Chapter 9 Flashcards
What are the 4 factors that affect population size?
Birth/Immigration and Emigration/Death
What is the formula for population growth rate with no immigration/emigration?
What do the variables mean?
N(t+1) - N(t) = (b-d)N(t)
b = birthrate
d = deathrate
N(t) = number of individuals in the population at a given time
What is the variable for the growth rate of a population? What does it mean compared to 0?
r = b-d
If r=0, then b=d, so population is constant
If r>0, then b>d, so population is increasing
If r<0, then b<d, so population is decreasing
Define life table
An age-specific account of mortality. Systematic patterns of mortality and survivorship within populations.
Define cohort
A group of individuals in a population born in the same period of time
Define survivorship. What variable is used for this?
The number of individuals surviving to a given age versus the entire original cohort size
lx
Define age-specific mortality. What variable is used for this?
Difference between the number of individuals alive for an age class and the next older age class.
dx
Define age-specific mortality rate. What variable is used for this?
Determined by the number of individuals dying during a given time by dividing the number alive at the beginning of each intervals
qx
Define life expectancy. What variable is used for this?
Average number of years an individual is expected to live from the time of it’s birth
E
What do each of these columns on a life table represent?
x
nx
lx
dx
qx
E
ex
x - age classes in years
nx - number of individuals of the cohort that are alive at age x
lx - survivorship
dx- difference between number of individuals alive for an age class and the next age class
qx - age-specific mortality rate
e - life expectancy
ex - average number of years an individual of a certain age is expected to live into the future
Define Age-specific life expectancy. What variable is used for this?
The average number of years an individual of a certain age is expected to live into the future.
Ex
Define a dynamic life table
The fate of a single cohort from birth to death.
Define dynamic composite life table
Constructed from individuals born over several time periods, not just one.
Define static life tables. What assumptions are made?
Sampling a population to obtain a distribution of age classes during a single period of time.
Assume: Ech age class sampled is in proportion to its numbers in the populations. AND age-specific births and mortality rates are constant over time.
What does a mortality curve represent?
It plots mortality rates against age
What does a survivorship curve plot?
Survivorship against age.
*Plotted on a log10 scale.
Define a Type I survivorship curve
High survival rate throughout life, most mortality occurring at the end.
Define a Type II survivorship curve
Survival rates do not vary much with age
Define a Type III survivorship curve
Mortality rate is very high early in life
Define birthrate
Births per 1000 individuals of a population per unit of time
Define crude birthrate
Number of birth during some time period divided by the estimated population size at the beginning of the time period multiplied by 1000
Define age-specific birthrate
Function of the number of females in the population. This further modifies the birthrate estimate for dimorphic species.
Define fecundity table
Shows fertility adjusted for morality.
Multiplies bx by death rate for each age cohort to find fecundity
What does bx represent?
Number of females born to each female in an age group
Define net productivity rate, its variable, and the variable in its relation to 1
The average number of females produced by a newborn female during her lifetime
R0
R0 = 1 ; population is stable
R0 > 1 ; population is growing
R0 < 1 ; population is declining
A population that is increasing in size has an intrinsic rate of population growth (r) that is
<0
What value do mortality rate curves end on?
1.0
Why are population projection matrices so complicated?
Because some species can move back and forth between life stages
The leading cause of current species extinctions is….
habitat destruction
A dynamic composite life table is different from a dynamic life table in that it uses individuals…
born over several time periods
Why is the b0 = 0 at time period x0 for some species?
Some species do not reproduce during the first time period
A population reaches a stable age distribution when the…
The proportion of individuals in each age group remains the same.
In a population projection matrix, S34 would represent…
the probability an individual in stage class 4 would revert to 3.
