Before revision:  We support our results regarding immigration rates through two related studies from the literature .
After revision:  We particularly highlight the incidence of the semi-log SAR for low immigration rates from a source pool, which has been alluded to in empirical studies. The two SAR forms might show good fits to data over a large span of areas but the extinction rates could be significantly higher for smaller areas when the semi-log relationship holds. This calls for a critical evaluation of extinction scenarios based on SARs so as to not underestimate the possible effects of habitat loss .