Practice question

The entire marsh can represent a species’ fundamental niche when experiments or observations show that the species can survive and reproduce throughout it in the absence of a competitor. Its realized niche may be only a restricted section, such as the marsh edge, because competition prevents occupation elsewhere. Calling the whole marsh merely “habitat” identifies the physical environment but does not express the contrast between potential and actual ecological use. A competitive zone would describe an interaction region, not the full set of conditions the species could occupy. The row appears to rely on an unstated diagram or species-removal scenario, so the keyed interpretation assumes that species B is physiologically capable of occupying the whole marsh and becomes restricted under natural competition. Fundamental niche must be established from performance, not simply from geographic area: conditions must permit a nonnegative population growth rate. The example illustrates how spatial range can be used as a proxy for niche breadth when environmental gradients map onto tolerance and resource use. Without the original figure, that assumed experimental context should accompany the item.