Investigating populations and abiotic factors

In general how do you investigate populations of organisms?

By observing the abundance and distribution of a species in a particular area

What is the benefit of sampling?

Makes the investigation faster

How do you take a sample?

• choose an area place your quadrat there

• Count the number of individuals of each species

• Repeat and average

• Estimate the total number of individuals or the total number of different species in the habitat

What must you keep in mind when sampling different habitats?

Use the same sampling technique for both

What are the two sampling techniques?

Random

• avoids bias

• Random number generators for coordinates

Non random

• required when there is a lot of variety in abiotic features in an area to make sure all areas are sampled

What is systematic sampling?

• A type of non-random sampling

• When samples are taken at fixed intervals

• Usually long a line

• E.g quadrants along a transect

• The line where abiotic factors gradually change

• Environmental gradient

What type of populations are frame quadrats used for ?

Immobile populations e.g plants

How can you use percentage cover to investigate a population?

• use a quadrat and place it on the ground at a random location picked my a random number generator

• count the number of squares that are covered by each plant species by more than half of the square

• divide this number by the number of squares in the quadrat and multiply by 100

• repeat this at several points within the area and average the results

How can point quadrats also be used to investigate plant populations?

• point quadrats are horizontal bars on 2 legs with a series of holes at set intervals along its length

• they are place at a random point in an area (coordinates generated by a random number generator)

• pins are dropped through the holes in the frame and every plant that each pin touches is records

• the number of individuals of each species is recorded in each quadrat

• percentage cover can be calculated by dividing the number of pins that have touches a species by the total number of pins

When are point quadrats useful?

When investigating area where there is lots of dense vegetation close to the ground

What should you do when using a point quadrat when the pin overlaps two species?

Count them all

What are transects used for?

• to investigate the distribution of plant populations along an environmental gradient

• to show the change of distribution of species along the transect

What are the 2 types of transects?

• Line transects - a tape measure placed along the transect and the species that touch the tape are recorded

• Belt transects - frame quadrats are placed next to each other along a transect (either along the whole transect or in fixed intervals )

What can be represented on a site diagram?

Abundance and distribution

X axis could be distance along a transect

Y axis could be the abundance of organism in (percentage cover)

How can you measure temperature rainfall and humidity?

• temperature - thermometer

• rainfall - rain gauge (funnel attached to measuring cylinder - can observe volume of rain collected over a period of time)

• humidity - electronic hygrometer

When might you need to measure oxygen availability ?

when investigating aquatic animals

How can you measure oxygen availability and solar input?

• oxygen sensor

• Light sensor

What edaphic factors?

soil conditions

How can you measure edaphic factors?

• pH using indicator liquid and a sample of soil mixed with water

• Using an electronic pH monitor

• Moisture content - mass of a sample of soil before and after being dried out in an oven at 80-100 degrees (find percentage decrease)

What is topography?

the shape and features of the earth surface

How can I measure topography?

• finding relief by using a gps and take height readings at different points across a surface

• or by using contour lines of a map

• slope angle by using a clinometer