Small Populations

Question 1

genetically effective population Ne

Answer 1

the number of breeding individuals in a population that contribute offspring that survive to adulthood
- usually 1/10th of pop census size
- high Ne allows for genetic diversity

Question 2

genetic diversity is driven by:

Answer 2

driven by natural selection (rapid in large), genetic drift (effective in small), migration (rapid way to get genetic variation) and mutation (rate too low to help small pop)

Question 3

population size needed to maintain evolution

Answer 3

s < 1/2Ne

Question 4

inbreeding depression

Answer 4

negative fitness

Question 5

where does inbreeding happen?

Answer 5

in small pops
measured in heterozygosity

Question 6

is inbreeding worse in the wild?

Answer 6

yes

Question 7

mechanisms of inbreeding depression

Answer 7

dominance - expression of harmful mutations
over dominance - loss of beneficial heterozygosity

Question 8

mildly harmful mutations

Answer 8

not removed by natural selection

Question 9

genetic erosion

Answer 9

increased chance of extinction

Question 10

PVA population viability analysis

Answer 10

• measures likelihood of extinction/survival
• helps choose management options
• can incorporate genetic risks

Question 11

4 sources of uncertainty

Answer 11

Demographic stochasticity
Environmental stochasticity
Genetic stochasticity
Natural catastrophes

Question 12

PVA lines

Answer 12

Deterministic (from an equation)
Stochastic runs come from different PVA simulations
Dotted line is the mean of the different runs
Then we can work out if management will be successful!
But there is some chance that small populations might go extinct

Question 13

add a modest level of inbreeding

Answer 13

Three lethal equivalents of inbreeding depression - they have different effects but none look great - trend to extinction at different rates
PVAs must include inbreeding depression for this reason
Inbreeding depression increases more homozygote recessive genes that might be harmful - bad in small populations where genetic drift removes some genetic variation

Question 14

lethal equivalents

Answer 14

a unit that measure inbreeding depression

Question 15

Percent of inbreeding depression due to recessive lethal alleles:

Answer 15

Homozygotes die
LE can also be made of sub-lethals that reduce fitness but can add up with other sub-lethal to be lethal

Question 16

three ways

Answer 16

one lethal, 3 quite bad sub-lethals or many minor sublethal have the same outcome of death
Worse in small populations because they accumulate so that many offspring are affected
Recessive lethal is purged by natural selection but sublethal are not as easily purged