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2.6 Ecosystem Changes. Snowshoe Hare and Canada Lynx. Population Growth. Population: a group the same species that live in the same place at the same time Resources: food, water, shelter, space and mates In theory populations can grow to an infinite size, but they are limited by resources

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Population growth
Population Growth

  • Population: a group the same species that live in the same place at the same time

  • Resources: food, water, shelter, space and mates

  • In theory populations can grow to an infinite size, but they are limited by resources

  • This causes individuals to compete for resources (remember intraspecific and interspecific competition!).

Factors that control populations
Factors that Control Populations

  • There are 4 main factors controlling population sizes:

    • Natality- births increase the population

    • Mortality - deaths decrease the population

    • Immigration - movement of individuals into an area increases the population

    • Emigration - movement of individuals out of an area decreases the population

Carrying capacity
Carrying Capacity

  • Carrying capacity: maximum number of individuals of a species that can be sustained indefinitely in a given space

  • No population can grow indefinitely! Resources = Limited!!

Limiting factors of populations
Limiting Factors of Populations

  • Factors (biotic or abiotic) which prevent population numbers from growing too large and overrunning an ecosystem.

  • Example:

    • Disease/ parasites

    • disasters

    • hunting & predation

    • competition for resources

    • (food, oxygen, nutrients)

Patterns of population growth
Patterns of Population Growth

  • “J” population growth curve

  • Exponential growth = starts out slow and then proceeds faster and faster

  • Occurs when a population has few resource limitations

  • Sudden collapse


Patterns of population growth1
Patterns of Population Growth

  • “S” growth curve

    (S for sigmoid)

  • Initially shows exponential growth then levels off at the carrying capacity.

  • Occurs when a population has limited resources.

  • Results in stable population

Population dynamics
Population Dynamics

  • A look at the factors that tend to increase or decrease the size of a population

  • The population size is determined by the interplay of biotic potential and environmental resistance.

  • Biotic potential- growth rate with unlimited resources

  • Environmental resistance - all the factors acting jointly to limit population growth

Biotic potential vs environmental resistance
Biotic Potential vs. Environmental Resistance

Biotic potential

(Growth Factors)

Environmental resistance

(Decrease Factors)

  • Favorable light, temperature

  • High reproductive rate

  • Adequate food supply

  • Ability to migrate habitats

  • Ability to adapt to environmental change

  • Too much or too little light and temperature

  • Low reproductive rate

  • Inadequate food supply

  • Inability to migrate habitats

  • Inability to adapt to environmental change

Density dependent factors
Density Dependent Factors

  • Density dependent factors

  • Depend on the size of the population

  • Effects of the factors increase as the population grows

  • Act as negative feedback

  • Tend to be biotic

  • Two categories:

    • Internal factors = Within a single species

      • limited resources

      • reduced fertility rates

    • External factors = between species

      • populations of predators or prey

      • diseases spread more easily in densely-populated areas

Density independent factors
Density Independent Factors

  • Do NOT depend on the size of the population

  • Tend to be abiotic

  • Effect the population regardless of its size

  • Examples:

    • 1. Weather

    • 2. Earthquakes

    • 3. Floods

    • 4. Fires

    • R-strategists are most

      affected by these factors

Reproductive strategies
Reproductive Strategies


Unstable environment


Stable environment

  • Small size

  • Many offspring are produced

  • Early maturity

  • Short life span

  • Each individual reproduces once

  • Type III survivorship curve

  • Affected by density Independent

  • Large size

  • Few offspring produced

  • Late maturity (long parental care)

  • Long life span

  • Individuals reproduce more than once

  • Mostly type I survivorship curve

  • Affected by density dependent

Survivorship curves
Survivorship Curves

  • Type I - high survival rate of the young, live most of their expected life span and die in old age. (ex. Humans)

  • Type II - relatively constant death rate, could be due to hunting or diseases. (ex. coral, squirrels, honey bees and many reptiles)

  • Type III - have many young, most of which die very early in their life. (ex. plants, oysters and sea urchins).

Pop quiz
Pop Quiz

  • What does parental care have to do with the shape of these curves?

  • What density dependent factor will always affect the population of white tailed deer in Wisconsin? (Only at certain times in the year)

  • What do you think the survivorship curve would be for a white-tailed deer population?

How has this ecosystem changed ecosystem 1
How has this ecosystem changed?Ecosystem #1



2 6 ecosystem changes

How has this ecosystem changed?Ecosystem #2



2 6 ecosystem changes





Ecological succession change over time
Ecological Succession: Change over Time

  • Two Types of Succession

    • Primary succession - An ecosystem starts from bare rock

    • Secondary succession – Ecosystem is built from a previous ecosystem

      • Starts with soil

Important terms
Important Terms

  • Sere: A set of stages of changes in an ecosystem.

    • A snapshot of ecosystem

  • Pioneer organisms: First species that begin to populate a sere, typically r-strategists.

    • Ex. Weeds, lichens

  • Climax community: Populations of organisms living together in a sere where all species are in balance.

    • Ex. A mature forest, many K-strategists

Primary succession
Primary Succession

  • No soil in a terrestrial system

  • No bottom sediment in an aquatic system

  • Takes hundreds to thousands of years

  • Need to build up soils/sediments to provide necessary nutrients

Primary succession occurs after a glacier retreats
Primary succession occurs after a glacier retreats

Image source: http://www.callipygia600.com/

2 6 ecosystem changes

Primary Ecological Succession

Lichens and




Balsam fir,

paper birch, and white spruce forest community

Jack pine,

black spruce,

and aspen

Heath mat

Small herbs

and shrubs


Secondary succession
Secondary Succession

  • Begins with soil from previous ecosystem

  • Ecosystem has been

    • Disturbed, Removed, or Destroyed

    • Abandoned farms

    • Burned forests

    • Deforestation

    • A huge storm

2 6 ecosystem changes

Secondary Succession

Mature oak and hickory forest

Young pine forest

with developing

understory of oak

and hickory trees

Shrubs and

small pine



weeds and





Conditions during succession
Conditions during succession

  • Early Stages (Pioneer Communities)

    • Gross Productivity = Low

      • Few producers

    • Net productivity = High

    • No consumers doing respiration

      • No taxes to take away!!

    • Nutrients in soil

  • Later Stages (Climax Community )

    • Nutrients in soil decrease

    • Gross Productivity is High

      • Many producers

    • Net productivity = low

      • Many consumers all doing respiration = a very large amount of taxes