Abstract Winter energy management in small passerines living year-round in boreal or alpine areas presumably results in strong selective pressure since they need to find food, at a time when natural resources diminish and become less available, and energy requirements increase dramatically. In this thesis energy management during the non-breeding season was studied in three species of tits (Parus spp.), from three different populations: Coll de Pal (Spanish Pyrenees), Lund (Southern Sweden) and Oulu (Northern Finland). Energy management strategies vary significantly between species and among populations and individuals of the same species. Such differences may depend on several environmental factors, food predictability and individual characteristics. Birds from the studied populations appear to react to energetic challenges on a short-term basis and in a highly flexible way. The coal tit (Parus ater) in Coll de Pal and the willow tit (Parus montanus) in Oulu, both hoarding species, relied mostly on short-term management of energy for winter survival. Social and residence status appeared to be the most important factors in determining the level of energy reserves, underlining the importance of food predictability for energy management in wintering tits. Further studies were carried out on two distinct populations of great tit (Parus major) exposed to different winter hardiness. Birds from both populations increased their resting metabolic rate (MR) with experimentally decreasing ambient temperatures. Birds from Oulu maintained higher expenditures than birds from Lund in all cases, but also experienced higher energetic cost of thermoregulation at the lowest temperatures. The differences probably did not arise from a differential insulation capacity between populations, despite the differences in plumage structure found, but from a differential metabolic acclimatization. Birds from Lund probably became hypothermic at the lowest temperatures, which may have exceeded the levels they were acclimatized for. The observed differences in basal MR in laboratory conditions were consistent in wild birds throughout the non-breeding season. Birds from both populations experienced similar patterns of variation in basal MR, with expenditures increasing with mass but decreasing with day length, size and age. Great tits modulate their energy expenditure in a flexible way as a means for surviving the non-breeding season. Further, despite such flexibility, populations appear to be locally adapted for such metabolic acclimatization. These results may have important implications on their life-history and distribution. Winter acclimatization appears to be a complex set of entangled strategies that are based on a metabolic adjustment to cope with changing energy requirements. Other mechanisms that apparently play a secondary role, for example the long term management of reserves through fattening or hoarding, or conserving heat through hypothermia and by developing a better insulative plumage, are certainly important emergency strategies that in natural conditions may explain how some populations can endure winter conditions.

<p>Modern economic activities, like industry and agriculture, as well as household activities, generate an important amount of refuse. The way we collect, transport, and dispose it will determine the level of environmental contamination. May animals exploit refuse as a food source (i.e., anthropogenic food subsidy) and gulls are the most important group. Refuse subsidizes energetically gull populations, which impacts on their acquisition and allocation of resources, as well as on the environment, with ecological and evolutionary consequences are not well understood. In this dissertation we evaluated potential impacts of refuse on gulls by doing a literature review as well as empirical research on the Kelp Gull (<i>Larus dominicanus</i>) in the Rio de la Plata Estuary in South America. Direct and indirect impacts of refuse on gull species and the environment have been observed during the review process. We have detected positive impacts of refuse on body size, chick growth, fecundity, reproductive success, and population dynamics. However, negative impacts were also found focusing on fecundity, reproductive success, and population dynamics. Indirect negative impacts on other species, water bodies, and airport security were also found. Refuse produces numerous impacts on gulls at the individual, population, and species levels, with indirect negative consequences on ecosystems. There is a need to reduce the access of gulls to sources of refuse to mitigate the existing and potential conflicts with human activities and other species, especially those that are threatened and endangered. During our empirical research we found that refuse was ingested and assimilated by Kelp Gull chicks during the chick rearing period and that the ecological niche width increased with the age of the chick. We propose that parents incorporate isotopically unique food sources to nestling’s diet during their growth, increasing isotopic diversity of nestlings. Additionally, we found that refuse could affect foraging decisions of females during the pre-incubation period, which could positively affect future fecundity and negatively impact reproductive success. We found also that refuse consumption on fecundity and reproductive success of gulls is generally studied at the colony level, using conventional diet techniques, but not much has been done using stable isotopes at the individual level, making comparisons among studies and conclusions difficult to address. We encourage other researchers to continue incorporating the isotopic ecology perspective to study the effect of food subsidies on gulls. Additionally, we found that Kelp Gull on the coast of the Rio de la Plata Estuary ingest plastic debris. We conclude that plastic bags and plastic films might be the most important source of contaminants for the Kelp Gull on the coast of the estuary. Main findings of this dissertation suggests the need for an improvement of waste management practices and a regulation of plastic production and use in Uruguay to reduce plastic ingestion by gulls. Finally, next steps for research are provided in this important area of environmental science and natural resource management.</p>

<div>Anthropogenically driven global change is disrupting ecosystems and habitats of many plant species, straining the ability of native species to survive and reproduce. The overarching goal of this research was to holistically work towards restoration of a threatened tree species by connecting research from different disciplines. In order to do so, the threatened butternut tree (<i>Juglans cinerea</i>) and its hybrids were used as a case study. Hybridization can incorporate stress tolerance in plants and could be a potential restoration tool. Evidence in some wild butternut populations indicates that naturalized hybrids of butternut with Japanese walnut (<i>Juglans ailantifolia</i>) may be more tolerant to butternut canker disease (BCD) than butternut, but this has not been formally tested. Thus, chapter 2 examined potential BCD tolerance within and between unadmixed and hybrid butternut inoculated with two BCD fungal isolates. Differences in canker growth were observed by fungal isolate, which could help to explain some differences in BCD severity found among butternut populations. Smaller and fewer cankers and greater genetic gains were detected in hybrid families, demonstrating that hybrids warrant further evaluation as a possible breeding tool for developing BCD-resistant butternut trees.</div><div>However, even with increased disease tolerance, hybrids must possess similar ecophysiological tolerances to their native progenitor to be an effective replacement. Butternut is extremely cold hardy, but Japanese walnuts are native to a warmer ecosystem, indicating potential disparities in extreme temperature tolerances between the two species and their hybrids. Thus, samples from mature trees were subjected to cold and heat treatments to compare relative extreme temperature tolerances within butternut and between butternut, Japanese walnut, and their hybrids. Within butternut, trees from colder areas exhibited less cold damage than those from warmer areas. Differences in heat damage among provenances occurred but did not follow a clear trend. Butternut exhibited greatest cold tolerance, Japanese walnut exhibited greatest heat tolerance, and hybrids were intermediate. Thus, the utility of hybrids for restoration could be limited at the extremes of the species’ distributions.</div><div>A second, but different type of freeze test was conducted for chapter 4 using seedlings to gain a more nuanced understanding of cold tolerance within butternut and between butternut and its hybrids. No survival or damage differences were detected in butternut provenances, although seedlings from the coldest provenances experienced more delayed budbreak at the two warmest treatments than those from warmer provenances. Interspecific differences were not observed in dieback but were detected in survival and budbreak. The hybrids had greater survival than butternut from warmer provenances at the lowest temperature treatment (-38 °C), but given that temperatures that low are extremely unlikely to occur in those provenances, it is not anticipated to give the hybrids an advantage if planted in those areas. However, the hybrids’ earlier budbreak could limit the success of restoration with these hybrids in the coldest extents of butternut’s range. </div><div>If hybrids, as well as genetically modified (GM) trees, are successfully developed for effective disease tolerance and to serve as an ecologically suitable replacement, success of restoration using hybrids will ultimately depend on those directly responsible for replanting efforts. A survey was administered to land managers in 46 organizations in Indiana to gauge perceptions of hybrid and GM trees, as well as current use of hybrid trees. Land managers had stronger concern for ecological, rather than economic, issues. Agreement was highest for using hybrid and GM trees for “conservation and restoration of at-risk species”, “timber production”, and “non-timber products (fruit, syrup, etc.)”. However, perceptions varied by characteristics, such as concern type, age, and the type of land they managed. Ecological concern and the type of land being managed most strongly predicted current hybrid use. Overall, results indicate the majority of land managers in Indiana would likely be agreeable to recommendations towards using hybrids. However, most nonetheless had strong ecological concerns about their suitability as a native replacement. It is important to note, though, that consistent with the results of previous studies, great variation was seen within the performance and characteristics of the butternut hybrids in chapters 2-4. Thus, it may be possible with careful selection and breeding to harness this variation to develop disease tolerant and ecologically similar hybrids acceptable to land managers.</div>