The ecological niche is one of the most fundamental concepts in Ecology. It has been defined as the environmental conditions required for the persistence of a species or as the role of a species in its community or as the impact of a species on its environment. The variety of definitions assigned to the ecological niche has led to controversies about its substance and even its usefulness. Different species occupy different places in the environment, i.e. niches. When two species are found in the same place, they have to differentiate their resource use, to avoid competition. This phenomenon occurs not only at the species level but also at the level of individuals. Individualized niches were studied initially in terms of food consumption and later the research focus was extended to behaviour. The aim of this thesis is to bring structure to the concept of individualized niches. After a comprehensive exploration of the ecological niche, I present some considerations related to the use of individualized niche and followingly I present a meta-analysis of a behavioural paradigm. In Manuscript 1 I establish that ecological niche is a very diverse concept by presenting a broad conceptual map and identifying research communities within scientific literature. In addition, I provide an overview of research practices when studying ecological niche. In Manuscript 2 I present a working definition of individualized niches, based on Hutchinson’s approach and then I discuss some considerations that arise from the implementation of this concept. In Manuscript 3 I present a meta-analysis of a behavioural test, the novel object paradigm, as a case study of individualized niches. This thesis intends to bring together the ecological niche concept and aspects of behavioural ecology research, in order to bring structure to the individualized niche concept. It highlights the importance of repeated measurements of focal individuals and the need for clarity when using diverse concepts.