Slide 8: Principles: Realised niche
The fundamental niche is never fully realised, due to competitive interactions between other species. Thus, the actual fraction of the fundamental niche that a species realises is a subset of the fundamental niche, and is termed the realised niche. As shown in the diagram, the area encircled on the left could represent the fundmental niche for a species A (represented by crosses). However, species B (represented by circles) may also be able to exist in the same niche to some extent, due to niche overlap, as shown on the middle diagram. Thus, the realised niche for species A also includes some of species B, and is not as large as it could be.