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The consequences of the variance‐mean rescaling effect on effective population size
Author(s) -
Pertoldi C.,
A. Bach L.,
S. F. Barker J.,
Lundberg P.,
Loeschcke V.
Publication year - 2007
Publication title -
oikos
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.672
H-Index - 179
eISSN - 1600-0706
pISSN - 0030-1299
DOI - 10.1111/j.0030-1299.2007.15672.x
Subject(s) - population size , harmonic mean , effective population size , population , statistics , rule of thumb , small population size , census , extinction (optical mineralogy) , variance (accounting) , mathematics , biology , ecology , econometrics , demography , genetic variation , economics , algorithm , paleontology , accounting , sociology
The effective population size (N e ), and the ratio between N e and census population size (N) are often used as measures of population viability. We show that using the harmonic mean of population sizes over time – a common proxy for N e – has some important evolutionary consequences and implications for conservation management. This stems from the fact that there is no unambiguous relationship between the arithmetic and harmonic means for populations fluctuating in size. As long as the variance of population size increases moderately with increasing arithmetic mean population size, the harmonic mean also increases. However, if the variance of population size increases more rapidly, which existing data often suggest, then the harmonic mean may actually decrease with increasing arithmetic mean. Thus maximizing N may not maximize N e, but could instead lower the adaptive potential and hence limit the evolutionary response to environmental change. Large census size has the clear advantage of lowering demographic stochasticity, and hence extinction risk, and under certain conditions large census size also minimizes the loss of genetic variation. Consequently, maximising census size has served as a useful dogma in ecology, genetics and conservation. Nonetheless, due to the intricate relationships among N e , population viability and the properties of population fluctuations, we suggest that this dogma should be taken only as a rule of thumb.