste ร  analyser la composition en isotopes naturels stables des diffรฉrentes composantes รฉtudiรฉes (James et al. 2000a ; Schindler et Lubetkin 2004). Cette mรฉthode est couramment mise en ล“uvre dans les travaux portant sur les rรฉseaux trophiques en riviรจre(Finlay et al. 2002 ; Anderson et Cabana 2007), en lac (France 1995, 1997), en estuaire (Cloem et al. 2002) et dans les sols (Schmidt et al. 2004). En effet, les isotopes stables tรฉmoignent de l’assimilation intรฉgrรฉe sur une certaine pรฉriode de temps, celle-ci correspondant au taux de renouvellement du tissu d’un organisme (Kling et al. 1992). Cette approche est basรฉe sur l’existence d’une relation รฉtroite entre les compositions isotopiques du consommateur et celles des sources qui composent sa diรจte (Eggers et Jones 2000). En fait, le ratio d’isotopes stables du carbone d’un consommateur est un reflet du ratio isotopique (plus ou moins 1 %0) de sa source de nourriture, donc de sa source d’รฉnergie(DeNiro et Epstein 1978; Peterson et Fry 1987; Jardine et al. 2003). Le ratio isotopique de l’azote permet, quant ร  lui, de dรฉterminer la position du consommateur dans le rรฉseau trophique รฉtant donnรฉ qu’ il y a un enrichissement d’environ 3,4 %0 par niveau trophique (Minagawa et Wada 1984). Les rapports d’isotopes stables (e.g. รด13C et ร”,sN) fournissentainsi des informations sur l’origine et la transformation de la matiรจre (Eggers et Jones 2000). La contribution des diffรฉrents types de nourriture ร  la diรจte des diffรฉrents groupes d’invertรฉbrรฉs peut รชtre estimรฉe ร  l’aide des modรจles de mรฉlange linรฉaires pondรฉrรฉs. Un modรจle de mรฉlange linรฉaire pondรฉrรฉ (concentration-weighted linear mixing mode!) prenden compte la proportion de chacune des sources de nourriture dans le rรฉgime alimentaire et considรจre aussi le rapport CIN de chaque source (Phillips et Koch 2002). Ce modรจle pennet de transformer les rapports en isotopes stables en composition de la diรจte, รฉtant donnรฉ que la signature isotopique d’un consommateur est le reflet de la signature de ses sources alimentaires et ]a proportion de ces sources dans sa diรจte. C’est ainsique cette technique pennet, d’une part, d’รฉvaluer les sources de MO dans les รฉcosystรจmes et, d’autre part, d’identifier ]a composition du rรฉgime alimentaire d’un consommateur donnรฉ.

Isotopie tool for the study of network architecture trophic

ย  ย One way to identify the type of food assimilated is to analyze the composition of natural stable isotopes of the different components studied (James et al. 2000a; Schindlerand Lubetkin 2004). This method has was used for the study of several environments,other: river (Finlay et al. 2002; Anderson and Cabana 2007), lakes (France 1995, 1997), estuaries (Cloern et al. 2002) and in soils (Schmidt et al. 2004). lndeed, stable isotopes reflect the assimilation integrated over a certain period time, the latter corresponding to therate of tissue turnover an organism (Kling et al. 1992). This approach is based on the existence of a close relationship between the compositions isotope consumer and tho sesources that comprise its diet (Eggers and Jones 2000). ln fact, the ratio of stable isotopes carbon of a consumer is a reflection of the isotopic ratio (more or less 1 %0) of its food source, therefore its energy source (DeNiro and Epstein 1978; Petersonand Fry 1987;ย Jardine et al. 2003). The isotope ratio of nitrogen allows in turn, determine the position of consumers in food web as there is an enrichment of approximately 3.4 %0 by trophic level (Minagawa and Wada 1984). Reports stable isotope (e.g. 8I3C and 815 N) thus provide infonnation on the origin and transformation of matter (Eggers and Jones 2000). The relative contribution of the different food sources to the diet of the different invertebrates groups can be estimated with concentration-weighted linear mixing models. A concentration-weighted linear mixing model considers the proportion of each food sources in the diet and also considers the ratio C/N of each source (Phillips and Koch 2002). This model can transfonn stable isotope ratios in composition of the diet. This is possible because the isotopic signature of a consumer reflect the isotopic signature of its diet and the proportion of each food source in its diet. Thus, this technique allows firstly, to evaluate sources and fluxes in the POM ecosystems and, secondly, to identify the diet of a specifie consumer. This work aims at characterizing the benthic food webs of seven boreal lakes and examining the relative importance of autochthonous and allochthonous sources of organic carbon in these food webs. To do so, we measured naturally occurring carbon and nitrogenstable isotope ratios of major components of benthic macroinvertebrate communities and their potential diet sources at various sites within the seven lakes. AIso, we established the trophic position of macroinvertebrates with their stable nitrogen isotope signature.

Potential food sources

ย  The littoral benthic environrnent is complex (Wetzel 2001; Hecky and Hesslein 1995). Indeed, it can harbor several types of food sources with multiple origins su ch as POM, DOM and SOM (Meili 1992; Gu et al. 1994; Hecky and Hesslein 1995; Giorgio and France 1996; Grey et al. 2001; Vos et al. 2002; Macalady and Walton-Day 2009), primary producers (epilithon, macrophytes and epixylon) (Osmond et al. 1981; Hecky and Hesslein 1995; Wetzel 2001) and terrestrial detritus (Hecky and Hesslein 1995; Caraco and Cole 2004; Carpenter et al. 2005). The POM has been removed from ca1culation of the linear mixing models because it does not inform us about the type of material that is eaten by organisms. It is not possible to say wh ether this source of carbon is allochthonous or authochthonous. Indeed, POM may be a mixture of several different carbon sources (Meili 1992; Wetzel 1995; Giorgio and France 1996; Grey et al. 2001). For instance, Giorgio and France (1996) showed that phytoplankton is frequently represented in the composition of POM and Fry and Sherr (1984) have shown that the isotopic signature of POM was related to phytoplankton productivity. In sorne lakes, POM is also composed ofterrestrial detritus (Wetz el 1995) and the isotopic signature of the POM is the isotopic value of this terrestrial detrltus (Jones et al. 1998). Grey et al. (2001) have found that in addition to terrestrial detritus and phytoplankton, POM also contains bacteria. Moreover, the isotopic value of the POM changes depending on its composition and the time of the year (Gu et al. 1994; Grey et al. 2001). ln our study, bl3C values of POM varied between -33.61 and -29.12 %0 and were within the range reported by Giorgio and France (1996) (i.e., between -35 and -20 %0).

Le rapport de stage ou le pfe est un document dโ€™analyse, de synthรจse et dโ€™รฉvaluation de votre apprentissage, cโ€™est pour cela chatpfe.com propose le tรฉlรฉchargement des modรจles complet de projet de fin dโ€™รฉtude, rapport de stage, mรฉmoire, pfe, thรจse, pour connaรฎtre la mรฉthodologie ร  avoir et savoir comment construire les parties dโ€™un projet de fin dโ€™รฉtude.

Table des matiรจres

REMERCIEMENTS
Rร‰SUMร‰
ABSTRA CT
INTRODUCTION Gร‰Nร‰RALE
CHAPITRE 1 ANALYSE EN ISOTOPES STABLES DE LA MACROFAUNE BENTHIQUE ET DE SES SOURCES DE NOURRITURE DANS LES ENVIRONNEMENTS LITTORA UX LA CUSTRES BOREA UXย 
1.1 RESUME EN FRANร‡AIS DE L’ ARTICLE
1.2 BENTHIC FOOD WEB STRUCTURE OF BOREAL LAKES ASSESSED BY STABLE ISOTOPE ANALYSIS
CHAPITRE 2 CONCLUSION
Rร‰Fร‰RENCES BIBLIOGRAPHIQUES

Rapport PFE, mรฉmoire et thรจse PDFTรฉlรฉcharger le rapport complet

Tรฉlรฉcharger aussi :

Laisser un commentaire

Votre adresse e-mail ne sera pas publiรฉe. Les champs obligatoires sont indiquรฉs avec *