ecosystem Flashcards
1
Q
What is an ecosystem?
A
All of the living organisms that interact with one another in a defined area, and also the physical factors present in that region • e.g. rock pool, large tree, playing field, or a particular stretch of river
2
Q
What are the 2 types of factors
that affect ecosystems?
A
Biotic and abiotic factors
3
Q
What are biotic factors?
A
The interactions between organisms that are living, or have once lived. Often involves competition, either within a population or between different populations, e.f. for food, space and breeding partners • Producers: Plants (and some photosynthetic bacteria), which supply chemical energy to all other organisms • Consumers: Primary consumers are herbivores which feed on plants, and which are eaten by carnivorous secondary consumers which are eaten by carnivorous tertiary consumers • Decomposers: e.g. Bacteria, fungi and some animals, feed on waste material or dead organisms
4
Q
What are abiotic factors?
A
The non-living or physical factors • Light • Temperature • Water availability • Oxygen availability • Edaphic (soil) factors
5
Q
Describe light as an abiotic
factor
A
In general the greater the availability of light, the greater the success of a plant species • Plants develop strategies to cope with different light intensities • In areas of low light they may have larger leaves • They may also develop photosynthetic pigments that require less light • They may have reproductive systems that only operate when light availability is at an optimum
6
Q
Describe temperature as an
abiotic factor
A
The greatest effect of temperature is on the enzymes controlling metabolic reactions • Plants and ectothermic animals will develop more rapidly in warmer temperatures • Changes in the temperature of an ecosystem (e.g. changing seasons), can trigger migration or hibernation of animal species, and leaf-fall, dormancy or flowering for plant species
7
Q
Describe water availability as
an abiotic factor
A
In most plant and animal populations, a lack of water leads to water stress, which, if severe, will lead to death • A lack of water will cause most plants to wilt as water is required to keep cells turgid and so keep the plant upright • Water is also required for photosynthesis
8
Q
Describe oxygen availability as
an abiotic factor
A
• In aquatic ecosystems, it is beneficial to have fast-flowing cold water as it contains high concentrations of oxygen • If water becomes too warm or the flow rate too slow, the resulting drop in oxygen concentration can lead to the suffocation of aquatic organisms • In waterlogged soil, the air spaces between the soil particles are filled with water, which reduces the oxygen available for plants
9
Q
Describe edaphic (soil) factors as abiotic factors
A
Different soil types have different particle sizes which affect the organisms that are able to survive: • Clay: fine particles, easily waterlogged and forms clumps when wet • Loam: different-size particles, retains water but doesn’t become waterlogged • Sandy: coarse, well-separated particles that allow free draining, doesn’t retain water and is easily eroded
10
Q
What is a trophic level?
A
The level at which an organism feeds in a food chain • Producers • Primary consumers • Secondary consumers • Tertiary consumers
11
Q
What is biomass?
A
The mass of living material present in a particular place or in particular organisms • Important measure in the study of food chains and webs, as it can be equated to energy content Biomass at trophic level = biomass in each organism x total number of organisms in trophic level • This represents the biomass present at a particular moment in time and does not take into account seasonal changes
12
Q
How is biomass measured?
A
By calculating the ‘dry mass’ of organisms present • Organisms have to be killed in order to be dried • Organisms are placed in an oven at 80°C until all the water has evaporated (2 identical mass readings) • Only a small sample is taken to minimise the destruction of organisms, but this may not be representative • Measured in grams per square metre (g m-2) for areas of land, and grams per cubic metre (g m-3) for areas of water
13
Q
Why does biomass decrease
as you move up trophic levels?
A
• Biomass consists of all the cells and tissues of the organisms present, including the carbohydrates and other carbon compounds • As carbon compounds are a store of energy, biomass can be equated to energy content • When animals eat, on a small proportion of the food they ingest is converted into new tissue • It is only this part of the biomass (and hence energy) that is available for the next trophic level to eat
14
Q
How is energy at trophic levels
measured?
A
Kiljoules per metre squared per year (kJ m-2 yr-1) • This allows for changes in photosynthetic production and consumer feeding patterns throughout the year
15
Q
What is ecological efficiency?
A
The efficiency with which biomass or energy is transferred from one trophic level to the next Biomass transferred x 100 Biomass intake
16
Q
Describe efficiency at producer
level
A
Producers only convert 1-3% of solar energy they receive into chemical energy and hence biomass • Not all of the solar energy available is used for photosynthesis - 90% is reflected, some is transmitted through the leaf, and some is of unusable wavelength • Other factors limit photosynthesis • A proportion of the energy is used as it used for photosynthetic reactions
17
Q
What is net production?
A
Net production = gross production - respiratory losses • The total solar energy that plants convert to organic matter is gross production • Plants use 20-50% of this energy in respiration • The rest is converted into biomass
18
Q
Describe efficiency at
consumer levels
A
Consumers convert at most 10% of the biomass in their food into their own organic tissue • Not all of the biomass of an organism is eaten e.g. plant roots and animal bones may not be consumed • Some energy is transferred to the environment as metabolic heat as a result of movement and respiration • Some parts of an organism are eaten but are indigestible - these are digested as faeces • Some energy is lost from the animal in excretory materials e.g. urine
19
Q
How do human activities
manipulate biomass through
ecosystems?
A
Agriculture involves planting species that we can eat (crops), and rearing animals for their food or produce • Plants and animals get the abiotic conditions they need to thrive e.g. watering, greenhouse use and stabling animals • Competition from other species is removed (pesticides) as well of the threat of predators (fences) • Agriculture creates very simple food chains, so the minimum energy is lost since there are fewer trophic levels than in the natural ecosystem • This ensures that as much energy as possible is transferred in biomass that can be eaten by humans
20
Q
What is decomposition?
A
A chemical process in which a compound is broken down into smaller molecules, or its constituent elements • Organic material must be processed into inorganic elements and compounds, which are a more usable form, and returned to the environment
21
Q
What is a decomposer?
A
An organism that feeds on and breaks down dead plant or animal matter, turning organic compounds into inorganic ones (nutrients) available to photosynthetic producers in the ecosystem. • Primarily microscopic fungi and bacteria, but also include large fungi e.g. toadstools
22
Q
Why are decomposers
saprotrophs?
A
They obtain their energy from dead
or waste organic material
(saprobiotic nutrition)
23
Q
How do decomposers digest
their food?
A
Externally by secreting enzymes onto dead organisms or organic waste matter • The enzymes breakdown complex organic molecules into simpler soluble molecules • The decomposers then absorb these molecules • Through this process, decomposers release stored inorganic compounds and elements back into the environment
24
Q
What are detritivores?
A
Another class of organism involved in decomposition • They help to speed up the decay process by feeding on detritus (dead and decaying material) • They break it down into smaller pieces of organic material, which increases the surface area for the decomposers to work on • They perform internal digestion • e.g. woodlice that breakdown wood, earthworms that help break down dead leaves
25
What is nitrogen fixation?
```
The combination of atmospheric
nitrogen (N2) with hydrogen (H2) to
produce ammonia (NH3) by nitrogenfixing
bacteria such as Azotobacter
and Rhizobium.
```
26
Describe 2 examples of
| nitrogen-fixing bacteria
```
• Azotobacter is a free-living soil
bacterium
• Rhizobium live inside root nodules
- these are growths on the roots of
leguminous plants e.g. peas,
beans and clover
• They contain the enzyme
nitrogenase for nitrogen-fixing
```
27
Describe the symbiotic
mutualistic relationship that
nitrogen-fixing bacteria have
with the plant
```
Both organisms benefit:
• The plant gains amino acids from
Rhizobium, which are produced by
fixing nitrogen gas in the air into
ammonia in the bacteria
• The bacteria gain carbohydrates
produced by the plant during
photosynthesis, which they can
use as an energy source
• Other bacteria then convert the
ammonia produced into other
organic compounds that can be
absorbed by plants
```
28
What is nitrification?
```
The process by which ammonium
compounds in the soil are converted
into nitrogen-containing molecules
that can be used by plant
• Free-living bacteria in the soil
called nitrifying bacteria, are used
```
29
Why does nitrification only
| occur in well-aerated soil?
It is an oxidation reaction
30
What are the steps involved in
| nitrification?
```
1. Nitrifying bacteria (e.g.
Nitrosomonas) oxidise
ammonium compounds intro
nitrites NO2-
2. Nitrobacter oxidise nitrites into
nitrates, NO3-
Nitrate ions are highly soluble, and
are therefore the form in which most
nitrogen enters a plant
```
31
What is denitrification?
```
When denitrifying bacteria convert
nitrates in the soil back to nitrogen
gas
• Only happens under anaerobic
conditions e.g. in waterlogged
soils
• The bacteria use the nitrates as a
source of energy for respiration
and nitrogen gas is released
```
32
What is ammonification?
```
The process by which decomposers
convert nitrogen-containing
molecules in dead organisms,
faeces, and urine into ammonium
compounds
```
33
What is the nitrogen cycle?
34
How is carbon recycled?
```
• CO2 in the atmosphere and
dissolved in the seas and oceans
provides the major source of
inorganic carbon for plants
• Carbon-containing compounds in
producers: CO2 is converted into
small carbon-containing organic
molecules by photosynthesis in
plants and other photosynthetic
organisms. This carbon is then
used in the production of
macromolecules e.g.
carbohydrates, proteins, and lipids
in producers
• Carbon-containing compounds in
consumers: Carbon
macromolecules are passed from
producers into primary consumers
when producers are eaten. They
are then passed up the food chain
when the consumer is consumed
• Carbon-containing compounds in
decomposers: When living
organisms die, the carbon
compounds in their bodies are
released into the atmosphere as
CO2 when decomposers respire
```
35
How do carbon dioxide levels
| fluctuate throughout the day?
```
Photosynthesis only takes place in
the light, so during the day
photosynthesis removes carbon
dioxide from the atmosphere
• All living organisms respire and
released CO2 through the day and
night
• Atmospheric CO2 levels are higher
at night that during the day
```
36
How do carbon dioxide levels
| fluctuate seasonally?
Localised carbon dioxide levels are
lower on a summer’s day than a
winter’s day, as photosynthesis rates
are higher
37
Why have global atmosphere
carbon dioxide levels
increased significantly over the
past 200 years?
```
The combustion of fossil fuels
• This has released Co2 back into
the atmosphere from carbon that
had previously been trapped for
millions of years below the Earth’s
surface
Deforestation
• This has removed large quantities
of synthesising biomass from
Earth
• Less CO2 is removed from the
atmosphere
• In many cases the cleared forest is
burnt, therefore releasing more
CO2` into the atmosphere
```
38
What does increased levels of
atmospheric carbon dioxide
cause?
• Traps more thermal energy in the
atmosphere
• Causes the greenhouse effect
39
Why does global warming
reduce the carbon bank in the
oceans?
```
• The higher the temperature of the
water in seas and oceans, the less
gas is dissolved
• Global warming reduces the
carbon bank in the oceans and
released more CO2 into the
atmosphere, further contributing
the the process in a positive
feedback loop
```
40
How do we find information
about how the atmosphere has
changed over time?
```
Samples are taken from deep
within a glacier
• When the ice formed air bubbles
were trapped within the ice
• These bubbles reflect the
composition of the atmosphere at
this point intimate
• Analysis of the gases present
within these bubbles therefore
reveals the composition of the
atmosphere at this point in history
```
41
What is succession?
```
A process by which ecosystems
change over time
• Occurs as a result of changes to
the environment (abiotic factors),
causing the plant and animal
species present to change
```
42
What are the 2 types of
| succession?
```
Primary succession - this occurs
on an area of land that has been
newly formed or exposed such as
bare rock. There is no soil or
organic material present to begin
with
• Secondary succession - this
occurs on areas of land where soil
is present, but it contains no plant
or animal species e.g. the bare
earth that remains after a forest
fire
```
43
When does primary succession
| occur nowadays?
```
• Volcanoes erupt, depositing lava -
when lava cools and solidifies,
igneous rock is created
• Sand is blown by the wind or
deposited buy the sea to create
new sand dunes
• Silt and mud are deposited at river
estuaries
• Glaciers retreat, depositing rubble
and exposing rock
```
44
What are seral stages (or
| sere)?
The steps involved in succession
• Pioneer community
• Intermediate community
• Climax community
45
Describe pioneer communities
```
• An inhospitable environment is
colonised by pioneer species
• They arrive as spores or seeds
carried by the wind from nearby
land masses, or by the dropping of
birds or animals passing through
• e.g. algae and lichen
```
46
What are the adaptation of
| pioneer species?
```
• The ability to produce large
quantities of seeds or spores,
which are blow by the wind and
deposited on the ‘new land’
• Seeds that germinate rapidly
• The ability to photosynthesise to
produce their own energy
• Tolerance to extreme
environments
• The ability to fix nitrogen from the
atmosphere, so adding to the
mineral content of the soil
```
47
Describe intermediate
| communities
```
• Over time weathering of the bare
rock produces particles that form
the basis of a soil
• When the organisms of the pioneer
species die and decompose, small
organic products are released into
the soil
• This organic component of soil is
called humus
• The soil becomes able to support
the growth of new species of plant
known as secondary colonisers
```
48
Describe secondary colonisers
```
• e.g. mosses
• They arrive as spores or seeds
• In some cases, pioneer species
will also provide a food source for
consumers, so some animal
species will start to colonise the
area
```
49
Describe tertiary colonisers
```
As environmental conditions
continue to improve, new species
of plant arrive e.g. ferns
• These plants have a waxy cuticle
that protects them from water loss
• These species can survive in
conditions without an abundance
of water
• However, they need to obtain most
of their water and mineral salts
from the soil
```
50
What happens at each stage of
| intermediate community?
```
• The rock continues to be eroded
and the mass of organic matter
increases
• When organisms decompose, they
contribute to a deeper, more
nutrient-rich soil which retains
more water
• This makes the abiotic conditions
more favourable initially for small
flowering plants e.g. grasses, then
shrubs, and finally small trees
• Plant and animal species that are
better adapted to the current
conditions in the ecosystem
outcompete many of the species
that were previously present to
become the dominant species
```
51
Describe the climax
| community
```
In a stable state and will show very
little change over time
• Which species make up the climax
community depends on the
climate, as different species are
better adapted for different
climates
```
52
Why is the climax community
| not often the most diverse?
```
Although biodiversity generally
increases as succession takes
place, it tends to reach a peak in
mid-succession
• It then tends to decrease due to
the dominant species outcompeting
pioneer and other
species, resulting in their
elimination
• The more successful the dominant
species, the less the biodiversity in
a given ecosystem
```
53
Describe succession on sand
| dunes
```
1. Pioneer species e.g. sea rocket
and prickly sandwort, colonise
the sand just above the high
water mark. These can tolerate
being sprayed with salty water,
lack of fresh water, and unstable
sand
2. Wind-blown sand builds up
around the base of these plants,
forming a mini sand dune. As
plants die and decay, nutrients
accumulate in this mini dune,
and as it gets bigger, plants like
sea sandwort and sea couch
grass colonise it. Sea couch
grass has underground stems
which helps to stabilise the sand
3. As stability and nutrients
increase, plants like sea spurge
and marram grass start to grow.
4. As sand dune and nutrients build
up, other plants colonise the
sand e.g. bird’s-foot trefoil, which
converts nitrogen into nitrate.
With nitrate available, more
species can colonise the dunes,
which stabilises them further
```
54
What is special about marram
| grass?
```
Its shoots trap wind-blown sand,
and as the sand accumulates, the
shoots grow taller to stay above the
growing dune, trapping more sand in
the process
```
55
Describe animal succession
```
• Primary consumers e.g. insects
and worms, are the first to
colonise an area as they consumer
and shelter in the mosses and
lichens present
• Secondary consumers will arrive
once a suitable food source has
been established, and the existing
plant cover will provide them with
suitable habitats
• Eventually larger organisms e.g.
mammals and reptiles will colonise
the area when the biotic
conditions are favourable
```
56
Why is animal succession
| slower than plant succession?
```
Animals must move in from
neighbouring areas, which is difficult
especially when ‘new land’ is
geographically isolated, e.g. a new
volcanic island
```
57
How do humans cause
| deflected succession?
```
Human activities can halt the
natural flow of succession and
prevent the ecosystem from
reaching a climax community
• When succession is stopper
artificially, the final stage formed is
called a plagioclimax
```
58
How does agriculture cause
| deflected succession?
```
• Grazing and trampling of
vegetation by domesticated
animals results in large areas
remaining as grassland
• Removing existing vegetation (e.g.
shrub land) to plant crops - the
crop becomes the final community
• Burning as a means of forest
clearance - this often leads to an
increase in biodiversity as it
provides space and nutrient-rich
ash for other species to grow, e.g.
shrubs
```
59
What does the distribution of
| organisms refer to?
```
Where individual organisms are
found within an ecosystem
• The distribution is usually uneven
throughout an ecosystem
• Organisms are generally found
where abiotic and biotic factors
favour them, therefore their
survival rate is high
```
60
How is distribution measured?
A line or belt transect is normally
used. Both are examples of
systematic sampling, which is a type
of non-random sampling
61
What is the difference between
a line transect and a belt
transect?
```
• A line transect involves laying a
line or surveyor’s tape along the
ground and taking samples at
regular intervals
• A belt transect provides more
information - 2 parallel lines are
marked, and samples are taken of
the area between these specified
points
```
62
How is distribution measured
| using systematic sampling?
```
Different areas within an overall
habitat are identified, which are then
sampled separately
• Allows scientists to study how the
differing abiotic factors in different
areas of the habitat affect the
distribution of a species
• e.g. Systematic sampling can be
used to study how plant species.
Change as you move inland from
the sea
• This would be used to study the
successional changes that take
place along a series of sand dunes
```
63
What does the abundance of
| organisms refer to?
```
The number of individuals of a
species present in an area at any
given time
Fluctuates daily:
• Immigration and births will
increase the number of individuals
• Emigration and deaths will
decrease the number of individuals
```
64
How is plant abundance
| measured?
Quadrats are placed randomly in an
| area
65
How is animal abundance
| measured?
```
Capture-mark-release-recapture
1. Capture as many individuals as
possible in a sample area
2. Mark or tag each individual
3. Release the marked animals
back into the 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 the 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
```
66
How is the biodiversity present
| in a habitat calculated
```
Simpson’s Index of Diversity (D):
D = diversity index
N = total number of organisms in the
ecosystem
N = number of individuals of each
species
• Always results in a value between
0 and 1. 0 represents no diversity,
and 1 represents infinite diversity
```
