Dissertations / Theses: 'Trophic ecology'

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Maine, Josiah J. "TROPHIC ECOLOGY OF INSECTIVOROUS BATS IN AGROECOSYSTEMS." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1599.

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Land-use change is a leading cause of biodiversity loss and ecosystem service degradation worldwide, but these changes do not affect all organisms equally. Understanding the factors that influence resistance to environmental change is vital for informed conservation. In particular, dietary generalists may withstand environmental change better than specialists due to their ability to exploit variable resources. Bats are voracious predators of insects, but vary widely in their degree of dietary specialization. In Chapter 1, I analyze the effect of land cover and morphology on dietary diversity and the two most common prey items (Lepidoptera and Coleoptera) of bats, selecting important independent variables using phylogenetic generalized least squares (PGLS) and model selection. Dietary diversity increased with increasing amount of cropland near the study area, consumption of Lepidoptera decreased with increasing habitat diversity, and consumption of Coleoptera decreased with increasing distance from the equator. Biodiversity (and hence, prey diversity) is expected to decrease with agricultural intensity, but the observed pattern suggests that dietary specialists may avoid agricultural habitats due to lack of preferred prey. Dietary specialists may thus be increasingly at risk as agricultural intensity increases around the world, and it is essential that we continue to document their ecological roles and the services they provide to society

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Vander, Zanden M. Jake. "Trophic position in aquatic food webs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ55390.pdf.

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Basu, Ben Kumar. "Plankton development and trophic interactions in rivers." Thesis, University of Ottawa (Canada), 1997. http://hdl.handle.net/10393/10146.

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The factors regulating the development and trophic interactions of planktonic communities were determined in 31 medium to large size temperate rivers. In addition, the Rideau River, Ontario, was studied in detail over three field seasons. Variables measured included: phytoplankton biomass as measured by chlorophyll $\alpha$ concentration; zooplankton biomass (rotifers and crustaceans); heterotrophic bacterial abundance; heterotrophic flagellate abundance; nutrient concentrations (phosphorus and nitrogen); dissolved organic carbon concentration; river discharge; water residence time; depth; temperature; and light attenuation. Phytoplankton was abundant in eutrophic rivers ($>$15 $\mu$g L$\sp{-1}$ of chlorophyll a) and was most strongly related to nutrient concentrations, primarily total phosphorus, which explained up to 76% of the variation in chlorophyll a. Phytoplankton biomass in the rivers was not related to the hydrological parameters of water residence time or discharge, possibly due to the short generation time of phytoplankton (hours to days). Light did not appear to limit phytoplankton biomass due to shallow depths and extensive vertical mixing. In the Rideau River phytoplankton biomass exhibited longitudinal heterogeneity, but in general increased in a downstream direction, concomitant with increases in nutrient concentrations. Phytoplankton biomass did not appear to be affected by zooplankton grazing in the rivers. However, phytoplankton biomass may have been negatively impacted by benthic filter feeders, in particular the invasive zebra mussel (Dreissena polymorpha), in the downstream reaches of the Rideau River. Zooplankton biomass in the rivers was low (usually 20 $\mu$g L$\sp{-1}$ dry mass) and small taxa dominated the zooplankton communities (e.g. rotifers, bosminids). Large zooplankton taxa, such as Daphnia sp., were much less abundant. Due to longer generation times (days to weeks), zooplankton biomass was primarily related to water residence time which explained 33% of the variation. Zooplankton appeared susceptible to advective loss in the rivers. A positive resource effect of either nutrients or phytoplankton on zooplankton biomass, typically observed in lakes, was weaker in the rivers. In comparison to lakes, zooplankton appeared less tightly coupled to phytoplankton. As with phytoplankton, zooplankton biomass in the Rideau River increased with downstream travel and appeared to be negatively affected by benthic filter feeders. Heterotrophic bacteria were abundant in the rivers (4.5 $\times$ 10$\sp6$ cells ml$\sp{-1})$ and, as in lakes, bacteria were most strongly related to nutrient concentrations (total phosphorus) and phytoplankton biomass (chlorophyll a). In contrast to lakes, no relationship between bacterial abundance and dissolved organic carbon was observed, possibly due to the more allochthonous, refractory nature of river dissolved organic carbon. Heterotrophic flagellates were also abundant in the rivers $(4.0\times10\sp{3}$ cells ml$\sp{-1})$ and were most strongly related to bacterial abundance and nutrient concentrations (total phosphorus). Neither bacterial nor flagellate abundance was related to water residence time. A negative relationship between zooplankton biomass and bacterial or flagellate abundance was not observed, possibly because of the low biomass (hence low grazing pressure) of zooplankton in the rivers. Due to the scarcity of zooplankton in rivers, there may be little transfer of energy from the planktonic microbial food web to planktonic metazoans.

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Ball, Simon John. "Picophytoplankton in lakes of different trophic state." Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301818.

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Mestre, Arias Laia. "Intraguild interactions, trophic ecology and dispersal in spider assemblages." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/117457.

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Les aranyes (Araneae) són un grup hiperdivers de depredadors àmpliament representat en comunitats naturals i en conreus, on s’alimenten de diferents tipus d’insectes i participen en el control biològic de plagues. Ocupen posicions intermèdies dins les xarxes tròfiques i estan implicades en interaccions intragremials amb altres depredadors. Tanmateix, la majoria d’estudis en ecologia tracten les aranyes com a un sol grup uniforme i, per tant, ignoren la gran diversitat d’interaccions interespecífiques i de connexions tròfiques en les comunitats d’artròpodes. Les xarxes tròfiques també estan influenciades per la dispersió dels individus a través del paisatge. Com que dispersar-se és costós, hom espera que els individus es basin en múltiples fonts d’informació sobre la qualitat de l’hàbitat abans de dispersar-se, però la recerca sobre la importància relativa de fonts d’informació diferents és molt escassa. Els objectius d’aquesta tesi doctoral eren, primer, estudiar les xarxes tròfiques d’artròpodes i les interaccions entre aranyes, formigues i ocells utilitzant com a sistema d’estudi un cultiu ecològic mediterrani de cítrics; segon, investigar l’efecte de la informació sobre sobre disponibilitat d’aliment i del subministrament d’aliment en la dispersió de les aranyes. Hi havia sis objectius concrets, (1) comparar l’efecte relatiu dels ocells i de les formigues en la comunitat d’aranyes; (2) comprovar l’impacte dels ocells en les aranyes diürnes i nocturnes de les capçades; (3) estudiar els efectes a llarg termini sobre la comunitat d’aranyes de les formigues que patrullen en les capçades; (4) desentrellar l’estructura de la xarxa tròfica dels artròpodes del cultiu amb anàlisis d’isòtops estables; (5) comprovar l’efecte dels indicadors de disponibilitat d’aliment en la selecció d’hàbitat i l’efecte del subministrament de preses en l’emigració de l’aranya colonial Cyrtophora citricola; i (6) contrastar la importància del subministrament de menjar a la mare i a la descendència en l’emigració a curta i a llarga distància d’Erigone dentipalpis. Durant un període de gairebé 2 anys, vam trobar que les formigues tenien un gran efecte sobre les aranyes constructores de teranyina de les famílies Araneidae and Theridiidae, mentre que no vam trobar cap efecte dels ocells. No obstant això, en un experiment d’exclusió d’ocells on vam utilitzar altres mètodes de mostreig, vam detectar una reducció dels aranèids i dels terídids causada pels ocells, la qual cosa emfasitza la importància del mostreig en el resultat dels experiments de camp en ecologia. Les dades a llarg termini també proporcionen informació essencial sobre processos ecològics: mentre que a l’inici d’un experiment de 8 anys d’exclusió de formigues, aquestes no tenien cap efecte sobre les aranyes, sí que van tenir un impacte profund sobre la comunitat d’aranyes durant els últims 4 anys: les formigues van afectar negativament l’abundància d’un ampli rang d’espècies d’aranyes independentment de la família a la qual les aranyes pertanyien. Les anàlisis d’isòtops estables van mostrar la posició tròfica de les 25 espècies més comunes d’aranyes i de les principals espècies de formigues i d’altres insectes. El nivell tròfic de les aranyes era molt més alt que el de les seves preses potencials, suggerint la prevalença de l’omnivoria i de la depredació intragremial en la xarxa tròfica. Les espècies d’aranyes de la mateixa família pertanyien a grups tròfics diferents, cosa que, juntament amb els resultats esmentats abans, mostra l’alt valor de les anàlisis a nivell d’espècie. Tant en C. citricola com en E. dentipalpis, la informació indirecta sobre la disponibilitat de menjar va tenir un paper clau en la dispersió, en contrast amb la importància limitada de la ingesta de menjar. Per tant, aquestes fonts d’informació han de ser considerades juntament amb les interaccions intragremials com a factors que influencien les poblacions d’aranyes.
Spiders (Araneae) are a hyperdiverse predator group and are widespread in both natural and arable communities, where they prey on many different types of insects and play a role in biological control. Spiders occupy intermediate positions in food webs and are involved in intraguild interactions with other predators. However, most studies treat the spider assemblage as a single uniform group, thus ignoring the sheer diversity of species interactions and trophic links within arthropod communities. Food webs are also influenced by the dispersal of individuals through the landscape. Because dispersal is costly, individuals are expected to rely on multiple sources of information about habitat quality before dispersing, although research on the relative importance of different information sources is largely lacking. The goals of this PhD thesis were first, to study arthropod food webs and the interactions between spiders, ants and birds using a Mediterranean organic citrus grove as study system; second, to investigate the effect of information about food availability and of actual food supply on spider dispersal. There were six specific objectives, namely (1) to compare the relative effect of birds and ants on the spider assemblage; (2) to test the differential impact of bird predation on diurnal and nocturnal canopy spiders; (3) to study the long-term effects of canopy-foraging ants on the spider assemblage; (4) to unravel the structure of the arthropod food web of the grove with stable isotope analyses; (5) to test the effect of cues of food availability on site-selection and of prey supply on emigration decisions of the colonial spider Cytrophora citricola; and (6) to test the importance of direct and maternal food supply on long- and short-distance emigration decisions of Erigone dentipalpis. Over an almost 2-year period, we found that ants had a strong effect on some web-building spiders of the families Araneidae and Theridiidae, whereas we did not find any effect of birds. However, in a bird exclusion experiment where we used other sampling methods, we detected a reduction of araneids and theridiids caused by birds, emphasizing the influence of sampling on the outcome of ecological field experiments. Long-term data also provided essential information about ecological processes: whereas in the beginning of an 8-year ant-exclusion experiment ants did not have any effect on spiders, they did have a pervasive impact on the spider assemblage for the last 4 years: ants negatively affected the abundance of a wide range of spider species independently of the family the spiders belonged to. Stable isotope analyses retrieved the trophic positions of the 25 most common spider species and of the main species of ants and other insects. The trophic level of spiders was much higher than that of their potential prey, suggesting a prevalence of omnivory and intraguild predation in the food web. Spider species from the same family belonged to different trophic groups, which, together with the aforementioned results, show the high value of species-level analyses. In both C. citricola and E. dentipalpis, indirect information of food availability played a key role in dispersal, in contrast to the limited importance of immediate food intake. These information sources thus need to be considered together with intraguild interactions as factors influencing spider populations.

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Woodstock, Matthew. "Trophic Ecology and Parasitism of a Mesopelagic Fish Assemblage." Thesis, NSUWorks, 2018. https://nsuworks.nova.edu/occ_stuetd/469.

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Mesopelagic (open ocean, 200-1000 m depth) fishes are important consumers of zooplankton and are prey of oceanic predators. Some mesopelagic fishes (e.g., myctophids and stomiids) undertake a diel vertical migration where they ascend to the near-surface waters during the night to feed and descend into the depths during the day to avoid predators. Other mesopelagic fishes (e.g., Sternoptyx spp.) do not vertically migrate and remain at deep depths throughout the day. While in the epipelagic zone (surface – 200 m depth), vertically migrating fishes become prey to upper-trophic level predators, such as: tunas and billfishes. Benthic fishes (e.g., macrourids) often vertically migrate as well, ascending into the pelagic zone to feed on pelagic organisms. Fishes of different depths and vertical migration habits likely have a different ecological role in food webs. The relationship between parasites and gut contents provides insights into ecological processes occurring within assemblages, as prey items are often vectors for parasites. This study examined the differences between the prey items present in the gastrointestinal cavity and parasites of 26 mesopelagic fish species in the Gulf of Mexico. Results showed that based on the proportionally dominant prey items per species, six different feeding guilds existed within this assemblage, five based on planktivory: copepodivores, predators of copepods and other zooplankton, predators of copepods and euphausiids, gelatinivores, generalists, crustacean decapodivores, and upper-trophic level predators. Larger fishes preyed on larger prey items and harbored more parasites. Sigmops elongatus exhibited an ontogenetic diet shift at 75 mm standard length, progressing from eating primarily copepods at small sizes to eating primarily euphausiids at large sizes. Compared to similar studies, this study revealed a higher parasitic infestation by trematodes, an endoparasite (parasite within the host) class often restricted to nearshore hosts, in Gulf of Mexico fishes. Helicometrina nimia, the dominant parasite of the gempylid Nealotus tripes, has not previously been recorded in hosts below 200 m depth, suggesting a foodweb pathway that transitions from nearshore to offshore. These data can be used to develop and refine models aimed at understanding ecosystem structure and connectivity.

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Pillay, Pradeep. "The ecological and evolutionary assembly of trophic metacommunities." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96666.

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Despite the important role spatial processes play in natural communities, far too little theoretical work has been devoted to exploring how complex food web communities may be assembled in space, and how the spatial structure of trophic interactions may provide a stabilizing mechanism for complex food web networks. In this thesis I develop a food web metacommunity model based on a classic Levins-type patch-dynamic model which views trophic interactions between species as occurring in a spatially subdivided habitat. I then use this model to explore both simple and complex trophic networks in an ecological and evolutionary context. I first review and evaluate previous attempts at defining a patch-dynamic metacommunity model of trophic interactions. After correcting the flaws in previously published models I develop a corrected model and apply it to simple trophic configurations. I show how the stability of simple trophic interactions, like omnivory loops, depends upon the interacting effects of space and network configuration. I then use the model to study the evolution of dispersal in a simple predator-prey system. Specifically, I investigate how both predator and prey dispersal rates will evolve in response to increasing patch extinction rates caused by locally strong top-down predator effects. I show how the predator's evolutionarily stable (ESS) dispersal rate will increase, as expected, in response to increasing local extinction, while the prey's ESS dispersal rate exhibits a counterintuitive nonmonotonic response – actually decreasing for some ranges of extinction. I explain how the prey's counterintuitive response arises because of the way trophic interactions between species play out at different spatial scales. After applying the model to simple networks I then explore the assembly of complex food webs. I show that, under very simple assumptions, diverse and complex food web networks can be assembled through the creation of network branches which provide opportunities for the build-up species and multiple food chain paths in the food web. I also show how these network branches can emerge simply as the result of the spatial distribution of trophic interactions, and the structural support provided by omnivory and generalist feeding links. I then attempt to determine if natural food webs show a relationship between biodiversity and network branching. To this end I examine a set of empirical food webs and observe a striking linear scaling relationship between food web size and the degree of branching in the minimum spanning tree of a food web. This empirical corroboration of the theory suggests that the theory reported here may be of value as a guide to how space and dispersal interact to structure natural food webs at large scales.
Malgré l'importance des processus spatiaux dans les communautés écologiques naturelles, peu de théories examinent le rôle de l'espace dans l'assemblage et la stabilisation des réseaux trophiques complexes. Dans cette thèse, je développe un modèle de réseau trophique spatial (métacommunauté) fondé sur un model dynamique de métapopulation du type Levins, où les interactions trophiques entres les espèces ont lieu au sein d'une série de populations locales. Ce modèle de métacommunauté me permet d'examiner les réseaux trophiques simples et complexes dans un contexte écologique et évolutif.Dans le premier chapitre, je résume et critique les modèles actuels de métacommunauté du type Levins incorporant les interactions trophiques dans un contexte spatial. Après avoir identifié les erreurs de ces modèles, je développe un modèle corrigé afin d'examiner des réseaux trophiques simples. Je montre que la stabilité des interactions trophiques simples (telles que les boucles omnivores) dépend de l'interaction entre la structure spatiale et la topologie du réseau trophique. Dans le deuxième chapitre, j'utilise ce modèle afin de déterminer l'évolution du taux de dispersion du prédateur et de sa proie lorsque la prédation favorise l'extinction des populations locales. Je montre que face à une augmentation du taux d'extinction, le taux de dispersion évolutivement stable du prédateur augmente de façon monotone alors que celui de la proie varie de façon non-monotone et diminue pour certains niveaux d'extinction. Je démontre que cette réponse contre-intuitive de la proie est due à la structure spatiale des interactions trophiques entre les espèces.Dans le troisième chapitre, j'utilise le modèle afin d'étudier l'assemblage de réseaux trophiques complexes dans l'espace. Je montre que l'addition de branches dans le réseau trophique (ramification) permet l'accumulation d'espèces dans des chaînes alimentaires distinctes et la création de réseaux trophiques complexes. Je démontre que cette ramification du réseau trophique est due à la distribution spatiale des interactions trophiques ainsi que le support structurel apporté par les boucles omnivores et généralistes.Dans le quatrième chapitre, j'essaye de déterminer si la relation entre la biodiversité et la ramification des réseaux trophiques observée dans le modèle est applicable aux réseaux trophiques naturels. Je montre qu'il existe une forte relation linéaire entre la taille des réseaux trophiques naturels et le nombre de branches qui caractérise leur arbre couvrant minimum. Cette vérification empirique du modèle indique que la théorie développée dans cette thèse pourrait permettre de mieux comprendre les rôles que jouent l'espace et de la dispersion dans l'assemblage et la structure des réseaux trophiques naturels à grandes échelles.

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Das, Indraneil. "Trophic ecology of a community of South Indian anuran amphibians." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305537.

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Wallace, Bryan Patrick Spotila James R. "The bioenergetics and trophic ecology of leatherback turtles (Dermochelys coriacea) /." Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/513.

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Hughes, Adam. "The trophic ecology of Psammechinus miliaris in Scottish sea lochs." Thesis, Open University, 2006. https://pure.uhi.ac.uk/portal/en/studentthesis/the-trophic-ecology-of-psammechinus-miliaris-in-scottish-sea-lochs(e43ce06b-4b20-4582-9beb-bdbc61b7a214).html.

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Understanding the trophic relationships between organisms is crucial to understanding ecosystem functioning and as such regular echinoids have been termed keystone through the action of their grazing. Much research has focused on this group’s action as herbivores, but as a group omnivory is common. The aim of this study was to investigate the trophic ecology of the locally super abundant regular echinoid species Psammechinus miliaris within Scottish sea lochs. To do this the study used manipulative field experiments combined with biochemical analysis of trophic proxies. The manipulative field experiments involved either the hand removal or the caging of P. miliaris to determine the impact the sea urchin grazinghas on benthic community structure. These studies revealed that grazing of P. miliaris can have a major influence on the biomass and structure of the benthic invertebrate communities. The biochemical analysis of trophic proxies was used to quantify the spatial and temporal variations in the trophic interactions of P. miliaris. These studies focused on the urchin gonad and compared differences in the gonadal somatic indices (reflecting nutritional and reproductive state) with the fatty acid biochemistry and stable isotope ratios of Carbon and Nitrogen. These studies revealed high levels of spatial and temporal heterogeneity in the trophic interactions of P. miliaris and suggested that the populations exhibited significant levels of omnivory. The combination of these studies showed that P.miliaris plays an important role in structuring benthic invertebrate communities and in the flow of energy through ecosystems and through this, ecosystem functioning.

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Wells, Brenda L. "ECOLOGICAL SPECIATION IN A MULTI-TROPHIC COMPLEX: GALL MIDGES, GOLDENRODS, AND PARASITOIDS." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1290387561.

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Weisser, W. W. "Foraging and life history strategies in multi-trophic communities." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240464.

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Cheung, Ma Shan. "Trophic transfer of metals along marine rocky shore food chains /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?AMCE%202007%20CHEUNG.

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Bornancin, Louis. "Lipopeptides from Cyanobacteria : structure and role in a trophic cascade." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT202.

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Dans le lagon de Moorea, en Polynésie Française, nous avons identifié un écosystème constitué de deux producteurs primaires (les cyanobactéries filamenteuses Lyngbya majuscula et Anabaena cf. torulosa), trois mollusques herbivores (Stylocheilus striatus, S. longicauda, et Bulla orientalis), un nudibranche carnivore (Gymnodoris ceylonica) et un crabe carnivore (Thalamita coerulipes). L. majuscula et A. cf torulosa prolifèrent sur de vastes zones jusqu’à épiphyter les coraux ; elles sont des producteurs importants de métabolites secondaires, principalement des lipopeptides cycliques, qui peuvent être toxiques ou répulsifs. Cependant, ces composés n’empêchent pas le lièvre de mer S. striatus de consommer les cyanobactéries. S. striatus, décrit comme un prédateur spécialiste de L. majuscula, est connu pour séquestrer et/ou biotransformer les métabolites secondaires de L. majuscula. Cependant nous avons également observé S. striatus, sur A. cf torulosa où il semble moins exposé à la prédation du nudibranch G. ceylonica que quand il est sur L. majuscula. Dans cet écosystème modèle, nous avons combiné le profilage des métabolomes des deux cyanobactéries et des expériences en écologie dans le but d’étudier le rôle des médiateurs chimiques dans la structuration de cet écosystème ; nous avons complété la caractérisation des profils métaboliques des deux cyanobactéries, étudié les transmissions verticale et horizontale des métabolites secondaires produits par les cyanobactéries le long de la chaine trophique, et étudié le rôle de ces composés dans les relations prédateurs-proies. De A. cf torulosa, nous avons isolé cinq analogues acyliques et deux analogues cyliques des laxaphycines que nous avons caractérisés par RMN (1D et 2D RMN : COSY, TOCSY, HSQC, HMBC, NOESY), spectrométrie de masse (spectrométrie de masse à haute résolution et fragmentation en MSn), ainsi que par dégradation chimique avec la méthode de Marfey. La présence de laxaphycines acycliques n’a jamais été décrite auparavant. Nous avons montré que les peptides de L. majuscula sont séquestrés sans biotransformation par les herbivores, alors que les herbivores présents sur A. cf torulosa biotransforment deux laxaphycines en quatre composés nouveaux que nous avons caractérisés. Il ne semble pas que la séquestration et la biotransformation soient opérées dans le but d’améliorer les défenses chimiques des herbivores mais plutôt comme un mécanisme de tolérance. Nous avons également montré que les mollusques herbivores utilisent les composés produits par les cyanobactéries comme signaux chimiques pour détecter à distance les cyanobactéries et pour le choix de leur nourriture. Ces expériences de choix semblent indiquer que S. striatus et B. orientalis sont des herbivores généralistes bien que l’influence des molécules des cyanobactéries suggère un comportement adaptatif permettant au mollusque de retrouver l’hôte sur lequel il a été prélevé
In the lagoon of Moorea in French Polynesia, we have identified a relatively simple tropical marine ecosystem consisting of two primary producers (two filamentous cyanobacteria, Lyngbya majuscula and Anabaena cf. torulosa), three herbivorous molluscs (Stylocheilus striatus, S. longicauda and Bulla orientalis), a carnivorous nudibranch (Gymnodoris ceylonica) and a carnivorous crab (Thalamita coerulipes). L. majuscula and A. cf torulosa, that bloom ephemerally across wide sandy areas and even on corals, are prolific producers of secondary metabolites, mainly cyclic lipopeptides, which may either be toxic or act as feeding deterrents to potential consumers. However, these compounds do not prevent the sea hare S. striatus, feeding on cyanobacteria. S. striatus, considered as L. majuscula specialist, is known to sequester and transform some secondary metabolites produced by L. majuscula,. However we found also S. striatus feeding on A. cf torulosa and in this case it was less susceptible to predation by the nudibranch G. ceylonicasa than when it fed on L. majuscula. In the study of this model ecosystem, we combine cyanobacterial metabolome profiling and ecological bioassays in order to study the cascading effects of chemical mediators in multi-trophic relationships; we completed the metabolic profile characterization of the two cyanobacteria, we studied vertical and horizontal transmissions of the cyanobacterial secondary metabolites along the trophic web, and studied the role of these compounds in predator-prey relationships. Focusing our attention on A. cf torulosa we isolated seven new lipopeptides, derived from the known laxaphycins, and characterized them using extensive NMR experiments (1D and 2D NMR: COSY, TOCSY, HSQC, HMBC, NOESY), mass spectrometry (HR-MS and fragmentation by MSn) and Marfey’s advanced method. It is the first time that acyclic analogs of laxaphycins have been described. Although the peptides from L. majuscula are found intact in herbivores, some lipopeptides from A. cf torulosa are biotransformed by sea hares into four new compounds we characterized. The sequestration and biotransformation by the herbivores may be considered as a tolerance mechanism rather than a defense mechanism. We demonstrate also that the herbivores use cyanobacterial compounds as chemical cues for cyanobacteria tracking and feeding choice. Our experiments suggest that S. striatus and B. orientalis are generalist consumers, although the influence of cyanobacterial chemical cues on their foraging preferences may suggest an adaptive behavior enabling the mollusc to track their host of origin

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Papacostas, Katherine J. "Spatial and Temporal Variability in Marine Invasion and Trophic Dynamics." Diss., Temple University Libraries, 2014. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/305874.

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Biology
Ph.D.
Species interactions are central to the study of community ecology, but these interactions can change with context. For instance, predator-prey interactions can vary with species introductions, spatial scale and temporal scale, and we are still learning how such factors can influence the strength of these interactions. Studying species interactions via multifaceted approaches and at different scales aids in the understanding of local and large scale processes, and can lead to predictions of how our ecosystems will persist in the face of continued anthropogenic alteration of the globe. The present series of studies sought to explore spatial and temporal variability in marine predator-prey interactions and invasion dynamics. The first objective was to assess biogeographic variability in predator invasions in the field. The second examined spatial variation in niche breadth via field collections, laboratory dissections, and database development, and the third involved a series of laboratory and field experiments as well as population modeling to examine temporal variability in native and non-native behavioral interactions. Specifically for the first objective, I examined the strength of marine invasive species-induced trophic cascades across latitude, hypothesizing that a non-native tertiary consumer could facilitate non-native basal prey establishment through the consumption of a native secondary consumer. I further predicted that the ecological importance of this cascade may be reduced in the subtropics relative to the temperate zone due to stronger predation pressure at lower latitudes. I found evidence of a trophic cascade in both regions, but it was only maintained under ambient predation pressure in the temperate zone. My results also suggest that strong predation pressure on the non-native intermediate predators in the subtropics may explain the weakened cascade under ambient conditions. For the second objective, I tested the hypothesis of increased specialization at lower latitudes using Brachyuran crabs as a model system and diet as my measure for niche breadth, while controlling for range size, body size and evolutionary relatedness. I compiled a dataset on 39 crab species' diets from existing studies and conducted my own diet analyses on species collected in a temperate, subtropical and tropical region, resulting in a global comparison. I found that latitudinal position was correlated with range size for temperate species, but not for tropical species, and found no correlation between the other focal variables and latitude. These results suggest that ecological mechanisms (i.e. competition strength) may be driving patterns of niche breadth in the temperate zone, while evolutionary mechanisms may be more important in predicting niche breadth patterns in tropical systems. For the third objective, I examined the influence of native and non-native prey naïveté on intermediate predator invasion success. I hypothesized that 1) naïveté is greatest in earlier stages of invasion across all trophic levels, decreasing the longer a non-native species is established in a system, 2) Native prey naïveté results in resource effects which increases invasion success, or 3) predator effects on non-native species would outweigh the importance of basal native prey naïveté, preventing an increase in non-native population growth. Through laboratory trials, I found support for naïveté being stronger at earlier stages of invasion, for both native basal prey and non-native intermediate predators. I also found weak predation on the more recently established intermediate predator in the field. However, my population model predicted that growth independent of basal prey naïveté. These results suggest that physiological traits, such as conversion efficiency and growth rates of the invasive crab may be driving its population growth more-so than foraging benefits. My studies surrounding the variability of species interactions are the first to examine the strength of invasive species-induced trophic cascades across latitude, one of very few marine empirical studies to examine diet breadth at a large spatial scale, and the first to examine multi-trophic behavioral effects on invasion success respectively. They highlight the importance of studying multi-trophic interactions, as examining more pieces of the food web is increasingly important in developing a broader understanding of interactions and adaptations within invaded communities. My research also highlights the importance of studying interactions from a macroecological perspective. Tracking both invasions and native species interactions through space and time provides insight into marine community dynamics and may elucidate possible mechanisms of species coexistence.
Temple University--Theses

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Valls, Mir Maria. "Trophic Ecology in Marine Ecosystems from the Balearic Sea (Western Mediterraniean)." Doctoral thesis, Universitat de les Illes Balears, 2017. http://hdl.handle.net/10803/461496.

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The conservation of marine ecosystem structure and functioning is a priority target within the context of the environmental management. This is especially important in oligotrophic systems such as the Balearic Sea, where food availability is a limiting factor. For such a target is fundamental to know the array of predator-prey interactions as a basis to understand the food web trophodynamics. In this Thesis, the trophic structure of the pelagic and benthic habitats off the Balearic Islands and the feeding ecology of three taxonomic groups (cephalopods, elasmobranchs and mesopelagic fishes) playing a key role in marine ecosystems, were investigated A relatively large food web (89 species) encompassing both the pelagic and the benthic habitats were analysed. The food webs extended up to 4 trophic levels in both habitats, and most species occupied intermediate trophic levels. A high partitioning rate of trophic resources was found, which might be related to the reduction of competition for food. The energy link between the pelagic and benthic communities (benthopelagic coupling; BPC) was stronger on the shelf break, where higher hydrodinamism mix the water column and associated nutrients, than on the slope. The geographical variability of oceanographic drivers (i.e. eddies, currents) influenced the strength of the BPC. Regarding species trophic interactions, stomach contents provided evidence of mesopelagic prey coupling pelagic and benthic habitats, especially down the shelf break. Rays from the shelf consumed mainly decapod crustaceans and teleosts, whereas sharks from the slope fed primarily upon mesopelagic prey (i.e myctophids, euphausiids). Sharks and rays variation in diet was driven by species specific ontogenetic stages and habitat use. The diet of the two squid Loligo vulgaris and L. forbesii, examined for the first time in the Mediterranean, showed their highly piscivorous habits. Their prey composition revealed a lack of diet overlap as a result of their bathymetric segregation. Both squids showed shifts in diet related to size and their reproduction period. The squid L. vulgaris feed on small benthic prey until they reach a size threshold and feed on benthopelagic fish thereafter. Seasonal changes in diet in both squid species, likely related to reproduction, might help improving their individual body condition. During this period, L. vulgaris increased the consumption of highly nutritive polychaetes, whereas the adults of L. forbesii carried out movements to deeper waters to feed on lipid-rich mesopelagic prey. Mesopelagic prey are important food resources for demersal species in the Balearic Sea and, as a result of their nycthemeral movements, they have important implications for the transport of mass and energy through the water column. The trophodynamics of this group revealed that food sources (δ13C) varied little over the spatial scales sampled (location and depth) but showed high seasonality, reflecting intra-annual changes in the species composition of the phytoplankton community. By contrast, spatio-temporal variations of mesopelagic trophic interactions (δ15N) were minimal. Important niche segregation was observed between the non-migratory stomiiforms and some of the extensive migratory myctophids. Finally, the comparative analysis of the trophic ecology of deep-sea cephalopods and elasmobranchs showed that they displayed different feeding strategies with a clear resource partitioning between and within taxa. Segregation of the isotopic space indicated a contrasting food source gradient (δ13C) stretching from pelagic (squids and cuttlefishes) to nektobenthic (octopuses and elasmobranchs) sources. However, deep-sea sharks off the Balearic Islands frequently preyed on mesopelagic species, as did squids and cuttlefishes. Cephalopods, in turn, constituted an important food resource for deep-sea sharks. Squid and shark species identified as benthopelagic feeders, play a key role in the transport of energy from midwater regions to the benthic community.

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Dias, Sérgia Catarina de Amorim Costa. "Ecology and trophic dynamics of the European eel, Anguilla anguilla L." Doctoral thesis, Instituto de Ciências Biomédicas Abel Salazar, 2009. http://hdl.handle.net/10216/50166.

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Dias, Sérgia Catarina de Amorim Costa. "Ecology and trophic dynamics of the European eel, Anguilla anguilla L." Tese, Instituto de Ciências Biomédicas Abel Salazar, 2009. http://hdl.handle.net/10216/50166.

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19

Rae, Caitlin. "The distribution and trophic ecology of Golden ghost crabs (Ocypode convexa)." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2018. https://ro.ecu.edu.au/theses/2058.

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Sandy beaches make up approximately three-quarters of the world’s shorelines. They are important ecosystems, hosting abundant invertebrate macrofaunal communities that provide food resource for vertebrate predators such as shorebirds, seabirds, marine mammals and fish. Although possessing a terrestrial appearance, food input on sandy beaches is derived predominantly from the sea. Such food input includes detrital matter, mostly in the form of wrack, and has the potential to support a great diversity of species, as well as stabilising energy fluxes and dynamics of consumer populations. The movement of detritus, along with other vectors such as organisms and nutrients, across ecosystem boundaries can alter productivity and change consumers’ distribution, abundance, and growth rates at multiple trophic levels in recipient systems. Ultimately, the input of nutrients and detritus can increase primary and secondary production and alter food web structures and community dynamics in recipient ecosystems, a process termed “spatial subsidy”. Ghost crabs (Ocypode spp.) form an important component within beach communities in several places around the world and are part of this trophic complexity. However, little is known of their densities, trophic structure and the role they play as vectors for spatial subsidies through movement of marine derived nutrients inland. The aim of this study was to determine the trophic ecology of the Golden ghost crab (Ocypode convexa) and understand what its role is in terms of marine connectivity along the Mid-West coastline of Western Australia. Using ghost crab burrows as a proxy for relative abundance, this study illustrated that Ocypode spp. are abundant and reside along beaches with minimal foot- and off-road vehicle traffic and exist in the upper intertidal zone in comparison to zones within the dune environment. In addition, from stomach content (percentage frequency (%F) and percentage volume (%V)) and stable isotope analyses (δ13C and δ15N), as well as laboratory assays, it was found that the Golden ghost crab is an omnivore that consumes a wide variety of plant and animal material. A larger proportion of its diet comprises material derived from the marine environment, compared to material derived from the terrestrial environment. These results support the importance of marine detritus as a spatial subsidy on beaches, and the important role ghost crabs are likely to play as iii consumers within sandy beach ecosystems, and as vectors for the transfer of marine material through the beach-dune food web.

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Meaden, Sean McClarey. "The tri-trophic interaction of plants, pathogenic bacteria and bacteriophages." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/22133.

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The ecology and evolution of pathogens are key factors in predicting the severity and spread of disease, as well as treatment outcomes. However, the effects of multiple trophic levels that include host, microbial competitors and viruses are typically overlooked. In this thesis I develop our understanding of bacteria-phage coevolution, microbial dispersal and the role of the microbiome in disease. The results of these experiments have direct implications for phage therapy: the use of bacteriophages to treat bacterial infections. Firstly, I explore the risks of phage application in the environment and draw parallels with the misuse of antibiotics in selecting for bacterial resistance. I then demonstrate that the evolution of resistance to phages in a plant pathogenic bacterium is context-dependent. Notably, I find a fitness cost in plant infections that is absent when the bacteria are cultured solely in the laboratory. I then characterize four novel phages and use a simple laboratory based assay to predict their potential as phage therapy agents in an agricultural context. Next I show that reservoir species of plant hosts can affect the evolution of virulence, when bacteria are passaged on both a focal and distant host, but find no evidence of local adaptation. I also show that the evolution of such traits can occur in a parallel manner at the genetic level. I then determine a compositional shift in the microbiota associated with the symptoms of bleeding canker disease in Horse Chestnut trees across the length of the UK. Finally, I find an age-elated decline in bacterial species richness and evidence for niche-assembly theories by investigating bacterial dispersal in UK Oak trees in a single woodland.

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Pardikes, Nicholas A. "Global Change and Trophic Interaction Diversity| Complex Local and Regional Processes." Thesis, University of Nevada, Reno, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10282934.

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The structure and functioning of ecosystems across the globe are rapidly changing due to several components of global environmental change (GEC). My dissertation aims to illustrate how regional and local aspects of GEC impact diverse assemblages of species and species interactions. All organisms are embedded in complex networks of species interactions, and future efforts to predict and mitigate the impacts of GEC on ecological communities will be facilitated by such studies that incorporate a suite of species and species interactions. This study advances our understanding of how GEC will impact ecological communities by investigating two questions about GEC: 1) How will shifts in global climate cycles (e.g., El Nino Southern Oscillation), as a consequence of global warming, impact a diverse assemblage of butterflies that exist across a heterogeneous landscape? 2) What are the consequences of woody plant encroachment on complex, specialized interactions between plants, insect herbivores, and natural enemies (e.g., insect parasitoids)? Furthermore, I helped develop a tool to identify characteristics of ecological communities that are essential for promoting the diversity of trophic interactions. While the loss of species diversity is well recognized, interactions among species are vanishing at an astonishing rate, yet we know little about factors that determine the diversity of interactions within a community. Using data from a long-term butterfly monitoring dataset, I was able to demonstrate the utility of large-scale climate indices (e.g., ENSO) for modeling biotic/abiotic relationships for migratory butterfly species. Next, I used encroaching juniper woodlands in the Intermountain West to uncover that population age structure of dominant tress, such as juniper, can affect plant-insect dynamics and have implications for future control efforts in the expanding woodlands. Additionally, reductions of understory plant diversity, as a consequence of juniper expansion, resulted in significantly lower parasitism rates and parasitoid species diversity. Finally, simulated food webs revealed that species diversity and, to a lesser degree, consumer diet breadth, promote the diversity of trophic interactions. As ecosystems across the globe experience changes and the loss of species diversity continues, these findings offer insight into how GEC will impact species and species interactions.

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Leroux, Shawn. "Constant and temporally variable spatial subsidies and the strength of trophic cascades." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95157.

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Natural ecosystems are open to flows of energy, materials, and organisms. These subsidies are ubiquitous and influence ecosystem structure and functioning at local and regional extents. Subsidized consumers can attain higher biomass and abundance than unsubsidized consumers but the indirect, cascading effects generated from subsidized consumers are not well understood. I derive ecosystem models to investigate the relationship between subsidies and trophic cascades. I show that the ratio of subsidy to equivalent in situ prey may not be the best predictor of consumer response to subsidies, particularly when subsidies are temporally variable. I predict strong generalist consumer responses to subsidies in ecosystems with high in situ prey and relatively frequent subsidies. Next, I use response ratios to quantify the relative effect of predator regulation of herbivores and consumer-mediated recycling on producers stocks. I observe that predator regulation of herbivores has a larger, positive, effect on producer stocks than consumer-mediated recycling, however, consumer-mediated recycling can influence producer biomass in many cases. The relative contribution of both mechanisms to cascading trophic interactions depends on feeding relationships between predator and prey, nutrient turnover rates and the rate of external nutrient loading. Trophic cascade theory and experiments to date, have been conducted in closed ecosystems but recent evidence suggests that predators can have cascading effects across ecosystem boundaries. I derive a model of a recipient ecosystem and demonstrate that ecosystems with higher rates of constant subsidies experience stronger trophic cascades because these subsidies facilitate higher secondary production and consumption. I extend this previous model to meta-ecosystem extents in order to consider the effects of reciprocal pulsed subsidies on ecosystem functioning. I show that reciprocal pulsed subsidies can be reinforcing, particularly when th
Les écosystèmes naturels sont ouverts aux flux d'énergie, de matière, et d'organismes. Omniprésents, ces apports allochtones ont un impact sur la structure et le fonctionnement des écosystèmes. S'il est clair que des consommateurs bénéficient directement de ces flux, nous n'avons qu'une connaissance rudimentaire de leurs effets indirects sur les réseaux trophiques. Je développe des modèles d'écosystème afin d'étudier la relation existante entre flux de matière et d'organismes et cascades trophiques. Je démontre ainsi que le ratio de la biomasse des apports sur la biomasse de proie locale ne prédit pas l'effet des flux sur les consommateurs, notamment lorsque ces apports sont variables dans le temps. L'impact des flux sur la biomasse de consommateur se révèle d'autant plus grand quand la biomasse de proie locale est importante et que les flux sont fréquent. J'examine ensuite l'impact relatif du contrôle des herbivores et du recyclage de nutriments par les prédateurs sur la population de plantes et montre que, bien que les deux soient positifs, l'effet du contrôle des herbivores est plus fort. La contribution relative de ces deux mécanismes pour les cascades trophiques dépend des interactions entres proies et prédateurs, des taux de recyclages et des flux de nutriments provenant de l'extérieur. Les cascades trophiques sont généralement étudiées et conceptualisées dans des écosystèmes fermés. Cependant, il a récemment été mis en évidence que les prédateurs peuvent avoir des effets indirects dépassant les frontières d'un écosystème. A l'aide d'un modèle d'écosystème bénéficiant de flux allochtones, je démontre en effet que les cascades trophiques sont d'autant plus fortes quand les écosystèmes reçoivent des flux de matière et d'organismes fréquents. Ce modèle est ensuite étendu à l'échelle de méta-écosystèmes afin d'examiner l'effet des flux réciproques et variables dans le temps sur la force des cascade

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23

Gartner, Adam. "Trophic implications of light reductions for Amphibolis Griffithii seagrass fauna." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2010. https://ro.ecu.edu.au/theses/134.

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The ongoing threat of seagrass loss from reduced light availability, coupled with our lack of knowledge of associated trophic responses has motivated this characterization of the flow-on effects of light reductions to Amphibolis griffithii seagrass fauna. Recently, field manipulations of varying light reductions, induced disturbances in a A. griffithii seagrass meadow that have been shown to effect potential food resources and the structural complexity of seagrass habitats for macroinvertebrates. This offered the opportunity to assess the flow-on effects to seagrass for fauna, a topic that has seldom been examined. This study investigated the effects of different light reduction intensity (high: ~92% reduction; moderate: ~84% reduction), duration (3, 6 and 9 mo) and timing (post-winter and post-summer) on the density, biomass and community composition of macroinvertebrate epifauna within an A. griffithii seagrass ecosystem (Western Australia). Shade structures, placed within a healthy A. griffithii meadow, were used to create the light reduction treatments. Following shading, there were significant interactions between all three light reduction factors, and generally there was decline in the density and biomass of fauna (between 38% and 89% in density) and the number of families with increasing duration and intensity of light reduction (between 11 and 53% fewer families in light reduction treatments). There was also an effect of time, with taxa abundance and family composition Post-summer differing to Post-winter.

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24

Zapata, Martha J. Zapata. "Spatial and temporal variability in aquatic-terrestrial trophic linkages in a subtropical estuary." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515139504483898.

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25

Vaga, Ralph M. "Experimental studies on trophic interactions in the plankton /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487264603217449.

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26

Zagars, Matiss. "Estuarine mangrove fish communities in southwestern Thailand : trophic ecology and movement patterns." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/160976.

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27

Fulcher, Alison S. "The ecology of planktonic rotifers in two lakes of contrasting trophic state." Thesis, Lancaster University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337362.

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28

Fleming, Nicholas Edward Christopher. "Gelatinous zooplankton in the North East Atlantic : distribution, seasonality and trophic ecology." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602506.

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This thesis explores the spatial and trophic ecology of jellyfish in the North East Atlantic using a multidisciplinary approach incorporating shoreline surveys, hydrodynamic modelling and stable isotope analysis. Shoreline surveys revealed a marked temporal and spatial segregation between coastal and oceanic species that remained consistent between sampling years. The utility of the sampling method was considered with respect to the monitoring of jellyfish aggregations in the vicinity of aquaculture on-growing facilities. These stranding data constituted the basis for a follow on study of the broad-scale drivers that transport blooms of the oceanic jellyfish Pelagia noctiluca into Irish/UK coastal waters. A Lagrangian particle-tracking modelling approach was used to consider the fate of hypothetical offshore blooms in the North East Atlantic, it displayed a high predictive ability when compared with actual stranding events across 1800km of the coastline. The remaining chapters of the thesis considered the ecological role of scyphozoan jellyfish from an isotopic perspective (δ13C and δ15N). Consideration was given to the effect of preservation method on the interpretation of isotopic data and to the top-down control of planktonic communities by three commonly occurring scyphozoan jellyfish species (A. aurita, C. lamarckii and C. capillata) from first appearance in the spring, through to eventual disappearance from the water column in the autumn. Distinct intra- and inter-specific shifts in trophic position were evident over time, with only a marginal niche overlap with the sympatric fish community; supporting the notion of a largely self-contained 'jelly-web' (sensu Robison,2004). The final chapter examines the role of jellyfish as hosts for invertebrate fauna, by revisiting the association between scyphozoan species and the hyperiid amphipod Hyperia galba. Isotopic, prevalence, and body size data revealed that amphipods used the jellyfish primarily as a short-term reproductive habitat, with the vast majority of the year spent outside of their gelatinous host.

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Newton, Paul William. "The trophic ecology of offshore demersal teleosts in the North Irish Sea." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250301.

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Crawford, K. J. "The trophic and spatial ecology of bats, inferred from stable isotope analysis." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501251.

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Plass-Johnson, Jeremiah Grahm. "The trophic ecology of parrotfish of Zanzibar application of stable isotope analysis." Thesis, Rhodes University, 2012. http://hdl.handle.net/10962/d1005477.

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Parrotfish are a critical component of the herbivore functional group on tropical coral reefs around the world because they mediate competition that occurs between algae and scleractinian corals. Also, because of their feeding technique, which consists of rasping at the substratum with their beak-like teeth, they play an important role in carbonate turnover and the clearing of reef surface area for the settlement of new sessile organisms. Because of these roles, parrotfishes are an important structuring component of coral reef communities. However, individual species can play different roles depending on their physiology, behaviour and ecology. Despite the possible ecological differences that may exist amongst species, specific roles of the fishes remain unclear as the group is most often studied at higher community levels. This thesis applied stable isotope analysis to differing levels of organisation within a parrotfish community to help elucidate their trophic ecology on coral reefs in Zanzibar. Firstly, blood and muscle tissues were compared to identify differences in their isotope signatures. In other organisms, blood turns over faster than muscle tissue so that muscle tissue represents the diet as integrated over a longer period of time. In most species of parrotfish the blood and muscle δ¹³C signatures were not found to be significantly different, but the δ¹⁵N signatures were significantly different between tissues. This indicated that the δ¹³C signature of both tissues would reveal similar dietary information. Conversely, differences in the δ¹⁵N signature indicated that the nitrogen relationship between tissues was more complicated. Secondly, spatial variability in parrotfish, coral, detritus and macroalgae isotope signatures was assessed at different scales. In macroalgae and coral tissues (zooxanthellae and polyp treated separately), the δ¹³C signatures were shown to differ with depth, presumably because of changes in photosynthetic processes related to depth-associated changes in light. While δ¹⁵N signatures were not affected by depth, all organisms showed enrichment at the Nyange reef, the closest reef to the capital of Zanzibar, Stone Town, presumably reflecting the effects of sewage outfall. These results show that processes that impact the δ¹⁵N signatures of primary producers (macroalgae and zooxanthellae) can be traced to higher trophic levels (coral polyps and fish). Lastly, δ¹³C and δ¹⁵N signatures were used to identify ontogenetic dietary changes in multiple species of parrotfish. Four of the species showed stages that varied from the diets that are normally assumed on the basis of their dentition and feeding technique. This indicates that functional roles based on taxonomy or morphology may fail to include possible ontogenetic dietary changes, and may also fail to elucidate the full impact a species could have on coral reef communities. The conclusions from these studies indicate that the species-specific ecological role of parrotfish in coral reef communities can be complex within and between species, and may differ amongst reefs. In light of the natural and anthropogenic pressures that affect coral reef systems, management decisions based on a more complete understanding of the role of these fish in coral reef communities will help decisions that maintain resilience in these fragile systems.

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Kurth, Benjamin Neal. "Trophic Ecology and Habitat Use of Atlantic Tarpon (Megalops atlanticus )." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6531.

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Fish can have complex life histories and use multiple habitats and resources throughout their life span. Consequently, their life histories are often poorly understood. The Atlantic Tarpon, Megalops atlanticus, is a large, typically migratory, elopomorph fish that is both ecologically and economically important. Atlantic Tarpon are under threat due to regional exploitation, loss of natal and juvenile habitat, poor water management, and offshore impacts. In addition, little is known about its lifelong habitat and resource use. In Chapter 1, I used stable isotope analysis of eye lens δ13C and δ15N values to explore patterns in trophic history and habitat use of 16 Atlantic Tarpon from West-Central Florida and Louisiana. The stable isotope chronologies showed 100% use of backcountry habitats during the early life history and an ontogenetic habitat shift to coastal waters at approximately 10 years of age and 140 cm total length. During the coastal phase Atlantic Tarpon displayed among-individual variability and within-individual consistency in basal resource use. In Chapter 2, mark-recapture data from a multi-year genetic tagging program were used to investigate survival and growth rates, ontogenetic habitat use, and migration of juvenile Atlantic Tarpon in Florida. The study found that juvenile Atlantic Tarpon take approximately 10 years to reach the length associated with maturity, and appear to have a high survival rate (~80%), possibly due to effective use of habitats with reduced competition and predation. Atlantic Tarpon underwent several ontogenetic habitat shifts throughout the juvenile phase. In addition, juvenile Atlantic Tarpon did not migrate long distances but instead showed fidelity to systems wherein only short movements were needed to shift habitat types. This work serves to fill critical gaps in our knowledge of Atlantic Tarpon life history and may aid in better management and conservation of the species.

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Leal, Miguel Albuquerque da Costa. "Trophic plasticity in the cnidarian-dinoflagellate symbiosis." Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/13738.

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Doutoramento em Biologia
Coral reefs are of utmost ecological and economical importance but are currently in global decline due to climate change and anthropogenic disturbances. Corals, as well as other cnidarian species, live in symbiosis with photosynthetic dinoflagellates of the genus Symbiodinium. This relationship provides the cnidarian host with alternative metabolic pathways, as the symbionts translocate photosynthetic carbon to the animal. Besides this autotrophic nutrition mode, symbiotic cnidarians also take up organic matter from the environment (heterotrophy). The nutritional balance between auto- and heterotrophy is critical for the functioning, fitness and resilience of the cnidariandinoflagellate symbiosis. New methodological approaches were developed to better understand the role of auto- and heterotrophy in the ecophysiology of cnidarians associated with Symbiodinium, and the ecological implications of this trophic plasticity. Specifically, the new approaches were developed to assess photophysiology, biomass production of the model organism Aiptasia sp. and molecular tools to investigate heterotrophy in the cnidarian-dinoflagellate symbiosis. Using these approaches, we were able to non-invasively assess the photophysiological spatial heterogeneity of symbiotic cnidarians and identify spatial patterns between chlorophyll fluorescence and relative content of chlorophyll a and green-fluorescent proteins. Optimal culture conditions to maximize the biomass production of Aiptasia pallida were identified, as well as their implications on the fatty acid composition of the anemones. Molecular trophic markers were used to determine prey digestion times in symbiotic cnidarians, which vary between 1-3 days depending on prey species, predator species and the feeding history of the predator. This method was also used to demonstrate that microalgae is a potential food source for symbiotic corals. By using a stable isotope approach to assess the trophic ecology of the facultative symbiotic Oculina arbuscula in situ, it was possible to demonstrate the importance of pico- and nanoplanktonic organisms, particularly autotrophic, in the nutrition of symbiotic corals. Finally, we showed the effects of functional diversity of Symbiodinium on the nutritional plasticity of the cnidarian-dinoflagellate symbiosis. Symbiont identity defines this plasticity through its individual metabolic requirements, capacity to fix carbon, quantity of translocated carbon and the host’s capacity to feed and digest prey.
Os recifes de coral são ecossistemas de elevada importância ecológica e económica. Contudo, encontram-se em declínio global devido ao efeito das alterações climáticas e outras perturbações de origem antropogénica. Os corais, tal como outros cnidários, vivem em simbiose com dinoflagelados fotossintéticos do género Symbiodinium. Esta associação permite ao hospedeiro dispor de vias metabólicas alternativas, uma vez que os simbiontes fixam carbono fotossinteticamente e translocam-no para o hospedeiro. Para além deste modo de nutrição autotrófico, estes cnidários também se alimentam de matéria orgânica disponível no meio ambiente (heterotrofia). O balanço nutricional entre auto- e heterotrofia é fundamental para o funcionamento, capacidade adaptativa e resiliência da simbiose entre cnidários e dinoflagelados. No presente trabalho foram utilizadas novas abordagens metodológicas para investigar a importância da auto- e heterotrofia na ecofisiologia de cnidários em simbiose com Symbiodinium e as implicações ecológicas desta plasticidade trófica. Os métodos aqui desenvolvidos estão relacionados com a fotofisiologia, produção de biomassa do organismo modelo Aiptasia pallida e métodos moleculares para investigar heterotrofia na simbiose entre cnidários e dinoflagelados. Foram utilizados métodos não invasivos para avaliar padrões espaciais fotofisiológicos em cnidários associados com Symbiodinium e explorar a relação entre a fluorescência da clorofila e a abundância relativa de clorofila a e proteínas verdes fluorescentes. As condições de cultivo que maximizam a produção de Aiptasia sp. foram identificadas, bem como as respetivas implicações na sua composição em ácidos gordos. A utilização de marcadores tróficos moleculares permitiu identificar que o tempo de digestão em cnidários associados com Symbiodinium varia entre 1 e 3 dias e que depende da espécie de predador e de presa, bem como do historial trófico do predador. O mesmo método molecular permitiu concluir que as microalgas são uma presa potencialmente importante para a nutrição de corais simbióticos. Adicionalmente, os resultados obtidos através da utilização de isótopos estáveis in situ, para avaliar a ecologia trófica do coral simbiótico facultativo Oculina arbuscula, confirmaram a importância que os organismos pico- e nanoplanctónicos, principalmente autotróficos, podem representar para a nutrição de corais simbióticos. Por fim, o efeito da diversidade funcional de Symbiodinium na plasticidade trófica da simbiose entre cnidários e dinoflagelados foi investigado. Concluiu-se que a identidade do simbionte define esta plasticidade através dos seus requisitos metabólicos individuais, capacidade para fixar carbono, quantidade de carbono translocado e a capacidade de ingestão e digestão de presas do cnidário hospedeiro.

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Morote, Córdoba Elvira. "Trophic ecology of hake, anchovy, sardine, round sardinella and bullet tuna larvae of NW Mediterranean: influence of trophic environment and ontogeny." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/52646.

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En esta Tesis Doctoral se ha analizado las relación de la comunidad ictioplanctonica con su ambiente físico y trófico en dos condiciones hidrográficas contrastadas (estratificación estival y mezcla otoñal) y se ha caracterizado la dieta larvaria de cinco especies de teleósteos presentes en el Noroeste del Mediterráneo: los tres clupeiformes de la región [anchoa (Engraulis encrasicolus), sardina (Sardina pilchardus) y alacha (Sardinella aurita)], un pequeño túnido [la melva (Auxis rochei)] y la especie de pez demersal más importante de la región [la merluza (Merluccius merluccius)]. Estas especies han sido elegidas porque representan dos morfotipos distintos, 1) morfotipo estilizado representado por los clupeiformes, con boca pequeña, cuerpo alargado y tracto digestivo ligado a la cola, y 2) morfotipo robusto representado por la melva y la merluza, con boca grande, cuerpo robusto y digestivo compacto e independiente de la cola. Además se han estudiado las variaciones de la dieta i) a lo largo del desarrollo, en relación ii) con la disponibilidad de presas y iii) con la morfología de las estructuras implicadas en la alimentación como son el sistema visual, el aparato bucal y el sistema digestivo. La alimentación es un aspecto de la ecología larvaria de los peces que en último termino afecta a la dinámica de sus poblaciones (a través de la supervivencia larvaria y las consiguientes fluctuaciones en el reclutamiento). Los factores que influyen en la preferencia de las larvas de peces por sus presas y las estrategias de alimentación han sido poco o nada estudiados para estas especies escogidas en el mar Catalán. Estos factores pueden diferir entre especies y cambiar a lo largo de la ontogenia. Esta tesis doctoral ha tenido como principal finalidad comprender las estrategias tróficas específicas de las larvas de estas cinco especies importantes en las pesquerías mediterráneas. A grandes rasgos se puede observar tres tipos de estrategias: 1) La que sigue la merluza, que desde el comienzo de la alimentación exógena se especializa en un tipo de presa (Clausocalanus spp.) y solo aumenta el número de copépodos que ingiere para responder al aumento de los requerimientos nutricionales de crecimiento. 2) La que siguen la anchoa y sardina, que muestran una baja intensidad alimenticia, y que varían el tamaño y número de presas poco a poco a lo largo del desarrollo sin grandes cambios en la dieta. 3) La descrita para la melva y la alacha, que contrariamente la las tres especies anteriores, son oportunistas y en su etapa larvaria ajustan los tipos de presa (y tamaños) conforme mejoran sus habilidades de una forma mucho más marcada que el resto de especies. El trabajo presentado en esta tesis ha estado dirigido a obtener información básica y necesaria para interpretar los patrones de distribución y dilucidar el efecto del tipo de ecología trófica de diversas especies de peces en la supervivencia larvaria. Ha sido la primera vez que se estudian las larvas de estas especies en el mar Catalán en relación a la distribución de sus presas potenciales del plancton para evaluar el papel que juega el acoplamiento espacio-temporal de larvas y presas en la estrategia alimentaria. También es la primera vez que se estudia la dieta de estas especies en relación a la morfología de estructuras relacionadas con la alimentación como son el sistema visual, la boca y el tracto digestivo. Los resultados de este trabajo muestran como la morfología opuesta del tipo de digestivo, junto con el tamaño de boca y ojos de las larvas explica las diferencias entre clupeiformes y melva y merluza en lo que se refiere a incidencia alimentaria de la población, tamaños extremos de presas grandes y agudeza visual, pero esto no es suficiente para explicar las estrategias de la alacha que se asemeja mas en sus hábitos alimentarios a la melva que a las especies morfológicamente similares (la anchoa y sardina), así como tampoco sirve para explicar las diferencias de dieta entre merluza y melva pese a que morfológicamente comparten características. Pese a que tanto la melva como la merluza parten de unas características morfológicas mas ventajosas como son el cuerpo robusto, tamaño de boca grande, mayor agudeza visual y digestivos con mayor capacidad de almacenaje, la melva sí refleja estas ventajas en unos hábitos predadores intensos y con incorporación de presas mas grandes y móviles conforme se desarrolla mientras que la merluza no cambia su dieta pese a que estaría capacitada para detectar y capturar presas más nutritivas. La merluza parte de un tamaño de boca relativamente grande al eclosionar que le permite ingerir presas grandes desde el comienzo de la alimentación exógena, patrón similar a las especies que nacen con desarrollo directo o con tamaños de larvas grandes, y no varía su dieta a lo largo del desarrollo larvario
We have analysed the relationship of the ictioplankton community with its fisical and trophic environment in two hydrographical contrasting conditions (summer stratification versus autumn mixed column), and we have characterized the larval diet of five teleost species in the NW Mediterranean: the three clupeiform of the region [anchovy (Engraulis encrasicolus), sardine (Sardina pilchardus) and round sardinella (Sardinella aurita)], a small tuna [bullet tuna (Auxis rochei)] and the most important demersal species of the region [hake (Merluccius merluccius)]. These species have been chosen because they represent two different morphotypes, 1) that of the clupeiforms, which correspond to a stylized larvae with small mouth, long body and digestive tract linked to the tail, and 2) that of bullet tuna and hake, which correspond to a robust larvae with big mouth, robust body and compact digestive tract independent of the tail. Moreover, we have studied the diet variations i) along development, in relation to ii) prey availability and iii) morphology of the feeding-related structures like visual system, mouth and digestive tract. Feeding is an important aspect of the larval fish ecology that affects the population dynamics (through larval survival and subsequence recruitment fluctuations). The factors that affect the larvae in their prey selection and the feeding strategies have been scarcely studied for these species in the Catalan Sea. These factors can be different depending on the species and can change with ontogeny. The main objective of this Ph.D has been to understand the specific trophic strategies of the larvae of these five important species in Mediterranean fisheries. We can point out three types of strategies: 1) The hake’s one, which from the onset specializes feeding in a prey type (Clausocalanus spp.) and only increases the number of copepods to respond to the nutritional requirements of growth. 2) Anchovy and sardine’s type, which show low feeding incidence at the beginning, and they change the size and number of preys step by step along development without showing abrupt changes in the diet. 3) Bullet tuna and hake’s type, opportunist species which deeply adjust their prey type (and size) in their larval period as they enhance their abilities. This research has aimed to obtain the basic and necessary information to explain the fish larval distribution and to elucidate the effect of the trophic ecology of several species of fishes in the larval survival. It has been the first time to study these species in the Catalan Sea in relation to the potential prey distribution to evaluate the rol of spatial-time match of larvae and preys in the feeding strategies. Moreover, it is the first time that the diet composition of the five species has been studied in relation to the morphology of the feeding-related structures such as the visual system, the mouth and the digestive tract. The results of this research highlights that the contrasting morphology of the digestive tract together with the mouth and eyes size can explain the differences in the feeding habits (feeding incidence, size range and visual acuity) among clupeiforms, bullet tuna and hake, but this is not enough to explain the strategies of round sardinella. The feeding habits of this clupeiform is closer to the bullet tuna’s than to the morphogically similar species (anchovy and sardine), nor serves to explain the differences between hake and bullet tuna diet despite sharing morphological characteristics. Although both bullet tuna and hake have a more favourable morphological features such as robust body, large mouth size, higher visual acuity and greater storage capacity, bullet tuna does reflect these advantages in an intense predatory habits with the incorporation of larger and more mobile prey as it develops, but hake diet does not change even though it would be able to detect and capture more nutritious prey. Hake has a relatively large mouth size at hatching therefore can eat larger prey since the beginning of exogenous feeding, similar to species that are born with direct development of larvae or large sizes, and does not change its diet during the course of larval development.

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McConville, Kristian. "Trophic and ecological implications of the gelatinous body form in zooplankton." Thesis, University of Plymouth, 2018. http://hdl.handle.net/10026.1/11835.

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Gelatinous zooplankton are characterised as different from other planktonic taxa due to the high relative water content of their tissues. This thesis investigates whether elevated somatic water content (expressed here as carbon percentage) has effects on the biology of zooplankton. My approach was to examine this at a range of scales with a variety of approaches, ranging from experiments on individual ephyra larvae of Aurelia aurita, through analysis of a zooplankton time series at the Plymouth L4 station, up to a large scale meta-analysis of zooplankton growth and body composition data. In this meta-analysis, carbon percentage varied continuously across the range of the zooplankton, ranging from 0.01% to 19.02% of wet mass, a difference of over three orders of magnitude. Specific growth rate (g, d-1) was negatively related to carbon percentage, both across the full range of zooplankton species, and within the subset of taxa traditionally classified as gelatinous. The addition of carbon percentage to models of zooplankton growth rate based on carbon mass alone doubled explanatory power. I present an empirical equation of maximum (food saturated) zooplankton growth that incorporates carbon mass and carbon as a percentage of wet mass. Applying this equation to a natural assemblage near Plymouth yielded sometimes double the secondary production, as compared to a simpler model based on crustacean growth. Both interspecifically and intraspecifically, carbon percentage was negatively related to carbon mass; more gelatinous taxa tended to have higher carbon masses. During the early development of Aurelia aurita ephyrae, carbon percentage was found to decrease from 2.36% (an intermediate value between crustaceans and classical gelatinous zooplankton) down to 0.1%, the adult value for Aurelia aurita. Juvenile forms of gelatinous taxa are often poorly sampled and their intermediate carbon percentages may help to form a continuum between those of crustaceans and adult cnidarians and ctenophores. As ingestion in the ephyrae was related to their diameter, models suggest that this dilution resulted in an increase in carbon-specific ingestion rate by an estimated 28% relative to an ephyra that did not dilute through development. At the species level, carbon percentage was negatively related to indices of temporal variation in numerical density but not related to rate of population increase. A wide variety of zooplanktonic taxa of different carbon percentages were found to increase in population at a rate that could be considered as forming a bloom. Likewise many gelatinous taxa at L4 did not form blooms. Thus the frequent reference to “jellyfish blooms” reflects, in part, the fact that unlike the other zooplankters that regularly reach even higher carbon concentrations, gelatinous taxa are simply more noticeable to the eye when at these concentrations. Calculating the carbon percentage of whole assemblages could be useful for investigating the influence of environmental parameters on zooplankton. Taken together, these results demonstrate the benefits of explicitly recognising the decoupling of metabolic and ecological body size seen in the gelatinous zooplankton.

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Velghe, Katherine. "Quantifying biodiversity in aquatic ecosystems: evaluating the causes for congruent patterns across trophic levels." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106467.

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Understanding the drivers and patterns of biological diversity has been a central tenet for ecologists over the past century. Aquatic ecosystems appear to be particularly sensitive to biodiversity declines and thus comprehending the causes of these biodiversity losses has become a pressing issue. The objectives of this thesis are twofold. First, I wanted to investigate the effect of phosphorus, a surrogate for productivity in aquatic ecosystems, on the diversity of two taxonomic groups across broad spatial and temporal scales. Secondly, I wanted to quantitatively assess the use of biodiversity indicators in aquatic ecosystems, with particular emphasis on the role of body size. In the first chapter of this thesis, I took a palaeolimnological approach to investigate how the species richness of subfossil diatoms and cladocera varies in response to phosphorus. From both our spatial and temporal analyses, a significant decline in species richness of diatoms and cladocera was observed as phosphorus increased. When subdivided according to habitat preference, only the littoral species richness showed a decline in species richness. We attribute this decline in species richness in the littoral taxa to the interplay of nutrients on littoral habitat heterogeneity. At low levels of phosphorus, the littoral zone is thought to be more productive and harbor a greater abundance of submerged macrophytes and is thus able to maintain a more diverse community. The second chapter of this thesis investigated the efficiency of cross-taxon congruence as a method for estimating biodiversity in aquatic ecosystems. I approached this subject by performing a spatial field study coupled to a meta-analysis of the published literature. The field survey and meta-analysis show that organisms of similar size tended to exhibit more congruent diversity patterns. I argue that this pattern arises because organisms of similar body size have similar life history traits and thus similar biodiversity responses to environmental gradients. I demonstrate that cross-taxon biodiversity indicators are most effective when estimating the diversity of communities of most similar body size. Overall, this research has expanded our understanding of patterns, drivers and similarities of biodiversity across trophic levels in aquatic ecosystems.
Au cours du siècle dernier, plusieurs écologistes ont tenté de comprendre les caractéristiques ainsi que les facteurs qui contrôlent la diversité biologique. Les écosystèmes aquatiques semblent être particulièrement sensibles au déclin de la biodiversité et donc en découvrir les causes devient alors une question pertinente. Cette thèse possède deux objectifs. Tout d'abord, je souhaite étudier l'effet du phosphore, un substitut de productivité dans les écosystèmes aquatiques, sur la diversité de deux groupes taxonomiques à travers de grandes échelles spatiales et temporelles. Deuxièmement, je désire évaluer, de façon quantitative, les indicateurs de biodiversité dans les écosystèmes aquatiques, et ce, en mettant l'emphase sur le rôle de la dimension des organismes. Dans le premier chapitre de cette thèse, j'ai utilisé une approche paléolimnologique pour étudier comment la richesse spécifique des diatomées et des cladocères fossilisés varie en fonction du taux de phosphore. Grâce à mes analyses temporelles et spatiales, j'ai noté une baisse significative de la richesse spécifique des diatomées et des cladocères avec une augmentation du phosphore. De plus, lorsque les communautés étaient divisées par leurs préférences d'habitat, seules les richesses spécifiques littorales ont démontré un déclin en fonction du phosphore. J'attribue ce déclin de la richesse spécifique dans les groupes littoraux à l'effet des nutriments sur l'hétérogénéité des habitats littoraux. À de bas niveaux de phosphore, la zone littorale est plus productive et peut accueillir de grandes abondances de macrophytes qui fournissent plus de niches écologiques pour les espèces, donc une plus grande diversité.Le deuxième chapitre de cette thèse porte sur l'utilisation de la richesse spécifique d'une communauté d'organismes pour estimer la richesse spécifique d'une autre. Cette méthode de substitution est utilisée pour estimer la biodiversité dans les écosystèmes aquatiques. J'ai abordé ce sujet en effectuant une étude spatiale jumelée à une méta-analyse des écrits. Mon analyse spatiale et ma méta-analyse illustrent que les groupes taxonomiques ayant des dimensions similaires ont tendance à présenter des patrons de diversité plus conformes. Je suppose que les organismes de tailles similaires démontrent plus de similarité en ce qui concerne leurs traits de vie et à leurs patrons de diversité lors de gradients environnementaux. Je démontre que les indicateurs utilisés pour prédire la biodiversité sont plus efficaces lorsque leurs tailles sont plus similaires. Conséquemment, cette recherche a permis d'agrandir nos connaissances des patrons, des processus et des similitudes de la richesse spécifique dans les écosystèmes aquatiques.

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Raper, Lafferty Diana Jean. "Evolutionary and ecological causes and consequences of trophic niche variation in ursids." Thesis, Mississippi State University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3716731.

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Individual variation and fitness are the cornerstones of evolution by natural selection. The trophic niche represents an important source of phenotypic variation on which natural selection can act. Although individual variation is fundamental to species-level ecological and evolutionary change, individual variation is often ignored in population-level approaches to wildlife ecology, conservation and management. Failing to link individual resource use to fitness or to biological outcomes related to fitness limits us to managing for the average resource needs of a population, which may be insufficient for protecting the diversity of resource use within populations and the underlying eco-evolutionary processes that generate that diversity. My goals were to provide insights into the mechanisms that generate and constrain intrapopulation trophic niche variation, evaluate whether linkages exist between individual biological outcomes and variation in food habits across the range of resources consumed within generalist consumer populations and examine how that variation manifests in population-level responses.

I investigated the causes and physiological consequences of intrapopulation trophic niche variation in two generalist consumers, the American black bear (Ursus americanus) and brown bear (U. arctos) across three sites in British Columbia, CAN and at one site in Alaska, USA. My primary tools included stable isotope analysis to estimate diet, enzyme-linked immunoassay of hair to quantify the hormone cortisol for indexing physiological stress, and genetic analyses to identify individuals, species, and sex and to estimate ancestry. I found that individual differences in resource use can result in similar biological outcomes and that similar resource use can result in different biological outcomes. Intra- and interspecific competition, sex-based differences in nutritional and social constraints and annual variation in food availability all influenced trophic niche variation and the resultant biological outcomes. I also found evidence of a link between intrapopulation trophic niche variation and population genetic structure. My results highlight the diverse ecological drivers and diverse consequences of trophic niche variation, which further illuminates why the trophic niche is a nexus for eco-evolutionary dynamics.

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Valentine, Shaley A. "Patterns of Threatened Vertebrates Based on Trophic Level, Diet, and Biogeography." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7194.

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Humans have indirectly and directly contributed to the extinction of over 500 species within the past 500 years, a rate far higher than we have seen in the past. The high extinction rate and the fact that 18% of vertebrates may become extinct within the next century have pushed Earth into a biodiversity crisis. Understanding what makes species more at risk of extinction is needed to protect Earth’s biodiversity. Generally, it is expected that predators have greater extinction risk than omnivores and herbivores because predators are larger in body size, depend on other animal species for food, need large home ranges, and have fewer individuals within their populations. However, no study to date has actually tested the assumption that predators have the highest extinction risk. This question is important to understand because diet is associated with the ecological role a species plays in an ecosystem. We compared the extinction risk of species with different diets to determine species in which trophic level are proportionately more at risk of extinction. We classified each species’ diet, trophic level (i.e.,predator, omnivore, and herbivore), body size, habitat, geographic region, system, and associated threats. We focused our analyses on all mammals, birds, and reptiles assessed by the International Union for the Conservation of Nature. We then compared the expected and observed proportions of threatened species within each trophic level and diet group at global, system, habitat, and regional scales. We found that predators, except scavengers, fish-eating birds, and obligate mammal and bird eaters, were not more threatened than expected. On the other hand, herbivores consistently had greater proportions of threatened species than expected. Specifically within herbivores, fruit, grass, and leaf-eating species had high proportions of threatened species. When we separated large-bodied and small-bodied species, we found that most large-bodied species, regardless of their trophic level, had greater proportions of threatened species. When we looked at the regions and habitats where species were more often threatened, we found that herbivores were highly threatened in south and Southeast Asia, sub-Saharan Africa, and Oceania. In addition, herbivores were highly threatened in tropical forests, marine coasts, and sometimes grasslands. Overall, terrestrial herbivores and marine predatory birds were highly threatened. We found that these patterns may have resulted from overexploitation, habitat alteration, and pollution targeting herbivores and sometimes omnivores. These findings suggest that we should shift conservation focus from predators to include herbivores. The most threatened species, tropical herbivores, scavengers, and mammal, bird, and fish eaters should be of highest conservation priority.

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Rielly, Elizabeth Wheeler. "Spatial variation drives patterns of community composition and trophic relationships in a marine system." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/345225.

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Biology
Ph.D.
Examining how ecological processes are influenced by spatial variation can provide valuable insights into how communities are formed and how they may change in dynamic landscapes. In this thesis I address three objectives surrounding the spatial and temporal variation in species’ recruitment and predation, the influence of habitat isolation on consumer-resource relationships, and the influence of habitat fragmentation on a multi-trophic system. I used marine invertebrates, specifically crustaceans, bivalves, and sessile species as a model system. First, I address the spatial and temporal variation in local and regional processes in a multispecies assemblage of marine sessile invertebrates. Using diverse communities of marine sessile invertebrates as a model system I tested the hypothesis that spatial and temporal variation in recruitment and predation would shape local communities, and that both recruitment and predation would have significant effects on the abundance and structure of adult communities. I found that both recruitment and predation vary through time and space leading to the emergence of regional community divergence. I also address how habitat isolation interacts with top-down and bottom-up processes in seagrass ecosystems. Spatial structure of the habitat may mediate top-down and bottom-up controls of species abundances through decreased habitat connectivity and increased habitat isolation. I manipulated top down and bottom up processes by excluding mesograzers, adding resources, or altering both factors in isolated and contiguous patches of artificial seagrass. I then measured epiphyte recruitment, epiphyte abundances, and macroalgae abundance. I paired this with epiphyte sampling from isolated natural seagrass patches. I found that habitat isolation significantly decreased the abundance of epiphytes settling on seagrass blades due to dispersal limitation for epiphytic invertebrates. I found that consumers had strong effects on epiphyte biomass in continuous habitats, but not isolated habitats. Resource additions increased macroalgae cover and epiphyte biomass only in isolated habitats. The results suggest that isolated habitats may be nutrient limited and that top-down effects are stronger in continuous habitats, while bottom-up effects may dominate in isolated habitats. In my third objective, I address how habitat fragmentation may alter marine food webs. I examined whether predation rates, prey, and predator behavior differed between continuous and fragmented seagrass habitat in a multi-trophic context at two sites in Barnegat Bay, NJ. I hypothesized that blue crab predation rates and foraging would decrease in fragmented seascapes, due to a reduction in adult blue crab densities, increasing survival rates of juvenile blue crabs and hard clams. I expected hard clams to exhibit weaker predator avoidance behavior in fragmented habitats because of decreased predation. I found that species’ responses to fragmentation were different based on trophic level. Clams experienced higher predation and burrowed deeper in continuous habitats at both sites. Densities of blue crabs, the primary predator of hard clams, were higher in continuous habitats at both sites. Predation on juvenile blue crabs was significantly higher in fragmented seagrass at one site. Our results suggest that in fragmented seascapes, the impact of fragmentation on higher trophic level predators may drive predation rates and prey responses across the seascape, which may lead to trophic cascades in fragmented habitats.
Temple University--Theses

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Moore, Travis Allan. "Trophic Dynamics and Feeding Ecology of the Southeast Florida Coastal Pelagic Fish Community." NSUWorks, 2014. http://nsuworks.nova.edu/occ_stuetd/3.

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The combined methods of stomach content analysis and stable 15N and 13C isotope biochemistry analysis were used to investigate the trophic dynamics and feeding ecology of coastal pelagic fishes in the waters off southeastern Florida, USA. The coastal pelagic fish complex includes blackfin tuna Thunnus atlanticus, dolphinfish Coryphaena hippurus, king mackerel Scomberomorus cavalla, little tunny Euthynnus alletteratus, skipjack tuna Katsuwonus pelamis, and wahoo Acanthocybium solandri. These coastal teleosts, particularly the tunas and wahoo, are primarily targeted by recreational anglers. However, there is a shortage of available trophic and diet composition data concerning these fishes of the coastal pelagic ecosystem. Stomach and muscle tissue samples were collected from the species of various lengths over a three-year period from March 2010 and March 2013. Across all six species, teleost fishes dominated the prey with an average 64.5% by occurrence, 63.7% by number, and 89.9% by weight. There were two dominant prey families: Clupeidae and Carangidae. Dolphinfish showed the lowest diet overlap among the six species, due to the highly diverse diet. The highest diet overlap occurred between king mackerel and little tunny. The mean δ15N ranged from 8.21 ‰ (wahoo) to 13.18 ‰ (king mackerel), and the mean δ13C ranged from -18.41 ‰ (king mackerel) to -16.70 ‰ (dolphinfish). Blackfin tuna exhibited the largest δ15N range (7.22 to 13.21 ‰), as well as the largest δ13C range (-19.13 to -12.99 ‰). The δ15N and δ13C signatures in the muscle tissue showed evidence of shifts to higher trophic levels with an increase in fish size and the formation of distinct trophic groups among the coastal pelagic predators. The δ13C also suggested an inshore-offshore spatial relationship among the coastal pelagic fish. The trophic dynamics and feeding ecology data generated by this study will provide valuable baseline data for the coastal pelagic complex and future ecosystem studies.

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Roche, David C. "Trophic Ecology of Green Turtles (Chelonia mydas) From Dry Tortugas National Park, Florida." NSUWorks, 2016. http://nsuworks.nova.edu/occ_stuetd/430.

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Located 100 km west of Key West, Florida, Dry Tortugas National Park (DRTO) is a largely untouched subtropical marine ecosystem that serves as an important developmental habitat, nesting ground, and foraging area for several species of sea turtles, including green turtles. The Park supports a recovering population of green turtles comprised of resident juveniles, subadults, and adults of both sexes; nesting females include residents and migrating females that only return to nest. Stable isotope analysis has been applied widely to describe the trophic ecology of green turtles, from urbanized bays with significant anthropogenic input, to relatively pristine ecosystems with healthy populations at carrying capacity. However, there is a paucity of published literature about the trophic ecology of green turtles in DRTO. This study describes the trophic ecology occupied by two distinct size groups (61 green turtles < 60 cm (SCL) and 98 green turtles > 60 cm (SCL)). Flipper tissue and plasma were analyzed for stable isotopic composition of C and N. Flipper tissue values for δ15N (3.41‰ to 9.69‰) and δ13C (-22.43‰ to -5.38‰) fall within literature values for green turtles, and the wide range of values indicated they could potentially feed at multiple trophic levels. Understanding the trophic ecology of this population of green sea turtles is instrumental to effective management and habitat preservation strategies in DRTO.

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Johnston, Nadine Marie. "The role of cannibalism in the trophic ecology and population dynamics of cephalopods." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605669.

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In common with most squid fisheries, the Falkland Islands fisheries for Illex argentinus and Loligo gahi are characterised by unpredictable, inter-annual variations in distribution and abundance. In recent years, much research effort has been directed at understanding the influences of physical oceanographic variability, such as sea surface temperature, on the recruitment, distribution and abundance of these species. This study considers the influence of predation and food availability on the recruitment, distribution and abundance of these species. Cannibalism (defined as intraspecific predation) is a feature of cephalopod feeding biology and impacts on natural mortality and population dynamics. The research provides the first comprehensive account of cannibalism in two commercially exploited squid species in the southwest Atlantic. The diets of I. argentinus and L. gahi were examined over a wide spatial area and over several years and results showed that this behaviour is related to population density and the availability of food. This study also quantified cannibalism in I. argentinus and L. gahi as a major source of natural mortality and has assessed the impact on the population dynamics of these species. This links between food availability at the base of the food chain and the distribution and abundance of I. argentinus and L. gahi were examined using satellite-derived chlorophyll-a data imaged by Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Results showed that phytoplankton biomass appeared to be related to I. argentinus biomass during the period of the fishery. The addition of information on food availability using SeaWiFS technology may improve current forecasting models for I. argentinus and L. gahi. Within season estimates of the natural mortality due to cannibalism may be used to make real-time modifications to the target escapement of the I. argentinus and L. gahi fishery populations.

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Hill, Jaclyn Marie. "A stable isotope approach to trophic ecology resolving food webs in intertidal ecosystems." Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1005459.

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There are broad differences in regional oceanography and primary production around the South African coast, which we might expect to give rise to major differences in trophic pathways. δ⁻¹³C and δ⁻¹⁵N isotopic ratios of suspended particulate matter (SPM), mussels, various intertidal consumers and common macroalgae along the South African coastline were explored using stable isotope analysis to investigate biogeographic and temporal variability of isotopic signatures of marine intertidal consumers and their food sources around the coast of South Africa, with a focus on evaluating the dependence of intertidal mussels on phytoplankton and macroalgal-derived organic carbon. Isotopic equilibration rates of four mussel tissues were determined through laboratory feeding experiments, which established that adductor tissue had the slowest isotopic turnover rate, and was subsequently used as an indication of overall mussel diet. Biogeographic, temporal and nearshore/offshore trends of isotopic ratios of SPM were investigated along 10km transects perpendicular to the coast and SPM exhibited overall trends of carbon depletion when moving from west to east along the coastline and from nearshore to offshore water, in both cases suggesting a shift from macrophyte detritus to a phytoplankton signature. δ⁻¹³C signatures of SPM also revealed temporal and biogeographic variation that had strong ties to local oceanography, being closely correlated to regional hydrographic features and tidal influences. Mixing models indicated filter feeders demonstrated over 50% dependence on nearshore SPM for organic carbon and it was possible to categorize them into geographic groups based on their carbon and nitrogen signatures, suggesting biogeographic shifts in resources. Biogeographic shifts in diet were also seen in some grazers. Difficulties in relating macroalgae to mussel diet led to investigations into the isotopic changes associated with macroalgal decomposition. Variation in photosynthetic fractionation, leaching and microbial mineralization are believed to have resulted from species-specific patterns of degradation. Although the strong links between carbon signatures and local oceanography indicate that stable isotope analysis is a powerful tool for the study of water mixing and coastal hydrography in relation to food-web analyses, substantial variation in fractionation of primary consumers, along with different periods of time integration between consumers and their food sources must be considered in future studies, to resolve trophic links in marine food webs successfully.

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Chandler, Louis Fairfax. "Trophic Ecology of Native and Introduced Catfishes in the Tidal James River, Virginia." VCU Scholars Compass, 1998. http://scholarscompass.vcu.edu/etd/4408.

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Species introductions have been linked to the decline of native taxa, and in many cases have resulted in the elimination of native species in both terrestrial and aquatic systems throughout the United States. In aquatic systems, a particular threat is the introduction of large piscivorous fish that may alter the native fish community structure. For example, introductions of large ictalurids such as blue catfish, (lctalurus furcatus), and flathead catfish, (Pylodictus olivaris), into coastal Virginia rivers, including the James River twenty years ago have resulted in the establishment of these large, predatory fishes. This study described the trophic ecology of four ictalurid catfishes in the tidal James River, Virginia including the native white catfish (Ameiurus catus), the possibly introduced channel catfish (Ictalurus punctatus), and the recently introduced blue catfish and flathead catfish. The objectives of this study were to determine the trophic ecology of these four catfishes in a coastal Virginia river, and to assess the potential predatory effects of large, recently introduced piscivorous ictalurids on the native fish assemblage, and especially anadromous clupeid fishes. A stratified sample of 4, 164 catfish was taken throughout the tidal freshwater reach of the James River during the summer and fall, 1996 and spring, 1997. Stomach content analysis revealed that blue catfish and flathead catfish are highly piscivorous, feeding on several families of native fishes. Flathead catfish consumed over 90% (frequency of occurrence) fish prey in most predator size classes and began consuming more fish prey at smaller sizes than blue catfish. Blue catfish shifted to a mostly piscivorous diet at predator lengths > 500 mm. Both blue catfish and flathead catfish consumed adult anadromous clupeids. The greatest numeric proportion (0.41) of anadromous clupeids consumed were juvenile Alosa spp. (<100 mm) taken by small blue catfish (<500 mm) during the fall sampling season. Piscivory was much less extensive in channel catfish and white catfish (less than 10% frequency of occurrence for all predator size classes). There is evidence of negative consequences to native fishes associated with the introductions of blue catfish and flathead catfish into Atlantic slope rivers. These consequences may conflict with current restoration efforts for native fishes such as the anadromous clupeids in these rivers.

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Freeman, Steven Mark. "The ecology of Astropecten irregularis and its potential role as a benthic predator in a soft-sediment community." Thesis, Bangor University, 1999. https://research.bangor.ac.uk/portal/en/theses/the-ecology-of-astropecten-irregularis-and-its-potential-role-as-a-benthic-predator-in-a-softsediment-community(d15f9871-8e48-41ae-8121-433d7b47e78d).html.

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Sobocinski, Kathryn L. "Fishes in Seagrass Habitats: Species Composition, Trophic Interactions, and Production." W&M ScholarWorks, 2014. https://scholarworks.wm.edu/etd/1539791566.

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The value of habitats in terms of biological production is of interest to ecologists and resource managers. Seagrasses are a commonly occurring habitat type in shallow marine waters and have been shown to support high abundances of fish and invertebrates. In lower Chesapeake Bay, seagrasses grow in a shallow fringe in the subtidal zone. Although, ample evidence exists for the value of these habitats as foraging and rearing areas for a variety of organisms, the connectivity among species and the benefits derived from these habitats in terms of production have not been well described, especially for small, seasonally occurring finfishes. The main objective of this research was to document fish occurrence and abundance, describe trophic interactions within the seagrass community, and quantify export of biomass from the habitat using a model species to demonstrate the value of these habitats in terms of finfish production.;To address the research objective, I employed a variety of models---statistical, ecosystem, and individual-based. In Chapter 1, I conducted as census of finfishes in seagrass habitats and compared contemporary occurrences and abundances to data from the 1970s. This chapter showed that the fish fauna in these habitats is dominated by a small number of abundant and commonly occurring species, including Spot (Leiostomus xanthurus), Silver Perch ( Bairdiella chrysoura), Bay Anchovy (Anchoa mitchilli), Atlantic Silverside (Menidia menidia), Dusky Pipefish ( Syngnathus floridae), and Northern Pipefish (Syngnathus fuscus ). While abundances had changed since the 1970s for some species, most were highly variable with no discernible trend. There was a small decrease in species richness from the historical dataset to the contemporary dataset and multivariate analysis showed a shift in community composition. The data from this chapter formed the basis for the ecosystem model developed in Chapter 2. In this model, biomass, production, and diet data were inputs, and using a mass-balance approach, a food web model was iteratively developed. There were 35 model compartments in the model and scenarios based upon historical data and future projections were developed for comparison. Mesozooplankton were the most highly connected group, while piscivorous birds, several piscivorous fishes, and mesograzers were all considered keystone groups, controlling food web dynamics. In Chapter 3, an individual-based model was developed for Silver Perch, to assess growth and production within a seagrass habitat. Because Silver Perch settle in this habitat, grow during the summer season, and migrate to deeper waters in the fall, they were an appropriate model species for determining the contribution of seagrass habitats to production. With high seasonal abundance and rapid growth (~0.19 g/d), this species contributes a considerable amount of biomass to Chesapeake Bay, biomass that originates in seagrass habitats and moved via trophic transfer.;This study presents a quantitative view of community ecology in lower Chesapeake Bay seagrass habitats. With changing temperatures and habitat loss, these habitats are at risk, and this study demonstrates that their value to the Chesapeake Bay food web extends beyond the small fringe of their occurrence.

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Malloy, Elizabeth. "Trophic Dynamic Interactions in a Temperate Karst River." TopSCHOLAR®, 2014. http://digitalcommons.wku.edu/theses/1437.

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Surface streams in karst landscapes are often characterized by high nutrient levels due to incomplete filtration through series of innumerable, below-ground conduits. Seasonal growth of the filamentous alga, Cladophora, is typically associated with nutrient-rich waters. This research compared macroinvertebrate food web structure between riverine reaches with contrasting underlying karst topography, nutrient levels, and Cladophora cover during summer 2012 and autumn 2013. Recent work in these reaches found a high correlation between Cladophora cover and nutrient content, particularly nitrate. Four questions were addressed during this study: 1. Do longitudinal trends in algal and consumer δ13C values relate to decreased DIC availability in larger watersheds? 2. Are trophic niche breadths narrower in more karstified reaches than in less karstified reaches due to longitudinal differences in Cladophora standing stocks? 3. Do differences in trophic-dynamic relationships between primary consumers and their food resources reflect the marked distinction in Cladophora standing stocks in two sections of the upper Green River that flow through differing levels of karstification? 4. Are consumers assimilating primarily autochthonous or allochthonous food resources? Consumers and algae became more 13C-depleted in downstream reaches, which is opposite to published data in other streams. Underlying causes for this pattern are uncertain, but one plausible cause is an increase in DIC availability downstream. Karstrelated hydrology may potentially alter or even reverse normal longitudinal gradients within in-stream producer and subsequently, consumer δ13C values. Since consumers were sampled during low-Cladophora conditions during 2013 and within a few weeks of the onset of the Cladophora bloom in 2012, stable isotopic results may be more representative of primary consumer diets during pre- Cladophora bloom periods. Although Cladophora cover was significantly higher in downstream reaches during both years, food-web structure was similar in all reaches. Consumer niche breadth was similar across reaches, and mixing model analyses suggested that primary consumers in all reaches assimilated similar amounts of Cladophora. The contribution of both autochthonous and allochthonous food resources to the assimilated diet of primary consumers appeared to be similarly important. These results suggest that allochthonous resources may be important in some midreach food webs, especially during periods of low algal growth.

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Kenworthy, Joseph. "Comparative estuarine dynamics : trophic linkages and ecosystem function." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/8240.

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Estuarine systems are of crucial importance to the provision of goods and services on a global scale. High human population densities in coastal systems have caused an increasing input of pollutants, of which nutrient pollution is of major concern. Increasingly, these areas are also impacted by physical disturbance, which can originate from anthropogenic sources (e.g. bait digging, shipping) or climate change causing increasingly frequent and intense storms. The individual impacts of such stressors on ecosystems have been investigated however their combined impacts have received less attention. Cumulative impacts of multiple stressors are unpredictable and will likely result in non-additive effects. Further, the effect of local environmental context on multiple stressors is a relatively understudied topic. Work in this thesis compared the combined impact of nutrient enrichment and physical disturbance in Scotland and Australia, using a series of manipulative field experiments. Results demonstrate that response to stressors is highly context dependent, varying between and within geographic locations. While the background levels of stress may vary, by comparing these two locations it is possible to comment on the adaptations and response that communities within different parts of the world display when subjected to additional stress. This study demonstrates that environmental context must be considered when implementing future management practices. Further work demonstrated that the impact of multiple stressors varies depending on how the stress is applied –whether stressors are applied simultaneously or whether there is a delay between two stressors. This study was among the first of its kind, assessing the implications of how multiple stressors react with each other given the order and intensity in which stressors were applied. Results demonstrated that systems can become sensitised to stress making them increasingly vulnerable to additional stress. Future research should be focussed on incorporating ecologically relevant scenarios of how stressors will impact estuaries while considering how environmental context will mediate impacts.

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Medeiros, Elvio S. F. "Trophic ecology and energy sources for fish on the floodplain of a regulated dryland river Macintyre River, Australia /." Connect to this title online, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051115.174552/.

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Buchheister, Andre. "Structure, Drivers, and Trophic Interactions of the Demersal Fish Community in Chesapeake Bay." W&M ScholarWorks, 2014. https://scholarworks.wm.edu/etd/1539616586.

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Management of fisheries resources is increasingly broadening its scope from single-species approaches to more holistic, ecosystem-based approaches that account for interactions of fish with a variety of ecological factors, such as predators, prey, and habitat. This ecosystem based fisheries management (EBFM) approach requires thorough biological and ecological understanding of systems pertaining to community structure, habitat suitability, and food web interactions. to strengthen the ecological underpinnings of EBFM efforts in Chesapeake Bay, the largest estuary in the USA, I conducted synoptic analyses examining the structure, function, and patterns of the bay's demersal fish community. This research relied on I0 years of data from a multi-species, bimonthly bottom trawl survey of the Chesapeake Bay mainstem. The unifying objectives of this work were to 1) synthesize basic biological and ecological information of many Chesapeake Bay fishes, and 2) examine the environmental drivers of community structure and trophic interactions in the Bay. One major hypothesis underlying the more detailed research objectives for each component was that bay-wide patterns in biomass and feeding habits of Chesapeake Bay fishes were mostly driven through bottom-up processes governed by a blend of small- and large-scale environmental factors. as food web structure and trophic interactions are governed by the presence, distribution, abundance, and behavior of species, Chapter 1 focused on evaluating patterns for these basic biological characteristics for a large suite of 50 species and investigating environmental factors that influence the community trends. Univariate and multivariate statistical modeling revealed that the demersal fish community (dominated by five species) was strongly structured along a salinity gradient, and other factors (e.g. dissolved oxygen, temperature, month, and year) helped regulate biomass and diversity trends. Chapter 2 synthesized diet information for 47 fish species, demonstrated the role of five prey groups (mysids, fishes, bivalves, polychaete worms, and crustaceans) in differentiating feeding guilds, and highlighted the importance of non-pelagic prey groups (especially the hyper-benthic mysids) in supporting the nutritional needs of fishes. Diets of 12 predator species were investigated in more detail in Chapter 3 to infer the dynamics of four important prey groups (mysids, bay anchovy, polychaetes, and bivalves) using advanced statistical modeling techniques. Results revealed generally coherent consumption trends across predators for a given prey, suggestive of prey availability driving consumptive patterns. Synchronous annual peaks in prey consumption were indicative of pulses in prey production (particularly mysids and bivalves) that were exploited by predator populations. to evaluate the population-scale effects of these bottom-up alterations in prey productivity, Chapter 4 relied on a simulation model to examine the potential effects that these annual changes in prey availability could have on consumption and production of one representative predator species. The model indicated that enhanced individual growth resulting from pulses in prey production could generate substantial gains in predator spawning stock biomass, recruitment, and fishery yield. However, the bottom-up effects on predator production had only modest effects on rebuilding times of a depleted population relative to controls on fishing mortality. This research represents one of the largest studies on community structure and trophic interactions for demersal fishes in an estuarine environment, contributing to a broader understanding of fish ecology within a complex and dynamic system. By filling research gaps identified for EBFM in Chesapeake Bay, this body of work also supports a more holistic management approach for the sustainable use of resources from the Chesapeake Bay and coastal waters of the Northwest Atlantic Ocean.

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Dissertations / Theses on the topic 'Trophic ecology'

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