Chapter 6 Ecosystem Balance

1
Chapter 6 Ecosystem Balance

• All the organisms in an ecosystem work together
  to capture energy and cycle matter
• This is to maintain balance and keep the
  ecosystem functioning
• Changes in the ecosystem is going to happen, no
  matter how stable the ecosystem is.
• Most changes are gradual, but some are severe
  (fires, storms, earthquakes) and cause rapid
  changes
• The ecosystem has to adapt to these changes to
  keep the flow of energy and matter going

2
Relationships in the ecosystem

• Species have several types of relationships with
  each other and their environment
• Predators Prey Relationship
• Consumers that actively hunt other living
  organisms are predators.
• The organism a predator eats is the prey.
• Predators are often prey to other predators
  higher in the food chain.
• The population size b/n predator prey are
  closely related
• If there is a big prey population available, a
  predator population will be large also
• If the prey population shrinks, the predator
  population will shrink also
• Ex snowshoe hare and lynx
• Fig 6.1, pg 89
• If the number of hares declines, the number of
  lynxes declines after about 1-2 years

3

• The lynx and hare populations rise and fall about
  once every 10 years, called its population cycle
• Population cycle is the amount of time between
  the rise and fall of a species population
• Large herbivores (hare, muskrat, large birds)
  have pop. cycles of about 10 years
• Small herbivores (mice, lemmings) have pop.
  cycles of about 4 years
• Why? Larger animals have longer cycles b/c they
  live longer and reproduce more slowly than
  smaller animals
• Predators often have pop. cycles that are the
  same as their prey because they depend on the
  prey to live.
• Ex arctic fox eats herbivores with a 4 year
  cycle, so the arctic fox has a 4 year cycle

4
Parasitism Relationship

• Parasitism-a relationship in which one organism
  feeds on the tissues or body fluids of another
  organism
• the parasite does not kill the organism first
• The organism the parasite feeds on is the host
• it lives on or in the body of the host
• It often ends up killing or harming the host
• Ex fleas, ticks, lice, some worms, protists
• It depends on the host for food, and many other
  functions
• Ex tapeworms cannot move and have no sense
  organs (sight, touch, smell)
• The tapeworm lives in intestines of mammals. It
  doesnt have to move or use any senses because
  the host does everything for it

5

• Population size of the parasite is close to the
  population of its host
• They are also density dependent on the population
  of the host.
• If the host population is crowded and live
  closely, then the parasite can be transferred
  easily to new hosts.
• Parasites are a density-dependent limiting
  factor.
• Symbiosis Relationship
• Any relationship in which two species live
  closely together is called symbiosis
• Parasitism is type of symbiosis, in which one
  organism harms another
• Symbiosis can either
• Harm one organism, benefit the other (parasitism)
• Benefit one organism, do nothing to the other
• Benefit both organisms

6

• When one organism benefits, and the other is left
  alone, this is called commensalism
• Ex barnacles live on the skin of whales without
  harming or helping the whale
• Barnacles benefit because the water passes over
  the whale giving it food
• When both species benefit this is called
  mutualism.
• Ex stinging ants and the acacia tree
• Ex flowers and insects
• The flower gives the insect food (nectar)
• The insect pollinates the flower by bringing
  pollen from another flower
• Ex yucca plant and yucca moth are so mutualistic
  that they cant survive without each other
• The moth lays its eggs inside the flower. It
  also gets food from the plant for its
  caterpillars.
• The flower is pollinated by the moth. The moth
  gets pollen from another yucca plant and brings
  it to its partner plant

7
Ecological Succession

• Environments will change causing old niches to
  have to change
• All the living things have to evolve to the
  changing environment of the ecosystem
• Brand new environments do become available to
  living things
• When volcanic eruptions, glaciers moving other
  natural occurrences happen, they can wipe out a
  complete current ecosystem, including the soil
• It is left with nothing but bare rock or cooled
  lava. No living things are present and no soil
• Organisms will begin to move immediately into
  this brand new lifeless habitat
• The order of the organisms moving in usually
  follows a specific pattern primary succession
• 1st thing to happen is colonization of new
  organisms and formation of new soil from rocks
• Rocks are broken down by lichen (a fungus/alga
  that releases acid) and weathering to form soil
• Lichenpioneer community b/c 1st to colonize

8

• 2nd, once there is soil, grass and small plants
  grow
• More soil is made from roots and dead leaves
• Lichen will be replaced by grass
• 3rd, After many generations, the soil is deep
  enough and fertile for nonwoody plants with deep
  roots
• At this point, small disturbances can cause
  drastic changes because the habitat is not stable
  yet
• 4th,Eventually, pine trees and others with
  shallow roots will grow when the soil is deep
  enough
• 5th Lastly, broadleaf trees and hardwood trees
  grow and replace many of the other pines
• This is the final stage of succession in most
  areas
• This ecosystem will probably not change much as
  long as there are no major disturbances
• It is called a climax community a community that
  does not undergo further succession
• Climax communities usually are very diverse, have
  many different species, and can survive most
  severe disturbances

9

• Primary succession occurs on bare rocks or areas
  where there are no organisms or soil
• Many times, a disturbance doesnt completely
  wipeout a habitat and its soil (fires, storms,
  human activity)
• When organisms begin to recolonize these areas it
  is called secondary succession succession that
  occurs where a disturbance eliminates most
  organisms but does not destroy the soil
• Secondary succession happens in the order of the
  later stages of primary succession.
• 1st fast growing grass and nonwoody plants grow
  and then shrubs
• 2nd fast growing trees like pines grow
• 3rd slow growing hardwood trees grow
• Then a climax community forms
• This can take several hundred years to reach
• If major disturbances occur too often, climax
  communities may never be reached
• Grasslands have difficulty reaching a climax
  community because frequent fires disrupt and kill
  trees and shrubs
• They get stuck at the grass-community level

10
Aquatic Succession

• Succession also occurs in aquatic habitats
• Ex a glacier retreats and forms a clear mountain
  lake
• It has no organisms living in it and few
  nutrients
• What is going to move in first, second, third???
• 1st small water plants, reeds will grow in the
  thin soil near the shore
• This supplies some organic matter for other small
  organisms
• 2nd, the water will gain more sediment, soil, and
  nutrients
• More organisms are supported, and water plants
  cover the surface of the lake
• 3rd, lake will fill with sediment and form a
  marsh
• Land plants will colonize
• It could eventually become a meadow covered with
  land plants and then grow into a forest

11
Island Succession

• Succession also occurs on islands just like on
  land
• New islands are formed by volcanic eruptions
• Organisms are quick to colonize on islands
  (seagulls)
• Any organism that colonizes on an island must
  have been carried by water, wind, or another
  organism
• Islands usually have large bird populations b/c
  birds can travel long distances easier than land
  animals
• New islands have many unfilled niches available
  to the organism that can reach the island
• The organism that would normally fill the niche,
  probably cant get there
• This allows a species to evolve into many niches
  b/c theres no competition
• Often results in new species (ex Galapagos
  finch)

12
Maintaining Stability in the Ecosystem

• Stability is the measure of how easily an
  ecosystem is affected by a disturbance and how
  quickly it goes back to its original condition
  after the disturbance
• The original condition of the ecosystem includes
  the biotic and abiotic factors, energy flow and
  nutrient cycle
• A more balanced ecosystem will be able to return
  to its original condition quicker and with fewer
  evolutionary changes in its organisms after a
  major disturbances
• A more complex food web increases the stability
  of an ecosystem
• All ecosystems are trying to maintain a state of
  balance, called equilibrium
• After a major disruption, ecosystems have to
  change drastically to adjust to the new
  conditions
• Sometimes the disruption can destroy an entire
  ecosystem
• A new ecosystem will eventually develop

13

• Dinosaurs were wiped out by a major disturbance
  (by a comet or climate changes)
• After that ecosystem was destroyed, many mammals
  evolved to the new ecosystem giving us many of
  the mammals we know of today
• It is impossible for scientists to predict how
  every change will affect an ecosystem
• There are too many abiotic and biotic factors
  which make the ecosystem too complex to predict
• Species are becoming extinct at a very high rate
  presently
• Human population growth is a major cause of this
  extinction rate
• Humans destroy habitats, introduce foreign
  species to new ecosystems, and pollute land,
  water and air

14
Land Biomes

• The ecosystems of Earth can be divided into
  major categories
• Biome-a major type of ecosystem with distinctive
  temperature, rainfall and organisms
• Land biomes depend on average temp and amount of
  precipitation
• Aquatic biomes depend on water depth, nutrients,
  and nearness to land
• Biomes are broad, general categories that will
  vary within each individual biome
• Biomes include ecosystems which include habitats
• The habitats and ecosystems within a biome will
  be different, but overall fit within a biome
  category
• 8 Land biomes desert, tundra, coniferous forest,
  deciduous forest, rain forest, steppe, praire,
  savanna
• Desert and tundra receive little water, support
  little biomass
• Forest biomes are 75 of Earths biomass
• Rain forest has more than 50 biomass
• Rain forest is the most diverse biome, it has the
  highest number of different species
• Rain forest destruction is very serious

15

• Grasslands contain about 8 of Earths biomass,
  but receive less precipitation than forest
  biomes. They have long dry seasons and have
  frequent fires
• Use the Biome map on pg 100-101