Chapter 36 Population Ecology Power Point Lectures for

Chapter 36 Population Ecology Power. Point® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko © 2010 Pearson Education, Inc.

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. © 2010 Pearson Education, Inc.

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 © 2010 Pearson Education, Inc.

• 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 © 2010 Pearson Education, Inc.

• Today, rabbits, foxes, and a long list of other non-native animal and plant species are – Still entrenched in Australia – Damaging the environment – Costing hundreds of millions of dollars in economic losses © 2010 Pearson Education, Inc.

Ecology 1. the study of how living things interact with their environment 2. describes the world © 2010 Pearson Education, Inc.

Environmentalism 1. is not ecology 2. conservation of natural resources © 2010 Pearson Education, Inc.

AN OVERVIEW OF POPULATION ECOLOGY Population- a group of individuals of a single species that occupy the same area © 2010 Pearson Education, Inc.

• Population ecology focuses on the factors that influence a population’s – Density – Structure – Size – Growth rate © 2010 Pearson Education, Inc.

An ecologist studying a population of black-browed albatross in the Falkland Islands, east of the tip of South America Figure 19. 1

• Population ecology is used to study – How to develop sustainable fisheries – How to control pests and pathogens – Human population growth © 2010 Pearson Education, Inc.

Population Density • Population density is the number of individuals of a species per unit of area or volume. Examples include – The number of largemouth bass per cubic kilometer (km 3) of a lake – The number of oak trees per square kilometer (km 2) in a forest – The number of nematodes per cubic meter (m 3) in a forest’s soil © 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 – Rodent burrows © 2010 Pearson Education, Inc.

Figure 19. 2

POPULATION GROWTH MODELS • Population size fluctuates as individuals – Are born – Immigrate into an area – Emigrate away – Die © 2010 Pearson Education, Inc.

The Exponential Growth Model: The Ideal of an Unlimited Environment • Exponential population growth (J shaped growth curve)- slow growth at first followed by increasingly faster rates of growth • describes the expansion of a population in an ideal and unlimited environment. © 2010 Pearson Education, Inc.

500 450 Population size (N) 400 350 300 250 200 150 100 50 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Time (months) Figure 19. 5

Figure 19. 5 a

• 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 © 2010 Pearson Education, Inc.

© 2010 Pearson Education, Inc.

The Logistic Growth Model: The Reality of a Limited Environment • Limiting factors – environmental factors that hold population growth in check – restrict the number of individuals that can occupy a habitat © 2010 Pearson Education, Inc.

• carrying capacity- maximum population size that can be sustained in an area © 2010 Pearson Education, Inc.

• logistic population growth (S shaped growth curve)- growth rate decreases as the population size approaches carrying capacity © 2010 Pearson Education, Inc.

© 2010 Pearson Education, Inc.

Breeding male fur seals (thousands) 10 8 6 4 2 0 1915 1925 1935 Year © 2010 Pearson Education, Inc. 1945

36. 4 Idealized models predict patterns of population growth § Logistic growth model – This growth model takes into account limiting factors – Limiting factors are environmental factors that restrict population growth – Formula © 2010©Pearson Education, Inc. Copyright 2009 Pearson Education, Inc.

© 2010 Pearson Education, Inc.

• The carrying capacity for a population varies, depending on – The species – The resources available in the habitat © 2010 Pearson Education, Inc.

• Organisms exhibiting equilibrial life history patterns occur in environments where the population size is at or near carrying capacity. © 2010 Pearson Education, Inc.

• The logistic model and the exponential model are theoretical ideals of population growth. • No natural population fits either one perfectly. © 2010 Pearson Education, Inc.

Number of individuals Exponential growth Carrying capacity Logistic growth 0 Time Figure 19. 7

opportunistic life history – take advantage of favorable conditions – small, short lived organisms © 2010 Pearson Education, Inc.

Dandelions have an opportunistic life history © 2010 Pearson Education, Inc. Table 19. 2 a

equilibrial life history – reach sexual maturity slowly – produce few, well cared for offspring – larger, longer lived organisms © 2010 Pearson Education, Inc.

Elephants have an equilibrial life history © 2010 Pearson Education, Inc. Table 19. 2 b

© 2010 Pearson Education, Inc. Table 19. 2

Regulation of Population Growth Density-Dependent Factors • The logistic model is a description of interspecific competition. • interspecific competition- competition between individuals of the same species for the same limited resources © 2010 Pearson Education, Inc.

• As population size increases – Competition becomes more intense – The growth rate declines in proportion to the intensity of competition © 2010 Pearson Education, Inc.

• density-dependent factor- a population-limiting factor whose effects intensify as the population increases in density © 2010 Pearson Education, Inc.

Average clutch size 12 11 10 9 8 0 10 20 30 40 50 60 70 80 90 Number of breeding pairs (a) Decreasing birth rate with increasing density in a population of great tits Figure 19. 8 a

100 Survivors (%) 80 60 40 20 40 60 80 100 120 Density (beetles/0. 5 g flour) (b) Decreasing survival rates with increasing density in a population of flour beetles Figure 19. 8 b

Density-dependent factors 1. Accumulation of toxic wastes 2. Limited food supply 3. Limited territory © 2010 Pearson Education, Inc.

Figure 19. 9

Density-Independent Factors • Density-independent factors 1. population-limiting factors whose intensity is unrelated to population density 2. abiotic factors: fires, floods, storms © 2010 Pearson Education, Inc.

Sudden decline Number of aphids Exponential growth Apr May Jun Jul Aug Sep Oct Nov Dec Weather change as a density-independent factor limiting growth of an aphid population Figure 19. 10

• In many natural populations, densityindependent 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 © 2010 Pearson Education, Inc.

Population Cycles • Some populations have regular boomand-bust cycles characterized by periods of rapid growth followed by steep population declines. © 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 © 2010 Pearson Education, Inc.

160 120 9 80 6 40 3 0 0 1850 Lynx population (thousands) Hare population (thousands) Lynx Snowshoe hare 1900 Year Figure 19. 11

• 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 © 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 © 2010 Pearson Education, Inc.

Conservation of Endangered Species • The U. S. Endangered Species Act defines – endangered species- species that is in danger of extinction – threatened species- species that is likely to become endangered © 2010 Pearson Education, Inc.

• A major factor in population decline is habitat destruction or modification. © 2010 Pearson Education, Inc.

• The red-cockaded woodpecker – Requires longleaf pine forests with clear flight paths between trees – Suffered from fire suppression, increasing the height of the vegetation on the forest floor – Recovered from near-extinction to sustainable populations due to controlled burning and other management methods © 2010 Pearson Education, Inc.

A red-cockaded woodpecker perches at the entrance to its nest in a long-leaf pine tree. High, dense undergrowth impedes the woodpeckers’ access to feeding grounds. Low undergrowth offers birds a clear flight path between nest sites and feeding grounds. Figure 19. 12

Invasive Species • invasive species – a non-native species that has spread far beyond the original point of introduction – Causes environmental or economic damage by colonizing and dominating suitable habitats • In the United States, invasive species cost about $137 billion a year. © 2010 Pearson Education, Inc.

• Invasive species typically exhibit an opportunistic life history pattern. © 2010 Pearson Education, Inc.

• Cheatgrass – Is an invasive species in the western United States – Currently covers more than 60 million acres of rangeland formerly dominated by native grasses and sagebrush – Produces seeds earlier and in greater abundance than native species – Forms highly flammable brush creating fires that native plants cannot tolerate © 2010 Pearson Education, Inc.

A reddish sea of cheatgrass threatens to overwhelm native sagebrush (green) Figure 19. 14

• European starlings – Are another invasive species – Were first released into New York in 1890 – Now number more than 200 million in the United States © 2010 Pearson Education, Inc.

Figure 19. 15

Biological Control of Pests • Invasive species may benefit from the absence of – Pathogens – Predators – Herbivores © 2010 Pearson Education, Inc.

Biological Control of Pests • Biological control – intentional release of a natural enemy to attack a pest population – used to manage an invasive species © 2010 Pearson Education, Inc.

• In 1950, the Australian government introduced a virus lethal to European rabbits into the rabbits’ Australian environment. © 2010 Pearson Education, Inc.

The Process of Science: Can Biological Control Defeat Kudzu? • Kudzu – Is an invasive Asian vine – Covers about 12, 000 square miles of the southeastern United States – Has a range limited by cold winters © 2010 Pearson Education, Inc.

Figure 19. 16

• Many strategies to control kudzu have been considered with little success. • A fungal pathogen called Myrothecium verrucaria appears to be a promising candidate for biological control. © 2010 Pearson Education, Inc.

Integrated Pest Management • Agricultural operations create their own highly managed ecosystems that – Have genetically similar individuals (a monoculture) – Are planted in close proximity to each other – Function as a “banquet” for – Plant-eating animals – Pathogenic bacteria – Viruses © 2010 Pearson Education, Inc.

• Like invasive species, most crop pests – Have an opportunistic life history pattern – Can cause extensive crop damage © 2010 Pearson Education, Inc.

Figure 19. 18

THE HUMAN POPULATION © 2010©Pearson Education, Inc. Copyright 2009 Pearson Education, Inc.

36. 9 The human population continues to increase, but the growth rate is slowing § Human population is expected to continue increasing for several decades § 95% of the increase is in developing nations © 2010©Pearson Education, Inc. Copyright 2009 Pearson Education, Inc.

80 10 Population increase 60 6 40 4 Total population size 20 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 2050 Year © 2010 Pearson Education, Inc. 8 2 0 Total population (in billions) Annual increase (in millions) 100

© 2010 Pearson Education, Inc.

Birth or death rate per 1, 000 population 50 40 30 20 10 Rate of increase (r) Birth rate Death rate 0 1900 1925 1950 1975 Year © 2010 Pearson Education, Inc. 2000 2025 2050

36. 11 CONNECTION: An ecological footprint is a measure of resource consumption § U. S. Census Bureau projection – 8 billion people within the next 20 years – 9. 5 billion by mid-21 st century © 2010©Pearson Education, Inc. Copyright 2009 Pearson Education, Inc.

36. 11 CONNECTION: An ecological footprint is a measure of resource consumption § Ecological footprint helps understand resource availability and usage § The United States has a – Big ecological footprint – Large ecological deficit © 2010©Pearson Education, Inc. Copyright 2009 Pearson Education, Inc.

© 2010 Pearson Education, Inc.

Concept Check §Predict which survivorship curve would best describe most whale species. • Type III © 2010 Pearson Education, Inc.

Answer §Predict which survivorship curve would best describe most whale species • Type I © 2010 Pearson Education, Inc.

Concept Check §Predict which survivorship curve would best describe a fish like a carp (Cyprinus carpio). A large female carp can produce more than a million eggs. • Type III © 2010 Pearson Education, Inc.

Answer §Predict which survivorship curve would best describe a fish like a carp (Cyprinus carpio). A large female carp can produce more than a million eggs. 3) Type III © 2010 Pearson Education, Inc.

Concept Check §Predict which survivorship curve would best describe most whale species. • Type III © 2010 Pearson Education, Inc.

Answer §Predict which survivorship curve would best describe most whale species • Type I © 2010 Pearson Education, Inc.

Concept Check §Predict which survivorship curve would best describe a fish like a carp (Cyprinus carpio). A large female carp can produce more than a million eggs. • Type III © 2010 Pearson Education, Inc.

Answer §Predict which survivorship curve would best describe a fish like a carp (Cyprinus carpio). A large female carp can produce more than a million eggs. 3) Type III © 2010 Pearson Education, Inc.

Concept Check §The ecological footprint is one way to calculate the Earth’s carrying capacity for human populations. At current consumption rates, a child born today in an industrialized country will add more to consumption and pollution during her/his lifetime than • 5 -10 children born in developing countries. • 10 -15 children born in developing countries. • 20 children born in developing countries. • 30 -50 children born in developing countries. © 2010 Pearson Education, Inc.

Answer §The ecological footprint is one way to calculate the Earth’s carrying capacity for human populations. At current consumption rates, a child born today in an industrialized country will add more to consumption and pollution during her/his lifetime than 4) 30 -50 children born in developing countries. © 2010 Pearson Education, Inc.

Thinking Like a Scientist §This figure plots the breeding populations of fur seals as they recovered from uncontrolled hunting. Based on this graph what is the approximate carrying capacity of the fur seal’s breeding habitat? © 2010 Pearson Education, Inc. • About 1000 seals. • About 5000 seals • About 10, 000 seals

Answer §This figure plots the breeding populations of fur seals as they recovered from uncontrolled hunting. Based on this graph what is the approximate carrying capacity of the fur seal’s breeding habitat? 3) © 2010 Pearson Education, Inc. About 10, 000 seals

Thinking Like a Scientist §The maximum rate of increase for the seal population on the island occurred during which decade? © 2010 Pearson Education, Inc. • 1910 -1920. • 1920 -1930. • 1930 -1940.

Answer §The maximum rate of increase for the seal population on the island occurred during which decade? 2) © 2010 Pearson Education, Inc. 1920 -1930.

Thinking Like a Scientist §This graph plots the difference between birth rates and death rates for Mexico during the 20 th century. During which quarter century did Mexico experience the greatest rate of population growth? © 2010 Pearson Education, Inc. • 1900 -1925. • 1925 -1950. • 1950 -1975. • 1975 -2000.

Answer §This graph plots the difference between birth rates and death rates for Mexico during the 20 th century. During which quarter century did Mexico experience the greatest rate of population growth? 3) © 2010 Pearson Education, Inc. 1950 -1975.

Science and Society §Most scientists agree that the most pressing environmental issue facing human society is population growth. Scientist disagree on whether the rising rate of consumption in the developed countries is a greater problem than the rapid population growth in undeveloped countries. How do you rate this problem? Strongly Disagree © 2010 Pearson Education, Inc. A B C D E Strongly Agree

Science and Society §Renewable resource management is challenging. Populations of whitetail deer today live in areas with few natural predators. Their populations have expanded exponentially. Population control methods include hunting—even in urban areas. Do you think that controlled hunting should be used to manage deer populations in urban areas? Strongly Disagree © 2010 Pearson Education, Inc. A B C D E Strongly Agree

Science and Society §Populous nations such as China have instituted strict policies to curb population growth. In 1979, China implemented a “one-child” policy. Do you think that such strict control methods are appropriate for population control? Strongly Disagree © 2010 Pearson Education, Inc. A B C D E Strongly Agree