Compared to the Species-Area Relationship (SAR) that measures the number of ALL species within a given habitat area, the Endemics-Area Relationship (EAR) only measures the number of endemic species within habitats of different sizes. The slope of this curve can also be used to estimate the reduction in species due to habitat loss using the model:
Sloss = cAz - c(A - a)z ; where S is the number of species, c is a constant, A is the original area, a is the new area, and z is the slope of the EAR curve.
Using the EAR rather than the SAR respects the fact that a non-endemic species that becomes extinct within one area, may still have a healthy population within a different area, and therefore, only the loss of endemics species are important for estimating extinction rates due to loss of habitat size.
Figure 1. The Endemics-Area Relationship curve.