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Biology Concepts and Applications | 9e Starr | Evers | Starr Chapter 40 Population Ecology © Cengage Learning 2015 © Cengage Learning 2015 The biosphere is the global ecosystem, the sum of all the planet’s ecosystems or all of life and where it lives. © Cengage Learning 2015 © Cengage Learning 2015 40.1 How Do We Describe Populations? • Ecological factors affect the size, density, distribution, and age structure of a population • Studying population ecology often involves the use of demographics, which often change over time • Demographics – Statistics that describe a population © Cengage Learning 2015 How Do We Describe Populations? • Biologists frequently use sampling techniques to estimate population size – Plot sampling estimates the total number of individuals in an area based on direct counts in a small portion of that area – Estimates from plot sampling are most accurate when the organisms counted are not very mobile and conditions across the area they occupy are more or less uniform © Cengage Learning 2015 How Do We Describe Populations? • Population density – Number of individuals per unit area or volume – Example: Number of dandelions per square meter of lawn • Population distribution – Describes how individuals are distributed – Individuals may be clumped, uniformly dispersed, or randomly dispersed in an area © Cengage Learning 2015 © Cengage Learning 2015 Figure 19.1 How Do We Describe Populations? • Scientists use mark-recapture sampling to estimate the population size of mobile animals, such as Florida Key deer • Mark-recapture sampling – Method of estimating population size of mobile animals by marking individuals, releasing them, then checking the proportion of marks among individuals recaptured at a later time © Cengage Learning 2015 40.2 Why Does the Size of a Population Change? • Immigration – Movement of individuals into a population – Population increases • Emigration – Movement of individuals out of a population – Population decreases • Zero population growth – Interval in which births equal deaths © Cengage Learning 2015 Why Does the Size of a Population Change? • Biotic potential – Maximum possible population growth rate under optimal conditions – Under ideal conditions (shelter, food, and other essential resources are unlimited, no predators or pathogens) a population’s growth rate reaches its biotic potential – Microbes have high biotic potentials – Large-bodied mammals have low biotic potentials © Cengage Learning 2015 Why Does the Size of a Population Change? Exponential Growth Curve © Cengage Learning 2015 Why Does the Size of a Population Change? Exponential Growth Curve © Cengage Learning 2015 40.3 What Constrains Population Growth? • Limiting factors – A necessary resource, the depletion of which halts population growth – Populations seldom reach their biotic potential because of the effects of limiting factors – Not always easy to identify all the factors that can restrict population growth © Cengage Learning 2015 What Constrains Population Growth? • Limiting factors – Examples: essential resources such as food, mineral ions, refuge from predators, and safe nesting sites – In any environment, one essential factor will run out first, and acts as the brake on population growth – Supplying the first limiting factors simply substitutes one for another – all natural populations eventually encounter limits © Cengage Learning 2015 What Constrains Population Growth? • Logistic growth – A pattern of logistic growth shows how a small population starts growing slowly in size, then grows rapidly, then levels off as the carrying capacity is reached – Plots out as an S-shaped curve © Cengage Learning 2015 What Constrains Population Growth? • Carrying capacity – Maximum number of individuals of a species that an environment can sustain – Ultimately, the sustainable supply of resources determines population size © Cengage Learning 2015 What Constrains Population Growth? Population size (number of individuals) initial carrying capacity © Cengage Learning 2015 2 3 4 new carrying capacity 1 What Constrains Population Growth? • 1944: 29 reindeer introduced to St. Matthew Island • 1957: 1,350 well-fed reindeer (lichens) • 1963: 6,000 hungry reindeer (carry capacity exceeded) • 1966: 42 live reindeer, and many bleached bones • 1980s: No reindeer © Cengage Learning 2015 What Constrains Population Growth? © Cengage Learning 2015 40.4 How Do Life History Patterns Vary? • Reproduction-related events that occur between birth and death make up a life history pattern • Life history pattern – A set of traits related to growth, survival, and reproduction such as life span, age-specific mortality, age at first reproduction, and number of breeding events © Cengage Learning 2015 How Do Life History Patterns Vary? © Cengage Learning 2015 How Do Life History Patterns Vary? • Type I survivorship curve – Elephants have type I survivorship, with low mortality until old age – Typical of large animals that bear one or few offspring at a time and provide extended parental care © Cengage Learning 2015 How Do Life History Patterns Vary? • Type II survivorship curve – Snowy egrets are type II population, with a fairly constant death rate – Typical of lizards, small mammals, and large birds © Cengage Learning 2015 How Do Life History Patterns Vary? • Type III survivorship curve – Sea urchins are type III; mortality is high for larvae and in old age, but low in adults – Typical of species that produce many small offspring and provide little or no parental care © Cengage Learning 2015 Percentage of survivors (log scale) 100 I 10 II 1 III 0.1 0 50 100 Percentage of maximum life span © Cengage Learning 2015 Figure 19.4 How Do Life History Patterns Vary? © Cengage Learning 2015 © Cengage Learning 2015 Figure 19.5a 500 Ideal conditions 20 rabbits to 475 rabbits in 12 months 450 400 Population size (N) Exponential growth of a rabbit population 350 300 250 200 150 100 50 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Time (months) © Cengage Learning 2015 Figure 19.5 Biology and Society: Multiplying Like Rabbits – In 1859, 12 pairs of European rabbits were released on a ranch in southern Australia. – By 1865, 20,000 rabbits were killed on just that one ranch. – By 1900, several hundred million rabbits were distributed over most of the continent. © Cengage Learning 2015 Inc. © 2010 Pearson Education, © Cengage Learning 2015 Figure 19.00 – The European rabbits • Destroyed farming and grazing land • Promoted soil erosion • Made grazing treacherous for cattle and sheep • Competed directly with native marsupials – The European red fox • Was introduced to control the rabbits • Spread across Australia • Ate several species of native birds and small mammals to extinction • Had little impact on the rabbit population © Cengage Learning 2015 – In 1950, the Australian government introduced a virus lethal to European rabbits into the rabbits’ Australian environment. –Did this work? © Cengage Learning 2015 40.6 How Has the Size of the Human Population Changed Over Time? • For most of history, the human population grew very slowly – In 2009, human population size surpassed 6.8 billion • Growth rate began to increase about 10,000 years ago, then soared during the past two centuries • Three trends promoted the large increases © Cengage Learning 2015 How Has the Size of the Human Population Changed Over Time? • Three factors of human population growth – Humans were able to migrate into new habitats and expand into new climate zones – Humans developed new technologies that increased the carrying capacity of existing habitats – Humans sidestepped some limiting factors that restrain growth of other species © Cengage Learning 2015 © Cengage Learning 2015 In the developing world – Death rates have dropped / High birth rates persist 1 Billion : 10,000 Years 2 Billion : 123 Years 3 Billion : 33 Years 4 Billion : 14 Years 5 Billion : 13 Years 6 Billion : 12 Years 7 Billion : 13 Years 8 Billion 12 Years 9 Billion : 24 Years © Cengage Learning 2015 How Has the Size of the Human Population Changed Over Time? • Human skills that override normal population limits – Learned to start fires, build shelters, make clothing, manufacture tools, and hunts together – Language allowed knowledge to pass through generations – Agriculture provided a more dependable food supply © Cengage Learning 2015 How Has the Size of the Human Population Changed Over Time? • Human skills that override normal population limits – Improved sanitation and medical advances (vaccines, antibiotics) cut the death toll from disease – Energy of fossil fuels allowed development of mechanized agriculture to sustain the ever larger population © Cengage Learning 2015 How Has the Size of the Human Population Changed Over Time? • Quality of life is inversely related to population growth, resource depletion, and pollution • Many governments now offer family planning programs to reduce fertility rates • Worldwide, total fertility rate has fallen from 6.5 in 1950 to 2.6 in 2008; and replacement fertility rate for developed countries is 2.1 © Cengage Learning 2015 How Has the Size of the Human Population Changed Over Time? © Cengage Learning 2015 How Has the Size of the Human Population Changed Over Time? • Age structure diagrams show the age distribution of individuals – The broader the base of an age structure diagram, the greater proportion of young people, and the greater expected growth – More than 1/3 of the world population is in the broad pre-reproductive base – World population growth can’t be slowed for many years, because 1.9 billion people are about to enter reproductive age © Cengage Learning 2015 How Has the Size of the Human Population Changed Over Time? © Cengage Learning 2015 How Has the Size of the Human Population Changed Over Time? • Future growth – World population is expected to reach 8.9 billion by 2050, and possibly to decline as the century ends – China and India each hold more than one billion people (together, 38% percent of the world population); the United States is third, with 307 million © Cengage Learning 2015 40.7 How Does Industrialization Affect Population Growth? • The most highly developed countries have the lowest birth rates and infant mortality, and the highest life expectancy • High population growth is correlated with low levels of economic development, and low per capita consumption of resources • Negative population growth in some countries also poses challenges © Cengage Learning 2015 How Does Industrialization Affect Population Growth? • On a per capita basis, people in highly developed countries use far more resources than those in less developed countries, and generate more waste and pollution © Cengage Learning 2015 How Does Industrialization Affect Population Growth? • Ecological footprint – Area of Earth’s surface required to sustainably support a particular level of development and consumption – People in China and India consume less than average – Per capita footprint of the United States is more than three times average © Cengage Learning 2015 How Does Industrialization Affect Population Growth? (cont’d.) © Cengage Learning 2015 11/25 Friday Schedule Populations 40 11/27 No Class 12/2 41 12/4 Trophic Levels 12/9 12/16 Ecology Succession Biomes & Human 43&44 12/11 Effect Final Exam © Cengage Learning 2015 Lecture Review Lab Final Exam 42 Vultures evolved an extreme gut to cope with disgusting dietary habits November 25, 2014 How is it that vultures can live on a diet of carrion that would at least lead to severe food-poisoning, and more likely kill most other animals? When vultures eat lunch they happily strip the rotting carcasses they find back to the bone. And if, however, the animal's hide is too tough to easily pierce with their beak, they don't hesitate to enter it using other routes, among them the back entrance -- so to speak: via the anus. Although their diet of meat that is both rotting and liberally contaminated with feces would likely kill most other animals, they are apparently immune to the cocktail of deadly microbes within their dinner such as Clostridia, Fuso- and Anthrax-bacteria. "To investigate vultures' ability to survive eating this putrid cocktail, we generated DNA profiles from the community of bacteria living on the face and gut of 50 vultures from the USA. Our findings enable us to reconstruct both the similarities, and differences, between the bacteria found in turkey vultures and black vultures, distributed widely in the Western Hemisphere. Apparently something radical happens to the bacteria ingested during passage through their digestive system," says Lars Hestbjerg Hansen, a professor at Aarhus University who together with PhD-student Michael Roggenbuck lead the study while he was at the University of Copenhagen. On average, the facial skin of vultures contained DNA from 528 different types of micro-organisms, whereas DNA from only 76 types of micro-organisms were found in the gut. Michael Roggenbuck explains: "Our results show there has been strong adaptation in vultures when it comes to dealing with the toxic bacteria they digest. On one hand vultures have developed an extremely tough digestive system, which simply acts to destroy the majority of the dangerous bacteria they ingest. On the other hand, vultures also appear to have developed a tolerance towards some of the deadly bacteria -- species that would kill other animals actively seem to flourish in the vulture lower intestine." © Cengage Learning 2015 How Do Life History Patterns Vary? • R-selection – Individuals who produce maximum number offspring as quickly as possible have a selective advantage – Occurs when population density is low and resources are abundant © Cengage Learning 2015 How Do Life History Patterns Vary? • K-selection – Individuals who produce offspring that outcompete others for limited resources have a selective advantage – Occurs when a population is near carrying capacity © Cengage Learning 2015 How Does Predation Affect Life History Traits? • Overfishing of cod – In response to fishing pressure on larger fish, Atlantic codfish began maturing faster and reproducing younger – A 1992 ban on cod fishing came too late to stop the Atlantic cod population from crashing – Life history changes were early signs of overfishing – had biologists recognized the signs, they might have been able to save the fishery and more than 35,000 jobs © Cengage Learning 2015