Plankton population dynamics: food web interactions and abiotic constraints

1. In this introduction, I try to follow some developments in plankton ecology, how they have led to current research topics, and how the contributions in this issue of Freshwater Biology are related to these fields of research. 2. Due to several favourable features, such as small size, short generation time and a relatively homogeneous habitat, planktonic organisms remain ideal subjects for theoretical and experimental population ecology. 3. Important current research topics involve: (1) the control of plankton communities by external abiotic factors; (2) bottom-up (limitation by resources) and top-down (control by predators) effects in the food web; (3) the importance of dormant resting stages and benthic-pelagic coupling in plankton dynamics; (4) costs and benefits of the mixotrophic strategy, i.e. the ability to combine a phototrophic and a phagotrophic mode of nutrition.