Tsakalakis, Ioannis (2015) Daily light oscillation as contributing factor to maintain phytoplankton diversity: a modelling approach. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 44 pp.

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Abstract

Resource-competition theory predicts the promotion of diversity by resource variations. Daily light oscillation is a periodic variation of an essential resource for phytoplankton growth occurring at any ecosystem. Several studies have revealed the importance of frequency and intensity of light oscillations on phytoplankton competition and diversity. In this study we focus on phytoplankton competition for one limiting nutrient under daily light oscillations, using a simple chemostat model. We investigate competition outcomes at different nutrient loads, for examining the possible contribution of daily light oscillations on the productivity diversity relationship, as well as at different latitudinal light conditions, for evaluating the effect of seasonality. We show that daily light oscillation increases the average nutrient concentration in the substrate leading to increasing nutrient concentrations with nutrient load. This controls a shift from gleaner's to opportunist's dominance, while coexistence at intermediate nutrient loads indicates a unimodal relationship of diversity with productivity. By using a simple expression of zooplankton top-down control and achieving multispecies coexistence, we show that these competitive outcomes are associated with temporal niches among phytoplankton species during the daily time. The multispecies community supports a unimodal productivity-diversity relationship, while the decrease of diversity at high nutrient loads is stronger when shading by phytoplankton biomass is considered. We also found a decrease of diversity with latitude associated with the disturbance of daily niches driven by seasonality. The results indicate that daily light oscillation can be a contributing process for niche creation and shaping of phytoplankton diversity in natural systems.

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