C.2 communities and ecosystem

Essential idea: Changes in community structure affect
and are affected by organisms.
C.2 Communities and Ecosystems
Essential idea: Changes in community
Birds-of-Paradise found in Indonesia which is
part of the Coral Triangle, one of the most
stable ecosystems on the Earth

Understandings, Applications and Skills
Statement Guidance
C.2 U.1 Most species occupy different trophic levels in multiple food chains.
C.2 U.2 A food web shows all the possible food chains in a community.
C.2 U.3 The percentage of ingested energy converted to biomass is dependent on the
respiration rate.
C.2 U.4 The type of stable ecosystem that will emerge in an area is predictable based on
climate.
C.2 U.5 In closed ecosystems energy but not matter is exchanged with the surroundings.
C.2 U.6 Disturbance influences the structure and rate of change within ecosystems.
C.2.A1 Conversion ratio in sustainable food production practices.
C.2.A2 Consideration of one example of how humans interfere with nutrient cycling
C.2.S1 Comparison of pyramids of energy from different ecosystems.
C.2.S2 Analysis of a climograph showing the relationship between temperature, rainfall
and the type of ecosystem.
C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between
nutrient stores and flows between taiga, desert and tropical rainforest.
C.2.S4 Analysis of data showing primary succession.
C.2.S5 Investigation into the effect of an environmental disturbance on an ecosystem. Examples of aspects to
investigate in the ecosystem
could be species diversity,
nutrient cycling, water
movement, erosion, leaf area
index, among others.

C.2 U.1 Most species occupy different trophic levels in multiple food
chains.
• A food chain is a linear
network of links in a food
web starting from producer
organisms (such
as grass or trees which use
radiation from the sun to make
their food) and ending at apex
predator species (like a
Loin), detrivores (like earthwor
ms or woodlice),
or decomposer species (such
as fungi or bacteria).
• A food chain also shows how
the organisms are related with
each other by the food they
eat. Each level of a food chain
represents a different trophic
level.

A food web is a diagram that shows how food chains are linked together into more
complex feeding relationships within a community. There can be more than one
producer in a food web, and consumers can occupy multiple positions (trophic levels)
C.2 U.2 A food web shows all the possible food chains in a community.

Energy: is an Open system on Earth

C.2 U.3 The percentage of ingested energy converted to biomass is
dependent on the respiration rate.
ECOSYSTEMS AND ENERGY FLOW
• The concept of energy flow
in ecosystems is a
cornerstone of ecology.
• Energy flow in ecosystems is
based on the assumption
that the laws of
thermodynamics apply to all
observable nature and thus
apply to trophic levels.
Two Laws of Matter and Energy
1. Matter and energy can not
be created or destroyed. The
law of conservation of matter
and energy.
2. When energy is changed
from one form to another
some is always degraded into
heat. Energy transfer is never
100% efficient.

Less then 0.5% of the Suns energy is converted into biomass. Only 5%
to 20% of that assimilated energy passes between trophic levels
Gross production: is the energy converted by plants into biomass
Net production: is the energy available to the heterotrophic component of the ecosystem
minus plant respiration during metabolic activities.
Net Production (NP) = Gross Production (GP) – Respiration (R)
or
NP = GP – R
Units = kJ m-2year-1
Example: Calculate the values of net production using the equation above
• Gross Production = 809 kJ/m2yr
• Respiration = 729 kJ/m2yr
809-729 = 80
• Net Production = 80 kJ/m2yr

I: food ingested by a consumer
A: a portion is assimilated across the
gut wall, convert nutrient to body
biomass (digestion, absorption)
E: remainder is expelled from the
body as waste products (egested
energy). animal excrete small portion
as nitrogen-containing compounds
(as ammonia, urea, uric acid)
(excreted energy)
R: of the energy assimilated, part is
used for respiration (respired energy)
P: remainder goes to production
(new growth and reproduction)
Energy use is a complex process. Not all consumers have the same efficiency
A simple model of energy flow through consumer

Energy decreases in each successive trophic level

C.2 S.1 Comparison of pyramids of energy from different ecosystems.

source of data: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/NetProductivity.html
To understand
why analyze the
energy pyramids
of the different
ecosystems.
Net productivity of different ecosystems varies greatly

1. High primary
productivity (by
producers) means
more energy is
available to the
ecosystem.
3. Higher the primary productivity and greater the
effeciency of energy transfer mean that more energy is
available at high trophic levels. This can support longer the
food chains, hence and more trophic levels increasing net
productivity. Ecosystems rarely have more than 4 or 5
trophic levels.
2. The higher the
efficiency of energy
transfer between
trophic levels the
higher the net
productivity. Energy
transfer is typically
10%.
Reasons for high net productivity of an ecosystem
(4 trophic levels)
(5 trophic levels)

Biogeochemical Cycles: (Are a closed system on Earth)
What is a Biogeochemical Cycle?
– Only so much matter on earth because it is acts as a closed
system.
• Energy enters as sunlight, but no matter usually exits or enters.
• Open system: Energy AND matter are exchanged.
– These cycles act as a way to recycle matter within the
biosphere from one form to another.
C.2 U.5 In closed ecosystems energy but not matter is exchanged with
the surroundings.

Energy Vs. Matter
• Energy is TRANSFERRED
– One-way flow of energy through food-chains and food webs.
• Energy from sun goes to plants, which then goes to consumers.
– Each trophic level loses ~90% of energy as heat.
– Only 10% of energy is used for life processes.
• Matter is TRANSFORMED
– This is why we have biogeochemical cycles.
– Only have a given amount of matter because Earth is a closed
ecosystem.
the surroundings.

Nutrient Cycles
• Carbon - key ingredient in living tissue
– “Carbon-based” life forms
• Nitrogen - required for amino acids used in protein
synthesis
– What are our sources of protein?
– What do we use proteins for?
• Phosphorus - required for DNA and RNA
– Why is this important?
the surroundings.

C.2 A.1 Conversion ratio in sustainable food production practices.
In commercial (animal) food production, farmers measure the food conversion ratio
(FCR). It is a measure of an animal's efficiency in converting feed mass into the desired output.
For dairy cows, for example, the output is milk, whereas animals raised for meat, for example,
pigs the output is the mass gained by the animal.
mass of the food eaten (g)
(increase in) desired output (g)
(per specified time period)FCR =
http://en.wikipedia.org/wiki/Feed_conversion_ratio
Animal FCR
Beef Cattle 5 - 20
Pigs 3 - 3.2
Sheep 4 - 6
Poultry 1.4 - 2
Salmon 1.2 - 3
The lower the FCR the more efficient
the method of food production.
It is calculated by:

http://en.wikipedia.org/wiki/Feed_conversion_ratio
A good (low) FCR is obtained by
minimizing the losses of energy by
respiration, for example:
• Restricting animal movement
• Slaughtering the animal at a young
age (older animals have higher FCRs
as they grow more slowly)
• Optimizing feed so it is efficiently
digested
How ethical are the practices that lead to a low FCR?
What is more important, efficient food production or the ethical
treatment of animals?
C.2 A.1 Conversion ratio in sustainable food production practices.
Animal FCR
Beef Cattle 5 - 20
Pigs 3 - 3.2
Sheep 4 - 6
Poultry 1.4 - 2
Salmon 1.2 - 3

C.2 A.2 Consideration of one example of how humans interfere with nutrient cycling.
Humans practices can accelerate the the flow of matter into and out of ecosystems. This
by implication (and often design) alters the nutrient cycling in ecosystems.
Phosphate
mined and
converted to
fertilizer.
Nitrate fertilizer
produced from
atmospheric
Nitrogen
(by the Haber
process)
Agriculture
Harvesting
of crops
Water run-off
(leaching) from
agricultural fields
results in build-
up of
phosphates and
nitrates in
waterways and
leads to
eutrophication.

Some Agents of Disturbance
• Fire
• Floods
• Drought
• Large Herbivores
• Storms
• Volcanoes
• Human Activity
C.2 U.6 Disturbance influences the structure and rate of change within
ecosystems.
Disturbances are events such as floods, fire, droughts, overgrazing,
and human activity that damage communities, remove organisms
from them, and alter resource availability

C.2 S.5 Investigation into the effect of an environmental disturbance on
an ecosystem.

C.2 S.5 Investigation into the effect of an environmental disturbance on
an ecosystem.
Your investigation should compare a site undergoing secondary succession with a primary ecosystem. This
can be extended to look at the various stages of secondary succession if local sites allow.
Ways of measuring the affect of
succession include:
• Species diversity
• Stem/Seedling density
• Biomass
• Canopy coverage / light
intensity at the surface
• Depth/Volume of leaf litter
• Soil nutrient levels
https://khorra.files.wordpress.co
m/2013/02/moving-glacier.jpg

Primary Succession
• Begins in a place without any soil:
Sides of volcanoes
Landslides
Flooding
• First, lichens that do not need soil
to survive grow on rocks
• Next, mosses grow to hold newly
made soil
• Known as PIONEER SPECIES
Ecological Succession
• Natural, gradual changes in the types of species that live in an area
• Can be primary or secondary
• The gradual replacement of one plant community by another over time
ecosystems.

Secondary Succession
• Begins in a place that already has soil and was once the home of
living organisms
• Occurs faster and has different pioneer species than primary
succession
• Example: after forest fires
ecosystems.

Climax Community
• A stable group of plants and animals that is the end result of the
succession process
• Does not always mean big trees
– Grasses in prairies
– Cacti in deserts
ecosystems.

C.2 S.4 Analysis of data showing primary succession.
Changes over time in total plant species
richness over time at select sites on Mount
Saint Helens, WA
http://www.nature.com/scitable/knowledge
/library/succession-a-closer-look-13256638
Use the examples to analyze data showing
primary succession
http://wps.pearsoncustom.com/
wps/media/objects/2128/21794
41/28_03.html

Biome is a geographical area that has a particular climate and sustains a specific
community of plants and animals (i.e. a type of ecosystem)
Biosphere is the total of
all areas where living things
are found (i.e. the totality of
biomes)
• The main factors affecting the distribution of biomes is temperature and rainfall
• These factors will vary according to latitude and longitude, elevation and proximity to the sea
• Temperature is influential because it affects the rate of metabolism – the phases in the life cycles
of many organisms are temperature dependent
• In the same way, the availability of fresh water (both in the soil and in rivers and lakes) is critical to
the growth and nutrition of organisms
• Rainfall and warmer temperatures are more common near the equator and less common at the
poles
http://ib.bioninja.com.au/options/option-g-ecology-and-conser/g2-ecosystems-and-biomes.html
C.2 S.2 Analysis of a climograph showing the relationship between
temperature, rainfall and the type of ecosystem.

The six major types of biome/ecosystem are outlined in the table below
Biome Temperature Rainfall Vegetation
Desert Hot (>30oC)in the day
Cold (<0oC) at night
Low Precipitation
Less than 30cm per year
Xerophytes
Adapted to water
conservation
Grassland Warm (20oC-30oC) Seasonal Droughts
Medium amount of rain
Grass with widely spaced
trees
Fires prevent trees from
invading
Shrub land Moderate (20oC-30oC) Rainy winters, dry
summers
Dry, woody shrubs
Regrow quickly
Coniferous Forrest
(Taiga)
Cold (0oC-15oC) Low Precipitation
Wet due to lack of
evaporation
Epiphytes, tall trees and
undergrowth
Large diversity in species
Tropical Rainforest Hot (20oC-30oC) High Precipitation
Over 250cm per year
Tundra Freezing (<0oC) Little Precipitation Small close to the ground
(e.g. mosses)
Perennial plants grow in
the summer

http://cispatm.pbworks.com/f/1209212862/biome_graph.jpg
n.b. The biomes in regions within the dashed line are strongly
influenced by other factors (e.g. seasonality of drought, fire,
animal grazing).
A climograph is a diagram which
shows the relative combination of
temperature and precipitation in an
area.
This modified climograph (first
developed by Robert Whittaker)
shows the stable
ecosystems/biomes that arise as a
result of the relative combination
of temperature and precipitation.
It is a graphical representation of
the biome summary table (last
slide).

C.2 S.3 Construction of Gersmehl diagrams to show the inter-relationships between
http://commons.wikimedia.org/wiki/File:Nutrient_cycle.svg
Gersmehl diagrams were first developed in 1976, by P.F. Gersmehl, to show the
differences in nutrient flow and storage between different ecosystems
Sinks for nutrient storage:
• Biomass (flora and fauna)
• Litter
• Soil

Nutrient inputs into the ecosystem:
• Nutrients dissolved in raindrops
• Nutrients from weathered rock
Nutrient outputs (losses) from the ecosystem:
• Nutrients lost through surface runoff
• Nutrients lost through leaching

When used to analyze a particular
ecosystem:
• Diameter of sinks are proportional
to the mass of nutrients stored in
each sink
• the thickness of the arrows are
proportional to the rate of
nutrient flow
Flows between the sinks:
• Littering (including withering, defoliation,
excretion, unconsumed parts left over, dead
bodies of animals, and so on) *
• Decomposition of the litter into inorganic
nutrients, which are then stored in the soil
• Nutrient uptake by plants
Human interactions are not considered – do not confuse
littering with dropping trash
*

• Litter (pine needles) is
the main store
• Slow rate of nutrient
transfer between
stores
• Soil is the main store
• Slow rate of nutrient
transfer between
stores (except for the
transfer from biomass
to litter)
• Biomass is the main
store (soil is nutrient
poor)
• Fast rate of nutrient
transfer between
stores
tagia
(temperate forest)
desert tropical rainforest
Image source: Allott, A. (2014). Biology: Course companion. S.l.: Oxford University Press.

C.2 U.4 The type of stable ecosystem that will emerge in an area is
predictable based on climate.
• The Coral Triangle is a geographical term used to describe the region that possesses the
world’s highest levels of marine biodiversity.
• The answer to why areas like the Coral Triangle harbor the world’s highest levels of
marine biodiversity begins not with the individual organisms, but with geologic
processes that began hundreds of millions of years ago. Plate tectonics, continental drift,
and the advance and retreat of glaciers. Glacial periods have covered the Earth with ice
at least 21 different times over the past several million years creating one of the most
stable climate on Earth.

More than 3,000 species of fish
live in the Coral Triangle,
including the largest fish -
the whale shark, and
the coelacanth. It also
provides habitat to six out of the
world's seven marine turtle
species.
This great biodiversity is thought
to be due to an extended period
of little to no climate change

Borneo lowland rain forest is
a tropical and subtropical of
the large island
of Borneo located in the
Coral Triangle. It supports
approximately 10,000 plant
species, 380 bird species and
several mammal species,
which include the Orangutan

Bibliography / Acknowledgments

C.2 communities and ecosystem

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