A wolf pack has 20 breeding males and 80 breeding females. Using the sex-ratio formula Ne = 4NmNf / (Nm + Nf), what is Ne?
A100 (the census size)
B32
C64
D80 (the number of females)
Ne = 4(20)(80) / (20 + 80) = 6400 / 100 = 64. This is well below the census size of 100, illustrating how unequal sex ratios alone reduce effective population size. The formula shows that Ne is limited by the rarer sex.
Question 2 True / False
A polygynous mating system — where one male monopolizes mating with many females — increases effective population size compared to a monogamous system of the same census size.
TTrue
FFalse
Answer: False
Polygyny dramatically increases variance in male reproductive success: dominant males contribute many offspring while other males contribute none. High variance in reproductive success reduces Ne because genetic ancestry becomes concentrated in a few lineages, amplifying genetic drift exactly as if the population were smaller.
Question 3 Short Answer
Why does a population bottleneck reduce effective population size for many generations afterward, even after census numbers have recovered?
Think about your answer, then reveal below.
Model answer: During the bottleneck, intense genetic drift removed rare alleles and reduced genetic diversity. Ne calculated over multiple generations reflects that period of near-zero breeding individuals; the genetic signatures of the bottleneck — reduced heterozygosity, elevated linkage disequilibrium — persist long after census recovery.
Genetic diversity lost during a bottleneck cannot be quickly regenerated by population growth alone. New mutations arise slowly, and Ne integrated over the bottleneck period remains low. Conservation geneticists use this to explain why recently recovered species (e.g., cheetahs, northern elephant seals) still show low genetic variation despite large current census numbers.