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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.