1. ECOSYSTEMS

2. What is an Ecosystem?
The biological community together with its associated non-living environment
Ecosystems consist of biotic and abiotic components

3. Biotic Components of an Ecosystem
Living things
Divided into two groups based on their source of food:
Autotrophs
Heterotrophs

4. Autotrophs
Require only inorganic nutrients and an outside energy source to produce organic nutrients
Also called producers as they produce food
Two types:
Photoautotrophs – produce organic nutrients via photosynthesis
Chemoautotrophs – produce organic nutrients using energy obtained from the oxidization of inorganic compounds

5. Examples of Autotrophs
Cyanobacteria
Photosynthetic protists
Plants
Algae
Chemosynthetic bacteria

6. Parasitic herb (Hyobanche sanguinea), Namaqualand
Heterotrophs
Require a source of preformed organic nutrients
Also called consumers as they consume food
All animals are heterotrophs, as are fungi, many bacteria and parasitic plants
Parasitic herb (Hyobanche sanguinea), Namaqualand

7. Types of Heterotrophs Herbivores – Feed on plants or algae
Carnivores – Feed on other animals
Omnivores – Feed on plants and animals
Detrivores – Feed on decomposing organic matter
Decomposers – Break down organic material

8. Examples of Heterotrophs
Herbivore
Herbivore
Carnivore
Carnivore
Decomposer
Decomposer

9. Energy Flow & Chemical Cycling
Every ecosystem is characterised by two fundamental processes:
Energy flow
One-way flow of energy through biotic community
Begins when producers absorb solar energy
Chemical cycling
Cyclical flow of materials from the abiotic environment, through the biotic community and back again to the abiotic environment

10. Energy Flow & Chemical Cycling
Energy flows through an ecosystem
Chemicals cycle through an ecosystem

11. Energy Flow
With few exceptions, all ecosystems depend on solar energy as a primary energy source
Primary productivity is the rate at which producers convert solar energy into biomass
Primary productivity is dependent upon sunlight, nutrient and water availability

12. Productivity of Ecosystems
Tropical rain forests have high productivity because of abundant rainfall and sunlight
Estuaries and marshes have high productivity because of high nutrient influx from rivers and streams

13. Productivity of Ecosystems

14. Energy Flow
Some of the energy captured from the sun is lost to the environment as heat when producers use energy for cellular respiration
Some energy also goes to detritus feeders through waste production and death
Only a portion (~10%) of the energy captured by producers is passed on to consumers

15. Energy Flow
Consumers also lose energy due to respiration, excretion, and death
At each trophic level, only ~10% of the energy is passed up to the next trophic level
All the energy taken in by producers is ultimately lost as heat through respiration

16. Energy Flow
Only 10% of the energy taken in by a herbivore goes to carnivores
The rest goes to detritus feeders, or is lost to the environment as heat

17. Energy Flow
Energy flow through an ecosystem is one way; it is not recycled
Autotrophs must continue to capture the sun’s energy for ecosystems to persist

18. Trophic Levels
Ecosystems have a trophic structure that represents the different feeding relationships that determine the route of energy flow and the pattern of chemical cycling
Species in an ecosystem are divided into different trophic levels based on their main source of nutrition

19. Trophic Levels Trophic levels include: Primary producers
Primary consumers
Secondary consumers
Tertiary consumers
Detritivores and decomposers

20. Primary Producers
Autotrophs support all other trophic levels either directly or indirectly by synthesising sugars and other organic molecules using light energy
EXCEPTION: In hot water deep-sea vents, chemosynthetic bacteria form the basis of the food chain. These bacteria obtain energy from chemical sources such as hydrogen sulfide (H2S) instead of from sunlight

21. Primary Consumers
Primary consumers are herbivores that consume the primary producers
For example, herbivorous insects, grazing mammals, seed-eating birds, aquatic zooplankton and some fish

22. Secondary Consumers
Secondary consumers are carnivores that eat herbivores
E.g. spiders, frogs, insect-eating birds, lions, many fish, sea-stars

23. Tertiary Consumers
Tertiary consumers are carnivores that eat other carnivores

24. Detritivores & Decomposers
These are consumers that derive energy from organic wastes and dead organisms
E.g. bacteria, fungi, and scavengers such as cockroaches and vultures
This level is an important part of the recycling process as it returns chemicals to the primary producers

25. Food Chains
A food chain depicts the transfer of energy from one trophic level to the next

26. Food Webs
Feeding relationships in nature are usually much more complex than a simple chain
E.g. several primary consumers may feed on the same plant species and one primary consumer may eat several types of plant
These complex feeding relationships are depicted in a diagram called a food web

27. Antarctic Food Web

28. Ecological Pyramids Food chains lose energy between trophic levels
Only about 10% of the energy of one trophic level is available to the next trophic level
This explains why few top carnivores can be supported in an ecosystem
The flow of energy between successive trophic levels can be depicted as an ecological pyramid

29. Productivity Pyramids
A productivity or energy pyramid depicts the amount of energy contained in each trophic level from the lowest, the producers, to the highest, the top carnivores
Trophic levels are stacked in blocks proportional in size to the energy acquired from the level below

30. Productivity Pyramid

31. Biomass Pyramid
In a biomass pyramid, each tier symbolises the total dry weight of all organisms in that level

32. QUESTION
Why could more people be supported on Earth if people were vegetarians than if they ate meat?