Understanding Populations

How Populations Change in Size

Objectives Describe the three main properties of a

population Describe exponential population growth Describe how the reproductive behavior of

individuals can affect the growth rate of the population

Explain how population sizes in nature are regulated

Population A group of

organisms of the same species that live in the same geographical area– Interbreeding– Refers to size and

number

Properties of a Population Density- Number of

individuals living in a given unit of area

Dispersion- Pattern of distribution of organisms in an area– Random– Clumped – Even

Describe populations and used to predict changes

How do Populations Grow?

Growth rate- Increase in the size of an organism or population over time– Positive- Births outnumber deaths – Negative- Deaths outnumber births– Zero- Births and deaths are equal

Reproductive Potential Reproductive potential-

Maximum number of offspring that an organism can produce

Increases:– More offspring produced

at a time– Reproduction begins

earlier in life Generation time-

Average time it takes to reach age at which members of a population begin reproducing

Biotic potential- Fastest rate at which a population can grow– Limited by reproductive

potential– Large organisms

Long generation time Slow population growth

– Small organisms Short generation time Fast population growth

Exponential Growth Growth in which

numbers increase by a certain factor in successive time periods

Plenty of food and space

No competition or predators

What Limits Population Growth?

Carrying Capacity- The maximum population that an ecosystem can support indefinitely

Estimated by observing population crashes Ex: Rabbits introduced into Australia in 1859

What Limits Population Growth?

Limiting resource- Natural resource that is consumed at the same rate at which the ecosystem produces it

Competition– Compete for mates, food, and homes– Territory- An area defended by one or

more individuals

Two Types of Population Regulation

Density Independent- A certain proportion of a population may die regardless of the population’s density– Severe weather and natural disasters

Density dependent- Deaths occur more quickly in crowded conditions – Limited resources, predation, and disease