Lecture 7: Quadrat Sampling Flashcards
What are two criteria to consider for optimal quadrat size and shape?
1) statistical: precision for lowest variance
2) ecological: organisms (N. Am.) /habitats scale (European)
Quadrat counts are suitable for 3 things
1) sessile, immobile organisms such as plants and sea anemones
2) relatively immobile organisms such as clams
3) Mobile animals caught on film
What are 2 factors affecting estimates for quadrat sampling?
1) edge effects (edge/ area ratio)
2) standard error (variability between quadrats)
These two factors need to be weighed against each other
Describe edge effect
The greater the edge the greater the number of decisions that have to be made on whether an organism is inside or outside the frame
What happens if the quadrat is dimensionless?
No edge effect
What three shapes are there for quadrat studies in order from least to most edge effect?
Circle, square, rectangle
What frame size is best to reduce SE? What is worst?
Best is smaller frames worst is larger frames
Why is there a larger mean weight for smaller quadrat sizes?
Because of cumulative edge effect.
What is the ideal-ish statistical quadrat design with plot size and number of samples?
Smaller plots with more samples
It is most desirable to have a larger number of smaller quadrats
Why do we want to use smaller frame sizes?
Many smaller frames have lower SE than fewer larger frames
What is the purpose of having nested quadrats?
Takes into account ecological scale
Determine the minimal area of a community to sample
What are example frame sizes for nested quadrats that take into account ecological scale?
Trees: 10 x 20m Shrubs: 5x5m Herbs: 1x1m Lichens and mosses: 0.1x0.1m i.e. 10x10cm
How do you get the minimum area of a community to sample and a species area curve?
The number of species increases as quadrat size is doubled and should eventually plateau at a scale that represents the minimum area of quadrat to use for study
Start with a small quadrat and double after counting the # of species.
Increase the list of new species discovered only, don’t keep recording species already seen.
Plot a minimum area curve called specie area curve
What is the flaw in determining the species area curve method?
If the starting point is unusual.
Rarity needs a different kind of design.
How do you read a species area curve?
The number of species added to list should increase as the quadrat size is doubled. The quadrat size where it plateaus is the minimum quadrat size necessary for community. If you get multiple plateaus then you have gone outside the community of interest and found new communities.
