Slides in this set
· Any group of living organisms + non-living things occurring together, and the interrelationships between them, can be
thought of as an ecosystem.
· The components of an ecosystem:
HABITAT: the place where an organism lives.
POPULATION: all of the organisms of one species, who live in the same place at the same time, and can breed together.
COMMUNITY: all the populations of different species who live in the same place at the same time, and can interact with each other.
· The role that each species plays in an ecosystem is called its niche.
Biotic + Abiotic
· Biotic factors describe the effects of the living components of an ecosystem food supply, predation + disease.
· Abiotic factors describe the effects of the non-living components of an ecosystem pH, temperature + soil type.
Ecosystems are Dynamic
· Population rises and falls.
· Can be very slightly or very noticeably.
· Any small changes in one species/population/community can affect another.
Energy + Ecosystems
· Matter is constantly recycled within an ecosystem. Energy is not recycled, it flows through the ecosystem.
· PRODUCERS organisms that supply energy to all other organisms (eg. plants).
· CONSUMERS animals and fungi are consumers. Primary consumers are herbivores and are eaten by carnivorous secondary
consumers which are eaten by tertiary consumers.
· DECOMPOSERS living things that feed on waste material or dead organisms.…read more
2.3.2 Understanding Energy Transfer
Transfer of Energy in an Ecosystem
· A food chain shows how energy is transferred from one living organism to another.
· The level at which an organism feed is called its trophic level.
· Within an ecosystem, living organisms are usually members of more than one food chain food webs.
Efficiency of Energy Transfer
· At each trophic level, some energy is lost from a food chain from respiration (eg.).
· Energy remains stored in dead organisms + waste material only available to decomposers.
· Less energy available to sustain living tissue at higher levels of the food chain, so less living tissue can be kept alive.
Measuring Efficiency of Energy Transfer
· Pyramids of Biomass:
The area of the bars is proportional to the dry mass of all the organisms at that trophic level.
Collect all the organisms and put them in an oven at 80°c until all the water in them has been evaporated.
Very destructive so the wet mass is usually measured to calculate the dry mass.
· Pyramids of Energy:
Different species may release different amounts of energy per unit mass.
Burning the organisms in a calorimeter + working out how much heat energy is released per gram.
This is calculated from the temperature rise of a known mass of water.
Also very destructive.
Pyramids only take a snapshot of an ecosystem at one moment in time + population sizes fluctuate over time.
Look at the rate at which energy passes through each trophic level pyramid of energy flow. The rate of energy flow is called productivity.
At the base of the food chain, the productivity of plants is called the primary productivity.
The gross primary productivity is the rate at which plants convert light energy into chemical energy.
Energy is lost when the plant respires, less energy is available to the primary consumer the remaining energy is called the net primary
productivity (NPP).…read more
2.3.3 Manipulating Energy Transfer
· Primary Productivity is the total amount of energy fixed by photosynthesis.
Improving Primary Productivity
· By manipulating environmental factors, humans can increase NPP making energy conversion more efficient, reducing
energy loss and increasing crop yields:
Light levels can limit the rate of photosynthesis so some crops are planted early to provide a longer growing season to harvest more light,
others are grown under light banks.
Drought-resistant strains of plants have been bred for countries that experience lack of water.
Temperature can limit the speed of chemical reactions in a plant so greenhouses can provide a warmer temperature for growing plants and
Improving Secondary Productivity
· It is possible for humans to manipulate energy transfer from producer to consumer:
A young animal invests larger proportion of its energy into grown than an adult does so harvesting animals just before adulthood minimises
loss of energy from the food chain.
Steroids can be used to make animals grow quicker (illegal now).
Selective breeding has been used to produce breed with faster growth rates, increased egg production + increased milk production.…read more
· Succession is a directional change in a community of organisms over time.
How Does Succession Happen?
· The Island of Surtsey in Iceland was created by a volcanic eruption but is now home to a community of plants. Development
of such a community from bare ground is known as primary succession:
Algae + Lichens begin to live on the bare rock (PIONEER COMMUNITY).
Erosion of the rock + build up of dead organisms produces enough soil for larger plants to grow. These success the algae + lichens.
Larger plants success these smaller plants, until a final, stable community is reached (CLIMAX COMMUNITY).
· Secondary succession takes place on a previously colonised, but disturbed/damaged, habitat.…read more
2.3.5 Studying Ecosystems
· It is impossible to count all the individuals in a habitat so they decided to sample small parts of the habitat using a quadrat.
· You can collect 2 types of data with a quadrat:
Presence/Absence of each species (DISTRIBUTION).
Estimate/Count the number of individuals (ABUNDANCE).
· Often hard to count certain species so scientists use percentage cover.
· To avoid bias + to get a representative sample, randomly position the quadrats across the habitat or take samples at regular
distances across the habitat.
· You may wants to look at the changes in abundance and distribution of species as you walk up a beach for example.
· A transect is a line taken across a habitat take samples at regular intervals along the tape.
· LINE TRANSECT at regular intervals, make a note of which species is touching the tape.
· BELT TRANSECT at regular intervals, place a quadrat next to the line, studying each.…read more