6.3.1 - measuring Distribution And Abundance

Question 1

What is distribution

Answer 1

Refers to where individual organisms are found within an ecosystem. Distribution is usually uneven throughout an ecosystem and organisms are typically found where the abiotic factors suit them. This allows their survival rate to be high as all the resources they need to live are available and predation is low

Question 2

How to measure distribution in an ecosystem

Answer 2

Line or belt transect. Both are forms of systematic and non random sampling but belt provides slightly more info.

Question 3

What is systematic sampling?

Answer 3

Different areas within an overall habitat are identified, which are then sampled separately. This has its advantages over random sampling as it allows us to identify how the differing abiotic factors in different areas affects the distribution of each species for example, systematic sampling may be used to see how species change from inland to the beach.

Question 4

What is abundance

Answer 4

The number of individuals of a species present in an area at any given time. This may fluctuate daily.

• immigration and births will inc numbers
• emigration and deaths will dec numbers

Question 5

What are populations?

Answer 5

A group of similar organisms living in a given area at a given time. And they can rarely be counted accurately. E.g. some animals elude capture and it is way too time consuming to capture all and counting them. If you do that it could damage environment as well

Question 6

What do we do to measure abundance then?

Answer 6

A sample can be used, however it can never be entirely representative of an entire population. To increase accuracy, a bigger sample size should be used. The bigger the sample size, the low chance it will influence the result. Random sampling should be used to reduce bias as well.

Question 7

How to measure plant abundance?

Answer 7

Quadrats are placed randomly in an area. Abundance is then measured in these quadrants by counting their numbers inside the quadrat.

The formula: number of individuals in a sample/area of sample = estimated population size

Question 8

How to measure animal abundance

Answer 8

Mark release recapture!

Capture as many as possible
Mark them
Release and allow time for redistribution
Recapture as many in the original sample area
Record number of marked an unmarked and release them all

Number of individuals in first sample x Second sample/ number of recaptured individuals = estimated pop size