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36 Lecture Ppt

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  • 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 36 Population Ecology
  • 2. Ecology Studies Where and How Organisms Live in the Biosphere
  • 3. 36.1 Ecology is studied at various levels
    • Ecology - study of the interactions of organisms with other organisms and with the physical environment
      • ecological interactions are selection pressures that result in evolutionary change, which in turn affects ecological interactions
    • Ecology is wide-ranging
      • Habitat - the place where the organism lives
      • Population - all the organisms within an area belonging to the same species
      • Community - all populations interacting at a locale
      • Ecosystem - encompasses a community of populations as well as abiotic environment
      • Biosphere - encompasses the zones of the Earth’s land, water, and air where living organisms are found
  • 4. Figure 36.1 Ecological levels
  • 5. Populations Are Not Static— They Change Over Time
  • 6. 36.2 Density and distribution are aspects of population structure
    • Density
      • Once population size has been estimated, it is possible to calculate the population density , the number of individuals per unit area
    • Distribution
      • Population distribution - the pattern of dispersal of individuals across an area
      • Availability of resources can affect where populations of a species are found
        • Resources are nonliving (abiotic) and living (biotic) components of an environment that support living organisms
      • Limiting factors - environmental aspects that particularly determine where an organism lives
      • Three descriptions— clumped, random , and uniform —are used to characterize observed patterns of distribution
      • Range - portion of the globe where the species can be found
  • 7. Figure 36.2A Distribution patterns of the creosote bush
  • 8. Figure 36.2B Nesting colony of Cape gannets off the coast of New Zealand
  • 9. 36.3 The growth rate results in population size changes
    • A population’s annual growth rate is dependent upon
      • Number of individuals born each year
      • Number of individuals that die each year
      • Annual immigration and emigration
    • Biotic potential of a population is the highest possible growth rate and is achieved when resources are unlimited
      • Depends primarily on:
        • Usual number of offspring per reproduction
        • Chances of survival until age of reproduction
        • How often each individual reproduces
        • Age at which reproduction begins
  • 10. Figure 36.3 Biotic potential varies
  • 11. 36.4 Survivorship curves illustrate age-related changes
    • Cohort - term used to describe population members that are same age and have same chances of surviving
      • Survivorship - probability of cohort members surviving to particular ages
        • If we plot the number surviving at each age, a survivorship curve is produced
    • Three types of survivorship curves
      • Type I Survivorship: Large mammals
        • They survive well past the midpoint of the life span, and death does not come until near the end of the life span
      • Type II Survivorship: Hydras, songbirds, and small mammals
        • Survivorship decreases at a constant rate throughout the life span
      • Type III Survivorship: Many invertebrates and fishes
        • Most individuals will probably die very young
  • 12. Figure 36.4A A life table for Dall sheep
  • 13.
    • Figure 36.4B Three typical survivorship curves
  • 14. 36.5 Age structure diagrams divide a population into age groupings
    • From the perspective of population growth, a population contains three age groups
      • Prereproductive
        • When the prereproductive group is the largest of the groups, the birthrate is higher than the death rate, and a p yramid-shaped diagram is expected
        • Under such conditions, even if the growth for that year were matched by the deaths for that year, the population would continue to grow in the following years
      • Reproductive
        • As the size of the reproductive group equals the size of the prereproductive group, a bell-shaped diagram results
      • Postreproductive
        • If the birthrate falls below the death rate, the prereproductive group becomes smaller than the reproductive group
        • The age structure diagram is then urn-shaped , because the postreproductive group is the largest
  • 15. Figure 36.5 Age structure diagrams
  • 16. 36.6 Patterns of population growth can be described graphically
    • Particular pattern of a population’s growth is dependent on
      • Biotic potential of population along with other factors, such as age structure
      • Availability of resources as well as other environmental factors
    • Exponential Growth - likened to compound interest at the bank: The more your money increases, the more interest you will get
      • Lag phase - Growth is slow because the number of individuals in the population is small
      • Exponential growth phase - Growth is accelerating due to biotic potential
    • Logistic Growth - as resources decrease, population growth levels off
      • Lag phase - Growth is slow because the number of individuals in the population is small
      • Exponential growth phase - Growth is accelerating due to biotic potential
      • Deceleration phase - The rate of population growth slows because of increased competition among individuals for available resources
      • Stable equilibrium phase - Although fluctuations can occur, little if any growth takes place because births and deaths are about equal
    • Carrying capacity - total number of individuals the resources of the environment can support for an extended period of time
  • 17. Figure 36.6A Exponential growth
  • 18. Figure 36.6B Logistic growth
  • 19. Application of Population Growth
    • The model predicts that exponential growth will occur only when population size is much lower than the carrying capacity
      • Example: Humans are using a fish population as a continuous food source
        • It would be best to maintain that population size in the exponential phase of growth when biotic potential is having its full effect and the birthrate is the highest
        • If people overfish, the fish population will sink into the lag phase, and it may be years before exponential growth recurs
  • 20. Environmental Interactions Influence Population Size
  • 21. 36.7 Density-independent factors affect population size
    • Ecologists have long recognized that environmental interactions play an important role in population size
      • An abiotic factor is usually a density-independent factor
        • Percentage of individuals killed remains the same regardless of the population size
      • Example: A drought on the Galápagos Islands
        • Caused the population size of one of Darwin’s finches ( Geospiza fortis ) to decline from 1,400 to 200 individuals
        • Caused a reduction in availability of seeds this species ate
        • This is a reduction of 86% of the original population size
  • 22. Figure 36.7A  Percentage that die per density of population
  • 23. Figure 36.7B Density-independent effect of a flood
  • 24. Figure 36.7B Density-independent effect of a flood (Cont.)
  • 25. 36.8 Density-dependent factors affect large populations more
    • Biotic factors tend to be density-dependent factors because percentage of population affected does increase as density of population increases
      • Competition - when members of same species attempt to use needed resources (such as light, food, or space) that are in limited supply
        • Not all members of population can have access to the resource necessary for survival or reproduction
      • Predation - when one living organism, the predator, eats another, the prey
        • Effect of predation on a prey population generally increases as the population grows more dense, because prey are easier to find when hiding places are limited
  • 26. Figure 36.8A Density-dependent effects: competition
  • 27. Figure 36.8B Density-dependent effects: predation
  • 28. The Life History Pattern Can Predict Extinction
  • 29. 36.9 Life history patterns consider several population characteristics
    • Energy is limited and must be distributed between
      • Its life span (short versus long)
      • Reproduction events (few versus many)
      • Care of offspring (little versus much)
    • Opportunistic population - live in a fluctuating environment
      • Population stays small until conditions promote exponential growth
      • Members are small in size, mature early, have a short life span, and provide limited parental care for a great number of offspring
      • Density-independent effects dramatically affect population size, which is large enough to survive an event that threatens to annihilate it
    • Equilibrium populations - live in relatively stable and predictable environments
      • Logistic population growth, and remains close to carrying capacity
      • Some, allowing population size to remain fairly stable
      • Allocate energy to their growth and survival and that of their few offspring
      • They are fairly large, slow to mature, and have a relatively long life span
  • 30. Figure 36.9A Dandelions are an opportunistic species
  • 31. Figure 36.9B Mountain gorillas are an equilibrium species
  • 32. 36.10 Certain species are more apt to become extinct than others
    • Extinction is the total disappearance of a species or higher group
      • Three factors can help determine whether an equilibrium species is in danger of extinction
        • Size of geographic range
        • Degree of habitat tolerance
        • Size of local populations
    • Results of population studies can assist conservationists and others who are trying to preserve biodiversity
      • Metapopulations - local populations connected to one another by individuals moving between them
  • 33. Figure 36.10 Highlighted factors indicate vulnerability to extinction for an equilibrium species
  • 34. Human Populations Vary Between Overpopulation and Overconsumption
  • 35. 36.11 World population growth is exponential
    • World’s population has risen steadily to a present size of about 6.5 billion people
      • Potential for future population growth can be appreciated by considering the doubling time , the length of time it takes for the population size to double
        • Currently, the doubling time is about 53 years
    • More-Developed and Less-Developed Countries
      • More-developed countries (MDCs) - countries in North America, Europe, Japan, and Australia
        • Population growth is low, and the people enjoy a good standard of living
        • The MDCs doubled their populations between 1850 and 1950 due to a decline in the death rate, the development of modern medicine, and improved socioeconomic conditions
        • Sequence of events (i.e., decreased death rate followed by decreased birthrate) is termed a demographic transition
      • Less-developed countries (LDCs) - countries in Latin America, Africa, and Asia
        • Population is growing rapidly, and majority of people live in poverty
        • Because of past exponential growth, the population of the LDCs may explode from 7 billion today to 9 billion in 2050
  • 36. Figure 36.11 World population growth over time
  • 37. Figure 36.11 World population growth over time (Cont.)
  • 38. 36.12 Age distributions in MDCs and LDCs are different
    • Laypeople sometimes think that if each couple has two children, zero population growth (no increase in population size) will occur
      • If more women enter reproductive years than there are older women leaving them, replacement reproduction results in population growth
      • Many MDCs have a stable age structure, but most LDCs have a youthful profile—a large proportion of the population is younger than 15
    • Population Growth and Environmental Impact
      • Population growth is putting extreme pressure on each country’s social organization, the Earth’s resources, and the biosphere
      • MDCs consume a larger proportion of the Earth’s resources than LDCs
    • Two possible types of overpopulation
      • First is due to population growth - more obvious in LDCs
      • Second is due to increased resource consumption - more obvious in MDCs where per capita consumption is much higher
  • 39. Figure 36.12 Age structures in more-developed and less-developed countries
  • 40. Connecting the Concepts: Chapter 36
    • An early definition of ecology was “scientific natural history”
      • Modern ecology has now grown from a simple descriptive field to an experimental, predictive science
    • Much of the success in the development of ecology has come from studies of populations and the creation of models that examine how populations change over time
      • Simplest models are based on population growth when resources are unlimited
        • Results in exponential population growth, a type only rarely seen in nature
      • Because so few natural populations exhibit exponential growth, population ecologists realized they must incorporate resource limitation into their models
      • Simplest models to account for limited resources result in logistic growth
        • Populations that exhibit logistic growth cease growth when they reach the environmental carrying capacity
    • Many modern ecological studies are concerned with identifying the factors that limit population growth and set the environmental carrying capacity
      • A combination of careful descriptive studies, experiments done in nature, and sophisticated models has allowed ecologists to accurately predict which factors have the greatest influence on population growth

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