chapter 51

Copyright © 2005 Brooks/Cole — Thomson Learning

Biology, Seventh Edition Solomon • Berg • Martin

Chapter 51

Introduction to Ecology:Introduction to Ecology:

Population EcologyPopulation Ecology


Biology, Seventh Edition CHAPTER 51 Introduction to Ecology: Population Ecology

• Population density• Number of individuals of a species

per unit at a given time

• Population dispersion (spacing)• Clumped dispersion• Uniform dispersion• Random dispersion



Dispersion of individuals with a

population



Dispersion in a sand pine population in Florida



• Four factors that produce changes in population size• Natality• Mortality• Immigration• Emigration



• Intrinsic rate of increase (rmax)• Maximum rate at which species or

population can increase under ideal conditions

• Carrying capacity (K) is the largest population that can be maintained–Exponential population growth (J-shaped

curve)–Logistic population curve (S-shaped

curve)



Exponential population growth



Carrying capacity and logistic population growth



• Density-dependent factors• Regulate population growth by

affecting a large proportion of the population as population rises

• Examples include predation, disease, and competition



Density-dependent factors and negative feedback



• Density-independent factors• Limit population growth but are not

influenced by changes in population density

• Examples include hurricanes and blizzards



• Semelparous reproduction• Expend their energy in a single,

immense reproductive effort

• Iteroparous reproduction• Exhibit repeated reproductive

cycles throughout their lifetimes



Semelparity



• Species exhibiting an r strategy• Emphasizes a high growth rate• Organisms typically have small

body size, high reproductive rates, short life spans, and they inhabit variable environments



• Species exhibiting a K strategy• Maintains a population near the

carrying capacity of the environment

• Species often have large body size, low reproductive rates, long life spans, and they inhabit stable environments



• Survivorship curves• Type I

–Mortality is greatest in old age

• Type II–Mortality is spread evenly across all

ages

• Type III–Mortality is greatest among the young



Survivorship curves



Survivorshipcurve for a herring gull population



• Source habitats• Preferred habitats• Local reproductive success is

greater than local mortality• Local individuals disperse from

source habitats



• Sink habitats• Lower-quality habitats• Individuals may suffer death or

poor reproductive success



Source and sink populations in a hypothetical metapopulation



• Human population growth• World population reached 6.3

billion in 2003• Per capita growth rate has declined

from peak in 1965 of about 2% per year to 1.3%

• Scientists predict zero population growth by the end of the 21st century



Human population growth



• Population characteristics• Highly developed countries

–Low birth rate, low infant mortality, low fertility rate, long life expectancies, and high GNI PPP

• Developing countries–High birth rate, high infant mortality,

high fertility rate, short life expectancies, and low GNI PPP



Comparison of 2003 population data in developed and developing countries



Birth and death rates in Mexico, 1900–2000



• Age structure influences dynamics• Possible for country to have

replacement-level fertility and still experience population growth

• Young age structure causes a positive population growth momentum as large prereproductive age group matures



Age structure diagrams



• Developing countries tend to have people overpopulation that degrades the environment

• Developed countries have consumption overpopulation that degrades the environment

chapter 51

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