23 - Ecosystems Flashcards
What is ecology?
The study of interactions between organisms and their environment
What is a producer?
An organism that makes its own energy and biomass using sunlight
What is a habitat?
An area which a population of organisms lives in
What is a niche?
The part of a habitat which an organism is best suited to
What is an environment?
All the conditions that surround a living organism
What is a consumer?
Organism which gets its biomass from producers or other consumers by eating them
What is a community?
All the living organisms in a habitat
What is a trophic level?
The level at which an organism feeds in a food chain
What is a detritivore?
An organism which consumes dead or decaying matter
What is a decomposer?
An organism which breaks down organic matter
What is an autotroph?
An organism which produces its own biomass
What is an abiotic factor?
A non-living factor which affects organisms
What is a biotic factor?
A living factor which affects organisms
What are heterotrophs?
Organisms which get their biomass by consuming organisms from other trophic levels
What is a population?
All the organisms of one species living in a habitat at one time
What is a microhabitat?
A small part of a habitat with specific conditions
What is an ecosystem?
All living and non-living organisms in a habitat and their interactions
Can abiotic and biotic factors affect each other?
Yes- each can affect the other
What are the 3 types of change which can affect population size?
- Cyclic changes 2. Directional changes (non-cyclic and go in 1 direction) 3. Unpredictable changes (no rhythm or constant direction)
What are 2 examples of cyclic changes?
Tides and day length
What is an example of a directional change?
Erosion
What is an example of an unpredictable change?
Natural disaster such as a tsunami
What is constantly recycled within an ecosystem?
Matter
What is not recycled within an ecosystem and why?
Energy, as it flows through the ecosystem
Are all ecosystems the same size?
No- they can be as small as a bacterial colony or be the whole Earth
What are 5 examples of abiotic factors?
- Light 2. Water availability 3. Soil type 4. Oxygen availability 5. Temperature
What are the 3 main types of soil?
- Clay 2. Loam 3. Sandy
How would you quantitatively represent a food chain?
Use a pyramid of number
What is a drawback of pyramids of number?
They only give an accurate impression of the flow of energy if the organisms are of a similar size
What is a drawback of using a pyramid of biomass?
As organisms have to be killed and dried to construct one, the sample size tends to be small
What type of biomass is used in a pyramid of biomass and why?
Dry mass as fresh mass is unreliable and varies
A pyramid of biomass is always what shape?
A pyramid
How do you calculate ecological efficiency?
(Biomass of primary consumer/Biomass of producer) x 100
What is productivity?
The rate at which energy passes through each trophic level
What is gross primary productivity?
The rate at which plants convert light energy to chemical energy
What (roughly) is this planet’s gross primary productivity?
Around 8%
What are 3 reasons gross primary productivity is less than 100%?
- Only 2/3 of glucose is used to respire 2. Only 40% of light energy enters the light reaction for photosynthesis 3. Only half of light energy is used for glucose production
How do you calculate net production?
Net production = Gross production - Respiratory losses
What is net production?
The amount of organic matter remaining after respiration
What are 7 ways of increasing net production?
- Increase light availability 2. Ensure ideal temperature 3. Use insecticides 4. Use fungicides 5. Ensure maximum nutrient availability 6. Use herbicides 7. Use irrigation/drought resistant strains
What is biomass?
The amount of living material present in a particular place or within organisms
What units is biomass measured in?
Grams per metre squared (on land) or per metre cubed (in water)
What is ecological efficiency?
The efficiency at which biomass or energy is transferred between one trophic level and the next
What is nearly always true about biomass and trophic levels?
Increasing trophic levels generally see a decrease in biomass
What are 4 reasons consumers do not convert all the biomass from their food into their own organic tissue?
- Not all biomass of an organism is eaten (i.e. bones) 2. Some energy transferred to environment as metabolic heat due to movement and respiration 3. Some energy lost via excretory materials 4. Some parts of an organism eaten but indigestible
What are 4 ways humans can manipulate biomass transfer in agriculture?
- Create very simple food chains 2. Keep abiotic factors ideal 3. Minimise interspecific competition 4. Remove threat of predators
What 2 things are the most common decomposers?
Microscopic fungi and bacteria
What is saprobiotic nutrition?
Obtaining nutrients from dead organic matter using extracellular digestion.
What do decomposers release back into the environment?
Stored inorganic compounds and elements
How does saprobiotic nutrition work?
The extracellular enzymes break down complex organic molecules into simpler, soluble ones which the decomposer then absorbs
What is the primary difference between detritivores and decomposers?
Decomposers digest using extracellular enzymes, detritivores perform internal digestion
What are 2 examples of detritivores?
Woodlice and earthworms
What is detritus?
Dead and decaying organic matter
What 2 classes of organic molecules have nitrogen as an essential component?
Amino acids and nucleic acids
What is the chemical formula of a nitrite ion?
NO₂⁻
What is the chemical formula of a nitrate ion?
NO₃⁻
What is the chemical formula of an ammonium ion?
NH₄⁺
Where do animals get their nitrogen from?
Their diet
Can plants uptake nitrogen directly from the atmosphere?
No
What 2 elements is nitrogen combined with for use by plants and animals?
Oxygen and hydrogen
What organisms allow plants to take up nitrogen?
Bacteria in the soil
Where do Rhizobium live?
In root nodules of leguminous plants
Where do Azotobacter live?
Free living in the soil
What are 3 examples of leguminous plants?
- Peas 2. Beans 3. Clover
How do plants benefit from their symbiotic relationship with Rhizobium?
Get nitrogen for amino acids in the form of ammonia
How do Rhizobium benefit from their symbiotic relationship with plants?
Gain carbohydrates from the plant for use as an energy source
What are 2 examples of nitrogen-fixing bacteria?
- Rhizobium 2. Azotobacter
What enzyme do nitrogen-fixing bacteria use?
Nitrogenase
What is nitrogen fixation?
Where bacteria contain the enzyme nitrogenase which combines atmospheric nitrogen with hydrogen to form ammonia
What is nitrification?
Conversion of ammonium compounds in the soil to nitrogen-containing molecules such as nitrates and nitrites
Where do nitrifying bacteria live?
Freely in the soil
What are 2 examples of nitrifying bacteria?
- Nitrosomonas 2. Nitrobacter
How are nitrates converted back to ammonia?
Denitrifying bacteria, which use the nitrates as respiratory substrates and release nitrogen
In what type of soil would more denitrification occur and why?
Waterlogged or otherwise anoxygenic soil due to the greater presence of denitrifying bacteria
What is a commercial example of nitrogen fixation?
Haber process
What is ammonification?
Conversion of nitrogen-containing compounds in dead organisms back into ammonia
What type of organisms do ammonification?
Saprobionts
Why do many plants have a symbiotic relationship with mycorrhizal fungi?
They increase root surface area
What does Nitrosomonas do?
Oxidise ammonia to nitrite ions, in order to release energy for them to live
How is farmers plowing fields linked to nitrification?
The process is oxygenic, so farmers plow fields for aeration
What does Nitrobacter do?
Oxidise nitrites to nitrate ions
How can atmospheric nitrogen be converted directly to nitrates?
Lightning causing atmospheric oxygen and nitrogen to react
What 2 enzymes are involved in ammonification?
Protease and deaminase
What type of bacteria are nitrifying bacteria?
Chemosynthetic
In what form does most nitrogen enter a plant and why?
Nitrates, as these are very soluble
Are atmospheric CO2 levels higher in the day or night?
Night
Why are atmospheric CO2 levels higher at night?
No photosynthesis taking place
Why are CO2 levels lower in summer?
More photosynthesis taking place
What are the 2 main reasons global CO2 levels have risen over the past 200 years?
Deforestation and burning fossil fuels
How do the oceans make global warming a positive feedback loop?
Higher temperatures mean less CO₂ is dissolved in the oceans, so more is released into the atmosphere
What are the two main types of succession?
Primary and secondary
What is succession?
The process in which new plants and animal populations replace old plant and animal populations over time.
What causes succession?
Changes to the abiotic factors within the environment causing the plant and animal species present to change
What is primary succession?
Succession which occurs on land where no soil or organic matter was present originally
What is secondary succession?
Succession which occurs on land where soil is present, but no plant or animal species
What would be an example of an environment where secondary succession could occur?
The bare earth left after a forest fire
What are 4 scenarios where primary succession would occur?
- Lava is deposited by volcanoes 2. Sand, blown by the wind or deposited by the sea, forming new sand dunes3. Silt and mud deposited at river estuaries 4. Glaciers retreat, depositing rubble and exposing bare rock
What are the steps of succession known as?
Seral stages
What are the 3 main seral stages? (in order)
- Pioneer community 2. Intermediate community 3. Climax community
What types of conditions, stability and species are present during the first seral stages?
Instability, harsh conditions, low species diversity
What types of conditions, stability and species are present during the later seral stages?
Greater stability, greater species diversity, less harsh conditions
What are 2 examples of pioneer species?
Algae and lichen
What species would be present during the pioneer community?
Pioneer species (colonisers)
What are 5 adaptations of pioneer species?
- Ability to produce large amounts of seeds or spores 2. Tolerance to extreme environments 3. Ability to fix atmospheric nitrogen to add nutrients to soil 4. Ability to photosynthesise 5. Rapidly germinating seeds
What are 2 methods by which pioneer species can be spread to an inhospitable environment?
- Spores or seeds carried by the wind from nearby landmasses 2. In bird or animal droppings
What are 4 things which might alter the land of a habitat in succession?
- Fire 2. Disease 3. Agriculture 4. Grazing
What happens in terms of succession after the land is altered?
Recolonisation
What is humus?
The organic component of soil
How is soil produced during primary succession?
Weathering of the rock produces the particles that form the basis of the soil, and when pioneer species die they release humus into the soil
How and when do secondary colonisers arrive?
Via spores or seeds as soon as the soil contains enough nutrients
What is an example of a secondary coloniser?
Moss
When do tertiary colonisers arrive?
When environmental conditions improve enough
What is a feature of tertiary colonisers?
They all have waxy cuticles, so can survive without an abundance of water
What is an example of a tertiary coloniser?
Ferns
Mass of what increases with each seral stage?
Organic matter
How much change occurs in a climax community?
Very little over time
What determines what species make up a climax community?
The climate
What part of the succession process tends to have the most biodiversity?
The intermediate community
Do animals also undergo succession?
Yes they do undergo succession in a similar way to plants
What is a plagioclimax community?
One formed when succession is stopped artificially
What are 3 ways in which plagioclimax occurs?
- Grazing and trampling of vegetation by domesticated animals 2. Removing existing vegetation to plant crops 3. Burning as a result of forest clearance
What is the abundance of organisms in an environment?
The number of individuals of a species present in an area at a given time
What 2 things increase the abundance of organisms in an environment?
Immigration and births
What 2 things decrease the abundance of organisms in an environment?
Emigration and deaths
What methods are used to measure distribution of species?
Line or belt transect
What type of sampling are line and belt transects?
Systematic
How do organisms tend to be distributed within a habitat?
Where biotic and abiotic factors favour them
Given that transects cannot be used on animals, what method tends to be used to measure their abundance?
Capture-mark-capture-release
What method is used to numerically measure biodiversity?
Simpson’s Index of Diversity
What are the 6 steps of capture-mark-capture-release?
- Capture as many individuals as possible in a sample area 2. Mark or tag each individual 3. Release marked animals and give them time to reintegrate into the environment 4. Recapture as many as possible in sample area 5. Record number of marked and unmarked animals in sample 6. Use Lincoln index to measure population size
