Biology Sylvia S. Mader Michael Windelspecht Chapter 44 Population Ecology Lecture Outline Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1

2 Outline 44.1 Scope of Ecology 44.2 Demographics of Populations 44.3 Population Growth Models 44.4 Regulation of Population Size 44.5 Life History Patterns 44.6 Human Population Growth

44.1 Scope of Ecology Ecology  The study of the interactions of organisms with Other organisms and the physical environment  Habitat - Place where an organism lives  Population - All the individuals of a species within a particular space  Community – Various populations of multiple species interacting with each other  Ecosystem - Community interacting with the environment  Biosphere - All the communities on Earth whose members exist in air and water and on land 3

Ecological Levels 4 OrganismPopulationCommunity Ecosystem © David Hall/Photo Researchers, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Demographics of Populations Demography is the statistical study of a population Demography includes  Population density  Population distribution  Growth rate of a population

Demographics of Populations Density and Distribution  Population Density - Number of individuals per unit area  Population Distribution - Pattern of dispersal of individuals across an area of interest  Limiting factors are environmental aspects that particularly determine where an organism lives 6

Distribution Patterns of the Creosote Bush 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Young, small shrubs b. Clumped Large shrubs a. Mature desert shrubs Medium shrubs c. Random d. Uniform (a): © The McGraw Hill Companies, Inc. Evelyn Jo Johnson, photographer

Demographics of Populations Population Growth  The rate of natural increase depends on The number of individuals born each year, and The number of individuals who die each year 8

9 Demographics of Populations Population Growth (continued)  Biotic Potential The maximum rate of natural increase for a population that can occur when resources are unlimited  Biotic potential depends on factors that influence the population’s reproduction, including The usual number of offspring surviving to reproductive age The amount of competition within the population Age of and number of reproductive opportunities Presence of disease and predators

Biotic Potential 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a.b. (mice): © E. R. Degginger/Photo Researchers, Inc.; (rhinos): © Corbis RF

Demographics of Populations Mortality Patterns  A cohort Composed of all the members of a population born at the same time –Life tables demonstrate how many members of a cohort are still alive after certain intervals of time  Survivorship The probability that newborn individuals of a cohort will survive to a particular age Survivorship Curves –A plot of the number of organisms surviving at each age 11

A Life Table for a Bluegrass Cohort 12

Demographics of Populations Survivorship Curves  Type I Characteristic of a population in which most individuals survive past the midpoint of the life span and death does not come until the end of the life span  Type II Death is linear over time (unrelated to age)  Type III Typical of a population in which most individuals die very young 13

Survivorship Curves 14 b: © Holt Studios/Photo Researchers, Inc.; c: © Bruce M. Johnson; d: © Digital Vison/Getty RF Images I I II III Number of Survivors Percent of Life Span Number of Survivors Percent of Life Span b. Bluegrasses d. Mosquitoes 1, million 10, Death occurs after midpoint. Death unrelated to age. Death comes early on. II Number of Survivors Percent of Life Span a. c. Lizards Percent of Life Span Number of Survivors 1, , Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Demographics of Populations Age Distribution  The proportion of the population that falls into various age categories  There are three major age groups Prereproductive Reproductive Postreprodutive  At least three age structure diagrams are possible Increasing population Stable population Decreasing population 15

Age Structure Diagrams 16 Increasing Population Decreasing Population Stable Population Age Structure Postreproductive Ages Reproductive Ages Prereproductive Ages Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Population Growth Models Two working models for population growth:  Semelparity Members of a population have only a single reproductive event in their lifetime –Ex: insects  Iteroparity Members of the population experience many reproductive events throughout their lifetime –Ex: most vertebrates, shrubs, and trees

Patterns of Reproduction 18 a.b. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © Breck P. Kent/Animals Animals/Earth Scenes; b: © Doug Sokell/Visuals Unlimited

19 Population Growth Models Exponential Growth  Rate of population growth increases as the total number of females increases  Biotic potential is having full effect and birthrate is a maximum during exponential growth  Phases of an exponential growth curve During the lag phase, growth is small because the population is small. During the exponential growth phase, growth is accelerating.

Model for Exponential Growth 20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display GenerationPopulation Size Number of Females , , , , , a R = 2.4 exponential growth lag b. c. Generations Population (thousands) To calculate population size from year to year, use this formula: N t+1 = RN t N t = number of females already present R = net reproductive rate N t+1 = population size the following year

Population Growth Models Logistic growth  Occurs when limiting environmental factors oppose growth  Phases of a logistic growth curve During the lag phase, growth is slow because the population is small. During the exponential growth phase, growth is accelerating. During the deceleration phase, growth slows down. During the stable equilibrium phase, there is little if any growth. 21

Model for Logistic Growth a. b. c N t K lag deceleration  N  t Growth of Yeast Cells in Laboratory Culture Time (t ) (hours) Number of individuals (N) Number of individuals added per 2-hour period Number of Yeast Cells exponential growth stable equilibrium phase Time (hours) To calculate population growth as time passes, use this formula: N = population size N/t = change in population size r = rate of natural increase K = carrying capacity K – N = effect of carrying capacity on population growth = rN K K – N Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.