6.3.1 ecosystems Flashcards
Ecosystem definition
a dynamic self‐sustaining system, consisting of the interactions between biotic (living) and abiotic (non‐living) factors
ecology definition
the study of ecosystems
population definition
all the members of one particular species living in a given area at one time
community definition
all the members of all the species living in a given area at one time
habitat definition
habitat is the place where a species lives
ecological niche definition
ecological niche is the role of an organism in its ecosystem
Biotic factors definition
interactions between living organisms in the ecosystem
abiotic factors definition
Non-living environmental factors, which affect the living organisms in the ecosystem
Give three examples of biotic factors
Interspecific competition (two different species)
Carnivory/predation
Herbivory/grazing
Give three examples of abiotic factors
Temperature
Water availability
Light intensity
what is the rule of energy?
Energy can not be created or destroyed, it can be trasnfered and converted from one form of energy to antoher
what is biomass?
dry mass of organisms, i.e. the mass of body tissues remaining once all water has been removed.
what is biomass in a stable environment?
created by autotrophs/producers via photosynthesis
initially transferred by Herbivory/grazing
transferred from dead organisms and waste to decomposers
lost from organisms’ bodies during respiration
how to measure biomass of an organism
- Collect a representative sample of (dead) organisms;
- Dry them in an oven at 80°C until constant mass is reached, i.e. regularly check the mass and continue the drying process until no further loss of mass is detected;
- Find the mass of this sample and carry out a multiplication in order to estimate the dry mass of all organisms in the trophic level.
How to we measure the energy content of an organism?
- Collect a representative sample of (dead) organisms;
- Dry them in an oven at 80°C until constant mass is reached;
- Burn the dried sample in oxygen, within a bomb calorimeter;
- Measure the temperature increase in the tank of water within the bomb calorimeter;
- Use the specific heat capacity of water to calculate the amount of energy that musthave been transferred from the sample to the water during combustion, in order to heat up the water by the recorded amount;
[Energy = SHC x mass of H2O x Temperature increase - Carry out a multiplication (by population size) to estimate the total energy content of all the organisms at the relevant trophic level.
what is the SHC of water?
4.2 in biology
trophic level definition
specific step in a food chain; the level in the food chain at which an organism feeds
Autotroph definition
an organism that is a producer, able to fix inorganic carbon to produce organic compounds
Photoautotroph definition
an organism that is a producer, converting light energy to chemical energy via photosynthesis and hence fixing inorganic carbon to produce organic compounds.
I.e plants
Chemoautotroph definition
an organism that is a producer, carrying out redox reactions that transfer chemical energy, and hence fixing inorganic carbon to produce organic compounds
I.e some Archaeans
Heterotroph definition
an organism that is a consumer or decomposer, feeding on the bodies of other organisms in order to obtain chemical energy in ready‐made organic compound
i.e animals and fungi
Producer definition
an organism with autotrophic nutrition, usually photosynthesis; fixes inorganic carbon to synthesise organic compounds.
first trophic level
Consumer definition
an organism with heterotrophic nutrition, which must feed on the bodies of other organisms in order to obtain chemical energy in ready‐made organiccompounds
second trophic level
Herbivore definition
a primary consumer
only feeds at the second trophic level
feeds directly on the producers
Carnivore/predator definition
secondary, tertiary or quaternary consumer
third trophic level or above
feeding on other consumers
Top carnivore/predator definition
a consumer which feeds on other consumers, but not fed upon
final step in the food chain (highest trophic level)
Omnivore definition
an organism that feeds at the 2nd AND the 3rd (or higher) trophic level (eats plants and animals)
Detritivore definition
heterotroph/consumer (usually an animal) which feed on detritus, includingdead bodies, fallen leaves or animal faeces. Detrivores do not need to hunt prey
Decomposer definition
microorganism (bacterium or fungus) which has saprotrophic nutrition: secretion of enzymes onto detritus, external digestion process, then absorption of the soluble nutrients released by digestion. Decomposers are a specialised subgroup of heterotrophs.
what do the arrows in food webs and chains represent?
the transfer both of chemical energy and of biomass
how are producers inefficient?
Some light hits bare rock, soil, concrete
Some light hits non‐photosynthetic parts of a plant
Some light is reflected off the waxy cuticle
Some light has a heating effect on leaves, leading to evaporation of water
Some light is transmitted straight through the leaves
There may be limiting factors on photosynthesis other than light intensity , such as low carbon dioxide concentration or low temperature.
There are heat losses during the reactions of photosynthesis
what are the typical units for a terrestrial (land) ecosystem?
kJ m^‐2 y^‐1
what are the typical units for an aquatic (water) ecosystem?
kJ m^‐3 y^‐1
What is the GPP?
Gross primary productivity - the light energy initially converted to chemical energy via photosynthesis
Why is GPP not unseful?
it doesn’t take into account the fact that a lot of the glucose made in photosynthesis is immediately respired, as the GPP figure includes energy which is about to be lost as heat during respiration
what is a more useful useful way to calculate the primary productitivity?
NPP = net primary productivity
What is the equation for net primary productivity
NPP = GPP – respiratory heat losses
why is NPP better than GPP?
NPP takeS into account the fact that much of the glucose made in photosynthesis is immediately respired, resulting in a loss of energy as heat
Overall what is NPP an indication of?
the amount of energy in the first trophic level
How can Primary productivity be increased?
Increase light intensity and day length - lights
Increase carbon dioxide availability - burn butane
Increase temperature - heaters
Increase water availability - irrigation
Increase soil mineral availability - fertilisers/legumes
Multiple cropping
primary productivity definition
Primary productivity (or production) is the rate of conversion of light energy to chemical energy via photosynthesis in producers
secondary productivity definition
the rate of conversion of chemical energy inconsumers’ food to chemical energy stored in consumers’ body tissues
How can secondary productivity be increased?
selectively bred/genetically modified animals
Restrict the movement of animals
Keep animals in warm
Routine antibiotic use
Feed protein‐rich food
Slaughter animals used for meat just before they reach full size
What are the reasons for losses of energy and biomass from a trophic level?
Not all the available food is eaten,
Not all food eaten can be fully digested - cellulose
Metabolic waste is excreted
heat losses during respiration
How to calculate ecological efficiency?
which two trophic levels have the lowest ecological efficinetcy
what is the %?
producers to primary consumers
4 ‐ 8%
why does producers to primary consumers have the lowest ecological efficinetcy
primary consumer may only eat a tiny proportion of the available food (catapillar and a leaf)
Primary consumers may not have cellulase so cant breakdown the cellulose from a plant
what is the % of ecological efficinecy of the higher trophic levels?
10 ‐ 12%
why does higher trophic levels have a higher ecological efficinetcy?
eat a very high proportion of the food
the meat which makes up the carnivore’s food has much higher digestibility than plant material (no cellulose)
primary succesion definition
Primary succession is a process of directional change in the species composition of an ecosystem; it begins with pioneer species colonising bare sand/rock and ends with the establishment of a stable climax community
what is the main key features of primary succesion?
no pre‐existing soil, only bare rock or sand particles
what are serial stages?
a series of predictable stages
a pioneer species to a climax community
what is a pioneer species?
The first organisms to colonise the bare rock/sand, they begin the process of succession
characteristics of pioneer species
small in size
Wind or water‐dispersed seeds
Tolerant of harsh conditions
give an example of a pioneer species
mosses and lichens
what happens to hte habtat during succession?
the species present in one seral stage modify the habitat, changing the biotic and abiotic conditions. The consequence is that the conditions then become suitable for different species to successfully colonise the habitat (which couldn’t survive previously).
what are some examples of changes to the ecosystem which occrus during succession?
Pioneer plants provide more shelter;
Roots stabilise loose rock and sand particles;
Decaying plants form humus;
Humus retains water and releases mineral ions as it further decomposes;
Humus mixed with rock particles forms new soil;
Decaying plants may release organic acids and decrease soil pH;
If legumes are present, the Rhizobium bacteria in their root nodules fix atmospheric nitrogen (N2) into ammonium (NH4+); nitrogen compounds are released into the soil when the legumes decay;
Microhabitats form as the conditions become more diverse, creating more different ecological niches in the ecosystem.
what happens to succession when the ecosystem changes?
Increasing biomass
Increasing primary productivity
Increasing biodiversity
climax community definition
stable community with high biodiversity and productivity that represents the end‐point of succession.
in a climax community what is the relationship between biotic and abiotic factors?
will be an equilibrium between biotic and abiotic factors in the ecosystem
what are the typical characteristics of a climax community?
High biomass
High productivity
High species richness and evenness
Stability
what is an example of succession?
sand dunes
what are the stages of sand dunes from pioneer to climax?
- sea holly and other xerophytes pioneer community
- mainly marram grass
- grassland community
- woodland climax community.
why is succesion in sand dunes easy to study, and how can it be studied?
walking inland from a beach, we can often see all the seral stages laid out in space: the further inland we go, the later the seral stage we are seeing
succession can be studied in this case by using a belt transect from the beach, over the dunes, through the grassland and into the woodland
deflected succession definition
Deflected succession is when human activity alters the course of (or prevents) succession in an ecosystem.
A plagioclimax is formed (false climax community)
what happens to deflected succession when human activity ceases?
the natural course of succession resumes, and the true climax community is reached
what are some examples of deflected succession?
Mowing a lawn
Agriculture
Regular, controlled burning
what is random sampling?
sample points are chosen at random so that the data generated is representative of the whole area and free of bias; this approach is suitable for uniform areas, e.g. a large field
what is opportunistic sampling?
Non-random
the ecologist selects the sample points to study based on convenience; this approach should be avoided as it creates bias and does not generate data that is representative of the whole habitat
what is systematic sampling?
Non-random
sampling along a transect
a tape measure is laid out across the habitat following the direction of a change in conditions; species touch the line are recorded (line transect approach), or quadrats are placed next to the line (belt transect approach) in order to widen the area being included; suitable for habitats that show systematic change from one side to the other
what is stratified sampling?
Non-random
if the ecosystem being studied is naturally divided into habitat areas e.g. (woodland, field, marsh) then the number of samples taken within each area should be in proportion to the size of that area, so that the data is representative for the whole ecosystem; within each area, the sample points are chosen at random.
what is the role of decomposers?
Mineral ions released
ammonification
Carbon dioxide released
forms humus
Decomposers ‘clean up’ ecosystems
Define carrying capacity
The maximum population size that an environment can support
Define nitrification:
The process by which ammonium compounds are converted into nitrites and nitrates
Define denitrification
The conversion of nitrates to nitrogen gas
Define nitrogen fixation
The incorporation of nitrogen gas into organic nitrogen containing compounds
What are the 3 ways nitrogen can be fixed?
- lightning
- fixation by microorganisms
- production of ammonia by the Haber process
Where do denitrifying bacteria get the oxygen needed for respiration?
From nitrates
In what form do plants take up nitrogen?
Nitrates
Define ammonification
The conversion of nitrogen compounds in dead organic matter or waste into ammonium compounds by decomposers
