Ecology

from Greek
• “oikos” – a place to live
• “logos” - study

1. Define ecology, ecosystem, population, species and habitat.

• Ecology – the study of relationships between living
organisms and between organisms and their environment

• Ecosystem – a community and its abiotic environment

• Community- a group of populations living and interacting
with each other in an area.

• Population – a group of organisms of the same species who
live in the same area at the same time

• Species – a group of organisms which can interbreed and
produce fertile offspring

• Habitat – the environment in which a species normally lives
or the location of a living organism.

Species< population< community< ecosystem

What is Ecology?

Ecology is how living and non-living

things affect each other in their
environment.

Break down dead organic matter and

wastes

What is a Population?

• A population is one species living in

a specific area.

• For example, all foxes living in an

area form a population.

• Another example, all dandelions

growing in an area form another
population.

What is a Community?

• A community is formed from all living

populations found in an area.

• All the foxes, dandelions,

grasshoppers, snakes, hawks, deer,
and skunks living in one area each
form their individual populations, but
together make up a community.

What is a Ecosystem?

•An ecosystem is formed by the

interactions between all living
and non-living things

•How do living and non-living

things interact in an
environment?

Non-living parts of your

community

• Buildings
• Roads
• Bodies of water
• Automobiles
• Traffic lights

How non-living and living

things affect each other

• Building more homes drives many animals

out of their natural habitats or communities.

• Littering can destroy an animals habitat.
• Air pollution from automobiles and factories

will affect the quality of life for all living
things in a community, including people.

Writing Activity

• Write a paragraph about the

effects that living and non-living
things have on each other.
Include three facts from this
presentation and one fact that
you discovered on your own.

Trophic relationships

Producers
• autotrophs
-plants in most ecosystems
-phytoplankton (protists, bacteria)
-chemosynthesis or
photosynthesis
6CO2 + 6H2O → C6H12O6 + 6O2

Consumers

Heterotrophs
-feed on producers or other
consumers
There are several classes:
• herbivores
-plant eaters
-primary consumers
• carnivores
-meat eaters
-secondary (tertiary) consumers
• omnivores
-eat both plants and animals

Decomposers

• saprophytes
-external digestion
-mostly bacteria and fungi
• detrivores
-feed on partially decomposed matter
-e.g. crabs, termites, worms
• scavengers
-e.g. vulture, crows, lobsters

Do you know why there are more herbivores than carnivores?

In a food chain, energy is passed from one link to another.
When a herbivore eats, only a fraction of the energy
(that it gets from the plant food) becomes new body mass;
the rest of the energy is lost as waste or used up by the
herbivore to carry out its life processes (e.g., movement,
digestion, reproduction). Therefore, when the herbivore is eaten
by a carnivore, it passes only a small amount of total energy
(that it has received) to the carnivore. Of the energy transferred
from the herbivore to the carnivore, some energy will be "wasted"
or "used up" by the carnivore. The carnivore then has to eat many
herbivores to get enough energy to grow.

Energy
piramid

The further along the food chain you go, the less food
(and hence energy) remains available.

A change in the size of one population in a food chain will
affect other populations.

This interdependence of the populations within a food chain
helps to maintain the balance of plant and animal populations
within a community. For example, when there are too many
giraffes; there will be insufficient trees and shrubs for all of
them to eat. Many giraffes will starve and die. Fewer giraffes
means more time for the trees and shrubs to grow to maturity
and multiply. Fewer giraffes also means less food is available
for the lions to eat and some lions will starve to death.
When there are fewer lions, the giraffe population will increase.

FOOD CHAIN

The trophic levels within an ecosystem are linked together.
A primary producers may be eaten by a primary consumer, which
in turn may be eaten by e seconary consumer, a so on. This feeding
sequence is called a food chain.

Trophic level 1 2 3

4

primary primary secondary teritary

producer consumer consumer consumer

grass

snail thrush hawk

maize chicken human
eucaltyptus koala

Food chains

As the energy flows from one organism to another a food chain
is established. Food chains may involve more than three
organisms. The secondary consumer may become the prey of
a tertiary (third) consumer, and so on. The last carnivore in the
food chain is called the top carnivore. Food chains, however,
are usually short; the fourth or fifth consumer is normally the
top carnivore.

The transfer of Energy in the Food Chain

When herbivores eat green plants they are taking energy into
their bodies. We can represent the amount of energy taken in
by a herbivore as an energy circle.

The herbivore will use this energy for movement and other
body activities, such as reproduction and movement.
Some parts of the plant which was eaten cannot be digested
by the herbivore; the energy in these parts of the plant passes
out of the herbivore's body as waste. Some of the energy,
however, is used for growth and remains as organic matter in
the herbivore's body. It is this energy which can be eaten by the
secondary consumer.

The circle above represents

the producer

.

All of the stored

energy

in the body of the producer organism is eaten by the

primary consumer

The circle above represents the

primary consumer.

Only the stored energy

is eaten by the secondary consumer.

The circle above represents the

secondary consumer.

Only a very small fraction

(shown in green) of the producer's

original energy is stored by the secondary consumer.
This energy is taken into the body of the tertiary consumer

As you can see from the diagram, only about 10% of the energy
which the plant used for growth is taken into the body of the
carnivore. The second consumer uses some of this energy for
its own body activities and some of the energy will be wasted.
Therefore, the amount of energy available for the tertiary
consumer is only 1% of the energy which the primary
consumer gained from the plant.

As the energy is passed along the food chain much of it is
either used or lost. Therefore there is a limit to the number of
organisms in a food chain. The top carnivore is usually the
third or fourth consumer.

verte

The pyramid below is a way of showing how the numbers of
organisms decrease along the food chain, finishing with the
top carnivore at the apex.
A = plankton, B = shrimp, C = fish, D = seagull

FOOD WEB

Most herbivorous eat more than one type of food, as do most
carnivorous. Thus, in any ecosystem, each population of consumer
will be a member of a number of different food chains/
of feeding interrealtionships called food web.

Wood web

Marine web

organism

Trophic
type

Prey/food

Predators/
grazers

Algae

Primary

producer

-

Krill, fish, blue

whale

Birds

Carnivorous
consumer

Kril, fish

Seals, killer

whales

Blue whales

Planktivorous
consumer

Algae,krill

Killer whales

Fish

Omnivorous
consumer

Algae, krill

Birds, seals,
killer whales

Killer whale

Top consumer

Blue whales,
fish, birds,

seals

-

Krill

Herbivorous
consument

algae

Fish, blue
whales, birds

Seal

carnivorous
consument

Fish, birds

Killer whales

What would happen if you removed one of the organisms from
the food web? Are there other organisms that could take its
place? How would the organism’s predators/grazers respond?
How would the organism’s prey/food respond?
Let’s start at the top and try a few scenarios:

1) What would you hypothesize might happen to the other
organisms in the web, if killer whales went extinct?

2) What might happen if we exhausted the fishery
(through over fishing), and fish were no longer a component of
our food web?

3) What might happen if we removed the algae from the food
web?

4) Which scenario above affected the most organisms?

5) What does this tell you about the importance of the base of
the food web?

Greenhouse effect and global warming

Global warming is the increase in the average temperature
of the Earth's near-surface air and oceans since the
mid-twentieth century, and its projected continuation.
The average global air temperature near the Earth's surface
increased 0.74

±

0.18 °

C

(1.33 ± 0.32 °

F

) during the h

undred years ending in 2005

The consequences of a global temperature rise
on polar ecosystems.

-increased rates of decomposition of detritus
previously trapped in permafrost
-expansion of the range of habitats available to
temperate species
-loss of ice habitat
-changes in distribution of prey species affecting
higher trophic levels
-increased success of pest species

Characteristics of population

1. Population size: number of individuals in the gene pool
2. Population density: number of individuals in a given area
3. Population distribution: pattern of distribution
(uniform, random, clumped)
4. Age structure: pre-reproductive, reproductive,
post-reproductive

Population size

How a population size can be affected?

-

natality=birth rate –the number of birth

-immigration- when individuals join the population from the
neighbouring ones
-mortality rate is a measure of the number of deaths
(in general, or due to a specific cause) in some population,
scaled to the size of that population, per unit time.
Mortality rate is typically expressed in units of deaths per
1000 individuals per year; thus, a mortality rate of 9.5 in
a population of 100,000 would mean 950 deaths per year
in that entire population.
-emigration- when individuals depart from population

Graph showing the population the s -shaped growth curve

lag phase
expotential phase
stationary/plateau phase

Carrying capacity of the environment

refers to the number of individuals who can be supported in
a given area within natural resource limits, and without
degrading the natural social, cultural and economic
environment for present and future generations.

uncontrolled development „overshoot and collapse”

As shown in previous, consumption of natural resources, including
deforestation, is very rapid. In the present in developing
countries it pushes up the carrying capacity very quickly, but
only in the short term.
In the longer term, it will have drastic environmental and
ecological consequences. The population will increase as the
carrying goes up and will continue even after it starts to decrease.
The result will be a deficit between population and the carrying
capacity, which may result in famine or refugees.
Desertification will progress for many long years leading to
extinction of civilization. There is much
evidence for this in human history: consider for example Egypt,
Greece, Mesopotamia, etc.
Such a pattern is called "overshoot and collapse."
The world is presently on this route.

Lincoln index

used to estimate the population size of an animal species and
is based on a capture –mark-relase –recapture method

In theory, mark / recapture techniques involve sampling a
population of animals and then marking all of the individuals
captured in a recognizable way. The marked animals are
then released back into the population and left to mingle for
a suitable period of time. Once they have become thoroughly
mixed into the population again, the population is resampled.

The assumption is then made that the proportion of marked
animals in the second sample is the same as the proportion
of marked animals to non-marked within the whole population.
Enough time must be allowed to elapse for complete mixing
to have occurred.

n1 = number of animals first marked and released.
n2 = number of animals captured in the second sample
m2 = number of marked animals in the second sample
N = Total Population then m2/n2 = n1/N

Since n2, m2 and n1 are all known, N can be worked out.

The results are then put into the following equation to arrive
at a population estimate:

or

N =  n1 x n2 / m2

These techniques have a number of limitations:

•The animal usually needs to be captured to be marked, which may injure
it, or alter its behaviour pattern.

•The mark used may harm the animal - for example a dot of a particular
paint may turn out to be toxic to the animal. Trials therefore need to be
done to ensure that the animal is not harmed in any way.

•Marks may be removed in between release and recapture.

•Marks may make individual animals more, or less attractive to predators
than non-marked individuals.

•The method assumes that all animals in the population are equally
catchable. However, 'catchability' of animals may vary with different life
stages, seasons, times of day etc. It is therefore better to sampling under
as similar conditions as possible and with the same amount of effort.

•Trapping responses of animals may vary. Some may become 'trap-shy'
and avoid the traps after the first capture.

Estimating population size

1. Capture-recapure technigques
The metod is useful for mobile animals

2. Quadrats method
The sampling area is jointed into the quadrats, the individuals
in quadrats are counted and then it is possible to estimate
the total number of the individuals within the area.
e.g. studied area: 1000 m2, 100 quardrats, each 1 m2, the total
of the sampled area: 100 m2. This represents 1/10 of the total.
The total number of individuals of a species in all 100 quadrats
must therefore be multiplied by ten give an estimation of the
whole population of that species in the area.
This method is used plants and sessile or very slow-moving
animals.

• quadrats normally consist of a square frame, 1 m2 is the
most frequently used size

• random sampling is usually carried out . The quadrat frame
is placed on the ground (or on what ever is investigated) and
plants/animals inside are counted, measured or collected,
depending on what the survey is on. This is done many
times in different points within the habitat to give a large
number of different samples.

• in the simplest form of random sampling, the quadrat is
thrown to fall at random within the site

Outline the use of transect to correlate the distribution of plant
or animal species with an abiotic variable.

• this is another way to assess distribution of organisms within a
habitat

• a tape is laid along the ground between two poles
see the course companion

Population spatial distribution

Carbon cycle

The carbon cycle is the biogeochemical cycle by which carbon
is exchanged between the biosphere, geosphere, hydrosphere,
and atmosphere of the Earth.

Carbon can be released back into the atmosphere in many different
ways:

•Through the respiration performed by plants and animals. This is an

exothermic reaction

and it involves the breaking down of glucose (or other organic molecules) into carbon dioxide and water.

•Through the decay of animal and plant matter. Fungi and bacteria
break down the carbon compounds in dead animals and plants and
convert the carbon to carbon dioxide if oxygen is present,
or methane if not.

•Through combustion of organic material which oxidizes the carbon
it contains, producing carbon dioxide (and other things, like water
vapor). Burning fossil fuels such as coal, petroleum products, and
natural gas releases carbon that has been stored in the geosphere for
millions of years. Burning agrofuels also releases carbon dioxide.

•Production of cement. Carbon dioxide is released when
limestone(calcium carbonate) is heated to produce lime (calcium oxide)
,a component of cement.

•At the surface of the oceans where the water becomes warmer,
dissolved carbon dioxide is released back into the atmosphere.

Carbon is taken from the atmosphere in several ways:

•When the sun is shining, plants perform photosynthesis to convert
carbon dioxide into carbohydrates, releasing oxygen in the process.

•The weathering of silicate rock. Carbonic acid reacts with
weathered rock to produce bicarbonate ion swhich are carried to
the ocean, where they are used to make marine carbonates.