What is the technical definition of a quadrat? Some sources I've read imply that a quadrat is a single square frame. Other written sources describe a quadrat as a square frame that is divided into equally sized subdivisions. Does the word 'quadrat' alone by definition perhaps refer to a single square frame that is considered to be a basic quadrat (or classic, if you like)? Is the frame that is divided into subdivisions (I've also seen referred to as a 'frame quadrat') therefore considered to be a type of specialized quadrat, perhaps utilized for extra precision in the practice of recording the abundance of a species being sampled? I am aware that there are also 'point' quadrats, but these I know are very different in model to the aforementioned quadrat frames (single or subdivided) and therefore something of their own (although used for the same purpose).
I really don't know which type of frame to picture when I read about quadrats. I wonder whether the word quadrat (that is without another preceding word like 'frame') refers exclusively to the single frame version, or if the word is used in a relaxed way and could mean either single or subdivided (aka. frame).
My confusion also brings me to something in a book I read about estimating population density. The book states:
Estimating population density - a method for plants and small mobile animals:
Place quadrats randomly
Count the number of organisms of the species you are investigating in each sample quadrat
Find the mean number per quadrat
Estimate the population size using the formula:
mean number of organisms x area of field/area per quadrat
The part of this that puzzles me is "find the mean number per quadrat." Because I don't know what type of quadrat to visualize, I'm unsure what you would do to obtain the mean. Would the quadrat in question not have to be one divided into subdivisions so that you would therefore carry out the equation: number of organisms in all subdivisions/number of subdivisions ?
Although this seems most sensible, I'm confused because the preceding text in this particular book seems to be discussing quadrats of a single frame only, and refers to them simply as 'quadrats.' In fact it isn't until the subsequent page of the book that 'frame quadrats' (i.e. quadrats that are subdivided) are introduced to the reader and discussed for the first time.
How then would you "find the mean number per quadrat?" Would you carry out repeats? In the case of plant species sampling, wouldn't you just keep getting more or less, if not exactly, the same data figure?
I'd be very appreciative if anyone might kindly shed some light on this!