Sampling Flashcards
(24 cards)
What are the 4 common ways of sampling to estimate the population?
Quadrants
Transects
Mark and recapture
Point
What type of area is useful for Quadrant sampling?
direct count of organisms in smaller ‘samples’ of the larger study area and are placed randomly or in a grid pattern on the sample area, occurrences of organisms in the squares are noted
When is Quadrant sampling used for? (3)
Impossible or impractical
Conjunction
Community composition
Used when direct counting of organisms is impossible or impractical
Used in conjunction with transects, but may be used singularly when the study area is relatively uniform
Well suited to determining community composition and features of population abundance; species density, frequency of occurrence, percentage cover and biomass (if harvested)
What does Quadrant sampling estimate?
to estimate population abundance (number), density and distribution.
Average Density =
Average Density = Total of no. of individuals counted / Number of quadrants x area of each quadrant
What is Mark and recapture sampling useful for? (3)
Used for highly mobile organisms.
Determining total population density for highly mobile species in a certain area (eg.butterflies)
Movements of individuals in the population can be tracked (especially when used in conjunction with electronic tracking device)
How is population calculated using mark and recapture?
Population is sampled by capturing as many individuals as possible, which are marked and released before being sampled again, after a suitable period of time.
What is transect sampling useful for? (3)
Useful for determining species distributions and determine changes (trends) along an environment gradient (eg. altitude).
Are used for sedentary or slow moving organisms.
When placed randomly, they provide a quick measure of species occurrences.
What are three different types of transect sampling?
different types (belt or line, continuous or interrupted)
What type of organism are both quadrants and transects used for?
Both quadrants and transects are used for sedentary or slow moving organisms
Total Population=
Total Population= No. of animals in 1st sample x No. of animals in 2nd sample/ No. of animals marked in 2nd sample
What are 3 factors that can interfere with the accuracy of population estimates?
Time between recapture
Time (too long/ too short) - may not mix
births and deaths could occur.
Emigration and immigration
What are 4 things to consider when using quadrant sampling?
Time consuming to do well.
plants and slow-moving animals are easily recorded, cryptic or moving animals need to be trapped or recorded using appropriate methods
Quadrant size must be appropriate for organisms to be sampled and information acquired.
Some disturbance if organisms are removed
What is transect sampling?
Lines are drawn across a map and organisms occurring along the line are sampled.
What are line transects? (2)
Species occurring on the line are recorded (all along the time or more usually at regular intervals).
They can be random or may follow an environmental gradient
What are 4 things to consider when using line transects sampling?
Suitable for plants and immobile or easily caught animals
Disturbance in environment can be minimised
Species occurring in abundance may be missed
Time efficient
What are belt transects?
measured strip located across the study area to highlight any transitions.
Along the belt quadrants are used to sample the plants and animals at regular intervals.
What are some conditions of belt transects? (4)
Time consuming to do well
Suitable for plants and immobile or easily caught animals
Good chance of recording most or all species
Efforts should be made to minimise disturbance to environment
What are 5 things to consider for mark and recapture sampling?
Time consuming to do well
Not suitable for immobile species, Used for highly mobile organisms.
Population should have a finite boundary
Period between samplings must allow for redistribution of marked animals in the population.
Marking should present little disturbance and should not affect behaviour
What are two types of point sampling?
Random and Systematic
What is point sampling?
Individual points are chosen on a map (grid reference or random numbers applied to a map grid) and the organisms are sampled at those points.
Mobile organisms may be sampled using traps or nets
What is point sampling useful for? (1)
Determining species abundance and community composition. If samples are large enough, population characteristics (eg. age structure, reproductive parameters) can be determined
What are 4 things to consider for point sampling?
Time efficient.
Suitable for most organisms.
Depending on methods used, disturbance to the environment can be minimised.
Species occurring in low abundance may be missed
Density=
Density = population/area
