23- ecosystems Flashcards
nitrogen cycle not included
What is an ecosystem?
An ecosystem is made up of all the living organisms that interact with one another in a defined area. Also the physical factors present in that region.
what factors affect an ecosystem?
All ecosystems are dynamic- they’re constantly changing. Biotic factors - living factors e.g the size of a population of a species. Abiotic factors- the non-living/ physical factors e.g amount of rainfall.
What are biotic factors, give examples
Often refer to the interactions between organisms that are in the ecosystem. These interactions include competition, either within a population or between populations. Also includes mutualism and parasitism.
Give 5 abiotic factors that effect an ecosystem
Light
Temperature
Water availability
Oxygen availability
Edaphic (soil) factors
Why does light affect an ecosystem?
light is required for photosynthesis, so in general, the greater the availability of light the greater the success of a plant species.
Plants can develop strategies to cope with different light intensities e.g areas of low light may have larger leaves, and may develop photosynthetic pigments that require less light or reproductive systems that only operate when light availability is at an optimum.
How does temperature affect an ecosystem?
Biggest effect is on enzymes controlling metabolic reactions. Plants will develop more rapidly in warmer temps, as will ectothermic animals.
Changes in temp of the ecosystem e.g due to changing seasons can tigger migration in some animal species, and hibernation in others. In some plant species it can trigger leaf fall, dormancy and flowering.`
How does water availability affect an ecosystem?
In most plant and animal populations, lack of water leads to stress, which if severe can lead to death.
Plants- lack of water causes wilt, as keeps cells turgid and therefore upright, photosynthesis needs water as well.
How does oxygen availability affect ecosystems?
in aquatic ecosystems, it is beneficial to have fast- flowing cold water as it contains high concs of oxygen. If water becomes too warm, or the flow rate is too slow, the dip in oxygen conc can lead to suffocation of the organisms.
In waterlogged soil, the air spaces between the soil particles are filled with water. This reduces the oxygen available for plants.
How do edaphic (soil) factors affect an ecosystem?
Clay- This has fine particles, easily waterlogged, and forms clumps when wet.
loam- has different sized particles, it retains water but doesn’t become waterlogged.
sandy- has coarse, well separated particles that allow free draining- sandy soil doesn’t retain water and is easily eroded.
What is biomass?
It is the mass of living material present in a particular place or in particular organisms. Can be equated to energy content.
How do you calculate the biomass at each trophic level?
Multiply the biomass present in each organism by the total number of organisms in that trophic level. This can then be represented as a pyramid of biomass. This pyramid represents the biomass present at a particular moment in time- it doesn’t take into account seasonal changes.
Why is the dry mass used to calculate biomass?
Using the mass of the fresh material present is the easiest way, however, water contents must be discounted and the presence of varying amounts of water in different organisms makes this technique very unreliable unless large samples are used.
What are the problems with using dry mass to calculate biomass?
organisms have to be killed in order to be dried. The organisms are placed in an oven at 80 degrees until all water is evaporated- identified by atleast 2 identical mass readings.
To minimise destruction of organisms, only a small sample is taken, however this sample might not be representative of the population as a whole.
What is ecological efficiency?
the efficiency with which biomass or energy is transferred from one trophic level to the next.
Why do producers only convert 1-3% of light energy into chemical energy, and hence, biomass?
- Not all solar energy available is used for photosynthesis - approximately 90% is reflected, some is transmitted through the leaf and some is of unstable wavelength.
- other factors my limit photosynthesis e.g water availability.
- a proportion of energy is lost as it is used for photosynthetic reactions.
What is the equation for net (biomass) production?
Net production = gross production - respiratory losses
Why do consumers only convert 10% of biomass into their own organic tissue?
- Not all of the biomass of an organism is eaten, e.g plant roots or animal bones aren’t consumed.
- Some energy is transferred to the environment as metabolic heat, as a result of movement and respiration.
- Some parts of an organism are eaten but are indigestible- these are egested as faeces.
- some energy is lost from the animal excretory materials e.g as urine
what is the equation for ecological efficiency?
([energy of biomass available after the transfer] / [ energy of biomass available before transfer]) X100
How can humans manipulate biomass through ecosystems?
Manipulate the environment to favour plant species that we can eat, and rear animals for food or their produce. Plants and animals are provided with the abiotic conditions that they need to thrive e.g. adequate watering and warmth. Competition from other species is removed - pesticides and herbicides - as well as the threat of predators - by creating barriers e.g. fences to exclude wild herbivores.
Why are food chains in agriculture kept to a minimum length?
minimum energy is lost as there are fewer trophic levels present than in the natural ecosystem. This ensures that as much energy as possible is transferred into biomass that can be eaten by humans.
What is decomposition?
The chemical process in which a compound is broken down into smaller molecules, or its constituent elements. Processes organic material into inorganic elements and compounds which are a more useable form, and returned to the environment.