I need simple explanation on the methods of estimating population size in an ecosystem.
methods of estimating population size
- Direct Census: direct count of all the individual organisms in a given area.
- Sample Census: random sample plots known as quadrats are used to estimating population size.
- Mark – Recapture Method: This alternative method is used because most animals move constantly. Each animal caught is marked and then released back into the population. After like two – three weeks another batch of animals is caught, which will include some of the animals caught previously (marked). Then estimated population (N) is given as: N=iXb/R Where i= number of initially caught animals marked; b=total number of animals caught in the second attempt (both marked and unmarked); R=number of marked animals recaptured.
- Indirect Method: this becomes necessary because the animal may be dangerous or nocturnal in habit. Its presence can be established by indicators such as faecal pellets, footprints, food residue, etc.
TWO METHODS OF ESTIMATING POPULATION SIZE
- Quadrat method: For immobile organisms such as plants—or for very small and slow-moving organisms—plots called quadrats may be used to determine population size and density. Each quadrat marks off an area of the same size—typically, a square area—within the habitat. A quadrat can be made by staking out an area with sticks and string or by using a wood, plastic, or metal square placed on the ground.
- Mark-recapture method: For organisms that move around, such as mammals, birds, or fish, a technique called the mark-recapture method is often used to determine population size. This method involves capturing a sample of animals and marking them in some way— for instance, using tags, bands, paint, or other body markings, as shown below. Then, the marked animals are released back into the environment and allowed to mix with the rest of the population.