Unit 4 Lecture 23

Question 1

Real populations _____

Answer 1

Fluctuate

Question 2

Explain the fluctuation about sheep in Tasmania

Answer 2

• Sheep in Tasmania grows rapidly and exponentially, this carrying capacity then stabilizes
• But there are fluctuations above and below carrying capacity… why?

Question 3

What conditions might populations fluctuate?

Answer 3

1. Populations might overshoot carrying capacity
   - and population growth will turn negative because there aren’t enough resources and end up cycling
2. Environment changes
   - One year there’s enough resources, but next year its not as good (can’t support as many)
3. Random chance births and deaths
4. Competition
5. Predators

Question 4

what happens when populations overshoot carrying capacity?

Answer 4

N>K

Question 5

When N>K the population is _______ and dN/dt is ______

Answer 5

Decreasing
Negative

Question 6

What is Delayed Density Dependence?

Answer 6

(Time lag) can cause populations to overshoot carrying capacity
- Really great grass year leads to lots of reproduction
- By the time the young labs grow up, the field is overgrazed, now death rates go up overshooting carrying capacity

Question 7

What is the equation for delayed density dependence?

Answer 7

𝑑𝑁/𝑑𝑡=𝑟𝑁(1−(𝑁((𝑡−𝜏))/𝐾)

𝜏 stands for time lag

Question 8

How time lag affects population fluctuations depends on what 2 things?

Answer 8

1. How long of a Time lag
2. How fast is intrinsic growth rate

Question 9

What is the experimental demonstration of delayed density dependence with flies

Answer 9

• Number of adult fruit flies v offspring adult fruit flies
• Adult flied were getting unlimited food but not for the laid flies, causing population crash
• f you limit food for both the adult and offspring, population crashes become rarer

Question 10

What are environmental factors the can cause population fluctuation?

Answer 10

• Changes in food abundance
• Changes in water availability
• Changes in temperature

Question 11

What is demographic stochasticity?

Answer 11

Random chance can also cause variation in death and birth rates

Question 12

Fluctuations can cause populations to go ______

Answer 12

Extinct
- Even when populations are growing geometrically or exponentially (i.e. no carrying capacity)
- λ > 1 is a population that is growing
- Effect is stronger in smaller populations

Question 13

What problems do small populations have when it comes to fluctuations

Answer 13

• Population fluctuations get populations close to 0
• Inbreeding reduces fitness of individuals
• Allee effect can further reduce population growth (harder to find a mate)

Question 14

Explain the predation cycle with the lynx and the hare

Answer 14

• Hare population sizes go up, then Lynx populations go up (with a lag) then the hare starts to crash, causing the lynx to crash, then the hare goes up again and so forth
• Hares are ‘K’ for the lynx; as hares go up, the carrying capacity for the lynx goes up so they can make more babies
• But when that goes up the lynx east even more hares, and this reduces the hare population and the carrying capacity, causing the lynx population to go down

Question 15

Explain this 𝑑𝑁/𝑑𝑡=𝑟𝑁−𝑎𝑁𝑃

Answer 15

rN: Exponential growth in absence of a predator

a: capture rate

NP: rate at which predators kill prey

Question 16

Explain this 𝑑𝑃/𝑑𝑡=𝑏𝑎𝑁𝑃−𝑚𝑃

Answer 16

b: rate at which prey is converted to predator babies

aNP: # prey encountered and killed

mP: per capita mortality rate x # individuals