Altitudinal gradients in Sub-Antarctic freshwater systems present unique opportunities to study the effect of distinct environmental gradients on benthic macroinvertebrate community composition and dispersal. This study investigates patterns in biodiversity, dispersal and population genetic structure of benthic macroinvertebrate fauna across an altitudinal gradient between two watersheds on Navarino Island in southern Chile. Patterns in diversity, density, evenness and functional feeding groups were not significantly different across the altitudinal gradient in both the Windhond and Róbalo Rivers. Taxa richness in both rivers generally increased from the headwaters of the river to the mouth, and functional feeding group patterns were consistent with the predictions of the River Continuum Concept. Population genetic structure and gene flow was investigated by sampling the mitochondrial cytochrome oxidase I gene in two invertebrate species with different dispersal strategies. Hyalella simplex (Amphipoda) is an obligate aquatic species, and Meridialaris chiloeense (Ephemeroptera) is an aquatic larvae and a terrestrial winged adult. Contrasting patterns of population genetic structure were observed. Results for Hyalella simplex indicate significant differentiation in genetic structure in the Amphipod populations between watersheds and lower genetic diversity in the Róbalo River samples, which may be a result of instream dispersal barriers. Meridialaris chiloeense exhibited weak population structure but higher genetic diversity, which suggests this species is able to disperse widely as a winged adult.

Much of Natural Science involves the study of patterns in nature and the documentation of how these patterns reflect and affect evolution. It is in this spirit that I have analyzed three distinct life history traits of austral South American forest passerines' to investigate whether their evolutionary patterns can be linked to evolutionary processes. This thesis reports six years of data on ten avian species from regular mist netting on Navarino Island, Chile. I found that the majority of species adhere to the same ecogeographical rules that govern the life history strategies of high latitude Northern Hemisphere birds. Eight of the species (Nancy says to list species but UVIC says abstract can only be a few words) have ancestors that originated in the tropics. The other two species have ancestors that originated in the Northern Hemisphere and expanded into the tropics where they evolved tropical life history strategies. The results of this study confirm the importance of the environment on avian speciation in newly accessible niches.

In the extensive and remote sub-Antarctic forests of South America, birds are the dominant terrestrial vertebrates. Despite considerable efforts to understand the ecology of birds breeding in these forests, our current knowledge for many species is still incomplete. During three breeding seasons (2014 – 2017), I studied the breeding ecology of the five most abundant open-cup forest-dwelling passerines in the sub-Antarctic forest of Navarino Island, Chile (55°04′S, 67°40′W). There were differences in some of the breeding strategies used by birds breeding on Navarino Island versus conspecific populations breeding at lower latitudes. Milvago chimango was the main nest predator of open-cup nesting forest passerines, and the main cause of nest failure. In addition, I found that species built their nests in sites with higher density and taller understory; however, these two factors decreased their nest survival. This mismatch could be due to a change in depredation risk on Navarino Island, and thus, passerines breeding there may be in an ecological trap. In addition, using light-level geolocators, I determined that the migratory connectivity of Elaenia albiceps is weak as a result of the large spatial spread of individuals on the wintering ground, and that the distances among individuals on the breeding grounds are not maintained in the wintering grounds. My study opens further questions about the mechanisms driving differences in breeding strategies among populations. In addition, further research is needed to assess hypotheses that could explain the mismatch between nest-site selection and nest survival and to understand what drives elaenias' movements, not only during winter but throughout their annual cycle.

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