3.2 Distribution Of Organisms

What do we call factors affecting organisms in the ecosystem that are directly related to other living things?

Biotic factors

Give examples of biotic factors.

Competition; disease; food availability; grazing; predation

What are abiotic factors?

Physical or non-living factors affecting organisms in an ecosystem

Give examples of abiotic factors.

Light intensity; soil moisture; oxygen concentration; ph; temperature

Give 3 reasons why it is impossible to count every organism in an ecosystem.

Too many organisms to count- counting errors; would take too long to count; leads to habitat damage

Why are several samples taken?

Representative sampling - makes results more reliable

What is a sample?

A small representation of a larger population

What is the relationship between the size of the area and the number of samples?

As the area to be samples increase, the number of samples required increases

What is the benefit of quantitative data?

Allows comparisons to be made and trends to be identified

What is a quadrat used for?

To sample and estimate the number of a species of plant in an ecosystem

How are quadrats thrown?

Randomly

Give sources of error in using a quadrat.

Organisms wrongly identified; organisms wrongly counted; too few samples taken

How are errors in using a quadrat minimised?

Use a key to identify organisms; do not count organisms unless fully in quadrat; take more samples

What is used to sample invertebrates in leaf litter?

Pitfall trap

Give sources of error in using pitfall traps.

Trap not level with soil surface; animals escaping from trap; animals being eaten in trap; animals drown in trap

How are errors when using a pitfall trap minimised?

Dig hole deep enough that trap is level with soil surface; put lid on trap; empty trap frequently; put drainage holes in trap

What piece of apparatus is used to measure light intensity?

Light meter

What is a source of error when using a light meter?

Light sensor being shaded by users

How would you minimise errors when using a light meter?

Ensure the light sensor is not shaded by the users

What piece of apparatus is used to measure temperature?

Thermometer

What is a source of error when using a thermometer?

It not being inserted deep enough into the soil/water

How would you minimise errors when using a thermometer?

Pushing the thermometer to half its depth into the soil/water

What piece of apparatus do we use to measure soil moisture?

Moisture meter and probe

What is a source of error when using a moisture meter?

Moisture remaining on the probe from a previous sample

How would you minimise errors when using a moisture meter?

Wipe the probe between samples/readings

What piece of apparatus do we use to measure soil ph?

Ph meter and probe

What is a source of error when using a ph meter?

Soil remaining on the probe after a previous sample

How would you minimise errors when using a ph meter?

Wipe the probe after previous sample

What is used to identify organisms?

Key

What kind of key is a series of numbered questions?

Paired statement key

Why should organisms not be removed from the ecosystem in order to identify them?

Causes ecological damage

Give the impact of high intensity grazing on biodiversity.

Decreases biodiversity

Give the impact of moderate intensity grazing on biodiversity.

Increases biodiversity

Give the impact of low intensity grazing on biodiversity.

Decreases biodiversity

Give the impact of high intensity predation on biodiversity.

Decreases biodiversity

Give the impact of moderate intensity predation on biodiversity.

Increases biodiversity

Give the impact of low intensity predation on biodiversity.

Decreases biodiversity

What effect does acid rain have on plants?

Damages leaves, reducing photosynthesis and reducing plant biodiversity

What effect does acid rain have on aquatic life?

Decreases ph of water

What effect does a decrease on water temperature have on biodiversity?

Reduces fish biodiversity due to enzymes not working optimally

Give the meaning of the term exploitation.

To remove resources from an ecosystem

Give 3 ways that humans exploit an ecosystem.

Overhunting; overfishing; overgrazing

What effect does overexploitation have on an ecosystem?

Reduces biodiversity

What is an indicator species?

A species which by its presence, absence or abundance shows the level of pollution in an ecosystem

What are lichens an indicator species for?

Sulfur dioxide in air

What species of lichen is most sensitive to sulfur dioxide pollution?

Hairy

What species of lichen is least sensitive to sulfur dioxide pollution?

Crusty

What are freshwater invertebrates indicator species for?

Dissolved oxygen concentration

Give freshwater invertebrate species found in clean water.

Mayfly and stonefly nymphs

Give freshwater invertebrate species found in water polluted with organic waste.

Sludgeworms, rat-tailed maggots