19 lecture presentation
- 1. © 2010 Pearson Education, Inc. AN OVERVIEW OF POPULATION ECOLOGY • Population ecology is the study of factors that affect population: – Density – Growth • A population is a group of individuals of a single species that occupy the same general area.
- 2. © 2010 Pearson Education, Inc. • Population ecology focuses on the factors that influence a population’s – Density – Structure – Size – Growth rate
- 3. Figure 19.1
- 4. © 2010 Pearson Education, Inc. • Population ecology is used to study – How to develop sustainable fisheries – How to control pests and pathogens – Human population growth
- 5. © 2010 Pearson Education, Inc. • Population density is the number of individuals of a species per unit of area or volume. For example – The number of oak trees per square kilometer (km2 ) in a forest Population Density
- 6. © 2010 Pearson Education, Inc. • How do we measure population density? – In most cases, it is impractical or impossible to count all individuals in a population. – In some cases, population densities are estimated by indirect indicators, such as – Number of bird nests
- 7. © 2010 Pearson Education, Inc. • The age structure of a population is the distribution of individuals among age groups. • The age structure of a population provides insight into – The history of a population’s survival – Reproductive success – How the population relates to environmental factors Population Age Structure
- 8. © 2010 Pearson Education, Inc. Life Tables and Survivorship Curves • Life tables – Track survivorship – Help to determine the most vulnerable stages of the life cycle
- 9. Table 19.1
- 10. © 2010 Pearson Education, Inc. Life History Traits as Evolutionary Adaptations• An organism’s life history is the set of traits that affect the organism’s schedule of – Reproduction – Survival
- 11. © 2010 Pearson Education, Inc. • Key life history traits are the – Age at first reproduction – Frequency of reproduction – Number of offspring – Amount of parental care provided
- 12. © 2010 Pearson Education, Inc. • Life history traits – Evolve – Represent a compromise of the competing needs for – Time – Energy – Nutrients
- 13. © 2010 Pearson Education, Inc. POPULATION GROWTH MODELS • Population size fluctuates as individuals – Are born – Immigrate into an area – Emigrate away – Die
- 14. The Exponential Growth Model: The Ideal of an Unlimited Environment • Exponential population growth describes the expansion of a population in an ideal and unlimited environment. © 2010 Pearson Education, Inc.
- 15. Time (months) Populationsize(N) 0 1 2 3 4 5 6 7 8 9 10 11 12 0 50 100 150 200 250 300 350 400 450 500 Figure 19.5
- 16. © 2010 Pearson Education, Inc. • Exponential growth explains how – A few dozen rabbits can multiple into millions – In certain circumstances following disasters, organisms that have opportunistic life history patterns can rapidly recolonize a habitat
- 17. Figure 19.5a
- 18. The Logistic Growth Model: The Reality of a Limited Environment • Limiting factors – Are environmental factors that hold population growth in check – Restrict the number of individuals that can occupy a habitat © 2010 Pearson Education, Inc.
- 19. © 2010 Pearson Education, Inc. • The carrying capacity is the maximum population size that a particular environment can sustain. • Logistic population growth occurs when the growth rate decreases as the population size approaches carrying capacity.
- 20. Year 1915 1925 1935 1945 0 2 4 6 8 10 Breedingmalefurseals (thousands) Figure 19.6
- 21. © 2010 Pearson Education, Inc. • The carrying capacity for a population varies, depending on – The species – The resources available in the habitat
- 22. © 2010 Pearson Education, Inc. • The logistic model and the exponential model are theoretical ideals of population growth. • No natural population fits either one perfectly.
- 24. Regulation of Population Growth Density-Dependent Factors • The logistic model is a description of intraspecific competition, competition between individuals of the same species for the same limited resources. © 2010 Pearson Education, Inc.
- 25. © 2010 Pearson Education, Inc. • As population size increases – Competition becomes more intense – The growth rate declines in proportion to the intensity of competition • A density-dependent factor is a population-limiting factor whose effects intensify as the population increases in density. Video: Wolves Agonistic Behavior Video: Snake Ritual Wrestling Video: Chimp Agonistic Behavior
- 26. Number of breeding pairs Averageclutchsize (a) Decreasing birth rate with increasing density in a population of great tits 0 10 20 30 40 50 60 70 80 90 8 9 10 11 12 Figure 19.8a
- 27. © 2010 Pearson Education, Inc. • Density-dependent factors may include – Accumulation of toxic wastes – Limited food supply – Limited territory
- 28. Figure 19.9
- 29. © 2010 Pearson Education, Inc. Density-Independent Factors • Density-independent factors – Are population-limiting factors whose intensity is unrelated to population density – Include abiotic factors such as – Fires – Floods – Storms Video: Giraffe Courtship Ritual Video: Blue-footed Boobies Courtship Ritual Video: Albatross Courtship Ritual
- 30. Exponential growth Sudden decline Apr May Jun Jul Aug Sep Oct Nov Dec Numberofaphids Figure 19.10
- 31. © 2010 Pearson Education, Inc. • In many natural populations, density-independent factors limit population size before density-dependent factors become important. • Over the long term, most populations are probably regulated by a mixture of – Density-independent factors – Density-dependent factors
- 32. © 2010 Pearson Education, Inc. Population Cycles • Some populations have regular boom-and-bust cycles characterized by periods of rapid growth followed by steep population declines.
- 33. © 2010 Pearson Education, Inc. • A well studied example of boom and bust cycles are the cycles of – Snowshoe hares – One of the hares’ predators, the lynx
- 34. Figure 19.11b
- 36. © 2010 Pearson Education, Inc. • The cause of these hare and lynx cycles may be – Winter food shortages for the hares – Overexploitation of hares by lynx – A combination of both of these mechanisms
- 37. © 2010 Pearson Education, Inc. APPLICATIONS OF POPULATION ECOLOGY • Population ecology is used to – Increase populations of organisms we wish to harvest – Decrease populations of pests – Save populations of organisms threatened with extinction
- 38. © 2010 Pearson Education, Inc. Conservation of Endangered Species • The U.S. Endangered Species Act defines – An endangered species as one that is in danger of extinction throughout all or a significant portion of its range – A threatened species as one that is likely to become endangered in the foreseeable future
- 39. © 2010 Pearson Education, Inc. • A major factor in population decline is habitat destruction or modification.
- 40. © 2010 Pearson Education, Inc. Sustainable Resource Management • According to the logistic growth model, the fastest growth rate occurs when a population size is at roughly half the carrying capacity.
- 41. © 2010 Pearson Education, Inc. • Theoretically, populations should be harvested down to this level, assuming that growth rate and carrying capacity are stable over time.
- 42. © 2010 Pearson Education, Inc. • In the northern Atlantic cod fishery – Estimates of cod stocks were too high – The practice of discarding young cod (not of legal size) at sea caused a higher mortality rate than was predicted – The fishery collapsed in 1992 and has not recovered
- 43. 1960 1970 1980 1990 2000 0 100 200 300 400 500 600 700 800 900Yield(thousandsofmetrictons) Figure 19.13
- 44. HUMAN POPULATION GROWTH The History of Human Population Growth • From 2000 to 500 years ago (in 1500) – Mortality was high – Births and deaths were about equal – The world population held steady at about 300 million © 2010 Pearson Education, Inc.
- 45. © 2010 Pearson Education, Inc. • The world’s population began to grow exponentially in the 1900s due to advances in – Nutrition – Sanitation – Health care Blast Animation: Population Dynamics
- 46. Annualincrease(millions) Population increase Total population size Year Totalpopulation(billions) 1500 1550 1600 1700 18001650 1750 1850 19501900 2000 2050 20 40 60 80 100 0 2 4 6 8 10 Figure 19.19
- 47. © 2010 Pearson Education, Inc. • Worldwide population growth rates reflect a mosaic of the changes occurring in different countries. – In the most developed nations, the overall growth rates are near zero. – In the developing world – Death rates have dropped – High birth rates persist
- 48. Table 19.3
- 49. © 2010 Pearson Education, Inc. Our Ecological Footprint • An ecological footprint is an estimate of the amount of land required to provide the raw materials an individual or a population consumes, including: – Food – Fuel – Water – Housing – Waste disposal
- 50. © 2010 Pearson Education, Inc. • The ecological footprint of the United States – Is 9.4 hectares per person – Represents almost twice what the U.S. land and resources can support. • The ecological impact of affluent nations is a problem of overconsumption, not overpopulation. • Compared to a family in rural India, Americans have an abundance of possessions.
- 51. Figure 19.22a
- 52. Figure 19.22b
- 53. © 2010 Pearson Education, Inc. • There is tremendous disparity in consumption throughout the world. • The world’s richest countries – Have 20% of the global population – Use 86% of the world’s resources • The rest of the world – Has 80% of the population – Uses just 14% of global resources
- 54. Evolution Connection: Humans as an Invasive Species • Pronghorn antelope – Roamed the open plains and shrub deserts of North America millions of years ago – Have a top speed of 97 km/h (60 mph) – Are the fastest mammal on the continent • Pronghorn speed is likely an adaptation to outrun American cheetahs, which went extinct about 10,000 years ago. © 2010 Pearson Education, Inc.
- 55. Figure 19.24
- 56. © 2010 Pearson Education, Inc. • About 10,000 years ago – Changes in the biotic and abiotic environments happened too rapidly for an evolutionary response – Many large North American mammals, in addition to American cheetahs, went extinct, including – Lions – Saber-toothed cats – Towering short-faced bears
- 57. © 2010 Pearson Education, Inc. • Although still hotly disputed, many scientists think that the extinction at the end of the ice age about 10,000 years ago was in part the result of the human invasion of North America, with humans serving as the damaging invasive species.
- 58. © 2010 Pearson Education, Inc. • Like other invasive species, humans may change the environment at an accelerating pace and too rapidly for other species to evolve and survive.
Editor's Notes
- #4: Figure 19.1 An ecologist styding a population of black-browed albatross in the Falkland Islands, east of the tip of South America
- #10: Table 19.1 Life Table for the U.S. Population in 2004
- #16: Figure 19.5 Exponential growth of a rabbit population
- #18: Figure 19.5a Exponential growth of a rabbit population
- #21: Figure 19.6 Logistic growth of a seal population
- #24: Figure 19.7 Comparison of exponential and logistic growth
- #27: Figure 19.8a Density-dependent regulation of population growth
- #29: Figure 19.9 Space as a limiting resource in a population of gannets
- #31: Figure 19.10 Weather change as a density-independent factor limiting growth of an aphid population
- #35: Figure 19.11b Population cycles of the snowshoe hare and the lynx
- #36: Figure 19.11a Population cycles of the snowshoe hare and the lynx
- #44: Figure 19.13 Collapse of northern cod fishery off Newfoundland
- #47: Figure 19.19 Five centuries of human population growth, projected to 2050
- #49: Table 19.3 Population Trends in 2008
- #52: Figure 19.22a Families in India (left) and the United States (right) display their possessions.
- #53: Figure 19.22b Families in India (left) and the United States (right) display their possessions.
- #56: Figure 19.24 A pronghorn antelope racing across the North American plains
- #59: Student Misconceptions and Concerns 1. Students may not appreciate the energy and effort that goes into the generation of their food and products they use daily. A simple analysis of packaging materials will reveal some of the daily investment in convenience. Consider some small task for your students to do to best estimate their ecological footprint. See Teaching Tip #5 below for a list of web sites where your students can calculate their ecological footprint. 2. We often grow tired and frustrated by the long list of problems caused by humans. Many feel helpless. You might consider referencing these web sites for basic ideas on what individuals can do to start to make a difference. 1) www.calacademy.org/exhibits/california_hotspot/what_you_can_do.htm 2) www.dep.state.pa.us/earthdaycentral/96/business/FS1977.htm 3) www.nwzaa.org/project-pages/green6.html Teaching Tips 1. You might surprise your class by noting that more people are alive today than have ever lived before and died. An examination of Figure 19.19 reveals why this is true. 2. The US government’s Census Bureau sponsors a US and World population clock at (www.census.gov/main/www/popclock.html ) for the most recent estimates of US and world human populations. 3. Medicare and Social Security will be increasingly impacted as the US population ages. By contrast, you might want to discuss the occupational outlook for professions that will address the growing needs of the elderly and the opportunity to invest in companies that will capitalize on these changes. 4. The United States has an ecological footprint greater than the land of the United States. Consider asking your class to explain how this is possible, and what this means to other countries. If you spend some time doing various conversions, you will find that the average ecological footprint of a person in the United States is about equal to the area of 18 football fields with end zones. This was calculated using the following figures. a) 1 football field with end zones is 57600 square feet (360 x 160 feet) b) 1 acre = 43560 sq. feet c) 2.47 acres = 1 hectare = 107,593 square feet d) 1.87 football fields in 1 hectare = 107,593 (1 hectare) sq. feet / 57600 sq. feet (football field with end zones) e) 17.6 football fields = 9.4 hectare x 1.87 football fields = average ecological footprint of each US citizen. 5. Many web resources are available for students to calculate their ecological footprint. A few of them are noted below. www.earthday.net/footprint/ www.footprintnetwork.org/en/index.php/GFN/page/calculators/ www.ecologyfund.com/ecology/res_bestfoot.html www.ecologicalfootprint.org/Global%20Footprint%20Calculator/GFPCalc.html www.myfootprint.org/en/visitor_information/