Phenotypic adjustments following environmental change are ubiquitous and trait changes arising through phenotypic plasticity often lag behind their environmental stimuli. Evolutionary biologists seeking to understand how adaptive plasticity can evolve have extensively studied this phenomenon. However, the ecological consequences of common features of plastic responses to environmental variability, including gradual phenotypic change (i.e., slower than the pace of environmental change), are underappreciated. We present a framework based on the unifying concept of phenotype x environment performance landscapes that encompasses gradual plasticity. Then, we experimentally investigate the environmental contexts where gradual plasticity is important, using freshwater phytoplankton populations exposed to thermal variation. Finally, based on our conceptual framework, we develop a mathematical model of gradual plasticity that explains population dynamics in variable environments better than common alternative models. Understanding and accounting for the ecological effects of plasticity in variable environments is critical to making vital predictions and advancing ecology.