Les kelps sont des espèces clés dans les écosystèmes marins tempérés, elles vivent en milieu intertidal le long des côtes où elles sont souvent exposées à des herbivores. Comme la plupart des organismes sessiles, les kelps ont développé des stratégies de défense contre l’herbivorie. Chez la laminaire Laminaria digitata, l’élicitation par les oligoguluronates induit des régulations transcriptomiques et l’activation de voies métaboliques, menant à la production et la libération de métabolites dans l’environnement, tels que des aldéhydes. De plus, cette espèce d’algue brune a montré des réponses systémiques suite à une élicitation. Des composés solubles dans l’eau de mer environnant les forêts de laminaires peuvent aussi modifier leur physiologie en réponse à l’élicitation. Une telle signalisation chimique à distance lors des réponses de défense rappelle les phénomènes de protection systémique et de potentialisation chez les plantes. Dans les forêts de laminaires, celle-ci pourrait jouer un rôle écologique majeur dans la structuration des algues marines et des communautés d’herbivores. Dans le contexte des interactions kelp/herbivores, nous avons étudié les réponses de défense et les processus de signalisation chez deux espèces emblématiques de laminaires originaires des côtes atlantiques et du Pacifique Sud, impliquées dans des interactions spécialisées avec leurs herbivores, L. digitata en interaction avec Patella pellucida (Bretagne, France) et Lessonia spicata avec Scurria scurra (Chili). Des approches combinées de métabolomique et de bio-essais ont été réalisées pour élucider la nature de potentiels signaux chimiques et leurs rôles biologiques et écologiques dans la défense des algues face aux herbivores. Les résultats ont montré que, en réponse à un broutage, les kelps présentent des modifications métaboliques telles que l’induction de voies de biosynthèse des acides gras, des oxylipines et d’acides aminés, ainsi que des modifications transcriptomiques. De plus, nous avons constaté que les laminaires co-incubées avec des algues broutées présentaient des changements de leur endo-métabolome en comparaison à des algues broutées, et semblaient moins consommées lors d’un broutage ultérieur, suggérant une perception et une intégration des composés algaux induits par l’herbivorie par les algues voisines. Des études de terrain et en laboratoire ayant précédemment mis en évidence une libération massive d’aldéhydes dans l’air et l’eau de mer après des stress biotiques et abiotiques, nous avons exploré les rôles biologiques d’une signalisation de type aldéhyde dans les interactions kelp/herbivores. Nous avons montré que les aldéhydes pouvaient modifier le métabolisme d’une algue par l’activation du métabolisme des acides gras, et que l’application de 4-HHE sur L. digitata pouvait réduire significativement une consommation algale ultérieure par les herbivores. Ainsi, ces résultats participent à une meilleure compréhension des réponses de défense suite à un broutage chez les laminaires, et confortent l’existence d’une signalisation à distance dans les interactions avec les herbivores, qui impliquerait des composés de défense émis par les algues, dont les aldéhydes. / Kelps are founding species of temperate marine ecosystems, they evolve in the intertidal coastal areas where they are often challenged by herbivores. As most of sessile organisms, kelps develop defensive strategies against herbivory. In the kelp Laminaria digitata, elicitation by oligoguluronates induced regulations of transcription and metabolic pathways, leading to production and release of metabolites, such as aldehydes, in the environment. Moreover, this kelp species feature systemic responses upon defense elicitation and waterborne compounds surrounding a kelp bed have shown to modify its defense physiology. Such distant chemical signaling during defense responses are reminiscent of systemy and priming mechanisms in plants. In marine kelp beds, it should have a major ecological role in structuring marine algal and herbivore communities. In the context of kelp/herbivore interactions, we investigated the defense responses and signaling processes in two emblematic kelp species from north Atlantic and South Pacific coasts, involved in specialized interactions with their herbivores, L. digitata in interaction with Patella pellucida (Brittany, France) and Lessonia spicata with Scurria scurra (Chile). Combined approaches of metabolomics and bio-assays were carried out to decipher the nature of the putative chemical cues, and their biological and ecological roles in algal defense against herbivores. Results showed that, in response to grazing, kelps featured metabolic modifications such as induction of fatty acids, oxylipins and amino acids biosynthetic pathways, as well as transcriptomic modifications. Moreover, we observed that kelps co-incubated with grazed algae exhibited endo-metabolome changes compared to grazed one, and seemed to be less consumed during a subsequent grazing, suggesting the perception and integration of herbivory-induced algal compounds in neighboring algae. As field and lab studies previously highlighted a strong release of aldehydes into the air and the seawater following biotic and abiotic stresses, we further explored the biological roles of aldehyde-based signaling in kelp/herbivore interactions. We found that aldehydes could modify algal metabolism, including the activation of fatty acid metabolism, and that the application of 4-HHE on L. digitata could significantly reduce later algal consumption by herbivores. Thus, these results contribute to a better understanding of defense responses following grazing in kelps, and revealed the occurrence of distance signaling during interaction with herbivores, which could involve algal emitted compounds, such as aldehydes.

No description available.

The Maasailand of Kenya and Tanzania supports one of the richest wildlife populations remaining on Earth. However, over the last century, Maasailand has experienced land transformation notably through conversion of former rangelands to croplands. With the anticipated human population increase in East Africa, more impacts should be envisaged on these rangelands. This thesis investigates the root causes and underlying drivers of land-use change in the Maasai-Steppe ecosystems, stemming from historical, socio-cultural, political as well as the biophysical conditions. To analyse the different drivers of change, an integrated methodological approach was employed. This included a collation of historical data and information derived from both gray and published literature, analysis of remote sensing and Geographical Information Systems (GIS) data, field surveys, workshops, observations, as well as personal communications. Observed land-use change from savannah rangelands to expansive croplands are mainly linked to government policies, land tenure, human population growth (which is also likely to be the largest future driver) and climatic conditions. Consequently these changes have impacted the agro-pastoralist community, whose main incomes for their livelihoods depend on pastoralism. Subsequent loss of formerly communal grazing lands to establish protected areas; large-scale farming and/or private ranches have aggravated the problems of sedentarization due to villagization and privatization policies of the formally mobile agro-pastoral communities. Land-use change also had negative impacts on migratory wildlife species, particularly those utilizing both protected areas and dispersal ranges in communal and/or private lands. The impacts ranged from loss of their migratory routes and corridors to massive declines of populations due to the loss of access to grazing resources. The study recommends government’s interventions for keeping the land open for access to grazing resources as well as opening up wildlife corridors, where it is deemed necessary for national interests.

Western spruce budworm (Choristoneura occidentalis) outbreaks periodically disturb Western US conifer forests by defoliating canopies, which could alter the quantity and chemistry of throughfall delivered to the forest floor. Our objectives were to: i) quantify throughfall water, carbon (C), nitrogen (N), and phosphorus (P) fluxes under budworm-impacted canopies, and ii) examine the influence of herbivore intensity on flux magnitudes. In June 2015, we installed throughfall collectors in two watersheds experiencing high and background levels of herbivory. In each watershed, four plots, each with three throughfall collectors, were established (n=24) collectors), and two bulk rainfall collectors were installed in areas without canopy cover. Throughfall and rainfall were collected from late June to early November 2015. Samples were analyzed for dissolved organic carbon (DOC), ammonium (NH4-N), and soluble reactive phosphorus (SRP). Over the sampling period, throughfall fluxes ranged 8.57 to 47.59 kg/ha for DOC, 0.004-0.011 kg/ha for NH4-N, and 007 - 0.29 kg/ha for SRP. Percent throughfall was slightly, but not significantly, higher in the high (48%) compared to the background watershed (42%). There were no differences in solute concentrations among the watersheds. Net throughfall fluxes, the sum of canopy uptake and leaching and dry/fog deposition, differed significantly for NH4-N by herbivory level and through time for NH4-N and DOC but not SRP. Over time, net NH4-N throughfall fluxes showed a clear transition from net uptake of NH4-N to net leaching of NH4-N in the high herbivory watershed. There was also a clearn NH4-N pulse in the high herbivory watershed after the first, but not subsequent, rainfall events. In this N-limited forest, altered throughfall N may affect soil nutrient cycling and downstream water quality.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science Johannesburg, September 2015 / Plant functional traits provide a means to investigate the diverse ecological strategies employed by plants and a tangible link to assess how the variability in these traits might influence ecosystem processes and functioning. The aim of this dissertation has been to determine how plant and soil nutrient dynamics in a savanna environment are affected by two primary drivers, one a top-down driver, being herbivory by large mammalian herbivores and the other a bottom-up driver, the variable N2-fixation capacity of tree species. To the best of my knowledge this is the most comprehensive study to date to investigate the bioavailability of soil nutrients and the link between these availabilities and plant functional traits. Furthermore this study provides important insight into the use of a novel technology, ion exchange resin capsules in a South African savanna context. By studying a selection of plant functional traits (nutrient concentrations, ratios as well as specific leaf area, relative chlorophyll content and leaf dry matter content) and soil nutrients (suite of macro- and micronutrients) associated with two species of savanna tree of contrasting N2-fixation capacities, I went about investigating how herbivory differentially influences the nutrient dynamics of this system. Selecting individuals of the N2-fixing Acacia tortilis and the non-N2-fixing Combretum hereroense both inside an exclosure and on the adjacent land allowed me to determine the potential impacts by herbivores. These include both direct impacts from foraging and indirect impacts through the regulation of nutrient input pathways via deposition of dung and urine. The work compiled for this dissertation is based on the experimental work conducted in a mesic savanna system in the Marakele Park (PTY) Ltd. During the course of this dissertation, I investigated herbaceous and woody biomass in relation to protection from and exposure to herbivory, determining any differences in the functional leaf traits between individuals inside and outside the exclosure, if these differences were exhibited in the associated herbaceous biomass as well as a comprehensive assessment of the bioavailability of 15 important micro- and macronutrients using ion exchange resin capsules. These capsules were incubated in the soil over the entire summer rainfall period, providing a cumulative view of nutrient bioavailability during the growing season. In this work I also demonstrated whether particular nutrients are associated with specific drivers (i.e. herbivory, canopy position or N2-fixation). Furthermore, these results were then looked at together to suggest the mechanism by which herbivory and N2-fixation drive nutrient dynamics and make recommendations on the use of these results in managing savanna systems in the future. Between the two sites, aboveground herbaceous biomass was significantly greater when protected from herbivores than on the adjacent land. Both exposure to herbivory and N2-fixation capacity were found to alter plant functional traits. Herbivore presence was associated with an increase in herbivore-resistant or structural traits such as C/N, C/P, foliar C and SLA as well as a reduction in N and P content. These less palatable leaves were accompanied by a significantly lower availability of a number of important soil elements, namely NO3-N, inorganic N, P, K, Na, Cu, B, Mg, and S. This suggests a feedback loop between these two components of the ecosystem. N2-fixation capacity is associated with greater concentrations of elements such as N and P and a reduction in traits that are illustrative of a greater structural investment into leaves. Soil nutrient bioavailability however, shows a reduction in certain nutrients when associated with Acacia. A number of nutrients which show a reduction in availability are those which are essential to N2-fixation machinery, namely B and Fe but also lower bioavailabilities of Al and Mg. Finally, Ca, NO3-N, B, Fe, Al and inorganic N were found in greater quantities below the tree canopy than beyond it. In conclusion both herbivory by large mammalian herbivores and N2-fixation have significant effects on tree health, through their regulation of limiting nutrients and alteration of leaf traits. Given the changes which these drivers are capable of exerting on plant and soil nutrient dynamics, this has important consequences for ecosystem processes and functioning and highlights potential considerations in the long-term sustainable management of savannas.

The impact of grazers on the primary production of marine ecosystems has largely been explored in tropical environments. A number of studies support theories on the functional importance of grazers in the community structure of coral reefs. However, large-bodied grazers, like juvenile green turtles, co-occur with herbivorous fishes in subtropical and tropical regions throughout the world and we know little about their combined impact on macroalgal communities and whether they compete for macroalgal resources. My dissertation research was composed of four studies that were conducted simultaneously to further our understanding of plant/herbivore interactions in marine ecosystems. Studies were conducted at the Trident Basin, a non-public military facility within the Port Canaveral Inlet at Cape Canaveral, Florida, USA. The macroalgal study (Chapter 1), determined the spatial and temporal distribution of the macroalgal community. The foraging habits of juvenile green turtles were compared with the macroalgal abundance within the Basin and over time (Chapter 2). Selection ‘for’ specific macroalgal species (based on their availability in the macroalgae study) was used to determine the level of overlap and/or partitioning of resources among herbivorous fishes and juvenile green turtles (Chapter 3). The final empirical study (Chapter 4) measured the impact on thallus height, diameter and/or branching of macroalgae as well as the macroalgal community composition from caging experiments that excluded herbivorous fishes and juvenile green turtles. The algal community was predominantly composed of nine red and green macroalgal species that were persistent year-round. Grazer-resistant macroalgae were rarely observed. Green turtles foraged on many of these same macroalgae but also opportunistically foraged on flotsam, including anthropogenic debris (e.g., plastic). The gut content of the major herbivorous fishes in the community (Abudefduf saxatilis, Archosargus probatocephalus, Diplodus holbrooki, and Lagodon rhomboides) foraged as omnivores depending on where they were captured within the Basin area or their size. All herbivores showed selection for less abundant green algae (i.e., Ulva spp.). Results of the exclusion of juvenile green turtles and large herbivorous fishes in caging experiments suggest that grazing by these large-bodied herbivores had no impact on the composition of the macroalgal community and little impact on the morphological structure of the macroalgal species that were examined. Collectively these four studies contribute to a better understanding of how multiple grazers have evolved to forage in macroalgal communities without detrimental effects on their food resources. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

Orientador: Augusto Shinya Abe / Banca: Francisco Tadeu Rantin / Banca: Denis Vieira de Andrade / Banca: Luiz Edivaldo Pezzato / Banca: Roberto Goiten / Resumo: Com base no hábito alimentar da espécie, no potencial dos quelônios em utilizar matéria vegetal e na importância da fibra e de seus constituintes para alimentação animal, esta pesquisa estudou o crescimento da tartaruga-da-Amazônia (Podocnemis expansa), a disponibilidade de minerais e a digestibilidade dos nutrientes em dietas com diferentes teores de fibra bruta. Os estudos foram realizados na Universidade Estadual Paulista (UNESP), entre maio e novembro de 2008, com duração de sete meses, utilizando 160 exemplares de tartaruga-da-Amazônia provenientes do município de Ribeirão Cascalheira, região do Rio das Mortes/MT, Brasil. O aumento nos teores de fibra na dieta até 16% melhorou o crescimento da tartaruga-da-Amazônia, onde as características de crescimento apresentaram os maiores valores. Entre 16 a 20% de fibra na dieta o crescimento das tartarugas diminuiu. O maior crescimento se deu com teores semelhantes aos encontrados na dieta natural da espécie, reforçando seu potencial para utilização de dieta herbívora. A disponibilidade de minerais e a digestibilidade dos nutrientes foram influenciadas pelos teores de fibra na dieta. A tartaruga-da-Amazônia apresenta elevado potencial de digestão da fibra dietética, comparável ao de ruminantes e outros répteis herbívoros, com sua digestibilidade aumentando com o aumento do teor de fibra na dieta / Abstract: Taking in consideration the potential the chelonians have for using vegetal matter and based on the eating habit of the specie and on the importance of fiber and its constituents for animal feeding, the present study aimed at evaluating the growth of the Arrau sideneck turtle (Podocnemis expansa) fed with diets of different contents of crude fiber and the availability of minerals and the digestibility of nutrients. This study was carried out Universidade Estadual Paulista (UNESP), between the months of May and November, 2008, and lasted seven months. The turtles used were 160 specimens of the Arrau sideneck turtle from Projeto Quelônios da Amazônia, State of Mato Grosso. The increase in the contents of fiber in the diet up to 16% improved the Arrau sideneck turtle's growth, when the growth characteristics showed their best values. In diets including 20% of fiber, the turtle's growth decreased. In diets including between 16 and 20% of fiber, the turtle's growth decreased. The highest rate occurred when using contents similar to those found in the natural diet of the species, corroborating its potential to use herbivore diet. The availability of minerals and the digestibility of nutrients were influenced by the contents of fiber in the diet. The Arrau sideneck turtle presents a high potential for dietary fiber digestion, comparable to that of the ruminants and other herbivore reptiles, with its digestibility increasing as the contents of fiber increase / Doutor

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references (leaves 52-62). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Chicago, Dept. of Ecology and Evolution, August 2003. / Includes bibliographical references. Also available on the Internet.

Coastal communities will be most affected by global climate change and are important to study to understand current and future ecological processes. The current model for global climate change predicts a change in rainfall, which will alter the salinity of coastal systems. Given the presence of eutrophication in many coastal waters, it is important to understand the effects that this increase in nutrients, coupled with changes in salinity, will have on these communities. This study was conducted to understand the effect of salinity increase on the growth and herbivory of the black mangrove, Avicennia germinans, in the presence of increased nutrients. Explicitly, the effects of changing salinity (high, medium, and low) were coupled with fertilizer additions of nitrogen, phosphorus, both, or no fertilizer. Nutrient enrichment differentially affected the growth and herbivory of the plants between salinity zones. The medium salinity zone consistently produced the greatest increases in growth and herbivory. Added nutrients did not have an effect on growth in the low salinity zone. However, added nitrogen increased some growth variables in the medium salinity zone and added phosphorus increased some growth variables in the high salinity zone. Phosphorus also increased herbivory. The results point to diverse processes acting along the salinity gradient. There appears to be differential N- and P-limitation along the gradient. Additionally, the growth differences indicate abiotic and biotic limitations across the salinity gradient, with debilitating salinity acting in the high salinity zone and competition acting in the low salinity zone.