TOPIC 4: ECOLOGY
4.1 Species, Communities and Ecosystems
Ecology: the study of relationships between living organisms and between organisms and their
environment (can be studied at 4 levels: ecosystem, community, population and organism)
Species: a group of organisms which can interbreed and produce fertile offspring
o Members of a species may be reproductively isolated in separate populations
Population: group of organisms of the same species who live in the same area at the same time
Community: a group of populations living and interacting with each other in an area
Ecosystem: A community of organisms and its abiotic environment (can be classified by type of
vegetation, depending on height and % of canopy cover)
Habitat: The environment in which a species normally lives
Abiotic Factors: Non-living factors of an ecosystem (e.g. rain, wind, temperature, pH, altitude)
o For many abiotic factors species have a tolerance range within which it functions best
Outside of this range the organism begins to suffer physiological stress and
functioning is affected
Biotic Factors: The living elements of an ecosystem (e.g. plants and animals)
o All biotic factors require energy to survive
Autotrophs: An organism which synthesises its own organic molecules from simple inorganic
substances (producers)
o Use photosynthesis to convert the light energy into chemical energy (glucose)
o Plants & algae are mostly autotrophic but some are not
Heterotrophs: An organism which derives energy from other living organisms
o Consumers: Heterotrophs that feed on living organisms by ingestion
Saprotrophs: heterotrophs that obtain organic nutrients from dead organisms
by external digestion (e.g. bacteria and fungi)
Detritivores: heterotrophs that obtain organic nutrients from detritus by
internal digestion (e.g. earthworms, woodlice)
Some species use both autotrophic & heterotrophic methods of nutrition (e.g. Venus fly trap)
The presence of two species within a given environment will be dependent upon potential
interactions between them
o If species are found in the same habitat they show positive association (e.g. symbiotic/
predator prey relationship)
o If two species don't occur in the same habitat they show negative association (e.g.
competition for resources)
o If two species don't interact there will be no association (independent distribution)
The presence of two species within an environment can be determined using quadrat sampling
o Quadrats are placed randomly within an area and the number of individuals of a given
species is counted or it is observed whether the species is present. This is repeated to
gain a representative data set
𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑐𝑜𝑢𝑛𝑡𝑒𝑑
o 𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑞𝑢𝑎𝑑𝑟𝑎𝑡𝑠 𝑠𝑎𝑚𝑝𝑙𝑒𝑑 × 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑒𝑎𝑐ℎ 𝑞𝑢𝑎𝑑𝑟𝑎𝑡
o Only effective for plants and sessile organisms
37
4.1 Species, Communities and Ecosystems
Ecology: the study of relationships between living organisms and between organisms and their
environment (can be studied at 4 levels: ecosystem, community, population and organism)
Species: a group of organisms which can interbreed and produce fertile offspring
o Members of a species may be reproductively isolated in separate populations
Population: group of organisms of the same species who live in the same area at the same time
Community: a group of populations living and interacting with each other in an area
Ecosystem: A community of organisms and its abiotic environment (can be classified by type of
vegetation, depending on height and % of canopy cover)
Habitat: The environment in which a species normally lives
Abiotic Factors: Non-living factors of an ecosystem (e.g. rain, wind, temperature, pH, altitude)
o For many abiotic factors species have a tolerance range within which it functions best
Outside of this range the organism begins to suffer physiological stress and
functioning is affected
Biotic Factors: The living elements of an ecosystem (e.g. plants and animals)
o All biotic factors require energy to survive
Autotrophs: An organism which synthesises its own organic molecules from simple inorganic
substances (producers)
o Use photosynthesis to convert the light energy into chemical energy (glucose)
o Plants & algae are mostly autotrophic but some are not
Heterotrophs: An organism which derives energy from other living organisms
o Consumers: Heterotrophs that feed on living organisms by ingestion
Saprotrophs: heterotrophs that obtain organic nutrients from dead organisms
by external digestion (e.g. bacteria and fungi)
Detritivores: heterotrophs that obtain organic nutrients from detritus by
internal digestion (e.g. earthworms, woodlice)
Some species use both autotrophic & heterotrophic methods of nutrition (e.g. Venus fly trap)
The presence of two species within a given environment will be dependent upon potential
interactions between them
o If species are found in the same habitat they show positive association (e.g. symbiotic/
predator prey relationship)
o If two species don't occur in the same habitat they show negative association (e.g.
competition for resources)
o If two species don't interact there will be no association (independent distribution)
The presence of two species within an environment can be determined using quadrat sampling
o Quadrats are placed randomly within an area and the number of individuals of a given
species is counted or it is observed whether the species is present. This is repeated to
gain a representative data set
𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑐𝑜𝑢𝑛𝑡𝑒𝑑
o 𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑞𝑢𝑎𝑑𝑟𝑎𝑡𝑠 𝑠𝑎𝑚𝑝𝑙𝑒𝑑 × 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑒𝑎𝑐ℎ 𝑞𝑢𝑎𝑑𝑟𝑎𝑡
o Only effective for plants and sessile organisms
37
