Chapter 5: Estimating Population Growth Rates

Question 1

exponential (or geometric) growth

Answer 1

• (per capita) rate of change in abundance that is not affected by density
• growth = increase or decrease

Question 2

examples of exponential decline

Answer 2

• Hawaiian monk seal: 3.9% decline per year
• Devil facial disease

Question 3

Malthus dilemma

Answer 3

contrast between exponential growth vs arithmetic growth

Question 4

Malthus dilemma: geometric growth

Answer 4

• population
• increases by a constant factor of 2

Question 5

Malthus dilemma: arithmetic growth

Answer 5

• food
• increases by constant difference of 2

Question 6

λ =

Answer 6

Nt + 1 / Nt

Question 7

when λ = 1

Answer 7

the population is stationary

Question 8

when λ < 1

Answer 8

the population decreases geometrically

Question 9

when λ > 1

Answer 9

the population increases geometrically

Question 10

% change per year =

Answer 10

(λ-1) * 100

Question 11

NT =

Answer 11

No * λT

Question 12

discrete time

Answer 12

change in N over 1 year

Question 13

discrete time equation

Answer 13

Nt + 1 = Nt (λt)

Question 14

continuous time

Answer 14

instantaneous change

Question 15

continuous time equation

Answer 15

dN/dt = rN

Question 16

r =

Answer 16

slope of a line

Question 17

continuous (exponential) growth equation

Answer 17

dN/dt = rN

Question 18

continuous (exponential) growth

Answer 18

• the rate of change in population size at each instant in time
• the instantaneous per capital growth rate

Question 19

per capita growth rate

Answer 19

the average contribution each individual makes to population change

Question 20

how to convert between λ and r

Answer 20

r = ln(λ)
λ = e^r

Question 21

when r = 0

Answer 21

the population is stable

Question 22

when r < 0

Answer 22

the population decreases exponentially

Question 23

when r > 0

Answer 23

the population increases exponentially

Question 24

advantages of λ

Answer 24

translates easily into ‘percent annual growth’ an easily understandable metric

Question 25

disadvantages of λ

Answer 25

cannot average over consecutive values

Question 26

advantages of r

Answer 26

• center around 0
• successive r values can be added or averaged over time
• r values can be divided to convert to different time scales

Question 27

disadvantages of r

Answer 27

a hard to explain logarithm of the proportionate population change per time step

Question 28

when use an exponential growth model for wild populations?

Answer 28

• often used as a null model to then identify deviations
• unaffected by density
• in newly established populations
• populations recovering from catastrophic declines
• invasive, pest outbreaks

Question 29

population growth is often ________

Answer 29

variable (stochasticity)

Question 30

what causes stochasticity in growth rate over time?

Answer 30

• sample variance
• process variance

Question 31

sample variance

Answer 31

• aka observation error
• nature is not varying, but our estimation error makes it seem like it

Question 32

process variance

Answer 32

the one actually affecting changes in abundance & the one we care about

Question 33

internal drivers of process variance

Answer 33

• age structure
• density dependence
• connectivity

Question 34

process variance: changes from interacting species

Answer 34

• predation
• competition
• parasitism
• human harvest

Question 35

process variance: stochastic factors

Answer 35

• environmental stochasticity
• demographic stochasticity

Question 36

demographic stochasticity

Answer 36

due to random deviation from mean birth and death rates

Question 37

where is demographic stochasticity especially important

Answer 37

small population

Question 38

where does demographic stochasticity arise from?

Answer 38

strictly from population size & not from any variability in the environment

Question 39

demographic stochasticity can cause …

Answer 39

declines in small populations

Question 40

environmental stochasticity

Answer 40

• due to extrinsic factors that cause mean vital rates to change randomly over time
• effects less dependent on population size

Question 41

environmental stochasticity examples

Answer 41

• early springs
• summer droughts
• hurricanes
• forest fires