POPULATION GROWTH & MEASUREMENT. AP Environmental Science Chapter 6. WHAT IS A POPULATION?. A group of interbreeding individuals within a geographical location. POPULATION SIZE is determined by: #of births (based on fertility rates) # of deaths # of indiv that
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AP Environmental Science
A group of interbreeding individuals within a geographical location.
POPULATION SIZE is determined by:
enter or leave the population
J-curve or Exponential Growth Curve
S-Curve or Logistics Curve
DENSITY: number of individuals per unit area or volume
Ex: Suppose there are
150 bullfrogs living in a
pond that covers an
area 3 square km.
What is the population density?
Population Density =
Number of Individuals (150 frogs)
Unit Area (3 sq KM)
= 50 bullfrogs per square kilometer!
Max population that a habitat can support
These limiting pressures keep a population in check such as carrying capacity:
In a J-curve,
the popul keeps
(exponentially over time).
4. Low % of disease
J-curve is usually a temporary situation=Population crash.
Change in N
Change in time
Rate of reproduction
N=2 cockroaches (male and female)
r= 2 cockroaches can produce 20 offspring in 3 months
a. The rate of growth (r) 20/2 adults or 10 per 1 adult.
b. The growth rate (r) equals 10
Isle Royale, Michigan
quickly in 1991-1995.
Wolf pop due to
Parvovirus passed on from domesticated dogs visiting the National Park.
Due to tick infestation.
1. Population at equilibrium.
dN = change of population over time
N = Population
K= Current Carrying Capacity
r= rate of change or reproductive rate of a speciesd
If the carrying capacity (K) = 100 wolves
If the N = 100 wolves (wolves bred successfully to increase population)
Look at the 1-N/K part: 1 - 100
1- 1 = 0
dN/dt = rN(0)=0!!!
There is no change in dN/dt-no population growth!
What if N=50? Plug it into 1-N/K to see how it affects the reproductive rate for a population.
1-50/100 = 1-1/2 = 1/2rN or half of the maximum reproductive rate for the wolves.
(1- 10) = (1-.10) = .90
dN = rN(.90) or dNis at a rate of
90% as fast as the max possible reproductive rate for the wolves!
Estimating population size by random sampling an ecosystem.
Focus on population density or animal abundance.
Model: n1 = m2 OR N= n1 x n2
N n2 m2
n1=#animal marked & released 1st time
n2=# animals captured during 2nd session
m2-# animals captured during 2nd session & are marked.
Equilibrium: the balance between births and deaths within a population
Factors/pressures that limit a population’s ability to increase (CC)
Different patterns of how a species or
population will inhabit a certain
1. Least Common
2. Found anywhere in envir.
3. High mobility such as wind blown
a. Plantations, orchards, etc.
…Is an organism’s ability to grow at the fastest rate.
(To replenish the species—innate!)
Hint: Rapid Repro
Short life span
Little/no parental care
Large # of offspring produced
Inhabit lower trophic levels (1st order consumers)
Hint: Longer Repro
Long life span
High parental care
Small # of offspring producedREPRODUCTIVE POTENTIAL COMPARISON
Bacterium can produce 19 million descendants in a few days!!
Mosquitoes live 10-14 days laying eggs every 3 days.
Mosquito rafts have 200-300 eggs;. hatch in 48 hours
Some species have higher reproductive potential!!
Human= 9 months
Elephants= 22 months
Oppossum = 12-13 days (marsupial)
Survival & recovery of population depends on a minimum population base—its critical number.
movement of indiv into an area
movement of individuals which leave an area.
Environmental Resistance Factors
If pop falls below critical number, breeding may fail and extinction could occur.
Threatened: species whose pops are declining rapidly
Endangered: near critical number and may become extinct.