Chapter 53- AP Biology
 The study of populations in relation to their environment
 Explores how biotic and abiotic factors influence the density, distribution, size and
age structure of populations
 What is a population?
 Density: number of individuals per unit area or volume
 Ex: number of oak trees per square kilometer in the Minnesota country
 Dispersion:
 Random
 Clumped- most common pattern of dispersion (plants, fungi)
 Uniform – often seen with territoriality
 5 moose in a township (24,000 square miles)
 10,000 Oak trees in 25 square miles
 Demography: study of the vital statistics of populations and how they change over
time
 Life Tables (Usually follow certain “cohorts”): death rate, birthrate, etc.
 Survivorship curves
 Reproductive Rates
 Type I: few offspring but
provided with good care; low
infant death rate
 Type II: Intermediate; death
rate remains constant over
time
 Type III: many offspring with
a high infant mortality; fish,
oysters, etc.
 Natural selection favors traits that improve an organism’s chances of survival and
reproductive success.
 “Life history traits are evolutionary outcomes reflected in their development,
physiology, and behavior”
 Semelparity: “beget once,” organism produces once in its lifetime (salmon, agave)
 Iteroparity: “repeted,” reproducing many times in a lifetime (humans, dogs)
 Two critical factors
 Survival rate of the offspring
 Likelihood that the adult will survive to reproduce once again
Population
during a
time interval
Births
=
and
immigrants
simplified: Δ N/ Δ t = B-D
Deaths
-
and
emigrants
 “Average births or deaths per unit of time in average population”
 Example: 34 births per year in a population of 1,000 (or 34/1,000)
annual per capita birth rate  b = .034
50 deaths per year in a population of 1,000
annual per capita death rate  d = .05
 In the equation Δ N/ Δ t = B-D
B = bN and D = dN
(r)
r=b–d
if (r > 0 ), then population is growing
if (r < 0 ), then population is declining
Zero growth population (ZGP) is when r = 0
Δ N/ Δ t = rN
 Under “perfect conditions,” with abundant resources, a population will grow
“without limit”
Δ N/ Δ t = rmaxN
 Result is a “J” curve
 Greater ( r) means faster growth
 Grew exponentially for 60 years when they were first protected from hunting
 In 2006, the United States had a population of about 300
million people. If there were 14 births and 8 deaths per
1,000 people, what was the country’s net population growth
that year (ignoring immigration and emigration)?
 In 2006, the United States had a population of about 300 million
people. If there were 14 births and 8 deaths per 1,000 people, what
was the country’s net population growth that year (ignoring
immigration and emigration)?
b
 8/1000 = .008 = annual per capita death rate  d
 14/1000 = .014 = annual per capita birth rate
 b – d = .006 annual per capita growth rate
 .006 x 300 million = 1,800,000 net growth in 1 year
 Carrying Capacity (k): the maximum population
size that a particular environment can sustain
 Varies over time
 Depends on limiting factors
 Result = change in r
 Logistic growth: per capita rate of increase (r )
approaches zero as carrying capacity (k) is
reached
 “as N increases, r decreases”
 k-selection: density-dependent selection, select
for traits that are sensitive to population density;
(when organisms are near carrying capacity).
 r-selection: density-independent selection, select
traits that maximize reproductive success at LOW
densities
When a farmer abandons his field, it is
quickly colonized by rapidly-growing
weeds. Is this a k-selected or r-selected
species?
 Density-dependent: trait or growth rate that is
affected by population density
 Ex: death rate may rise due to overpopulation
 Density-independent: trait or growth rate that is
NOT affected by population density
 Ex: death rate may rise due to forest fires
 Competition
 Territoriality
 Disease
 Predation
 Toxic wastes
 Intrinsic factors (stress  hormones)
 Complex interactions between biotic and abiotic factors that cause
variation in the size of populations
 ZGP (Stable population)
 High birth rate – high death rate
OR
 Low birth rate – low death rate
 Demographic transition = movement towards low
birth rate and low death rate
 Sanitation
 Better Health Care
 Improved Education access
 Relative number of individuals of each age group in
a population
 Estimated at 7.8 – 10.8 billion
 Ecological footprint: sum of aggregate land and water area required by each
person, city, or nation to produce all the resources it consumes and absorb all the
waste it generates.
 Find the density and dispersion of a given species
 Interpret life tables, survivorship curves, and age structure tables
 Identify and describe “r” strategists and “k” strategists
 Interpret logistic and exponential population growth models
 Identify and describe density-dependent and density-independent factors