1 of 30© Boardworks Ltd 2011 Investigating Ecosystems.

1 of 30 © Boardworks Ltd 2011

Investigating Ecosystems


The environment is made of many different types of ecosystems, such as seashores, forests, lakes and deserts.

Each ecosystem can be divided into a:

community – the living (biotic) part, i.e. all the different organisms living in that particular habitat.

habitat – the non-living (abiotic) part, i.e. the physical area in which organisms live

Each community is made up of many different populations. A population is all the members of a particular species living in one habitat – for example, the population of red squirrels in an oak wood.

Ecological terms


Ecological terms


Self-supporting ecosystems

Some ecosystems are self-supporting. This means they do not need any external input apart from an energy source, such as the Sun.

An example of a self-supporting ecosystem is a rain forest. Energy comes from the Sun and is used by plants to make carbohydrates during photosynthesis. These carbohydrates provide energy for animals. Dead animals and plants return nutrients to the soil.

Some ecosystems need more external input. An example is an intensively-farmed corn field. As crops are removed from the ecosystem, the farmer must replace nutrients each year, often in the form of fertilizer.


Habitats

The availability of these physical factors will affect the number and distribution of organisms within the habitat.

A habitat has all of the things that an organism needs to survive, such as the right amounts of oxygen, water, light and shelter.

If these factors are not plentiful in a particular habitat, organisms will compete for them.


Physical factors affecting organisms


Competition in the forest


Investigating biodiversity


Sampling in a habitat

It would be impossible to count all the individual organisms in a habitat by hand. Instead, we count a sample from a small area and multiply this by the total area of the habitat. This gives an estimate of the total population.

Common sampling methods include:

quadrats

belt and line transects.

Animals are harder to sample than plants because they move around. Methods used to collect animals include:

pooters

nets

pit-fall traps.


Sampling a population


Estimating population size

Once you have collected sample data, you can estimate the number of organisms in the entire habitat by scaling up.

When estimating the size of an animal population, you can use capture–recapture methods, then calculate the total population size.

population size = no. in 2nd sample previously marked

no. in 1st sample × no. in 2nd sample


Assumptions

For the capture–recapture method to work, certain assumptions must be made.

Assume that the population size has remained the same (no deaths or animals moving to or from the habitat)

Assume that the sampling methods used each time are identical

Assume that marking an organism does not affect its survival (for example, by making it more obvious to predators).


Hints for investigating ecosystems

When carrying out ecological investigations, it is important that your methods are valid and your data is reproducible.

If possible, repeat your experiment several times. If your results are not similar, your experiment may not be reproducible.

In order to make your findings valid and reproducible, your sample size should be large. For example, when using capture–recapture methods, a small sample size will mean that few animals will be captured in both samples.

Remember to chose methods suitable to the organisms you are studying. For example, line transects can be problematic if there are many plants touching the line, or if it is difficult to count the individual plants, as in the case of grass.


Random sampling and quadrats


Identifying organisms


Zonation

high tide

low tide

What can you observe about the distribution of barnacles on this shoreline? What do you think might have caused this?

Zonation occurs in habitats such as sea shores and wetlands. A gradual change in an abiotic factor (like water availability or salinity) leads to a gradual change in the distribution of species across the habitat.


A line transect is useful for examining the effect of zonation on biodiversity.

Mapping line transects

This graph shows the presence of each species along the line transect. In this case, the line transect crosses a stream.

0 1 2 3 4 5 6 7distance along transect (m)

A line transect does not reflect the density of each species along the line, so it is only useful as a basic analytical tool.


Kite diagrams

When plotting the population data, one should plot half the population above the line and half below, then join the points to form a kite shape.

Kite diagrams show the distribution and density of different organisms.


What is biodiversity?


Biodiversity in natural ecosystems

Native woodlands are natural ecosystems, as are lakes.

Biodiversity is a measure of how many different species are present in an area.

Natural ecosystems have high biodiversity because they have developed over many years, and because there may be few external factors acting on the habitat.


Fish farms and forestry plantations are examples of artificial ecosystems. They have been created by people, not by nature.

Biodiversity in man-made ecosystems

Artificial ecosystems tend to have low biodiversity – only a few different species live in them.

This is because they are often carefully controlled by people. For example, farmers use pesticides to kill weeds, insects and fungi that share a habitat with the farmer’s crops.


High or low biodiversity?


Glossary


Anagrams


Multiple-choice quiz

1 of 30© Boardworks Ltd 2011 Investigating Ecosystems.

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