Key concepts
In this session we will focus on summarising what you need to know about:
- Concept of an ecosystem
- Structure and ecosystem function related to abiotic factors and biotic factors
- Factors that influence terrestrial and aquatic primary production
Terminology&Definitions
Ecosystem - a community plus the physical environment that it occupies at a given time
Abiotic factors – non-living factors . Eg soil, air.
Biotic factors – living factors. Eg trees, insects.
Producer – organism that manufactures food by photosynthesis.
Herbivore – an organism that feeds on plants only.
Carnivore – an organism that feeds on animals only.
Omnivore – an organism that feeds on both plants and animals.
Saprotroph – an organism that feeds on dead and decaying matter. (fungi)
Decomposers – an organism that causes the decay of dead and dying organisms.
(bacteria)
Scavenger – an organism that feeds on remains of animals.
Predator – an animal that hunts for its food.
Prey – an animal that is hunted and is food for the predator.
Food chain – a chain showing feeding relationships between organisms.
Content
An ecosystem is a community of living organisms interacting with each other and
their environment. Ecosystems occur in all sizes. A tidal pool, a pond, ariver, and a yellowwood forest are all examples of ecosystems. The living
organisms (plants and animals) are referred to as biotic factors.The non-livingcomponents make up the abiotic factors. Organisms living in a particular
ecosystem are adapted to the prevailing abiotic and biotic conditions.
Abiotic components
Abiotic factors may be grouped together as:
- Physical / Climatic factors: sunlight, water, temperature and gases.
- Edaphic factors: soil type, soil pH.
- Physiographic factors: slope, aspect and altitude and latitude.
Climatic factors:
Sunlight
- Light is a fundamental necessity.
- The amount of sunlight an ecosystem receives is called insolation. This is
critical for plant survival, especially in aquatic ecosystems. Light decreasesand water depth increases.
- Amount of light changes from season to season.
- In summer – days are longer, ecosystems gets more hours of sunlight than
during short winter days.
- The amount of sunlight affects other features of the ecosystem such as
temperature, and the types of plants and animals that are found there.
Temperature
- Temperature increases with an increase in both latitude and altitude.
- Temperature affects the rate at which photosynthesis, respiration and
decomposition take place. The higher the temperature, the faster the processes.
Water
- Water is one of the most important factors in the ecosystem.
- It is the main component of living cells and is essential for all living
organisms.
- About 80% of the human body and 90% of the plant body consists of water.
- Water is evenly distributed over the earth.
- It is abundant in aquatic ecosystems and least in deserts
- Plants are adapted to the available amount of water in the following ways:
- Xerophytes are plants that are able to live in dry habitats, or in regions with
low annual rainfall. These plants are resistant to drought, have to cope withshortage of water, high temperatures and light intensities and dry warm winds.
ie Cactus, Aloe
- Hydrophytes are plants that are able to live entirely or partially in submerged
water ot in very wet soil. These plants have to cope with a water surplus. ieWater lily, Water hyacinth
- Mesophytes are plants that need an average, regular supply of water. ie Fruit
trees, wheat
