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The aim of this Ph.D. thesis is to analyze the potential effects of the main risks that Spanish exporters have been exposed to since the global financial crisis using rm-level data and microeconometric techniques. This thesis is divided into three chapters, exploring in each one of the factors which have been detrimental to Spanish trade. Firstly, Chapter 1 analyzes the effect taribarriers on the exports of Spanish goods and finds that higher taris reduce exports levels through extensive and intensive margins. Speciffically, a 1 % tariff reduces the probability of exportingto a specific market by nearly 0.08 pp. on average, while exported values diminish by around0.9 %. The chapter also quantifies the effect of tariffs applied by the United States on speci ccountry-product markets within the European Union in 2019 as a consequence of illegal aids for the plane maker Airbus. In this case, as tariffs were applied only to certain markets, trade diversion was easier for American firms, and as a consequence a 1 % tariff resulted in a 3.5 % reduction of American imports from Spain. Secondly, Chapter 2 explores the impact of Brexit related uncertainty on Spanish rms' trade with this market and with alternative countries. After the 2016 Brexit referendum there was a high degree of uncertainty about the nal shape of bilateral trade relations between the European Union and the United Kingdom, especially for particular sectors and rms. Within this context, the chapter explores whether a fraction of Spanish trade with the United Kingdom was diverted to other markets after the referendum. The results indicate a close to full trade diversion, mostly to other European countries, for those firms more exposed to that particular market (above 10 %). Given a particular share, trade diversion is more limited for imports relative to exports and for big companies. Lastly, Chapter 3 explores the effects of bank lending shocks on the export behavior of Spanish rms. Credit supply shocks have big effects on both the intensive margin (amount exported) and the extensive margin of trade (decision to export).

Resumen: This classroom project was carried out by two pre-service teachers of English as a practicum in a public primary school and the target population was third graders. The main object was to implement English song in order to explore, report, and reflect upon young students understanding of vocabulary. In this implementation, the theoretical framework involved remarkable notions about how to teach vocabulary from authors such as, (Howard, 2000), (Alali and Schmitt, 2012) and (Grigg, 2012), and using music in the classroom by (Arntson, 2013), and (Murphey, 1990). The literature review considered different investigations related to using songs to teach vocabulary. Based on practitioners and the observers reflection after the implementation it was discovered that the usage of music particularly English songs had a positive effect in learners attitude and learning in the classroom. The results showed that learners took advantage of this implementation when the songs proposed were carried out taking into consideration their proficiently level, and also when the classes were conducted using modeling as well as visual aids. Thus, the adaptation of songs as a tool to teach English should not be taken for granted inasmuch as learners responded positively towards it during the proceedings. Also, this project created a remarkable environment in which students were engaged as well as involved during the learning process.

En los últimos años, las exportaciones españolas han aumentado signifi cativamente, en un contexto de ampliación de la base de empresas exportadoras españolas, liderada por las PYMes, aunque las ventas al exterior están concentradas en una pequeña fracción de exportadores grandes y estables. En cualquier caso, el crecimiento potencial de las exportaciones ha mejorado gracias a la ampliación de la base estable de exportadores y a la diversificación geográfica hacia mercados emergentes. Las empresas exportadoras son más grandes y productivas que aquellas que solo operan en el mercado nacional. A su vez, dentro de los exportadores, las empresas estables y más diversifi cadas geográfi camente son más eficientes y de mayor tamaño que el resto de las compañías presentes en los mercados internacionales. Ampliaciones adicionales de la base exportadora estable requieren mejoras de la eficiencia del segmento de las PYMES. La eliminación de los obstáculos que restringen el crecimiento y la capacidad de innovación de estas empresas es un factor clave para consolidar su presencia en los mercados internacionales a largo plazo.

This research focused on the systematics and biogeography of mouse opossums of the genus Marmosa (Mammalia: Didelphimorphia: Didelphidae), with special emphasis on species found in the complicated geography of north-central South America. Via the four chapters of this dissertation, I presented information obtained through fieldwork, examination of museum specimens, DNA sequencing, phylogenetic analyses, georeferencing (including consultation of field notes and collectors), and ecological niche modeling. In Chapter 1, I conducted phylogenetic analyses of species of Marmosa based on sequence data of the mitochondrial cytochrome-b gene (CYTB), in part to test the monophyly of species previously recognized based on morphological criteria. This study revealed the existence of unrecognized species and identified novel interspecific relationships. All trans-Andean species of the subgenus Marmosa were recovered as a clade, suggesting that the uplift of the Andes might have played an important role in the diversification of the genus. In Chapter 2, I documented the presence of M. waterhousei in the Venezuelan Andes. This finding implied that the species might have crossed the dry Depresion del Tachira during a glacial period. In Chapter 3, I investigated the phylogeography of M. robinsoni , a species predominately distributed across the dry forests of northern South America. I conducted phylogenetic analyses based on sequence data of one mitochondrial and one nuclear gene. The results confirmed the monophyly of a dry-forest clade formed by M. robinsoni and M. xerophila and showed the existence of two major clades within M. robinsoni that corresponded roughly to an east/west division. Results of ancestral area reconstructions identified multiple dispersal events out of the greater Maracaibo basin. Lastly, in Chapter 4 I used ecological niche modeling to test the geographic predictions of competition between a sister species pair, M. robinsoni and M. xerophila . The results strongly suggest that M. xerophila may isolate populations of M. robinsoni in the Peninsula de Paraguana of northern Venezuela---representing a novel example of geographic isolation caused by competition. Together, these studies contributed to a better understanding of the taxonomy, phylogenetics, and biogeography of the genus Marmosa; provide novel information relevant to the biogeography of dry-forest species in northwestern South America; and propose a refinement of the concept of ecological vicariance to incorporate the possibility that biotic interactions could lead to geographic isolation.