Chapter 3 Notes: Communities, Biomes, and Ecosystems

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Chapter 3 Notes Communities, Biomes, and
Ecosystems
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Limiting Factors

• Recall from chapter 2, that all ecosystems have
  biotic and abiotic factors.
• In every ecosystem, there are always certain
  factors that are abundant and other factors that
  are scarce or hard to come by.
• Those factors that are important but scarce or
  hard to come by in an ecosystem are referred to
  as limiting factors. Especially if those factors
  are essential for life.

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Limiting Factors

• If you are a plant or animal that lives in a
  desert, the main limiting factor might be water.
• If you are a plant in the rainforest that is
  competing for sunlight, sunlight might be the
  limiting factor in that ecosystem.
• If you are a moose that depends on plants that
  are high in nutrients, then forest fires might be
  the main limiting factor for a moose, because
  forest fires increase the amount of nutrients
  available in a boreal forest ecosystem.

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Limiting Factors in Ecosystems
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Range of Tolerance

• All living organisms have a range of tolerance
  for certain factors that they can withstand.
• A range of tolerance can be described as a zone
  within an upper limit and lower limit of
  environmental characteristics.
• Moose have a range of tolerance for temperatures
  down to about -40 and up to about 60 degrees
  Fahrenheit.
• Above or below these temperatures, moose may
  undergo physiological stress.

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Range of Tolerance for Organisms
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Ecological Succession

• As ecosystems mature, eventually they reach a
  stage of maturity called a climax community.
• Climax communities are not ecologically
  productive in terms of biomass and diversity.
• Once an ecosystem reaches the stage of climax
  community, some type of natural or man-made
  disturbance must take place in order to restore
  the climax community to a more productive state.

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Climax Community
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Ecological Succession

• Examples of natural disturbances could be
  volcanic eruptions, forest fires, glaciation,
  flooding, water and wind erosion, storms,
  hurricanes etc.
• Examples of man-made disturbances could be
  building roads, agriculture, prescribed forest
  fires, logging, clear cutting, development of
  land etc.
• After a disturbance occurs, ecosystems go through
  a natural progression or a series of changes
  called an ecological succession.

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Ecological Succession

• One type of ecological succession is called a
  primary succession. In primary succession, the
  disturbance causes such a severe change that
  usually the only thing left is bare rock.
• In the case of primary succession, the disturbed
  area must reestablish a new layer of soil before
  plants can move in and reestablish an area.
• Plants and animals that are the first to
  reestablish an area after a disturbance are
  called pioneer species. lichens are an important
  pioneer species in primary succession.

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Primary Succession
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Ecological Succession

• Lichens are important pioneering species, because
  they are one of the few examples of living
  organisms that can survive on bare rock.
• They are also important because they also help
  create new soil by producing acids that help
  chemically break down the rock into soil, so that
  other species can come in and grow after them.
• If a disturbance occurs, but the soil in the area
  is still intact, then another type of succession
  occurs called secondary succession.

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Secondary Succession
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Ecological Succession

• A good example of an event that may cause a
  secondary succession is a forest fire. In a
  forest fire, the trees and vegetation are
  removed, but the soil remains intact. Nutrients
  from the trees are released back into the soil
  once the trees are burned.
• Fireweed, alders and willows are all good
  examples of pioneer species that help reestablish
  an area after a forest fire because they are
  shade-intolerant.
• These pioneer species help the ecosystem by
  either nitrogen fixation or they allow
  shade-tolerant species like birch and aspen to
  eventually grow and recolonize.

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Ecological Succession
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Biomes

• A group of ecosystems in an area with a similar
  climate makes up a biome.
• The condition of the atmosphere at any given time
  or place is the weather.
• The average weather conditions in an area
  including its temperature and precipitation is
  called its climate.
• Climates are determined by the distance north or
  south of the equator which is called the latitude.

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Latitude, Weather, and Climate
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Major Biomes of the World
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Biomes

• Tundra low precipitation (15-25 cm), cold temps
  (-34-12 C), low growing vegetation, animals
  adapted to the cold (caribou, polar bears, arctic
  fox, arctic ground squirrels), permafrost, cold
  and dark winters.
• Boreal forest moderate prec. (30-84 cm), cold
  temps (-54-21 C), coniferous trees dominate,
  animals of the boreal forest (moose, lynx, hare,
  red squirrel, owls, hawks), short and moist
  summers, cold and dry winters.

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Biomes

• Tundra

• Boreal Forest (Taiga)

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Biomes

• Temperate forest moderate prec. (75-150 cm),
  moderate temps (-30-30 C), deciduous broadleaf
  trees dominate, animals of the temperate forest
  (deer, squirrels, turkeys, hawks, owls, raccoons
  etc.), well-defined seasons, hot summer, cold
  winter.
• Temperate woodland or chaparral moderate prec.
  (38-100 cm), warm temps (10-40 C), shrubs
  dominant vegetation, animals of the chaparral
  (coyotes, jackrabbits, lizards, snakes, insects),
  summers hot and dry, winters cool and wet.

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Biomes

• Temperate Deciduous Forest

• Temperate Woodland or Chaparral

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Biomes

• Temperate grassland moderate prec. (50-89 cm),
  moderate temps. (-40-38 C), grasses are dominant
  vegetation, animals of the grassland (gazelles,
  bison, horses, lions, antelope, deer, mice,
  coyotes, fox, wolves, snakes, insects), summers
  hot, winters cold, regular fires.
• Desert low prec. (2-26 cm), temps vary, cacti
  and other plants adapted to arid conditions
  dominate, desert animals (lizards, coyotes,
  snakes, jackrabbits, sheep, vultures).

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Biomes

• Temperate Grassland or Prairie

• Desert

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Biomes

• Tropical savanna moderate prec. (50-130 cm),
  high temps (20-30 C), grasses and scattered
  trees, savanna animals (lions, hyenas, cheetahs,
  elephants, giraffes, zebras etc.), hot and rainy
  summers, cool and dry winters.
• Tropical seasonal forest high prec. (more than
  200 cm per year), high temps (20-25 C), forest
  vegetation, tropical seasonal forest animals
  (elephants, tigers, monkeys etc.), deciduous
  trees drop their leaves in the dry season,
  rainfall is seasonal.

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Biomes

• Tropical Savanna

• Tropical Seasonal (Deciduous) Forest

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Biomes

• Tropical rain forest extremely high prec.
  (200-1000 cm per year), high temps. (24-27 C),
  large diversity of plant life, tropical rain
  forest animals (chimpanzees, Bengal tigers,
  orangutans, toucans, sloths, cobras, jaguars,
  insects), high humidity, no seasons, hot and wet
  all the time.
• Mountains mountainous terrain varies with
  elevation, changes in elevation resemble changes
  in latitude from an ecological standpoint.
• Polar cold all year, covered in ice, no
  vegetation, animals highly dependant on the sea
  for food. (polar bears, penguins, krill, seals)

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Biomes

• Tropical Rainforest

• Polar

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Mountain Biomes
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Aquatic Ecosystems

• A large portion of the earth is water. It should
  be no surprise that many ecosystems in the world
  are aquatic ecosystems.
• Approximately 97.5 of the water in the world is
  saltwater (oceans).
• Roughly 2.5 of the water is freshwater.
• How much of the 2.5 freshwater is found in...
• Glaciers?
• Groundwater?
• Lakes and rivers?

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Distribution of water graph
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River and Stream Ecosystems

• As streams travel from their headwaters to their
  destination (ocean, stream confluence, lake etc.)
  the character of the stream changes creating
  different habitats.
• Stream headwaters have a steep gradient, low
  volume (discharge), waters are cold and rich in
  oxygen but poor in nutrients. Stoneflies,
  caddisflies, mayflies, rainbow trout, grayling.
• Streams closer to their destination have a
  shallow gradient, high volume, warm waters that
  are low in oxygen but rich in nutrients.

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River Continuum Concept
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Lake Ecosystems

• Lakes are either Eutrophic (shallow, warm, more
  sunlight, nutrient rich, more vegetation)
• or Oligotrophic (deep, cold, less sunlight,
  nutrient poor, less vegetation).
• Most of the life in a lake is found close to the
  shoreline (littoral zone). More light means more
  plants. More plants means more food.
• The open water area in the middle of the lake is
  called the limnetic zone. The food chain in the
  limnetic zone is dependent on algae and plankton.

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Lake Ecology
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Lake Ecology
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Lake Zones
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Lake Zones
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Lake Ecosystems

• The bottom of a lake is the benthic zone. The
  zone in a lake below light is the profundal zone,
  which is generally the most unproductive.
• No sunlight means no plants. No plants means no
  food. Not much life on the bottom except mostly
  decomposers and detritivores.
• Seasonal changes in the water temperature and
  water chemistry cause changes in lake ecology.
• 4 degrees Celsius (39-40 F) is when water is most
  dense. This causes thermal stratification.

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Thermal Stratification in Lakes

• During the summer the top layer of the lake (the
  epilimnion) warms up faster than the bottom.
• The bottom of the lake stays at 4 Celsius because
  the water at 4 Celsius has the highest density.
• As autumn approaches the epilimnion cools off and
  eventually reaches 4 Celsius.
• When this occurs the density throughout the lake
  is the same and wind causes the water throughout
  the lake to mix nutrients. Dissolved oxygen is
  replaced and carbon dioxide is removed.

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Thermal Stratification in Lakes

• As winter approaches, the temperature of the
  epilimnion lowers until it reaches 0 Celsius.
• At 0 Celsius the top of the lake freezes and the
  bottom of the lake (the hypolimnion) stays at a
  constant temperature of 4 Celsius.
• As spring approaches, the ice melts and begins
  warming until it reaches 4 Celsius.
• Once it reaches 4 Celsius, once again the wind
  causes the lake to mix and turnover.
• The name of these critical time periods are
  called spring and fall turnover.

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Thermal Stratification

• Spring and Fall Turnover is important to lake
  ecosystems, because during summer and winter the
  amount of carbon dioxide increases, the pH lowers
  (becomes acidic), and the amount of dissolved
  oxygen decreases.
• Spring and Fall Turnover helps to replenish the
  lake ecosystem with new nutrients and dissolved
  oxygen, and it helps to eliminate the amount of
  carbon dioxide that has accumulated by cellular
  respiration of animals.
• It also helps regulate the pH levels of the lake.

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Thermal Stratification
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Other Important Aquatic Ecosystems

• Wetlands marshes, swamps, and bogs.
• Estuaries Freshwater and saltwater mix.
• Intertidal zones Land meets the ocean.
• Open Ocean (Pelagic) similar in many ways to
  lake ecology only bigger. There are different
  zones of the open ocean like the photic zone,
  aphotic zone, benthic zone and abyssal zone.
• Coastal Ocean and Coral Reefs the most diverse
  ecosystem of the ocean.

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Marine Ecosystems
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Marine Ecosystems