Ecological Succession

Natural Changes in Ecosystems

1. Natural selection - species change (adapt) to their environment

2. Adaptive radiation - new species arise.

3. Ecological succession – changes the types of organisms that live in an ecosystem.

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Ecological Succession

Two Types of Succession:

1. Primary Succession

2. Secondary Succession

Changes in the types and amount of species in an ecosystem over time.

Changes in biodiversity in an ecosystem over time.

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Primary Succession• Change in community composition on a site which previously

has had no living organisms.

• Very gradual, species introduced slowly.

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Example: Colonization following a large scale disturbance (volcanic eruption)

time

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Primary Succession

Example:

Glacial Retreat

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LichenLichens are an example of Mutualism• 2 organisms, both benefit• fungus and algae

•Lichens secrete (release) chemicals that break down rock.•This type of weathering (plus wind, rain and freezing) helps produce soil.

Pioneer species: organisms like lichen and plants that are the firstorganisms to survive and reproduce in an area.

Pioneer species: change environment by producing soil and providing food for other organisms.

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Pioneer Species

• First plants to colonize an area: mosses, lichens & herbs• Rapid colonizers• Rapid growth (opportunistic)• Relatively poor competitors in established environments• Due to symbiotic relationship (algae use photosynthesis),

they can survive in low nutrient environments.

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Climax communities = a mature community

Tropical rainforests, grasslands and deserts are all examples of climax communities.

Appear to be unchanged but this is a mistaken assumption.

HOW MIGHT CLIMAX COMMUNITIES CHANGE OVER TIME?

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Climax community??Climax community??

May take 100’s or 1000’s of years to reach this stageStage at which system has reached steady state

equilibrium

Most permanent of all the stages

Determined by climatic or soil factors unless humans interfere (e.g. poor soil quality, grazing, preventing forest fires, selective logging)

Difficult to identifyDifficult to identify

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Secondary Succession

Succession in an area that has been cleared or modified by a disturbance and already has a soil base in place

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An example of secondary succession

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Oldfield (farming) succession

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Changes During Succession

Graphs showing changes in biomass and species composition with succession.

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Other Ecological Pyramid Changes during Succession

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• Include events such as storms, fires, flooding, Tsunamis, droughts, overgrazing, and human activities

– They damage biological communities

– They remove organisms from communities

– They alter the availability of resources

How Natural Events Affect Ecosystems

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Succession due to Natural Events

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How Natural Events Affect Ecosystems

• Read p. 115 – 116

• List at least one affect of each of the following on an ecosystem

1. Flooding

2. Tsunamis

3. Drought

Mountain Pine Beetle

Insect Infestations

Insect Infestations

• Read the article on the mountain pine beetle and complete the attached assignment.

Insect Infestations

The mountain pine beetle is a small insect, less than acentimetre long, which lives most of its life under the barkof pine trees, including lodgepole, ponderosa and westernwhite pine. Normally these insects play an important role inthe life of a forest. They attack old or weakened trees,speeding the development of a younger forest. However,unusual hot, dry summers and mild winters in centralBritish Columbia during the last few years, along withforests filled with mature pine trees, have lead to anepidemic.To date, beetles have destroyed millions of lodge-pole pinein BC – the province’s most commercially harvested tree.

How Does the Beetle Damage the Pine Tree?

The mountain pine beetle is as small as a grain of rice, but in largenumbers it can take down the pine from the inside.It accomplishes thisby attacking the trees in large groups. A female beetle starts theprocess by licking trees until it finds a pine mature enough — at least80 years old. Once it has located the tree, the female begins boringthrough the bark, while at the same time secreting a pheromone thatattracts male beetles to the site. When the males join in the attack, theytoo release a pheromone to attract more females, who in turn attractmore males until a large enough population descends on the tree. Thetree, however, is far from helpless. In response, it secretes a highlytoxic resin similar to pitch to kill the beetles. Should the number ofbeetles attacking the tree be too few, the tree can usually withstand it.

But swarming isn't the only tactic the beetle has: a symbiotic relationship with ablue-stained fungus also gives it another advantage over the trees. The

beetlescarry spores of this fungus in compartments in their mouths, and as they tunneltheir way underneath the bark of the tree, they release these spores into thetree. As the fungus spreads through the tree, it stops the spread of the toxicresin and lets the beetles continue tunnelling.

The fungus and the beetles work their way through the tree, with the beetleslaying their eggs in hollows created underneath the bark. The larvae born fromthese eggs feed on the fungus as part of their development into adults and inthe process, carry away spores from the fungus inside their mouths. When thebeetles emerge from the now-dead tree in search of a new host, they'll bearmed with their symbiotic partner. "They are more of a complex than twoseparate organisms," said Allan Carroll, a research scientist with the CanadianForest Service. "The beetle needs the fungus to feed and to stop the resin andthe fungus couldn't get anywhere without the beetles."

An example of mutualism.

Why has the beetle spread?The spread of the beetle can be traced to two separate issues: forestmanagement and climate change. Forest management practices designed tolimit forest fires have inadvertently supplied the beetles with an overabundanceof mature pine to feast on. As part of an evolutionary tactic to spread at theexpense of other trees, pine cones don't release their seeds until heated by fire.When other trees begin crowding a pine stand, the dense forest becomes moresusceptible to forest fires. When fires do happen they clear out the old forestbut leave behind the released pinecone seeds, allowing a new stand of pinetree to grow where the old one existed, unimpeded by other trees. But forestmanagement practices geared towards preventing forest fires has allowed thetrees to mature beyond their expected age, making the forests older and thusmore desirable to the beetles. Carroll estimates that less than one per cent ofthe pine that would have historically burned from forest fires burns today. Whilethe abundance of food is behind the population explosion, a lack of cold wintersto wipe out the beetles and curb the infestations is also to blame. Pine beetlesdie when temperatures get below -30 C. Warming of the region brought on byclimate change has also helped the beetles survive in climates it wouldnormally find inhospitable, such as forests east of the Rockies like the PeaceRiver valley.