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Ecology of Populations. Essential knowledge 2.D.1:. All biological systems from cells and organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy.

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Essential knowledge 2 d 1
Essential knowledge 2.D.1:

  • All biological systems from cells and organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy.

    • a. Cell activities are affected by interactions with biotic and abiotic factors. (Temperature, Water availability, Sunlight)

    • b. Organism activities are affected by interactions with biotic and abiotic factors. {Symbiosis (mutualism, commensalism, parasitism),Predator–prey relationships, Water and nutrient availability, temperature, salinity, pH}

Essential knowledge 2 d 11
Essential knowledge 2.D.1:

  • c. The stability of populations, communities and ecosystems is affected by interactions with biotic and abiotic factors. (Water and nutrient availability, Availability of nesting materials and sites, Food chains and food webs, Species diversity, Population density, Algal blooms)

Essential knowledge 2 d 3
Essential knowledge 2.D.3:

  • Biological systems are affected by disruptions to their dynamic homeostasis.

    • a. Disruptions at the molecular and cellular levels affect the health of the organism. (Physiological responses to toxic substances,Dehydration)

    • b. Disruptions to ecosystems impact the dynamic homeostasis or balance of the ecosystem. (Invasive and/or eruptive species, Human impact, Hurricanes, floods, earthquakes, volcanoes, fires, Water limitation, Salination)

Essential knowledge 4 a 5
Essential knowledge 4.A.5:

  • Communities are composed of populations of organisms that interact in complex ways.

    • a. The structure of a community is measured and described in terms of species composition and species diversity.

    • b. Mathematical or computer models are used to illustrate and investigate population interactions within and environmental impacts on a community. (Predator/prey relationships spreadsheet model, Symbiotic relationship, Graphical representation of field data, Introduction of species, Global climate change models)

Essential knowledge 4 a 51
Essential knowledge 4.A.5:

  • c. Mathematical models and graphical representations are used to illustrate population growth patterns and interactions.

    • 1. Reproduction without constraints results in the exponential growth of a population.

    • 2. A population can produce a density of individuals that exceeds the system’s resource availability.

    • 3. As limits to growth due to density-dependent and density independent factors are imposed, a logistic growth model generally ensues.

    • 4. Demographics data with respect to age distributions and fecundity can be used to study human populations.

Essential knowledge 4 b 3
Essential knowledge 4.B.3:

  • Interactions between and within populations influence patterns of species distribution and abundance.

    • a. Interactions between populations affect the distributions and abundance of populations.

      • 1. Competition, parasitism, predation, mutualism and commensalism can affect population dynamics.

      • 2. Relationships among interacting populations can be characterized by positive and negative effects, and can be modeled mathematically (predator/prey, epidemiological models, invasive species).

      • 3. Many complex symbiotic relationships exist in an ecosystem, and feedback control systems play a role in the functioning of these ecosystems.

Essential knowledge 4 b 31
Essential knowledge 4.B.3:

  • b. A population of organisms has properties that are different from those of the individuals that make up the population. The cooperation and competition between individuals contributes to these different properties.

  • c. Species-specific and environmental catastrophes, geological events, the sudden influx/depletion of abiotic resources or increased human activities affect species distribution and abundance. (Loss of keystone species, Kudzu,Dutch elm disease)

Scope of ecology
Scope of Ecology

  • Ecology

    • The study of the interactions of organisms with

      • other organisms, and

      • The physical environment

    • Population - All the individuals of a species within a particular space

    • Community – Specified populations interacting with each other

    • Ecosystem - Community interacting with environment

Demographics of populations
Demographics of Populations dispersion, and demography

  • Demography is the statistical study of a population, which includes its density, distribution, rate of growth

Density and distribution of populations
Density and Distribution of Populations dispersion, and demography

  • Population Density - Number of individuals per unit area or volume

  • Population Distribution - Pattern of dispersal of individuals within a space of interest

    • Ecologists analyze what causes the spatial and temporal “patchiness” of organisms

    • Affected by the availability of resources

Density a dynamic perspective
Density: A Dynamic Perspective dispersion, and demography

  • Determining the density of natural populations

    • Is possible, but difficult to accomplish

  • In most cases

  • Density dispersion, and demography is the result of a dynamic interplay

Patterns of dispersion
Patterns of Dispersion dispersion, and demography

  • Environmental and social factors

    • Influence the spacing of individuals in a population

  • A dispersion, and demographyclumped dispersion

    • Is one in which individuals aggregate in patches

  • A dispersion, and demographyuniform dispersion

    • Is one in which individuals are evenly distributed

  • A dispersion, and demographyrandom dispersion

    • Is one in which the position of each individual is independent of other individuals

Population growth
Population Growth dispersion, and demography

  • Exponential Growth

    • Rate of increase increases as the total number of females increases

  • Biotic Potential

    • Maximum population growth that can possibly occur under ideal circumstances

  • Environmental Resistance

    • All environmental conditions that prevent populations from achieving biotic potential

Mortality patterns
Mortality Patterns dispersion, and demography

  • A cohort

  • Survivorship

    • The probability that newborn individuals of a cohort will survive to a particular age

    • Survivorship Curves

Survivorship curves
Survivorship Curves dispersion, and demography

  • A survivorship curve is a graphic way of representing the data in a life table that shows the differential mortality rates in relation to age

  • Type I curve types shows low infant mortality

    • These species produce few offspring but provide them with a high degree of parental care. This increases the likelihood that they will survive to maturity

    • Show a low rmax

  • Type II types curve mortality is more constant over the life span

  • Type III types curve have high death rates for very young. Death rates drop as individuals survive to increased ages

  • Species produce very large numbers of offspring but provide little or no care for them

  • Have a high rmax

Population growth models
Population Growth Models population

  • Discrete breeding - members of population have only one single reproductive event in their lifetime

    • Many insects, annual plants

  • Continuous breeding - members of population experience many reproductive events throughout their lifetime

  • The populationexponential model describes population growth in an idealized, unlimited environment

  • It is useful to study population growth in an idealized situation

Per capita rate of increase
Per Capita Rate of Increase population

  • If immigration and emigration are ignored

dN population



  • Zero population growth

  • The population growth equation can be expressed as

dN population



G = rN

G =

N = population size

r = intrinsic rate of increase

If r is constant, then the rate at which population grows depends on the number of individuals already in the population (N), value of r depends on the kind of organism

G = dN/dt (∆N/∆t) = change in # of individuals over a given time

r = (b-d) = birth rate - death rate

G = rN or ∆N/∆t = (b-d)N

Exponential growth
Exponential Growth population

  • Exponential population growth

    • Is population increase under idealized conditions (unlimited resources)

  • Under these conditions

dN population



  • The equation of exponential population growth is

  • Exponential population population growth

    • Results in a J-shaped curve

  • The called logistic growth model includes the concept of carrying capacity

  • Exponential growth

    • Cannot be sustained for long in any population

  • A more realistic population model

  • Carrying capacity ( called K)

    • Is the maximum population size the environment can support with no net increase or decrease

    • The value of K varies, depending on species and habitat

( called K N)






  • The logistic growth equation

    • Includes K, the carrying capacity

  • The called logistic model of population growth

The logistic model and real populations
The Logistic Model and Real Populations called

  • The growth of laboratory populations of paramecia

    • Fits an S-shaped curve

Population dynamics
Population Dynamics called

  • The study of population dynamics

    • Focuses on the complex interactions between biotic and abiotic factors that cause variation in population size

Population change and population density
Population Change and Population Density called

  • In density-independent populations

  • In density-dependent populations

    • Birth rates fall and death rates rise with population density

Density dependent factors
Density-dependent factors called

  • Population limiting factors whose effects depend on population density

  • As the number of individuals increases, so does the percentage of individuals affected

Competition for resources
Competition for Resources called

  • In crowded populations, increasing population density

    • Intensifies intraspecific competition for resources

Competition called

  • Intraspecific competition is competition between members of the same species for resources that are limited supply (food, shelter, mates)

  • Populations usually compete for resources unless population is heldbelow carrying capacity by other factors

Food supply
Food supply called

  • Individuals in a large population have a smaller share of the limited food supply

Territoriality called

  • In many vertebrates and some invertebrates

    • Territoriality may limit density

Health called

  • Population density can influence the health and survival of organisms

Predation called

  • As a prey population builds up predators may feed preferentially on that species

  • The major limiting factor for predator populations is the availability of its prey

Toxic wastes
Toxic Wastes called

  • The accumulation of toxic wastes

    • Can contribute to density-dependent regulation of population size

Intrinsic factors
Intrinsic Factors called

  • For some populations

Density independent factors
Density-independent factors fashion may increase survival of both species involved

  • Population limiting factors whose occurrence is not affected by population density

  • Abiotic factors such as climate and weather, fire, physical disruption of habitat

  • Limit population size well before resources or other density-dependent factors become important

  • Most populations are probably fashion may increase survival of both species involvedregulated by a mixture of density-independent and density dependent factors

  • Many populations are fairly stable and near carrying capacity that is regulated by density-dependent factors

The logistic model and life histories
The Logistic Model and Life Histories fashion may increase survival of both species involved

  • Life history traits favored by natural selection

    • May vary with population density and environmental conditions

  • Populations vary on factors such as number of births per reproduction, age of reproduction, life span of individuals, probability of living entire life spans (survivorship curves)

  • Natural selection shapes the life histories of species

  • K fashion may increase survival of both species involved-selection, or density-dependent selection

    • Selects for life history traits that aresensitive to population density

  • r-selection, or density-independent selection

Opportunistic life history r strategists
Opportunistic life history ( fashion may increase survival of both species involvedr-strategists)

  • Small bodied species, reproduce when young, produce many offspring, populations tend to grow exponentially when conditions are favorable

  • Such populations typically live in unpredictable environments and are controlled by density-independent factors

  • Emphasis on quantity of reproduction rather than on individual survivorship or quality

  • Exhibit type III survivorship curves

Equilibrial life history k strategists
Equilibrial life history ( fashion may increase survival of both species involvedK-strategists)

  • Larger bodied species, produce few slowly maturing offspring but provide care for their young

  • Population size stable, near carrying capacity, held there by density-dependent factors

  • Natural selection resulted in production of better-adapted offspring

  • Exhibit type I survivorship curve

Human population
Human Population fashion may increase survival of both species involved

  • Human population growth has slowed after centuries of exponential increase

  • No population can grow indefinitely

The global human population
The Global Human Population fashion may increase survival of both species involved

  • The human population

    • Increased relatively slowly until about 1650 and then began to grow exponentially

Human population growth
Human Population Growth fashion may increase survival of both species involved

  • Human population has an exponential growth pattern

  • Doubling time currently estimated at 53 years

  • Population Size

    • 1800 1 Billion

    • 1930 2 Billion

    • 1960 3 Billion

    • 2000 6 Billion

Country development
Country Development fashion may increase survival of both species involved

  • More-Developed Countries (MDCs)

    • Slow population growth

    • High standard of living

    • Completed Demographic Transition (decreased deathrate followed by decreased birthrate)

      • North America and Europe

  • Less-Developed Countries (LDCs)

    • Low standard of living

      • Latin America

      • Africa and Asia

Infant mortality and life expectancy
Infant Mortality and Life Expectancy fashion may increase survival of both species involved

  • Infant mortality and life expectancy at birth

    • Vary widely among developed and developing countries but do not capture the wide range of the human condition

Age structure
Age Structure fashion may increase survival of both species involved

  • One important demographic factor in present and future growth trends

    • Divide populations into three age groups

      • Pre-Reproductive

      • Reproductive

      • Post-Reproductive

  • Age structure fashion may increase survival of both species involved

    • Is commonly represented in pyramids

Age distributions
Age Distributions fashion may increase survival of both species involved

  • At least three structures possible

    • Increasing (pyramid-shaped) - prereproductive group is largest of three groups

    • Stable (bell-shaped) - reproductive group equals size of prereproductive group

    • Decreasing (urn-shaped) - prereproductive group becomes smaller than reproductive group, postreproductive group is the largest

  • Age structure fashion may increase survival of both species involved diagrams

    • Can illuminate social conditions and help us plan for the future

Environmental impact
Environmental Impact fashion may increase survival of both species involved

  • Environmental impact of a population is measured in terms of:

    • Population size

    • Resource consumption per capita

Global carrying capacity
Global Carrying Capacity country’s social organization, the Earth’s resources, and the Biosphere

  • Just how many humans can the biosphere support?

Estimates of carrying capacity
Estimates of Carrying Capacity country’s social organization, the Earth’s resources, and the Biosphere

  • The carrying capacity of Earth for humans is uncertain

U s population
U.S.Population country’s social organization, the Earth’s resources, and the Biosphere

  • 281.4 M (4/00)

    • Most people are Caucasian (69.1%)

    • Hispanic (12.5%) - 60% from Mexico

    • Asian (3.7%) - ~36% live in California

    • Black (12.1%)

  • 40% of population under 18 belong to minority group - minorities increasing

  • U.S. – 73 people/mi country’s social organization, the Earth’s resources, and the Biosphere2

  • Diamond Bar – 14.9 mi2 / 38.8 km2

  • Population – 58, 763

  • Density – 1,515 people/km2 or

    3,944 people/mi2

Mumbai india world s most densely populated city
Mumbai, India - World’s Most Densely Populated City country’s social organization, the Earth’s resources, and the Biosphere

  • 14.35 million people/484 km2

  • Density = 29,650 people/km2(DB-1,515/km2)

    • 75,925 people/mi2 (DB-3,944/km2)

  • 29,650 people/km2 (density-Mumbai) X 38.8 km2 (D.B.) = 1,150,420 people (DB-58,763)

  • Others:

    • Shenzhen, China (5th) - 466 km2 / 8 million people (17,150 people/km2)

    • Seoul, South Korea - 16,700 people/km2

    • Taipei, Taiwan - 15,200 people/km2

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