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Population Dynamics. Evolution, Natural Selection, and Human Impacts for Introduction to Environmental Science. Population Levels. Population Density – is the number of individuals of a population at a given time.

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Population dynamics

Population Dynamics

Evolution, Natural Selection, and Human Impacts for Introduction to Environmental Science

Population levels
Population Levels

  • Population Density – is the number of individuals of a population at a given time.

  • Ecological Population Density – the number of individuals (n) per unit of habitat area

  • Population dispersion – spatial values of population including clumping, uniform, and random (see figure in text)

Age structure
Age Structure

  • This is a breakdown of the major contributors to populations in ecosystems

    • Prereproductive

    • Reproductive

    • Postreproductive

      The population growth rate swings based upon biotic and abiotic factors leading to growth or decline

Response to stress
Response to stress

  • Populations change = (births + immigration) –

  • (deaths + emigration)

    A balance is considered Zero Population Growth (ZPG)

    What are the implications of ZPG?

Population stresses
Population Stresses

  • Carrying capacity (K) is defined as the number of individuals of a given species that can be sustained indefinitely – spatially.

  • Population could grow exponentially with unlimited resources considered its maximum rate ( r) with unlimited biotic or reproductive potential

This shows the growth of Japan and approach to meeting its carrying capacity.

*Carrying Capacity:A Model with Logistically Varying Limits by

PERRIN S. MEYER1 and JESSE H. AUSUBEL2 in Technological Forecasting and Social Change 61(3):209-214, 1999.

Population stresses1
Population Stresses carrying capacity

  • Any population growing exponentially goes through a “J” shaped growth, but most of the time environmental influences create an “S” shaped pattern in growth

Curve demonstrating the population of rabbits carrying capacity

*MIT System Dynamics in Education Project Under the Supervision of Dr. Jay W. Forrester by Leslie A. Martin

This shows exponential growth leading to overshoot and carrying capacity

Population dieback of species like the reindeer in Alaska

Population density
Population Density carrying capacity

  • Density – Dependent population controls include competition for resources including predation, parasitism, and disease. Some more drastic controls include diseases like the Bubonic Plague in Europe in fourteenth century.

Density-Independent carrying capacity factors affect populations regardless of the size like natural disasters and use of chemicals (like pesticides causing cancers, etc…)

Population curves
Population Curves carrying capacity

  • Populations could be stable, cyclic or irruptive due to various factors

    • Predation, like the classic Lynx and Snowshoe Hare demonstrate a classic predator-prey population curve in nature.

Reproductive strategies
Reproductive Strategies carrying capacity

  • “r” strategists (Type III)- numerous offspring with a low survival rate to adulthood

    - include many invertebrates and other animals that produce enough offspring to preserve their genetic variability

Reproductive strategies1
Reproductive Strategies carrying capacity

  • “K” strategists (Type I)

    - few offspring with high survivorship includes a high degree of parental investment to insure offspring success

    - examples include many mammals (i.e., humans, marine mammals, river otter, etc…)

r- and K- selected Organisms carrying capacity

Courtesy of www.bio.indiana.edu

Survivorship curves
Survivorship Curves carrying capacity

  • These curves demonstrate

    • Late Loss Populations (K – strategists)

    • Constant Loss Populations (K – strategists)

    • Early Loss Populations (usually r-strategists)

      These could be done regionally for human age population studies

Classic survivorship where I is a curve representing a carrying capacity

Late loss population; II is a Constant loss like songbirds; and

III is an Early loss curve like those that are r-strategists

posted by carrying capacityBruce W. Grant, Department of Biology,

Widener University, Chester, PA  19013

The emergence of life
The Emergence of Life carrying capacity

  • Taxonomically, species have been identified and the process by which they have adapted (changes over a long period of time) are due to genetic variations and Natural Selection. Charles Darwin observed many ecological similarities and differences verses geographical location, which led to the Natural Selection theory. Selection is a process, complex system of stresses, that lead to adaptations.

Evolution, Adaptation, and Natural Selection carrying capacityhttp://www.mhhe.com/biosci/genbio/virtual_labs/BL_12/BL_12.html

  • Heritable Changes in population’s genetic makeup through successive generations is Evolution

  • The sum all genes in a population is called the gene pool

  • A gene with two or more molecular forms is called an Allele

  • New alleles are referred to as mutations

  • A genetic trait that is that leads to survival in environmental conditions is called an Adaptation


Natural selection
Natural Selection carrying capacity

  • This is a process in which a population has

    • Variation among individuals in some attribute or trait

    • Fitness differences a consistent relationship between that trait and some measure of reproductive success

    • Inheritance (consistent relationship) for that trait between parents and their offspring (at least partially independent of the environment)

    • http://www.pbs.org/wgbh/evolution/library/11/2/quicktime/e_s_4.html

Three types of selection
Three Types of Selection carrying capacity

  • Stabilizing tends to eliminate individuals on the ends of a population without shifting the mean population

  • Directional tends to shift allele frequency so that the mean genetic outcome changes

  • Disruptive (Diversifying) favors individuals at the extremes and reduces the norm, but does not shift the mean genetic outcome

Coevolution carrying capacity

  • If two different species interact over a long period of time, changes in the gene pool of one species will lead to changes in the gene pool of the second species.

Evolution carrying capacity

  • Microevolution – works on a species levels with changes over time

  • Macroevolution goes beyond the species level and longer geological time periods.

  • There are misconceptions about this theory… Fitness versus Fittest

Species carrying capacity

  • Geologically speaking the start of the Cenozoic Era (65 million years), started with 99% of all species on earth being extinct!

    • Large scale continental movement

    • Gradual climate caused by shifting continents

    • Rapid climate change caused by catastrophic events (5 great ones)

    • Major extinctions: 65, 180, 250, 345 and 500 million years ago

Human impacts
Human Impacts carrying capacity

  • Simplifying ecosystems

  • Altering species control

  • Eliminating predators

  • Introducing new species

  • Overharvesting resources

  • Interfering with geochemical cycles

  • Gentically modifying organisms, thus affecting Selection pressures

Bobbi low
Bobbi Low carrying capacity

  • “We haven’t evolved to be environmental altruists – but we can solve environmental problems”

    We must work with, rather than against, our evolved tendencies.

    Eliminate selfish genes

Species interactions
Species Interactions carrying capacity

  • Symbiotic Relationships

    • Mutualism

    • Commensalism

    • Parasitism

SEM of lichen: the linear fungal hyphae and the roundball-like algal groupings.

Island biogeography
Island Biogeography roundball-like algal groupings.

  • MacArthur and Wilson’s theory

    • Larger Islands support more biodiversity

    • Islands closer to the mainland also support more biodiversity

    • Islands farther from the mainland support less biodiversity and sometimes smaller-sized species

Island biogeography1
Island Biogeography roundball-like algal groupings.

Island biogeography2
Island Biogeography roundball-like algal groupings.


Island biogeography3
Island Biogeography roundball-like algal groupings.