Global amphibian declines: A problem in applied ecology

Declines and losses of amphibian populations are a global problem with comp lex local causes. These may include ultraviolet radiation, predation, habit at modification, environmental acidity and toxicants, diseases, changes in climate or weather patterns, and interactions among these factors. Understa nding the extent of the problem and its nature requires an understanding of how local factors affect the dynamics of local populations. Hypotheses abo ut population behavior must be tested against appropriate null hypotheses. We generated null hypotheses for the behavior of amphibian populations usin g a model, and we used them to test hypotheses about the behavior of 85 tim e series taken from the literature. Our results suggest that most amphibian populations should decrease more often than they increase, due to highly v ariable recruitment and less variable adult mortality. During the period co vered by our data (1951-1997), more amphibian populations decreased than ou r model predicted. However, there was no indication that the proportion of populations decreasing changed over time. In addition, our review of the li terature suggests that many if not most amphibians exist in metapopulations . Understanding the dynamics of amphibian populations will require an integ ration of studies on and within local populations and at the metapopulation level.