Differences in estimates of extinction risk between occupancy and abundance data

Abstract

Temporal trends in populations are often measured with presence–absence and abundance data. These data types are inherently different, but quantitative comparisons of threat statuses assessed through occupancy or abundance data are currently lacking. We applied International Union for Conservation of Nature (IUCN) criteria to estimate extinction risk of amphibians on the basis of data collected over 25 years. We examined whether occupancy and abundance models provided consistent threat status. Occupancy and abundance data suggested declines for the study species in the study area, but occupancy generally showed smaller proportional changes compared with abundance data. Abundance data yielded higher threat categories than occupancy data but were generally associated with larger uncertainties. With abundance data, population declines were found sooner than with occupancy data, but occupancy data estimates were more robust; thus, we advocate the integration of multiple measures of decline when assessing threat status.