Download Population Dynamics

Population Dynamics
Populations
! Population: a group of organisms of the
same species that are living within a
certain area
–  Species: a group of organisms that are able to
reproduce and produce fertile offspring
! Population Size: the number of organisms
in a given population
–  The human population size of Tolland is about
16,000
Growth of Populations
! No population continues to grow
unchecked
! Population Growth: the increase of a
population with time
–  Under Ideal conditions the size of a population
will increase indefinitely showing a growth
curve like a “J”
! Ideal Conditions: unlimited food, absence of
disease, lack of predators, favorable temperatures,
etc.
J-Curve
Growth of Populations
! Biotic Potential: the highest rate of
reproduction under ideal conditions
! Limiting Factors: circumstances that keep
organisms from reaching their biotic
potential (factors that limit the growth of a
population)
–  Examples: disease, predators, lack of food,
lack of water, lack of space
S-Curve
! Typical population growth curve
Population Growth Rate Curve
! Shows how fast a population grows
Yeast population growth rate
200
180
160
Increase in Cell Number
140
120
100
80
60
40
20
0
1
2
3
4
5
6
Tim e (hours)
7
8
9
10
Carrying Capacity
! Carrying Capacity: The maximum number
of organisms in a certain population that a
given environment is capable of sustaining
under a specific set of conditions
! At carrying capacity, birthrate balances
death rate and the population stabilizes
! Birthrate: the number of organisms born or
produced in a given period of time
! Death Rate: the number of organisms that die in a
given period of time
Population Density
! Population density: the size of a
population that occupies a given area at
any given point in time
! As population density increases, the
growth rate of a typical population will
decrease
–  As you go up the S-curve, the rate of growth
(slope of the line) decreases (levels off)
Limiting Factors
! Density-dependent limiting factors:
influence of any limiting factor that varies
with the population density
–  Examples: food, water, space, predators
! Density-independent limiting factors: not
related to population density
–  Examples: temperature, natural disaster
Predation and Food
! Predation: feeding of one organism on another
! Predation is density-dependent
–  The more prey, the more likely a predator is to catch
one
–  As population density decreases, predators are less
able to catch prey
! Predation is a limiting factor for the prey
population
! Food availability (prey population) is a limiting
factor for the predator population
Regulation of Population Size:
Predator/Prey Graph
Effects of Predation
! Predation maintains population size of the prey
near carrying capacity preventing overpopulation
–  Overpopulation of the prey population could damage
other populations and in turn damage the prey
population
! Predation can act as a form of natural selection
–  Example: Wolves will kill the slowest deer
Interacting Populations
! Symbiosis: long-term interactions between
two species
–  Commensalism
! One organism benefits,
the other is not affected
Remora & Zebra Shark
–  Mutualism
! Both organisms benefit
Clown Fish & Anemone
–  Parasitism
! One organism benefits (parasite), but the other is
harmed (host)
! Parasite examples: fleas, leaches, tapeworms
Parasitism
! Parasitism can be a limiting factor
! Density-dependent
–  Likelihood of transferring parasites within a population
increases as population density increases
Disease
! Density-dependent limiting factor
–  The denser the population, the greater the
chance of a disease spreading
! Sometimes humans use disease-causing
organisms (bacteria) to limit other
populations (i.e., pests)
Oxygen
! In an open system, oxygen is density-
independent
! In a closed system, oxygen is densitydependent
–  trapped in an air-tight space
–  aquatic environments
Interspecific Competition
! Competition among populations of DIFFERENT
SPECIES
! Density-dependent limiting factor
! 3 Possible outcomes:
–  Extinction
! Example: P. aurelia v. P. caudatum
–  Emigration
–  Adaptation
! Example: Finches in the Galapagos Islands
Competition in Paramecium
Competition in Paramecium
Competition in Paramecium
P. bursaria
Competition in Paramecium
Competition in Paramecium
Competitive exclusion
Competition in Paramecium
Resource specialization
Intraspecific Competition
! Competition between members of the same
species
! Density-dependent
! Ways species avoid intraspecific competition:
–  Life cycles & life spans
–  Social Hierarchy/Pecking Order (must be
reestablished if new members join the population)
–  Role separation
–  Behavioral & physiological changes
–  Emigration
–  Territoriality
! Extinction IS NOT an outcome of intraspecific
competition
Human Population – Without
Limits?
! The current human population growth is J-
shaped (ideal conditions)
! Rate of growth is declining slightly
Age Structure Diagrams
(aka Population Pyramids)
! Show the percentage of a population in
each age group
! Shape of the pyramid indicates the growth
rate
POSTREPRODUCTIVE
REPRODUCTIVE
PREREPRODUCTIVE