Lecture 9: Populations: Population growth & regulation

Question 1

per-capita phenomenon

Answer 1

Population growth via births and deaths

Question 2

Total population growth

Answer 2

the individual reproductive rate multiplied
by the population size

Question 3

the bigger the population size, what gets greater?

Answer 3

the numerical growth

Question 4

what is an appropriate and convenient way to view growth?

Answer 4

in discrete time steps (generations, years)

Question 5

when counting a population when should they be taken and why?

Answer 5

it needs to be taken at the same time each time step, to be sure that the same birth and death cycles are included

Question 6

Geometric growth

Answer 6

• Growth via discrete time steps
• Population size is a function of starting population size, per capita growth factor, and number of time steps
• lines on the graph do not represent anything, data is only present on the dots

Question 7

geometric growth formula

Answer 7

Nt = (N0)(λ^t)

Question 8

explain the variables in the geometric growth formula

Answer 8

• N = Number of individuals
• λ (lambda) = Geometric growth factor
• t = Number of discrete time steps.

Question 9

what is the geometric growth factor (λ)

Answer 9

• it is a multiplier
• ratio of population size/population size the previous year

Question 10

what happens to organisms with a continuous growth?

Answer 10

they reproduce and die at a relatively steady rate at all times

Question 11

what is exponential growth

Answer 11

-Growth (positive or negative) at a continuous rate that is a proportion of the total number of individuals at any given time.
-Population size is a function of starting population size, the growth rate, and the time that has elapsed
- lines on the graph represent the data

Question 12

exponential growth formula

Answer 12

Nt = (N0)(e^rt)

Question 13

explain the variables for the exponential growth formula

Answer 13

• r = Exponential growth rate.
• e = the exponential constant.
• N = Number of individuals
• t = Time elapsed.

Question 14

what is e^r in the exponential growth formula replacing and why

Answer 14

• it replaces λ
• to describe that all individuals have a chance of reproducing at any time, not just at a discrete time step

Question 15

geometric growth (λ) - decreasing population size

Answer 15

• 0 < λ < 1
• λ is in between 0 and 1, not inclusive

Question 16

geometric growth (λ) - constant population size

Answer 16

λ = 1

Question 17

geometric growth (λ) - increasing population size

Answer 17

λ > 1

Question 18

exponential growth (r) - decrease in population size

Answer 18

r < 0

Question 19

exponential growth (r) - constant population size

Answer 19

r = 0

Question 20

exponential growth (r) - increase in population size

Answer 20

r > 0

Question 21

if λ<1 or r<0, what does the graph look like?

Answer 21

it will be a negative exponential shaped graph

Question 22

if λ=1 or r=0, what does the graph look like?

Answer 22

it will be a horizontal line

Question 23

if λ>1 or r>0, what does the graph look like?

Answer 23

it will be a positive exponential shaped graph

Question 24

what do we do when birth and death rates vary with age

Answer 24

we have to account for the growth rate/factor or each age class for accurate calculations

Question 25

why is identifying age structures important

Answer 25

populations with the same birth and death rates but different age structures will grow at different rates

Question 26

how is population growth shaped in a population with age structures

Answer 26

it will have different birth and death rates for different age classes

Question 27

rapid and slow maturation in population growth

Answer 27

-Rapid maturation: limits age-class bias -Slow maturation and bias in fecundity: maximizes age-class bias

Question 28

what is a life table

Answer 28

it is used to organize the information for age structured populations and to calculate growth.

Question 29

who does the life table typically track

Answer 29

-it tracks females and number of female offspring per reproductive female -contribution of individual males are hard to track

Question 30

Cohort tracking approach

Answer 30

follows a group of individuals from birth through to death

Question 31

Cohort tracking approach - what it requires

Answer 31

requires that all individuals can to be marked and tracked for their whole life

Question 32

Cohort tracking approach - pros and cons

Answer 32

- pros: provides rich data - cons: no replication for strange years because age is confounded by time

Question 33

Static age structure approach

Answer 33

Quantifies the survival and fecundity of all individuals of all ages in a population at a single time interval

Question 34

Static age structure approach - what it requires

Answer 34

Requires a way to assess survival and fecundity within a single time interval.

Question 35

Static age structure approach - pros and cons

Answer 35

- pros: All age classes face the same environment at the time of census, so age not confounded by time - cons: it is unclear if the data is generalizable across years

Question 36

general patterns of survivorship - type I

Answer 36

High initial survival, followed by age-specific mortality in later age classes (ex: big mammals)

Question 37

general patterns of survivorship - type II

Answer 37

- Constant survival – organisms of all ages face the same likelihood of dying (small mammals) - graph is negative and linear

Question 38

general patterns of survivorship - type III

Answer 38

- High mortality early in life then escape major sources of mortality(ex: plants and invertebrates) - graph is negative and exponential shaped

Question 39

define fecundity

Answer 39

the amount of offspring an organism produces

Question 40

consequences of age structured populations: example of fisheries

Answer 40

- fishing practices selectively target the most important age class of population stability - results in the collapse of many fisheries worldwide

Question 41

how were fishing practices selectively targeting the important age class

Answer 41

- edible fish have reproductive bursts later in life - fisheries get paid more for catching bigger (older) fish - these fisheries ended up catching the oldest class of large, reproductively mature fish that were responsible for the reproductive output of the population

Question 42

what are cultural shifts in humans that slow population growth

Answer 42

- Fewer children: lower fecundity rate reflecting very high childhood survival - Later reproduction: slower generation time reduces per capita growth rate per year, similar to later age of reproductive maturity

Question 43

what factors constitute to human population growth

Answer 43

- Survival at all life stages is greatly improved globally. - Fecundity rates in many parts of the world are unchanged from a historical time when many children died and adult life expectancy was much shorter.