(i)
Seasonal changes
e.g. change in temperature
from winter to summer, rainfall patterns etc.
Lower winter temperatures and scarcer food
resources can cause animals to migrate or hibernate.
Hot dry seasons cause draught and death
from dehydration or lack of food.
Rainy seasons cause flooding, drowning
animals.
High temperatures reduce the concentration
of oxygen in water, affecting aquatic life.
(The general rule for gases is they
become more soluble the lower the temperature.)
(ii)
Impacts of human activity
Agriculture.
factories, building housing estates, mining, motorways etc.
Even within the same
area e.g. differences between neighbouring industrial, 'suburban' and rural
parts - you will observe the success and failure of organisms in
their respective ecosystems.
I've dealt with global warming separately
in the 3rd section below.
(iii)
Global warming
'Climate change' is becoming one of
the biggest factors in he future of the environmental and also comes under the
heading of 'human activity' since the current evidence suggests it
is being accelerated by burning fossil fuels giving higher
levels of carbon dioxide in the atmosphere.
Seas and land are warming places, e.g.
causing species of animals to move further north in the northern
atmosphere.
The increase in atmospheric CO2
levels leads to more of the gas to dissolve in water - seas,
oceans etc. making the water more acidic (lowering the pH).
This, combined with an increase in
water temperature, is having major impact on the stability
of fragile ecosystems like coral reefs, which become
imbalanced and degraded e.g. coral dies, populations of
other coral residing organisms are reduced.
The warmer more acidic water causes
the shells of organisms like molluscs to dissolve and become
thinner.
With warmer temperatures expanding
water, plus rising sea levels due to melting ice, low lying
land is being flooded leading to loss of habitat and
migration of species and reduction of populations.
Increased rainfall OR drought are other
prediction of climate change science.
This can lead to increased flooding of
habitats, which can also be washed away,
OR lack of water, lack of plant
growth, both contributing to the death of animals.
(In Africa the Sahara Desert is
increasing in area all the time, no rain, no vegetation and
accompanying animals.)
(iv)
Geographic changes
In terms of thousands/millions of years,
land bridges between continents rise and fall, permitting or
inhibiting movement of animals.
On a smaller scale, after the last
ice-age, sea levels rose as the ice melted and Great Britain
becomes separated from continental Europe - this cuts off
populations of plants and animals who may evolve to form
sub-species.
Global warming is raising the temperature
of cold mountainous regions sufficiently to cause the melting of
glaciers. The warmer 'upland' climate means 'lowland' plants and
animals can also compete for the 'upland' resources, so that
'lowland' species can be found at higher altitudes than before.
See also
environmental changes and effects on biodiversity
(Overlaps with the initial discussion of with
causes environmental changes above)
A change in environmental conditions
usually means an increase or decrease in one of the abiotic factors
described.
A change in the environment can affect an
individual organism, both promoting or retarding its wellbeing.
On a larger scale, such changes can also
affect the size of a population of a species in a community AND
therefore affect the size of the populations of other species of
organisms if they depend on it higher up a food chain.
A change in an abiotic factor can not only
change population sizes, but also their distribution - climate
change, especially rise in temperature, is leading to significant
geographical movement of species of birds, fish and other marine
organisms.
Various abiotic factors are discussed below
with suitable examples of plants or animals.
1.
Light intensity
Generally speaking the abiotic factor of
light intensity only affects plants.
Lack of light inhibits plant growth - rate
of
photosynthesis slowed
down.
All 'green' plants need good access to
light for photosynthesis, but in growing they produce areas of shade
from sunlight (and sometimes more moist conditions too).
Under the shade of trees, the grass
population might be reduced, but replaced by fungi and mosses which can
cope much better with lower intensity sunlight.
2.
Water access - moisture level
- usually a weather factor
Most plants and animals need access to a continuous
source of water - without access to water for a long period plant growth
will be stunted and eventually most plants will wither and die
and animals will die of dehydration.
Water is needed for all biochemical
process of living organisms - water is both a reactant and a
solvent.
Some plants are adapted to survive in relatively
dry conditions, but most cannot and their populations decline if the
climate changes.
Desert plants are adapted to
retain water.
However, with the opposite situation, most
plants cannot survive in very boggy waterlogged ground, but a
few species are adapted to marshy conditions.
The availability of water also greatly
affects the distribution of animals too.
The wet and dry season sequence e.g.
Africa, causes great migrations of wild animal herds seeking
food and water.
The geographical migration routes
follow the seasonal changes - often to the north and
returning to the south following the pattern of rainfall -
the rain promotes plant growth and pools of water to drink
from.
Drought conditions will affect almost all
species of plants and animals e.g. scenes you see in parts of
Africa where every food chain is affected.
Plants are rare in deserts, but after
rain their distribution of changes dramatically - after
heavy rain the flowers grow in abundance and produce seeds
while adequate water is available.
3.
pH and chemical composition of the soil
The relative acidity
of land and water mainly depends on the local geology.
For more on pH
e.g.
the pH of the soil.
Distribution of plants and animals can
depend on changes in soil composition due to underlying
differences in geology e.g. limestone (slightly alkaline) and
sandstone (slightly acidic).
Some plants are adapted to live in quite
acid conditions e.g. heather grow best on acidic soils and other
plant species have adapted to moorland peat conditions.
Other plants are
adapted to live in the mildly alkaline soils in limestone country.
If you swap the locations for these groups of plants they will not
flourish to the same extent as when grown in their native habitat.
In the garden and on the farm you treat
soil that is too acidic (too low a pH) with lime to increase the
pH and the soil fertility.
4. Mineral content of soil
The nutrient mineral content can depend on local
geology and pH of soil.
Apart from water, oxygen and carbon
dioxide (not regarded as minerals), plants also require important nutrients from the soil e.g. absorbing ions that
supply the plant with elements such as nitrogen (nitrate),
phosphorus (phosphate), potassium, calcium, iron, magnesium and
sulfur (sulfate).
Deficiency of any important nutrient in
soil can inhibit the growth of healthy plants and the
population will decrease - in turn this can affect-decrease the
populations of species that feed on the plants.
Deficiencies in minerals can be remedied
with fertilisers containing nitrogen, phosphorus,
potassium, iron, calcium etc., but don't apply to much!
5. Temperature (usually a climate abiotic
factor)
Many populations are only stable if the
ambient environmental temperature lies within a certain range - a
climate-weather factor.
Populations of fish and other aquatic life are quite sensitive to
the temperature of the water.
Global warming is having an effect on
populations and the distribution of many species of plants and
animals - both aquatic and land based e.g. species are moving
further north in Europe.
There is evidence of populations of
certain marine species moving to more northerly waters as sea
temperatures rise around the UK coast e.g. cod and haddock which
prefer colder water are moving northwards towards the Icelandic
fishing grounds.
Similarly there is evidence
of both bird and insects species (e.g. certain butterflies) extending their territory further
north on mainland Britain as our climate is warming up.
Species of birds usually associated with
Mediterranean countries are now regularly appearing in much greater
numbers in northern European
countries than previous decades.
Warm water discharged from power
stations can cause a local warming effect and species
preferring a milder climate can flourish in the river, and
sometimes species not native to surrounding ecosystem!
6. Wind intensity and direction
(another climate-weather abiotic factor)
Plants in particular can be affected by
weather conditions such as the effect of wind.
Some plants can cope with harsh weather
conditions, but others will only survive in a sheltered habitat.
Birds can be blown off course and not
reach their breeding grounds causing a decline in population.
In fact any sort of bad weather can takes
it toll on migrating flocks of birds e.g. becoming exhausted and
dying.
7.
Carbon dioxide level
Plants need carbon dioxide for
photosynthesis, although
only around 0.04% of air, it would be unusual to fall below this
level and affect plant growth and for animals its a waste gas
from respiration.
On the other hand, oceans are becoming
slightly more concentrated with carbon dioxide from fossil fuel
burning. This has two effects.
(i) This will increase the rate of photosynthesis of marine
organisms in the surface water.
(ii) The pH falls slightly, making the
water more acidic - this is having detrimental effects on
coral reefs.
8. Oxygen level
- usually a pollution effect - see below in next section
Since 21% of air is oxygen, all plants and
animals not living in water are highly unlikely to suffer from
lack of oxygen.
However, the oxygen concentration in water
(fresh or sea) is crucial for aquatic animals.
e.g. if water is polluted with fertiliser
runoff from farmland (nitrates and phosphate), you get excess
growth of weeds and algae. They decay and use up all the oxygen
in the water, killing most aquatic life (fish, molluscs etc.) -
a phenomena called eutrophication.
9. Pollution
This a relatively 'modern' abiotic factor
is entirely due to human activity!
The level and nature of pollution can
affect the populations of both plants and animals and their
distribution.
Unfortunately chemicals like pesticides
build up in food chains and at stage they get more
concentrated as you move from one trophic level to another.
This is an example of
bioaccumulation.
A 'classic' tragic case is small
mammals taking in pesticides in their plant food and then
birds of prey catching and eating the small contaminated
mammals. The poisoning effects on the birds included reduced
fertility, decline in successful hatchings and death.
Excessive use of artificial fertilisers
results in too high a level of nutrients in ponds, streams,
lakes or rivers.
This causes eutrophication -
excessive growth of algae that blocks out sunlight to plants
below the surface. The plants decay as microorganisms feed
on them and using any oxygen around to respire. When most of
the oxygen is used up, most respiring aquatic life dies e.g.
fish, insects and crustaceans.
Lichen are used as a pollution indicator
species - they are NOT tolerant of high pollution levels -
particularly acidic gases like sulfur dioxide and oxidising
gases like ozone and nitrogen dioxide.
Lichen are unable to survive if the level
of sulfur dioxide is too high (from burning fossil fuels).
If the local rocks and walls are covered
in lichen, its usually a good sign of relatively low pollution
levels - but you will find far species and higher numbers of
lichens in rural locations compared to urban locations - less
traffic, less pollution from acidic gases like nitrogen oxides
and sulfur dioxide.
Statistical surveys show that the
number of lichen species steadily increases as you move out
from a town centre out into the countryside well away from
any busy main roads/
You should have noticed that most of the
abiotic factors discussed above seem only to apply to plants,
BUT NOTE, plants are usually the primary food producer at the
bottom of a food chain.
If plants are affected by an
adverse change in environmental conditions, so are all the
animals in the succeeding food chain - and that may
include us too!
