10- the nature of ecosystems Flashcards
individual
A single organism.
species
A group of organisms with similar characteristics that are all potentially capable of interbreeding to produce fertile offspring.
population
A group of organisms of the same species that live and interact in the same habitat.
community
All the different populations of species that live and interact in the same habitat.
ecosystem
The community of living organisms and the abiotic environment found in that environment.
trophic level
The position that an organism in an ecosystem occupies in a food chain.
example of trophic level
sun → grass → mouse → owl.
6 different trophic levels
- Producer (autotroph): Organisms that make their own food.
- Primary consumer (herbivore): Eat plant material.
- Secondary consumer (carnivore): Eat primary consumers.
- Tertiary consumer (carnivore): Eat secondary consumers.
- Decomposers: Fungi and bacteria that eat dead organisms and animal waste.
- Detritivores: Eat dead organisms.
pyramids of numbers
• Shows the number of organisms at each trophic level.
• In general, up a food chain, the size of individuals increases and the number decreases.
advantages of pyramids of numbers
• Easiest to measure / produce.
• Non-invasive (no organisms killed).
disadvantages of pyramids of numbers
• Can be distorted by large organisms (e.g. one oak tree at base makes it inverted).
• Numerous small consumers can unbalance the pyramid.
pyramids of biomass
• Shows the total dry mass of organisms at each trophic level.
• In general, it is pyramid shaped, as one cannot weigh more than they eat.
advantages of pyramids of biomass
Usually upright - more realistic representation of food web.
disadvantages of pyramids of biomass
• Needs more data to construct, as it is based on dry mass.
• Organisms are killed.
• Doesn’t account for the rate of production of biomass.
pyramids of energy
• Shows the amount of energy at each trophic level.
• Always upright, as energy is always lost at each trophic level.
advantages of pyramids of energy
Always upright, as energy is always lost at each trophic level - most accurate.
disadvantages of pyramids of energy
• Difficult to construct / measure.
• Many samples must be taken over a long period of time and all samples must be killed, dried, weighed and burnt to measure the energy content.
quadrats
• A square frame of a given size, randomly placed in the area being sampled.
• The species inside the quadrat are identified.
analysis used by quadrats
- individual counts
- species frequency
- percentage cover
analysis using quadrats- individual counts
The number of individuals within the quadrat.
analysis using quadrats- species frequency
• A record of the number of quadrats in which a species was found.
• e.g. If a species was found in 12 out of 40, the frequency is 30%.
analysis using quadrats- percentage cover
• Used when it is difficult to identify individual plants, like grass.
• The percentage area of the quadrat covered by the species is estimated.
types of quadrats
• point quadrat
• Provide an alternative way to measure percentage cover.
• A needle is dropped through a hole in the frame. The species it hits are recorded. The hits divided by the repeats give the percentage cover.
• e.g. If a species is hit 66 times out of 200, the percentage cover is 33%.
line transect
A line is placed across the habitat and species in contact with it are recorded.
