Ecosystem processes and biodiversity : theoretical studies and experiments with an aquatic model ecosystem

University dissertation from Stockholm : Stockholms universitet

Abstract: Today, human enterprise has implications for all of nature, from the well being of the smallest organism, to the alteration of global biogeochemical cycles. To understand how major ecosystem processes are affected by environmental changes and decreasing biodiversity is crucial as many of natures services depend of such processes. In this thesis I have investigated two aspects thereof: 1) the effect of changing temperature on ecosystem structure and community metabolism, and 2) the importance of species composition and species richness for ecosystem processes. I found that different sensitivity of photosynthesis and metabolic rates based on internal energy sources to temperature will have important consequences for herbivores causing decreased herbivore biomass with increasing temperature. I also showed that the response of phytoplankton biomass to temperature might be very difficult to predict >from knowledge of species physiology since indirect effect and trophic interactions in ecosystems determine which limiting factor, e.g. predation, nutrient limitation or growth efficiency is most crucial. A result from an experiment where four different zooplankton species where grown in single culture as well as in polyculture indicated that species-specific interactions are important for ecosystem processes even within a guild of species that is assumed to be one well-defined functional group. Partial similarity between species in resource utilization explains moderated response to trophic regulation and also has implications for the relation between species richness and ecosystem functioning. The last paper makes the point that the magnitude and reliability of ecosystem process rates are closely linked to species richness and mechanisms of species invasions and extinction. A mathematical model explores the mechanisms thereof in detail.

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