Relation between nutritional mode and ecophysiological niche widthand its effect on distribution pattern and habitat specificity ofchrysomonad flagellates

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Distribution pattern of organisms, the links between the organisms ecology and their distribution pattern as well as the generalizability of such pattern are a crucial basis for assessing the dynamic nature of ecosystems and their associated biodiversity. The interplay between biodiversity and ecosystem functions raises the question of how the functional differentiation between taxa is related to their distribution pattern. One of the most obvious functional differentiations is that of nutritional strategies, i.e. heterotrophic versus mixotrophic versus phototrophic. Ideal targets for addressing such overarching research questions are microbial eukaryotes due to their overwhelming diversity and functional differentiation. The chrysomonads (chrysophytes) are a particularly well suited model group as they are widespread and among the dominant flagellates in a wide range of habitats, a wide range of nutritional strategies is realized within this group and chrysomonads with different strategies typically co-exist in many different habitats. Further, they are comparatively well investigated and members of this group have a long tradition as protist model species in ecology and ecophysiology. Heterotrophy evolved several times independently within the chrysomonads. Here we hypothesize that, in general, heterotrophic taxa may tolerate a wider range of physicochemical conditions as compared to mixotrophic and phototrophic taxa. Further we hypothesize that, in consequence, the distribution pattern of chrysomonad taxa differ between phototophic, mixotrophic and heterotrophic taxa, i.e. correlate with their ecology rather than with their phylogeny. In a first working package we will characterize chrysomonad growth rates as a function of food and nutrient concentration, food quality and light intensity as a basis for comparative analyses of the niche width of heterotrophic and phototrophic strains. In a subsequent working package we will test the assumption that the fundamental niche width systematically differs between heterotrophic, mixotrophic and phototrophic chrysophyte lineages. We complement these ecophysiological analyses with field surveys focusing on the regional distribution pattern with respect to habitat characteristics. We specifically hypothesize that distribution pattern of phototrophic chrysomonads are more restricted to habitats of similar abiotic conditions as are those of heterotrophic chrysomonads and that seasonality is more pronounced in phototrophic chrysomonads as compared to heterotrophic chrysophytes. In sum, this study will provide a sound basis for linking the functional diversity of ecosystems with their associated biodiversity exemplified for species distribution pattern and ecophysiological niche widths of chrysomonads.