Population dynamics

Question 1

Give the ‘fundamental equation for ecology’. Explain all the terms.

Answer 1

N(t+1) = N(t) + bN(t) - dN(t) + (I - EN(t))

N(t) = no. individuals at time t
bN(t) = no. of births at time t
dN(t) = no. of deaths at time t
I - EN(t) = immigration - emigration (net migration) at time t

Question 2

Define a source population.

Answer 2

One that is increasing, generaly because b>d.

Question 3

Define a sink population.

Answer 3

One that is decreasing, generally d>b.

Question 4

What kind of habitat do source populations have?

Answer 4

High quality.

Question 5

What kind of habitat do sink populations have?

Answer 5

Low quality.

Question 6

Are most populations open or closed?

Answer 6

Open

Question 7

What is a pseudo-sink population?

Answer 7

One that appears to be declining but isn’t, e.g. d>b but I>E.

Question 8

N stands for density. What does this mean?

Answer 8

Number of organisms per unit area, n/A.

Question 9

What is ‘r’?

Answer 9

Population growth rate.

r = b-d

Question 10

If r=0, what does this say about the population?

Answer 10

The population stays the same size.

Question 11

If r<0, what does that say about the population?

Answer 11

The population is shrinking.

Question 12

If r>0, what does that say about the population?

Answer 12

The population is increasing.

Question 13

r + 1 = ?

Answer 13

λ

Question 14

What does λ always imply?

Answer 14

Discrete data.

Question 15

What is discrete data?

Answer 15

Data that falls into distinct categories.

Question 16

There are 2 types of mean. What are they?

Answer 16

1. Arithmetic mean = SUM the values and divide by how many there are
2. Geometric mean = MULTIPLY all their values and divide by how many there are

Question 17

Which mean is always slightly higher than the other?

Answer 17

The arithmetic mean is higher than the geometric mean.

Question 18

What kind of time do difference equations refer to, discrete or continuous?

Answer 18

Discrete time, e.g. 1/2/3 years. Time that does not overlap.

Question 19

Discrete data does not take into account immigration or emigration. True or false?

Answer 19

True.

Question 20

What kind of time do differential equations refer to, discrete or continuous?

Answer 20

Continuous, time with overlapping generations.

Question 21

What factors contribute to positive density dependence?

Answer 21

Those that increase density, i.e. increasing birth rate.

Question 22

What factors contribute to negative density dependence?

Answer 22

Those that decrease density, i.e. increasing death rate.

Question 23

What does the equation dN/dt mean?

Answer 23

Rate of change in a population.

dN = density
dt = time

Question 24

What causes demographic stochasticity in populations?

Answer 24

Chance events.

Question 25

What causes environmental stochasticity in populations?

Answer 25

The weather/climate etc.

Question 26

In populations with environmental stochasticity, does r vary each year?

Answer 26

Yes.

Question 27

In populations with environmental stochasticity, are events random?

Answer 27

Yes.

Question 28

In populations with environmental stochasticity, λ is fixed and will not change over time. True or false?

Answer 28

False - λ changes over time as it varies in relation to abiotic factors like temperature and rainfall.

Question 29

What does dN/dt represent on a graph?

Answer 29

The gradient.

Question 30

What kind of equation is N(t+1) = λN(t), a difference of differential equation?

Answer 30

A difference equation.

Question 31

What kind of equation is dN/dt = rN, a difference of differential equation?

Answer 31

A differential equation.

Question 32

What is the equation for discrete time growth?

Answer 32

Nt+1 = (1 + r)Nt

Question 33

Why is Nt+1 = (1 + r)Nt the same as Nt+1 = λNt?

Answer 33

Because λ is the same as (1 + r).