Ecosystems Flashcards
What is an ecosystem?
An ecosystem is made up of all the living organisms that interact with one another in a defined area
Biotic factors affection ecosystems:
- Space
- Breeding partners
- Food
- Disease
Abiotic factors affecting ecosystems:
- Light
- Temperature
- Water availability
- Oxygen availability
- Soil factors
What are the different soil factors?
- Clay - fine particles, easily waterlogged, forms clumps when wet
- Loam - different sized particles, retains water, does not become waterlogged
- Sandy - coarse, well separated particles that allow free draining, soil does not retain water and is easily eroded
What is biomass?
Mass of living material present in a particular place or in a particular organism
How can biomass be measured?
- Measure the mass of fresh material present
- Water content must be discounted, so organisms need to be killed and are place in an oven until all water is evaporated
- Then mass is taken
- Therefore, only a small sample is often taken to avoid destruction of ecosystem
Why is energy transfer not 100% efficient at the producer level?
- Not all of solar energy available is used for photosynthesis
- Most of it is reflected
- Some is transmitted through the leaf
- Some is an useable wavelength
- Other factors may limit photosynthesis
- Some energy converted as it is used for photosynthetic reactions
How can net production be calculated?
gross production-respiratory losses
Why is energy transfer not 100% efficient at consumer levels?
- Not all of biomass of an organism is eaten, e.g. plant roots or animal bones
- Some energy transferred to environment as metabolic heat
- Some parts of an organism are eaten but indigestible
- Energy ‘lost’ from animal in excretory materials, such as urine
How can ecological efficient be calculated?
Energy available after the transfer/ Energy available before transfer x100
Nitrogen Cycle:
- Nitrogen fixation from mutualistic (Rhizobium) or free-living (Azotobacter) nitrogen fixing bacteria in the soil
- Nitrification by nitrifying bacteria (Nitrosomonas) oxidise ammonia into NO2-
- Nitrification by nitrifying bacteria (Nitrobacter) oxidised NO2- into NO3-
- Denitrification by denitrifying bacteria (Pseudomonas) nitrates back to nitrogen gas
- Ammonification where decomposers convert nitrogen containing compounds in dead organisms into ammonium compounds
Carbon cycle:
- Respiration
- Photosynthesis
- Combustion (fossil fuels)
- Decomposition
- Feeding
What is a decomposer?
Organism that feeds on and breaks down dead plant or animal matter, usually microscopic fungi and bacteria
Why are decomposers saprotrophs?
Because they obtain their energy from dead or waste organic material. They digest their food externally by secreting enzymes onto dead organisms and then absorb the simple molecules
What are detritivores?
- Organisms that help speed up the decay process by feeding on dead and decaying matter
- They break it down into smaller pieces of organic matter which increases the surface area for the decomposers to work on
What are the two types of succession?
- Primary succession
2. Secondary succession
What is primary succession?
Occurs on an area of land that has been newly formed or exposed as bare rock. There is no soil or organic material present to begin with
What is secondary succession?
Occurs on an area of land where soil is present, but it contains no animal or plant species, e.g. the bare earth that remains after a forest fire
What are the main seral stages of succession?
- Pioneer community
- Intermediate community
- Climax community
What is the rate of primary succession, compared to secondary succession?
Primary succession is a slow process, whereas secondary succession is a rapid process
Pioneer community:
- Colonisation of inhospitable environment by pioneer species e.g. lichen/algae
- Species arrive as seeds or spores carried by wind or sometimes by the droppings of birds
- Adaptations of pioneer species are:
1. Seeds that germinate rapidly
2. Ability to photosynthesise
3. Tolerant to extreme environments
4. Ability to fix nitrogen from atmosphere, adding mineral content to the soil in intermediate community
Intermediate community:
- Weathering of bare rock produces particles that form the basis of soil
- When organisms of pioneer species die, small organic products released into soil, known as humus
- Soil becomes able to support growth of new species of plant (secondary colonisers) as it contains minerals, such as nitrates from pioneer species
- New species also arrive as spores or seeds
- E.g. mosses
- Pioneer species can also provide a food source for consumers so few animal species will start to colonise the area
- As environment conditions improve, new species of plant arrive (tertiary colonisers)
- At each stage, the rock continues to be eroded and mass of organic matter increases, soil also becomes more nutrient rich
- This makes abiotic factors more favourable initially for small flowering plants, like grasses, later shrubs, then finally small trees
- At each seral stage, different plant and animal species are better adapted to current conditions in ecosystem
- These organisms outcompete many of the species that were previously present and become the dominant species
Climax community:
- Community is in a stable state
- Few dominant plant and animal species, best adapted to the environment
- In temperate climate, there is plenty of water so large trees will dominate
- In a sub-arctic environment, herbs or shrubs will be favoured due to low water availability
- Climax community often not the most biodiverse
Deflected succession:
- Human activities can halt the natural flow of succession
- Prevents ecosystem from reaching climax community
- Final stage formed is known as a plagioclimax
Methods of deflected succession:
- Grazing and trampling vegetation by domesticated animals results in large areas remaining as grassland
- Removing existing vegetation to plant crops, crops become the climax community
- Burning as a means of forest clearance, often leads to a rich biodiversity as it provides space and nutrient rich ash for other species to grow
