Global amphibian population declines

Alford et al. address several questions related to the biological and statistical analysis of declines in global amphibian populations. They argue that, by emphasizing the global mean, we have masked spatial and temporal variation in amphibian population trends. Admittedly, information is lost when any summary statistic is used, but global amphibian declines should not be inferred by estimating missing values. Furthermore, they contend that we do not distinguish between a global decline with global causes and the cumulative effects of local declines with local causes. But we did not address the issue of causation: we reported widespread declines in extant, mostly lowland populations, whereas the recent focus has been on extinctions at high-altitude sites1,2.