Graduate Thesis Or Dissertation


Lichen Studies of Tropical Dry Forest: A Systematic and Ecological Approach Public Deposited

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  • In recent years, our ecological knowledge of tropical dry forests has increased dramatically. However, whole components of the ecosystem, like lichenized fungi, remain mostly unknown. Crustose lichens in these forests are so abundant, that they are responsible for the characteristic appearance of a “white bark forest” during the dry season. The aim of this dissertation is to incorporate lichens into our understanding of the functioning of tropical dry forests. Prior to this work, lichens in this ecosystem were not considered at all in ecological studies and only in recent years we started having a better understanding of what species are present. The thesis is divided in two sections: Chapters 2 and 3 deal with particular cases of lichen systematics, while chapters 4, 5 and 6 deal with ecological studies of lichens at the ecosystem level and how they interact with other organisms. All the chapters revolve around lichens of the tropical dry forest of the Chamela-Cuixmala Biosphere Reserve in Mexico. In Chapter 2, new collections of the supposedly extinct and doubtfully lichenized fungus genus Polypyrenula were found. Given that anatomical studies of the fresh collections were not congruent with its current systematic position, a molecular approach was followed using the genes ITS, mtSSU and nuLSU. Our molecular analysis demonstrated that the monospecific genus, previously included in the family Pyrenulaceae, belongs instead in the Trypetheliaceae, but outside the core genera in the family. We extend the distribution of Polypyrenula to South America, provided new information on its phorophytic associations, corroborated that it is a facultatively lichenized fungus, and reinstated the name Polypyrenula sexlocularis as the correct name for the species. In Chapter 3, one new genus and two new species of lichens in the family Graphidaceae were described based on morphological, chemical and molecular data of the genes ITS, mtSSU, and nuLSU. The new genus Jocatoa in the subfamily Graphidoideae is described to accommodate the orphan species Medusulina texana. While the new species Gymnographopsis corticola and Redonographa parvispora are described in the subfamily Redonographoideae, together being the only two known corticolous species in the subfamily. A phylogenetic analysis including all the genera in the family Graphidaceae, with available sequences, is presented to accommodate the new genus and to validate for the first time the position of Gymnographopsis. Diagnostic anatomical and ecological characters are discussed for Redonographoideae. Gymnographopsis is newly reported to the Northern Hemisphere. In Chapter 4, we estimate the total lichen biomass at the ecosystem level. Calculations were based on the bark area of trees, density of different sizes of trees per hectare, dry mass of lichens per unit area, and the percentage of lichen cover per tree. The epiphytic lichen biomass in the forest was 1.30 to 1.92 t/ha, of which 180 kg per hectare were located on the lowest 2.5 m of the main trunk of the trees. Lichen biomass represents 59 percent of the foliar biomass in the system, suggesting a significant ecological role that so far is unexplored. To our knowledge, this is the first time that a lichen biomass estimate is provided for an ecosystem in which crustose lichens are the dominant growth form. In Chapter 5, the lichen consumption component of herbivory in the tropical dry forest was analyzed and compared to the leaf herbivory component. Lichen herbivory rates were calculated using high definition photographs of permanent microplots across a four-year period. The annual rate of lichen consumption was 11.5%, with no significant difference between years, even in the presence of catastrophic events like the category 4 hurricane Patricia. Lichen biomass annual consumption per hectare represents 28.5% of the biomass lost to total herbivory when considering leaf folivory (chewing) and lichenivory together. The results show that lichen consumption is an established and regular process in the forest dynamics of the tropical dry forest. A discussion on the animals responsible for lichen herbivory is presented. In Chapter 6, caterpillars of a moth species of the family Psychidae were discovered living inside mobile bags made from silk and completely covered with small pieces of lichens. The lichens used as construction material for the caterpillar bags were identified with molecular techniques and compared to a newly generated database of genetic barcodes for the lichens in the area. Of the approximately 300 lichen species expected to occur in the area, only five of them were used by the caterpillars. There was a strong selectivity for micro-foliose lichens of the family Physciaceae, even though they represent a small fraction of the mostly crustose lichens present in the forest. In this dissertation new aspects in the study of tropical dry forest were revealed. Lichens that were previously ignored were shown to be diverse, abundant and key components in the dynamics of the ecosystem. Lichens revealed levels of biomass comparable with the biomass of leaves in the forest and were consumed at similar rates. Preliminary data from this dissertation points towards a major component of the trophic web of the ecosystem that is sustained by lichens. Of particular importance is the potential of lichens to maintain the functionality of the ecosystem during the extended dry seasons. We suggest that the crustose lichen component should not be underestimated a priori in ecological studies, especially in areas with significant lichen cover.
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  • Financial support for my PhD was provided by the Mexican government via CONACYT (Reg. 217222) and SEP (scholarship BC-2239. Este artículo se ha realizado con el apoyo de beca de la Secretaría de Educación Pública y del Gobierno Mexicano) and by Oregon State University and the Botany & Plant Pathology Department. Colateral funding for field work was provided to M. A. Herrera Campos by PAPIIT-UNAM (project IN225808, Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica) and CONABIO (Proyect FB1647/JF157 “Inventario y base de datos de los líquenes de la selva seca de Jalisco”).
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  • Ongoing Research
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  • 2019-03-25 to 2021-04-26



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