Ecosystems Flashcards
Define habitat
The environment in which a species usually lives
Define population
- Group of organisms of the same species
- Who live in the same area at the same time
Define community
Populations of different species living and interacting with each other
Define ecosystem
Interactions between all living organisms in an area and the surrounding abiotic environment
Define abiotic factors
Non-living factors
- e.g. temperature, pH, light levels, humidity
Define biotic factors
Living factors
- e.g. competition for food, breeding sites, disease, predators
Discuss how abiotic factors can affect the distribution of species in an ecosystem
Organisms have limits of tolerance and zones of stress
- e.g. high temperature will melt arctic ice - less hunting grounds for polar bears
Why are ecosystems defined as ‘dynamic’?
Biotic and/or abiotic factors are constantly changing
Where does most energy originate from?
The Sun
How is light energy converted to chemical energy?
By photosynthesis in green plants
Define producer
Organisms that convert light energy to chemical energy
- e.g. plants
Define consumer
Organisms that feed on other organisms
- e.g. bird, cat, fox
Define trophic level
- Position in a food chain / web
- e.g. producer, primary consumer, secondary consumer, tertiary consumer
What is meant by a food chain or food web?
- Shows feeding relationships
- By showing which organism eats which organism
- Shows the flow of energy from producer to top consumer through trophic levels
How does chemical energy flow through food chains/webs?
By feeding
What do arrows in a food chain/web represent?
Direction of energy transfer
How is energy supplied to ecosystems?
- In the form of light energy from the Sun
- Converted to chemical energy by producers (producing carbohydrates)
- Chemical energy is used by all organisms and is eventually converted to heat
Explain how energy and nutrients are transferred in ecosystems
- Energy enters ecosystems from the Sun
- Light energy is converted into chemical energy by producers
- Energy flows through food chains by means of feeding
- Nutrients are recycled within ecosystems
- Nutrients not lost but transformed into different compounds
What is biomass?
Total amount of living material in a particular place or in particular organisms
How is biomass calculated?
- ‘Dry mass’ measured - Mass of organism without any water
- Units = g m-2
What happens to biomass along food chains?
Decreases due to loss of carbon dioxide, water and other waste products e.g. urea
How does the flow of energy differ from the flow of inorganic nutrients in an ecosystem?
Chemical nutrients and energy tend to flow in the same direction for most of an ecosystem, but the main difference is that the nutrient cycle is recycled in the ecosystem while the energy flow is ultimately lost from the ecosystem to the universe at large.
What is a pyramid of biomass?
- Representation of total biomass
- At each level of a food chain
What is a pyramid of energy?
- Representation of energy lost at each level of a food chain
- Approximately 90% of energy lost at each tropic level
Define gross production
Total solar energy that plants convert to organic matter
Define net production
- Energy converted to biomass by plants
- After energy has been used for respiration
What is the equation for net production of a producer?
Net production = gross production - respiratory losses
Why do producers only convert 1-3% of light energy into biomass?
- Approximately 90% of light is reflected
- Other factors also limit photosynthesis
- Some energy lost during photosynthetic reactions
Define ecological efficiency
- Efficiency with which biomass of energy is transferred
- From one trophic level to the next
What is the equation for calculating efficiency at a consumer level?
Ecological efficiency = energy (or biomass) available after transfer / energy (or biomass) available before transfer x 100
Outline how the percentage efficiency of energy transfer between producers and herbivores can be estimated
primary consumer energy /
producer energy
× 100
Method:
- Sample of producers collected
- Sample of herbivores (primary consumers) collected
- Both samples collected from the same area
- Measure biomass
- Energy content calculated of producer and herbivore
- Using calorimeter
Outline how a bomb calorimeter can be used to calculate the energy content of a producer
- Dry mass of organic material burnt in oxygen
- Temperature rise of water measured
- Known volume of water used
- Energy calculated using equation E = m x c x ΔT
- (E = energy, m = mass of water, c = specific heat capacity, ΔT = change in temperature)
Why do most food chains/webs have at most 5 trophic levels?
- Over 90% of energy is lost at each trophic level
- Not enough energy to support more trophic levels
Animals in the highest trophic level of a food chain will often be the largest in body size but will be few in numbers. What accounts for the small numbers?
Energy losses through the food chain
How does energy loss occur between trophic levels?
- Loss of carbon dioxide, water, and other waste products e.g. urea
- Energy used for movement
- Not all parts of organism are eaten or digested
- Excreted/egested in urine and feces
- Heat loss to the surroundings
- Respiration/metabolism
How can humans maximise the efficiency of the transfer of energy up food chains from primary consumers?
- Keep animals warm
- Reduce animal movement
- Vaccinate animals
- Selective breeding for improved animals
- Slaughter just before full size
Define heterotroph
- Obtains organic molecules from other organisms
- Requires chemical energy from ingested nutrients
Define autotroph
- Synthesises own organic molecules from inorganic sources
- Photosynthesises
Define detritivore
- Heterotrophs
- Obtain organic nutrients from waste by internal digestion
Define saprotroph
- Organism that secretes enzymes on dead organic matter and absorbs the products of digestion (e.g. fungi)
- Heterotrophs
State one role of saprotrophic organisms in the ecosystem
Decomposer - breaks down organic material into inorganic material
Define decomposition
Compound is broken down into smaller molecules
Explain the role of decomposers in an ecosystem
- Feed on organic matter
- Release energy as heat, accelerating decomposition
- Recycle nutrients
- Detoxify waste
Producers extract phosphates and nitrates from soil. Outline how these ions are used in the synthesis of organic molecules
- Ions attached to carbon compounds
- Phosphates used to make DNA
- Nitrates used to make amino acids
Outline the process of nitrogen fixation
- Atmospheric nitrogen (N2) converted to ammonia (NH3)
- By nitrogen fixing bacteria
- React N2 and H+ ions to form NH3
Give two examples of nitrogen-fixing bacteria
- Azotobacter
- Lives in soil
- Rhizobium
- Lives inside root nodules of leguminous plants
- e.g peas, beans
Explain why plants and Rhizobium bacteria have a symbiotic mutualistic relationship
- Both organisms benefit
- Plant gains amino acids from Rhizobium
- Produced by fixing nitrogen gas
- Bacteria gains carbohydrates from plant
- Produced by photosynthesis
Outline the process of nitrification
- Ammonium ions (NH4+) oxidised to form nitrite ions (NO2-)
- Nitrite ions (NO2-) oxidised to form nitrate ions (NO3-)
- By nitrifying bacteria
Give examples of nitrifying bacteria
- Nitrosomonas
- Oxidises ammonium compounds into nitrites
- Nitrobacter
- Oxidises nitrites into nitrates
Why is nitrification necessary in the nitrogen cycle?
- Nitrate ions highly soluble
- Easier for plants to absorb and use
What conditions are necessary for nitrification?
- Aerobic
- Process involves oxidation reactions
Describe the process of denitrification
- Reduction of nitrates (NO3-) in soil to nitrogen gas (N2)
- By denitrifying bacteria
What conditions are necessary for denitrification?
- Anaerobic
- Nitrates used as source of energy for anaerobic respiration
Describe the process of ammonification
- Conversion of nitrogen-containing molecules in dead organisms, urine or faeces
- Into ammonium compounds
- By decomposers / saprobionts
- In form of urea / uric acid
How are nitrogen containing compounds incorporated into plants and animals?
- Amino acids
- Nucleic acids
Describe the steps that must occur for plant protein to be converted to animal protein
- Animal ingests plants
- Protein hydrolysed to amino acids
- Amino acids move into blood and cells
- Synthesis of proteins by translation
Describe the natural fluctuations in carbon dioxide levels over the year
- Decrease from May to October - rates of photosynthesis greater than respiration
- Increase from November to April - rates of respiration greater than photosynthesis
- CO2 concentrations are greater on land than in the sea
Explain what can cause atmospheric carbon dioxide levels to increase
- Respiration - CO2 released by respiration of plants, animals and decomposers
- Combustion - burning of forests/fossil fuels releases CO2 as a waste product
- Deforestation - fewer trees and plants mean less CO2 removed from atmosphere
Why does increased atmospheric carbon dioxide levels contribute to global warming?
- CO2 is greenhouse gas
- Traps thermal energy in the atmosphere
How does the amount of CO2 dissolved in oceans vary with temperature?
- Higher temperature = less CO2 dissolved
- As global warming increases, more CO2 released into atmosphere from oceans
- Creates positive feedback loop
Outline the carbon cycle
- Producers absorb carbon dioxide from air
- Producers carry out photosynthesis and make carbohydrates
- Carbon passes along food chains
- Respiration releases carbon dioxide
- Carbon dioxide released from dead matter by respiration of decomposers
- Fossils made from some dead organic matter
- Combustion of fossil fuels releases carbon dioxide into the air
- Limestone from shellfish are sinks of carbon
Outline the roles bacteria play in the carbon cycle
- Decomposition of dead organic material by saprotrophic bacteria
- Decomposition leads to CO2 release by respiration
- Photosynthetic bacteria fix CO2 in photosynthesis
Define succession
Process by which ecosystems change over time
Define primary succession
- Occurs on land that has been newly formed or exposed
- No soil or organic material present
- e.g. after volcanic eruption, glacial retreat, silt deposit
Define secondary succession
- Occurs on land where soil is present, but no plant or animal species
- e.g. after forest fire
What name is given to each step of succession?
Seral stage
What is a pioneer community?
- Colonisers of barren land
- First stage of primary succession
How do pioneer species reach barren land?
- Spores or seeds
- Carried by wind or animals
Provide common examples of pioneer species
- Lichen
- Algae
Outline the adaptations that enable pioneer species to colonise barren land
- Produce large numbers of seeds/spores
- Blown by wind to reach new land
- Seeds germinate rapidly
- Photosynthesise to produce own energy
- Tolerant to extreme environments
- Can fix nitrogen from atmosphere
- Adds to mineral content of soil
How does soil start to form?
Weathering of bare rock
How do pioneer species improve conditions for other organisms?
Release nutrients into soil when die and decompose
Define humus
Organic component of soil
Define intermediate community
Any seral stage between the pioneer community and climax community
Outline the usual intermediate stages of succession
- Pioneer species die and decompose
- Nutrients released into soil
- Mosses and fern seeds carried in by wind/animals
- More weathering and decomposition produces thicker layer of soil
- Abiotic conditions changed
- Less hostile and more suitable for organisms
- Biomass increases
- Organisms better adapted to new conditions outcompete existing species
Define climax community
- Final seral stage
- Comprised of a few dominant plant and animal species
- Community in stable state
- Little change over time
When does biodiversity reach its maximum?
- Mid-succession
- Then decreases towards climax community
- Due to few dominant species outcompeting all others
Outline the process of succession
- Pioneer species is first to colonise bare ground
- Only species adapted to extreme conditions grow and survive
- Organic material accumulates, changing the conditions
- Development of soil enables seeds of small shallow-rooted plants to establish
- Conditions improve, other plants compete and replace the existing plants
- Biodiversity increases as range of habitats increases
- Eventually stable climax community develops, dominated by trees
- Dominant species outcompetes others for light/space etc.
- Remains unchanged unless conditions in the habitat change
Describe the differences between a pioneer community and a climax community
- Pioneers arrive before climax community
- Pioneer communities subject to more succession
- Pioneer community has lower biodiversity
- Pioneer community is less stable
- Pioneer community has lower biomass
Why is animal succession slower than plant succession?
- Animals must move in from neighbouring areas
- Primary consumers require plants to eat
Define deflected succession
Stopping of succession by human activity
Define plagioclimax
Final stage of artificially stopped succession
Outline how agriculture causes deflected succession
- Grazing of crops by domesticated animals
- Large areas remain as grassland
- Removing existing vegetation to plant crops
- Crop becomes final community
- Burning to clear forests
- Provides space and nutrient-rich ash for other species to grow
How can scientists sample all stages of succession in a habitat?
Line or belt transect
Define organism distribution
Where individuals are found in an ecosystem
Define organism abundance
Total number of organisms in an ecosystem
How is distribution measured?
- Line or belt transect
- Systematic sampling
- Using quadrats
- Random sampling
Why may abundance fluctuate on a daily basis?
- Immigration and births will increase number of individuals
- Emigration and death will decrease number of individuals
How is plant abundance measured?
Using quadrats
How is estimated plant abundance calculated?
Estimated number in population = Number of individuals in sample / Area of sample
How is animal abundance measured?
Mark-release-recapture technique
Outline the mark-release-recapture technique
- Capture as many individuals as possible in sample area
- Mark/tag each individual
- Release marked animals back into sample area
- Allow time for them to redistribute
- Recapture as many individuals as possible in sample area
- Record number of marked and unmarked individuals in sample
How is the estimated population size calculated from the mark-release-recapture technique?
Estimated population = Number of individuals in 1st sample x Number of individuals in 2nd sample / Number of recaptured marked individuals
What assumptions are necessary for the mark-release-recapture technique?
- Proportion of marked to unmarked individuals in second sample same as proportion in
population as a whole - Marked individuals released are evenly distributed amongst remaining population
- No immigration or emigration
- Few deaths and births
- Method of marking is not toxic or make individual more liable to predation
- Mark/tag not lost during investigation
How is the biodiversity of a habitat calculated?
Simpson’s Index of Diversity
