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Understanding Populations How Populations Change in Size.

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Presentation on theme: "Understanding Populations How Populations Change in Size."— Presentation transcript:

1 Understanding Populations How Populations Change in Size

2 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

3 Population A group of organisms of the same species that live in the same geographical area –Interbreeding –Refers to size and number

4 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

5 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

6 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

7 Exponential Growth Growth in which numbers increase by a certain factor in successive time periods Plenty of food and space No competition or predators

8 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

9 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

10 Two Types of Population Regulation Density Independent- A certain proportion of a population may die regardless of the populations density –Severe weather and natural disasters Density dependent- Deaths occur more quickly in crowded conditions –Limited resources, predation, and disease

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