How many species are there on Earth? Different models to approximate global species diversity (and is this even possible?)

About 2 million species are currently known to science, but the ‘true‘ species number on Earth is without doubt considerably higher, with the largest number of unknown species being insect. Various models have tried to estimate global biodiversity, however, modelling approaches and predictions differ widely. I will introduce several fundamental ways to estimate global species numbers and discuss conceptual strengths and weaknesses. The lecture will close with an outlook and an appraisal of whether it will be realistic to know how many species there are on Earth.