Download Chapter 4 Population Biology

Chapter 5
Population Biology
Describing Populations
• Geographic range – where they are located
• Density – how many organisms in a certain
area
• Distribution – how they are spread out in
the area
-3 patterns
*randomly
*uniform
*clumped
Population Growth
1. General
A. Populations are groups of organisms of the same
species
B. Population growth is the change in the size of a
population with time
C. Scientists have found clear patterns of how and
why populations grow
-4 things change the populations size
*births
*deaths
*immigration
*emigration
2. How fast do populations grow
A. Populations do not grow in a linear fashion
B. Populations grow in an exponential fashion
i. The initial increase in # is slow due to the
small # of organisms able to reproduce, then
the rate increases rapidly as the total # of
organisms potentially reproductive organisms
increases
ii. Exponential growth occurs when the # of
organisms increases by an ever increasing rate,
this results in a population explosion
iii. This results in a J shaped curve, see fig. 5.3
on page 115
3.
Limits of the environment
A. Populations cannot grow indefinitely
B. Population size does have a limit
C. Populations do have limiting factors in their
environment. These limiting factors slow the growth of a
population.
i. Ex. Food availability and space
C. This leveling off of population growth results in an
s-shaped curve (this is called logistic growth)
i. See fig. 5.4 page 118
ii. There is a plateau when the # of organisms the
environment can support is reached
D. The # of organisms of a population that a particular
environment can support over a period of time is known as its
carrying capacity
i. Often represented by the letter K
E. When populations are under the carrying capacity, births
will exceed deaths
F. If the population overshoots the carrying capacity, deaths
will exceed births until populations are once again at carrying
capacity
*Life History Patterns
1. In nature, some populations remain in equilibrium (a state
of rest or balance), some do not
A. This occurs because there are 2 basic growth
patterns, called life history patterns, that populations
can follow
i. Some populations reproduce very rapidly
and produce many offspring (r-selected)
1. Ex. mosquitoes
ii. Some populations have a slow rate of
reproduction with few young (k-selected)
1. Ex. elephants
iii. Which type a specie uses depends mainly on
environmental factors
B. Species in an unpredictable and rapidly changing
environment survive better with a rapid life history pattern
(r-selected species)
i. These organisms usually have similar adaptations
1. Ex. Small body size, mature rapidly,
reproduce early, & have short life span, many young
ii. Ex. Mosquitoes
iii. Populations of these organisms increase and decrease
rapidly as their environment changes
1. The small surviving population will begin
reproducing exponentially when conditions are
favorable again
C. Species that live in a more stable
environment usually have a slow rate life
history pattern
(k-selected)
i. Ex. Elephants
ii. Are usually large in size, long lived,
produce few young and mature slowly
iii. These organisms usually maintain
populations near the carrying capacity
Environmental limits to population growth
a. Limiting factors regulate the size of a population
b. Ecologists have recognized 2 types of limiting factors
i. Density-dependent factors have an increasing
effect on a population as the population increases
in size
1. Ex. Disease, parasites, competition
ii. Density-independent factors affect all
populations regardless of their density
1. Usually abiotic factors
2. Ex. Temperature, storms, drought etc.
• Interactions among organisms that limit population
size
Populations are also controlled by various
interactions among organisms within the
community
-Predation/Herbivory
-Competition
*interspecific
*intraspecific
-Symbiosis
-Disease
-Overcrowding/Stress
Predation (animals killing and eating other animals)
and Herbivory (animals feeding on plants) affects on
population size
A. necessary in a community, it ensures the
continuation of the flow of energy
throughout the ecosystem (animals have to eat)
B. It also may be a limiting factor on a prey
population size
C. Most prey populations are controlled in
some way by predators
D. Populations of predators and prey change over years,
many in a cyclical fashion
-Usually with the populations increasing and
decreasing at the same times
E. Predators help to weed out the sick, old, young and week
i. This leaves the strong and well adapted left to
reproduce
3. The effects of competition
A. Organisms within a population compete for
resources (food, water, shelter, etc)
B. When population is low, resources are abundant
C. As population increases the competition for
resource increases and there may not be enough for
everyone
D. Density-dependent factor
E. When the population becomes to big and the
demand for the resources is greater than the supply of
resources, the population size decreases
F. Interspecific – between different species
G. Intraspecific – within a species
4. The effects of overcrowding and stress
A. When populations become crowded, individuals
may exhibit stress
B. Symptoms of stress from overcrowding include
aggression, decrease in parental care, decreased
fertility, and decreased resistance to disease
C. All of these symptoms can lead to a decrease in
population size (which relieves the overcrowding)
Section 2: Human Population
*World Population
1. General
A. Demography is the study of human population
size, density and distribution, movement and
birth/death rates
2. Human Population Growth
A. humans consciously change their environment,
so human population is different than other
populations
B. humans have reduced or eliminated many of
their limiting factors which have allowed the
human population to grow
i. medical advances
ii. agriculture advances
iii. eliminate competition
3. Calculating growth rate
A. 4 factors affect human population growth
i. birth rate
ii. death rate
iii. immigration - movement into a population
iv. emigration - movement out of a population
B. to calculate population growth rate we must take all of
these factors into account
i. (birth rate + immigration) - (death rate +
emigration ) = population growth
ii. this just tells how many new individual are in a
population
iii. if the PGR is positive it means more individuals
are entering the population than leaving it, if the
PGR is zero it means that individuals are entering
and leaving the population at the same rat, and if
the PGR is negative it means that more individuals
are leaving the population than entering it
4. Demographic Transition – page 144
A. Tracks birth rates and death rates as a country
develops
B. There is a general trend as the country develops
*stage 1 = high birth and death rates
*stage 2 = death rate begins to fall, birth rate
remains high for a while
*stage 3 = birth rate declines until it meets the
death rate
5. Doubling time
A. the time needed for a population to double in size
B. a country with a slow doubling time is considered a
developed country, while a country with a rapid
doubling time is considered a developing country
6. Age Structure
A. refers to the proportions of the population that are
in different age levels
B. shows the proportions of males and females in each
age group and those within child bearing age and
elderly (can help us predict trends in population
growth)
C. if the percentage of people in each age category is
fairly equal the population is considered stable,
rapidly growing populations have higher numbers in
lower age groups (more people in child bearing age)
Chapter 6
Biodiversity
The number of different types of organisms
in an area
-ecosystem diversity – different types
of ecosystems
-species diversity – different types of
organisms
-genetic diversity – different genetics
within a population
Biodiversity is important because…
-the ecosystem has value to humans
*ex. materials that we use,
medicines, food, etc.
-it helps keep the ecosystem stable
*if everything in the ecosystem is
the same, then everything is
susceptible to the same forces
-aesthetic value (beauty)
HIPPO – five ways humans are
decreasing biodiversity in nature
H- habitat destruction
I – invasive species
P – population expansion
P – pollution
O – over-exploitation