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Unformatted text preview: Ecology: Population
Growth is a feature common to all populations of living organisms Outline
1. Key concepts 2. Population growth 3. Limiting factors on growth 4. What contributes to the growth of a
population 5. Population density 6. Regulation of population size 7. Human population growth 8. Key terms 9. Conclusions Key Concepts:
1. Natural populations have the potential to grow exponentially. 2. Both density dependent and density independent factors affect population growth. 3. Human population growth has accelerated in the last century. Population growth
Population: individuals of a given species that occur together at one place and time Population change: growth rate = births - deaths Exponential growth: rapid, requires ideal conditions Carrying capacity: the number of individuals an environment can support Population growth
Growth is a feature common to all populations of living organisms. While we have a perception that growth implies an increase, populations may exhibit positive growth and grow larger, or... they may show negative growth and grow smaller. Populations may even remain the same size and exhibit what is known as zero growth. Populations which experience positive growth exhibit one of two growth patterns. Exponential: In exponential growth, the time required to double the size of the population becomes shorter and shorter. When plotted as a graph of numbers vs. time, this produces a characteristic J-shaped growth curve. Exponential Growth Logistical Growth
Obviously, there is some limit to the growth of a natural population. Some combination of factors which will limit a population's size. This set of factors represents the carrying capacity of a given environment and the affects are illustrated with a S-curve. S-curve Growth Limiting Factors on Growth Limiting factor Essential resources Food Minerals Water Space Carrying capacity What contributes to the growth of a population?
Growth is the result of the difference between the number of births and deaths for a population during a given period of time. Mortality and survivorship Mortality and survivorship
Population growth rate depends on the ages of the organisms in it Mortality: death rate Survivorship: proportion of an original population that survives to a certain age Survival curves: shapes vary with type of population, number of young, sexual or asexual reproduction, level of care for young Survivorship What contributes to the growth of a population?
Also contributing to growth are the new individuals joining the population from Other populations. This is immigration. Just as immigration can have an impact on the size of a population, so can individuals leaving the population, or emigration. Population density
Population density (the number of organisms per unit of area) influences its survival Regulation of population size
Density-independent limiting factors: soil nutrients, weather, physical features Density-dependent limiting factors: competition for resources accumulation of poisonous wastes Demography Statistical study of human populations predicts how population size will change Age stucture: bar graph shows current composition of population by age and gender can be used to predict future size based on number of females and birth rate Age Structure Diagram U.S. http://www.census.gov/ipc/www/idbpyr.html Green - Pre-reproductive years Dark Blue- Reproductive years Light blue - Post- reproductive years Population of the U.S. The human population explosion Exponential increase began in 19 Century:
th industrial revolution, better nutrition, advances in medicine, etc. lowered death rate, increased birth rate Carrying capacity has been increased by human technology Current increases in population are higher in developing countries Estimating Earth's carrying capacity for humans is a complex problem
Predictions of the human population vary from 7.3 to 10.7 billion people by the year 2050. Will the earth be overpopulated by this time?
http://www.mnsu.edu/emuseum/information/population/ http://www.ibiblio.org/lunarbin/worldpop Population density Survivorship curve Exponential population growth Logistic population growth Density-dependent factor Density-independent factor Birth rate Death rate Age structure Demography A population is a group of individuals of the same species occupying a given area The growth rate can be determined by calculating the rate of birth, death, immigration, and emigration Carrying capacity is the maximum number of individuals in a population that can be sustained in an environment In Conclusion In Conclusion The availability of sustainable resources dictates population size Limiting factors such as competition for resources, disease and predation are densitydependent Patterns of reproduction, death, and migration vary over the life span for a species In Conclusion The availability of sustainable resources dictates population size The human population growth rate varies in various parts of the world Rapid growth of human population occurred We have the unique opportunity (responsibility?) to decide our fate and the fate of the rest of the biosphere ...
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This note was uploaded on 05/05/2008 for the course BIO 52010 taught by Professor Zhao during the Fall '07 term at University of Texas at Austin.
- Fall '07