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HOW POPULATIONS CHANGE

HOW POPULATIONS CHANGE. Chapter 8 Section 1 . a population is…. all the members of a species living in the same place at the same time . 3 Properties of populations…. SIZE – number of individuals in the population H ow many?

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HOW POPULATIONS CHANGE

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  1. HOW POPULATIONS CHANGE Chapter 8 Section 1

  2. a population is… all the members of a species living in the same place at the same time

  3. 3 Properties of populations… SIZE – number of individuals in the population How many? DENSITY – number of individuals per area or volume How tightly packed? DISPERSION – the distribution or arrangement of a population within a given space • can be dispersed evenly (uniformly), clumped, random

  4. What factors affect the size of a population? • Births, Deaths, Immigration and Emigration • Immigration - when individuals move into a population • Emigration- when individuals leave a population

  5. Emigration after the Civil War Confederate Colonies of Brazil: The Confederados • at the end of the Civil War (1860's) some Confederates left the US (emigrated) to South America • numbered in the thousands • settled primarily in Brazil – coastal areas • some returned to their homes in the United States, but many more settled permanently in Brazil and their descendants are living there today

  6. How does a population change? • Populations grow when… there are more births than deaths or when individuals move into the population. • Populations decline when… there are more deaths than births or when individuals leave the population .

  7. Population Growth is… a change in the size of a population over time GROWTH RATE = birth rate – death rate Growth rates can be… positive, negative or zero • positive growth – more births than deaths • negative growth – fewer births than deaths • zero growth – number of births = number of deaths

  8. Growth Rate

  9. Reproductive Potential The maximum number of offspring that each member of a population can produce • Some species have higher reproductive potentials than others • Insects have a large reproductive potential as compared to humans

  10. Reproductive Strategies “R” strategists – overcome massive loss of offspring by producing many offspring – in hopes that some will survive • Example – insects “K” strategists – have fewer offspring and longer generation times • Example - humans

  11. R strategist (many offspring) or K strategist (few offspring)

  12. 2 Types of population growth models … exponential growth and logistic growth

  13. Exponential Growth • Populations sometimes undergo exponential growth which means that the population grows faster and faster • “J” shaped graph • Exponential growth occurs in nature only when there is plenty of food and space and little or no competition or predators

  14. Exponential Growth of Human Population

  15. Logistical growth • Populations sometimes undergo logistical growth which means the growth rate decreases with increasing number of individuals until it becomes zero when the population reaches a maximum • “S” shaped graph

  16. Logistical growth

  17. Linear Growth • means a population grows by a fixed amount each generation • a steady increase in a population • this type of growth is not characteristics of most populations

  18. What limits the growth of a population? Carrying Capacity – the maximum population size that an environment (or ecosystem) can sustain • Populations cannot grow indefinitely • A population may increase beyond its carrying capacity but this cannot be maintained • Because ecosystems change, the carrying capacity is difficult to predict or calculate exactly

  19. What else limits a population? • RESOURCES- water, sunlight, minerals,… • The most severely limited resources will determine the carrying capacity of an environment! • COMPETITION - for food, shelter (habitat) and mates • PREDATORS

  20. 2 types of Limiting Factors in Ecosystems Density Dependent Factors Resources that decrease as a population increases Density Independent Factors Environmental factors that affect all populations equally

  21. Density Dependent Factor(s)– Resources that decrease as a population increases • regulate a population when individuals are densely packed (crowded) together Examples – limited resources, predation, disease, food, water, shelter, space,….

  22. Density Independent Factor(s) – Environmental factors that affect all populations equally • regulate a population regardless of the population’s density – this type of regulation affects all members of a population Examples – severe weather, current, natural disasters, climate, temperature, precipitation, salinity,…

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