An Introduction

Ecosystem
 A community of interdependent organisms and the interactions with the physical environment in which they live.
 It can also be defined as the abiotic and biotic factors and the interactions between them.
 The interaction between organisms and the environment is the key!

Abiotic and Biotic factors
 Biotic Factor: A living, biological factor that may influence an organism or a system.
Example: predation, disease, competition
Abiotic factor: A non-living, physical factor that may influence an organism or a system
Examples: Temperature, salinity, pH, light

Differentiate between the following terms:
 Organism
 Species
 Population
 Community
 Niche
 Habitat

In your notebook, draw a picture of a bunch of little organisms
 Label: The organisms of the same type
(species)
 Circle: individuals of the same species
(Population)
 Draw interactions between the populations
(Community)

Compare the terms habitat and niche
 Sometimes people confuse these terms.
 Figure out the differences between the terms.

Niche vs habitat
 A habitat is where an organism lives. The habitat must provide a source of food, water and shelter for the organism.
 Niche: The role of the organism. This is largely to do with the trophic level of the organism.
 For example: plants produce food for the rest of the food chain. Tigers keep herbivore populations under control.

Abiotic and Biotic factors
 Biotic Factor: A living, biological factor that may influence an organism or a system.
Example: predation, disease, competition
Abiotic factor: A non-living, physical factor that may influence an organism or a system
Examples: Temperature, salinity, pH, light

Which factors are biotic?
 Rabbits
 Cacti
 Daylight hours
 Precipitation
 Moss
 Soil composition
 Bacteria

Limiting factors
 An abiotic factor can limit the population size if there is too much or too little of it. Even if there is the right amount of other factors
 Examples to consider:
Sunlight
Precipitation
Salinity
Nutrients in the soil

Trophic levels
 Ecostems are often broken up and described according to feeding relationships.
Trophic level:
 The position of an organism in a food chain
 A group of organisms that occupy the same place in a food chain

Trophic levels in food chains
Be able to give an example of each!
 Primary producers (autotrophs)
 Primary consumers (herbivores)
 Secondary consumers(carnivores)
 Tertiary consumers (top carnivores)
 Decomposers
 Detrivores
 Scavengers

Energy flow and material cycling

l Autotroph - “self” + “feed” l An organism that obtains organic food molecules without eating other organisms but by using energy from the sun or inorganic molecules to make organic molecules l Remember: This trophic level supports all of the others l The role of producers is to convert energy into a form useable for other organisms

Producers l Most producers are photosynthetic
(e.g. algae, mosses, diatoms, some bacteria, plants etc.) but some are chemosynthetic (e.g. hydrothermal vent bacteria)
(H 2 )

Decomposer l
An organism that obtains energy by breaking down dead organic matter, including dead plants, dead animals and animal waste, into more simple substances l
Examples include: bacteria and fungi
L
Interconnects all trophic levels since the organic material making up all living organisms is eventually broken down l
Role of decomposers is to return valuable nutrients to the system so they can be used again

Compare detritus feeders to decomposers:

Consumer l
Heterotroph - “other” + “feed” l
An organism that obtains its nutrition by eating other organisms l
Primary consumer (herbivore) - eats producers e.g. sea urchin, copepod l
Secondary consumer (carnivore) - eats primary consumers e.g. wolf eel, herring l
Tertiary consumer - eats secondary consumers e.g. sea otter, seal l
Quaternary consumer - eats tertiary consumers e.g. killer whale

Consumers
 The role of the consumer is to transfer energy from one trophic level to the next.
 Notice that consumers have different names, depending on what they eat:
 Herbivores: plant eaters
 Carnivores: meat eaters
 Omnivores: eat plants and animals

Food Chains

Food webs
L
An ecosystem’s trophic structure determines energy flow and nutrient cycling

Food webs

Trophic levels

Pyramid of biomass

Second Law of Thermodynamics
 There is a tendency for numbers and quantities of biomass and energy to decrease along food chains.
 The pyramids become smaller at the top because around 90% of the energy is “lost” between each level and only 10% is available in the body of the organism for transfer to the next level.

Energy transfer in a food chain:
First law of thermodynamics

The end!