Download TOPIC 2: Ecosystems NOTES CASE STUDIES

TOPIC 2: Ecosystems
2.1 Structure
NOTES

Biotic: Living organisms in a system.

Abiotic: The chemical and physical factors in an ecosystem.

Distinguish between biotic
and abiotic (physical)
components of an
ecosystem.

Define the term trophic
level.
Each of several hierarchical levels in an ecosystem, comprising organisms
that share the same function in the food chain and the same nutritional
relationship to the primary sources of energy.

Identify and explain
trophic levels in food
chains and food webs,
selected from the local
environment.
*Trophic level: Position of an organism within a food chain.

Explain the principles of
pyramids of numbers,
pyramids of biomass and
pyramids of productivity,
and construct such
pyramids from given data.
1st trophic level (producers): Produce their own food from simple
inorganic processes (support energy requirements for all other trophic
levels).
2nd trophic level (primary consumer/herbivore): Feed on producers to
obtain energy.
3rd trophic level (secondary consumer/carnivore): Feed on lower level
consumers or producers to obtain energy.
4th trophic level (tertiary consumer/carnivore): Feed on lower level
consumers to obtain energy.
*Pyramids are graphical models of the quantitative differences that exist
between the trophic levels of a single ecosystem.
1.
2.
CASE STUDIES/EXAMPLES
Biotic examples: plants, animals, fungi,
microbes.
Abiotic examples: Temperature, moisture,
salinity, soil type, light, air.
First example:
Producer example: plants which capture the
sun’s energy and convert it to glucose.
Primary consumer example: grasshopper
Secondary consumer example: rat
Tertiary consumer: snake
Second example:
1.
Pyramid of numbers example:
Pyramids of numbers: shows the number of organisms at each
trophic level in a food chain. The length of each bar gives a measure
of the relative numbers.
Advantages: This is a simple easy method of giving an overview and
is good at comparing changes in population numbers with time or
season.
Disadvantages: All organisms are included regardless of their size,
also they do not allow for juveniles or immature forms. Numbers
can be too great to represent accurately.
Pyramids of biomass: Contains the biomass (mass of each
individual × number of individuals) at each trophic level. Biomass is
the quantity of (dry) organic matter in an organism, a population, a
particular trophic level or an ecosystem. The units of a pyramid of
biomass are units of mass per unit area (often grams per square
meter/g m-2 or volume of water (g m-3) or sometimes as energy
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content (joules, J).
2.
Pyramid of biomass example:
Advantages: Overcomes the problems of pyramids of number.
Disadvantages: Only uses samples from populations, so it is
impossible to measure biomass exactly. Also the time of the year
that biomass is measured affects the result.
3. Pyramids of productivity: Contains the flow of energy through
each trophic level. It shows the energy being generated and
available as food to the next trophic level during a fixed period of
time.
Advantages: Show the actual energy transferred and allows for rate
of production. Allows comparison of ecosystems based on relative
energy flows.
Disadvantages: It is very difficult and complex to collect energy data
as the rate of biomass production over time is required.


Discuss how the pyramid
structure affects the
functioning of an
ecosystem.

Because energy is lost through food chains, carnivores are at risk from
disturbance.

Disturbance at the lowest level (producers) directly affects the
existence of species at consumer level and ultimately the top carnivores.
Define the terms species,
population, community,
niche and habitat with
reference to local
examples.
Species: A group of organisms that interbreed and produce fertile offspring.
Population: A group of organisms of the same species living in the same
area at the same time, and which are capable of interbreeding.
Community: A group of populations living and interacting with each other
in a common habitat.
Niche: When species share a habitat and the resources in it. An organism’s
ecological niche depends not only on where it lives but on what it does.
Habitat: The environment in which a species normally lives.
3. Pyramid of productivity example:
Species example:
2
Population example:
Community example:
Niche example:
Habitat example:
Competition: A common demand by 2 or more organisms upon limited
Examples of intraspecific competition: In a
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
Describe and explain
population interactions using
examples of named species.
2.2 Measuring Physical Components of
the System

List the significant abiotic
(physical) factors of an
ecosystem.

Describe and evaluate
methods for measuring at
least three abiotic factors
within an ecosystem.
supply of a resource i.e. food, water, light, space, mates, nesting sites. May be
intraspecific where the competition is between members of the same
species or interspecific where the competition for a resource is between
individuals of different species.
Predation: The interaction of two organisms where the predator (which has
a higher trophic level) feeds on the prey (lower trophic level).
Herbivory: An animal (herbivore) eating a green plant.
Parasitism: The relationship between two species in which one species (the
parasite) lives in or on another (the host), gaining its food from it.
Mutualism: A relation between two or more species in which both or all
benefit and none suffer.
seagull colony on an oceanic outcrop, as the
population grows, so does the pressure for
good nesting sites. (As the population grows
so does the competition between individuals
for the same resources.)
Examples of interspecific competition:
Competition for a resource like water
between amphibians, reptiles and mammals
in an ecosystem.
Examples of predation: Lions eating zebras.
Examples of herbivory: Herbivores include
animals such as elephants, cattle, rabbits,
insects.
Examples of parasitism: Vampire bats or
intestinal worms.
Examples of mutualism: Lichens are an
example of mutualism. It benefits from
obtaining sugars from the photosynthetic
alga. The alga or bacterium benefits from
minerals and water lichens absorb and pass
on to it.
PH, Temperature, Light intensity, Salinity, Turbidity, Dissolved oxygen.

PH - PH meter

Temperature - Thermometer (C degrees)

Dissolved oxygen - Oxygen meter (PPM)

Light intensity - Light meter (LUX)

Salinity - Salinity meter (ppt)

Marine—salinity, dissolved oxygen, wave action
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
Freshwater—turbidity, temperature, dissolved oxygen

Terrestrial—temperature, wind speed, particle size, slope, soil
moisture, drainage, mineral content.
2.3 Measuring Biotic Components of
the System

Construct simple keys and
use published keys for the
identification of
organisms.

Describe and evaluate
methods for estimating
abundance of organisms.
Keys called dichotomous keys are used to identify species, the key is written
so that the identification is done in steps. At each step two options are given
based on different possible characteristics of the organism you are looking
at. You go through all the steps until the name of the species is discovered.
Example of a dichotomous key:
Simpson’s diversity index: This method allows for an estimate of the total
population size of an animal in a study area. This method includes collecting
a sample from the population, then marking them, releasing them back into
the wild and then re-sampling a time later and counting how many marked
individuals you found in the second capture. Also known as capture-markrelease-recapture.
The formula for calculating is as follows:
Where:
D = diversity index
N = total number of organisms of all species found n = number of individuals
of a particular species
n = number of individuals of a particular species

Describe and evaluate
Biomass is a measurement of the mass of living material at a trophic level or
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methods for estimating
the biomass of trophic
levels in a community.
within an ecosystem.

Define the term
biodiversity.
Biodiversity is a measure of the relative abundance of different living
organisms within an ecosystem.

Apply Simpson’s diversity
index and outline its
significance.
A numerical measure of species diversity that is derived from both the
number of species (variety) and their proportional abundance.
2.4 Biomes
Since all organisms are made of roughly the same organic molecules in
similar proportions, a measure of their dry weight is a rough measure of the
energy they contain. Therefore, material brought into the lab must be dried
completely before measuring its mass. Normally, this is accomplished by
placing the material in a warm drying oven and allowing it to dry completely
over a day or two before weighing it.
Biome: A collection of ecosystems sharing similar climatic conditions.

Define the term biome.

Explain the distribution,
structure, and relative
productivity of tropical
rainforests, deserts,
tundra, and any one other
biome.
Examples of biomes: tundra, tropical
rainforest, desert.
Tropical rainforest:
 High productivity
 High precipitation (2500 mm yr¹) throughout the year
 High isolation
 High temperature (26 ℃)
 Good nutrient cycling/ high right of decomposure
 Highest NP
Tundra:
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Low productivity
Low insolation (days are shorter)
Low precipitation (50 mm yr¹)
Low temperature
Poor nutrient cycling (because its locked in the permafrost
therefore it has a low rate of decomposure)
For 1-2 months the productivity is very high because the sun is up
for almost the whole day.
Desert:
 Very low productivity
 Low precipitation (Under 250 mm yr¹)
 High insolation (but all water is evaporated or absorbed by the
ground)

Hot days & Cold nights
 Low nutrient cycle
 Species adapted to survive
Grassland:
 Wide diversity, but low levels of productivity
 Enough precipitation to prevent deserts forming, but not enough to
support forests
 Nutrient cycle is sufficient
 Insolation, precipitation and evaporation rates are balanced
 Grass can grow under the surface even in cold periods, waiting to
emerge until the ground warms.
2.5 Function

Explain the role of
produces, consumers, and
decomposers in the
ecosystem.
Producers: organisms that make their own organic material from simple
inorganic substances. For most of the biosphere the main producers are
photosynthetic plants and algae that synthesis glucose from carbon dioxide
and water.
The glucose produced is used both as an energy source and combines with
other molecules from the soil to build biomass. It is this biomass that
provides the total theoretical energy available to all non photosynthesizing
organisms in the ecosystem.
Consumers: organisms that obtain organic molecules by eating or digesting
Producers example:
Consumers example:
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other organisms. These are the herbivores and carnivores of the ecosystem.
By eating other organisms they gain both food as an energy supply and
nutrient molecules from within the biomass ingested.
Decomposers: the waste managers of any ecosystem. They are the final link
in a food web breaking down dead organic matter from producers and
consumers and ultimately returning energy to the atmosphere in respiration
and inorganic molecules back to the soil during decomposition.
Decomposers example:

Describe photosynthesis
and respiration in terms
of inputs, outputs, and
energy transformations.
1.
Photosynthesis (CO2 + H2O --> C6H12O6 + O2)

Inputs: carbon dioxide and water

Outputs: Glucose and oxygen

Producers transform light energy (from the sun)
into chemical energy
2.

Respiration (C6H12O6 + O2 --> CO2 + H2O + Heat)

Inputs: Glucose and oxygen

Outputs: Carbon dioxide and water

Transformations: chemical energy turns into heat
Describe and explain the
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transfer and
transformation of energy
as it flows through an
ecosystem.

Almost all ecosystems are driven by energy from the sun (solar radiation)
Describe and explain the
transfer and
transformation of
materials as they cycle
within an ecosystem.


Define the terms gross
productivity, net productivity,
primary productivity, and
secondary productivity.




Define the terms and
calculate the values of
both gross primary
productivity (GPP) and
net primary productivity
(NPP) from given data.
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
Gross productivity (GP): The total gain in energy or biomass per
unit area per unit time, which could be through photosynthesis in
primary producers or absorption in consumers.
Net productivity (NP): The gain in energy or biomass per unit area
per unit time remaining after allowing for respiratory losses (R).
Primary productivity: The gain by producers in energy or biomass
per unit area per unit time (can refer to either net or gross
productivity).
Secondary productivity: The biomass gained by heterotrophic
organisms, through feeding and absorption, measured in units of
mass or energy per unit area per unit time.
Gross primary productivity (GPP): The total gain in energy or
biomass per unit area per unit time fixed by photosynthesis in green
plants.
Net primary productivity (NPP): The gain by producers in energy
or biomass per unit area per unit time remaining after allowing for
respiratory losses (R).
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
Define the terms and
calculate the values of
both gross secondary
productivity (GSP) and net
secondary productivity
(NSP) from given data.
2.6 Changes

Explain the concepts of
limiting factors and
carrying capacity in the
context of population
growth.


Gross secondary productivity (GSP): The total gain by consumers
in energy or biomass per unit area per unit time through
absorption.
Net secondary productivity (NSP): The gain by consumers in
energy or biomass per unit area per unit time remaining after
allowing for respiratory losses (R).
Carrying capacity is the maximum number of organisms that an area or
ecosystem can sustainably support. It is dependent on the resource
allocation of an ecosystem and the extent of the competition for those
resources.
Limiting factors are factors that limit the distribution or numbers of a
particular population.
Population limiting factors:
Example: In a seagull colony space for
breeding sites may be the limiting factor that
regulates how large the population can grow
and so the Carrying capacity of that habitat
would be set by the availability of suitable
nest sites.
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
Describe and explain “S”
and “J” population growth
curves.
S curves are associated with exponential growth but above certain size the
growth rate slows down gradually, finally transforming into a population of
constant size. Numbers stabilize at the carrying capacity of the environment.
S curve example:
J curves show a rapid increase and a boom pattern. At first population
grows exponentially and then it suddenly collapses. Collapse is
called dieback. Often in this type of curve population exceeds the carrying
capacity before it collapses. This is called overshoot.
J curve example:
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
Describe the role of
density-dependent and
density-independent
factors, and internal and
external factors, in the
regulation of populations.

Describe the principles
associated with
survivorship curves
including, K- and rstrategists.

Describe the concept and
processes of succession in
a named habitat.

Explain the changes in
energy flow, gross and net
productivity, diversity,
and mineral cycling in
different stages of
succession.
2.7 Measuring Changes in the System

Describe and evaluate
methods for measuring
changes in abiotic and
biotic components of an
ecosystem along an
environmental gradient.
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
Describe and evaluate
methods for measuring
change in the abiotic and
biotic components of an
ecosystem due to a
specific human activity.

Describe and evaluate the
use of environmental
impact assessments
(EPAs).
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