Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 52 Population Ecology
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Earth’s Fluctuating Populations To understand human population growth, we must consider general principles of population ecology
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population ecology is the study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size The fur seal population of St. Paul Island, off the coast of Alaska, has experienced dramatic fluctuations in size
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Concept 52.1: Dynamic biological processes influence population density, dispersion, and demography A population is a group of individuals of a single species living in the same general area
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density and Dispersion Density is the number of individuals per unit area or volume Dispersion is the pattern of spacing among individuals within the boundaries of the population
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density: A Dynamic Perspective Determining the density of natural populations is difficult In most cases, it is impractical or impossible to count all individuals in a population Density is the result of an interplay between processes that add individuals to a population and those that remove individuals
LE 52-2 Population size Emigration Deaths Immigration Births
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Patterns of Dispersion Environmental and social factors influence spacing of individuals in a population
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a clumped dispersion, individuals aggregate in patches A clumped dispersion may be influenced by resource availability and behavior Video: Flapping Geese (clumped) Video: Flapping Geese (clumped)
LE 52-3a Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A uniform dispersion is one in which individuals are evenly distributed It may be influenced by social interactions such as territoriality Video: Albatross Courtship (uniform) Video: Albatross Courtship (uniform)
LE 52-3b Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a random dispersion, the position of each individual is independent of other individuals Video: Prokaryotic Flagella (Salmonella typhimurium) (random) Video: Prokaryotic Flagella (Salmonella typhimurium) (random)
LE 52-3c Random. Dandelions grow from windblown seeds that land at random and later germinate.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Survivorship curves can be classified into three general types: Type I, Type II, and Type III
LE 52-5 III II 100 Percentage of maximum life span Number of survivors (log scale) , I
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LE 52-8a Most weedy plants, such as this dandelion, grow quickly and produce a large number of seeds, ensuring that at least some will grow into plants and eventually produce seeds themselves.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other types of plants produce a moderate number of large seeds that provide a large store of energy that will help seedlings become established
LE 52-8b Some plants, such as this coconut palm, produce a moderate number of very large seeds. The large endosperm provides nutrients for the embryo, an adaptation that helps ensure the success of a relatively large fraction of offspring.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential Growth Exponential population growth is population increase under idealized conditions Under these conditions, the rate of reproduction is at its maximum, called the intrinsic rate of increase
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Equation of exponential population growth: dN dt r max N
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential population growth results in a J- shaped curve
LE 52-9 Number of generations Population size (N) 2,000 = 1.0N 1,000 1, dN dt = 0.5N dN dt
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The J-shaped curve of exponential growth characterizes some rebounding populations
LE Year Elephant population 8,000 4,000 6,000 2,
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.4: The logistic growth model includes the concept of carrying capacity Exponential growth cannot be sustained for long in any population A more realistic population model limits growth by incorporating carrying capacity
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Carrying capacity (K) is the maximum population size the environment can support
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic growth equation includes K, the carrying capacity dN dt ( K N ) K r max N
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The logistic model of population growth produces a sigmoid (S-shaped) curve
LE Number of generations Population size (N) K = 1,500 1,500 2,000 1, Logistic growth Exponential growth = 1.0N dN dt = 1.0N dN dt 1,500 – N 1,500
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Logistic Model and Real Populations The growth of laboratory populations of paramecia fits an S-shaped curve
LE 52-13a Time (days) Number of Paramecium/mL 1, A Paramecium population in the lab
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some populations overshoot K before settling down to a relatively stable density
LE 52-13b Time (days) Number of Daphnia/50 mL A Daphnia population in the lab
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some populations fluctuate greatly around K
LE 52-13c Time (years) Number of females A song sparrow population in its natural habitat
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic model fits few real populations but is useful for estimating possible growth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Logistic Model and Life Histories Life history traits favored by natural selection may vary with population density and environmental conditions K-selection, or density-dependent selection, selects for life history traits that are sensitive to population density r-selection, or density-independent selection, selects for life history traits that maximize reproduction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The concepts of K-selection and r-selection are somewhat controversial and have been criticized by ecologists as oversimplifications
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.5: Populations are regulated by a complex interaction of biotic and abiotic influences There are two general questions about regulation of population growth: – What environmental factors stop a population from growing? – Why do some populations show radical fluctuations in size over time, while others remain stable?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Change and Population Density In density-independent populations, birth rate and death rate do not change with population density In density-dependent populations, birth rates fall and death rates rise with population density
LE Population density Equilibrium density Density- independent birth rate Density-dependent death rate Population density Equilibrium density Density- independent death rate Density-dependent birth rate Population density Equilibrium density Density- dependent death rate Density-dependent birth rate per capita Birth or death rate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density-Dependent Population Regulation Density-dependent birth and death rates are an example of negative feedback that regulates population growth They are affected by many factors, such as competition for resources, territoriality, health, predation, toxic wastes, and intrinsic factors
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Competition for Resources In crowded populations, increasing population density intensifies intraspecific competition for resources
LE ,000 Average number of seeds per reproducing individual (log scale) 1, Plants per m 2 (log scale) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply. Average clutch size Females per unit area
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Territoriality In many vertebrates and some invertebrates, territoriality may limit density
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cheetahs are highly territorial, using chemical communication to warn other cheetahs of their boundaries
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Oceanic birds exhibit territoriality in nesting behavior
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Health Population density can influence the health and survival of organisms In dense populations, pathogens can spread more rapidly
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Predation As a prey population builds up, predators may feed preferentially on that species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Toxic Wastes Accumulation of toxic wastes can contribute to density-dependent regulation of population size
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Intrinsic Factors For some populations, intrinsic (physiological) factors appear to regulate population size
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Dynamics The study of population dynamics focuses on the complex interactions between biotic and abiotic factors that cause variation in population size
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stability and Fluctuation Long-term population studies have challenged the hypothesis that populations of large mammals are relatively stable over time
LE Year Moose population size 2,500 Steady decline probably caused largely by wolf predation 2,000 1,500 1, Dramatic collapse caused by severe winter weather and food shortage, leading to starvation of more than 75% of the population
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Extreme fluctuations in population size are typically more common in invertebrates than in large mammals
LE Year Commercial catch (kg) of male crabs (log scale) 730, ,000 10,
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metapopulations and Immigration Metapopulations are groups of populations linked by immigration and emigration High levels of immigration combined with higher survival can result in greater stability in populations
LE Year Number of breeding females Small islands Mandarte Island
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many populations undergo boom-and-bust cycles Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors
LE Year Hare population size (thousands) 1850 Snowshoe hare Lynx population size (thousands) Lynx
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.6: Human population growth has slowed after centuries of exponential increase No population can grow indefinitely, and humans are no exception
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Global Human Population The human population increased relatively slowly until about 1650 and then began to grow exponentially
LE B.C. Human population (billions) B.C B.C B.C B.C. The Plague A.D A.D.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Though the global population is still growing, the rate of growth began to slow about 40 years ago
LE Annual percent increase Year
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regional Patterns of Population Change To maintain population stability, a regional human population can exist in one of two configurations: – Zero population growth = High birth rate – High death rate – Zero population growth = Low birth rate – Low death rate The demographic transition is the move from the first state toward the second state
LE Birth or death rate per 1,000 people Sweden 2050 Year Birth rate Death rate Mexico Birth rate Death rate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The demographic transition is associated with various factors in developed and developing countries
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age Structure One important demographic factor in present and future growth trends is a country’s age structure Age structure is the relative number of individuals at each age It is commonly represented in pyramids
LE Rapid growth Afghanistan Age Male Percent of population Female –49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0– –84 75–79 70–74 65–69 60–64 55–59 50–54 Slow growth United States Age Male Percent of population Female –49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0– –84 75–79 70–74 65–69 60–64 55–59 50–54 8 Decrease Italy Male Percent of population Female
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age structure diagrams can predict a population’s growth trends They can illuminate social conditions and help us plan for the future
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Infant Mortality and Life Expectancy Infant mortality and life expectancy at birth vary greatly among developed and developing countries but do not capture the wide range of the human condition
LE Infant mortality (deaths per 1,000 births) Developed countries 60 Developing countries Life expectancy (years) Developed countries 60 Developing countries
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Global Carrying Capacity How many humans can the biosphere support?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Estimates of Carrying Capacity The carrying capacity of Earth for humans is uncertain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Footprint The ecological footprint concept summarizes the aggregate land and water area needed to sustain the people of a nation It is one measure of how close we are to the carrying capacity of Earth Countries vary greatly in footprint size and available ecological capacity
LE Ecological footprint (ha per person) Available ecological capacity (ha per person) New Zealand Australia Canada Sweden World China India Spain UK Japan Germany Norway USA Netherlands
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At more than 6 billion people, the world is already in ecological deficit