Download number of individuals - Trinity Regional School

POPULATION GROWTH
3 things contribute to population size
1. Number of births
2. Number of deaths
3. Number of individuals that enter or leave
Immigration
Emigration
Populations group of organisms of the
same species living in the same
ecosystem.
As living organisms, the ecosystem must
provide
• Enough energy
• Space for shelter
• Mates for reproduction
When conditions are favorable
the number of offspring produced
increases exponentially.
Growth doubles regularly
within a given period of time.
Exponential growth is time limited.
Does not continue for any length of time.
Is not indicative of natural growth.
So why does it happen:
Problems:
Logistic growth is more realistic. Basically
more offspring are born initially than those
that die. Continues until changes affect
ecosystem and/or population.
Birthrate
Deathrate
Logistical population growth occurs in 5 stages:
• 1. Species is introduced into a community.
Niche is established.
2. exponential growth begins. Why?
Birthrate?
Deathrate?
3. Population continues to grow but at a
slower rate.
4. As niche is further established, growth
continues to slow.
Birthrate?
Deathrate?
5. Steady state. Average growth rate=0
0 means there will be some fluctuation
but not a continual rise as seen in step
2. BR begins to equal DR.
Carrying capacity:
Carrying Capacity
Exponential growth
Remember limiting factors--extinction
overpopulation
food supply
space
mate
Which is less dense?
Which allows for more growth?
Which has less competition?
Which will limit growth?
Density-Dependent Limiting FactorThe rate at which a population can grow
is dependent on the number of individuals
living in that community.
Is observed in large populations rather
than smaller ones.
Will lead to--
Competition: overpopulated species
compete for food, space,
sunlight, water, oxygen,
minerals/nutrients
w/in same species: DDLF
w/different species: compete to
decrease competition –
ecology and evolution
competition
natural selection
Predation: predator / prey relationship
predator # = prey # steady balance
predator # prey # eat more prey
than are born--# of
prey decreases
Prey DR increases faster than BR
This would result in…
a. Lack of food for predator
b. Predator # drops, allows prey to recover
Prohibited species-introduced into ecosystem, not native, grows exponentially
for a long time because there is no
natural predator. Wrecks havoc with
community.
Evolutionary fix:
prey- new defenses
predator-changes in metabolism and
structure
Symbiosis: special relationship between
predator and host.
Mutualism: both benefit
Commensalism: predator benefits/host
not affected
Parasitism: predator benefits/host injured
high density communities allows for:
1. easy travel
2. large number of hosts available
Crowding and stress: each species requires
specific territory.
number of territories available = DDLF
Overcrowding leads toCompetition fighting stress changes
In endocrine and immune systems of
Species affected changes in BR
Density-Independent Limiting Factor:
the number of individuals is not a
limiting factor to the growth of the
population.
Outside factors limit growtha. Disease
b. Weather
c. Climate change
Cause population to grow then fall
DDLF and DILF work together
Some questions to consider—
1. Why would populations change over?
2. Human population grew exponentially
about 500 years ago. Why? 300 years ago?
3. Why do populations in underdeveloped
countries continue to grow exponentially
while the rest of the world is at the steady
state?
Demographics and age structure diagrams:
Demography=scientific study of human
growth and populations.
1. birthrate
2. death rate
3. age structure
Demographic transition=a dramatic
change in birth and death rates.
A
C
B
*
D
As both BR and DR change, population growth
eventually evens out. DT reaches completion when
BR falls to meet DR and population growth stops.
Age Structure: actual numbers of
individuals in a population not the
only factor in population growth.
Age plays a key factor in growth.
When a large % or
a population is young,
exponential growth will
continue.
When a large % of a
population is old, there
is a different concern.
Human population growth
500 years ago…
What part in this growth will economics,
science, medicine, conservation play in
controlling the growth?