Thesis (Ph. D.)--Oregon State University, 2002. / Typescript (photocopy). Includes bibliographical references (leaves 229-246). Also available on the World Wide Web.

Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Ecology and Evolution." Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xvi, 166 p.; also includes graphics (some col.). Includes bibliographical references. Available online via OhioLINK's ETD Center.

Thesis (Ph. D.)--College of William and Mary. / Vita. Includes bibliographical references. Also available online.

Orientadores: Paulo Sergio Moreira Carvalho de Oliveira, Sebastian Felipe Sendoya Echeverry / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-23T06:11:49Z (GMT). No. of bitstreams: 1 Vidal_MayraCadorin_M.pdf: 1986442 bytes, checksum: da9ed52c0a73527b0590731f5ee8d10b (MD5) Previous issue date: 2013 / Resumo: Exploradores do mutualismo - indivíduos que utilizam recursos/serviços produzidos pelos mutualistas sem recompensá-lo - podem trazer sérios danos aos mutualistas explorados, principalmente quando acaba matando um dos parceiros mutualistas. Plantas portadoras de NEFs podem manter mutualismos com formigas visitantes, que defendem a planta contra insetos herbívoros. No cerrado de Itirapina (SP), encontramos larvas de uma nova espécie de díptero do gênero Rhinoleucophenga (Drosophilidae) que constroem abrigos de consistência pegajosa em cima dos NEFs de Q. grandiflora. Assim, larvas de Rhinoleucophenga podem interferir no mutualismo formiga-planta, agindo potencialmente como exploradora dessa interação. O presente estudo teve como objetivos principais investigar a história natural dessas larvas, principalmente aspectos do comportamento e interação com Qualea e formigas, e analisar seu possível efeito sobre o mutualismo formiga-Q.grandiflora. Durante observações de campo comprovamos que formigas e outros insetos visitantes dos NEFs podem ficar presos ao abrigo larval e servir de alimento para o díptero. Larvas de Rhinoleucophenga sp. nov. ocorrem em 85% dos indivíduos de Q. grandiflora, principalmente na época chuvosa ocupando preferencialmente nectários ativos, perto do ápice e na face abaxial dos ramos. No levantamento da mirmecofauna visitante de Q. grandiflora encontramos 27 morfoespécies de formigas, sendo as duas mais frequentes Camponotus crassus, e uma espécie do gênero Brachymyrmex, as mesmas que foram mais comumente encontradas presas aos abrigos das larvas mirmecófagas. Vimos que as larvas expõem uma substância líquida na abertura de seu abrigo, que comprovamos possuir composição química muito similar a do néctar extrafloral de Q. grandiflora, o que sugere que as larvas utilizam o néctar da própria planta para atrair suas presas. Na presença de larvas de Rhinoleucophenga, menos formigas visitam as plantas e também por menos tempo. Esse forrageamento diferenciado resultou em menor ataque de formigas a cupins vivos (herbívoros simulados). Além disso, na presença das larvas mirmecófagas houve maior abundância de herbívoros mastigadores e maior área foliar removida por herbívoros. Podemos afirmar que as larvas de Rhinoleucophenga sp. nov. utilizam o recurso da planta sem beneficiá-la. Além disso, as larvas do díptero também prejudicam a planta e suas formigas mutualísticas, uma vez que alimentando-se delas, aumentam a incidência de herbívoros e a herbivoria foliar na planta. Dessa forma, as larvas de Rhinoleucophenga sp. nov. estão agindo como exploradoras e do mutualismo formiga-Qualea grandiflora e predadoras de topo, causando efeito cascata nesse sistema / Abstract: Exploiters of mutualism - individuals that use resources/services offered by mutualists giving nothing in return - can cause serious damages to mutualists, especially when it involves the death of one of the partners. Plants bearing EFNs usually maintain mutualism with aggressive ants, which defend the plant against herbivores. In a cerrado area at Itirapina (SP), we found a new dipteran species of the genus Rhinoleucophenga (Drosophilidae) whose larvae construct sticky shelters on top of active EFNs of Q. grandiflora. Field observations revealed those ants and others insects that visit the EFNs can get trapped at the sticky larval shelters, and are consumed by the larvae. We hypothesized that Rhinoleucophenga larvae could be interfering with the ant-Qualea mutualism, and thus be acting as an exploiter of this interaction. Here, we investigate the natural history of Rhinoleucophenga larvae, mainly its behavior and association with ants and Qualea, and their possible effect on the ant-Qualea mutualism. Larvae of Rhinoleucophenga sp. nov. occur in 85% of the individuals of Qualea grandiflora inspected at Itirapina. Rhinoleucophenga larvae occur mostly during the rainy season, mainly at the apex and abaxial surface of the branches. We found 27 ant species visiting Qualea. The two most frequent visiting species, Brachymyrmex sp. 1 and Camponotus crassus, were most common insects trapped at larval shelters. Chemical analyses revealed that Rhinoleucophenga larvae use Qualea's extrafloral nectar to attract insect prey to their shelters. Qualea branches infested by ant-preying Rhinoleucophenga larvae had ant visitors for less time and in lower numbers than dipteran-free branches. This negative effect on ant foraging activity resulted in decreased levels of ant aggression to live termite-baits (i.e., simulated herbivores) on leaves of dipteran-infested compared to dipteran-free branches. Controlled field experiments demonstrated that branches hosting Rhinoleucophenga larvae had higher numbers of chewing herbivores and higher levels of foliar herbivory than dipteran-free branches. By using Qualea's EFNs as larval shelters and as attractants to ant prey, larvae of Rhinoleucophenga sp. nov. negatively affect both the plant and ant visitors, with cascading effects ultimately resulting in increased herbivore damage to leaves. Thus we can conclude that ant-eating Rhinoleucophenga larvae are acting as exploiters of the mutualism between ants and Q. grandiflora and also as top predator, causing cascade effect on this system / Mestrado / Ecologia / Mestra em Ecologia

Two species of hake (Merluccius capensis and Merluccius paradoxus) account for most of Namibia’s fisheries catch, and they are important secondary consumers in the Benguela Current ecosystem. Inferences on their trophic relationships have been based mainly on stomach content analyses. However, such data are limited temporally because they represent only snapshots of recent feeding, and are quantitatively biased because of variation in the digestion rates of different prey. The principal aim of the thesis was to understand the trophic relationships of two hake species relative to each other, their known prey and top predators (demersal sharks) in the northern Benguela Current ecosystem (Namibia), using time-integrating trophic biomarkers. By using stable isotope (carbon and nitrogen) and fatty acid signatures of their muscle tissues, my overall objectives were to produce new knowledge about 1) hake ontogenic trophic relationships, 2) the contributions of different prey to hake diets, 3) hake dietary differences, and 4) some aspects of hake’s trophic relationships with demersal sharks. Tissues of hake (n=358), their potential prey (n=455), and demersal sharks (n=42) were collected between 2008 and 2012 during demersal bottom trawl surveys off Namibia, for stable isotope and fatty acid analyses. And more...

Previous research into bottom-up processes on saltmarshes has mainly focused on the influence of plant succession on herbivores. This study will present original research exploring the influence of bottom-up processes in a saltmarsh ecosystem between three trophic levels: Orchestia, redshanks, and sparrowhawks. Density dependence, may be the dominant top-down effect when higher numbers of sparrowhawks and redshanks are present, and may mask top-down and bottom-up trait effects which are constant. Bottom-up effects begin to emerge when cold conditions force redshanks from muddy creeks onto the saltmarsh to forage for Orchestia, because their primary prey, Corophium become less available. Larger flocks form and feeding on Orchestia requires them to balance a need to profit from the best available feeding patches and to be vigilant to sparrowhawk attack. Redshank vulnerability is compounded, because Orchestia hide in cold temperatures, so probing in the soil with their heads down makes them more vulnerable to sparrowhawk attack. Larger flocks may be able to exploit areas closer to sparrowhawk-concealing cover at the terrestrial boundary because they feel safer in greater numbers. Warmer temperatures make Orchestia more active which attracts redshanks, which can simultaneously feed and be vigilant because they peck and catch crawling and jumping Orchestia with their heads up. Consequently, increased flock size may temporarily depress Orchestia abundance, so that redshanks become spaced, leaving isolated individuals more vulnerable to attack. Therefore, it is a temperature-dependent bottom-up process which impacts upon both Orchestia and redshank behaviour, which then may influence the hunting success of sparrowhawks. Whether the characteristics of this saltmarsh ecosystem and the trophic dynamics can be compared to other examples is questionable. Saltmarshes probably differ in their topography and the way in which environmental conditions affect them that then defines which species are present and how these species interact.