Stochasticity and stage structure

Question 1

Define exponential growth.

Answer 1

Growth that becomes ever-more rapid in response to increasing population size.

Question 2

What size populations does environmental stochasticity affect?

Answer 2

All sizes.

Question 3

What affect does increasing environmental variation have on exponential growth?

Answer 3

Lowers exponential growth rate.

Question 4

Why does environmental variation decrease growth rate?

Answer 4

As individuals adapt to changing conditions the least fit ones will die.

Question 5

Which mean, the arithmetic or geometric, does environmental stochasticity consider?

Answer 5

The geometric mean.

Question 6

What kind of factors does environmental stochasticity affect. Give 3 examples.

Answer 6

1. Fecundity
2. Mortality
3. Competitive ability

Question 7

What size populations does demographic stochasticity affect and why?

Answer 7

Small populations. When there are fewer individuals in a population chance events have a larger effect.

Question 8

Give an example of a chance event that creates demographic stochasticity.

Answer 8

Death before mating.

Question 9

The simplest model of exponential growth makes 3 assumptions about organisms. What are they?

Answer 9

They are the same

1. age
2. sex
3. size

Question 10

The simplest model of exponential growth takes into account disparity between organisms. True or false?

Answer 10

False - it assumes they are all the same.

Question 11

Give a case study of where demographic stochasticity had an affect on a population.

Answer 11

Kakapos in New Zealand - in a small population females were preferentially predated.

Question 12

In the Kakapos case study, sex determination in the offspring correlated to food abundance. Which food ratio produced which gender?

Answer 12

Low food = females

High food = males

Question 13

Define a cohort.

Answer 13

A group with a shared character, e.g. age.

Question 14

Define survivorship.

Answer 14

The proportion of a population surviving to a given age.

Question 15

How do you calculate survivorship?

Answer 15

Proportion of survivors/initial population size

Question 16

There are 3 types of survivorship curve. Explain Type I.

Answer 16

There is a low mortality rate early on That increases with time. These animals have few offpspring that are heavily invested in by the parents so are less likely to die young. Because there are fewer of them if they die when they reach maturity it has a greater effect on the population.

Question 17

Give an example of a group of animals that fit Type I survivorship curves.

Answer 17

Mammals.

Question 18

There are 3 types of survivorship curve. Explain Type II.

Answer 18

The mortality rate is relatively constant throughout an organism’s lifetime.

Question 19

Give examples of animal groups that fit Type II survivorship curves.

Answer 19

Birds or reptiles.

Question 20

There are 3 types of survivorship curve. Explain Type III.

Answer 20

Mortality rate decreases with increasing age. This is because these organisms have huge volumes of offspring so the mortality rate is very high early on.

Question 21

Give examples of animal groups that fit Type III survivorship curves.

Answer 21

Fish.

Question 22

Define the mortality rate.

Answer 22

Proportion of individuals that die in a year.

Question 23

How do you calculate mortality rate?

Answer 23

Number of deaths in a year/number of original individuals

Question 24

How do you calculate survival rate as a factor?

Answer 24

1 - mortality rate.

Question 25

Define the fecundity rate.

Answer 25

The number of offspring a female is expected to have in her lifetime (if she survives).

Question 26

How do you calculate the fecundity rate?

Answer 26

Survival rate x birth rate

Question 27

What is R(0)?

Answer 27

The net reproduction rate

Question 28

Define the net reproduction rate.

Answer 28

The average number of offspring females in a population are expected to have in their lifetime.

Question 29

How do you calculate the net reproduction rate?

Answer 29

The sum of all the fecundity values (in a study of multiple females in a population).

Question 30

If R(0) = 1, what does this mean?

Answer 30

There is no population growth, the female only replaces herself.

Question 31

When R(0) > 1, what does this mean?

Answer 31

There is population growth.

Question 32

When R(0) < 1, what does this mean?

Answer 32

There is population decline.

Question 33

Which other term is R(0) similar to?

Answer 33

λ

Question 34

How do you calculate survival rate as a number?

Answer 34

Total population size x the survivorship value.

Question 35

When R(0) or λ are constant, a single growth model can be applied to the population. Why?

Answer 35

We are only interested in the total number of individuals within the population, not the details of the population.

Question 36

What does the model N(t+1) = λN(t) signify?

Answer 36

The proportion of individuals at each life stage stays constant over time.

Question 37

When a population becomes too large why is N(t+1) = λN(t) no longer an appropriate model?

Answer 37

Other factors come into play, like competition.

Question 38

Why are stage-structured models important in conservation?

Answer 38

They can indicate which cohort needs to be culled to manage a large population.

Question 39

What is a life stage?

Answer 39

A cohort of the same age.

Question 40

Generally the larger the population, the lower the fecundity rate. True or false?

Answer 40

False - fecundity rate increases with population size.

Question 41

Which kind of variation has a greater impact on exponential growth?

Answer 41

Environmental stochasticity.