BIOLOGY CONCEPTS CONNECTIONS Fourth Edition Neil A Campbell

BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 35 Population Dynamics Modules 35. 1 – 35. 5 From Power. Point® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Keep track of all graphing exericises!!! If you are not sure how to get

The Spread of Shakespeare's Starlings • In the 1800 s and early 1900 s, introducing foreign species of animals and plants to North America was a popular, unregulated activity • In 1890, a group of Shakespeare enthusiasts released about 120 starlings in New York's Central Park – It was part of a project to bring to America every bird species mentioned in Shakespeare’s works Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Today, the starling range extends from Mexico to Alaska • Their population is estimated at well over 100 million Current 1955 1945 1935 1925 1945 1905 1915 1935 1925 1935 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Over 5 million starlings have been counted in a single roost • Starlings are omnivorous, aggressive, and tenacious • They cause destruction and often replace native bird species • Attempts to eradicate starlings have been unsuccessful Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The starling population in North America has some features in common with the global human population – Both are expanding and are virtually uncontrolled – Both are harming other species • Population ecology is concerned with changes in population size and the factors that regulate populations over time Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

35. 1 Populations are defined in several ways • Ecologists define a population as a single-species group of individuals that use common resources and are regulated by the same environmental factors – Individuals in a population have a high likelihood of interacting and breeding with one another • Researchers must define a population by geographic boundaries appropriate to the questions being asked – Small contained area, i. e. sea anemones in a tide pool – Expanded view, i. e. humans exposed to HIV includes all humans on planet. • Two important characteristics of population included density and dispersion. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

POPULATION STRUCTURE AND DYNAMICS 35. 2 Density and dispersion patterns are important population variables • Population density is the number of individuals in a given area or volume • It is sometimes possible to count all the individuals in a population – More often, density is estimated by sampling • Divide area in plots, count numbers in a few of those plots, and get an average density, then multiply average times total number of plots. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• One useful sampling technique for estimating population density is the mark-recapture method – see Eco packet exercise Figure 35. 2 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The dispersion pattern of a population refers to the way individuals are spaced within their area – Clumped – Uniform – Random Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Clumped dispersion is a pattern in which individuals are aggregated in patches – This is the most common dispersion pattern in nature – It often results from an unequal distribution of resources in the environment Figure 35. 2 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• A uniform pattern of dispersion often results from interactions among individuals of a population – Territorial behavior and competition for water are examples of such interactions Figure 35. 2 C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Random dispersion is characterized by individuals in a population spaced in a patternless, unpredictable way – Example: clams living in a mudflat – Environmental conditions and social interactions make random dispersion rare Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

35. 3 Idealized models help us understand population growth • Idealized models describe two kinds of population growth – exponential growth – logistic growth Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Exponential growth is the accelerating increase that occurs during a time when growth is unregulated • A J-shaped growth curve, described by the equation G = r. N, is typical of exponential growth – G = the population growth rate – r = the intrinsic rate of increase, or an organism's maximum capacity to reproduce (birth rate – death rate) – N = the population size Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Exponential growth model. This models the growth of a population under ideal conditions with unlimited resources. The rate of growth is exponential and depends on the number of individuals in the population: • The graph shows a J-shaped curve, representing population size increasing without limit. As N increases, so does G. This type of growth, if exhibited by a bacterium growing in an unlimited environment, would result in an inconceivably large number of bacteria in less than two days • No population can grow exponentially indefinitley • Starlings 100 -> 1 million in 100 years • 2 elephants -> 19 million in 750 years Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Slope = Growth rate Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Logistic growth is slowed by populationlimiting factors – It tends to level off at carrying capacity – Carrying capacity is the maximum population size that an environment can support at a particular time with no degradation to the habitat Figure 35. 3 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The equation G = r. N(K - N)/K describes a logistic growth curve – K = carrying capacity – The term (K - N)/K accounts for the leveling off of the curve – K varies based on species and resources available Figure 35. 3 C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The logistic growth model predicts that – a population's growth rate will be low when the population size is either small or large (death rate rises/birth rate falls) – a population’s growth rate will be highest when the population is at an intermediate level relative to the carrying capacity (birth rate rises/ death rate falls) Neither model perfect, represents a starting point. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cougar Lab -> to be continued at later date Copyright © 2003 Pearson Education,

35. 4 Multiple factors may limit population growth • Increasing population density directly influences density-dependent rates – such as declining birth rate or increasing death rate • The regulation of growth in a natural population is determined by several factors – limited food supply – the buildup of toxic wastes – increased disease – predation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Field studies of the song sparrow have demonstrated that birth rates may decline as a limited food supply is divided among more and more individuals Figure 35. 4 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Density-independent factors limit population no matter the size and are often abiotic factors, i. e. fires, flood, storms, seasonal temperature change or moisture, and human activity – Aphids show exponential growth in the spring and then rapidly die off when the climate becomes hot and dry in the summer Figure 35. 4 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Most populations are probably regulated by a mixture of factors – Density-dependent birth and death rates – Abiotic factors such as climate and disturbances • Populations often fluctuate in number – A natural population of song sparrows often grows rapidly and is then drastically reduced by severe winter weather Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 35. 4 C

35. 5 Some populations have "boom-and-bust" cycles • Some populations go through boom-and-bust cycles of growth and decline • Example: the population cycles of the lynx and the snowshoe hare – The lynx is one of the main predators of the snowshoe hare in the far northern forests of Canada and Alaska Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Lynx and hare • http: //www. footprintnetwork. org/en/index. ph p/GFN/page/personal_footprint/ Copyright © 2003 Pearson

– About every 10 years, both hare and lynx populations have a rapid increase (a "boom") followed by a sharp decline (a "bust") Figure 35. 5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• For the lynx, prey availability often determines population changes. • Recent studies suggest that the 10 -year cycles of the snowshoe hare largely driven by – Excessive predation. . . – But they are also influenced by fluctuations in the hare's food supply • Population cycles may also result from a time lag in the response of predators to rising prey numbers Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

LIFE HISTORIES AND THEIR EVOLUTION 35. 6 Life tables track mortality and survivorship in populations • Life tables and survivorship curves predict an individual's statistical chance of dying or surviving during each interval in its life • Life tables predict how long, on average, an individual of a given age can expect to live Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

– This table was compiled using 1995 data from the U. S. Centers for

• Population ecologists have adopted this technique, constructing life tables for various plant

• Survivorship curves plot the proportion of individuals alive at each age • Three types of survivorship curves reflect important species differences in life history Figure 35. 6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Survivorship curves • Type 1 (whales, elephants, humans) = low birth rates, low infant mortality, and life histories that fit the K-selection model • Type 2 (squirrels, Hydra) = intermediate • Type 3 (oysters, sea lettuce) = high birth rates, high infant mortality and life histories fitting the r-selection model Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

35. 7 Evolution shapes life histories • An organism's life history is the series of events from birth through reproduction to death • Life history traits include – the age at which reproduction first occurs – the frequency of reproduction – the number of offspring – the amount of parental care given – the energy cost of reproduction Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The effects of predation on life history traits of guppies has been tested by field experiments for several years. – Heritability demonstrated by retention of characteristics over generations in predator-free environments. Experimental transplant of guppies Predator: Killifish; preys mainly on small guppies Guppies: Larger at sexual maturity than those in “pike-cichlid” pools – Guppies from pikecichlid population moved to where small offspring were preyed on. Soon fewer, larger offspring produced Predator: Pike-cichlid; preys mainly on large guppies Guppies: Smaller at sexual maturity than those in “killifish” pools Figure 35. 7 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• In nature, every population has a particular life history adapted to its environment • The agave illustrates what ecologists call "big-bang reproduction" – It is able to store nutrients until environmental conditions favor reproductive success – Might not bloom for years, until large enough rainfall acts as trigger. Figure 35. 7 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Natural selection favors a combination of life history traits that maximizes an individual's output of viable, fertile offspring Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Selection for life history traits that maximize reproductive success in uncrowded, unpredictable environments is called r-selection – Such populations maximize r, the intrinsic rate of increase – Individuals of these populations mature early and produce a large number of offspring at a time – Many insect and weed species exhibit r-selection Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Selection for life history traits that maximize reproductive success in populations that live at densities close to the carrying capacity (K) of their environment is called K-selection – Individuals mature and reproduce at a later age and produce a few, well-cared-for offspring – Mammals exhibit K-selection Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

THE HUMAN POPULATION 35. 8 Connection: The human population has been growing exponentially for centuries • The human population as a whole has doubled three times in the last three centuries • The human population now stands at about 6. 1 billion and may reach 9. 3 billion by the year 2050 • Most of the increase is due to improved health and technology – These have affected death rates Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The history of human population growth Figure 35. 8 A Copyright ©

• The ecological footprint represents the amount of productive land needed to support a nation’s resource needs • The ecological capacity of the world may already be smaller than its ecological footprint Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Ecological footprint in relation to ecological capacity Figure 35. 8 B Copyright

• The exponential growth of the human population is probably the greatest crisis

The case for curing cancer • Is finding a cure for cancer a good thing as related to the overall population problems facing the world today? • Think about it for a few moments and then discuss with your partner pros and cons for curing cancer. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Red Alert!!!! Extra Credit!!!!! 25 pts. !!!!!!! • What’s your ecological footprint? • New website see home page for link and assignment information. • DUE WED May 7 th!!! Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

35. 9 Birth and death rates and age structure affect population growth • Population stability is achieved when there is zero population growth – Zero population growth is when birth rates equal death rates • There are two possible ways to reach zero population growth (ZPG) – ZPG = High birth rates - high death rates – ZPG = Low birth rates - low death rates Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The demographic transition is the shift from high birth and death rates to low birth and death rates – During this transition, populations may grow rapidly until birth rates decline Figure 35. 9 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The age structure of a population is the proportion of individuals in different agegroups – Age structure affects population growth – http: //geosim. cs. vt. edu/Java/Intl. Pop. html – Hand out paper – Do “World” as a class – Europe and USA done in computer lab next week Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

RAPID GROWTH SLOW GROWTH ZERO GROWTH/DECREASE Kenya United States Italy Male Female Ages 45+ Ages 15– 44 Under 15 Percent of population Male Female Under 15 Percent of population Figure 35. 9 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Age-structure diagrams not only reveal a population's growth trends – They also indicate social conditions • Increasing the status and education of women may help to reduce family size Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

35. 10 Connection: Principles of population ecology have practical applications • Principles of population ecology may be used to – manage wildlife, fisheries, and forests for sustainable yield – reverse the decline of threatened or endangered species – reduce pest populations Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Renewable resource management is the harvesting of crops without damaging the resource – However, human economic and political pressures often outweigh ecological concerns – There is frequently insufficient scientific information Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The collapse of the northern 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Collapse of northern cod fishery Figure 35. 10 A Copyright © 2003

• For species that are in decline or facing extinction, resource managers try to increase population size • Carrying capacity is usually increased by providing additional habitat or improving the quality of existing habitat Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Endangered species Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Endangered species often have subtle habitat requirements – The red-cockaded woodpecker was recently recovered from near-extinction by protecting its pine habitat and using controlled fires to reduce undergrowth Figure 35. 10 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Integrated pest management (IPM) uses a combination of biological, chemical, and cultural methods to control agricultural pests • IPM relies on knowledge of – the population ecology of the pest – its associated predators and parasites – crop growth dynamics • One objective of IPM is to minimize environmental and health risks by relying on natural biological control when possible Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings