Extended Data Fig. 4: Species Accumulation Index (SAI) values and curves from the surrogacy analysis, indicating the effectiveness of tetrapods (combined or individually) as surrogates for freshwater species (combined) targets.
From: One-quarter of freshwater fauna threatened with extinction
Values and curves are shown for two alternative conservation strategies: a) maximises rarity-weighted richness, and b) maximises inclusion of the most range-restricted species. See Methods for a full explanation of each strategy. Surrogate effectiveness is measured using the Species Accumulation Index (SAI): values range from −∞ to 1, with 1 indicating perfect surrogacy, values between 1 and 0 indicating positive surrogacy, 0 indicating no surrogacy, and values less than 0 indicating negative surrogacy. In each panel, median SAI values are provided, with lower and upper confidence intervals in brackets. Blue lines are the optimal curves (accumulation of target diversity based on target priority areas); red lines are the surrogate curves (accumulation of target diversity based on surrogate priority areas); and grey lines are the random curves (accumulation of target diversity based on random selection of areas). Confidence intervals (95%, based on 100 randomisations) are shown in lighter shading around curves; most are too small to be visible.
