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CHAPTER 5: POPULATIONS How Populations Grow (5-1) Limits to Population Growth (5-2) Human Population Growth (5-3) 5-1: How Populations Grow POPULATION A population is a group of organisms that belong to the same species and live in a given area. A. 3 Factors That Influence Population Size 1. Birth Rate 2. Death Rate 3. Migration a. b. immigration = movement of organisms into an area emigration = movement of organisms out of an area 4. Calculation of Population Growth Population Growth Rate = (Birth Rate+Immigration) – (Death Rate+Emigration) Zero population growth is when: Birth Rate+Immigration = Death Rate+Emigration B. Population Dynamics = Change in population size over time Biotic Potential + Environmental Resistance = Carrying Capacity 1. Biotic Potential = The maximum rate at which a species can increase if unchecked 1. Biotic Potential Considerations Include: a. age at which reproduction begins b. frequency of reproduction during life c. # of offspring per reproductive event d. survival rate of offspring to reproductive age e. length of reproductive ability 1. Biotic Potential Creates a growth curve that is exponential (logarithmic, J-shaped curve). Many species, particularly herbivores, generally have higher birth rates 2. Environmental Resistance = The sum of all the forces that cause death or lowers reproduction This includes: Resource Availability (food/water) Predation Disease/parasites Climatic factors Numerous human created elements 3. Carrying Capacity = The number of organisms that can be supported in a given area at a given time Carrying Capacity – The Kaibab If humans do not harvest part of the herd by using licensed hunters, natural forces of disease and starvation will bring about the reduction with starvation and disease. QUESTION: Are human populations ultimately controlled by the same equation? C. Change in Population Size Over Time Population increases for living things are generally exponential 1. Exponential Growth (J-Shaped) a. Type of exponential growth that shows slow growth at first, followed by increasingly faster rates of growth b. Under natural conditions, the exponential phase of growth may drop off sharply due to environmental constraints c. Note: Happens to a population only briefly when encountering a new habitat. J-Shaped Growth Curve 2. Logistic Growth (S-Shaped) a. A growth model that starts off like the Jshaped form, but eventually the rate of growth slows and stabilizes at a certain level 2. Logistic Growth (S-Shaped) 2. Logistic Growth (S-Shaped) b. Environmental resistance ultimately limits growth in the S-shaped growth model. c. Real-world populations vary in complex ways, and may show either a J- or an S-shaped growth form at different times in their history. 5-2: Limits to Population Growth 1. Density Dependent Controls Remove higher % of individuals as population size increases Density Dependent Controls: a. INTRASPECIFIC COMPETITION Intraspecific competition = Among same species •Includes mate competition Chuckwallas Density Dependent Controls: b. INTERSPECIFIC COMPETITION Interspecific Competition – Between species Does not include mate competition Big Horn Sheep and Burros Density Dependent Controls: c. PREDATION one organism feeding on another C. PREDATION 1. Types a) Equilibrium – prey can avoid predator b) Boom-Bust cycle – lynx and hare c. PREDATION 2. Plant Defenses a) Morphological (body forms) – thorns, spines b) Chemical – poisons c. PREDATION 3. Animal Defenses a) Morphological 1. size – hide, frighten 2. coloration – camouflage, warning, mimicry 3. other - sting, bite, run c. PREDATION 3. Animal Defenses b) Chemical – poison c. PREDATION 3. Animal Defenses c) Vigilance (intelligence) – watch for predators, learned behavior c. PREDATION 3. Animal Defenses d) Broken wing display 1. Density Dependent Controls d. PARASITISM d) Parasitism - Predators feed on prey but do not kill it immediately Freshwater Leech 1. Density Dependent Controls e. CROWDING AND STRESS e) Crowding and Stress 1. Density Dependent Controls f. MIGRATION f) Migration Zebra and Wildebeest Migration 2. Density Independent Controls a) Remove a certain % of the population regardless of number of individuals in the population b) Are typically random or extreme abiotic events (weather, natural disaster) 2. Density Independent Controls Floods are an example of a density-independent factor. This is the aftermath of Katrina in New Orleans. 2. Density Independent Controls c. After extreme abiotic events, new habitats are opened for organisms to create new logistic growth 5-3: Human Population Growth 5-3 Human Population Growth A. Human Populations 1. Growth rates were low for much of human history, but rates started increasing in the 1700’s and became exponential in the 1950’s, exhibiting a J-shaped curve ever since. Time PreIndustrial Transition al Culture Agriculture Moving into cities B D High High Large Family Large Family High DECREASING DECREASING Industrial Living in cities Post Industrial Strategy Technology Smaller Families and Labor Laws College degree to compete Low LOW LOW Graph How Can Economic Development Help Reduce Birth Rates • Demographic Transition Human Population Growth: Past History and Current Conditions YEAR POPULATION 1804 1 billion 1974 4 billion 2005 6.2 billion 2011 6.9 billion End of 21st Century Estimated 8.5 – 11 billion Human Population Growth: Past History and Current Conditions 2. World population growth is fastest in developing countries 3. Education is a key in developing countries: a) If educated to 2nd or 3rd grade = 8 babies/female b) Women with higher education/careers = delay childbirth and typically have fewer children Human Population Growth: Past History and Current Conditions COUNTRY Developed Less-developed: China, India, parts of Africa, and Latin America ANNUAL GROWTH RATE 0.4% 1.8 - 3% B. Effects of Large Human Population 1. Food and agriculture a) Only three plants provide 50% of our food supply - wheat, rice and corn b) Crops are genetically identical - not resistant to disease or weather, lose 70 to 80% of a crop Effects of a Large Human Population 2. Usable land a) high percentage of potentially usable land is being cultivated b) agricultural land is the fastest growing area of land being destroyed c) removal of tropical forest removes circulating water and deserts are getting bigger Deforestation in the Tropics Effects of a Large Human Population 3. Other human impacts a) Global warming – the increase in atmospheric CO2 concentrations during the last 150 years concerns ecologists because of its potential effect on global temperature through the greenhouse effect. Effects of a Large Human Population b) Ozone depletion - increased UV radiation hits the earth 1979 2003 Effects of a Large Human Population c) Acid rain/Water pollution The Parthenon in Greece shows discoloration and chemical weathering effects from air pollution and acid rain Statue of Queen Victoria - England Effects of a Large Human Population d) Habitat destruction/soil destruction Effects of a Large Human Population e) Biodiversity loss Fragmentation of habitat causes species to go extinct. Habitat Loss, Pollution, Invasive Species, Overuse/Killing by Humans Effects of a Large Human Population f) Waste build-up Example: Open Pit Mining Effects of a Large Human Population g) Non-native/exotic species – would not be present without the direct or indirect help of humans Termites, Africanized Honey Bees, Myconia, Ice Plant, Tiger Mosquito Walking catfish Starlings