Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 36 Population Dynamics
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Spread of Shakespeare's Starlings The European Starling has become an abundant and destructive pest in North America – Introduced in 1890 because of mention in Shakespeare – Like the human population, is expanding and uncontrolled Population ecology is concerned with changes in population size and the factors that regulate populations over time
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 36.1 Population ecology is the study of how and why populations change A population is a group of individuals of a single species that occupy the same general area – Boundaries defined in relation to question being studied
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings POPULATION STRUCTURE AND DYNAMICS 36.2 Density and dispersion patterns are important population variables Population density is the number of individuals of a species per unit area or volume Environmental and social factors influence the spacing of individuals in various dispersion patterns – Clumped – Uniform – Random
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Video: Flapping Geese (clumped) Video: Flapping Geese (clumped) Video: Albatross Courtship (uniform) Video: Albatross Courtship (uniform) Video: Prokaryotic Flagella (Salmonella typhimurium) (random) Video: Prokaryotic Flagella (Salmonella typhimurium) (random)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 36.3 Life tables track mortality and survivorship in populations Life tables show how long an individual of a given age is expected to live Survivorship curves plot the proportion of individuals alive at each age – Type I: Many individuals survive to maturity – Type II: Mortality constant over life span – Type III: High death rates for the very young, lower for those that survive longer
LE Percentage of maximum life span Percentage of survivors (log scale) 50 III II I 1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 36.4 Idealized models help us understand population growth Exponential growth model gives an idealized picture of unregulated population growth – Under ideal conditions, whole population multiplies by a constant factor
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – G = rN describes the J-shaped curve of exponential growth G = population growth rate r = intrinsic rate of increase – Population members' maximum capacity to reproduce N = population size
LE 36-04a Number of bacterial cells (N) Time (min) G rN TimeNumber of Cells 0 minutes ( 2 hours) 3 hours 4 hours 12 hours 8 hours ,096 16,777,216 68,719,476,736 2 24 2 36 2 12 2 9 2 6 2 5 2 4 2 3 2 2 2 1 2 0
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Logistic growth model represents the slowing of population growth as a result of limiting factors – Limiting factors: environmental factors that restrict population growth – G = rN(K - N)/K describes the S-shaped curve of logistic growth K = carrying capacity (K - N)/K accounts for the leveling off of the curve
LE 36-04b Breeding male fur seals (thousands) 1945 Year
LE 36-04c Time 0 Number of individuals (N) G rN (K N) K G rN K
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Predictions of logistic growth model for natural populations Growth rate low when population is either small or large Growth rate highest when population is at intermediate level Does not fit any natural population perfectly Useful starting point for studying population growth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 36.5 Multiple factors may limit population growth Population growth is density dependent – Birth rates decline and death rates rise in response to increasing population density – Organisms compete for limited resources – Density affects health of organisms Abiotic factors may limit population growth before limiting factors become important
LE 36-05a Density of females 0 Clutch size
LE 36-05b Sudden decline Number of aphids Apr May Jun Jul Aug Sep OctNovDec Exponential growth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most populations are regulated by a mixture of factors and show fluctuation over time
LE 36-05c Number of females Time (years)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 36.6 Some populations have "boom-and-bust" cycles Some populations fluctuate in density with regularity – May have complex causes Example: snowshoe hare and lynx cycles
LE Hare population size (thousands) Year Lynx Snowshoe hare Lynx population size (thousands)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LIFE HISTORIES AND THEIR EVOLUTION 36.7 Evolution shapes life histories An organism's life history is the series of events from birth through reproduction to death – Key life history traits Age of first reproduction Frequency of reproduction Number of offspring Amount of parental care
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Natural selection will favor the combination of life history traits that maximizes an individual's output of viable, fertile offspring – "Big-bang" vs. reproduction throughout life span – r-selection Maximizes reproductive success in uncrowded, unpredictable environments Individuals mature early, produce many offspring
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – K-selection Common when population density is close to carrying capacity Later maturity and reproduction Few, well-cared-for offspring Concept of r- and K-selection has been criticized as oversimplified – Has stimulated research on factors influencing evolution of life histories (example: guppies)
LE 36-07b Experimental transplant of guppies Predator: Killifish; preys mainly on small, immature guppies Guppies: Larger at sexual maturity than those in pike-cichlid pools Guppies: Smaller at sexual maturity than those in killifish pools Predator: Pike-cichlid; preys mainly on large, mature guppies
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 36.8 Principles of population ecology have practical applications Principles of population ecology are useful in sustainable resource management – Maximum sustained yield – Improvement of habitat or provision of additional habitat to increase K – Reduction of population size – Challenged by economic and political pressures
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings THE HUMAN POPULATION CONNECTION 36.9 Human population growth has started to slow after centuries of exponential increase The human population now stands at over 6.4 billion Even with slowing growth, predicted to reach 7.3 to 8 billion by 2025
LE 36-09a Human population size (billions) A.D A.D B.C B.C B.C B.C B.C. The Plague
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What is Earth's human carrying capacity? – Ecological footprint Amount of land needed to support human demands on Earth's resources Exceeds ecological capacity in many countries – World is already in ecological deficit Problem is not just overpopulation, but overconsumption Possible limiting factors: food, space
LE 36-09b Ecological footprint (ha per person) 16 India Available ecological capacity (ha per person) China World Spain UK Japan Norway Netherlands Germany USA Sweden Canada Australia New Zealand
LE 36-09c Traffic in downtown Cairo, Egypt Refugee camp in Zaire Manhattan, New York City
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Birth and death rates and age structure affect population growth Demographic transition – Shift from high birth rates and death rates to low birth rates and death rates – Has occurred in most developed countries – Population size continues to grow until birth rate equals death rate – Reduced family size key Related to status of women
LE 36-10a Birth or death rate per 1,00 0 population Birth rate Year Death rate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age structure of a population – Proportion of individuals in different age groups – Affects population's future growth – Indicates social conditions – Varies in developing and developed countries Demographic differences – Infant mortality – Life expectancy at birth
LE 36-10b 85 Age 80 75 19 5959 70 7 60 6 50 5 40 4 30 3 20 2 10 1 00 Male Female Afghanistan Rapid growth Percent of population Male Female Primary reproductive ages Slow growth United States Male Female Italy Decrease