12 Biology - Unit 3.2

Trophic Levels

An organisms position in a food chain.

Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers → Quaternary Consumers

How is energy lost between Trophic Levels

• Respiration (released as heat)

• Movement and activity

• Waste (uneaten parts, excretion). 

Roles of Decomposers in Ecosystems and Food Chains

Decomposers break down waste to recycle nutrients from the waste for the ecosystem to reuse.

Food Chains

Show the order of trophic level and flow of energy

Food Webs

A complex network of interrelated food chains

Ecological Pyramids

Represent how energy of biomass is distributed across trophic levels.

Why isn’t all sunlight used as energy by plants

Plants can’t absorb all of it since the wavelengths which emit green light would be reflected. 

Predation

One organism (the predator) hunts and kills another organism (the prey) for food. (

Competition

Occurs when two or more organisms compete for the same limited resource (e.g. food, water, shelter, mates.).

Mutualism

A relationship where both species benefit.

Commensalism

One species benefits while the other is unaffected (neither harmed nor benefited).

Parasitism

One species (the parasite) benefits while the other (the host) is harmed.

Ecological Niche

The role and space that an organism fills in an ecosystem, including all its interactions with the biotic and abiotic factors in an environment.

Fundamental Niche

All the potential resources that a species can use in its environment.

• Requires the absence of competition.

Realised Niche

Some habitats and resources are not available because competitors occupy them.

• This is what the species actually uses. 

Competitive Exclusion Principle

The exclusion of a species from a community by another organism better adapted to that particular ecological niche.

• When one species has even the slightest advantage over another, the one with the advantage will dominate in the long term.

Niche Partitioning

Niche partitioning happens when different species share the same habitat but use it in different ways This reduces competition and allows them to live together. 

Keystone Species

A plant or animal that plays a unique and crucial role in the way an ecosystem functions

• they have an influence on an ecosystem that is disproportionate to their abundance.

Carrying Capacity

Is the population size that can be supported indefinitely on the available resources and services of that ecosystem. 

Limiting Factor

A limiting factor is an abiotic or biotic factor that restricts the number of individuals in a population

• because of these limiting factors, each ecosystem has a finite capacity for growth connected to its carrying capacity.

Ecological Succession

The change in structure and species composition of a community over time.

• All successions involve changes in structure and function until a climax community (end point of the ecological succession)1 is reached

Pioneer Species

• Ability to fixate nitrogen

• Tolerance to extreme conditions

• Rapid germination of seeds

• Ability to photosynthesise efficiently.

Climax Community

Final state of the ecosystem in the stage of ecological succession with little change in species composition and change in ecosystem.

Primary Succession

Ecological succession onto regions that have never been colonised and involves no habitats

Secondary Succession

Refers to reintroduction of organisms (pioneer species) into an ecosystem that may have been destroyed completely and made uninhabitable.