Ch. 10 Population Growth & Regulation Flashcards
Life tables contain..
Information about births and deaths that is essential to predict trends or future population size
___ show how survival and reproductive rates vary with age, size, or life cycle stage.
Life tables
Age-specific survival rate (Sx)
Chance that an individual of age x will survive to age x+1
Survivorship (Ix)
Proportion of individuals that survive from birth to age x
Fecundity (Fx)
Average number of offspring produced by a female while she is of age x
Cohort
Individuals born at the same time
- Cohort life table
- follows fate of a group of individuals all born at the same time
- mostly used for non-mobile organisms
- Static life table
- survival and reproduction of individuals of different ages during a single time period are recorded
- requires estimating the age of individuals
- easier for mobile or long-lived organisms
- Survivorship curves
Plot of number of individuals from a hypothetical cohort that will survive to reach certain ages
- Survivorship curve
Type I
Most individuals survive to old age
Ex: most Dall mountain sheep survive to old age
Ex: U.S. Females
- Survivorship curve
Type II
Chance of surviving remains constant throughout life
Ex: song thrushes have about the same chance of survival at any age
- Survivorship curve
Type III
Individuals die at high rates when young, those that reach adulthood survive well
Ex: oysters
Ex: species that produce large numbers of offspring
Ex: out of a million Cleome seeds, only 39 survive to produce 1-year-old plants
Survivorship curves can vary…
- among populations of a species
- between males and females
- among cohorts that experience different environmental conditions
- Age structure
- proportion of population in each age class
- influences whether a population will increase or decrease in size, and how fast the population will grow
- Rapid growth
Younger age groups are larger
Ex: Guatemala, Nigeria, Saudi Arabia
- Zero growth
Relatively similar-sized age groups
Ex: Spain, Austria, Greece
- Negative growth
Older age groups are larger
Ex: Germany, Bulgaria, Italy
Which population can sustain social security longer?
Rapid growth
- more younger people to pay taxes for older people’s social security
To predict population size for following year, two things must be calculated:
- survival
- fecundity
Growth rate (lambda)
Ratio of population size in year t+1 to population size in year t
Lambda > 1, population grows
Lambda < 1, population declines
Lambda = 1, population is stable
Stable age distribution
If age structure does not change from one year to the next
Continuous growth
When individuals leave an average of more than one offspring over substantial periods of time
Geometric growth
- population reproduces in synchrony at regular time intervals, and growth rate remains the same
- population increases by a constant proportion
- visualize geometric growth as a set of discrete points
Translation
The population size at the next period
Predicted to be simply the current population size * the geometric growth rate
Exponential growth
- reproduces continuously -> generations overlap
- continuous, a line
Exponential growth
r =
Exponential population growth rate or intrinsic rate of increase
Exponential growth
Closed population
b-d (instantaneous birth rate - instantaneous death rate)
Exponential growth
Open population
(b + immigration) - (b + emigration)
Doubling time
Number of years it will take the population to double in size
Net reproductive rate
Mean number of offspring produced by an “average” individual during its lifetime
Growth rate may change independently of ___ or as a function of ___.
Density
- Density-independent factors
- factors such as temperature and precipitation, and catastrophes such as floods or hurricanes
- such factors affect density, but the effects are not related to density
- birth & death rates are not affected
Ex: the insect population size fluctuations are correlated with temperature and rainfall
- Density-dependent factors
- cause birth & death rates, and dispersal rates to change as population density changes
Ex: when sending a bunch of horses from US to Germany, the horse population density increased, one horse could have gotten infected with a disease, they disease would spread quickly, and all the horses would have mostly been dead by the time they got to Germany.
Ex: in song sparrows, number of eggs laid per female decreased with density, as did number of young that survived
Density-dependent factors
As densities increase…
- birth rates often decrease
- death rates increase
- dispersal from the population increases
- all tend to decrease population size
Population regulation
Occurs when density-dependent factors cause population to
- increase when density is low
- decrease when density is high
- can maintain population at relatively stable size in stable environment
Density-independent factors can have large effects on population size as well, but they do not regulate population size
Logistic growth
- Population increases rapidly at first
- then stabilizes at carrying capacity (K)
- growth rate decreases as population size nears carrying capacity
Carrying capacity (K)
Maximum population size that can theoretically be supported indefinitely by environment
At carrying capacity, growth rate is ___.
Zero
How does logistic differ from exponential and geometric growth?
- In exponential growth, r is assumed to be constant
- in logistic growth, we assume that r declines as density increases
- initially, logistic growth is similar to exponential growth
- eventually, a population that grows logistically levels off at the carrying capacity
N
Population density
r
Per capita growth rate
K
Carrying capacity
1 - N/K
Discounts growth as N approaches K
Logistic growth
When N is small,
As density increases,
As density approaches K,
- A population with logistic growth increases at a rate close to r
- growth rate decreases
- growth approaches zero
- Logistic growth curve
- slope of curve at any point = rate of population growth at that time
- inclination point has max growth rate -> max sustainable yield
- management goal to maintain population close to K/2
- Ecological footprint
- total area required to support a human population
- humans are different because of our technologies that can alter K (agriculture, medicine, energy utilization)
Ecological footprint approach
Carrying capacity depends on amount of resources used by each person
___ is the environmental impact of a population.
Ecological footprint
