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How organisms interact with
their environment
What is Ecology?
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Ecology: the study of relationships between
organisms and the environment.
Ecologists will study populations, rates of
photosynthesis, nutrient cycles, soil
chemistry, etc., to try to piece together how
ecosystems work.
Ecosystem: includes all the organisms that
live in an area and the physical environment
with which those organisms interact.
Ecologists typically concentrate on one
level of ecology
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Ecology is such a complex field, that it is necessary
for ecologists to narrow their studies to a particular
level. The 4 main levels of ecology are:
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Ecosystem: studies focus on energy flow and nutrient
cycling, and include investigating the living and nonliving
components.
Organismal: studies focus on ways in which an individual
organism meets the challenges of its environment.
Population: studies mainly focus on factors affecting
population size and distribution.
Community: studies focus on the interactions of living
organisms of many species in a particular area.
Energy in Ecosystems
All organisms require energy to live
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Some organisms make (produce) their own
energy
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Producers/autotrophs
 Usually plants that use energy from the sun
to make their own food
 Can also be chemosynthetic bacteria that
use inorganic molecules to make their own
carbohydrates (food)
All organisms require energy continued…
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Many organisms get their energy from other
organisms
 Consumers/Heterotrophs (primary, secondary,
tertiary, etc.)
 Herbivores– get their energy from eating
plants
 Carnivores– get their energy from eating
other animals
 Omnivores– eat plants and animals
 Detritivores– eat only “dead” organisms
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Decomposers– bacteria and fungi that break
down large molecules found in waste into smaller
molecules
Autotroph/Heterotrophs
Energy Flow: The food chain
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All energy in an
ecosystem begins
with the producers
that make their own
food/energy
A food chain shows
that the energy then
flows from the
producers to the
primary consumer
and beyond
Food Chains
Energy Flow: The Food Web
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Food chains in an ecosystem often overlap
as a result of an organism being eaten by
more than one type of consumer
The diagram that shows how energy flows
between all of the organisms in an
ecosystem is known as a food web (a
series of overlapping food chains)
A Food Web
A Food Web
A Food Web
Another way to look at energy flow: the
trophic level pyramid
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Trophic level pyramids also show how
energy flows in an ecosystem
Producers form the base of the pyramid
because they are the base of the food web
Primary consumers are the next level,
followed by secondary consumers, etc.
Energy Pyramid or Trophic Levels
Tertiary Consumer
Secondary
Consumer
Primary
consumer
Producers
Trophic Level Pyramid
Why is the bottom of the pyramid so much bigger
than the top?
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The size of each level represents the amount of
energy that is available at that level
Only about 10% of the available energy makes
its from one level to the next level (not all of an
organism is eaten, some energy is lost as heat
during metabolism, etc.
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Since producers create their own food/energy from the sun
or molecules, they have 100% energy
Using the 10% assumption, the primary producers would
only have 10% of the producers’ original energy
Secondary consumers would have 1%, tertiary consumers
0.10%, etc.
Pyramid shape continued…
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The result is that
many producers are
required at the
bottom of a pyramid
to support only a few
higher-level
consumers at the
very top
This low level of
energy transfer
keeps food chains
fairly short
Energy Flow
Flow of Energy
More Pyramids
Why aren’t detritivores part of the trophic
level pyramid?
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Detritivores rarely pass energy onto the next
level in the pyramid. Rather, they obtain
some of the energy that is “lost” in each
energy transfer by consuming the energy in
the “leftovers” that might not otherwise be
eaten.
Since they don’t pass energy on to higher
levels of the pyramid, they are not shown in
the pyramid
Why do some ecosystems have more extensive food
webs and species richness than others?
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The species richness in an ecosystem is entirely
dependent upon the producers
If conditions (temperature, sunlight, water, etc.)
are good there will be many producers and high
primary productivity (increase in mass of
producers)
More producers = more energy available for
consumers = more consumers=high species
richness
Tropical rainforests and estuaries have high
productivity and species richness, while deserts and
temperate grasslands have much lower values
Important Cycles
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In addition to energy, more than 20 different
substances must be present in an ecosystem
for life processes to occur.
The main elements required for life are
CHON.
Unlike energy, these substances are
constantly recycled within an ecosystem.
Cycle Overview
Carbon Cycle
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Carbon makes up about .03% of the
atmosphere.
The increase in the burning of fossils fuels is
currently adding CO2 to the atmosphere
faster than it is being removed.
This increase has started the debate over
Global Warming, excess CO2 seems to act
like a blanket, preventing heat from escaping
into the atmoshere.
Carbon Cycle
Carbon Cycle
Carbon Cycle
Nitrogen Cycle
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Nitrogen makes up about 79% of the atmosphere.
Plants can not use this nitrogen to make their
proteins. This is a problem.
Bacteria provide the solution.
Nitrogen Fixing bacteria convert the nitrogen from
the air into nitrates that can be used by the plants.
Nitrates are compounds that contain nitrogen and
oxygen.
Animals eat the plants, thus passing the nitrogen
along.
Nitrogen Cycle
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Decomposing organisms: Bacteria cause the
protein (containing nitrogen) in the decaying
animal to combine with hydrogen. This forms
ammonia.
Metabolic wastes are also changed into
ammonia by bacteria.
The process of making ammonia is called
ammonification.
Nitrogen Cycle
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Different bacteria then change the ammonia
to nitrates, which can be absorbed by the
roots of plants.
This process is called nitrification.
It would not be a cycle if nitrogen were not
returned to the air. Guess who does this?
Why yes, bacteria do! The process that
sends nitrogen back to the air is called
denitrification.
Nitrogen Cycle
Water Cycle
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You are already familiar with the water cycle.
Words you should know: precipitation,
transpiration, evaporation, run off.
Water Cycle
Water Cycle
Organisms and their interactions
with their environment
Abiotic and Biotic components influence
populations of species
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Abiotic factors are nonliving factors that
can affect organisms. Examples include
light, temperature, pH, and salinity.
Biotic factors are living factors that can
affect organisms. Examples include
predation, competition, and food
resources.
Abiotic and biotic factors play a role in
defining an organism’s niche.
Habitat vs. Niche
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An organism’s living conditions consist of
both its habitat and its niche. How do they
differ?
 Habitat: the area where an organism
lives
 Niche: the role that an organism plays
in its habitat; its “way of life”
 describes how a species uses the biotic
and abiotic resources for growth,
survival and reproduction
Two Types of Niches
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Fundamental niche: range of conditions
and resources that a species can tolerate
and use
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This can be very large for some species
Realized niche: range of resources and
conditions actually used by a species
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Much smaller than the fundamental niche
Niche continued
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The realized niche helps to explain why so
many species can coexist in the same habitat
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Ex: warbler foraging zones
What happens when two species try to
occupy the same niche?
Two species can occupy the same niche
for a short time, but one species will
eventually out-compete the other
Dealing with change
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The size of an organism’s niche can greatly affect
how threatened an organism is by changes to its
niche
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Generalists can tolerate some change to
their niche because they have a large
range of conditions they can tolerate
and resources they can use
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Ex: humans, possums (live in suburban areas and can
survive on garbage)
Specialists are greatly affected by
change due to having a very small
niche; they may use a very limited
resource
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Ex: koalas (live in trees and eat eucalyptus), pandas
(eat bamboo)
Dealing with change cont.
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Some organisms can acclimate (adjust) to
changed conditions
 Happens in a short period of time
 Adjusting tolerance to abiotic factors
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Ex: humans at high elevations will acclimate to
lower oxygen levels by producing more red blood
cells to carry oxygen
Dealing with change cont.
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Organisms may acclimate to changing conditions in
two ways:
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Conformers will actually change as their
external (outside) conditions change
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Ex: lizard body temperature matches whatever the
external temperature is
Regulators use energy to control some
of their internal conditions even when
external conditions change
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Ex: human body temperature remains relatively stable
even as temperatures range from cold to hot
Dealing with change cont.
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A species may also adapt to changes in
its habitat
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Takes a long time
Involves genetic changes in the whole species
(not one organism) over a many generations
Also known as evolution
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Ex: Finch species in the Galapagos islands have
evolved beak sizes and shapes that are ideal for the
type of food they eat
Populations
Population Dynamics
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What types of things affect the size of a
population?
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Immigration: New members entering a
population from outside the area
Emigration: Members of an existing
population leaving the area
Birth Rate
Death Rate
Survivorship Curves
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Much of a death rate for a population depends on the
particular species. Survivorship curves show the
likelihood that an organism will survive at a
particular age during its typical lifespan.
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Type I: Small chance of dying until late in life
Type II: Equal chance of dying at any point during lifespan
Type III: High chance of dying when young, but lives to old
age if survives early life
A Scary Story
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Visualize a single bacterium. Now visualize
this bacterium reproducing asexually so that
now there are two bacteria. These two
bacteria reproduce to bring the total to four
bacteria. If this reproduction continued for
only a day and a half (36 hrs) the bacteria
would form a layer a foot deep over the entire
Earth! Yikes!
So why aren’t we swimming in bacteria?
There are environmental limits on
population growth
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The bacteria example represents what is called
exponential population growth: where a
population grows rapidly in a short period of
time.
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On a graph, exponential growth is characterized by a Jshaped curve.
Although a species may go through a period of exponential
growth, this type of growth cannot continue indefinitely.
More on environmental limits on
population growth
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Exponential growth requires unlimited
resources, which do not exist in nature.
Therefore, there is a limit to the total
number of individuals that can occupy a
given amount of space called a carrying
capacity.
More on Carrying Capacity
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The carrying capacity differs for each species, as
well as with space and time.
For example, the carrying capacity for bacteria is
much greater than that for humans. Also, available
space and resources are not constant, and as these
change, so will the population’s carrying capacity.
Limiting factors affect carrying capacity and
include: food, shelter, predator levels, water,
nutrients, etc.
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Density-independent factors affect a population the
same way, regardless of its size (ex: fires and floods)
Density-dependent factors begin to affect a population
when it increases in size (ex: food and nesting sites)
The logistic growth model accounts for
limiting factors
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Due to limiting factors, many populations more
closely fit a model of logistic population growth.
This type of growth is characterized by an S-shaped
curve.
The population grows almost exponentially until
carrying capacity is reached, begins to slow, then
stays at this capacity (birth rates = death rates)
Relationships
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Competition: Community interaction for the
same materials
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Intraspecific: competition with same species
Interspecific: competition with other species
Predator/Prey: predator feeds on the prey
Predator/Prey Relationship
Relationships
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Symbiotic Relationships: relationship when
two organisms interact in a way that affects
the survival of one or both members.
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Commensalism: one organism that can benefit
from another organism called a host. The host is
not harmed or helped.
Mutualism: two organisms benefit from each
other.
Parasitism: when an organism obtains its food
from a host and the host is harmed.