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Environmental Science
Chapters 5 & 6
Interactions of the ecosystem
&
Ecosystem Balance
Your Job, Your Niche…
• Each organism is specially adapter to the
habitat in which it lives
• They also have their own, individual, role in
the ecosystem called their niche.
– You can think of a niche as an organism’s JOB.
• Each organism is specialized to do their niche
the best way possible… This is why we say
they are highly specialized
Keystone Predator
• Last Chapter we discussed that a consumer
that actively hunts other organisms to feed on
are called Predator
• The organism being predated upon is called
the Prey
• However, some predators actually promote a
great niche diversity by keeping the balance in
check.
– These predators are called keystone predators
Sea Otter – Keystone Predator
Keystone Predator - Wolves
Divergent Evolution
The Central Theory of Biology
• Evolution is the change in the inherited traits
of a population of organisms through
successive generations
• If these changes no longer allow the
organisms to interbreed, they are considered
a different species
– We call this speciation
• Through evolution, organisms become very
specialized to their habitat over an extremely
long period of time
Natural Selection
• Natural selection is the scientific name for
survival of the fittest
– Also often referred to as “Only the strong survive”
• The strongest organism for survival is said to be
the most fit for survival
• An organism that is “fit” in one ecosystem may
not be fit if the ecosystem changes
• Sometimes mutations occur that create new
traits
– These traits may increase or decrease fitness
depending on the ecosystem
• Over time, this is how evolution occurs…
Convergent Evolution
• Sometimes, organisms that live in similar
ecosystems evolve similar fitness traits. This
has nothing to do with related organisms.
• The (unrelated) organisms “converged” upon
the same fix to the problem
• This is why birds and butterflies both can fly
even though they are not closely related…
Coevolution
• Organisms that interact with each other in an
ecosystem may actually become adapted to the
things the other organism does
– They may even become adapted to the other
organism.
• Each party in a coevolutionary relationship exerts
selective pressures on the other, thereby
affecting each others' evolution.
• This can be between a predator and its prey or
even organisms that help each other survive
Evolution Selects Beneficial Mutations
• A common misconception is that evolution is
progressive
– Progressive evolution would be if an animal
evolved what it “needed to survive”
• Instead, evolution simply selects for a
mutation already available in a population.
– If this mutation increases fitness, the organism
will be more successful in producing young
– If the organisms young also has the mutation, they
too will be more successful
Carrying Capacity
• The carrying capacity of a biological species in an
environment is the population size of the species
that the environment can sustain indefinitely,
given the food, habitat, water and other
necessities available in the environment.
• In population biology, carrying capacity is
defined as the environment's maximal load
• Once a population exceeds their carrying
capacity it is likely to crash (due to a die off) well
below the carrying capacity
• This is usually represented by an S-shaped curve
Exponential Growth
• Sometimes a population will grow as if it has no
carrying capacity and will continuously multiply
• This is called Exponential Growth and it is forms
a J curve on a population graph
• Exponential growth is not sustainable as long as
resources are limited (not infinite)
• Human population growth is currently considered
exponential
• Eventually, all exponential growth will reach its
carrying capacity and become an S-curve
Limiting Factors
• There are two kinds of limiting factors that
assure that all populations will eventually be
an S curve
– Density dependent Limiting Factors are
dependent on the size of the total population
• Available food, space, water, etc
– Density Independent Limiting Factors are factors
that affect the same amount of a population
regardless of its size
• Climate, Natural Disasters, etc
Parasitism
• Parasitism is a type of symbiotic relationship
between organisms of different species where
one organism, the parasite, benefits at the
expense of the host.
• The parasite is often nourished by the host
and may even use the host as part of their
reproductive cycle.
• The parasite doesn’t usually kill the host, but
rather weakens it or damages it
• If the parasite kills the host it is called a
parasitoid
Symbiosis
• Any relationship in which two organisms live
closely together is called symbiosis
– There are several types of symbiosis that depend
on how the organisms interact.
– We already mentioned that parasitism is the
symbiotic relationship in which one organism is
harmed and the other benefits from the harm
– A symbiotic relationship that benefits one
organism but does not effect the other is called
commensalism
– If both organisms benefit from the symbiotic
relationship it is called mutualism
Commensalism
Mutualism
Questions of Relationship
Succession
• Succession refers to more or less predictable
and orderly changes in the composition or
structure of an ecological community.
• These changes are such that they make the
habitat more inhabitable by other species
• Succession can occur because a new habitat is
formed (volcanic island) or because a disaster
destroys the habitat (volcanic eruption)
• It can either be a primary succession which
leaves the habitat without even soil
• Or secondary succession if the soil remains
Primary Succession
• Succession that begins in areas where no soil is
initially present is called primary succession
• The process of life returning to an area of primary
succession is orderly.
– First the rocks will be colonized by lichens which is a
fungus and algal organism that live in a mutuality
relationship.
• Lichens secret acid that break rock down into soil.
• Because these are the first organisms to inhabit
they are called pioneer species
• Once the first soil forms it will become inhabited
by various plants…
Primary Succession Order
• First the Lichens arrive and create a rudimentary soil
• Next hardy weed and grass species arrive. After years
of these grasses and weeds growing they cover the
lichens and the lichens die off
• As the grasses and weeds grow and die they make the
soil level deeper and rich with nutrients
• Once the soil is deep enough small fast growing trees
begin to grow like Jack Pine and Aspen
• As these trees drop needles and leaves the soil level
becomes deeper eventually allowing hardwood trees
like maples and oaks to live
• Once the ecosystem has reached dense hardwood it
stops changing and is said to be a climax community
Secondary Succession
• Secondary Succession occurs where a
disturbance eliminates most of the organisms but
does not destroy the soil
– IE: Forest fire, Hurricane, ETC
• The successive steps are similar to primary
succession but usually lack the lichen stage and
occur quicker
• Fast growing grasses and weed are replaced by
small fast growing trees and eventually the climax
community of slow growing hardwood trees
Aquatic Succession
• Succession can occur in an aquatic system just as
it can on land (usually by natural disaster or
human pollution)
• Aquatic ecosystems are very dependent on the
amount of nutrients available
• A baron lake without plant life will support little
to no life
• As debris falls into the water and is broken down
it makes a thin layer of nutrient poor soil which
can allow for fast growing alga and reeds to grow
• Eventually these reeds are replaced by slower
growing, hardier, aquatic plants which act as food
for other organisms
Island Succession
• When new islands form or old islands are
destroyed by hurricanes succession again takes
place
• An island ecosystem is a unique ecosystem
because most of the organisms are isolated from
the rest of the world (excluding some birds)
• This gives rare opportunities for a few organisms
to take advantage of a large number of niches
• For this reason, island populations are prone to
speciation
Ecosystem Stability
• Stability is the measure of how easily an
ecosystem is affected by a disturbance or
disaster and how quickly it returns to its
original condition
• “original condition” includes all of its biotic
and abiotic factors as well as the energy flow
and nutrient cycles
• Even a regularly disturbed ecosystem can be
relatively stable with the right organisms
• The state of balance an ecosystem returns to
is called equalibrium
The Current GREAT Extinction
• This world has seen 5 great extinctions since live
first arrived on it 3.5 billion years ago.
• Some of these extinctions were so great that that
over 90% of the worlds species died off
• We estimate that only about 1% of all of the
species that have ever existed still exist today
• By most accounts, we are currently the cause of
the 6th and greatest mass extinction
• This is due to human habitat destruction, over
hunting, pollution, disturbance, etc
Biomes
• The ecosystems of Earth can be divided into
several broad categories.
• A major type of ecosystem with distinctive
temperature, rainfall, and organisms is called a
biome
• Biomes can be either terrestrial or aquatic
• Land biomes are usually determined by
climate and rainfall
• Aquatic biomes are usually determined by
water depth, nutrients, and nearness to land