Organisms can adaptively change their traits by phenotypic plasticity without changing their genotype composition and by microevolution as a result of natural selection. These adaptations can occur at short timescales, so that the adaptations potentially influence ecological interactions and dynamics. Such adaptations are referred to “rapid adaptation”. We have been studying how rapid adaptations influence predator-prey interactions and consequently alter population dynamics of predators and prey, using planktonic algae, bacteria, protozoa and rotifers as model organisms. In this talk, I first explain how our prey organisms adaptively change their traits in response to predation and show that both evolutionary and plastic changes are important mechanisms of adaptation. Then, I discuss how these adaptations influence ecological interactions and dynamics. We use both theoretical and empirical approaches in order to better understand the relationships between rapid adaptations and ecological dynamics. Our study results strongly support the idea that organisms can have dynamically changing traits and this feature produces the feedbacks between trait adaptations and ecological dynamics.