A STATISTICAL TEST OF UNBIASED EVOLUTION OF BODY SIZE IN BIRDS

Of the approximately 9500 bird species, the vast majority is small-bodied. That is a general feature of evolutionary lineages, also observed for instance in mammals and plants. The avian interspecific body size distribution is right-skewed even on a logarithmic scale. That has previously been interp...

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Bibliographic Details
Published in:Evolution 2002-12, Vol.56 (12), p.2499-2504
Main Author: Bokma, Folmer
Format: Article
Language:English
Subjects:
Animals
Aves
Biological Evolution
Biological taxonomies
Birds
Birds - anatomy & histology
Birds - classification
Birds - genetics
Body Constitution - genetics
Body size
body size evolution
Data Interpretation, Statistical
Evolution
evolutionary trend
Extinct species
extinction
Frequency distribution
macroevolution
Models, Statistical
Monte Carlo Method
Phylogeny
Physical growth
REGULAR ARTICLES
Skewed distribution
Speciation
Species
Statistics
Time Factors
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Summary:Of the approximately 9500 bird species, the vast majority is small-bodied. That is a general feature of evolutionary lineages, also observed for instance in mammals and plants. The avian interspecific body size distribution is right-skewed even on a logarithmic scale. That has previously been interpreted as evidence that body size evolution has been biased. However, a procedure to test for unbiased evolution from the shape of body size distributions was lacking. In the present paper unbiased body size evolution is defined precisely, and a statistical test is developed based on Monte Carlo simulation of unbiased evolution. Application of the test to birds suggests that it is highly unlikely that avian body size evolution has been unbiased as defined. Several possible explanations for this result are discussed. A plausible explanation is that the general model of unbiased evolution assumes that population size and generation time do not affect the evolutionary variability of body size; that is, that micro- and macroevolution are decoupled, which theory suggests is not likely to be the case.
ISSN:0014-3820
1558-5646
DOI:10.1554/0014-3820(2002)056[2499:ASTOUE]2.0.CO;2