Relationship between phytoplankton paleoproduction and diversity in contrasting trophic states

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With the increasing rate of species extinctions following anthropogenic perturbation, there is a growing interest in biodiversity research. Although productivity and species richness relationships have been tested and applied in contemporary aquatic ecological studies, none have been applied to paleoecology with contrasting trophic states. The present study explores the applicability of a contemporary production and species richness relationship in high-resolution paleoecological records with low, intermediate and mid to high productive aquatic systems. Results from our study reveal that diatom species richness was positively correlated in low to intermediate productive lakes. In contrast, the relationship was hump shaped (unimodal) in a mid to high productive system concurrent with the species diversity analyses. Contrasting relationships between diatom species richness and stable isotope records (δ13C and δ15N) suggested that the nutrient biogeochemical cycle might play an important role in controlling species richness. From fossil pigment records we show that the variations in algal functional group signatures were highest in intermediate state. Collectively, these results suggest that the hump shaped (unimodal) relationship between diatom species richness and production might be limited to high productive systems with maximum richness and diversity in intermediate states, which is also supported in contemporary studies. Moreover, fossil pigment records as proxies for algal functional groups reveal that in a mid to high productive system with intense watershed scale disturbances, community composition of algal functional groups declined favoring certain diatoms. Our results demonstrate the applicability of production and diversity relationship theory in paleo-perspective and that recent watershed scale land use changes might affect the species diversity in aquatic systems.