Investing populations

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  • Created by: Hindleyc
  • Created on: 03-01-19 21:02
What can size of population be estimated by?
-Randomly placed quadrats, or quadrats along a belt transect for slow moving or non-motile organisms. The mark-release recapture method for motile organisms
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How do they do it
Small samples of habitat studied in detail
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WHy
Counting every organism virtually impossible , time consuming and would almost certainly cause damage to habitat being studied
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what does this sample need to me?
Representative of habitat as whole for reliable conc to be drawn from findings
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What sampling techniques are used in study of habitats
-random sampling using frame or point quadrants or -systematic sampling along a belt transect
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What does a point quadrat consist of
horizontal bar supported by 2 legs at set intervals along are 10 holes through each of which a pin may be dropped.
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How does it work
Each species that the pin touches is then recorded
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What is a frame quadrat
Square frame divided by wire or string into equally sized subdivisions
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How is it often designed
so it can be folded to make it more compact for storage and transport
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How do they do it
Quadrat placed at different locations within the area being studied. abundance of each species within quadrat is recorded
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What are 3 factors to consider when using quadrats
size of quadrat, number of sample quadrats to record within the study area, position of each quadrat
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What does size of quadrat to use depend on
Size of plant or animals being counted and how they are distributed within the area,
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Why
Larger species require larger quadrats (and reverse)
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Where a population of species is not evenly distributed throughout the area what would suit it
large number of small quadrats will give more representative results that a small number of large ones
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The larger the number of sample quadrats the more..
reliable the results will be
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What needs to be made because recording of species within a quadrat is time-consuming task
a balance needs to be struck b/w the reliability of results and time available
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Greater the no. of species diff species present in the area being studied...
The greater the number of quadrats required to produce reliable results for a valid conclusion
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Why does the position of each quadrat within the study area have significance
To produce statistically significant results a technique known as random sampling must be used
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Why is sampling at random important?
To avoid bias in collecting data- ensures reliable data
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If 2 locations?
Close as possible to minimise soil,climatic and other abiotic differences
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example of random sampling method
Lay out 2 long tape measures at right angle along 2 sides of study area, obtain series of coordinates by using random number generator - computer or table. Place quadrat at intersection of each pair of coordinates and record species within it
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Why use systematic sampling along a belt transect
Sometimes more informative to measure abundance and distribution of a species in a systematic rather than a random manner
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When is it important
Where some form of gradual change takes place in communities of plants and animals eg stages of succession
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How is it made? (belt transect)
Stretching tape/string across ground in straight line, frame quadrat laid down alongside the line and species within recorded then moved its own length along line and process repeated giving record of species in a continuous belt
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How is abundance measured
Rand sampling with quadrats and counting along transect used to obtain measures of abundance- no, of indiviuals of a species within a given area
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What about for species that don't move around
Can be measured in several ways depending on. size and habitat of species being counted
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eg Frequency
likelihood of a particular species occurring in a quadrat
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When is this method useful
Where a species hard to count gives quick idea of species present and general distribution within an area. doesn't provide info on density and detailed distribution of a species
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Other eg-
percentage cover
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What does this do
estimate of area within a quadrat that a particular plant species covers
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When is this useful
Where species particularly abundant or difficult to count. adv in these situations are that data can be collected rapidly and individual plants don't need to be counted
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When is this less useful
Where organisms occur in overlapping layers (more probably plants)
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What do mark-release and recapture techniques work for?
Motile organisms that move away when approached often hidden and therefore difficult to find and identify - altogether diff techniques to estimate abundance of most animals
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Method
Known number of animals are caught , marked in some way and then released back into the community, sometime later a given number of individuals is collected randomly and the number of marked individuals is recorded
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How can size of population be calculated (estimate population size)
total no. of individuals in the 1st sample x total no. individuals in the second sample / number of marked individuals recaptured
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What does technique rely on
Number of assumptions
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1
Proportion of marked to unmarked individuals in the 2nd sample is the same as proportion of m to unmarked individuals in population as a whole
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2
Marked individuals from 1st sample distribute themselves evenly among the remainder of the population and have sufficient time to do so
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3
Population has definite boundary so that there is no immigration into or emigration out of the population
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4
There are few, if any, deaths and births within the population
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what must method of marking be
not toxic to the individual nor does it make the individual more conspicuous and therefore more liable to predation
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last assumption :)
mark or label is not lost or rubbed off during the investigation
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Other cards in this set

Card 2

Front

How do they do it

Back

Small samples of habitat studied in detail

Card 3

Front

WHy

Back

Preview of the front of card 3

Card 4

Front

what does this sample need to me?

Back

Preview of the front of card 4

Card 5

Front

What sampling techniques are used in study of habitats

Back

Preview of the front of card 5
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