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Ecology 1: Two-Page Summary Overall Summary of ecosystems Ecosystems consist of a community of species in a physical environment. These species each have a population (the total number of individuals in that species) and a habitat (the place they live, feed etc. in the ecosystem). The species also have relationships, particularly feeding relationships (species eat other species) and competition (where different species depend on the same resources, e.g. food, water, sunlight). The feeding relationships determine the main roles that organisms have in the ecosystem – we say that different organisms occupy different trophic levels in an ecosystem. A set of feeding relationships between one series of organisms is known as a food chain. In an ecosystem, there are many food chains, and they are interconnected because organisms have feeding relationships with many different other organisms. So food chains in a network known as a food web. The mass or number of organisms at different trophic levels in a food chain can be expressed visually using a pyramid of biomass or a pyramid of numbers. Biological component of an ecosystem – main roles producers (plants) – which produce their own food (are autotrophs) consumers (animals that eat plants or other animals) (are heterotrophs) decomposers (organisms that recycle nutrients from dead material) (many are saprotrophs) Physical environment The non-living component of an ecosystem Habitats and populations habitat (part of ecosystem where a species lives) population (number of organisms of 1 species) community (all populations in an ecosystem) Sampling Sampling: counting organisms in part of an ecosystem to estimate population Quadrat: 0.5m or 1m square used to enclose a sample Random: samples should be selected at random so they are representative Bias: Unrepresentative results due to non-random sampling Ecology 1: Two-Page Summary Interactions feeding (organisms eat each other; plants, animals, and decomposers recycle the same nutrients) competition - animals (for food, shelter, mates, nesting sites) competition – plants (carbon dioxide, minerals, water, light) interactions between organisms and environment (e.g. beavers building dams) Ecological pyramids pyramids of numbers (number of organisms in each trophic level) pyramids of biomass (dry mass of organisms in each trophic level) most of the material that is passed into a trophic level is not available to the next trophic level as: 1. some matter is not eaten (inedible) 2. some matter eaten but not digested (indigestible) 3. some absorbed matter is then excreted 4. some matter is respired to release energy Energy conversion and transfer in ecosystems 1. The ultimate source of energy in an ecosystem is light energy from the sun 2. The sun’s energy is fixed in photosynthesis by producers to produce chemical energy 3. Chemical energy is transferred between trophic levels by feeding 4. Energy is lost from the ecosystem as heat energy a. in all trophic levels by respiration fuels life processes and releases heat b. Decomposition also results in release of heat energy to the environment as the decomposers also respire.