The ecosystem
Many organisms live together in an ecosystem, and each of them have an important role to play in maintaining the balance of that ecosystem
Roles of organisms
- Producer – An organism that makes its own organic nutrients, usually from sunlight via photosynthesis
- Consumer – An organism that gains energy by feeding on other organisms. They can be further classified into primary, secondary, tertiary consumers
- Herbivores – Animals that gain energy by eating plants
- Carnivores – Animals that gain energy by eating other consumers
- Decomposers – Organisms that gain energy by breaking down dead, or organic waste material
Energy flow through an ecosystem
The principle source of energy input into the ecosystem is the sun. Plants use photosynthesis to convert light energy (from sunlight) into chemical energy in nutrients.
The chemical energy stored in food gets transferred to the environment.
Trophic levels
A trophic level is the position of an organism in a food chain, food web, pyramid of numbers, or the pyramid of biomass.
All the things mentioned above demonstrate the direction of energy transfer within organisms .
All feeding relationships begin with the producers. Producers then are eaten by consumers.
The energy flow is as follows:
Primary producers -> Primary consumers -> Secondary consumers -> Tertiary consumers -> Quaternary consumers
Energy transfer along trophic levels
Starting from the producers, energy is transferred from one trophic level to the next.
At each level, 90% of the original energy is lost due to various factors:
- Respiration – Energy is used to respire
- Movement – Energy is used for movement
- Maintenance of body temperature – Energy is used in homeostasis
- Indigestable material within an organism – Some parts of eaten marterial cannot be digested or used by the consumer
Therefore higher the trophic level, the smaller the amount of energy that is available to them.
For this reason it is rare to see more than 5 trophic levels. Organisms higher up would not be able to sustain themselves due to the lack of energy.
Food chains & food webs
Food chains show the transfer of energy from one organism to the next, beginning with producers.
A food web is a network of interconnected food chains
Food pyramids
Food pyramids are graphical representations (in the form of pyramids) that show feeding relationships of organisms at each trophic level.
The pyramid of numbers simply show the number of organisms in each trophic level. Unfortunately, this can at times be somewhat misleading. It is misleading because it may not depict the true amount of energy in each trophic level.
For instance, 10000 aphids may feed off a single large oak tree. Using this information for the pyramid of numbers gives us a fairly odd looking pyramid. It makes it feel as if there may not be ‘enough’ producers to support the food chain.
Instead, the pyramid of biomass is a much more accurate representation of the actual energy levels in each trophic level. The oak tree has more than enough energy to support the food chain.
Carbon, water, and nitrogen cycles
Carbon cycle
Water cycle
Nitrogen cycle
Population size
A population is a group of organisms of one species living in the same area at the same time.
A community is a combination of all populations of different species in an ecosystem.
An ecosystem is a unit containing the community of organisms and their environment, interacting together.
Sigmoid population curve
There are four main phases of growth for a population which we will look at in more detail below.
Some important factors that can influence population growth are as follows:
- Food supply
- Predation
- Disease
- Lag phase
- The population growth begins slowly from a few individuals
- Log phase
- Exponential growth due to ideal conditions and maximum growth rate is achieved
- Stationary phase
- The carrying capacity of the environment is reached i.e. the maximum population size that the environment can support
- This could be due to limitation of resources such as food, space, etc.
- Decline/death phase
- Sudden environmental change causes an inability of the environment to support the population