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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
Ecologists studying populations might study the factors that affect the growth and regulation of population size
  • Ecologists studying communities want to know how interactions such as predation and competition affect the organization of a community
demographics of populations
Demographics of Populations
  • 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
  • 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
  • Determining the density of natural populations
    • Is possible, but difficult to accomplish
  • In most cases
patterns of dispersion
Patterns of Dispersion
  • Environmental and social factors
    • Influence the spacing of individuals in a population
A clumped dispersion
    • Is one in which individuals aggregate in patches
A uniform dispersion
    • Is one in which individuals are evenly distributed
A random dispersion
    • Is one in which the position of each individual is independent of other individuals
population growth
Population Growth
  • 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
  • A cohort
  • Survivorship
    • The probability that newborn individuals of a cohort will survive to a particular age
    • Survivorship Curves
survivorship curves
Survivorship Curves
  • 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
The survivorship curve for Belding’s ground squirrels
    • Shows that the death rate is relatively constant
Type I curve 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 III 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
  • 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 exponential 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
  • If immigration and emigration are ignored



  • Zero population growth
  • The population growth equation can be expressed as



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
  • Exponential population growth
    • Is population increase under idealized conditions (unlimited resources)
  • Under these conditions



  • The equation of exponential population growth is
Exponential population growth
    • Results in a J-shaped curve
The J-shaped curve of exponential growth
    • Is characteristic of some populations that are rebounding
Environmental factors that restrict population growth are called population-limiting factors
  • Environmental factors limit the growth of populations, preventing exponential growth
  • Logistic growth model - idealized population growth that is slowed by limiting factors
The 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 (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
(K N)






  • The logistic growth equation
    • Includes K, the carrying capacity
the logistic model and real populations
The Logistic Model and Real Populations
  • The growth of laboratory populations of paramecia
    • Fits an S-shaped curve
Some populations overshoot K
    • Before settling down to a relatively stable density
The logistic model fits few real populations
    • But is useful for estimating possible growth
population dynamics
Population Dynamics
  • 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
  • In density-independent populations
  • In density-dependent populations
    • Birth rates fall and death rates rise with population density
density dependent factors
Density-dependent factors
  • 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
  • In crowded populations, increasing population density
    • Intensifies intraspecific competition for resources
  • 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
  • Individuals in a large population have a smaller share of the limited food supply
  • In many vertebrates and some invertebrates
    • Territoriality may limit density
Cheetahs are highly territorial
    • Using chemical communication to warn other cheetahs of their boundaries
Oceanic birds
    • Exhibit territoriality in nesting behavior
  • Population density can influence the health and survival of organisms
  • 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
  • The accumulation of toxic wastes
    • Can contribute to density-dependent regulation of population size
intrinsic factors
Intrinsic Factors
  • For some populations
Mutualism - two species acting in a mutually beneficial fashion may increase survival of both species involved
density independent factors
Density-independent factors
  • 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 regulated 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
  • 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-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 (r-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 (K-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
  • Human population growth has slowed after centuries of exponential increase
  • No population can grow indefinitely
the global human population
The Global Human Population
  • The human population
    • Increased relatively slowly until about 1650 and then began to grow exponentially
human population growth
Human Population Growth
  • 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
  • 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
  • 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
  • One important demographic factor in present and future growth trends
    • Divide populations into three age groups
      • Pre-Reproductive
      • Reproductive
      • Post-Reproductive
Age structure
    • Is commonly represented in pyramids
age distributions
Age Distributions
  • 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 diagrams
    • Can illuminate social conditions and help us plan for the future
environmental impact
Environmental Impact
  • Environmental impact of a population is measured in terms of:
    • Population size
    • Resource consumption per capita
Population growth is putting extreme pressure on each country’s social organization, the Earth’s resources, and the Biosphere
global carrying capacity
Global Carrying Capacity
  • Just how many humans can the biosphere support?
estimates of carrying capacity
Estimates of Carrying Capacity
  • The carrying capacity of Earth for humans is uncertain
u s population
  • 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/mi2
  • 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
  • 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