Layers of the Rain Forest - DOC

Document Sample
Layers of the Rain Forest - DOC Powered By Docstoc
					                           Environmental Science
              The study of the impact of humans on the environment

      Draws from all science disciplines and other fields.
      Gives an understanding of the relationship between Humans and the world
       we live in.
      Achieves many of its goals using pure sciences such as chemistry and biology.

Environmental science focuses on three main areas:

   1. Conservation and Protection of natural resources
   2. Communicating and Educating about environmental issues.
   3. Research

Environmental science began when scientists realised that parts of the subjects
used, such as ecology, biology, chemistry, geography and geology, all played a part
in the environment.

So what is the environment?

The environment is everything that surrounds us; both natural and produced by


Humans and Their Models

One common conclusion of scientific inquiry is that the world of nature is often
very complex. To understand this complexity, scientists usually try to envisage the
phenomena of nature as simplified versions of reality known as a system. A system
can be defined as a collection of interrelated parts that work together by way of
some driving process.

In the world of science, the word model is quite similar in meaning to the term
system. Models in science tend to be simplified representations of reality that can
be explained mathematically and through the use of graphics. The following
graphical model is used to help explain the processes involved in scientific
understanding. The arrows in this graphically model suggest a continuous
interaction between perceptible phenomena and theory through the processes of
explanation and validation. This simple graphical model, while an extreme
abstraction of the real world, is quite useful in explaining how scientific
understanding works.

The general relationship between perceptible phenomena and theory using
scientific method for understanding. The interaction between perceptible
phenomena and theory is arrived at through the processes of explanation and

In Physical Geography, and many other fields of knowledge, systems and models are
used extensively as aids in explaining natural phenomena around us.

Definitions of Systems and Models

As suggested in the previous section, a system is an assemblage of interrelated
parts that work together by way of some driving process (see diagram below).
Systems are often visualized or modeled as component blocks that have
connections drawn between them. For example, the illustration below describes the
interception of solar radiation by the Earth. In this system, the Earth and Sun, the
parts or component blocks, are represented by two colored circles of different
size. The process of solar emission and the interception of the Sun's emitted
radiation by the Earth (the connection) is illustrated by the drawn lines.

Simple visual model of solar radiation being emitted from the Sun and intercepted
by the Earth.

Most systems share the same common characteristics. These common
characteristics include the following:

   1. Systems have a structure that is defined by its parts and processes.
   2. Systems are generalizations of reality.
   3. Systems tend to function in the same way. This involves the inputs and
      outputs of material (energy and/or matter) that is then processed causing it
      to change in some way. The various parts of a system have functional as well
      as structural relationships between each other.
   4. The fact that functional relationships exist between the parts suggests the
      flow and transfer of some type of energy and/or matter.
   5. Systems often exchange energy and/or matter beyond their defined
      boundary with the outside environment, and other systems, through various
      input and output processes.
   6. Functional relationships can only occur because of the presence of a driving
   7. The parts that make up a system show some degree of integration - in other
      words the parts work well together.
Within the boundary of a system we can find three kinds of properties:

Elements - are the kinds of parts (things or substances) that make up a system.
These parts may be atoms or molecules, or larger bodies of matter like sand grains,
rain drops, plants, animals, etc.

Attributes - are characteristics of the elements that may be perceived and
measured. For example: quantity, size, colour, volume, temperature, and mass.

Relationships - are the associations that occur between elements and attributes.
These associations are based on cause and effect.

We can define the state of the system by determining the value of its properties
(the elements, attributes, and/or relationships).

Scientists have examined and classified many types of systems. Some of the
classified types include:

Isolated System - a system that has no interactions beyond its boundary layer.
Many controlled laboratory experiments are this type of system.

Closed System - is a system that transfers energy, but not matter, across its
boundary to the surrounding environment. Our planet is often viewed as a closed

Open System - is a system that transfers both matter and energy can cross its
boundary to the surrounding environment. Most ecosystems are example of open

Control System - a system that can be intelligently manipulated by the action of

Ecosystem - is a system that models relationships and interactions between the
various biotic and abiotic components making up a community or organisms and their
surrounding physical environment.
Structure of Systems

Systems exist at every scale of size and are often arranged in some kind of
hierarchical fashion. Large systems are often composed of one or more smaller
systems working within its various elements. Processes within these smaller
systems can often be connected directly or indirectly to processes found in the
larger system. A good example of a system within systems is the hierarchy of
systems found in our Universe.

   o At the top level we have what we call the Cosmos or Universe.
   o Elements of that system are galaxies, stars, planets, black holes etc.
   o The structure of this system is thought to have been brought about by a
   massive explosion called the BIG BANG and it is controlled by gravity and the
   other 3 forces: the electromagnetic force, the strong force and the weak
   o Within this system (our Universe) there are Solar Systems.
   o Within this system there are planetary systems for example, Earth.
   o On Earth there is interaction between its lithosphere (crust), atmosphere
   and hydrosphere and this is known as a biosphere.

Biospheres are regions of the Earth, or other planet, where living organisms exist.

If a planetary system has a biosphere, dynamic interactions between the
lithosphere, atmosphere and hydrosphere will develop.

These interactions can be called an environmental system. The scale of this can
range from massive to a single plant.

The Earth’s biosphere is made up of ECOSYSTEMS. A population of species
grouped together into communities that interact with each other and the
ABIOTIC environment.

An organism is alive because it is a biological system.
Environmental Systems as Energy Systems

We define an environmental system as a system where life interacts with the
various abiotic components found in the atmosphere, hydrosphere, and lithosphere.
Environmental systems also involve the capture, movement, storage, and use of
energy. Thus, environmental systems are also energy systems.

In environmental systems, energy moves from the abiotic environment to life
through processes like plant photosynthesis. Photosynthesis packages this energy
into simple organic compounds like glucose and starch. Both of these organic
molecules can be stored for future use. The following chemical formula describes
how plants capture the Sun's light energy and convert it into chemical energy:

                 6CO2 + 6H2O + light energy → C6H12O6 + 6O2

The energy of light is used by plants in this reaction to chemically change carbon
dioxide (CO2) and water (H2O) into oxygen (O2) and the energy rich organic
molecule glucose (C6H12O6).

The chemical energy of photosynthesis can be passed on to other living or biotic
components of an environmental system through biomass consumption or
decomposition by consumer organisms. When needed for metabolic processes, the
fixed organic energy stored in an organism can be released to do work via
respiration or fermentation.

Food Chain as an Example of a System

A food chain models the movement of energy in an ecosystem (a form of
environmental system). The diagram below illustrates the movement of energy in a
typical food chain. In this diagram, we begin the food chain with 100,000 units of
light energy from the Sun. Note the amount of energy available at each successive
level (called trophic levels) of this system becomes progressively less. Only 10
units of energy are available at the last level (carnivores) of the food chain. A
number of factors limit the assimilation of energy from one level to the next.
The Sun is the original source of energy, in the
form of light, for the food chain. (100,000
Units of Energy)

         Plants capture approximately 1% of
         the available light energy from the
         Sun for biomass production by way of
         photosynthesis. Photosynthesis can be
         described chemically as: Light Energy
         + 6CO2 + 6H2O ==> C6H12O6+ 6O2
         (1,000 Units of Energy)

      Herbivores consume approximately 10%
      of the plant biomass produced in a
      typical food chain.(100 Units of Energy)
                                Carnivores capture and consume about 10%
                                of the energy stored by the herbivores.

                                (10 Units of Energy)

Why is the above illustration an example of a system? The concept of what makes
something a system was fully explained in part b above. In this topic, it was
suggested that all systems share the following seven common characteristics:

   1. Systems have a structure that is defined by its parts and processes. In the
      above example, the structure consists of the system's three types of
      properties. This system has the following elements: the Sun, plants,
      herbivores and carnivores. Within this system the main characteristic, or
      attribute, of the elements being perceived is units of energy. The last
      component that makes up the structure of this system is the cause and
      effect relationships between the elements and attributes. For example, the
      Sun creates energy via nuclear fusion. This energy is radiated from the
      Sun's surface and received by the surface of the Earth. On the surface of
      the Earth plants capture some of this solar radiation in the chloroplasts that
      exist in their tissues. Through photosynthesis the plants convert the radiant
      energy into energy rich organic matter. Some of the energy fixed by the
      plants is passed on to herbivores through consumption. Finally, a portion of
      the energy assimilated by the herbivores is then passed on to carnivores
      through consumption.

   2. Systems are generalizations of reality. The food chain process described
      above is a simple abstraction of what actually happens in a variety of
      different types of terrestrial ecosystems of much greater complexity.
      Systems tend to function in the same way. All systems consist of groups of
      parts that interact with each other according to various cause and effect
      processes. In the food chain model, the parts are the Sun, plants,
      herbivores and carnivores. There are two main processes taking place in this
      system. The first involves the movement of energy, in the form of radiation,
   from the Sun to the plants. The second process involves the movement of
   energy, in the form of organic molecules, from plants to herbivores, and then
   finally to carnivores through biomass consumption.

3. The various parts of a system have functional as well as structural
   relationships between each other. The structure within the food chain is
   defined by the functional relationships between the elements and attributes
   of the system.

4. The fact that functional relationships exist between the parts suggests the
   flow and transfer of some type of energy or matter. Systems exchange
   energy and matter internally and with their surrounding environment through
   various processes of input and output. The main material being transferred
   into this system (input) is energy in the form of solar radiation. The solar
   radiation is then fixed into organic matter (output) by way of
   photosynthesis in the plants. Herbivores consume the constructed plant
   organic molecules for nutrition to run their metabolism. The herbivores then
   provide food for the carnivores.

5 Systems often exchange energy and/or matter beyond their defined
  boundary with the outside environment, and other systems, through various
  input and output processes. The organisms found in a food chains transfer
  organic matter into the detritus food chain when they shed tissues or die.
  This transfer represents a net output of matter out of the food chain. With
  decomposition, the organic matter is converted into inorganic nutrients
  which can be taken up by plants in the food chain to produce new organic
  matter. This transfer represents a net input of matter into the food chain

6 Functional relationships can only occur because of the presence of a driving
  force. The driving force in the food chain is the Sun.
The parts that make up a system show some degree of integration - in other
words the parts work well together. Integration in the food chain comes
primarily from the process of evolution. It was through evolution that plants,
herbivores, and carnivores came about and developed ecological associations
between each other.


A biome is described by its vegetation, precipitation and temperature. An
ecosystem is a POPULATION of SPECIES grouped together into
COMMUNITIES that interact with each other and the ABIOTIC environment.

A biome is a group of ecosystems in a larger region. Therefore the ecosystems
of the world are grouped into regions called biomes.

A biome is therefore a large region characterised by a certain type of climate
and certain types of animal and plant communities.

The hierarchy is:

The biosphere is divided into

Biomes which are divided into


Biomes are described by the vegetation because the plants that grow in a
particular region are the most noticeable thing about that region. The plant life
also determines the other organisms that live there.

E.G. Mahogany trees grow in tropical rainforests because they cannot survive
dry, cold weather and it follows that organisms that depend on those trees, live
where they grow.
   Plants in biomes have adaptations that enable them to survive there. These
   adaptations may size, shape or colour for example.

   E.G. Desert plants such as cacti have no leaves but have specialised structures
   instead that allow them to conserve and retain water.

   Plants that grow in the tundra are usually short because of a lack of water and a
   short summer growing season.

   Biomes and Climate

   The plants that grow in the biomes are determined by the climate of those
   regions. The climate of a region refers to the weather conditions such as:
   Precipitation, Temperature, Wind and Humidity; over a long period of time. The
   2 main factors that determine a regions climate are TEMPERATURE and

   Most organisms are adapted to survive within a specific range of temperatures
   and cannot survive if the temperature
   goes too far outside that range. Plants
   are also affected by the length of the
   growing season.

   Precipitation is another factor that
   limits the organisms found in a biome as
   all organisms need water.

Look at the Temperature-Precipitation Pyramid. Notice how much more vegetation
exists in hot, wet tropical ran forest than in a dry, desert area.

Different species live in different parts of the world. However, species that live
in the same biome look and act similar although they may live far away from each
other. This happens because similar niches become available in each biome.
In order to fill these niches animals adapt and begin to behave and look similar to
other animals in other parts of the world.

Latitude and Altitude

These are factors that cause biomes and vegetation to vary.

Latitude is the distance
north or south of the
equator and is measured in

Altitude is the height of
an object above sea-level.

Climate varies with
latitude and altitude.
E.G. Climate gets colder as
latitude and altitude
increase. Therefore, as they change so do biomes and vegetation. Trees of the
tropical rain forests usually grow near the equator while the mosses and lichens of
the tundra usually grow nearer to the poles.
Layers of the Rain Forest

Different types of plants grow at different levels, or layers, of the rain forest.
The 4 main layers are:

   o The Emergent Layer

   o The Upper Canopy
   o The Lower Copy
   o The Understory

The top layer, or emergent layer, contains the tallest trees which grow to around
60m or 70m and grow and emerge into direct sunlight.

The layer below is known as the canopy and trees grow to a height of over 30m.
These trees form a dense layer and can absorb up to 93% of the sunlight
                           (Environmental Science, page 158).

                            The canopy can be split into the upper and lower
                            canopies. As one might imagine, the lower canopy
                            receives less sunlight than the upper.

                            Plants known as Epiphytes, such as orchids, use the
                            whole surface of a tree as a place to live using them for

                            Some grow high up where their leaves can reach the
                            sunlight needed for photosynthesis to occur.

Growing on these trees allows the epiphytes to absorb water and nutrients that
run down the trees after it rains.
Most animals that live in the rain forest live in the canopy because they rely on the
abundant supply of flowers and fruits that grow there.

Very little light reaches below the canopy and this layer is known as the

The trees and shrubs that grow here have adapted to living in shaded areas.

The majority of the plants that grow here do not grow taller than about 3.5m.

Plants with large, flat leaves grow on the forest floor and capture the small amount
of sunlight that gets through.

Many medicines come from tropical rain forest plants.

Chemists extract chemicals from them to ascertain if they have any use in fighting
or curing disease.

E.G. The Rosy Periwinkle of Madagascar contain 2 chemicals of medical use:


   o Vinblastine is used to treat Hodgkin’s Disease – a form of cancer.

   o Vincristine is used to treat childhood leukaemia.
                            Diversity of Species

The tropical rain forest is the biome with the greatest variety of species.

The diversity of the vegetation has led
to the evolution of a community with a
wide variety of animals.

Some of these animals have fantastic
adaptations for capturing prey while
others have adaptations that they use to
avoid and escape predators.

                                                    The Collared Anteater

                                                   The Costa Rican Mantis

The Wreathed Hornbill
                        Threats to the Rain Forests

20% of the Earth was once covered in tropical rain forests but today they cover
only about 7%!!!! (Environmental Science, page 160). This is due to them being
cleared for agriculture, logging or the search for more oil.

Approximately 100 acres of tropical rain forest are cleared every minute of the
day (Environmental Science, page 160).

This process is destroying habitats and it is this habitat destruction that is the
main reason for species
becoming extinct.

The plants and animals
are threatened by
trading. Many species of
plant, that are only found
here, are valuable to

Animals are threatened
because of the ‘exotic
pet’ market. They are
illegally trapped and sold
at high prices.

It is estimated that 50 million people live in the tropical rain forests and they too
are threatened by habitat destruction.

Their building materials, food, traditions and culture come from the rain forests
and are uniquely connected to them.

Plants absorb water through their roots and transport it to their stems and leaves.
Water then evaporates through the pores (stomata) in the leaves through the
process of TRANSPIRATION. When The water transpires into the air, it will
travel downwind and fall as rain elsewhere. Deforestation can therefore change
the climate.

Cutting a forest down or replacing it with smaller plants means that a lot of the
rainfall is not absorbed. Instead it runs of the soil causing flooding and soil
erosion and the climate downwind will become dryer.

Temperate Rain Forests
These are found in Australia, New Zealand and North America. They have high
humidity, large amounts of precipitation and moderate temperatures.

                                   The picture shows the only temperate rain
                                   forest in North America. It is located in the
                                   Pacific Northwest in the Olympic National Park,
                                   Washington State.

                                   The forest is dominated by trees that grow to
                                   90m tall such as the Silka spruce and the
                                   Douglas fir. Other trees that can be found here
                                   are the Pacific silver fir and the Redwood.

                                  The temperate rain forest rarely freezes
                                  because of its year round moderate
                                  temperatures. This is due to the Pacific Ocean
blowing cool ocean winds over the forest. As the winds meet the coastal
mountains, a large amount of rainfall is produced and this keeps the temperate
rainforest cool and moist.
                      Temperate Deciduous Forests

In these forests trees drop their flat, broad leaves every autumn and if you were
to walk through such a forest in North America at this time you will see a vivid
array of yellows, oranges and reds on the trees and forest floor.

It is much quieter than it would be in the summer months as the majority of the
bird population have flown south for the winter. However, there would be a great
deal of activity amongst the squirrel and chipmunk communities as they gather up
and store the food they will need during the long cold winter.

                                                     This type of forest once
                                                     dominated massive areas of
                                                     the Earth but these days they
                                                     are mainly found between the
                                                     latitudes of 30o and 50o north.

The growing season lasts for between 4 to 6 months, the
range of temperatures can go from 35oC to below
freezing (0oC) and because of this extreme range of
temperatures there is very little water available for the

Earlier I mentioned the variety of colour during autumn as
the deciduous trees shed their leaves and there is also a
change in temperature. There is enough moisture for
decomposition of the leaves and other vegetation to occur
but the temperature is low. This causes the
decomposition of any organic matter to occur at a slow
rate which means that the soil will contain a lot more
nutrients and organic matter than a tropical rain forest.
Plants of the deciduous forest grow in layers – similar to a
tropical rain forest.
The canopy is dominated by trees such as the mighty oak, birch trees and maple
trees. The understory is covered with shrubs and small trees but because more
light can penetrate the floor of the deciduous forest, in comparison to the tropical
rain forest, more plants such as herbs, mosses and ferns grow there.

These temperate forest plants have adapted so as to be able to survive seasonal

The bulbs and seeds of plants such as herbs lay dormant. In the winter time the
moisture in the soil freezes causing any remaining leaves on the trees to fall.

When spring breaks the sunlight increases and the temperature rises. The seeds
germinate, rhizomes (underground stems) grow new shoots and stems and the trees
grow new leaves. The cycle begins once more.

                                               The plants are also used by the
                                               forest animals for food and shelter.

                                               Deer and other herbivores feed on
                                               grass and leaves from trees and

                                               Many birds
nest in the safety of the canopy. Because many of these
birds cannot survive the winter here they fly south in the
autumn in search of warmer weather and a good supply of
food. These birds are known as MIGRATORY. Every spring
they will return north to nest and feed.

Animals that don’t migrate have different ways of surviving
the winter. For example, certain mammals reduce their
activity levels in order to eat less food for energy.

                   Grasshoppers will eat most types of
                   vegetation that is found in the forest.

This is the coniferous forest of the north which stretches across the northern
hemisphere just below the
Artic Circle.

                  Winters can last anywhere from 6 to 10 months and average
                  temperatures are below freezing; sometimes reaching -20oC.

                  Plant growth occurs during the very short summer due to almost
                  constant daylight and large amounts of precipitation.

                  Students to research how animals avoid predation in the Taiga
                  and how this affects the animals that depend on them to
                      Grassland, Desert and Tundra

Biomes are dominated by smaller plants in areas of not enough precipitation for the
larger trees to grow.

Deserts are found where there is little or no rainfall causing very few plants to

Therefore, warm areas with very little precipitation are savannas’ and deserts.

Temperate regions have grassland, chapparal and deserts.

Cold areas have tundra and deserts.


Some parts of South America, western India, northern Australia and Africa are
covered in grassland known as
savanna. This is a tropical biome
dominated by, as you might
imagine, grasses, small trees and

                    The aptly named ‘wet season’ is when the majority of the rain
                    falls which only lasts for a few months of the year and this is
                    the only time that the plants get a chance to grow.

                    This vegetation supports many different herbivores including
                    elephants, antelope and giraffes and, of course, the carnivore
                    predators that hunt, kill and eat them such as lions and
Plants of the savanna need to be able to survive long periods of time without water
and so during the dry season plants either lose their leaves or die down to the
ground and lay dormant. When the wet season arrives they start to grow again.

The root systems of many of the plants are horizontal allowing them to draw water
from as large an area as possible.

The coarse grasses have vertical leaves in order to expose less of the surface area
of the leaves to the sun and conserve water. Some trees lose their leaves during
                                                  the dry season too in order to
                                                  conserve water.

                                                 As a defence against hungry
                                                 herbivores, some shrubs and
                                                 trees have sharp leaves or thorns
                                                 to protect them.

                                                  Elephants and other grazing
herbivores, have a migratory way of life. They follow the rains in order to find
watering holes and newly sprouted grass and of course some of these animals are
stalked by predators for food.

Different species of herbivores eat vegetation at different heights. For example,
gazelles eat grasses whereas giraffes eat leaves from the higher branches of

The majority of the animals of the savanna give birth during the wet season
because there is plenty of food and therefore the new born are more likely to
Temperate Grasslands

These grasslands cover large areas of
the interior of continents where the
rainfall is moderate but not enough
for trees to grow. The pampas of
South America, the prairies of North
America, the steppes of Asia and the
veldt in South Africa are all
temperate grasslands.

                              The South American Pampas

A major role is sometimes played by mountains in the maintenance of grasslands.

E.g. rain clouds moving east, from the west, in North America release the majority
                                 of their moisture as they move over the Rocky
                                 mountains. Because of this the shortgrass prairie
                                 (east of the Rockies) gets very little rain which
                                 makes it look almost like a desert.

                               The growth of taller grass and shrubs occurs
                               further east as the amount of rainfall increases.

                               Plants of the grassland dry out in summer causing
                               fires to start through lightning strikes!
                               The vegetation consists of only a single layer but
                               contains many species of grasses and wild flowers
The height of the different grasses
and the depth of their roots vary
depending on the amount of rainfall
that grassland receives. The root
systems of the various plants form
dense layers that can survive fire and

Trees and shrubs will grow only in areas where the soil contains extra water and so
they will usually be found on the banks of rivers and streams.

The soils of the grasslands are very fertile. As can be seen from the climatogram,
the winters on these grasslands are cold and the summers warm and the plants die
back to their roots in winter.

Because of the low temperatures during the winter months, decomposition of
organic matter is very slow and the rate at which the dead plants die is slower than
the rate at which new plants are added each year. This means that the amount of
organic matter in the soil increases year by year.

This therefore means that the grasslands have the most fertile soil in the world
and because of this the majority of grasslands have been converted to farmland to
grow crops like wheat and corn.

Farming and overgrazing have altered the grasslands because the grain crops
mentioned earlier cannot hold the soil in place as well as the grasses they have
replaced. This is because the crop roots are a lot shallower and the ground is
ploughed regularly causing soil erosion to happen eventually.

Erosion also happens due to overgrazing because when the grasses are constantly
eaten and trodden on they cannot regrow or hold the soil. This constant use can
turn once extremely fertile grasslands into desert like biomes.

Temperate woodland biomes have
fairly dry climates but get enough
rainfall to support more plants
than a desert can.

Chaparrals are temperate
shrublands that have communities
of scattered coniferous trees such
as junipers and piñon pines.

Temperate woodlands are too dry to support forests but receives enough
precipitation so that vegetation grows in ‘bunches’.

                                         The chaparral is found in all 5 areas of
                                         the world that have Mediterranean
                                         climates. These parts of the world have
                                         fairly dry, coastal climates with little or
                                         no rain during the summer. They are
                                         found in the mid-
                                         latitudes at about
                                         30o north and south
                                         of the equator.

Most plants in chaparrals are small trees and low lying
evergreen shrubs that grow in dense patches. These include
                                      manzanita and herbs
                                      such as bay and sage.

                                     These plants have small
                                     leathery leaves that hold
                                     water. Their leaves also
                                     contain oils that promote
burning which is an advantage due to the fact that naturally
occurring fires destroy the trees that could compete for light and space. They can
also resprout from only the smallest surviving piece of plant material.
A very common adaptation of chaparral animals is camouflage. Camouflage is the
ability to blend into the environment because of shape and/or colouring which then
allows the animal to move through the brush without being noticed.

The greatest threat to chaparral biomes is Man! Because they get a lot of sun,
have mild climates and are near the oceans, we have seen them as areas that can be
developed for residential and commercial use. Golf courses on the south coast of
Spain are a good example of this.


These are areas that receive very little rainfall and have
widely scattered vegetation. In extreme cases it never
rains and so there is no vegetation present in that area.
They are the driest places on Earth!

Even in hot deserts near the equator there is very little
moisture in the air giving rise to rapid temperature changes
                                     over any 24 hour period;
                                     ranging anywhere from
                                     around 40oC during the
                                     day to 0oC at night. One
                                     can often find deserts
                                     near mountain ranges
                                     which will stop the movement of rain clouds
                                     over the area.

As one would expect, for plants to live in the desert, they have all have adapted in
order to be able to obtain and conserve water.

Plants known as succulents, such as cacti, have fleshy, thick stems and leaves that
can store water and a waxy coating that stops water loss. Sharp spines on the
cacti help protect it from being eaten by thirsty animals. Because deserts are so
dry, rainfall hardly ever gets deep into the soil and so the roots of many of the
plants spread out near to the surface of the soil so as to obtain as much water as
If the water level of a plant falls below between 50% and
75% of its mass it is usually fatal for the plant. However,
some desert plants have adapted to be able to survive even
their water level drops to as low as 30% of their mass!
(Environmental Science pg 170). Other plants have adapted so
that when it gets too dry they die off and drop seeds that lay
dormant in the soil until it rains again.

       Once it rains again, the seeds quickly germinate and grow then bloom
       before the soil dries out again. A lot of the shrubs shed their leaves when
       it’s dry and grow new ones when the rains come again.

       Desert animals, such as the amphibious
       Spadefoot Toad, survive the desert heat by
       aestivating. They bury themselves in the
       ground and sleep.

       Reptiles have scaly skin that is thick and
       stops water loss. The Elf Owl nests in cacti
       to avoid predators. Insects have bodies covered in armour in order to
       retain water. However, the majority of desert creatures are nocturnal –
they are active at night time when it is cooler.


This is situated in the northern arctic regions and no trees grow here as the
winters are too cold and dry. In some areas of the tundra the permafrost (the
deeper layers of soil) is frozen permanently and because of this the top layer of
soil, or topsoil, is very thin. When the thin layer of topsoil thaws in the summer,
the terrain becomes very spongy and moist and has bogs dotted all over it. These
wet areas are ideal breeding grounds for massive numbers of swarming insects
such as mosquitoes and black flies. This also makes it an ideal breeding ground for
the many birds that feed on the insects.
                          Aquatic Ecosystems
Freshwater ecosystems are made up
of rivers, lakes and wetlands.

Marine ecosystems include coral
reefs, estuaries and the oceans.

These aquatic ecosystems perform
many environmental functions and
support many animal and plant species. However, pollution, development and
overuse are threatening to harm and disrupt many of these ecosystems.

                                   For example the Manatee lives in both fresh and
                                   salt water. In North America most manatees are
                                   found in the estuaries, bays and coastal
                                   ecosystems of states such as Florida.

                                   They are often called sea cows because of the
                                   way they lazily graze on the aquatic vegetation.
                                   They grow to 3m to 4m in length and weigh
                                   between 360kg to 545kg. However, manatees
                                   are, unfortunately, sometimes hit by boats
                                   because they live in shallow water and cannot
                                   swim fast enough to get out of the way of the

Freshwater Ecosystems

The types of organisms that live in an aquatic ecosystem depends on the salinity of
the water (the amount of dissolved salts that are contained in the water).

Factors such as sunlight, oxygen, temperature and nutrients determine which
organisms live in which areas of the water. For example the Sun can only reach a
certain distance below the surface of the water and so the majority of
photosynthetic organisms live on or near to the surface.
The organisms are grouped by their location and by their adaptations. Three
groups of these aquatic organisms include plankton, nekton and benthos. Plankton
are organisms that cannot swim against the current – they drift and phytoplankton
are microscopic drifting plants that are the food base for most aquatic systems.
Drifting animals, that maybe microscopic or as big as jellyfish, are called

Nekton are free swimming organisms such as fish, whales or turtles for example.
Benthos are bottom dwelling organisms such as worms, clams, mussels or barnacles
and many of these organisms live their lives attached to hard surfaces. Organisms
called decomposers, which break down dead organic matter, are also present in
aquatic ecosystems.

Lakes, ponds, rivers, streams and wetlands are the various types of freshwater

Lakes, ponds and wetlands can form naturally where the groundwater reaches the
surface of the Earth. Beavers can create ponds by damming up streams. Humans
create artificial lakes intentionally in order to use them for irrigation, energy,
water storage and recreation.

Lakes and ponds can be structured into horizontal and vertical zones and in the
nutrient rich littoral zone - near the shore - the aquatic life is diverse and
abundant. Reeds etc. are rooted in the mud under the water and their stems or
leaves are above the water. Pond lilies and other plants that have floating leaves
are also rooted there too.

Further from the shoreline in
the open water, there are no
rooted plants. This is where
the phytoplankton make their
own food through the process
of photosynthesis.
As can be seen in the diagram
the amount of sunlight and
nutrients influence the types of organisms in ponds and lakes and where they will
be located in the lakes and ponds.
In some bodies of freshwater some areas are so deep that photosynthesis does
not occur because there is too little light. In these areas decomposers such as
bacteria feed on dead animals and plants that drift down. Fish that are adapted to
cooler water also live here. The dead and decaying plants and animals eventually
fall to the bottom of the pond or lake (the benthic zone) where decomposers,
clams and insect larvae live.

Some of the animals that live in the ponds and lakes have interesting adaptations
                                    that help them to gain what they need to
                                    survive there. For example, cat fish have
                                    whiskers that help them sense food as they
                                    swim along the dark bottom of the lake. Water
                                    beetles use hairs under their bodies to trap air
                                    in order to breathe while they dive for food.
                                    Amphibians burrow into the mud in the littoral
                                    zone to avoid very cold temperatures in regions
                                    where the ponds and lakes freeze over.

An increase in the amount of nutrients in an aquatic
ecosystem is known as eutrophication. A pond or lake
that has large amounts of algae and plant growth, as
can be seen here, is known as a eutrophic lake or pond.

As the amount of algae and plants grows, the number
of bacteria feeding on the decaying organisms also
grows and these bacteria use the oxygen that is
dissolved in the water. This reduces the amount of
dissolved oxygen in the water eventually killing the
organisms that need oxygen to survive. Lakes and
ponds can become eutrophic over a long period of time
but this can be speeded up through ‘runoff’. Runoff is
precipitation, such as rain, that can wash fertilisers,
sewage and animal waste into the body of water.
Freshwater Wetlands

These are areas of land that are covered in water for at least part of the year.
There are two man types: swamps and marshes.

Swamps are dominated by woody plants such as trees and shrubs while marshes
contain non-woody plants such as reeds.

Wetlands perform many environmental functions:

    Trapping and filtering pollutants, nutrients and
     sediments and thereby stopping them from
     entering the reservoirs, lakes and oceans.

    Reducing the threat of floods, protecting
     agriculture, buildings, roads and human health
     and safety.

    Buffering shorelines against erosion.

    Providing habitat for rare, threatened,
     endangered and migratory species.

    Providing spawning grounds and habitat for commercially important fish and

    Providing recreational areas for activities such as fishing, bird watching,
     photography and painting, canoeing and hiking.

Wetlands act as filters and sponges because they absorb and remove pollutants
from the water that flows through them and in doing so improve the water quality
of rivers, lakes and reservoirs downstream.

Wetland vegetation also traps carbon which could otherwise be released as carbon
dioxide (CO2) that may be linked to rising atmospheric temperature.

Freshwater marshes tend to occur on low, flat lands that have little water
movement. Plants such as reeds and rushes root themselves in the rich bottom
sediments of the shallows and the leaves of these plants stick out above the
surface of the water all year round.

The nutrient rich benthic zones of the marshes contain plants, many types of
decomposers and scavengers. Water fowl such as ducks have flat beaks that have
adapted in order for the bird to sift through the water for fish and insects.
Herons have spear like beaks that enable them to grab fish and probe the mud for
frogs. Marshes also attract many migratory birds from tropical and temperate

The salinity of marshes varies. Some have water that is as salty as the oceans
whereas others have only slightly salty (brackish) water and this dictates the
organisms that live in and around the marshes as they will be adapted to a specific
range of water salinity.


Swamps are found on flat, badly drained land that is usually near a stream. The
plant life (trees and shrubs etc.) in a swamp depends on the salinity of the water
and the climate of the area; e.g. mangroves are trees that grow in saltwater
swamps in tropical climates.

Freshwater swamps are great habitats for amphibians such as frogs, newts and
salamanders because of the consistent moist environment.
                                               Swamps also attract birds such as
                                              wood ducks that nest in hollow
                                              trees that are near or over the

                                                Reptiles such as alligators are the
                                                predators of the swamps and will
                                                eat any organism that crosses their
The Impact of Humans on Wetlands

                                      At one time wetlands were considered to be
                                      wastelands that provided breeding grounds
                                      for disease carrying insects and because of
                                      this many
                                      wetlands have
                                      been drained,
                                      filled and cleared
                                      for farms and
                                      residential and
commercial developments. For example the Florida
Everglades once covered 8 million acres of southern
Florida but now covers less than 2 million acres
(Environmental Science, Arms, page 189).

The importance of the wetlands as water purifiers and flood preventors has now
been recognised. Wetlands are vital habitats for wildlife and laws are now in place
to protect them.


Many rivers originate from snow melt in mountains and at its
headwaters it is usually cold, full of oxygen and moves quickly
through a shallow riverbed. As a river flows down a mountain
it becomes slower, wider, warmer and contains more
                                vegetation and less oxygen.

                              A river changes with the land
                              and the climate it flows
                              through. For example, as we mentioned earlier,
                              runoff may wash sediment and nutrients from the
                              land into the water and these substances will affect
                              the health and growth of the organisms in the water.
Near the headwaters, mosses anchor themselves to rocks using root like
structures called rhizoids. Fish such as trout and minnows are adapted to the
oxygen rich cold waters. The trout is a powerful swimmer and has a streamlined
body that gives very little resistance to the strong currents of the headwaters.

Further downstream plants set roots in the rich sediment and some plants leaves
vary in shape depending on the strength of the current. Fish such as carp and
catfish also live in these calmer waters.

The human population and industry have affected the health of the rivers. We use
the water from the rivers to use in the home and industry take water to use as a
coolant, for example. Sewage (treated to various levels or, in some cases, not at
all) is disposed of in rivers as well as garbage and this has polluted the water with
toxins. These toxins, in some areas, have made river fish unsuitable to eat and
have killed many other river organisms.

Runoff from the land puts pesticides and other poisons into the watercourse and
covers the riverbed with toxic sediments.

The massive dams that have been built also alter the ecosystems in and around the

Marine Ecosystems

These are ecosystems that
contain salt water and are
found in and around the world’s

In open water the amount of
sunlight and nutrients vary for
one part of the ocean to another. In coastal areas we usually find that the salinity
and water level change during the day.
Coastal Wetlands

These areas are covered with salt water for all or at least part of the day. They
provide nesting and habitat for a wide variety of fish and other wildlife. The
coastal wetlands also protect areas from flooding by absorbing the excess rain.
They filter out sediments and pollutants and support recreational areas for hunting
fishing and boating.

Many of these wetlands form in estuaries. An estuary is an area where fresh river
water and salty sea water mix.
This section will introduce basic concepts that ecologists use to study ecosystems.
It will explore Properties of populations, how populations change in size in response
to their environment and how populations of different species interact.

Orcas – AKA Killer Whales – hunt and eat sea lions.

Would a change in the number of sea lions have an effect on the orcas?

Would it make a difference if the sea lions were the only food source for the

A population is the members of a species living in the same area at the same time.
It is a reproductive group because organisms usual breed with members of their
own population. For example, a field full of poppies will breed with each other and
not with poppies in a field in another county. Population refers to the group in
general and the number of individuals in it.

The famous biologist Charles Darwin calculated that a pair of elephants could
theoretically produce 19 million descendants inside 750 years pointing out that the
actual number of elephants was limited by their environment.
You have been offered a job for one month (31 days) and you have been given 2
salary options.

You can either receive £10 per week with a £5 per week raise every week or you
can receive 1 penny for your first day and then double the previous day’s pay for
each of the remaining 30 days.

Choose one of the two options and calculate your salary for the month. Once you
have done that calculate what the other option would pay.

Populations may grow in size by either of these 2 ways as we will see as we

Populations can be described in terms of density, dispersion or size.

A population’s density is the number of individuals per unit area or volume such as
the number of a particular species of fish in a lake.

A population’s dispersion is the relative arrangement or distribution of the
individuals within a known amount of space. This dispersion could be random,
clustered or evenly spread and these properties can be used to predict changes
within populations.

Populations Growth

Each new offspring or birth increases the number of individuals in a population and
each death decreases that number of individuals. The change n the size of a
population over time can be shown by the following equation:


A change in the size of a population over a specific period of time is known as its

The growth rate and death rate of a population changes over time because birth
rates and death rates increase and/or decrease. Growth rates can be positive,
negative or zero and for the growth rate to be zero, the average number of births
must equal the average number of deaths.

For example, if each pair of adults in the population managed to produce 2
offspring, and each of the offspring survived to reproduce, the population would
stay the same size. If the adults are not replaced in the population by new births
then the population will decrease; that is the growth rate will be negative. (complete
lab worksheet)

How Fast?

A female sea turtle could lay as many as 2000 eggs n her lifetime and if all of them
were to survive, the turtle population would grow extremely fast!!

Unfortunately not all of the hatchlings survive and populations usually remain about
the same size year after year. This is because various factors kill many individuals
before they have a chance to reproduce and it is these factors that control the
size of populations.

The fastest rate that a species’ population can grow s called its biotic potential
and it is limited by the maximum number of offspring each member of the
population can produce. This is called its reproductive potential. As one might
imagine, some species have a much higher reproductive potential than others. For
example, as mentioned earlier, Darwin calculated that a pair of elephants could
produce 19 million descendants in under 750 years; whereas a single bacterium can
produce 19 million descendants in of days or weeks!!!
                    Environmental Science 2010-2011

Population Growth Lab Worksheet

Count out 5 beans to represent the starting population of a species.

Assume that 20% of the species each have 2 offspring and also assume that 20%
of the species die each year.


Calculate the number of beans to add or subtract for 1 year. If necessary, round
to whole numbers and add to or remove beans from your population as required.

Record the change, if any, in population size.

Repeat modelling your species population over a period of 10 years.

Draw a graph of your results.
Independent variable on the x-axis, dependent variable on the y-axis.