Boom, Bust, and Body Size
Increased fitness through density-dependent effects eventually leads to smaller body sizes, which in turn leads to decreased fitness. Researchers at the Savannah River Ecology Lab, led by Joe Pechmann, urged caution in interpreting datasets suggesting declines by calling attention to the boom and bust cycles characteristic of many amphibian populations. David Green demonstrated the amplitude of these boom–bust cycles correlated with the risk of population extirpation. Indeed, if a bust was severe enough, it would extirpate an amphibian population. After realizing that amphibian population declines were widespread and becoming a global problem, in the late 1980s scientists organized and began working to discover the nature of these threats and ways to blunt their effects. Rather than simply counting the number of individuals in a population, fitness metrics use the positive relationship between female body size and fecundity to assess population vigor.