Population Dynamics What is a population? • A population is defined as being “all the organisms of the same type living in a certain area.” Can you think of any specific examples of a population? Population Distribution • Distribution - the arrangement of members of a population in a certain area. • Influenced by Abiotic and Biotic Factors. • Define Abiotic and Biotic and give examples for each. Abiotic – Nonliving (ex. Light, temperature, atmosphere) Biotic – Living (ex. Food, bacteria, etc.) 3 Types of Distribution • Clumped – Population is represented by scattered groups of individuals. • Uniform – Individuals are spread out. • Random – No pattern in the spacing of individuals. 4 Factors Controlling Population Size • Natality (Birth) Rate – The number of births in a population. • Mortality (Death) Rate – The number of deaths in a population. • Immigration – The number of individuals entering a population. • Emigration – The number of individuals leaving a population. Growth Rate • How do we define Growth Rate? Birth Rate - Death Rate = Growth Rate 4 Stages of Growth Rate 1. Lag Phase – Slow Growth 2. Growth Phase – Fast Growth 3. Stationary Phase – No Growth 4. Death Phase – Decline in Growth Factors Controlling Population Phases • List at least 2 factors that would lead to each of the 4 phases of Growth Rate. • Resources • State of Environment So what???? • What is the significance of all this information? Present Population Earth’s population growth rates (per year): • Africa – 2.5% • Western Asia – 2.2% • Southeastern Asia – 1.6% • Central America – 2.3% • East Asia – 0.9% • Australia – 0.7% • North America – 0.6% • Europe – 0.1% Consider this………. • Earth’s population is increasing at a rate of 1.4%. Therefore, the population of Earth now will double in……. 50 years. Factors Affecting Human Population Size Population change equation Population Change = (Births + Immigration) – (Deaths + Emigration) Crude birth rate (BR) Crude death rate (DR) Refer to Figure 10-3, p. 177 U.S. Birth Rates: 1910-2100 Births per thousand population 32 30 28 26 24 22 20 18 End of World War II 16 Demographic 14 Depression Baby boom Baby bust Echo baby boom transition 0 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Year Fig. 10-8, p. 180 Population Age Structure Male Female Rapid Growth Slow Growth Zero Growth Negative Growth Guatemala United States Spain Germany Nigeria Australia Austria Bulgaria Saudi Arabia Canada Greece Sweden Ages 0-14 Ages 15-44 Ages 45-85+ Fig. 10-14 p. 184 World Population Clock US Population Clock What can be done? • Family Planning • Government Regulation? Population Notes Part 2 Exponential Growth “A rapid increase of a population.” Represented by a “J Curve” Can this trend continue? Limits to Exponential Growth • As populations begin to run out of resources and room, their numbers begin to level. If there were no limiting factors, and the population could continue to grow forever, the curve would be J- shaped. BUT... Because most populations have to deal with limits (for example, running out of food or space), they can only increase to a certain point- this leveling off of the population size creates an S-shaped curve. Carrying capacity (designated as K) is the number of organisms of one species that an environment can support Carrying capacity (K) Exponential growth Carrying Capacity If population size is under K, births will exceed deaths, population will increase But, if the population size rises over K, deaths will exceed births, population will decrease Limiting Factors • “An environmental condition that can limit the maximum number of individuals in a population.” • Can be Density Independent or Density Dependent. Dependent vs. Independent • Density Independent – Natural occurrences that will happen no matter how large the population is. Example – floods, fires, earthquakes, volcanic eruptions, tsunamis, etc. • Density Dependent – Natural occurrences that will happen due to a large number of individuals in a population. Example – diseases, famine, resources gone, invader species. Interspecific & Intraspecific Competition • Interspecific Competition – 2 populations of the same/similar species overlap within an ecosystem and compete for food/water or other resources. • Intraspecific Competition – 2 populations of different species compete for resources. K-Selective & R-Selective Populations • K-Selective – individuals have a long life span, fewer offspring, live in a stable environment. Tend to have an S-curve growth. • R-Selective – individuals have a short life span, lots of offspring, and live in a selective environment. Questions • Why can’t the carrying capacity of Earth be determined? • 2 parents decide to have 6 kids. When the parents die, what is the growth in that family? What if they only had 2 kids? • Why are humans growing exponentially each year? Question #1 – Humans are always changing and adapting the environment, extending the carrying capacity. Question #2 – The growth is +4 in that family. The growth is 0 in that family Question #3 – More babies are being born, less people dying due to better health care, production of food, improved way of life.
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