Studying Populations and Limiting Factors

Population density The number of individuals in a specific area.

How to calculate population density Number of Individuals Number of Individuals Population density = Unit Area

An Example of Calculating Population Density If you have 50 monarch butterflies in a garden that measures 10 m 2, the population density would be: __50_ butterflies 10 m 2 = 5 butterflies per square meter. 10 m 2 = 5 butterflies per square meter.

Methods of determining population size

Direct observation Count all the organisms in an area

Indirect observation Count based on tracks, nests, holes, and use estimation. Count based on tracks, nests, holes, and use estimation.

Sampling Count the number in a measured area then multiply by the total area.

An Example of Sampling –For example there are 18 ladybugs in this area. Multiply the number of individuals by the number of areas that size. –18 ladybugs X 10 areas = 180 ladybugs most likely live in an area that size.

Mark and Recapture A method of estimation. An animal is captured, marked, then released. Another group of animals is captured. The number of marked animals in this group indicates the population size.

An Example of Mark and Recapture Deer mice are caught in a trap. Deer mice are caught in a trap. Ecologists count the mice and mark each mouse’s belly with a dot of hair dye and release it. Ecologists count the mice and mark each mouse’s belly with a dot of hair dye and release it. Two weeks later they capture mice again and see how many of the new group were marked. Two weeks later they capture mice again and see how many of the new group were marked. Using a mathematical formula they can estimate the total population of mice in the field. Using a mathematical formula they can estimate the total population of mice in the field.

Birth Rate The number of births in a population in a certain amount of time. The number of births in a population in a certain amount of time. –Example: A population of 1,000 snow geese produces 1,400 goslings in a year. The birth rate in this population would be 1,400 goslings per year.

Death Rate The number of deaths in a population in a certain amount of time. The number of deaths in a population in a certain amount of time. –Example: 100 geese die in a year. The death rate would be 100 geese per year.

Changes in population size Changes due to birth rate and death rate. Changes due to birth rate and death rate. –If birth rate > death rate the population size increases. –If birth rate < death rate the population size decreases.

Immigration Moving into a population.

Emigration Moving OUT of a population

Limiting Factors Environmental factors that prevent a population from increasing. Environmental factors that prevent a population from increasing.

Examples of Limiting Factors 1. Food – animals need enough food to survive and reproduce. 2. Space – animals need enough space to build homes, obtain enough food to survive without limiting the food source. 3. Weather conditions – many animals require certain types of weather to reproduce, also a single storm can wipe out a population

Carrying Capacity The largest population that an area can support.