B23 - Ecosystems

Question 1

What is ecology?

Answer 1

• study of relationships between organisms and the environment
• can help to understand the interdependence of living organisms

Question 2

What is an ecosystem?

Answer 2

• made up of all the living organisms that interact with one another in a defined area (also includes the physical factors in that region)
• boundaries of a particular ecosystem being studied are defined by the person/team carrying out the study

Question 3

What factors affect ecosystems?

Answer 3

• biotic:
  
  • living factors
  • e.g. presence of shrews, hedgehogs, size of population
  • competition between two animal populations
• abiotic:
  
  • non-living/physical factors
  • e.g. amount of rainfall, yearly temperature range of the ecosystem

Question 4

What are biotic factors?

Answer 4

• interactions between organisms that are living
• involves competition (within/between) for food, territory, breeding partners

Question 5

What are abiotic factors?

Answer 5

• light:
  
  • needed for photosynthesis
  • the greater the light availability, the greater the success of a plant species
  • adaptations include larger leaves in areas with low light intensity
• temperature:
  
  • it’s greatest effect is on the enzymes of controlling metabolic reactions
  • plants develop more rapidly in warmer temps.
  • changing temp. of an ecosystem can trigger migration in some animal species and hibernation in others
• water availability:
  
  • lack of water can lead to water stress which will lead to death
  • it will also cause most plants to wilt as water is required for turgidity and photosynthesis
• oxygen availability:
  
  • aquatic ecosystems = beneficial to have fast-flowing cold water as it contains high concentrations of oxygen
  • warm water will have a slower flow rate and a drop in O2 conc will cause the organisms to suffocate
  • waterlogged soil, spaces between soil particles are filled with water
• edaphic (soil) factors:
  
  • clay = fine particles, easily waterlogged, forms clumps when wet
  • loam = different-sized particles, retains water but does not become waterlogged
  • sandy = coarse, well-separated particles that allow free draining (does not retain water and is easily eroded)

Question 6

What is biomass transfer?

Answer 6

-

Question 7

What are trophic levels?

Answer 7

• each stage in a food chain is a trophic level
• the first trophic level is always a producer
  
  • converts light energy into chemical energy by photosynthesis
• the next one is always consumers
  
  • they obtain energy by feeding on other organisms
• the following trophic levels are labelled successively
• they usually go up to quaternary consumer as there is not enough biomass to support the following organisms

Question 8

What are decomposers?

Answer 8

• they break down dead organisms releasing nutrients back into the ecosystem

Question 9

What is biomass?

Answer 9

• mass of living material present in a particular/organisms
• biomass = biomass of each organisms x total no. of organisms
• this represents biomass at a particular moment in time (does not take into account seasonal changes)
  
  • easiest method = fresh material present
  • most accurate = dry mass (killing organisms and placing them in the oven at 80 degrees C)
  • to minimise destruction of organisms, only a small sample is taken
• units = g m -2 / g m -3

Question 10

What is the efficiency of biomass and energy transfer between trophic levels?

Answer 10

• biomass in each trophic level is almost always less than the one below
• when animals eat, only a small proportion of the food is converted into new tissue
• energy available for each trophic level is kJ m-2 yr-1
• efficiency with which biomass is transferred from one trophic level to another is ecological efficiency

Question 11

What is efficiency at producer level?

Answer 11

• producers only convert 1-3% of the sunlight into chemical energy (biomass)
  
  • not all of the solar energy available is used for photosynthesis (90%)
  • water availability may limit photosynthesis
  • proportion of energy is lost as it is used for photosynthetic reactions
• net production = gross production - respiratory losses
• producer = primary production
• consumer = secondary production

Question 12

What is the efficiency at consumer levels?

Answer 12

• can convert at most 10% of the biomass in their food to their own organic tissue
  
  • not all biomass of organism is eaten
  • some energy is transferred to the environment as metabolic heat (movement and respiration)
  • some parts are eaten but indigestible
  • some energy is lost in excretory materials (urine)

Question 13

What is ecological efficiency?

Answer 13

• (energy available after transfer / energy available before transfer) x 100

Question 14

How do human activities manipulate biomass through ecosystems?

Answer 14

• agriculture
  
  • involves manipulating environment to favour plant species that we eat/to rear animals for food or produce
  • plants/animals are provided with optimal abiotic conditions needed to thrive
  • competition from other species is removed (pesticides) as well as the threat of predators
• natural ecosystem:
  
  • humans occupy second, third, or fourth trophic level
  • only small proportion of energy is passed down at each trophic level
• agriculture creates simple food chains
  
  • farming animals = only three trophic levels (animal feed, livestock, humans)
  • cultivating plants = two trophic levels (crops, humans) so minimum energy is lost as there are fewer trophic levels present

Question 15

Where is energy from in the ecosystem?

Answer 15

• linear flow through ecosystem
• enters from the Sun and transferred to the atmosphere as heat
• nutrients constantly have to be recycled through ecosystems in order for plants and animals to grow
  
  • used up by living organisms and there is no large external source supplying this

Question 16

What is decomposition?

Answer 16

• chemical process in which a compound is broken down into smaller molecules
• an essential element may not be able to be used directly so it is processed into inorganic elements/compounds instead
  
  • e.g. carbon, nitrogen

Question 17

What are decomposers?

Answer 17

• organisms that feed on/break down dead plant and animal matter
  
  • organic compounds into inorganic ones (nutrients)
  • this allows for the nutrients to be used by the photosynthetic producers
• e.g. microscopic fungi, bacteria
• they are saprotrophs (obtain energy from dead/waste organic material)
  
  • digest their food externally by secreting enzymes onto the dead matter
  • these break down the complex organic molecules and the decomposers absorb them
  • they then release the inorganic compounds back into the environment

Question 18

What are detritivores?

Answer 18

• help speed up decomposition by feeding on detritus (dead/decaying material)
  
  • break them down into smaller pieces of organic material
  • increases SA for decomposers to feed on
• e.g. woodlice, earthworms
• they perform internal digestion

Question 19

What is the role of nitrogen?

Answer 19

• essential for the production of amino acids/nucleic acids
  
  • animals obtain nitrogen from the food they eat
  • plants need to take in nitrogen from the environment
• nitrogen is abundant in the atmosphere but cannot be taken up by plants in this form
  
  • it needs to be combined with hydrogen/oxygen
  • bacteria can help with this process

Question 20

What is nitrogen fixation?

Answer 20

• nitrogen-fixing bacteria (Azotobacter/Rhizobium) contain nitrogenase
  
  • combines N2 with H2 to produce NH3 (ammonia)
• Azotobacter
  
  • free-living soil bacterium
• Rhizobium
  
  • lives inside root nodules (growths on roots of leguminous plants)
• bacteria have symbiotic (interaction) mutualistic relationship with the plant
  
  • Rhizobium = plant gains amino acids which are produced by fixing N2 in the air into ammonia
  • bacteria gain carbohydrates produced by the plant during photosynthesis

Question 21

What is nitrification?

Answer 21

• ammonium compounds converted into nitrogen-containing molecules (can be used by plants)
• nitrifying bacteria are involved (oxidation reaction)
• 1) nitrifying bacteria (Nitrosominas) oxidises ammonium compounds into nitrites (NO2-)
• 2) Nitrobacter oxidises nitrites into nitrates (NO3-)
  
  • nitrate ions are highly soluble and can enter plants

Question 22

What is denitrification?

Answer 22

• (absence of O2) denitrifying bacteria converts the nitrates in the soil back into N2
• only takes place under anaerobic conditions
  
  • bacteria use nitrates as a source of energy for respiration and N2 is released

Question 23

What is ammonification?

Answer 23

• where decomposers convert nitrogen-containing molecules in dead organisms, faeces, and urine into ammonium compounds

Question 24

What is the role of carbon?

Answer 24

• component of major organic molecules present in living organisms (fats, carbs, proteins)
• the main source for land-living organisms is the atmosphere
  
  • there is a constant cycling of carbon between the atmosphere, land, and living organisms

Question 25

What is the carbon cycle?

Answer 25

- CO2 in atmosphere/dissolved in seas and oceans provides the major source of *inorganic* carbon for plants - producers (photosynthesis): - CO2 is converted into to small carbon-containing *organic* molecules - carbon is used in the production of *macromolecules* such as carbs, proteins, lipids - consumers (feeding): - macromolecules are passed from producers into primary consumers - subsequently passed up the food chain when consumer itself is consumed - decomposers (death): - decomposition releases the carbon compounds in dead organisms - carbon is released as CO2 when the decomposers respire - if dead organic matter accumulates in areas where decomposers are not present, (bottom of ocean/bogs) they become trapped - this then forms *fossil fuels*

Question 26

Why do CO2 levels fluctuate?

Answer 26

- photosynthesis only takes place in the light (day) - this removes CO2 from the atmosphere - respiration is carried out by all living organisms throughout the day and night - this releases CO2 at a relatively constant rate - so CO2 levels are higher at night than during the day - localised CO2 levels also fluctuate seasonally - lower in summer than in winter - combustion of fossil fuels = released CO2 back into atmosphere - deforestation = removed significant quantities of photosynthesising biomass from Earth (less CO2 removed) - higher the temp. = less gas dissolved - more CO2 is released into the atmosphere - samples are taken from the depths of glaciers to gain information about how the atmosphere has changed over time - bubbles reflect the composition of the atmosphere at that point in time

Question 27

What does a dynamic ecosystem mean?

Answer 27

- ecosystem is constantly changing - one process by which they change is succession

Question 28

What is succession?

Answer 28

- it is a process by which ecosystems change over time - this occurs as a result of changes to the environment (abiotic factors, causing the plant/animal species to change)

Question 29

What are the two types of succession?

Answer 29

- primary succession: - occurs on an area of land that has been *newly formed* or exposed to *bare rock* - there is *no soil* or organic material present to begin with - secondary succession: - occurs on areas of land where *soil is present*, but it contains *no plant or animal species* e.g. bare earth that remains after a forest fire

Question 30

When does primary succession take place?

Answer 30

- volcanic eruptions: - (depositing lava) and when this cools and solidifies, *igneous rock* is created - sand is blown by the wind/deposited by the sea to create *new sand dunes* - silt/mud are deposited at river estuaries (where rivers meet the mouth of the sea) - glaciers retreat depositing rubble and *exposing rock*

Question 31

What are the stages of succession?

Answer 31

- each stage is called *seral* stage (key species that change abiotic factors can be identified at each stage) - main seral stage are pioneer, intermediate, and climax communities - move from hostile conditions —> less hostile - low species diversity —> high species diversity - instability —> stability Stages: - (1) start with barren land and through primary succession (slow process) change to pioneer community colonisers (e.g. lichens) - (2) through primary succession, this changes into intermediate community - consists of secondary colonisers (e.g. mosses), tertiary colonisers (e.g. grasses) and scrubland (shrubs and small trees) - (3) secondary succession (rapid process) of intermediate community can lead to land altered e.g. due to a fire, disease, grazing and agriculture - (4) then through primary succession of intermediate community, this changes into climax community (dominant species e.g. woodland) - (5) secondary succession of climax community can lead to land altered and secondary succession of land altered can lead to recolonisation

Question 32

What is a pioneer community?

Answer 32

- primary succession occurs through colonisation of inhospitable environment through pioneer species - species arrive as spores or seeds deposited by wind from nearby land/through bird droppings - this represents the first seral stage - e.g. algae, lichen

Question 33

What are the adaptations of pioneer species?

Answer 33

- ability to produce large quantities of seeds and spores - blown by the wind and deposited on the new land - seeds that germinate rapidly - ability to photosynthesise to produce own energy - light, rainfall and air (and so CO2) are often only abiotic factors present - tolerance to extreme environments - ability to fix nitrogen from the atmosphere (adds to mineral content of soil)

Question 34

What is the distribution of organisms?

Answer 34

- where individual organisms are found within an ecosystem and is usually uneven throughout the ecosystem - they are usually found where abiotic/biotic factors favour them (high survival rates due to availability of resources and low pressure/predation)

Question 35

How can you measure distribution of organisms?

Answer 35

- line transect: laying a line/surveyor's tape along the ground and taking samples at *regular intervals* - belt transect: two parallel are marked and samples are taken of the are *between* these specified points - both are forms of systematic sampling and a type of non-random sampling

Question 36

What is systematic sampling?

Answer 36

- different areas within an overall habitat are identified, then sampled separately - has an advantage over random sampling since it allows to study how different *abiotic factors* in different areas affect the *distribution* of the species - e.g. how plant species change as you move inland from the sea - this is useful to study successional changes that take place along a series of sand dunes

Question 37

What is the abundance of organisms?

Answer 37

- the number of individuals of a species present in an area at any given time - may fluctuate daily through - immigration/births = increase the no. of individuals - emigration/death = decrease the no. of individuals

Question 38

How to measure populations?

Answer 38

- a group of similar organisms living in a given area at a given time - can rarely be counted accurately since some animals can elude capture, might be too time-consuming to capture all members of the population, counting process could damage the environment etc. - to increase accuracy of a sample, increase sample size since the greater the number of individuals studied, the lower the probability of chance influencing the results - random sampling = reduce the effects of sampling bias

Question 39

How to measure plant abundance?

Answer 39

- section an area 10mx10m - make co-ordinates and use a random co ordinate generator to place a quadrat - count the number of individual plants contained within the quadrat and use the formula: estimated number of populations (m^-2) = number of individuals in sample / area of sample (m^2)

Question 40

How to measure animal abundance?

Answer 40

- use the capture-mark-release-recapture technique : (1) capture as many individuals as possible in a sample area (2) mark/tag each individual (3) release marked animals back into sample area and allow time for them to redistribute themselves throughout the habitat (4) recapture as many individuals as possible in the original sample area (5) record number of marked and unmarked individuals present in the sample (release all individuals back into their habitat) (6) use the Lincoln index to estimate the population size : estimated population size = (no. of individuals in 1st sample x no. of individuals in 2nd sample) / number of recaptured marked individuals

Question 41

How can you calculate the biodiversity in a habitat?

Answer 41

- using Simpson's index of Diversity: - D = diversity index - N = total number of organisms in the ecosystem - n = number of individuals of each species ** D = 1 - (Σ (n/N)^2 ) ** - 0 = no biodiversity - 1 = infinite biodiversity (the higher the value, the more diverse the habitat)

Question 42

What is the intermediate community?

Answer 42

- where over time particles of bare rock are produced but cannot support other species on its own - so organic component (*humus*) is released into the soil, when organisms of the pioneer species die and decompose - this helps to support the growth of new plant species (*secondary colonisers*) = contains minerals like nitrates and can retain water - secondary colonisers = spores/seeds - e.g. mosses - ** pioneer species can also provide a food source for consumers so some animal species can colonise the area ** - as the rock erodes, the mass of organic matter increases - when organisms decompose, they provide a deeper and a more nutrient-rich soil - this makes abiotic conditions more favourable for small flowering plants

Question 43

What are tertiary colonisers (intermediate community)?

Answer 43

- new species of plant that arrive due to improved environmental conditions - e.g. ferns (waxy cuticle to protect from water loss) - these species can survive in conditions without an abundance of water (need to obtain most of water/mineral salts from the soil)

Question 44

How are organisms at each seral stage different?

Answer 44

- different plant and animal species are better adapted to current conditions in ecosystem - they outcompete the previously present species and become the *dominant* species - these species are the most abundant species by mass in the ecosystem at a given time

Question 45

What is the climax community?

Answer 45

- final seral stage - where the community reaches a *stable state*, so there’s very little change over time - normally few dominant plant/animal species - species present depends on the climate of the ecosystem - temperate = mild temps., plenty of water (large trees) - sub-arctic = low temps./water availability (herbs/shrubs) - due to the dominant species (outcompete pioneer and other species), biodiversity is often quite low at this stage - it reaches a peak in *mid-succession*

Question 46

What is animal succession?

Answer 46

- primary consumers = insects, worms - they are the first to colonise an area as they consume and shelter in the mosses/lichens - ** a slower process than plant succession as the animal species need to move themselves (especially if the ‘new land’ is geographically isolated ** - secondary consumers = arrive once a suitable food source has been established - existing plant cover provides them with suitable habitats - these species also move in from *neighbouring areas* - eventually larger organisms like mammals/reptiles colonise the area when *biotic* factors are favourable

Question 47

What is deflected succession?

Answer 47

- where human activity halts the natural flow of succession and prevents the ecosystem from reaching a climax community - *plagioclimax* = final stage formed when succession is stopped artificially - ** extra **: - it is an important conservation technique - helps to ensure the survival of certain species by preserving their habitat in its current form (preventing it from reaching its final stage) - *ecological land management* helps to prevent further succession from occurring

Question 48

What factors cause deflected succession?

Answer 48

- grazing/tramp,ing of vegetation by domesticated animals - removal of existing vegetation (shrub land) to plant crops (final community) - burning as a means of forest clearance - increases biodiversity and allows other species to grow (by burning the already existing species/organisms)