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Transcript of Ecology
the study of interactions between organisms and their environment.
What is Ecology?
Habitats and the Niche
Ecology is the scientific study of the interactions between living things and their environment.
There are several different levels of ecological interaction
In order for
ecosystems to stay balanced
, there has to be a
great deal of biodiversity
within that ecosystem.
where an organism lives
is called its
A habitat includes both biotic and abiotic factors.
A niche is the full range of physical and biological conditions in which an organism lives, and the way in which the organism uses those conditions.
No two species can share the same niche in the same habitat.
different species can occupy niches that are very similar.
because organisms are in
how and why
they interact is key for
understanding our own place in the world.
The combined portions of the planet in which all life exists, including land, water, and air.
All the living (biotic) and nonliving (abiotic) things in one area.
A group of different populations interacting in the same area
A group of individuals that belong to the same species and live in the same area
Biodiversity is the variety of life living in a particular place.
Biodiversity is important
health of an ecosystem
everything is interconnected and relies on each other. Humans rely on biodiversity for food, medicine, clean water and air,
and many other things.
core of every organism's interaction
with the environment is its
need for energy
to power life's processes.
Without a constant stream of energy, living systems cannot function. Sunlight is the main source for life on Earth.
Of all the
, only a
small amount (less than 1%) is used by living things
. But although the amount seems small, it can do so much!
plants, some algae, and certain bacteria can capture energy from sunlight
and use that energy to
. These organisms are called
Autotrophs (from the Greek autos = self, and trophe = nutrition) use energy from the sun to fuel the assembly of simple inorganic compounds into complex organic molecules. These organic molecules are what combine to produce living tissue.
they make their own food, autotrophs
are also called
producers. Producers are able to convert light energy
to chemical energy through photosynthesis.
Producers are essential
to the flow of energy through the biosphere because without them
organisms would have no way of converting the sun's energy.
are the main
autotrophs and producers.
algae and photosynthetic bacteria
fill this role.
heterotrophs (from the Greek heterone = (an)other, and trophe = nutrition), obtain energy from the food they consume.
There are many
different types of consumers. Herbivores obtain energy by eating only plants.
Some herbivores are
cows, giraffes, caterpillars, and deer.
If an organism's habitat is its address, its niche is its occupation.
For instance, part of the description of
an organism's niche includes its place in the food web
range of temperatures
it needs to survive, the
type of food
an organism eats,
how it obtains that food, the physical conditions
the organism requires to survive, as well as
when and how the organism reproduces.
The species are similar, yet each warbler has a different niche within the forest.
...But what happens if a new species with an almost identical niche is introduced to the forest?
For instance, the three species of North American
warbler live in the same spruce tree, but feed at different elevations and in different parts of those trees.
live together in ecological communities, they interact constantly
. These interactions help
shape the ecosystem
in which they live.
Community interactions, such as competition, predation,
and various forms of
Competition occurs when organisms of the same or different species attempt to use an ecological resource in the same place at the same time.
The term "
" refers to
any necessity of life,
water, nutrients, light, food, or space.
in nature often results in a
winner and a loser
, with the losing organism
failing to survive.
Predation is an interaction in which one organism captures and feeds on another organism.
The organism that does the
killing and eating
is called the
food organism is called the prey.
Any relationship in which two species live closely together is called symbiosis.
There are three main types of symbiotic relationships:
mutualism, commensalism, and parasitism.
In mutualism, both species benefit from the relationship.
clown fish live in sea anemones, which protect them from predators.
In return, the clown fish helps with
water circulation and fertilization
of the sea anemone.
In commensalism, one member of the relationship benefits and the other is neither helped nor harmed.
themselves to a
no known service
for the whale (nor do they harm it), yet they
benefit from the movement of the water caused by the swimming whale
because it carries
In parasitism, one organism lives on or inside another organism and harms it.
obtains all or part of its nutrients from the other organism
, called the
parasites weaken but do not kill their host
(which is usually larger than the parasite).
Tapeworms (which live in the intestines of mammals), fleas, and lice are all considered parasites.
How Populations Grow
To better understand
why populations change
as they do, we need to look at population biology.
Three important characteristics of a population are its geographic distribution, density, and growth rate.
Geographic distribution, or range, describes the area inhabited by a population.
can vary in size
few cubic centimeters
occupied by bacteria in a rotting apple, or to the
millions of square kilometers
occupied by migrating whales in the Pacific Ocean.
Population density is the number of individuals per unit area.
This number can
depending on the
species and its ecosystem.
Natural populations may stay the same size from year to year, but they can also grow or shrink rapidly.
factors can affect population
number of births, the number of deaths, and the number of individuals that enter or leave the population.
a population will increase or decrease
depending on how many individuals are added to it or removed from it.
populations grow if more individuals are born than die in any period of time.
A population can also
birthrate is greater than its death rate.
birthrate equals the death rate
more or less
. If the
death rate is greater
than the birthrate, the
Immigration, the movement of individuals into an area,
is another factor that can cause a population to
Emigration, the movement of individuals out of an area,
can cause a population to
If a population has
plenty of space and food
, and is
protected from predators and disease,
then organisms in that population will multiply and
the population size will increase.
Exponential growth occurs when the individuals in a population reproduce at a constant rate.
At first, the number of individuals in an exponentially growing population
the population becomes larger and larger until it
approaches an infinitely large size
Under ideal conditions
with unlimited resources,
a population will grow exponentially
(shown as a
Exponential growth does
in natural populations
for very long
. But what could cause population growth to stop or to slow down?
As resources become less available, the growth
of a population
slows or stops. Logistic growth,
shown by an
, occurs when a population's
growth slows or stops following
a period of
Population growth may slow down when the birthrate or immigration decreases, when the death rate or emigration increases, or when both occur at the same rate.
birthrate and death rate are the same
, or when the rate of
immigration is equal
to the rate of
population growth will slow
down or even stop for a time.
Limits To Growth
to how much an
ecosystem can support
population size of a species that the environment can sustain with the given amount of food, habitat, water (and other necessities) available
in the environment.
If the carrying capacity is
overshot, degradation to the environment will occur
, and the species will not be able to live sustainably, resulting in a
population crash or decline.
If you examine
, you will find that many of them follow a
logistic growth curve.
This is due to the fact that in the natural world there are
many factors that can slow the growth of a population.
Aside from carrying capacity, another thing that can
cause the growth of a population to decrease is known as a limiting factor.
Some examples of
limiting factors are, competition, predation, parasitism, drought, and amount of food or water.
These factors operate
population is large and dense,
not so much when the population is small and scattered.
Density dependent limiting factors include competition, predation, parasitism, and disease.
limiting factor that depends on population size
is known as a
limiting factor. These types of factors
only become limiting when the population density reaches a certain level.
Density independent limiting factors affect all populations in similar ways, regardless of the population size.
density independent limiting factors are
unusual weather, natural disasters, seasonal cycles, and destructive human activities
(like damming rivers and clear cutting forests).
can nearly extinguish populations, extremes of
hot and cold weather
can hurt a population, and
droughts can affect entire food webs.
Environments are always changing
, and most populations can adapt to
certain amount of change with relatively minor increases and decreases in population size.
However, major upsets in an ecosystem can lead to long term declines in certain populations.
Cycles of Matter
Energy is crucial
to an ecosystem, but all organisms need more than energy to survive. They
also need water, minerals, and other life sustaining compounds.
In most organisms,
of the body is made up of just four elements:
oxygen, carbon, hydrogen and nitrogen.
Although these four elements are common on earth,
organisms cannot use them unless the elements are in a chemical form that cells can take up.
Energy and matter move
. Unlike the one-way flow of energy,
matter is recycled within (and between) ecosystems
by being passed from one organism to another.
Matter can cycle
through the biosphere because
biological systems do not use up matter
it. The matter is assembled into
, or passed out of the body as
Simply put, biogeochemcial
cycles pass the same molecules around again and again
within the biosphere.
The Water Cycle
All living things
require water to survive
. But where does all this water come from?
It moves between the ocean, atmosphere, and land. Water
enter the atmosphere as water vapor
(a gas), when they
evaporate from the ocean
or other bodies of water.
The process by which
liquid to gas
can also enter the atmosphere by
evaporating from the leaves of plants in the process of transpiration.
During the day, the
sun heats the atmosphere
. As the
warm, moist air rises, it cools
. Eventually, the water
into tiny droplets that form
droplets become large
in the form of
precipitation (rain, snow, sleet, or hail)
much of the
precipitation runs off
the surface of the ground and
enters a river or stream
that carries the runoff back to an
ocean or lake.
Rain also seeps into the soil
, some of it deeply enough to become
Water in the soil
enters through the roots, and the water cycle begins again.
The Carbon Cycle
plays many roles, and is a
key ingredient of living tissue.
Carbon and oxygen together form
carbon dioxide gas (CO2)
, an important component of the
main types of
move carbon through its cycle:
(such as photosynthesis, respiration, and decomposition)
take up and release carbon and oxygen.
(such as erosion and volcanic activity)
release carbon dioxide to the atmosphere and ocean
Mixed biogeochemical processes
(such as the burial and
decomposition of dead organisms
and their conversion into fossil fuels),
store carbon underground
(such as mining, burning fossil fuels, and cutting and burning forests)
release carbon dioxide into the atmosphere.
carbon cycle, plants absorb carbon dioxide from the atmosphere and use it
(combined with water they get from the soil)
to make the substances they need for growth.
The process of
carbon atoms from carbon dioxide into sugars. Animals,
such as a rabbit,
eat the plants and use the carbon to build their own tissues
such as the fox,
eat the rabbit and then use the carbon for their own needs
. These animals
return carbon dioxide into the air when they breathe and when they die,
since the carbon is returned to the soil during
may then be
used in a new plant or small microorganisms.
Ultimately, the same carbon atom can
move through many organisms
end in the same place where it began
The Nitrogen Cycle
All organisms require nitrogen to make amino acids,
which in turn are used to
Many different forms of nitrogen occur naturally in the biosphere.
nitrogen gas makes up 78%
Nitrogen containing substances
, such as ammonia, nitrate ions and nitrite ions, are found in the
wastes produced by many organisms
dead and decaying organic matter.
Although nitrogen gas is the most abundant form of nitrogen on Earth, only certain types of bacteria can use this form directly.
Such bacteria, which
live in the soil and on the roots of certain plants (called legumes) convert nitrogen gas into ammonia
in a process known as
convert the ammonia into nitrates and nitrites
, which the
producers then use to make proteins. Consumers then eat the producers, and reuse the nitrogen to make their own proteins.
die, decomposers return nitrogen to the soil as ammonia.
may be taken up again by producers, and the nitrites/nitrates are converted to nitrogen gas by bacteria
(a process called
This releases nitrogen into the atmosphere once again, and the cycle repeats.
But what happens to the
in an ecosystem when
one organism eats another?
Energy flows through an ecosystem in one direction; from the sun, to autotrophs (producers), and then to various heterotrophs (consumers)
The relationship between producers and consumers connect organisms into feeding networks based on who eats whom.
energy stored by producers
through an ecosystem along
a food chain, a series of steps in which organisms transfer energy by eating and by being eaten.
However, in most
, feeding relationships are
than can be shown in a
simple food chain
among the various organisms in an ecosystem
form a network of complex interactions
, ecologists describe these relationships as a
A food web links all the food chains in an ecosystem together.
The arrow always goes from the organism that is being eaten to the organism that is eating it
(the arrow is going into the mouth of the consumer).
Each step in a food chain or food web is called a trophic level
Producers make up the first trophic level, and consumers make up the second, third, or higher trophic level.
depends on the trophic level below it
Producers make their own food. Primary consumers (herbivores) eat producers. Secondary consumers (carnivores and omnivores) eat producers, and primary consumers. Tertiary consumers eat all other consumers.
amount of energy or matter
can be represented by an
(also known as an
) is a diagram that shows the
relative amounts of energy or matter contained within each trophic level in a food chain or food web.
part of the energy that is stored in one trophic level is passed on to the next level.
This is because organisms use
much of the energy that they consume
for life processes, such as
respiration, movement, and reproduction
. Some of the
to the atmosphere
10% of the energy
available within one trophic level is
transferred to organisms at the next trophic level.
The more levels that exist between a producer and top-level consumer in an ecosystem, the less energy there is that remains in the original amount.
carnivores obtain their energy through eating other animals.
Some carnivores are
snakes, dogs, and owls.
Omnivores are organisms which get their energy from eating both plants and animals.
Some examples of omnivores are
humans, bears, and crows.
Detritivores feed on plant and other dead matter.
Some examples of detritivores are
earthworms, snails, and crabs.
Detritivores are also known as decomposers, since they break down organic matter. Bacteria and fungi
get their energy from eating other organisms
, they are known as
In this example,
grass is eaten by the rabbit (an herbivore), which is then eaten by a fox (a carnivore)