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8.5    Local Environment Notes - Section 1

   

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The distribution, diversity and numbers of plants and animals found in ecosystems are determined by the biotic and abiotic factors

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Section 1          Local Environment          :::          Populations

 

 

8.5.1.a

Describe the differences between abiotic and biotic features of the environment

   

8.5.1.b

Compare the abiotic characteristics of aquatic and terrestrial environments

   

8.5.1.c

Identify the factors determining the distribution and abundance of a species in each environment

   

8.5.1.d

Describe and explain the short- and long-term consequences on the ecosystem of members of the same species competing for resources

 

8.5.1.e

Explain the need to use sampling techniques to make population estimates when total counts cannot be made

   

8.5.1.i

Perform a first-hand investigation using transect, random quadrat, capture-recapture and tagging/marking methods to make estimates of real or simulated populations of organisms and use the available evidence to discuss the advantages and disadvantages of these methods

   


 

 

8.5.1.a

Describe the differences between abiotic and biotic features of the environment

 

 

The environment is everything that is external to the organism.  Both nonliving and living factors interact to make up the total environment of organisms.

 

Abiotic Factors

 

Abiotic factors are the non-living features of the environment.  These factors rarely threaten the survival of a species but will greatly affect their populations.  They effect the type of ecosystem and therefore the distribution and abundance of organisms within that ecosystem.

q       Physical factors include temperature, light, landform, tides, shelter

q       Chemical factors include amount of water, salinity, soil nutrients

 

Biotic factors

 

Biotic factors are the living organisms that occur in the environment.  The distribution and abundance of organisms in an ecosystem is greatly affected by the organisms that live in the ecosystem.  An organism may be affected by:

 

·               Activities of members of the same species

        Competing for resources

        A mate for reproduction

·               Activities of members of different species.

        A source of food

        A predator or a parasite

        A disease causing organism

  

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8.5.1.b

Compare the abiotic characteristics of aquatic and terrestrial environments

 

 

Abiotic features of Aquatic and Terrestrial Environments

 

Abiotic features of the environment vary greatly from place to place.  The greatest diversity exists between the abiotic features of an aquatic (water) environment and a terrestrial (land) environment.

 

The table below shows differences in the abiotic feature of these two environments.

 

Abiotic feature

Aquatic environment

Terrestrial environment

Buoyancy

Water exerts an upward force on objects in it allowing floatation.

Air provides little floatation or support for organisms.

Viscosity

Refers to the resistance to movement – “stickiness”

Water has a greater resistance to movement then air.

Air has a smaller resistance to movement than water.

Light

Available light decreases with depth.

Light is readily available

Water

Abundant supply of water

Availability of water varies greatly

Oxygen availability

The availability of oxygen is low

Oxygen availability is high

Nutrients

Dissolved minerals are readily available

Availability of dissolved minerals varies greatly depending on soil type and quality, and water.

Temperature variation

In large bodies of water, temperature is relatively constant.  Temperature also decreases with depth.

On land large and rapid temperature changes can occur.  Temperature also decreases with altitude.

   

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8.5.1.c

Identify the factors determining the distribution and abundance of a species in each environment

 

Numbers of Organisms

 

Population refers to members of the same species living in the same habitat.

¨      The distribution of an organism refers to where an organism is found.

¨      The abundance of an organism refers to the numbers of an organism in the area.

All the organisms living in the same area makes up a community [eg the marine animals and plants found on a coastal rock platform make up a rock platform community].  A community of organisms and their environment interacting as a unit is termed an ecosystem.

 

The particular set of abiotic and biotic factors determines the distribution and abundance of a species.  The factors include:

·        European rabbits are rarely found in Northern Australia.  The main reason affecting their distribution is the climate (particularly heat) (Climate is a set of abiotic factors)

·        An adequate supply of water and a balance of inorganic nutrients are needed in the soil.  Some plants will not grow in sandy soil because it cannot hold enough water or nutrients.

·        Members of the same species can influence their own numbers in a community.  Under population can be a problem

        Large herds allow members to protect their young from predators.

        Low numbers may mean finding a mate is very difficult (eg whales)

   

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8.5.1.d

Describe and explain the short- and long-term consequences on the ecosystem of members of the same species competing for resources

 

 

Competition and Ecosystems

 

An ecosystem is any space containing living organisms interacting with each other and with the non-living parts of that environment.  In such a system there is an exchange of materials and energy between the organisms and their environment.

 

In any community, all the organisms are part of one, large food web.  Therefore, the numbers of one species will affect the numbers of other species.  Changes to any part of a community – living or non-living – can set off a whole series of other changes.

 

Organisms belonging to the same species use the same resources.  If these resources are limited the individuals must compete with one another.  Competition for resources limits population size.  Population increases create more intense competition for resources that has a greater effect on limiting the population.

 

Generally, plant populations tend to be limited by competition for resources, particularly light, water and minerals (the abiotic environment).  The population of plant eating organisms tends to be limited by the availability of food and the number of predators.  Predator populations tend to be limited by competition for food (plant eating organisms).

 

In the short-term there is usually a constant change in the population of individual species.  The short-term consequence on the ecosystem is a constant change in available resources for the organism.  This occurs because, as the population changes, resource-use changes.  More resources mean a bigger population, which then results in fewer resources per individual resulting in a population decrease.

 

In the long term the population of an individual organism remains fairly constant.  The long-term consequence for the ecosystem is stability.  Stability occurs because competition produces environmental changes to return populations to an average level.  It is important to remember that stable ecosystems are not static – they do slowly change.  Further, they can change rapidly if there are major changes in the environment.

   

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8.5.1.e

Explain the need to use sampling techniques to make population estimates when total counts cannot be made

   

8.5.1.i

Perform a first-hand investigation using transect, random quadrat, capture-recapture and tagging/marking methods to make estimates of real or simulated populations of organisms and use the available evidence to discuss the advantages and disadvantages of these methods

 

 

Sampling techniques

 

To count the total population of a plant or animal species in an area could be an enormous job and take a long time.  When the organisms are in huge numbers, scattered over a large area, mobile or difficult to see or capture it is often impossible to complete a total count of all the organisms in an area.

 

To make the job easier, only certain areas or positions are studied.  This involves a method called sampling.  Example of the sampling techniques used to estimate population numbers are:

¨      Selection of random quadrats

¨      Line transect

¨      Capture and recapture

¨      Tagging / marking methods.

 

 

 

Random Quadrats

 

The random quadrat method is usually used for estimating large numbers of small organisms that cannot move, living in a relatively defined area.  A sample area is selected by placing a square frame, called a quadrat, on the ground.  A one square metre frame is generally used.  The number of organisms within the quadrat is counted several times and averaged.

 

An estimate of the total population is determined by moving the quadrat around the area being studied.  Each new position of the quadrat is selected at random.  Counts in each sample are made and the total area calculated.  The number of sample plots used depends on time available, accuracy required and the total area being investigated and a number of other factors.

 

Random Quadrat Method

 

1.      Mark out a 2cm x 2cm square on the map.

2.      Count the number of organisms (dots) in this square (square A)

3.      Record this number.

4.      Repeat steps 1,2& 3 for TWO other areas (square B & C).

5.      Measure the size of the rectangle map area in cm2and then

6.      Calculate the number of 2cm x 2cm squares in this rectangle map area by dividing total area by 4.

 

 

The Line Transect

 

Sometimes it is useful to determine the change in population along a line between two points.  For example, on a rock platform the numbers of particular organisms change as you walk along a line moving away from the wave area.  This change is influenced by a number of abiotic factors.  The change in the population along a transect can be measured by using a quadrat at intervals or by making appropriate observations.

 

 

Capture / Recapture

 

Counting the population of organisms that can move can be very difficult.  It is usual to calculate an estimate after counting a number of samples of the population.  A technique known as: capture – recapture can be used.

 

In this method

 

·         A number of organisms are captured and counted

·         These captured organisms are then “tagged” [No captured and tagged]

·         The tagged organisms are then released.

Once released the organisms move around in their environment.

·         Another group of these organisms are (re)captured – this will include some tagged and some untagged organisms [No recaptured & tagged; No recaptured & untagged]

·         The number of tagged and the number of untagged organisms is counted.

·         The data is recorded in a table.

 

·         An estimate of the population can be calculated using the following formula:

 

Pop. estimate            =            No recaptured & untagged            x No captured & tagged

                                                                        No recaptured & tagged

 

·         The “recapturing” steps can be repeated several times to get several estimates.  These estimates can be graphed or averaged to get a more reliable population estimate.

  

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