Transcript Ecological Succession and Population_Growth (2)

SUCCESSION
EQ: How does succession lead to a
climax community?
Succession
• Primary Succession
• Occurs in places where life has never existed before
• There is no soil!
• Pioneer species are the first species to arrive
• Often moss or lichen (Freddy Fungus took a LICHEN to Alice Algae and now
their relationship is on the rocks)
• Clings to the rocks and breaks it down to create soil
• Secondary Succession
• Occurs where life has previously existed but was wiped out for some
reason
• SOIL IS AVAILABLE!
• Both types of succession end in a stable climax
community
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POPULATION
GROWTH
EQ: How do populations impact
the environment? How does the
environment impact populations?
Exponential Growth
• The simplest form of
population growth is
exponential
• Population growth that
expands faster and faster
• 2 becomes 4 becomes 8
becomes 16 becomes 32…
• This does not realistically
occur
Logistical Growth
• Growth in which there
are a series of phases
and ends in a steady
state where the
number of individuals
leaving the population
is equal to the number
of individuals entering
the population
Points of a Logistical Growth Curve
• A : The species is first
introduced to the
environment
• Growth is slow
• B : A period of exponential
growth occurs
• C : Growth slows
• D : population growth
reaches a peak – the
maximum number of
individuals that can survive
in the environment
• E : Steady state
Terms
• Growth occurs when birth rate is higher than death rate
• Steady state is when there is no population growth on
average
• Carrying capacity is the average number of individuals in a
population at steady state
Limits to growth
• There are two types of limits to population growth –
density dependant and density independent.
• Density dependant means that the extent to which a
factor limits population growth is dependant on the
amount of individuals already in the population
• Density independent means that the factor limits
population growth regardless of the number of
individuals already in the population.
• A limiting resource is something that each organism
needs to live and which is in limited supply
• Food is such a resource
Density Dependant Factors
• Competition
• If there is only a limited amount
of resources available to the
individuals they will compete for
them
• Only the strongest individuals in
a large population will get use
of the resources and be able to
have young
• Called intraspecific competition
if it occurs within a species
Density Dependant Factors
• Predation
• The act of one organism eating another
• The organism doing the eating is the predator and the organism being
eaten is the prey
• Causes a decrease in the prey population
• If the predators don’t eat too many individuals than birthrate can replace
those that die keeping the population in steady state
• If the predation is intense the population decreases
• The number of prey and the number of predators are inter
related – if the predators eat all the prey they will begin to
starve to death; if the predators are scarce than the prey can
have a jump in population
Predator – Prey Relationships
• Prey are introduced to the
environment – multiply and
are happy
• Predator population
increases because of
plentiful prey
• Prey population decreases
because of plentiful
predators
• Predators population
decreases because of lack
of prey
• Prey population increases
because predator
population decreased
Good News
• Predators often have a lot of variety in their diet and
therefore the fluctuations between predator and prey
interactions are not usually this dramatic
• Some predators only take a bite out of the prey allowing
it to survive another day
• Most prey items usually have some defense against being
eaten
Density Dependant Factors
• Parasitism
• One organism lives on or in
another organism eventually
causing harm to the host
• Very few marine organisms
are parasite free
• Parasites can be spread
among individuals so the
larger the population the
greater risk for any one
individual to die of a parasite
Density Dependant Factors
• Crowding and Stress
• The more individuals in a population the faster they use up the
limited resources available to them
• Eventually there is not enough resources left to support any
more individuals so the population levels off
• The more crowded a population the more stress comes into
play weakening immune systems and making individuals more
prone to illness
Density Independent Factors
• Climate is the main
density independent
factor that affects
organisms
• El Nino which raises or
lowers the water
temperature can affect
food sources
Geographic Distribution
• Main factor in determining
population size
• Where a population is located
across the Earth