Sensitivity analyses of decision rules in World Conservation Union (IUCN) Red List criteria using Australian plants Original Research Article

The World Conservation Union (IUCN) has developed quantitative criteria for assessing the conservation status of species. The criteria comprise five decision rules that specify threshold values in rates of decline, distributional range size, population size and risk of extinction. The criteria are currently under review to identify and resolve difficulties in their application. Four issues raised in the review include (i) the effect of skewed size distributions on the assessment of the number of populations or locations, (ii) the effect of varying scales on measurement and assessment of distributional range, (iii) structural parity between the range and population criteria (B and C), and (iv) the treatment of missing data. Unless resolved, these issues may result in biases in the outcomes of Red List assessments. We applied sensitivity analyses to explore the nature of these biases and examined how they might be overcome with relatively minor modifications to the criteria. We applied these analyses to a data set comprising 135 rare or threatened vascular plant species from south-eastern Australia. The analyses suggest that biases may be reduced by: excluding very small locations and subpopulations from consideration; adopting a scale for area of occupancy thresholds that is commensurate with a biologically appropriate scale for measurement; implementing a common structure of decision rules in range and population criteria to minimise differences in the way continuing declines, fragmentation and fluctuations are assessed; and adopting a precautionary protocol for invoking ‘Data Deficient’ status when assessments based on only one or few criteria fail to identify threatened status.