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POPULATIONS
Chapter 20
Lab Biology
Chapter 26
Honors Biology
Anticipatory Set: Count the
number of dolphins in this
picture…
Does this represent a population of
dolphins?
PROPERTIES OF POPULATIONS
Grp. Of organisms of the same species in a
particular place at the same time.
Population Size no. of individuals it contains
(how do we measure it?)
Population Density measures how crowded a
population is (indiv. Per unit of area or volume)
Dispersion spatial distribution of individuals
within the population
Clumped
Even
random
POPULATION DISPERSION
POPULATION DYNAMICS
(CHANGE OVER TIME)
Birth rate – no. of births occurring in a
period of time
Death rate – number of deaths in a period
of time
Life expectancy –how long on average an
individual is expected to live
Continue…
Age Structure the distribution of individuals
among different ages in a population
Patterns of Mortality tends to conform to one of
three curves on a graph called survivorship curves
they show the likelihood of survival at different
ages throughout the lifetime of the organism.
POPULATION GROWTH RATE
Growth rate the amount by which a population’s size
changes in a given time
This depends on 4 processes:
Birth
Death
Emigration
immigration
FORMULAS FOR GROWTH RATE!!
Loss…
Birth rate – death rate = growth rate
(per capita use 1,000)
Gain…
To find the no. of new indiv. That will be added to
the population in a yr. Multiply the per capita
growth rate by the no. of indiv. In the popul.
EXPONENTIAL MODEL
Exponential Model describes a population that
increase rapidly after only a few generations
Exponential Growth the larger the population gets
the faster it grows
PREDICTIONS BASED ON THE
EXPONENTIAL MODEL
View population growth over time
Represented by a J – shaped curve
LIMITATIONS OF THE
EXPONENTIAL MODEL
Exponential growth occurs only under rare
conditions and for short periods of time
Why: resource get depleted and waste
builds up
Limiting factor – a factor that restrains the growth of a
population
LOGISTIC MODEL
A population growth builds on the exponential model but
accounts for the influence of limiting factors
Carrying capacity: the no. of indiv. The environment can
support over a long period of time.
Logistic growth
ENVIRONMENTAL
RESISTANCE
Environmental resistance can be classified into
two broad categories
Density-independent factors
Density-dependent factors
POPULATION REGULATION
2 Kinds of limiting factors control population size:
1. Density-independent factors: limit populations
regardless of their density
Examples: climate, weather, floods, fires, pesticide use,
pollutant release, and overhunting
2. Density-dependent factors: can cause birth rates to
drop and/or death rates to increase
Population growth slows resulting in an S-shaped growth
curve (or S-curve)
DENSITYINDEPENDENT
FACTORS
Some species have evolved means of limiting
their losses
Examples: seasonally migrating to a better climate
or entering a period of dormancy when conditions
deteriorate
DENSITY-DEPENDENT
FACTORS
Density-dependent factors can cause birth
rates to drop and/or death rates to increase
Population growth slows resulting in an S-shaped
growth curve (or S-curve)
DENSITY-DEPENDENT
FACTORS
Carrying capacity is determined by the
continuous availability of resources
DENSITY-DEPENDENT
FACTORS
Include community interactions
Predation
Parasitism
Competition
HISTORY OF HUMAN
POPULATION
GROWTH
1. Development of Agriculture – “agricultural
revolution” stabilized and increase available
food supply
2. Population Explosion –
3. Population Growth today –
- developed countries
- developing countries