The loss of large apex predators, and their subsequent reintroduction, has been identified as a substantial driver on the structure and function of ecological communities through behavioral mediated trophic cascades (BMTCs). The reintroduction of wolves (Canis lupus) to Yellowstone National Park (YNP) has served as foundational case study of BMTCs. In our system, it has been suggested that wolves have established a ‘landscape of fear’ in which the primary prey, elk (Cervus elaphus), now avoid risky places, which ultimately led to the recovery of the vegetation community. Although this case is frequently cited as a well-understood example of a landscape of fear, researchers never quantified whether elk avoided risky places, a critical component of the BMTC hypothesis. Thus, I employed numerous quantitative approaches to evaluate the role of wolves and cougars on elk habitat selection in northern Yellowstone. The results from this work suggest that the daily activity schedule of wolves provide a temporally predictable period of risk that allows elk to use risky places during safe times. As such, diel predator activity flattened (i.e., made less risky) the landscape of fear for 16 hours per day, 7 days a week, which permitted elk to forage on deciduous woody plants despite the presence of wolves. Thus, suggests that any trophic cascade in northern Yellowstone is likely driven by the consumptive effects of wolves on elk. In addition, my results suggest that daily activity patterns are an important component of predation risk, and as such, provide a predictable avenue for elk to avoid predators despite residing in an environment spatially saturated with wolves and cougars. Thus, the ability of elk to avoid predators through fine-scale spatial decisions provides support for my findings that the current spatial distribution of prey is largely driven by the consumptive effects of predators on the prey population, rather than a landscape of fear. In combination, these results suggest that the landscape of fear, and more generally, fear effects, may be of less relevance to conservation and management than direct killing within free-living, large landscapes.

This thesis is focused on the fish spatial distribution and its changes mainly during the diel cycle. In the first part, I described the fish spatial distribution in the tropical lake ecosystem of Lake Turkana. The second part deals with the fish spatial distribution in a temperate reservoir on the different spatial scales from in/offshore habitats over the fine-scale to the level of individuals. The linkage of fish distribution patterns with selected environmental variables was also evaluated.

The seasonal and diel feeding habits of the goosander, Mergus merganser, the red-breasted merganser, M. serrator, gulls (Larus canus, L. argentatus and L. fuscusj and terns, Sterna hirundo/paradisaea were studied at 64V05'N. Birds' activity patterns were influenced by the nocturnal spawning of the river lamprey (Lampetra fluviatilis). Food selection and food consumption by hand-raised mergansers together with aquarium studies of the diel activity patterns of their most important prey supplemented the field data. River lamprey dominated the diet of the goosander by weight and the sculpin Cottus gobio by number. The fish consumption of the goosanders was found to be about 12% of the available river lamprey biomass and about 17% of the sculpin biomass during the breeding season. In experimental situations the river lamprey was a low- pritority species compared with salmon , Salmo salar, brown trout, 53. trutta, and minnow, Phoxinus phoxinus, when presented to satiated birds of both Mergus species. When hungry, however, the birds caught the available prey irrespective of species, but they selected larger prey when two size classes were present. Experimental results were compared with field data on availability, consumption and the escape behaviour of the various fish species. The rivers emptying in the Bothnian Bay are regarded as important feeding areas for birds breeding along the coast. In early spring they get access to abundant and reliable food resources, e.g the river lamprey. Later on the three-spined stickleback, Gasterosteus aculeatus, supply both Mergus species with food in the river and also along the coast. From the middle of June potential food supply available to birds decreases in the rivers and becomes more abundant in the coastal area. / <p>S. 1-41: sammanfattning, s. 43-227: 7 uppsatser</p> / digitalisering@umu

Unregulated North Swedish rivers show large seasonal variations in their physical characteristics. During winter the whole littoral zone freezes solid, and in spring the water flow increases rapidly and the same areas become flooded. The two mayflies Parameletus chelifer and P. minor are common in the North Swedish river Vindelälven. They probably pass through a dormant egg stage in its mid-stream section. The first tiny nymphs appeared in January to March, but they did not become abundant until the ice broke up in May. At this time they migrated rapidly to the flooded upper littoral, some continuing into the tributaries. During  the migration phase, both species used chemoreception to orient themselves towards the flooded areas. The shoreward migration allowed the nymphs to avoid high current velocity, and to utilize unexploited food resources. The two species differed with respect to utilization of the upper littoral. Most Parameletus chelifer nymphs colo­nized a seasonal stream, while the P. minor nymphs were equally abundant at the river margin as in a seasonal stream. Both temperature and food quality differed between the river margin and the seasonal stream. Compared to P. minor specimens, those of Parameletus chelifer showed a somewhat higher optimum tempe­rature, and they gained advantage of the higher food quality observed in the seasonal stream. Parameletus chelifer specimens colonizing a seasonal stream had higher growth rate, higher fecundity, and probably also advanced emergence as well as larger adult size compared with those remaining at the river margin. In addition mortality from fish predation may be lowered by utilizing shallow seasonal streams. Specimens of P. minor had higher growth rate, larger adult size and advanced emergence in the seasonal stream compared with those at the river margin. Nevertheless, fecundity was equal in both habitats and the mortality caused by predation seemed almost similar in both habitats. In most years Parameletus chelifer specimens utilizing the seasonal stream thus obtain a higher fitness than those utilizing the river margin. In P. minor this diffe­rence was not so pronounced. However, due to mortality risks caused by an early desiccation of the seasonal stream, the long-term reproductive output of the two species probably varies irregularly in the two habitats. / digitalisering@umu

Submitted by Ricardo Cedraz Duque Moliterno (ricardo.moliterno@uefs.br) on 2016-03-12T00:12:47Z No. of bitstreams: 1 Disserta??o - C?ssia Alves de S?.pdf: 408040 bytes, checksum: a24d9c29b600bca2f7903bdca077b81c (MD5) / Made available in DSpace on 2016-03-12T00:12:47Z (GMT). No. of bitstreams: 1 Disserta??o - C?ssia Alves de S?.pdf: 408040 bytes, checksum: a24d9c29b600bca2f7903bdca077b81c (MD5) Previous issue date: 2013-03-21 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / The daily activity pattern of social wasps can be influenced by different mechanisms such as environmental restrictions or interspecific interactions. However, the importance of interspecific interactions on the determination of the daily activity patterns may decrease on habitats with high environmental complexity. In this sense, we evaluated two hypotheses in order to understand what factors affect the daily activity patterns of social wasps: 1) The abundance overlap of different species during the day is lower when environmental complexity is greater, and 2) Thermal restrictions may constrain wasp activity. We counted the abundance of several wasp species foraging throughout the day on extrafloral nectaries in two plantations of caupi bean: on esurrounded by a pasture matrix (low structural complexity) and the other surrounded by fruit trees (high structural complexity). Afterwards, we evaluated the abundance overlap during the day, the abundance variations per hour and the preferential time of start and end of day activity. Temporal overlapping between species during the day was high for both plantations. The majority of species had a bimodal abundance pattern, with one abundance peak during the morning and the other during the afternoon. Species of major size started their activity during later hours, while species of minor size were active on every hour. These results indicate two scenarios: first, competition seems to below in these communities and second, temperature seems to be particularly restrictive for the activity of species of greater size. / A coleta de recursos gluc?dios pelas vespas sociais ao longo do dia pode variar como resposta a diferentes mecanismos, podendo responder a restri??es ambientais ou a intera??es interespec?ficas. Por?m, a import?ncia relativa das intera??es interespec?ficas pode ser reduzida em sistemas com maior complexidade ambiental. Para compreender esse efeito, avaliamos as seguintes hip?teses: 1) A sobreposi??o nos hor?rios de forrageamento das esp?cies de vespas sociais ao longo do dia ? menor quando a complexidade ambiental ? maior e 2) o padr?o de atividade di?rio das vespas ao longo do dia ? determinado por restri??es ambientais. Para isso, quantificamos a abund?ncia de diferentes esp?cies de vespas sociais forrageando em nect?rios extraflorais em duas planta??es de do feij?o caupi: uma circundada por matriz de pasto (baixa complexidade estrutural) e outra por frut?feras (alta complexidade estrutural). Iniciamos as observa??es e coletas ao longo do dia, depois que os NEFs do feij?o estavam ativos, e avaliamos o padr?o de sobreposi??o temporal de abund?ncia, o padr?o de abund?ncia em cada hor?rio, bem como a rela??o entre o hor?rio de in?cio e fim de atividade e o tamanho de cada esp?cie. A sobreposi??o temporal foi alta para as duas ?reas. O padr?o de abund?ncia foi bimodal ao longo do dia. As esp?cies de maior tamanho entraram em atividade em hor?rios mais tardios enquanto as esp?cies de pequeno tamanho n?o apresentaram um padr?o de inicio e fim de atividade. Esses resultados indicam que a competi??o entre esp?cies de vespas sociais ? baixa, permitindo a alta sobreposi??o do hor?rio de atividade nas duas ?reas. J? a temperatura parece restringir o hor?rio de atividade para vespas de grande porte.