The geographical distribution of the Gulf of Bothnia zooplankton species is presented together with observations of abundancies and vertical distributions. The historical development of this plankton community in the last 70 years is discussed.Spring and summer development of the plankton fauna was studiedin the Bothnian Bay. Compared to in southern parts of the Balticit could be shown that the start of development in spring formany species was only moderately later in the Bothnian Bay. Theperiod of maximal biomass was in late summer and autumn.In a study of horizontal distribution large between-station variations were found. These variations were not random as close stations formed homogenous groups. Several cases of patchiness were established. Systematically appearing differences in age-distributions were proposed as a factor in the formation of patchiness.The selective prédation on zooplankton by Baltic herring was studied in the Bothnian Bay. Besides chosing certain species herring selects the older and larger stages of these species. Egg-bearing Eurytemora females were more heavily preyed upon than the males.From literature information and own observations it was proposed that in sence of production the Bothnian Bay and the Bothnian Sea are two very different systems. Climatic effects cause a delay of primary production in spring enabling the pelagic consumers to develop in phase with the producers in the Bothnian Bay. Contrary to systems with a spring peak in phytoplankton growth this situation will lead to high pelagial efficiency leaving little to feed the benthic communities. / digitalisering@umu

Predation is a strong dective force on invertebrate prey. Asellus aquaticus differs in pigmentation reed and submerged vegetation habitats in lakes. Light pigmented individuals al vegetation dominated by Chara sp. while dark pigmented individuals dominate in the reeds. These differences have been hypothesized to result from background matching. Predation pressure from fish is belived to be highest in Chara sp., while invertebrate predators are more common in the reeds. In this study I investigatedif predation from perch and damselfly larvae create different se1ection pressure on pigmentation and size of the Asellus, and if selection is affected by the structure of the habitat. The study vas carried out in aquaria in a loboratory. Regarding predation from perch a tendancy to be selective against dark pigmented individuals in Chara substrate was seen. Mortality increased with body size in Asellus, regardless of pigmentation. In the experiment mortality of Asellus decreased with body length. The results illdicate that it is not as important for Asellus to be cryptic in the reeds since it is not exposed to visual predation on the same level as in the Chara sp. where it is preferable to be small and cryptic. In the reed, large individuals are probably favorued since common predators, such as damselfly larvae, are size-limited in their prey choice.

<p>  </p> <p>Predators and parasites are critical, interconnected members of the community and have the potential to influence host populations. Predators, in particular, can have direct and indirect impacts on disease dynamics. By removing hosts and their parasites, predators alter both host and parasite populations and ultimately shape disease transmission. Our ability to accurately predict disease dynamics requires understanding the ecological effects of predation on prey and host densities and its role in the coevolution of host resistance and parasite virulence. While the impact of predators on disease dynamics has received considerable attention, research has focused on selective predation on infected prey. There is, however, substantial evidence that some predators avoid infected prey, preferentially attacking uninfected individuals. Such different strategies of prey selectivity by predators modulate host-parasite interactions, changing the fitness payoffs both for hosts and their parasites. I use empirical results and theoretical predictions as a framework to discuss the mechanisms by which predation for infected versus uninfected individuals can affect disease dynamics. First, by integrating hypotheses from behavioral ecology and disease ecology, I outlined novel perspectives that complement the prevailing view of selective predation of infected individuals (Chapter 1). Then, exploring short-term ecological outcomes and long-term host-parasite coevolution, I investigated patterns of <em>Daphnia dentifera</em> host population densities and host susceptibility over several generations under different types of predation pressure, including selective predation on infected and uninfected individuals (Chapter 2). Finally, building on the results of this research, I developed a high school project-based lesson plan that facilitates the instruction of the nature of science, implementing on-going ecological research in activities to improve student learning based on a constructivist approach to learning (Chapter 3). Together this research highlights the differential ecological and evolutionary outcomes of host-parasite interactions under varying community contexts.</p>

This study investigates size-selective predation of four groups predaceous aquatic insects: adults and larvae of diving beetles (Dytiscidae), larvae of dragonflies (Odonata) and aquatic true bugs (Heteroptera) using laboratory feeding experiments and relates the results to morphometric data obtained for each predator.

Orientador: Prof. Dr. Norberto Anibal Maidana / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Matemática , 2017. / Doenças infecciosas acometem populações de presas e a escolha predatória de presas suscetíveis pode levá - la à extinção. Propusemos e analisamos um modelo matemático de interação presa - predador, com a população de presas dividida em duas classes: suscetíveis e infectadas. A subpopulação de presas suscetíveis, torna - se infectada por contato direto com a subpopulação de presas infectadas e o predador consome somente as presas suscetíveis. A análise do modelo permitiu estabelecer limiares para a propagação da doença na ausência bem como na presença de predadores, além de condições de existência e estabilidade dos pontos de equilíbrio biológicamente viáveis. Por meio de simulações numéricas determinamos as diferentes características biológicas apresentadas pelo modelo, assim como ilustramos os resultados analíticos. / Infectious diseases affect prey populations and the predatory choice of susceptible preys may lead them to extinction. We propose and analyzed a mathematical model of prey - predator interaction, with prey population divided into two classes: susceptible and infected. The subpopulation of susceptible preys becomes infected by direct contact with the subpopulation of infected preys, and the predator consumes only the susceptible ones. The analysis of the model allowed to establish thresholds for the propagation of the disease in the absence of predators, in the presence of them as well as conditions of existence and stability of biologically viable equilibrium points. Analysing the system by numerical simulations, we determine different biological characteristics presented by the model and illustrate analytical results.