APES - Unit 3: Populations

specialists

• have smaller range of tolerance (narrower ecological niche)

• specific food requirements

• less adaptable to new conditions

• ex. panda (only eats bamboo)

generalists

• have larger range of tolerance (broader ecological niche)

• broad food requirements

• high adaptability

• ex. rats, raccoons

K-selected vs. R-selected species: lifespan, time to reproductive maturity, # of reproductive events, # of offspring, size of offspring, parental care, population growth rate, population regulation, & population dynamics

“quality” vs. “quantity”

• lifespan: long vs. short

• time to reproductive maturity: long (so low biotic potential) vs. short (so high biotic potential)

• # of reproductive events: more vs. few or one

• # of offspring: few vs. many

• size of offspring: large vs. small

• parental care: present vs. absent

• population growth rate: slow vs. fast

• population regulation: density dependent vs. density independent

• population dynamics: stable, near carrying capacity vs. highly variable

Do most species fit cleanly into K-selected or r-selected? Explain.

No; it’s a spectrum

survivorship curve

line that shows survival rate of cohort (group of same-aged individuals) in population from birth to death

• See 3.3 notes for survivorship graph w/ different Types!

  • X-axis: age

  • Y-axis: % surviving

Type I

mostly K-selected (ex. most mammals)

• high survivorship in early life b/c high parental care

• high survivorship in mid-life b/c large size & defensive behavior

• rapid decrease in survivorship in late life b/c old age sets in

Type II

between K and r (ex. prey animals)

• steadily decreasing survivorship

Type III

mostly r-selected (ex. insects, fish, plants)

• low survivorship in early life b/c little to no parental care

• slow, steady decline in survivorship in mid-life (few make it here)

• slow decline in survivorship in old age (even fewer make it here)

growth rate

r; percent increase in population, usually per year - tells if population is getting smaller, larger, or staying the same; always written as percent

• positive: growing

• negative: shrinking

• ex. growth rate of 5% for a population of 100 means it will grow to 105

How to read a growth rate (ex. 2% growth rate)

2 are added per every 100 individuals

What changes the population size?

births and immigration increase the population size, deaths and emigration decrease it

equation for population size

population size = OG + (immigrations + births) - (emigrations + deaths)

exponential population growth

• as the population gets larger, it grows quicker - graph is shaped like a J

• when population has all resources (food, water, space, shelter) it needs, protection from predators/disease, & waste products removed

• ex. invasive species b/c no natural predators

biotic potential

max possible growth rate - happens if no limiting resources

Realistically, do populations consistently grow exponentially? Explain.

no - b/c not realistic to continue to have no limiting factors

three phases of exponential population growth

1. exponential growth

2. growth slows

3. growth stops/stabilizes - when population reaches carrying capacity

logistic population growth

shows the 3 phases of exponential growth - graph is shaped like an S

• see 3.4/3.5 notes for graph

carrying capacity

k; max population size that can be supported by an ecosystem w/o running out of resources

overshoot

when population exceeds carrying capacity; typically causes a die-off, where many individuals die from lack of resources

Do populations always hover around their carrying capacity once they reach it? Explain.

No - severe resource depletion can sometimes happen, causing a population crash (more severe die-off where most individuals die)

• ex. reindeer introduced to St. Paul Island ate all the lichen (takes long time to grow back), so population crashed

limiting factors

factors that control population size; keep most natural populations from growing out of control and determine carrying capacity for a species in specific ecosystem

• 2 categories: density dependent & density independent

density dependent limiting factors

have most effect on dense populations (individuals close together)

• ex. disease, competition, overcrowding, predation/herbivory

density independent limiting factors

affect dense and less dense populations in same way

• ex. natural disasters, bad weather

Why are islands good for studying populatoins?

less immigration/emigration - population changes are based mostly on birth/death rates

How to find the carrying capacity on a logistic growth graph

look for an area where the population is roughly stable for a while

age structure

describes relative numbers of individuals of each age class within a population

• x-axis = number or percent of individuals

• y-axis = age cohorts (5-year increments)

• males on left, females on right

• use to predict how fast country may grow

see 3.6 notes for what each shape means!

How to predict future population growth/decline using an age structure diagram

• populations with many individuals in reproductive age (14-44) or pre-reproductive age (up to 14) will grow rapidly

• populations will many individuals past reproductive age (44+) will grow slowly

Total Fertility Rate (TFR)

average number of children a woman in a population bears throughout lifetime

What happens with a high TFR?

high birth rate, so typically higher population growth unless high infant mortality too

replacement level fertility

the TFR required to offset the deaths in a population and keep the population size stable

• is typically ~2.1 in developed countries, higher in less-developed countries

infant mortality rate (IMR)

number of child (<1 year old) deaths per 1000 people in a population

Where is IMR higher and why?

in less-developed countries due to lack of access to healthcare, clean water, & enough food

How do IMR and TFR correlate?

IMR is typically higher with high TFR; so when there’s a shrinking population, there’s a lower IMR b/c ppl prioritize healthcare for mom and baby

Global IMR data

about 48% until ~1800s → has dropped to 4.3% by 2020

What factors affect TFR?

• development/affluence (more developed/wealthy nations have lower TFR)

  • & individual income - lower income = higher TFR

• education & economic opportunity for women (lowers TFR b/c later age of first pregnancy)

• access to family planning education (and also contraception) - lowers TFR

• less need to children to provide income through agricultural labor (lowers TFR)

• government policies - can increase or decrease TFR

How does government policy affect TFR?

plays huge role in fertility by coercive (forceful) or noncoercive (encouraging) policies

• decrease TFR: forced or “voluntary” sterilization (eugenics), China’s one-child policy (caused missing generation of women), microcredits or loans to women to start businesses

• increase TFR: tax credits for having more kids, paid parental leave from work, healthcare access

demography

study of human populations

demographic transition

when growth rate in a country shifts from rapid to slow; has 4 phases (where the factors that affect TFR causes changes):

• Stage 1: Preindustrial

• Stage 2: Industrializing/Developing

• Stage 3: Developed/Industrialized

• Stage 4: Post-Industrialized/Highly Developed

see 3.9 notes for graph and population pyramids for the stages

Stage 1: Preindustrial

high IMR & death rate with high TFR, so little to no growth b/c high CBR & CDR balance out

• virtually no country today is in this stage

Stage 2: Industrializing/Developing

• IMR & CDR decline b/c modernizations bring clean water, healthcare, stable food supply

• TFR still high, one factor being generational lag (need time for education & societal change to spread)

• rapid growth b/c high CBR, declining CDR

Stage 3: Developed/Industrialized

modernized economy & society increases family income, so TFR decreases; growth rate slows as CBR drops closer to CDR

Stage 4: Post-Industrialized/Highly Developed

TFR decreases more b/c families are more wealthy, CBR drops lowers than CDR; so population decline

• very wealthy modernized countries

How did the agricultural revolution affect human population growth?

• population growth was slow before the agricultural revolution

• agriculture allowed faster population growth b/c farming an rea can support 500 times more people than hunting-gathering in the same area can

How did the industrial revolution affect human population growth?

• brought better sanitation, growing urban areas, knowledge of medicine/nutrition, & improved food availability

• so decreased death rate and increased life expectancy but birth rate still high → rapid population growth

crude birth rate (CBR) and crude death rate (CDR) + how to calculate

births and deaths per 1000 people in a population

• CBR = # of births / total population * 1000

• CDR = # of deaths / total population * 1000

What is the global CBR and CDR? What is the global population growth rate? The doubling time?

• CBR = 20, CDR = 8

• r = (20 - 8 ) / 10 = 1.2%

• doubling time = 70 / 1.2 = 58.3 years

How to calculate growth rate

r = (CBR - CDR) / 10

• answer will already have the correct decimal place to add a % sign (b/c CDR and CBR are per 1,000, growth rate is % (per 100), and dividing them by 10 in equation)

• include crude immigration or emigration rates if given (calculate them in same way as CBR and CDR… or, if you have to calculate CBR and CDR anyways, adding immigration/emigration into those equations produces the same result in the end)

Rule of 70

time in years for a population to double is 70 / growth rate

• add answer to initial year if it asks in what year the population will be doubled from the initial year

million

×10⁶

billion

×10⁹

percent change

[(new - old) / old] * 100%