Biology unit 4 notes

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  • Created by: jaymini
  • Created on: 09-06-13 15:04

Populations and ecosystems

Ecology- study of the inter relationships between organisms and their environment (living and non-living)

Biosphere- life supporting layer of land, air and water that surround the Earth


Self-contained functional units

Two main processes to consider: the flow of energy through the system and the cycling of elements within the system

Within each ecosystem there are a number of species which are made up of many groups that make up a population


Group of interbreeding organisms of one species in a habitat

Populations of different species form a community


All the populations of different organisms living and interacting in a particular place at the same time


Place where a community of organisms lives

Many habitats within an ecosystem

Within each habitat there are smaller units each with their own microclimate= microhabitats

Ecological niche

How an organism fits into the environment- where it lives and what it does there

No two species occupy the same ecological niche

Investigating populations

Number of individuals in a given space= abundance

It would damage the habitat to sample a whole population so we use a sample representative of the whole


Need to consider:

Size of the quadrat to use- depends on size of plant or animals being counted and how they are distributed within the area

Number of sample quadrats to record within the study area- larger number of sample quadrats the more reliable the results but can be time consuming. Greater number of species the greater number of sample quadrats needed to give valid results

Position of each quadrat within the study area- to produce statistically significant results random sampling must be used

Random sampling

Used to avoid bias data

To get truly random sampling we must lay out 2 long tape measures at 90° angle along two sides of study area, obtain coordinates by using a random number generator and place quadrat at intersection of each pair of coordinates and record data

Systematic sampling along transect

More informative to measure abundance and distribution of a species in a systematic way

Line transect- a piece of string or tape is used and anything that passes the line is recorded

Belt transect- strip usually a metre wide which is marked using a second line parallel to the first and anything between the two is recorded

Measuring abundance

Random sampling is used to obtain measures of abundance

Measured using:

Frequency- likelihood of a particular species occurring in a quadrat used when counting in grass where it is difficult to accurately measure

Percentage cover- estimate the area within a quadrat that a plant covers

Mark-release-recapture technique

Used to measure the abundance of animals in a population

Known number are caught, marked in some way, and then released back into the community and sometime later a given number are recaptured randomly and the number marked is recorded.

Population size = Number of animals marked X total caught second time

                                     Number of marked animals caught second time

Relies on…



Hey, these are great concise notes! thank you for putting them up. Do you mind telling me What grade you got for this?

Marta Kohls

Great notes! 

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