Topic 2.1: Structure

Assessment 2.1.1: Distinguish between biotic and abiotic (physical) components of an ecosystem

Biotic: refers to the living components of an ecosystem. (the community)

Abiotic: refers to the non-living factors of an ecosystem. (the environment)

Ecosystems are made up of living and non-living components. The living part of the environment consists of the organic part of the ecosystem; animals, plants, algae, fungi and bacteria. These are called biotic components. The non-living part of the environment is made up of physical components such as; air, light, water, temperature, soil, minerals and climatic atmosphere. These are called abiotic components. These two components work together to sustain the environment.

Assessment 2.1.2: Define the term trophic level

Trophic Level: the feeding level within a food chain
  • Trophic level 1 – producer
  • Trophic level 2 – herbivore (primary consumers)
  • Trophic level 3 – carnivore (secondary consumers)
  • Trophic level 4 – carnivore (tertiary consumer)

external image 6547-004-81B9888F.gif

Assessment 2.1.3: Identify and explain trophic levels in food chains and food webs selected from the local environment.

external image graden-food-chain.gif

àFood Chain: A series of organism each dependent on the next as source of food
àFood Web: made from many interconnecting food chains
àProducers: Organism that produces its own energy through photosynthesis
àConsumers: Organisms that cannot make their own food and eat other organisms to obtain energy and matter
àDecomposers: Organisms which feed on the dead biomass created by the ecosystem
àHerbivores: Consumers that only eat plant
àCarnivores: Consumer that only eat meat
àOmnivores: consumers that eat both plant and meat
àTop carnivores: Carnivores that have no predator

Assessment 2.1.4: Explain the principles of pyramids of numbers, pyramids of biomass, and pyramids of productivity, and construct such pyramids from given data

Pyramids: graphical models of the quantitative differences that exist between the trophic level of a single ecosystem
external image biomass-upright-pyramid.jpeg
Pyramids of biomass: the standing stock of each trophic level measure in units such as g m^-2/J m^-2. They represent the biomass present at a given time.
:As pyramids of number but uses dry mass of all organisms at each trophic level.
  • Overcomes the problems of pyramids of number.
  • Only uses samples from populations, so it is impossible to measure biomass exactly.also the time of the year that biomass is measured affects the result.

external image upright-pyramid-of-numbers-grassland-pond.jpeg
Pyramids of numbers: the numbers of producers and consumers coexisting in an ecosystem, have limitation in showing useful feeding relationships.
:A bar diagram that indicates the relative numbers of organisms at each trophic level in a food chain. The length of each bar gives a measure of the relative numbers. Pyramids begin with producers, usually the greatest number at the bottom decreasing upwards.

  • This is a simple easy method of giving an overview and is good at comparing changes in population numbers with time or season.

  • All organisms are included regardless of their size, therefore a system say based on an oak tree would be inverted (have a small bottom and bet larger as it goes up trophic levels). Also they do not allow for juvenilles or immature forms. Numbers can be to great to represent accurately.

external image pyramid.gif

Pyramids of productivity: the flow of energy thought a trophic level and invariably shows a decrease along the food chain. Measure in unit e.g. J m^-2 yr^-1
:The bars are drawn in proportion to the total energy utilized at each trophic level. Also the productivity of producers in a given area measured for a standard time, and the proportion utilized by consumers can be calculated.

  • Most accurate system shows the actual energy transferred and allows for rate of production.
  • It is very difficult and complex to to collect energy data.

Assessment 2.1.5: Discuss how the pyramid structure affects the functioning of an ecosystem


Assessment 2.1.6: Define the terms species, population, habitat, niche, community and ecosystem with reference to local examples

àEcosystem: a community of interdependent organisms and the physical environment they inhabit
à Ecology: the study of the inter-relationships of organisms with each other and the environment
àSpecies: a group of organism that interbreed and produce fertile offspring
àPopulation: number of a group of organism of the same species living in the same area at the same time, and which are capable of interbreeding
àHabitat: the environment where a species normally live
àNiche: where, when and how a species live at its best
àCommunity: a group of population living and interacting with each other in a common habitat
àEnvironment: the non-living and living surrounding

Assessment 2.1.7: Describe and explain population interactions using examples of named species.

àCompetition: when resources are limiting, population are bound to compete in order to survive
-within a species=intraspecific competition; between different species=interspecific competition
external image 250px-Lion_hyena_competition.jpg

àParasitism: where one organism [parasite] benefits at the expense of another [the host] from which it derives food

-Ecotoparasites-live on the surfaces of its host e.g. Mosquitoes and leeches
-Endoparasites-live inside their host e.g. pearl fish
File:Eastern Phoebe-nest-Brown-headed-Cowbird-egg.jpg
File:Eastern Phoebe-nest-Brown-headed-Cowbird-egg.jpg

àMutualism: both of the species are benefit from the relationship
E.g. between coral and algae, where the coral filter feed for floating detritus and the algae can carry out photosynthesis
File:Common clownfish curves dnsmpl.jpg
File:Common clownfish curves dnsmpl.jpg

àPredation: where one organism hunts and eats other animals

File:Leopard kill - KNP - 001.jpg
File:Leopard kill - KNP - 001.jpg

Heribory: the consumption of autotrophs by a primary consumers