Download Populations - Westford Academy Ap Bio

ECOLOGY:
the study of how organisms interact with
each other and their environment
Populations
• Population
– A group of
individuals of the
same species that
live in the same area
– N = Size
• Demography
– The study of the
characteristics of
the population (size,
growth, density)
• How & why do the
number of individuals
in a population change
over time?
Dispersion
• The pattern of spacing among individuals
within the boundaries of the population
Due to resources and animal behavior
Consistent resources
Seeds randomly falling
Territory
Competition for resources
Survivorship Curves
Type I:
-High survivorship
-Most approach max. life
span
-Ex: humans
Type II:
-Constant survivorship
(i.e. random death)
-Ex: songbirds, rodents
Type III:
-High death rates early in life
-High survivorship after maturity
-Ex: many plants, organisms with
free-swimming larvae (oysters)
Fecundity
• Ability to reproduce (reproductive rate)
-Grow quickly
-Reach sexual maturity at
young age
-Produce many small eggs or
seeds
-Grow slowly
-Invest energy and time
in traits that improve
survival
-Devote much time and
energy into raising
offspring
2 Strategies: r-selection vs. K-selection
r-selection
Small size of organism
K-selection
Large size of organism
Energy used to make each
individual is low
Many offspring are produced
Early maturity
Energy used to make each
individual is high
Few offspring are produced
Late maturity, often after a
prolonged period of parental
care
Long life expectancy
Individuals can reproduce more
than once in their lifetime
Type I or II survivorship pattern
Short life expectancy
Each individual typically
reproduces only once
Type III survivorship pattern
Population Growth
• r = growth rate = (births – deaths)/N
N = population size
• +, -, or 0
• rmax for each species
– Reproductive
maturity (age)
– Clutch size
– Frequency of
reproduction
– Fitness
Limiting Factors
• Density-independent
factors
– Change birthrates and
death rates irrespective of
population size
– Usually abiotic
• Ex: variation in weather
patterns
– Natural disasters,
extremes of climates, etc.
• Density-dependent
factors
– Change in intensity as a
function of population
size
– Biotic
• Ex: increased predation
when a deer population
increases
– Cause logistic population
growth
– Competition for
resources, parasites and
disease, predation, etc.
Growth Patterns
• Exponential Growth
–
–
–
–
J shaped curve
Density Independent
r>0
Ex: individuals in a new
habitat
• Logistic Growth
– S shaped curve
– Density Dependent
(limiting factors)
– As N increases,
r decreases until r = 0
Carrying Capacity (K)
• The maximum number of individuals in a
population that can be supported in a
particular habitat
• Limiting factors slow/stop growth
– Food, space, water, soil quality, nesting sites,
etc.
• K can change depending on conditions and
varies among species and populations
–Differences in limiting factors
Logistic Growth Equation
• Initial growth is exponential (r is constant)
• As N increases, limiting factors cause r to
decrease until the population reaches K
– Result N=K and r=0
Why Do Some Populations Cycle?
• Some populations exhibit population cycles—
regular fluctuations in size.
• Most likely due to a density-dependent factor.
• Example: Hare (prey) & Lynx (predator)
Predation, disease, or food shortages intensify at high population density (cause crash)
Age Structure and Population Growth in
Human Populations
UNIFORM in developed countries
BOTTOM-HEAVY in developing
countries
Analyzing an age pyramid can give biologists important information about
a population’s history, and also help them predict a population’s future.
Demographic Transition
• From high births & deaths to low births & deaths
• Occurs as a country develops/industrializes
Analyzing Change in Human Population Growth Rate
-Increased over past 250 years
-Sharp growth has consequences for planet
-Ecological footprint
-Overpopulation of humans linked to
-Habitat loss & species extinction
-Declines in living standards
-Political instability
-Shortages of basic resources
-Growth rate has already peaked and is now
declining (since 1970) but still positive
-Zero population growth = fertility at
replacement rate (number of offspring equal
to male & female who produced them)
Animal Behavior
Innate Behaviors
(from GENETICS)
Learned Behaviors
(from EXPERIENCES)
• Reflex behavior
• Classic conditioning
– Involuntary & protective
• Kinesis
– Association of stimuli
• Habituation
– Movement rate
• Taxis
– Response wanes w/o effect
• Insight behavior
– Movement direction
• Stereotyped
– 1st attempt = correct
• Imprinting
– Reproducible
– Fixed action patterns
– Adopt during critical period
• Operant conditioning
– Trial & error learning
Bozeman Animal Behavior