Managing Small Populations

Why?

  • Loss of prairie grasslands → >95% loss

  • loss of main prey item

  • poisoning

  • trapping

BLACK FOOTED FERRETS

Disease

  • Bubonic (sylvatic) plauge 

  • 1906 earthquake let rats flourish→ plague

  • Rats brought plague to grasslands and took out prairie dogs (main ferret food source)

  • Dogs to the midwest brought canine distemper 

Extinction?

  • 1970s they were feared extinct

  • In 1981; about 100 found on ranch 

  • 1985; around 40

Captive Breeding

  • Down to about 18 individuals

  • Black Footed Ferret Species Survival Plan 

  • Producing about 400 individuals a year

Challenges

  • Population bottleneck: Sudden and considerable reduction in population size

    • Genetic diversity reduced

    • Allele frequency 

  • Genetic drift: change in allele frequencies within population due to sampling error (random events)

  • Sampling error: statistical error when subset is not representative of the entire population 

  • Founder effects: small sample from the source population

Random mating:

  • Small samples often produce frequencies that are different from population 

Size of Captive Populations

  • Smaller populations have greater differences in allele frequencies over time 

  • Lost + fixed 

  • Higher starting frequency more likely it is to be fixed 

  • Smaller populations have greater chance of being fixed

Effective Population Size

  • Loses heterozygosity at the same time as the actual population