Differences in population size variability among populations and species of the family Salmonidae

1. How population sizes vary with time is an important ecological question with both practical and theoretical implications. Because population size variability corresponds to the operation of density-dependent mechanisms and the presence of stable states, numerous researchers have attempted to conduct broad taxonomic comparisons of population size variability. 2. Most comparisons of population size variability suggest a general lack of taxonomic differences. However, these comparisons may conflate differences within taxonomic levels with differences among taxonomic levels. Further, the degree to which intraspecific differences may affect broader inferences has generally not been estimated and has largely been ignored. 3. To address this uncertainty, we examined intraspecific differences in population size variability for a total of 131 populations distributed among nine species of the Salmonidae. We extended this comparison to the interspecific level by developing species level estimates of population size variability. 4. We used a jackknife (re-sampling) approach to estimate intra- and interspecific variation in population size variability. We found significant intraspecific differences in how population sizes vary with time in all six species of salmonids where it could be tested as well as clear interspecific differences. Further, despite significant interspecific variation, the majority of variation present was at the intraspecific level. Finally, we found that classic and recently developed measures of population variability lead to concordant inferences. 5. The presence of significant intraspecific differences in all species examined suggests that the ability to detect broad taxonomic patterns in how population sizes change over time may be limited if variance is not properly partitioned among and within taxonomic levels.