Investihgating populations Flashcards
(18 cards)
what is abundance?
-the number of individuals of a species in a given space
what are the sampling techniques used in studying habitats?
- random sampling using frame quadrats or point quadrats
- systematic sampling along a belt transect
what is a point quadrat?
- a point quadrat which consists of a horizontal bar supported by two legs
- at set intervals along the horizontal bar are ten holes, through each of which a long pin may be dropped
- each species that the pin touches is then recorded
what are frame quadrats?
- a frame quadrat which is a square frame divided by string or wire into equally sized subdivisions
- it is often designed so that is can be folded to make it more compact for storage and transport
- the quadrat is placed in different locations within the area being studies
- the abundance of each species within the quadrat is then recorded
what are the factors to consider when using quadrats?
- the size of the quadrat
- the number of sample quadrats to record within the study area
- the position of each quadrat within the study area
how do you consider the size of quadrat to use?
- this will depend on the size of the plants or animals being counted and how they are distributed within the area
- larger species require larger quadrats
- where a population of species is not evenly distributed throughout the area, a large number of small quadrats will give more representative results than a small number of large ones
how do you consider the number of sample quadrats to record within the study area?
- the larger the number of sample quadrats the more reliable the results will be
- as the recording of species within a quadrat is a time consuming task a balance needs to be struc between the reliability of the results and the ime available
- the greater the number of different species present in the area being studied, the greater the number of quadrats required to produce reliable results for a valid conclusion
how do you consider the position of each quadrat within the study area?
-to produce statistically significant results a technique known as random sampling must be used
how do you carry out a random sample?
- lay out two long tape measures at right angles, along two sides of the study area
- obtain a series of coordinates by using random numbers aken from a table or generated by a computer
- place a quadrat at the intersection of each pair of coordinates and record the species within it
how do you carry out systematic sampling along belt transects?
- a belt transect can be made by stretching a string or tape across the ground in a straight line
- a frame quadrat is laid down alongside the line and the species within it recorded
- it is then moved its own length along the line and the process repeated which gives a record of species in a continuous belt
what is frequency?
- which is the likely hood of a particular species occurring in a quadrat
- if for example a species occurs in 15 out of 30 quadrats, the frequency of its occurance is 50%
- this method is useful where a species such as gradd, is hard to count
- it gives a quick idea of the species present and their general distribution within an area
- however it does not provide information on the density and detailed of a species
what is percentage cover?
- percentage cover is an estrimate of the area within a quadrat that a particular plant species covers
- the advantages in these situations are that data can be collected rapidly and individual plants do not need to be conted
- it is less useful where organisms occur in several overlapping layers
how do you obtyain reliable results?
- it is necessary to ensure that the sample size is large that is many quadrats are used and the mena of all the samples is obtained
- the larger the number of samples, the more representative the community as a whole will be the results
how do you carry out mark release recapture?
- a known number of animals are caught, marked in some way, and then released back into the community
- some time later a given number of individuals is collected randomly and the number of marked individuals is recorded
how do you calculate the estimated population size?
-tolal number of individuals in the first sample multiblied by the total number of individuals in the second sample divided by the number of marked individuals recaptured
what assumptions does mark release recapture make?
- the proportion of marked to unmarked individuals in the second sample is the same as the proportion of marked to unmarked individuals in the population as a whole
- the marked individuals released from the first sample dispute themselves evenly amongst the remainder of the population and have sufficient time to do so
- the population has a definite boundary so that there is no immigration into or emigration out of the population
- there are few if any deaths and birthd within the population
- the method of marking is not toxic to the individual nor does it make the individual more conspicupus and therefore more liable to prediction
- the mark or label is not lost or rubbed off during the investigation
what is abundance?
-abundance is the number of individuals of a species within a given area
how is abundance measures?
- frequency
- percentage cover
