Ecology

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Ecosystem – All

living organisms and all the non-living components in a particular area, and their

interactions.They are dynamic

systems, changing all the time.

Habitat – The

place where an organism lives.

Population – All the organisms of one

species in a habitat.

Abiotic factors – The non-living

features of the ecosystem.

(Temperature, Water availability,

light intensity, pH)

Biotic factors – The living features of

the ecosystem.

(Presence of

predators, Food availability, disease, competition)

Producer – An organism that produces

organic molecules using sunlight energy.

(Plants)

Consumer – An organism that eats

other organisms.

(Animals)

Decomposer – An organism that breaks

down dead or undigested organic material.

(Bacteria, Fungi)

Trophic level – A stage in a food

chain occupied by a particular group of organisms, producers are the 1st

trophic level in a food chain.

Detrivores – Small invertebrates that

break down dead matter.

Saprophytes – Microbes that digest

dead matter through extra-cellular digestion.

Energy

is transferred through ecosystems

Main route which energy

enters an ecosystem is photosynthesis. Plants (producers) convert sunlight

energy into a form of energy other organisms can use.

Energy is transferred through the living organisms of an ecosystem when

organisms eat other organisms.

-Producers eaten by primary consumers.

-Primary consumers eaten by secondary consumers.

-Secondary consumers eaten by tertiary consumers.

Food chains/Food webs show how energy is transferred through an ecosystem.

Food chains show simple lines of energy transfer.

Food webs show lots of food chains in an ecosystem and how they overlap.

Energy that’s locked up in the things that can’t be eaten (bones, faeces) gets

recycled back into ecosystem by decomposers.

The length of a food chain is limited by:

-Amount of solar energy available

-Efficiency of the producer

-Big energy losses at each trophic level

Not

all energy gets transferred to the next trophic level

Only around 10% of the

total energy is passed on.

Some energy (60%) isn’t taken in by the

organism in the first place:

-Plants can’t use all the light energy that reaches their leaves, some is

the wrong wavelength, some is reflected, some passes straight through the

leaves.

-Some sunlight can’t be used because it hits parts of the plant that can’t

photosynthesise.

-Some parts of food aren’t eaten so the energy isn’t taken in (bones, roots).

-Some parts of food are indigestible so come out of organism as waste.

Rest of energy (40%) is absorbed – gross productivity.

But not all is available at next trophic level:

-30% of this energy is lost to the environment when organisms use energy

produced from respiration for movement/body heat – respiratory loss.

-10% becomes biomass (stored/used for growth) – net productivity.

Net productivity – amount of energy available to the next trophic level.

Net productivity = gross productivity – respiratory loss

% efficiency of energy transfer = (total energy received ÷ net productivity) x

100

Measuring

energy transfer between trophic levels

Calculate amount of energy/biomass

in a sample of organisms at a trophic level:

-Directly measure energy in joules by burning organisms in a calorimeter, the amount

of heat given off is how much energy is in them.

-Indirectly measure energy in organisms by measuring their dry mass (biomass).

Biomass is created using energy, so it’s an indicator of how much energy the

organism contains.

Multiply results of the sample by the number of organisms in the population =

total amount of energy in the organisms at that trophic level.

The difference in energy between trophic levels = amount of energy transferred.

Problem – consumers may have taken in energy from sources other than the

producer measured, so the difference wouldn’t be an accurate measure of energy

transferred between only those 2 organisms. Need to include all the individual

organisms at each trophic level.

Human

activities can increase the energy transfer through an ecosystem

Farming methods increase

productivity by increasing energy transfer:

-Herbicides kill weeds that compete with crops for energy. Reducing competition

means crops receive more energy, grow faster, larger.

-Fungicides kill fungal infections, crops use more energy for growth and less

energy for fighting infection.

-Insecticides kill insects that eat crops, less biomass lost from crops.

-Natural predators introduced to ecosystem eat the pests, crops lose less

energy/biomass.

-Fertilisers provide crops with minerals needed for growth, replaces lost

minerals so more energy used for growth.

-Rearing livestock intensively, controlled growth conditions, more energy used

for growth and less for other activities, more biomass produced.

Animals kept in warm, indoor pens where movement is restricted – less energy

wasted keeping warm and moving around. <Ethical issues: may cause pain,

distress.

Animals given food high in energy, increases energy input, more available for

growth.

Benefit – more food produced in shorter time, often at lower cost.

The Nitrogen Cycle shows how Nitrogen is

recycled in ecosystems

Plants/Animals

need N to make amino acids to make proteins and nucleic acids

(DNA/RNA).

Atmosphere contains 78% N, bacteria must convert it into N compounds

so it’s usable.

Nitrogen fixation

N in atmosphere is turned into ammonia by bacteria Rhizobium. The ammonia

can be used by plants. Rhizobium are found in root nodules of leguminous

plants. They form a mutualistic relationship with plants, they provide plants

with N compounds, the plants provide them with carbohydrates.

Ammonification

N compounds from dead organisms and animal waste are turned into ammonium

compounds by decomposers.

Nitrification

When ammonium compounds in the soil are changed into N compounds that

can be used by plants. Nitrifying bacteria Nitrosomonas change ammonium

compounds into nitrites. Other nitrifying bacteria Nitrobacter change nitrites

into nitrates.

Denitrification

When the nitrates in the soil are converted into N gas by

denitrifying bacteria, they use nitrates in the soil to carry out respiration and

produce N gas. This happens under anaerobic conditions – no oxygen

(waterlogged soils).

Nitrogen also gets into an ecosystem by

-lightning (fixes atmospheric nitrogen)

-artificial fertilisers (produced from atmospheric nitrogen)

-on an industrial scale in the Haber process.

Succession

The

process by which an ecosystem changes over time.

The biotic conditions change as the abiotic conditions change.

Primary succession – happens on land

that’s been newly formed/exposed. There’s no soil/organic

material to start with.

Eg.

Volcano erupts to form new rock surface.

Sea level drops exposing new area

of land.

Secondary succession – happens on

land that’s been cleared of all the plants, but where

the soil remains.

Eg.

After forest fire.

Where a forest has been cut down by humans.

Succession occurs in stages called seral stages.

1. Primary succession starts when species colonise a new land.

Seeds/spores blown in by wind begin to grow. The first species to colonise the

area – pioneer species. Abiotic conditions hostile: no soil to retain water.

2. Pioneer species can grow because they’re specialised to cope with these

conditions. Eg. Marram grass can grow on sand dunes because it has deep roots

to get water and can tolerate salty environment.

3. The pioneer species changes the abiotic conditions, they die and

microorganisms decompose the dead organic material, forms basic soil. Makes

conditions less hostile: basic soil can retain water, new organisms can grow.

These then die, are decomposed, adds more organic material, makes soil

deeper/richer in minerals.

4. Larger plants can grow, as more move in they create more habitats.

1. Secondary succession happens in the same way, but because there’s a soil

layer, succession starts at a later seral stage, the pioneer species are larger

plants.

2.

3.

4.

5. At each stage, plants/animals that are better adapted for the improved

conditions move in, out-compete the plants/animals there, become new dominant

species.

6. Ecosystem becomes more complex, new species move in alongside existing

species, species diversity increases, amount of biomass increases.

7. Final seral stage – climax community – ecosystem is supporting the

largest/most complex community it can, it’s in a steady state.

Formation

of a sand dune

Pioneer species - sea rocket colonises

the sand, can tolerate salt water spray, lack of fresh water and unstable sand.

Wind-blown sand builds up around the

base of these plants, forming a ‘mini’ sand dune. As the plants die and decay,

nutrients accumulate in this mini dune. As they dune gets bigger, plants like

sea couch grass colonise it, which has underground stems to help stabilise the sand.

With more stability and accumulation of

more nutrients, plants like marram grass start to grow. Marram grass shoots

trap windblown sand and the shoots grow taller to stay above the growing dune,

trapping more sand.

As the sand dune and nutrients build

up, other plants colonise the sand. Many have nodules in their roots which

contain bacteria that convert nitrogen to nitrates. With nitrates available,

more species can colonise the dunes, stabilising them further.

Rock –> Woodland.

Pioneer species – lichens grow on and

break down rocks, releasing minerals.

Lichens dies, decomposed, forms thin soil which thickens as more organic

material is formed. Other species can grow (mosses).

Larger plants that need more water can move in as soil deepens, soil continues

to deepen as larger plants die and decompose.

Small trees begin to grow, out-compete smaller plants to become dominant

species, diversity increases.

Soil is deep/rich in nutrients to support large trees, these become dominant

species, climax community is formed.

Different ecosystems have different climax communities

The species which make up a climax community depend on what the climate is like

in the ecosystem. The climax community for a particular climate is called its

climatic climax.

Succession can be prevented/deflected

Human activities can prevent succession, stopping climax community from

developing, when succession is stopped artificially, the climax community is

called a plagioclimax.

Deflected succession is when succession is prevented by humans, but the

plagioclimax that develops is different to any of the natural seral stages of

the ecosystem. The path of succession is deflected from its natural course.

Investigating

ecosystems

Investigating populations:

Abundance – the number of individuals

of one species in a particular area.

Distribution – where a particular

species in within the area you’re investigating.

Too time-consuming to measure no. of individuals and distribution of every

species so you take samples.

Samples should be random, avoid bias – random number generator to select

coordinates.

Repeat process, more reliable estimate or whole area.

Quadrats – square frame placed

randomly, record individuals contained within quadrat or calculate % cover.

Point quadrats – frame with pins

lowered into quadrat, record each species touching a pin.

Transects – investigate distribution,

line placed across habitat, species touching line are recorded. Belt – data collected along transect

using frame quadrats continuously. Interrupted

– use quadrats at intervals along transect.

Factors

affecting population size

Population size – total number of

organisms of one species in a habitat.

Population size varies due to abiotic factors:

When abiotic conditions are ideal for a species, organisms grow fast and

reproduce successfully. AND VICE VERSA

Population size varies due to biotic factors:

Interspecific competition – competition between different species

They compete for the same resources, results in the resources available to both

populations being reduced, both will be limited by lower amount of food, less energy

for growth and reproduction, population size of both species decreases.

Affects species distribution, if 2 species are competing and 1 is better

adapted, the less adapted species is likely to be out-competed and its

population decreases.

Intraspecific competition –

competition within a species

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