Single-Species Populations II: Population Limitation and The Determinants of Population Size

Question 1

Toy or simulation models are often used by ecologists to

Answer 1

• explore the logical consequences of their assumptions
• ruling out the least parsimonious explanations for their observations.

Question 2

Describe the continuous-time logistic model of population growth

Answer 2

• Dn/dt against t shows a parable

Question 3

Under discrete time logistics…

Answer 3

• absolute growth rate is equal to the per capita growth rate

Question 4

Per capita growth rate

Answer 4

the change in population size in a single-time step

Question 5

What are the advantages of discrete time logistics?

Answer 5

• behaves in the same way as the continuous-time version, but with a smooth approach to equilibrium
• negative density dependence: when per capita population rate is plotted against Nt, it shows a linear decline

Question 6

A life history trait is

Answer 6

any trait that influences demography

Question 7

Demography

Answer 7

aka population dynamics

Question 8

Factors affecting r

Answer 8

1) Typical number of offspring per clutch or brood
2) Number of clutches/broods per year
3) Mortality rate through reproductive life
4) Age at first reproduction
5) Reproductive lifespan

Question 9

What is the consequences of multimodal r?

Answer 9

V hard to estimate

Question 10

K

Answer 10

• a property of the environment
• not independent
• stochastic - a random (not constant) variable

Question 11

Modelling must account for

Answer 11

• population fluctuations found in the wild
• regulation mechanisms causing these

Question 12

What is K dependent upon?

Answer 12

• food availability
• growth rate
• weather

Question 13

When K is a function of environmental resource:

Answer 13

• average population size is equal to the mean K
• annually fluctuates alongside variability in K
  – when environmental resource is high, average population size will be high, and vice versa

Question 14

When K is a function of the weather:

Answer 14

• average population size crashes in response to catastrophic events
• it then recovers
• rapidity of this cycle repeat can also be studied using observational data

Question 15

Describe grey heron populations demography

Answer 15

crash periodically in response to harsh winters that freeze waters and therefore prevent food acquisition, resulting in mass starvation

Question 16

In which years have grey heron populations crashed

Answer 16

• 1930
• 1940
• 1947
• 1963

Question 17

Describe the response of r-selected breeders to population fluctuation

Answer 17

since r-reproducing species such as Arvicolinae voles tend to have:
- a high number offspring per clutch or brood
- a high number of clutches or broods per year
- a low age of first reproduction
- a high reproductive lifespan
- high mortality rate through reproductive life;
they are less able to respond in real-time to population fluctuations.

Question 18

Describe the response of K-selected breeders to population fluctuation

Answer 18

tawny owl (Strix aluco) has:
- low number of offspring per clutch or brood
- low number of clutches or broods per year
- high age of first reproduction
- short reproductive lifespan
- low mortality rate through reproductive life;
can more easily adapt its reproductive lifestyle to these changes.

Question 19

What is one advantage of being a K-breeder?

Answer 19

maintain a consistency of abundance despite population changes

Question 20

in response to weather catastrophes, … species will recover faster than … species

Answer 20

r, K

Question 21

Describe the fast recovery of r-breeders

Answer 21

• high reproductive rates
• recovery time is inversely proportional to r: the higher the r, the faster the recovery from catastrophe, and the less vulnerable the species to environmental perturbation

Question 22

Describe the population demography of the European rabbit (Oryctolagus cuniculus)

Answer 22

• very high r producing species
• littler size of 1-14
• litter frequency of one per month at low density

Question 23

Give the rabbit demography story

Answer 23

• In 1859, 13 rabbits were introduced into Australia for the purposes of recreational hunting
• In 1866, 14,000 rabbit shootings were recorded
• by 1940 there was an estimated 60 million rabbit population in Australia
• several hunting programmes and bounty rewards have not been able to regulate their population

Question 24

Describe the population demography of humpback whales (Megaptera novaeangliae)

Answer 24

• extremely low r
• litter size of 1-2
• litter frequency of every two to three years
• take 5-10 years for first reproduction to occur on sexual maturity
• recovery from hunting is still ongoing

Question 25

Describe the r/K continuum

Answer 25

arises through the selection of the property r

Question 26

r/K continuum aka

Answer 26

fast/slow

Question 27

Describe breeding when catastrophe level is low

Answer 27

• competition for resources is high
• all resources are put into current child to facilitate competition, and cannot be allocated into the production of more children
• favours large body size, late maturation, and few large offspring: low r value

Question 28

Describe breeding when catastrophe level is high

Answer 28

• r-selected species face less competition because hazards are more frequent
• more time is spent in recovery
• high r is therefore selected for, favouring small body size, large and frequent litters or broods and early sexual maturity: r-selected traits

Question 29

Describe r-selected species

Answer 29

tend to be more vulnerable to feedforward loops, where hazards select for higher r, and the resulting r-selected traits increase susceptibility to hazards

Question 30

Give an example of a r-selected species

Answer 30

Cyanistes caeruleus

Question 31

Life history traits are under selection, depending on the frequency of

Answer 31

hazards.