Populations in ecosystems

Why do we use randomly placed quadrats?

Used in a fairly uniform area

Avoids bias

Data is therefore representative

Allows the use of stats tests

What three things must we consider when using quadrats?

Size of the species and distribution of species within an area

Number of samples being taken in the area

Position of each quadrat

Describe the process of random sampling

1. Set out a grid- two long tape measures at right angles to eachother

2. Obtain random pairs of coordinates

3. Place a quadrat at the intersection of the pairs of coordinates

4. count the organisms

5. record data

6. repeat

How many repeats?

A large number to make sure results are reliable, a minimum of 10-15

Enough to carry out a stats test

So can calculate a running mean

Describe the process of using quadrats along a belt transect

1. Lay out a tape measure and place a frame quadrat at right angles to the line at predetermined regular intervals

2. Using a point quadrat lower the pins into the vegetation and record the species touching the pins. Do not just count the tallest species touching the pins. There may be other plants growing underneath, which should also be recorded

3. Flip the frame quadrat over away from the transect and use the point quadrat to obtain a second set of data

What is an advantage of a belt transect?

Gives information on abundance

What is a disadvantage of a belt transect?

takes longer than line transect

Define abundance

is the number of individual species within a given area.

Define percentage cover

is an estimate of an area within a quadrat that a particular species covers.

Describe the mark release recapture method

1. Capture a number of animals

2. carefully mark them (avoids chance of detection)

3. Release them and allow time to re-integrate with population

4. Collect 2nd sample

5. Count and record number of marked and unmarked organisms

6. Use MRR formula to estimate population size

What equation can be used to estimate population size?

Estimated total population= Number of organisms in sample 1 X number of organisms in sample 2

number of marked organisms recaptured

What are assumptions that MRR method relies on?

Some organisms may die, migrate or reproduce

More likely to be caught than others

May not mix evenly back into population

Mark may rub off

What is succession?

Succession is a change in community over time.

Describe the features of a pioneer community

Low diversity

harsh environmental conditions

only pioneer species that are adapted to meet conditions can grow here

Describe the features of a climax community

High diversity

environmental conditions not so harsh

many more species can grow here

Describe the process of succession

Change in plant communities at a site over time- from pioneer species to climax community

At each stage plant community alters the soil and microclimate, allowing the establishment of other species

One community of plants is therefore replaced by another as the succession develops. (plants outcompete eachother)

Eventually a climax community is reached where the vegetation is in a state of equilibrium with the environment and there is no further influx of new species

What are the features of a pioneer species?

Production of vast quantities of wind dispersal seeds or spores, so they can easily reach isolated situations such as volcanic islands

Rapid germination of seeds on arrival

ability to photosynthesise

ability to fix nitrogen from the atmosphere

tolerance to extreme conditions

What are the stages of primary succession?

1. Pioneer species colonise area

2. weathering of rock and death/decomposition of pioneers produce sand or soil

3. As pioneer species die and decompose, they add nutrients to the soil created from weathering

4. Soil becomes adequately nutritious to support a community of small plants

5. Mosses then colonise the area, followed by ferns. Biodiversity increases and environment becomes less hostile

6. Organisms die and decompose along with the continued weathering a thicker layer of soil builds up

7. small flowering plants become established, followed by grasses, shrubs and then trees

8. The climax community comprises a balanced equilibrium of species with few, if any replacing those that have become established. Biodiversity decreases

Explain why pioneer species gradually become replaced by other plant species during succession

The new species outcompete the pioneer species.

What is a climax community?

A stable community where no further succession occurs.

What are the most common features of succession?

Abiotic factors become less hostile

Greater number and variety of habitats and food sources

more complex food webs

increase in biomass

change in species composition

New species outcompete each other

Describe secondary succession and compare with primary succession

Land clearance for agriculture or forest fire

Secondary succession is faster as soil is already present.

No death and decomposition of pioneers produce sand species.

No soil present in primary succession

Common features of succession are present in both

What happens to the hostility of the environment as succession progresses?

Becomes less hostile

Define ecology

The study of relationships between organisms and their environment

What is a biotic factor?

Any living component within an environment in which the action of the organism affects the life of another organism

What is an abiotic factor?

A non-living (chemical or physical) factor in the environment that affects the life of an organism

Name some biotic factors

Competition, predation, disease and availability of food

Name some abiotic factors

Temperature, pH, water availability and humidity, light

Define ecosystem

Areas in which organisms interact with both the environment and with each other- can range in size

Define population

All of the organisms of a single species living in the same area

Define community

All of the population of different species present in an environment at the same time

Define a habitat

Within an ecosystem, there are many areas where different organisms can live

Define ecological niche

Where an organism lives and what role it plays within the ecosystem

Define intraspecific competition

Occurs between individuals of the same species. They compete for resources such as, food, water, breeding sites, habitats, mates, mineral ions and light

Define interspecific competition

Occurs between individuals of different species and there is competition for resources such as food, water and habitats

What causes the fluctuation cycles?

Predation by the predator

Changes in the food supply

A combination of both

What does conservation of habitats frequently involve?

Involves management of succession

What 3 reasons are there for conservation?

Ethical, Economic and cultural/ aesthetics