Studying Populations Section 21 2 Determine Population Size

Studying Populations Section 21 -2

Determine Population Size • Determining Population Size • Some methods of determining the size of populations are direct and indirect observations, Sampling, and Mark and recapture studies

Determine Population Size • Direct Observation…Count all of its members • Indirect Observation…Observing signs such as nests then figuring the average number of birds per nests and multiplying it by the number of nests

Determine Population Size • Sampling…usually done when there is a very large area to be covered usually an estimate which is an approximation of a number based on reasonable assumptions

Determine Population Size • Mark and recapture studies… First animals are caught in a way that they are not harmed, they count the animals and then mark them in a way to identify them. The animals are then released. Animals are again captured. The percentage with the markings go into a mathematical formula to estimate the total population.

Mark and Recapture Studies

Changes In Population Size • Populations can change in size when new members join a population or when members leave a population.

Changes In Population Size • Birth Rate…The number of births in a population in a certain amount of time • Death Rate… The number of deaths in a population in a certain amount of time.

Changes In Population Size • Population Statement If the Birth rate > death rate, population size If the Death rate > birth rate population size

Changes In Population Size • Immigration---Moving into a population • Emigration--- Leaving a population

Limiting Factors • Limiting Factor--An environmental factor that causes a population to decrease – Food and water – Space – weather

Carrying Capacity • The largest population that an area can support