Lecture Note 14: Population Ecology PDF

12/3/20 Lecture 14 Population Ecology Individual Organism What’s beyond the level of individuals? 1 12/3/20 Population Ecology • Ecology: the study of the interaction - Among organisms Between organisms and their environment - • Population: all the individuals of a species in a given ar...

12/3/20 Lecture 14 Population Ecology Individual Organism What’s beyond the level of individuals? 1 12/3/20 Population Ecology • Ecology: the study of the interaction - Among organisms Between organisms and their environment - • Population: all the individuals of a species in a given area - Human population on the world Tree population in a tropical rain forest - • Population Ecology studies the properties of populations: 1. Population size 2. Population density 3. Patterns of dispersion 4. Demographics 5. Population growth 6. Limits on population growth 2 12/3/20 1. Population Size • Population size: the number of individuals living in the defined area • Factors that alter population size: - - Birth Death Immigration Emigration • Estimating size of a population: - Basic census: count all individuals in a group Mark-recapture: trap some individuals; mark and release them; note marked individuals in recapture - - 1 Researcher captures 100 beetles in a trap, marks each with a dab of paint. Add individuals Remove individuals 2 After one week, a trap is set again, resulting in a captured group of marked and unmarked individuals. 3 Total population is estimated as equivalent to the percentage of marked individuals in the second trap. Figure 13.1 3 12/3/20 2. Population Density • Population density: the number of individual organisms per unit area within the defined geographical range - Different species exist at different densities in the same environment - The same species may achieve one density in one environment but another in another environment Lecture Activity: Which county in NJ is most populous/largest/densest? Most Populous County in NJ: Bergen Middlesex Essex Largest County in NJ: Ocean Burlington Atlantic Smallest County in NJ: Hudson Union Essex Densest County in NJ: Hudson Essex Union 4 12/3/20 3. Pattern of Dispersion • Pattern of dispersion: how a population is distributed in space - Clumped: most frequent; aggregations (high densities) in resource-rich areas - Uniform: equal spacing between individuals - e.g. territory animals - Random: uncommon; minimally influenced by interactions with other members in the population Figure 13.2 5 12/3/20 Dispersion Pattern of Population in NJ Determining Factors: - Proximity to NYC - Housing availability - School system - Shopping center - Culture ……. Dispersion Pattern of Population in USA Top 10 Megacities 6 12/3/20 Dispersion Pattern of World Population Most populous: China, India, US, Indonesia, Brazil 4. Demographics • Demographics: the vital statistics which can impact on present and future population size - Age structure: size of the group of organisms at the same age; determined by birth rate, generation time, and death rate - Sex ratio: number of females; whether males are allowed to mate multiple females; whether males contribute to the raising of offspring 7 12/3/20 Age (b) United States in 2000 Age (a) South Africa in 2000 Reproductive years Males Females (population in millions) Males Females (population in millions) Figure 13.13 5. Population Growth Population Growth: exponential increase; in proportion to population size 2007: 6.6 billion video 1999: 6 billion 1970: 4 billion 1930: 2 billion 1800: 1 billion Dawn of Christianity: 250 million Agricultural era: 5 million Egyptian empire: 100 million Human populations (billions) • Year Figure 13.3 8 12/3/20 Annual Growth Rate in 2009: China: 0.51 India: 1.34 US: 0.86 Indonesia: 1.15 Brazil: 0.91 How long would it take to double a population? Time until population doubles (years) 139 70 47 35 28 Growth rate (% increase per year) Figure 13.4b 9 12/3/20 6. Limits on Population Growth - Carrying capacity: the maximum number of individuals that can be supported in a given environment If all plant growth fed humans and nothing else, earth’s resources can support a human population of 20 billion Carrying capacity No Growth Population size • Time Figure 13.6 6. Limits on Population Growth • Density-dependent factors: increase with population size - Limited food supply, increased risk of disease, increase in waste levels • Density-independent factors: not influenced by population numbers - Droughts, temperature extremes, natural disasters 10 12/3/20 American family Malian (African) family Figure 13.10 • UN has released three projections on human population growth - Fertility rates High growth rate Medium growth rate Low growth rate - Life expectancy Human population (billions) There is uncertainty about future human population growth rates - Demographic transition Year Figure 13.8 11 12/3/20 • Fertility rate: the average number of children born to a woman over her lifetime Low Med High Current fertility rates vary markedly among countries. 12 12/3/20 • Life expectancy: the average number of complete years of life remaining à Has been increasing over time • Demographic transition: a decrease in death rate is followed by a decrease in birth rate 1 Birth and Relative birth and death rates death rates are high. 2 Death rate drops while the birth rate remains the same. Growth rate increases. Developing country 3 Birth rate drops. Birth rate Growth rate = birth rate – death rate Developed country Death rate Time Figure 13.5 13 12/3/20 Human population growth is affected by not only science, but also social values and ethics Germany $31,900 Spain $27,400 United Kingdom $31,800 South Korea $24,500 United States $44,000 Chile $12,700 Vietnam $3,100 Mexico $10,700 Venezuela $7,200 Cambodia $2,700 Bangladesh $2,300 Tanzania $800 Angola $4,400 Chad $1,500 Yemen $1,000 Per capita income (in U.S. dollars) 0 0.1 0.28 0.4 99 97 99 97 99 96 87 90 93 0.9 0.92 1.0 1.15 1.5 1.73 2.1 2.1 2.18 2.3 64 32 62 54 3.46 39 30 Population growth rate Female literacy (percent increase per year) (percent of population) Figure 13.14 14