# IB Environmental Systems and Societies/Structure
#### 2.1 Structure

2.1.1 Distinguish between biotic and abiotic (physical) components of an ecosystem
   * Biotic: All the plants, animals, algae, fungi and microbes in an ecosystem (All living things)
   * Abiotic: The chemical and physical factors in an ecosystem (non living) for example: Temperature, moisture, salinity, soil type, light, air.
2.1.2 Define the term trophic level.
   * The position that an organism occupies in a food chain, or a group of organisms in a community that occupy the same position in food chains.
2.1.3 Identify and explain trophic levels in food chains and food webs selected from the local environment.
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 are graphical models of the quantitative differences that exist between the trophic levels of a single ecosystem. A pyramid of biomass represents the standing stock of each trophic level measured in units such as grams of biomass per square metre (g m–2). Biomass may also be measured in units of energy, such as J m–2. In accordance with the second law of thermodynamics, there is a tendency for numbers and quantities of biomass and energy to decrease along food chains; therefore the pyramids become narrower as one ascends. Pyramids of numbers can sometimes display different patterns, for example, when individuals at lower trophic levels are relatively large. Similarly, pyramids of biomass can show greater quantities at higher trophic levels because they represent the biomass present at a given time (there may be marked seasonal variations). Both pyramids of numbers and pyramids of biomass represent storages.Pyramids of productivity refer to the flow of energy through a trophic level and invariably show a decrease along the food chain. For example, the turnover of two retail outlets cannot be compared by simply comparing the goods displayed on the shelves; the rates at which the shelves are being stocked and the goods sold also need to be known. Similarly, a business may have substantial assets but cash flow may be very limited. In the same way, pyramids of biomass simply represent the momentary stock, whereas pyramids of productivity show the rate at which that stock is being generated. Biomass, measured in units of mass or energy (for example, g m–2 or J m–2), should be distinguished from productivity measured in units of flow (for example, g m–2yr–1or J m–2yr–1). A pyramid of energy may be represented either as the standing stock (biomass) measured in units of energy (J m–2) or as productivity measured in units of flow of energy (J m–2yr–1), depending on the text consulted. As this is confusing, this syllabus avoids the term pyramid of energy.
2.1.5 Discuss how the pyramid structure affects the functioning of an ecosystem.
   * Because energy is lost through food chains, carnivores are at risk from disturbance.
   * Disturbance at the lowest level (producers) directly affects the existence of species at consumer level and ultimately the top carnivores.
2.1.6 Define the terms species, population, habitat, niche, community and ecosystem with reference to local examples.
   * Species: A group of organisms that interbreed and produce fertile offspring.
   * Population: A group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.
   * Habitat: The environment in which a species normally lives.
   * Niche: A species’ share of a habitat and the resources in it. An organism’s ecological niche depends not only on where it lives but also on what it does.
   * Community: A group of populations living and interacting with each other in a common habitat.
   * Ecosystem: A community of interdependent organisms and the physical environment they inhabit.
2.1.7 Describe and explain population interactions using examples of named species.
   * Competition: Interspecific (between species) and intraspecific (within species) FOR RESOURCES: Space, Water, Food, Sunlight, Mates
   * Predation: Ex) Lynx and Snowshoe have (negative feedback mechanisms. Carnivores of any level eating organism of other species.
   * Symbiosis: Where two organisms live together.
   * Parasitism: Ectoparasites... Ex) Ticks, Fleas, Leaches. Endoparasites.... Ex) Tapeworms
   * Mutualism: Live together, both benefit.... Ex) clown fish and sea anemone
   * Commensalism: Where one animal benefits but nothing happens to the other.