Population Growth Models Carrying Capacity The maximum number of individuals of a species the environment can continuously support The closer the population to the carrying capacity, the more likely its resources will become scarce and that biotic effects such as competition and predation will become apparent 1 44.4 Regulation of Population Size Density-independent Factors The population density does not influence the intensity of the factors effect Natural disasters Density-dependent Factors The percentage of the population affected increases as the population density increases Competition Predation Parasitism 2 Density-independent Effects 3 a. Low density of mice b. High density of mice Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Density-dependent Effect 4 2,000 1,500 1, Number of Reindeer exponential growth decline as a result of sudden resource depletion Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Paul Janosi/Valan Photos Density-dependent Effects -- Competition 5 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Low density of birdsb. High density of birds Density-dependent Effects -- Predation 6 a. Low density of miceb. High density of mice Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 44.5 Life History Patterns Life histories contain characteristics of a population such as The number of births per reproduction The age of reproduction The life span The probability of an individual living the entire life span Each population distributes energy among its life span, reproduction events, and care of offspring. Related species may have different life history patterns. 7 Parental Care Among Frogs and Toads 8 a. Mouth-brooding frog, Rhinoderma darwinii b. Strawberry poison arrow frog, Dendrobates pumilio c. Midwife toad, Alyces obstetricans (a): Michael Fogden/Animals Animals; (b): Michael Fogden/Animals Animals; (c): Tom McHugh/Photo Researchers, Inc. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9 Life History Patterns r is the rate of natural increase of a population. K is the carrying capacity of the environment. Some populations are subject to r-selection, and other populations are subject to K- selection. 10 Life History Patterns r - Selection In unstable or predictable environments, population growth is controlled by density-independent factors. Population size is low relative to K. r - Strategists (opportunistic species) Produce large numbers of offspring Have a small body size Mature early Have a short life span Do not invest energy in parental care Tend to be good dispersers and colonizers Life History Patterns K - Selection In stable, predictable environments, population size is controlled by density-dependent factors. Population size tends to be near K. K - Strategists (equilibrium species) Produce small numbers of offspring Have a large body size Mature late Have a long life span Invest energy in parental care Tend to be strong competitors 11 Life History Strategies 12 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (dandelions): Ted Levin/Animals Animals; (bears): Michio Hoshino/Minden Pictures Opportunistic Species (r-strategist) Small individuals Short life span Fast to mature Many offspring Little or no care of offspring Many offspring die before reproducing Early reproductive age Equilibrium Species (K-strategist) Large individuals Long life span Slow to mature Few and large offspring Much care of offspring Most young survive to reproductive age Adapted to stable environment Ecology Focus: When a Population Grows Too Large White-tailed deer are prolific breeders Female deer breed their first year, and once they start breeding, produce about two young each year of life. A century ago, the white-tailed deer population was less than half a million Today, it is well over 200 million Natural predators of deer, such as wolves and mountain lions, are now absent from most regions. 13 Ecology Focus: When a Population Grows Too Large Populations that are too large may suffer from starvation as they deplete their own food supply For example, after deer hunting was banned on Long Island, New York, the deer population quickly outgrew available food resources 14 White-tailed Deer 15 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b. (a): Tony Campbell/Shutterstock Images; (b): Altrendo Images/Getty Images 44.6 Human Population Growth The human population is undergoing exponential growth Present size is 6.7 billion people The doubling time of the human population is currently estimated at 52 years Population Size Billion Billion Billion Billion 16 Human Population Growth More-Developed Countries (MDCs) North America, Europe, Japan, and Australia Slow population growth High standard of living A demographic transition (decreased death rate followed by decreased birth rate) has occurred, so population growth has stabilized. 17 18 Human Population Growth Less-Developed Countries (LDCs) Latin America, Africa, and Asia Rapid population growth Low standard of living Strategies to reduce population growth Family planning programs Social progress, which may reduce the desire for large families Delay the onset of childbearing World Population Growth 19 lowest growth highest growth less-developed countries more-developed countries a.b. Billions of People Year Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b(Top): The McGraw-Hill Companies, Inc./Jill Braaten, photographer; b(Bottom): Robert Harding/Robert Harding World Imagery/Corbis Human Population Growth Age Distributions Populations of MDCs and LDCs can be divided into three age groups Prereproductive Reproductive Postreproductive MDCs and LDCs have different age structure diagrams Many MDCs have a stable age structure Most LDCs have a youthful profile and are experiencing population growth 20 Age Structure Diagrams 79 7074 6569 6064 5559 5054 4549 4044 3539 3034 2529 2024 1519 1014 59 0 79 7074 6569 6064 5559 5054 4549 4044 3539 3034 2529 2024 1519 1014 59 04 0 b. Less-developed countries (LDCs) c. a. More-developed countries (MDCs) Millions postreproductive reproductive prereproductive Age (in years) postreproductive reproductive Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. c: Still Pictures/Peter Arnold, Inc. Human Population Growth Population Growth and Environmental Impact Environmental impact of a population is measured in terms of: Population size Resource consumption per capita Resultant pollution due to resource consumption There are two types of overpopulation Overpopulation due to population growth Overpopulation due to increased resource consumption 22 Environmental Impact Caused by MDCs & LDCs 23 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PopulationHazardous Waste ProductionConsumption a.b. c. paper metals fossil fuels MDCs = more-developed countriesLDCs = less-developed countries MDCs 22% LDCs 10% LDCs 40% MDCs 60% LDCs 25% MDCs 75% MDCs 80% LDCs 20% MDCs 90% LDCs 78%