A decline in species-specific habitat quality that leads to reduced survival and/or reproductive success in a population e.g. related to changes in food availability cover or climate (Source: IUCN)
Loss of suitable habitat for a given species such that the particular species no longer occurs in that area (Source: D.B. Lindenmayer, J.Fischer Habitat Fragmentation and Landscape Change, Island Press, 2013). This concept also includes habitat fragmentation, caused by geological processess or human activities.