Does Mother Nature really prefer rare species or are log-left-skewed SADs a sampling artefact?
Article first published online: 16 JUL 2003
Volume 6, Issue 8, pages 766–773, August 2003
How to Cite
McGill, B. J. (2003), Does Mother Nature really prefer rare species or are log-left-skewed SADs a sampling artefact?. Ecology Letters, 6: 766–773. doi: 10.1046/j.1461-0248.2003.00491.x
- Issue published online: 16 JUL 2003
- Article first published online: 16 JUL 2003
- Editor, B. Maurer Manuscript received 26 March 2003 First decision made 1 May 2003 Manuscript accepted 1 June 2003
- species abundance distributions;
Intensively sampled species abundance distributions (SADs) show left-skew on a log scale. That is, there are too many rare species to fit a lognormal distribution. I propose that this log-left-skew might be a sampling artefact. Monte Carlo simulations show that taking progressively larger samples from a log-unskewed distribution (such as the lognormal) causes log-skew to decrease asymptotically (move towards −∞) until it reaches the level of the underlying distribution (zero in this case). In contrast, accumulating certain types of repeated small samples results in a log-skew that becomes progressively more log-left-skewed to a level well beyond the underlying distribution. These repeated samples correspond to samples from the same site over many years or from many sites in 1 year. Data from empirical datasets show that log-skew generally goes from positive (right-skewed) to negative (left-skewed) as the number of temporally or spatially replicated samples increases. This suggests caution when interpreting log-left-skew as a pattern that needs biological interpretation.