Energy Flow Food Chains and Webs Carbon Cycle Man and His Environment (Part I) Energy Flow Food Chains and Webs Carbon Cycle

18.1 What is Ecology? Organisms continually interact with one another, as well as the surroundings Ecology is the study of these interactions Ecologists study both the living and non-living (physical) environment The living (or biotic) environment consists of all the living things that an organism interacts with The non-living (or abiotic) environment consists of physical factors such as light, water and pH of the soil/water

What are some key ecological terms? Habitat Population Community Ecosystem

What is a habitat? The place where an organism lives is its habitat For example, Wading birds called redshanks live in the mud of the mangrove swamp, so the mangrove swamp is the habitat of the redshanks

What is a population? A group of organisms of the same species living in a particular habitat make up a population. For example, in the mangrove habitat, all the redshanks living in that particular mangrove swamp make up a population Another population is made up of all the mangrove trees living in that particular mangrove swamp

What is a community? All the populations of organisms living and interacting with one another in a particular habitat make up a community. For example: The mangrove community is made up of mangrove trees and other plants, animals like redshanks, mudskippers and sand flies, and microorganisms living in the mud of that mangrove swamp

What is an ecosystem? Living organisms interacting with one another and with their abiotic environment make up an ecosystem For example: The ecosystem of mangrove community is made up of all the organisms in the mangrove community and all the physical factors that make up its abiotic environment. These factors include the salt concentration of seawater, its pH, the temperature , the amount of oxygen dissolved in the mud, the amount of light falling on the trees and the amount of nutrients in the mud

18.2 The Abiotic Environment Physical features that make up the abiotic environment include: Light intensity Temperature Amount of water available Oxygen content Salinity (salt concentration) of soil or water pH of soil or water *** Refer to Discover Biology Textbook Page 305 to 307 for more details

18.3 The Biotic Environment The living or biotic environment comprises all the living organism that an organism interacts with in its habitats An habitat is the place where an organism lives e.g a pond, stream, river, forest or desert

Why do organisms affect other organisms? The organisms in any habitat are never completely independent The life of each organism depends on and is influenced by other organisms around it Hence the organisms are known to be interdependent

What is an ecological community? When different populations of plants and animals live together and interact within the same environment, they make up an ecological community The various populations in any community live interdependently A change in one population affects the other populations of the community

18.4 The Ecosystem An ecosystem is an ecological system formed by the interaction of living organisms and their non-living environment When considering an ecosystem, we are considering both the biotic and the abiotic environments in that ecosystem.

The Ecosystem An ecosystem uses both energy and inorganic nutrients Energy enters an ecosystem (from the sun) Energy is converted into chemical energy and is passed from organism to organism through the ecosystem Energy is lost to the environment as it flows through the ecosystem The energy that is lost as heat cannot be recycled in the ecosystem. Hence, energy has to be constantly supplied to the ecosystem.

The Ecosystem Inorganic nutrients, on the other hand, need not be supplied from outside the ecosystem They are obtained from the abiotic environment and flow through the ecosystem in a cycle In a ‘balanced’ ecosystem, nutrients are continually recycled and are not lost i.e. nutrient cycling

5. Burning of fossil fuels For example – The Carbon Cycle (Nutrient Cycling) Carbon is present in all biological molecules and it is recycled in the following manner: Atmosphere 1. Photosynthesis 2. Respiration 5. Burning of fossil fuels Plants Animals 3. Dead Organisms 4. Fossil Fuels 16

Energy Flow Two key process which sustain the ecosystem are energy flow from the Sun to plants and then to other organisms, and nutrient cycling. A terrarium is an example of a mini ecosystem.

How do energy and nutrients flow through an ecosystem? The living organisms in any ecosystems are made up of producers, consumers and decomposers Energy and nutrients are transferred from producers to consumers to decomposers through feeding

Energy Flow – Food Chains The sequence of food transfer from one trophic level to another is called a food chain A food chain is a series of organisms through which energy is transferred in the form of food A food chain always begins with a producer 19

Energy Flow – Trophic Levels At the base of all food chains are the producers – producers convert energy from the sun or light energy into chemical energy and store it as food during photosynthesis. Producers are mainly green plants, but algae and certain bacteria that can photosynthesize are also producers Producers are the only organisms that can manufacture or produce complex organic food from inogranic raw materials

Energy Flow – Trophic Levels All organisms above the producers are consumers. Consumers obtain their energy by feeding on other organisms Herbivores feed directly on plants or algae (Primary Consumers) Carnivores feed on other consumers (e.g herbivores) (Secondary Consumers) Carnivores that feed on other carnivores are known as Tertiary Consumers

Decomposers obtain their energy by breaking down dead organisms, faeces and excretoary products When the dead organisms and waste matter are broken down, the materials locked up in them are released 22

Examples of decomposers: Fungi, bacteria and earthworms These materials, such as inorganic nutrients, carbon and nitrogen compounds, return to the physical environment and are used again by green plants Examples of decomposers: Fungi, bacteria and earthworms 23

Energy Flow – Food Web In a community, food chains are interlinked to form a food web 24

Food Chain and Food Web A food chain: Primary Consumer (herbivore) Secondary Consumer (carnivore) Tertiary Consumer (carnivore) Producer (green plant) A food web: caterpillar green plant grasshopper spider bird aphid aphid ladybird ladybird 16 April 2017

Ecological Pyramids We can compare the trophic levels in a food chain using ecological pyramids There are 3 types of ecological pyramids: Pyramid of numbers Pyramid of biomass Pyramid of energy

The Pyramid of Numbers The pyramid of numbers allows us to compare the number of organisms present in each trophic level at a particular time The length (or area) of the rectangle represents the number of organisms for each species **Refer to Discover Biology Textbook Page 314 on how to construct pyramid of numbers 27

The Pyramid of Biomass A pyramid of biomass allows us to compare the mass of organisms present in each trophic level in the area at a particular time The pyramid of biomass is constructed based on the dry mass (mass without water content) of organisms in each trophic level at any one time **Refer to Discover Biology Textbook Page 314 on how to construct pyramid of biomass 28

Variations in ecological pyramids Most ecological pyramids are pyramid-shaped, but there are important exceptions A pyramid of numbers may be upside down or inverted if: Organisms of one trophic level are parasitic on organisms of another trophic level Many small organisms of one trophic level feed on a large organism of another trophic level. For example: Tree Aphid Protozoa

Example of inverted pyramid of numbers Parasitic Protozoa Aphids Tree In this case, the pyramid of numbers is inverted. The bottom of the pyramid is represented by only one tree. Many aphids are parasitic on the tree and many protozoa are parasitic on the aphids However, the pyramid of biomass remains broad at the bottom and narrow towards the apex (highest point). Refer to the next slide.

Pyramid of Biomass for Tree, Aphid and Protozoa Parasitic Protozoa Aphids Tree The pyramid of biomass remains broad at the bottom and narrow towards the apex (highest point) for the same food chain. This is because one tree has a comparatively large biomass to support the other populations.

Another example of inverted pyramid of numbers The pyramid may also become inverted if the producer is too large. An inverted pyramid of numbers:

Variations in ecological pyramids Most ecological pyramids are pyramid-shaped, but there are important exceptions A pyramid of numbers may be upside down or inverted if: Organisms of one trophic level are parasitic on organisms of another trophic level Many small organisms of one trophic level feed on a large organism of another trophic level. Pyramids of biomass for rapidly reproducing organisms are also not pyramid-shaped.

Example of inverted pyramid of biomass Since the pyramid of biomass is based on standing mass (mass at a particular time), it does not take into account the rate of reproduction (productivity) of the organisms This is a disadvantage when considering organism that reproduce rapidly e.g. Phytoplankton Zooplankton Small fish Large fish

Example of inverted pyramid of biomass Phytoplankton are microscopic plant-like organisms that can make food by photosynthesis Zooplankton are microscopic primary consumers that feed on phytoplankton The pyramid below gives the impression that the biomass of phytoplankton is smaller than that of zooplankton, which is not possible Large fish Small fish Zooplankton Phytoplankton

Example of inverted pyramid of biomass What happens is that the rate of reproduction of phytoplankton is fast enough to replace the organisms that were eaten by zooplankton Large fish Small fish Zooplankton Phytoplankton

The Pyramid of Energy The pyramid of energy represents the total energy in the various trophic levels of a food chain Unlike the pyramid of biomass, the total energy content in each trophic level over a period of time (i.e. one year) is determined Rate at which the organisms in each trophic level reproduce is considered In other words, the pyramid of energy is thus constructed based on the total energy level in each trophic level over a certain period of time, for example, one year. 37

The Pyramid of Energy A lot of energy is lost to the environment as food is transferred from one trophic level to the next. Energy may be lost to the environment: As heat during respiration at every trophic level In uneaten body parts Through undigested matter egested by consumers Through waste products excreted by consumers, for example, urea 38

The Pyramid of Energy A lot of energy is lost to the environment as food is transferred from one trophic level to the next. Energy may be lost to the environment: As heat during respiration at every trophic level In uneaten body parts Through undigested matter egested by consumers Through waste products excreted by consumers, for example, urea Lost as energy trapped in uneaten body parts, faeces and excretory products Heat lost during respiration Tertiary Consumer (10 kJ) Secondary Consumer (100 kJ) Primary Consumer (1000 kJ) Producer (10000 kJ) 39

The Pyramid of Energy More and more energy is lost as we go down a food chain The total energy level is highest at the first trophic level and lowest at the last trophic level Hence, a pyramid of energy is always broad at the base and narrow towards the top Lost as energy trapped in uneaten body parts, faeces and excretory products Heat lost during respiration Tertiary Consumer (10 kJ) Secondary Consumer (100 kJ) Primary Consumer (1000 kJ) Producer (10000 kJ) 40

The Pyramid of Energy More and more energy is lost as we go down a food chain The total energy level is highest at the first trophic level and lowest at the last trophic level Hence, a pyramid of energy is always broad at the base and narrow towards the top Lost as energy trapped in uneaten body parts, faeces and excretory products Heat lost during respiration Tertiary Consumer (10 kJ) Secondary Consumer (100 kJ) Primary Consumer (1000 kJ) Producer (10000 kJ) 41

The Pyramid of Energy Usually, we can assume about 90% of the energy is lost when it is transferred from one trophic level to the next The greatest amount of energy is lost during its transfer from producer to primary consumer Lost as energy trapped in uneaten body parts, faeces and excretory products Heat lost during respiration Tertiary Consumer (10 kJ) Secondary Consumer (100 kJ) Primary Consumer (1000 kJ) Producer (10000 kJ) 42

Differences between a pyramid of biomass and pyramid of energy Related to the biomass of organisms Related to the energy content of organisms Constructed based on the biomass at any given time Constructed based on energy content over a period of time Does not consider rate of reproduction of organisms Takes into consideration the rate of reproduction of organisms ***Refer to Discover Biology Textbook Page 318 for some examples of food chains to show variations between ecological pyramids

Short food chains are more efficient in energy transfer Since energy is lost at each trophic level, less and less energy is available for organism at the next level as we go down the food chain Hence, food chains are generally short A shorter food chain means more energy is available to the final consumer Why????? Because less energy is lost to the environment Therefore, shorter food chains are more efficient than long food chains

Non-cyclic energy flow in an ecosystem The first source of energy in a ecosystem is the sun As energy flow through the ecosystem, some of the energy is lost to the environment as heat Energy that is lost as heat cannot be recycled Hence, energy has to be constantly supplied to the ecosystem In an ecosystem, energy does not flow in a cycle. Therefore, energy flow is non-cyclic or linear

Non-cyclic energy flow in an ecosystem 5 excretion Secondary consumers (carnivores) 4 respiration egestion energy lost in uneaten body parts, faeces and excretory products (usable energy) feeding (holozoic nutrition) heat lost to environment 3 5 excretion Primary consumers (Herbivores) 4 respiration egestion heat lost to environment feeding (holozoic nutrition) 3 faeces and excretory products + dead bodies of organisms 4 Producers (Green plants) respiration decomposition 2 photosynthesis + CO2 CO2 Sun (light energy) heat released to environment 1

18.5 Nutrient Cycling in an Ecosystem Carbon, oxygen, nitrogen and water are essential nutrients for life In natural ecosystems, these nutrients are released back into the soil when organisms die Decomposers (e.g. fungi and bacteria) break down dead organisms The materials locked up in the dead organisms can then be returned to the physical environment to be used again by green plants Hence, in a balanced ecosystem, nutrients are never lost but are continually recycled

The Carbon Cycle Carbon is constantly being removed from and released into the environment, in the form of carbon dioxide. Hence, the carbon dioxide concentration in the environment remains relatively constant

Removal of carbon dioxide from the environment

Release of carbon dioxide from the environment

The Carbon Cycle

Importance of the carbon cycle Ensures that there is a continuous supply of carbon dioxide for plants to carry out photosynthesis Photosynthesis converts energy from the sun into chemical energy in food, which other non-photosynthetic organisms can use to stay alive Enables energy to flow through the ecosystem Carbon compounds carry the trapped solar energy from organism to organism in the food chains of an ecosystem

Nutrient cycling in the ecosystem made up of Abiotic Environment Biotic Environment consists of consists of Physical factors All the living things an organism interacts with involved in Important processes Non-cyclic energy flow in the ecosystem Nutrient cycling in the ecosystem e.g. Physical factors Carbon dioxide is removed from the environment by green plants during photosynthesis. Carbon dioxide is released into the environment through respiration, combustion and decay. Tertiary Consumer (Carnivore) 1 kJ Secondary Consumer (Carnivore) 10 kJ Energy lost in uneaten body parts, faeces and excretory products Primary Consumer (Herbivore) 100 kJ Energy lost in as heat to environment during respiration Producer (Green plant) 1000 kJ Light energy Sun 53

Some video resources… http://www.youtube.com/watch?v=GnffYkN1UDk http://www.youtube.com/watch?v=O3CZFfyed3M