11.2 - Types of sampling Flashcards
What is sampling?
Sampling is taking measurements of a limited number of individual organisms in an area to estimate the total number of organisms, species distribution, or measured characteristics in the entire habitat.
Why is sampling necessary in biodiversity studies?
It is often impossible to count or measure all organisms in an area, so sampling provides an estimate without counting every individual.
What is abundance in ecological sampling?
Abundance refers to the number of individuals of a species present in a given area.
How can sampling be used to measure characteristics of organisms?
By measuring a sample of organisms (e.g., plant height) and calculating an average, a more reliable estimate of the characteristic for the whole population can be obtained.
What are the two main types of sampling?
Random sampling and non-random sampling.
What is random sampling?
A sampling method where individuals are selected by chance, ensuring each organism has an equal likelihood of being chosen. This eliminates bias.
How do you perform random sampling using a quadrat?
- Mark out a grid using two tape measures at right angles.
- Use a random number generator to select x and y coordinates.
- Place a quadrat at the selected coordinates.
- Record the organisms present or measure a specific characteristic.
- Repeat for multiple quadrat placements to ensure reliable data.
What is non-random sampling?
A sampling method where the sample is not chosen randomly. This can be useful when studying specific patterns or distributions.
What are the three types of non-random sampling?
Opportunistic, stratified, and systematic sampling.
What is opportunistic sampling? Why is it weak?
Opportunistic sampling involves selecting organisms that are easily available.
It is the weakest method because it is highly biased and may not be representative of the entire population.
What is stratified sampling?
A method where the population is divided into subgroups (strata) based on a characteristic (e.g., males and females). A random sample is then taken from each subgroup proportional to its size.
When is stratified sampling useful?
When studying populations with distinct subgroups.
When ensuring all groups are fairly represented in the sample.
What is systematic sampling?
A method where samples are taken at fixed intervals along a transect, allowing for the study of gradual changes in species distribution.
What are the two types of transects used in systematic sampling?
Line transects and belt transects.
What is a line transect?
A single line is marked across the habitat, and organisms touching the line are recorded at set intervals.
What is a belt transect? How does it improve accuracy?
Two parallel lines are marked, and samples are taken from the entire area between them.
It provides more data than a line transect, making it more reliable.
Why is sampling never completely representative of a habitat?
Due to sampling bias and chance.
What is sampling bias? How can it be reduced?
Bias occurs when certain areas are chosen unfairly, either deliberately or accidentally (e.g., picking a flower-rich spot).
It can be reduced by using random sampling, which removes human selection.
What is chance in sampling, and how can it be minimized?
Chance occurs when the selected sample is not representative by luck (e.g., only catching the largest worms).
It can be minimized by using a larger sample size, reducing the effect of anomalies.
Why does increasing sample size improve reliability?
It reduces the influence of anomalies.
It increases the accuracy of the estimated population data.
