How populations grow

1. How populations grow Ch 15 B3.5

2. What is a population • Population – consists of all the individuals of a species that live together in one place at one time. • Demography – the statistical study of all populations. • Demographer - Study the composition of a population and try to predict how the size of the population will change.

3. Three features of a population • Population size – the number of individuals in a population • Can affect the population’s ability to survive. • Natural disturbances (fires and flood) are more of a danger to a small population than a large population. • Small populations tend have more inbreeding • Example …

4. Cheetah (Acinonyx jubatus) • Very small population • Genetically identical • A disaster (new disease) could cause their extinction

5. Three features of a population 2. Population density – is the number of individuals that live in a given area. • Spread out population (dispersed widely) won’t interact and breed. 3. Dispersion – is the way the individuals of the population are arranged in space. • Spacing of populations affect how they interact with each other and the environment.

7. Modeling population growth • Population model – is the hypothetical population that attempts to exhibit the key characteristic of a real population. • Growth rate – simple model describes the rate of population growth as the difference between the birthrate and the death rate.

8. Growth rate and population size • Exponential growth curve – is a curve in which the rate of a population stays the same, as a result the population size increasing steadily. • Carrying capacity – the population size that an environment can sustain.

13. Resources and population size • Density dependent resources – resources that are depleted at a rate that depends on the population density of the population that use them. • Limited resources, food and water • Logistic model – is a population model in which exponential growth is limited by a density dependent factor. • Excellent estimate of population growth in nature. • Competition for food, shelter, mates and limited resources tends to increase as a population approaches it carrying capacity.

14. Logistic model

15. Growth patterns in real populations • Density independent factors – growth of an organism that is limited by environmental conditions. • Weather and climate • Example, mosquito populations increase in the summer when it is warn and decrease in the winter. • R-strategies – grow exponentially when environmental conditions allow them to reproduce.

16. R-strategies • Short life span • Reproduce and mature early and have many offspring with little or no parental care. • Example cockroaches (American cockroach, Periplanetaamericana, )

17. K-strategies – organisms that grow slowly with long life span, fewer offspring, slow maturing process and reproduction late in life. • Example Fin Whale (Balaenopteraphysalus)