Lecture 13 - Population Parameters and Demographics

Question 1

Define population.

Answer 1

A group of organisms of the same species occupying a particular space at a particular time.

Question 2

Define demes

Answer 2

“demes” which are groups of interbreeding organisms within that much larger population.

Question 3

Who defines boundaries of populations?

Answer 3

Boundaries of populations are established by ecologists. Both in spatial and temporal extent.

Question 4

What’s the difference between unitary and modular individuals?

Answer 4

unitary (ex: humans,fish, deer, mouse: zygote develops into an adult, adult is genetically distinct)’

modular individuals (zygote gives rise to an adult that can make more modules. Ex: plants, corals, etc. Clonal, not genetically distinct)

Question 5

Define population size

Answer 5

measure of # of individuals per unit area.

Question 6

Name 2 factors needed to be considered when deciding on the technique to calculate population density

Answer 6

size and how mobile

Question 7

What size of animals tend to be more abundant?

Answer 7

Small animals tend to be more abundant

Question 8

Name two techniques to calculate absolute size of populations. What kind of organisms are each best suited for?

Answer 8

1. Quadrat: For sessile organisms (don’t move, for plants and many invertebrates)
Sampling area of any shape.
* Replicate
* Randomly positioned
* Accurate count

2. Capture-recapture method (mobile animals)

Question 9

Explain how the capture recapture method works. What assumption do we need to make?

Answer 9

Capture → mark (Marked individuals need to be homogeneously distributed in their environment for this method to work.) → release → recapture

Ratio of marked individuals of recapture is the ratio of marked/unmarked ratio in the population, so can find the total number of individuals in population.

Assumes that there are no individuals immigrating or emigrating → closed population.

Question 10

How do ecologists study chance in size of populations?

Answer 10

To study changes in size , ecologists use demographics techniques (quantitative methods to assess the change in population size due to mortality(survivorship) and natality, immigration and emigration.

Question 11

What’s a life table? Define two types.

Answer 11

Life table : a table that records mortality of a population.
Life tables help to understand population growthi.e. the schedule of birth and dea

2 types:
Cohort table: follows all the individuals born at the same time from birth to death
Static table: is snapshot of a population over a short time interval. The individuals are of different ages.

Data is of females or individuals that produce seeds

Question 12

For a cohort life table, give the following formulas:
1. Proportion surviving at start of age interval x
(lx)
2. # dying within age interval [x to x+1]
(dx)
3. Rate of mortality
(qx)

Answer 12

1. lx=nx/n0
2. dx=nx-nx+1
3. qx=dx/nx

Question 13

Name 3 categories of patterns of survivor-ship. Are these populations hybrid or non hybrid usually?

Answer 13

1. High juvenile survivorship (ex: humans)
2. Constant rates of survival → probability of dying is constant regardless of your age. (ex: birds, rodents)
3. Low juvenile survivorship (Ex: fishes, sea turtles)

• populations are often a hybrid of these 3 types.

Question 14

2 reasons why ecologists construct life tables.

Answer 14

1. Estimate how population will change

2. Useful when information cannot be readily gathered - long lived slow growing populations.

Question 15

Define Capacity for increase.

Answer 15

Survivorship AND Fertility

Question 16

Define Net reproduction rate R0, how it’s measured and 3 defining values.

Answer 16

bx = # female offspring per female aged x per 5-year period
R0 = # daughters produced/female during lifetime = Sum(x=0->inf) lx*bx

R0 = 1 → population is constant because 1 female is only reproducing another female
R0> 1 → growth
R0< 1 → decline

Question 17

1. Define Idealized populations by Lokta.

2. What age group does geometric growth dictate?

Answer 17

1. Population that have a fixed schedule of natality & mortality increase in a geometric way.
   dN/dt=rN → integrated form Nt=N0e^(rt)where r is the intrinsic capacity for increase
2. Geometric growth dictates a fixed and unchanging age distribution, the stable age distribution.

Question 18

1. In the idealized populations formula (Lokta) what does r define?
2. What does it depend on?
3. What are 3 factors that influence r?
4. Name 3 reasons to measure r.

Answer 18

r allows us to calculate instantaneous changes in population size for time scale less than a generation.
r = ln(R0)/G = per capita birth rate - per capita death rate
r=0 no change in population
r>0 population increasing
r<0 population decreasing

2. Depends on the environment. For ex: when too much moisture in the air, beetles produce a lot of offspring
3. Factors influencing r:
   age at first reproduction,
   # of progeny per reproductive event,
   # of reproductive event
4. Reasons to measure r:
   population growth,
   sensitive to environmental change that ecologists may not detect,
   predict population density

Question 19

Why do ecologists construct life tables?

Answer 19

Estimate how population will change –decline (biodiversity loss)–gain (harvest for human use)

Useful when information cannot be readily gathered –long lived slow growing populations (e.g. Sequoia, Elephants

Question 20

how do ecologists construct life tables?

Answer 20

Keep track of FEMALES or, in plants, the individuals that produce seeds

Question 21

Define G, generation time.

Answer 21

Generation time: the mean time period between the production or “birth” of parents and production or “birth” of their offspring.
G = Sum(x=0->inf) xlxbx / R0