Interactions Within Ecosystems

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Interactions Within Ecosystems
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Cast of Food Web Characters

• Tertiary Consumers Animals that eat animals
  that eat animals
• Secondary Consumers Animals that eat animals
  that eat plants
• Primary Consumers Animals that eat plants
• Primary Producers Plants and Phytoplankton
  organisms using the sun for energy

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Groups of living things interact within ecosystems

• The environment can be organized into five levels
• Biome region with similar climate, types of
  plants, and animals
• Ecosystem The living and non-living things that
  interact in one environment.
• Community The living organisms of an ecosystem
• Population A group of organisms of the same
  species that live in the same area.
• Organism A single living thing, made up of one
  or many cells, that is capable of growing and
  reproducing.

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Patterns Exist in Populations
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• Patterns in Living Space
• Animals in a habitat are located based on food
  supplies, water, and shelter locations.
• Some animals live in large groups for safety (
  fish and elephants )

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• Patterns in Time
• Population sizes can change with seasons
• Many organisms migrate to other areas (monarch
  butterflies and birds)

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rch/monarch13.jpg
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Organisms Interact in Different Ways

• Organisms may cooperate, compete, or depend on
  each other for survival
• Predator and Prey relationships
• Predators can affect how the prey populations are
  distributed (fish in large groups)
• Prey can affect the location and number in
  predator populations (birds feeding on insects
  migrate to the areas where the insects are
  plentiful)

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Organisms Interact in Different Ways

• Competition
• Competition is the struggle between individuals
  or different populations for a limited resource

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• All the organisms in any ecosystem have some
  effect on every other organism in that ecosystem.
• Also any resource in any ecosystem exists only in
  a limited supply.
• When these two conditions apply jointly,
  competition takes place.

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Example Seagull

• In a seagull colony on an oceanic outcrop, as the
  population grows, so the pressure for good
  nesting sites increases.

• This can affect the number of eggs that each
  female can successfully hatch, and so affects the
  birth rate of the population as a whole.
• This sort of interaction is called a Density
  Dependent factor - the effect is depends on the
  population density ( low density small effect,
  high density large effect).
• This mainly associated with pressure for food,
  nutrients or space.

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• Competition can happen with the same species
  (plants compete for light, space, and nutrients)
• Competition between different species (hyenas and
  vultures compete for remains of dead animals)

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INTRASPECIFIC COMPETITION.

• Competition between members of the same species
• When the numbers of a population are small, there
  is little real competition between individuals
  for resources.
• Provided the numbers are not too small for
  individuals to find mates, population growth will
  be high.

• As the population grows, so does the competition
  between individuals for the same resources until
  eventually the carry capacity of the ecosystem is
  reached.
• In this situation, often the stronger individuals
  claim the larger share of the resources.

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Intraspecific continued

• Some species deal with intraspecific competition
  by being territorial.
• An individual or pair hold an area and fend off
  rivals.
• Individuals that are the most successful
  reproductively will hold the biggest territory
  and hence have access to more resources.

• Example animals will often spray urine to mark
  their territories and claim their area

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• Intraspecific competition tends stabilize
  populations dependent upon the controlling
  resources.

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Intraspecific produces something called logistic
growth

• The graph illustrates this for a colony of yeast
  grown in a constant but limited supply of
  nutrient.
• During the first few days the colony grows slowly
  as it starts to multiply (lag phase) then it
  starts to grow very rapidly as the multiplying
  colony has a plentiful nutrient supply
  (exponential phase).
• Eventually the population size stabilizes as only
  a set number of yeast cells can exploit the
  limited resources (stationary phase). Anymore
  yeast cells and there is not enough food to go
  around.

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INTERSPECIFIC COMPETITION

• Individuals of different species competing for
  the same resource.

• Interspecific competition may result in a
  balance, in which both species share the
  resource.
• The other outcome is that one species may totally
  out compete the other, this is the principal of
  competitive exclusion.

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Interspecific Competition

• An example of both of these outcomes can be seen
  in a garden that has become overrun by weeds.
• A number of weed species coexist together, but
  often the original domestic plants have been
  totally excluded.

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Interspecific

• Think of it like 2 species intersecting

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• In a woodland light is a limiting resource.
• Plant species that can not get enough light will
  die out in a woodland.
• This is especially true of small flowering plants
  on the woodland floor that are not only shaded
  out by trees but by shrubs and bushes as well.
  Beech trees have very closely overlapping leaves,
  resulting in an almost bare woodland floor.

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• But even in Beech woods, flowers manage to grow
  in the spring. Carpets of Snowdrops, Primroses
  and Bluebells an integral part of all Northern
  European deciduous woodlands in the spring.
• The key to these species success is that they
  grow, flower and reproduce before the shrub and
  tree species burst into leaf.
• They avoid competing directly with species that
  would out compete them for light by completing
  the stages of their yearly cycle that require the
  most energy and therefore the greatest
  photosynthesis when competition is less.

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Organisms Interact in Different Ways

• Cooperation
• Some organisms work together to benefit each
  other
• Killer whales hunt in pods (groups)
• Ants, bees, and termites (members of a colony
  have different roles and responsibilitiesqueen
  bee, worker bees, etc.)

• http//www.apitherapy.com.au/contents/media/l_bee
  20pollen20dw.jpg

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Survival of One Species Might Depend on Another
Species

• Symbiosis two different species who live
  together in a close relationship
• Both species benefit
• One species benefits while the other is not
  affected
• One species benefits while the other is harmed

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Types of Symbiosis

• Mutualism Two species interacting with each
  other that benefits both species. (bees and
  flowers)

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Types of Symbiosis

• Commensalism two species interacting with each
  other with one species benefiting and the other
  unaffected. (jellyfish and fish)

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Types of Symbiosis

• Parasitism two species interacting while one
  species benefits and the host species is harmed
• Examples of human parasites.

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Populations Change Over Time

• Population growth and decline
• Predator-prey interactions can affect population
  increase or decrease ( as a wolf population
  increases the moose population decreases)
• Birth rate may decline or increase

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Populations Change Over Time

• Limiting factors any factor or condition that
  limits the growth of a population in an ecosystem
  (food, water, light, large group of predators,
  small group of prey)

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ion/homestudy/wildlife/wildlife/limit.phtml?print
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Maintaining a Balance in an Ecosystem

• Carrying Capacity the maximum number of
  individuals that an ecosystem can support.
• Limiting factors affect the carrying capacity

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capacity_chart.gif
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Main Points on Organism Interactions in Ecosystems

• Groups of living things interact within
  ecosystems (biome, ecosystem, community,
  population, organism)
• Organisms can interact in different ways
  (symbiosis mutualism, commensalism, parasitism)

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Bioaccumulation the accumulation of a
contaminant or toxin in or on an organism from
all sources (e.g., food, water, air). An
increase in the concentration of a chemical in a
biological organism over time, compared to the
chemical's concentration in the environment.
Compounds accumulate in living things any time
they are taken up and stored faster than they are
broken down (metabolized) or excreted.

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Biomagnification the increase in concentration
of toxin as it passes through successive levels
of the food web

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Ospreys and eagles are tertiary consumers and
this makes them particularly vulnerable to DDT
because of bioaccumulation and
biomagnification.
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Ecosystem structure

• Food Chain
• Shows the flow of energy from one organism to the
  next

• Trophic Level
• The feeding level based on an organisms source of
  nutrients
• Nearly all energy that sustains a food chain
  begins with the sun

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Trophic level

• The position that an organism occupies in a food
  chain, or a group of organisms in a community
  that occupy the same position in food chains.
• It is possible to classify the way organisms
  obtain energy into two categories.

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• Producers or Autotrophs These manufacture their
  own food from simple inorganic substances
  (plants)
• Consumers or Heterotrophs Feed on autotrophs or
  other heterotrophs to obtain energy (herbivores,
  carnivores, omnivores, detrivores and decomposers
  
• But within the consumers their is a feeding
  hierarchy of Plants capture the suns energy and
  convert it to glucose, herbivores eat plants and
  carnivores eat herbivores - different feeding
  levels
• (Greek for food is trophe)

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• Trophic level 1 - producer
• Trophic level 2 - herbivore (primary consumers)
• Trophic level 3 - carnivore (secondary consumers)
  
• Trophic level 4 - carnivore (tertiary consumer)
• The first trophic level, the autotrophs supports
  the energy requirements of all the other trophic
  levels above.

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Use the terms producer , consumer, decomposer,
herbivore, carnivore and top carnivore to explain
the following diagram
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Trophic Levels

• Producers (autotrophs)
• Use photosynthesis to create nutrients from sun
  and compounds
• Primary consumers (herbivores)
• Mainly feed on grass, leaves, plants

• Secondary consumers (carnivores)
• Feed on the flesh of animals (mainly herbivores)
  
• Tertiary or higher consumers (carnivores)
• Feed primarily of the flesh of other animals
  herbivores or carnivores

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Food Chain

• Ecosystems have an hierarchy of feeding
  relationships (trophic levels) that determine the
  pathway of energy flow in the ecosystem.
• The energy flow in the ecosystem can be
  illustrated as a Food chain.

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Limits to Food Chains
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• It is possible to construct food chains for an
  entire ecosystem, but this starts to create a
  problem.
• The food chains below are form a European Oak
  Woodland. In fact they are based on real food
  chains at Wytham Wood in Oxford

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• In the four different food chains only ten
  species are listed and some of them are in more
  than one food chain.
• If we continued to list all the species in the
  wood and their interactions in every food chain
  the list would run for many pages.
• Food chains only illustrate a direct feeding
  relationship between one organism and another in
  a single hierarchy.
• The reality though is very different. The diet of
  almost all consumers is not limited to a single
  food species. So a single species can appear in
  more than one food chain.

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• A further limitation of representing feeding
  relationships by food chains is when a species
  feeds at more than one trophic level.
• Voles are omnivores and as well as eating insects
  they also eat plants.
• We would then have to list all the food chains
  again that contained voles but moving them to the
  second trophic level rather than the third in a
  shorter food chain.

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• The reality is that there is a complex network of
  interrelated food chains which create a food web.

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Food Web
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Ecological pyramids

• A bar diagram that indicates the relative numbers
  of organisms at each trophic level in a food
  chain. The length of each bar gives a measure of
  the relative numbers.
• Pyramids begin with producers, usually the
  greatest number at the bottom decreasing upwards.

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Pyramid

• Advantages
• It is a simple easy method of giving an overview
  and is good at comparing changes in population
  numbers with time or season.

• Disadvantages
• All organisms are included regardless of their
  size, therefore a system say based on an oak tree
  would be inverted (have a small bottom and bet
  larger as it goes up trophic levels). Also they
  do not allow for juveniles or immature forms.
  Numbers can be to great to represent accurately.

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Pyramids

• Biomass Pyramid
• Measures mass per area (kgm-2)

• Energy Pyramid
• Measures energy in Joules or kilocalories
  (kcalm-2) or (Jm-2)

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Pyramids of biomass

• As pyramids of number but uses dry mass of all
  organisms at each trophic level.

Advantages Overcomes the problems of pyramids of
number. Disadvantages Only uses samples from
populations, so it is impossible to measure
biomass exactly. Also the time of the year
that biomass is measured affects the result.
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Biomass Pyramid

• -Biomass shows the mass of all species in a given
  area
• Units are generally given in kilograms per
  meter2.
• -Biomass pyramids attempt to quantify mass per
  unit area by trophic level
• Extrapolate by multiplying to account for total
  area

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Biomass Pyramid Extrapolation

• The total biomass of a meter2 is calculated as
  32kg/m2. If this square meter were representative
  of an area that is 1 km2, what is the biomass of
  the area?
• 32 kg 1,000,000 m2 3.2 x 107 kgkm-2
• 1m2 1 km2

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Pyramids of energy

• The bars are drawn in proportion to the total
  energy utilized at each trophic level. Also the
  productivity of producers in a given area
  measured for a standard time, and the proportion
  utilized by consumers can be calculated.
• Advantages
• Most accurate system shows the actual energy
  transferred and allows for rate of production.
• Disadvantages
• It is very difficult and complex to collect
  energy data.

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Why use ecological pyramids.

• Ecological pyramids allow you to examine easily
  energy transfers and losses.
• They give an idea of what feed s on what and what
  organisms exist at the different trophic levels.
• They also help to demonstrate that ecosystems are
  unified systems, that they are in balance.