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Evaluating the effect of stage‐specific survivorship on the N e / N ratio
Author(s) -
Waples Robin S.
Publication year - 2002
Publication title -
molecular ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.619
H-Index - 225
eISSN - 1365-294X
pISSN - 0962-1083
DOI - 10.1046/j.1365-294x.2002.01504.x
Subject(s) - survivorship curve , biology , population , statistics , inbreeding , demography , effective population size , population size , ecology , mathematics , genetic variation , sociology
Evaluating effective population size ( N e ) and the effective size to census size ratio ( N e / N ) in species with Type III survivorship curves is complicated when key demographic parameters [mean ( k̄ ) and variance ( V k ) of family size] are measured during early life stages. The method of Crow & Morton (1955) for scaling demographic data collected at a juvenile stage to expected values at adulthood is extended to consider sequential episodes of random and family correlated survival. Results show the following: (i) The order in which the episodes of random and family‐correlated survival occur does not affect N e or N e / N ; (ii) If a population experiences an episode of family‐correlated survival, N e / N scaled to its expected value in a population of constant size ( k̄ = 2) is simply the survival rate during the family‐correlated stage. If multiple such stages occur, scaled N e / N is the product of the survivals during all family‐correlated life stages; (iii) Under the assumption of random post‐enumeration survival, adjusting the variance effective size to its expected value at k̄ = 2 is equivalent to computing the inbreeding effective size at the earlier life stage. Application to experimental data for hatchery populations of Pacific salmon ( Oncorhynchus spp.) indicates that nonrandom survival during the marine phase led to estimated reductions in effective size of 0–62% (mean 19%) in 12 different cohorts. This approach can provide insights into N e / N in highly fecund species, including some marine species in which N e has been estimated to be several orders of magnitude less than N .