ECOSYSTEMS AND COMMUNITIES

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ECOSYSTEMS AND COMMUNITIES
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OUTLINE

• Succession
• Primary, Secondary
• Terrestrial, Aquatic
• Climax Communities - Biomes
• Deserts,Grasslands, Tropical Rainforests
• Aquatic Ecosystems

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SUCCESSION

• Ecosystems are dynamic.
• Succession A series of regular, predictable
  changes in the structure of a community over
  time.
• Occurs because perturbations to an area often
  make the environment less suitable for current
  organisms and more suitable for others.

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• Primary Succession - Begins with bare mineral
  surfaces or water.
• Secondary Succession - Begins with disturbance of
  an existing ecosystem.

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Terrestrial Primary Succession

• Pioneer Community Collection of organisms able
  to colonize bare rock (ie lichens).
• Lichens help break down rock and accumulate
  debris, helping to form a thin soil layer.
• Soil layer begins to support small life forms.

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• Life forms replace lichen community.
• New community replaced by perennial plant
  community.
• Perennial plant community replaced by shrubs.
• Shrubs replaced by shade intolerant trees.
• Shade intolerant trees replaced by shade tolerant
  trees.
• Eventually a climax community is reached -
  Stable, long-lasting.

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• In general, climax communities are more stable
  and have larger, more diverse populations of
  species than earlier stages of succession.
• Successional (seral) stage - each step in the
  process.

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Aquatic Primary Succession

• Except for oceans, most aquatic systems are
  considered temporary.
• All aquatic systems receive inputs of soil
  particles and organic matter from land. - results
  in gradual filling of shallow bodies of water.
• Plants can begin to take root.

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Secondary Succession

• Occurs when an existing community is disturbed or
  destroyed.
• With most disturbances, most of the soil remains,
  and many nutrients necessary for plant growth may
  be available for reestablishment of the previous
  ecosystem.
• Tends to be more rapid than primary growth.

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In our area succession may go like this.
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The climax community is well-suited to the
environment and can achieve relative stability.
We have an Oak/hickory climax community.
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Climax Communities - Biomes

• Terrestrial climax communities with wide
  geographic distributions. Usually defined by
  undisturbed natural plant communities.
• Two main non-biological factors determining
  biomes
• Temperature
• Precipitation

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Deserts

• Less than 25cm annual precipitation.
• Precipitation unevenly distributed throughout the
  year.
• Large daily temp fluctuations.
• Most species exhibit specialized adaptations to
  climate.

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Grasslands

• Receive 25-75cm of annual precip.
• Fire regime usually present.
• Rainfall sporadic enough to cause draughts
• Historically evolved with large herds of
  migratory grazing mammals.

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Tropical Rainforests

• Located near equator where temp is relatively
  warm and constant.
• Most areas receive over 200cm annual rainfall.
• Laterite soil allows high levels of leaching,
  thus most nutrients are tied-up in biomass.
• Very high species diversity.

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Tropical Forest biome in Guatemala
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View across the canopy, Guatemala
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Open forest floors are characteristic of tropical
rain forests. Massive recycling by forest floor
decomposers keeps the floor clean of debris.
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Massive root systems of trees help the tree
retrieve nutrients from the poor soil.
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Unfortunately much of the tropical rainforests
are being cleared for crop lands.
It is estimated that an area the size of a
football field is cleared every second.
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This is an image from a satellite over the Amazon
rainforest. Notice the areas being cleared around
the road.
Human kind is in a deliberate war against nature,
and were winning.
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Tropical Deforestation

• Forests cleared for logging, agriculture
• Effects
• Increased erosion and sedimentation
• Altered evaporation rates and changes in local
  weather patterns
• Increased energy reflection
• Decreased carbon uptake

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Temperate rain forests found Along the pacific
northwest grow some of the largest trees in the
world.
95 of the redwood forests have been logged.
Only 3 of the original forest remains.
Yosemite National Park
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Near Klamath, California. Few stands of redwoods
remain.
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Impacts, Issues
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Temperate Deciduous Forests

• Grow in areas with moderate rain.
• Average temperatures that change significantly
  with the season.
• Long warm summers
• Cold but not too severe winters
• Abundant precipitation throughout the year.
• Dominant species include oak, hickory, maple,
  poplar and sycamore.

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Fall colors from an Eastern Deciduous Forest
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Northern Boreal Forest (Taiga)

• Found just south of the tundra
• Winters are long, dry, and extremely cold
• 6-8 hour days in winter and 19 hour days in the
  summer.
• Dominated by spruce, fir, cedar, hemlock, and
  pine.

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Northern Boreal Forest, Canada
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High Altitude Coniferous Forest, USA
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Altitude and Latitude

• As altitude increases, average temperature
  decreases.
• As you move from sea level to mountain tops, it
  is possible to pass through a series of biomes
  similar to what you would encounter moving from
  the equator to the north pole.

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Major Aquatic Ecosystems

• Four factors influencing aquatic ecosystems
• Penetration of suns rays
• Nature of bottom substrate
• Water temperature
• Amount of dissolved materials

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• Pelagic Marine Ecosystems
• Pelagic Region - Open sea
• Phytoplankton - microscopic plants floating in
  the ocean. (perform photosynthesis)
• Zooplankton - Microscopic animals of many kinds -
  feed on phytoplankton.
• Productive aquatic ecosystems are those in which
  essential nutrients are common.

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• Benthic Marine Ecosystems
• Bottom of the sea
• Substrate is very important in community
  development
• Estuaries
• Shallow, partially enclosed areas where
  freshwater enters the ocean
• Extensive production because of shallow, warm,
  nutrient-rich areas

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Freshwater Ecosystems

• Two broad Categories
• Stationary Water
• Running Water (Downhill)

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Lakes and Ponds

• Littoral and Limnetic zones - presence or absence
  of rooted vegetation.
• Productivity of a lake determined by many
  factors.
• Cold temps - Shallow depth - Erosion sediments
  from land, Dissolved oxygen levels
• Oligotrophic - Deep, cold, nutrient-poor
• Eutrophic - Shallow, warm, nutrient-rich

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Streams and Rivers

• Even though most streams are shallow, it is
  difficult for most photosynthetic organisms to
  accumulate nutrients necessary for growth.
• Most clear streams are not very productive
• Most debris is input from terrestrial sources

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SUMMARY

• Ecosystems change when one organism replaces
  another. (succession)
• Regional terrestrial climax communities are
  called biomes.
• Primary determinants are annual rainfall
  distribution and temperature fluctuations.
• Aquatic ecosystems can be divided into marine
  (salt water) and freshwater ecosystems.

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SUMMARY cont.

• Oceans are divided into pelagic, benthic, and
  estuary regions.
• Lakes are categorized as oligotrophic or
  eutrophic, depending on the temperature and
  nutrient status.
• Streams get most of their nutrient from land,
  thus stream-side land uses are of prime
  importance.

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Environmental Close-UpThe Changing Nature of
the Climax Concept.

• Post-disturbance climax community often differs
  from the pre-disturbance climax community.
• Ecologists now feel that the land will not return
  to some preordained condition, and the new
  condition depends on many other factors besides
  climate.

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• All communities change - even climax communities,
  although climax communities may change very
  slowly.
• So even though the term climax infers a false
  endpoint, is this still a viable concept ?

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