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Does Mother Nature really prefer rare species or are log‐left‐skewed SADs a sampling artefact?
Author(s) -
McGill Brian J.
Publication year - 2003
Publication title -
ecology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.852
H-Index - 265
eISSN - 1461-0248
pISSN - 1461-023X
DOI - 10.1046/j.1461-0248.2003.00491.x
Subject(s) - log normal distribution , skew , sampling (signal processing) , skewness , statistics , mathematics , contrast (vision) , heavy tailed distribution , log log plot , relative abundance distribution , distribution (mathematics) , statistical physics , monte carlo method , biology , abundance (ecology) , binary logarithm , ecology , combinatorics , physics , probability distribution , relative species abundance , mathematical analysis , astronomy , detector , optics
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.