Final answer:
The method of counting individuals of a tree species between two fixed points is known as a line-transect survey. This is different from the quadrat method used for immobile organisms and the mark and recapture technique used for mobile organisms to measure population size and density.
Step-by-step explanation:
A researcher who is counting the number of individuals of a tree species between two fixed points is making a line-transect survey. This method involves walking along a line and counting the individuals of the species that are found adjacent to the line. It is commonly used for plants and immobile organisms.
Methods to Determine Population Size and Density
Various methods are used for different types of organisms to measure population size and density, such as quadrats for immobile organisms such as plants, and mark and recapture for mobile organisms like mammals, birds, or fish.
The quadrat method involves placing a square frame of known size at multiple random locations within the habitat and counting the number of individuals inside to estimate the population size and density.
On the other hand, mark and recapture involves marking a sample of individuals, releasing them, and then recapturing a sample at a later time to estimate population size.