Chapter 5 Interactions in the Ecosystem

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Chapter 5Interactions in the Ecosystem

• Habitat-the place in an ecosystem where an
  organism lives
• Organisms adapt to their habitat by the way they
  gather food, reproduce, and avoid predators
• Organisms also have a specific role in the
  ecosystem called a niche
• Niche-the role of an organism in the ecosystem,
  what the organism does, its job
• Niches must include biotic and abiotic factors
  food sources, predators, temperature, sunlight
  and water amounts, time of day or night
• All members of a species have the same niche, two
  different species cannot share the exact same
  niche in the same habitat
• Niches can be similar though
• Different species of the Anolis lizard eat
  insects, but just different sizes.
• If two species try to share the exact same niche
  in the same habitat, they will be forced to
  compete.

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• There can be only one winner in a competition, so
  one species will be forced to move or die out
• This causes competitive exclusion-the extinction
  of a population due to the direct competition
  with another species for a resource
• The species is not extinct entirely, just from
  the location
• Fundamental niche- the entire niche that an
  organism could have
• Realized niche- the niche that the organism
  actually has
• Many times, one species will help define the
  niche of another species
• Ex barnacle species
• Species A(Chthamalus stellatus), Species
  B(Balanus balanoides)

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Niche Diversity

• The number of different niches in an ecosystem
• Niche diversity is often determined by abiotic
  factors
• Marshes have many organisms but very few
  niches(jobs) because the environment is constant
• Deserts have few organisms, but many different
  niches(jobs) because of harsher environment
  (temperature and moisture)
• Predator-an organism that actively hunts other
  organisms
• Prey-the organism that is hunted
• Predators decrease the population size of their
  prey species
• Now more resources are available to other
  species, so a new niche is formed
• Predators increase niche diversity
• Keystone predator- predator that promotes the
  increase in niche diversity in a habitat
• Ex sea stars and mussels studied by Robert Paine

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Evolution and Adaptation

• Evolution-a change in the characteristics of a
  population of organisms over time
• Within a species, the individuals have genetic
  variations
• Sometimes, a certain variation (characteristic)
  allows the individuals to produce more offspring
• Since the characteristic is genetic, it will be
  passed on from generation to generation
• More individuals in the species population will
  have this characteristic/trait
• Over a long period of time, these individuals
  with the changes, adaptations,will outnumber
  the others without the adaptation
• The species will have evolved

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• Evolution causes population to adapt to very
  specific niches in one environment
• This reduces competition with other species
• Ex 5 species of warblers
• All live in spruce trees prey on insects
• Difference is each species feeds on a different
  part of the tree
• Specialized species- a species with a very small
  niche
• Exkoala bear and eucalyptus trees
• Specialized species are very vulnerable to
  extinction
• Generalized species-a species with a very wide
  niche
• Generalized species have several food sources
• Exmice and cockroaches
• Generalized species can survive a constantly
  changing environment by changing their behaviors
  to fit the new environment

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• Convergent Evolution-the independent development
  of similar adaptations in two species with
  similar niches
• In English, that means two different species that
  live in two different ecosystems develop similar
  adaptations because they both have similar niches
• Ex birds and bats
• Each are a different species and can live in
  different ecosystems and habitats. What do both
  of them have?
• Both developed wings because their niche requires
  them to fly
• This development does not have to occur in the
  same time period
• Ex dolphins(exists today) and ichthyosaur(extinct
  reptile from the Jurassic period)
• Both have adaptations for swimming (fins,
  streamlined body shape, pointed nose)

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• Coevolution-occurs when species that interact
  closely become adapted to one another
• In English, two species live and interact so
  closely that they change together
• Ex plants and caterpillars
• Many plants have poisonous chemicals that most
  insects cannot resist, except for some
  caterpillars
• These caterpillars adapt and eat only on the
  poisonous plants
• The plants have made the poison, and the
  caterpillar adapted to the poison
• Sometimes both species will benefit from the
  coevolution
• Ex acacia tree and stinging ants in Central and
  South America
• The acacia tree has hollow, pointed tubes that
  the ants live in and are protected from predators
• The ants attack animals trying to eat the acacia,
  clear vegetation around the tree so it gets more
  sunlight (why?)
• Now, the ants and the acacia tree need each other
  to survive

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Populations

• Populations are controlled by biotic and abiotic
  factors
• Thomas Malthus(1798-England) observed that human
  population can quickly grow past what the
  environment can support--causing famine and
  disease
• He inspired Charles Darwin(On the Origin of
  Species)
• What does this mean?
• There is no exception to the rule that every
  organic being naturally increases at so high a
  rate, that, if not destroyed, the Earth would
  soon be covered by the progeny(descendants) of a
  single pair.
• Darwin said that organisms produce more offspring
  than the Earth can provide for.
• This leads to the organisms competing for
  resources
• Only the most fit with the best adaptations
  will survive. This is called natural selection

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• Population growth in which the rate of growth in
  each generation is a multiple of the previous
  generation is exponential growth
• Start with 2 elephants
• Next generation has 6 elephants
• Next generation has 18 elephants
• And on and on
• All populations have the potential to grow
  exponentially IF it has the perfect environment
• In reality, populations are limited by food,
  climate, predators and many other things
• Populations are limited to short growth periods
  and certain geographic areas
• Each ecosystem has a carrying capacity for every
  species in it.
• Carrying capacitythe number of individuals of a
  species that can be supported by an ecosystem

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• What happens as populations grow?
• Resources (food living space) are used and
  become hard to find
• Competition starts among a species
• Death rate increases, birth rate decreases
• Population growth slows
• Population growth will eventually stop when
  births deaths
• This can be graphed with an S-shaped curve (Fig.
  5-9, pg. 81)
• Small population starts off growing quickly
  (exponentially) because of unlimited resources
• As population approaches its carrying capacity,
  growth slows
• Growth stops once it reaches its carrying
  capacity

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Limiting Factors

• Carrying capacity has things that slow growth of
  the population limiting factors
• If the factors affect populations more when the
  population grows, it is a density-dependent
  limiting factor (based on size of population)
• Ex food supply, predation, disease, living
  space, water
• Factors that affect population growth regardless
  of the size are density-independent limiting
  factors(not based on size of population)
• Ex climate, natural disasters, human
  disturbances
• Populations controlled by density-dependent
  factors show a S-shaped growth curve
• Populations controlled by density-independent
  factors show a boom-and-bust growth curve
• Population grows exponentially under favorable
  conditions, and then drops sharply when
  conditions change (insects Fig 5.11 pg 83)

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Human Population Growth

• Human growth has been exponential for a long time
• We have had continued growth because of advances
  in farming, technology, energy development,
  transportation, medicine
• Eventually, our resources will be depleted
• No population can grow exponentially forever
• What can we do to save resources?