how changes occur naturally in ecosystems
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How Changes Occur Naturally in Ecosystems. The Stickleback: Adapt or Die. Occupied oceans of the northern hemisphere Trapped in lakes as the glaciers retreated Adapted to freshwater environment, forming a new species of sticklebacks In BC pairs of sticklebacks developed

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the stickleback adapt or die
The Stickleback: Adapt or Die
  • Occupied oceans of the northern hemisphere
  • Trapped in lakes as the glaciers retreated
  • Adapted to freshwater environment, forming a new species of sticklebacks
  • In BC pairs of sticklebacks developed
    • Lake bottom: feed on snails and clams – chunky bodies with wide mouths – little armour and fewer spines than ancestors
    • Open water: slender bodies

and narrow mouths – retained

more spines and armoured

side plates – lighter in colour

how organisms adapt to change
How Organisms Adapt to Change
  • Living organisms changes as the abiotic and biotic elements of an ecosystem change
  • Natural Selection: members of a species having certain characteristics that give them an advantage will be in better condition to mate
    • Will pass on favourable characteristics to offspring

Example: the Galapagos finches

  • Scientists believe that 13 species developed from a single species from South America

Adaptive Radiation: the change from a common ancestor into a number of different species that “radiate out” to inhabit different niches

    • Examples: Sticklebacks and Cichlid (more than 300 species from a single ancestor)
  • Galapagos finches: each species adapted to the ground or in trees; each gathers and eat different food; evolved different size beaks and shapes depending on food source
how ecosystems change over time
How Ecosystems Change Over Time

Ecological Succession: changes that take place over time in the types of organisms that live in an area

There are 2 types of ecological succession:

Primary Succession

Secondary Succession

1 primary succession
1. Primary Succession
  • Occurs in an area where no soil exists (bare rock)
  • Natural events (ex. retreating glaciers) can scrape rock bare, or new rock could form after a volcanic eruption
  • Wind and rain carry spores of organisms, like lichens, to these areas
  • Lichens...
    • An organism consisting of a fungus and an alga
    • Obtain nutrients from rocks by secreting chemicals that break down the rock

Weathering by lichens, wind, rain, and freezing begin soil formation

Dead lichens provide additional organic matter to developing soil

RESULT: Soil accumulates (even though it could take hundreds of years


Spores from plants, like mosses, will be deposited by the wind and start to grow

    • Most have adapted to grow in harsh/nutrient poor conditions
  • Pioneer Species: lichens and plants that are the 1st organisms to survive and reproduce in an area
  • Pioneer species change the biotic and abiotic environment in many ways...
    • Decay and create more soil
    • Make soil more fertile and increase ability to hold moisture
    • Provide food for insects and other organisms, introducing animals to the community

Each stage of primary succession is gradual and introduces different populations of micro-organisms, plants and animals that will compete for nutrient, moisture, and sunlight

As these organisms

decompose, they contribute

more organic matter to the

soil layer

Eventually, seeds of trees

will germinate


1st trees usually requires lots of light (ex. deciduous trees of boreal forests)

  • The shade will change abiotic conditions as soil becomes cooler and more moist
    • Only shade tolerant plants will grow
  • As more niches are created, there is be greater diversity in organisms  creating more complex food webs

Primary succession occurs in the same way globally

    • Coniferous forests in northern latitudes
    • Deciduous forests in temperate zones
    • Tropical forests in tropical zones

See Figure 3.8 on page 112-113 for a detailed breakdown!

2 mature communities
2. Mature Communities
  • Climax Community: a mature community that is the result of primary succession
    • Includes boreal forests, tropical rainforests, grasslands, and deserts
  • Even though a climax community may appear unchanged, there was always changes occurring because of small disturbances
    • Alder may grow because a tree has fallen, allowing more sunlight through
  • Scientists now prefer “mature community”, reflecting the idea that it is always changing
3 secondary succession
3. Secondary Succession
  • Occurs as a result of a disturbance to an area that already has soil and was once the home of living organisms
  • Occurs much faster than primary succession because soil and nutrients already exist
    • Primary might takes 100’s of years, secondary could only take decades
  • Often depends on the recovery of existing plants, such as trees, and on species that can rapidly reproduce in new conditions of increased sunlight and open areas
how natural events affect ecosystems
How Natural Events Affect Ecosystems


Occurs in coastal areas, rivers, and lakes when the volume of water exceeds the ability of the water body to contain it

Can be part of a normal cycle or caused by heavy rainfall, increased run-off, melting snow, or an extreme natural event (tsunami)

Can result in soil erosion and soil pollution (if chemicals are present)


Can cause widespread disease

if untreated sewage enters

drinking water supplies

Climate change could cause

an increase in flooding due to

heavier rains



A huge, rapidly moving ocean wave

Usually caused by large earthquakes or underwater volcano eruptions

On land, the wave carries away or destroys plants and animals (affecting food webs)

Salt water changes composition of soil  plants that can’t survive salty environment won’t grow



  • Usually occurs when there is a below-average amount of precipitation over a period of many months or years
  • Ecosystems usually recover when regular precipitation pattern re-establish
  • destroys habitats when water is scarce and animals die
    • Can result in crop failure and livestock deaths
  • Made worse by climate change
  • Experienced by Australia, western Europe, and Africa


  • Have an important role in natural succession of forests
    • Mountain pine beetle destroys older trees  nutrients get recycled
    • Younger trees usually able to resist by producing resin
  • If many insects attack or if tree is stressed (overcrowding, drought, grazing) it won’t produce as much resin
    • Beetle carries a fungus which than destroys plant tissues and prevent resin production

Cold winters, which kill beetle larvae, are affected by global warming

Suppression of forest fires has resulted in a large number of host trees

Because beetle

population isn’t in

check, other species are

losing their homes