APES Chapter 8

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Community Ecology

• APES Chapter 8

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8-1 Community Structure and Species Diversity

• Ecologist use 3 characteristics to describe a
  biological community.
• Physical appearance- sizes, stratification, and
  distribution of its population and species
• Edge Effect
• Species diversity- a combination of numbers of
  different species (richness) and abundance of
  individuals with each species (species evenness)
• High richness usually means low evenness (few s
  per species)
• Factors affecting diversity are latitude in
  terrestrial communities and pollution in aquatic
  communities.
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• Niche structure- the number of ecological niches,
  similarities/differences, and interaction of
  species with each other.

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Species Equilibrium model (Theory of island
biogeography)

• The number of different species on an island
  (species richness) is determined by how fast a
  species arrives, how fast old species become
  extinct, island size and distance from mainland.
• Important
• Balance between rate of immigration of species
  and rate of extinction of existing species.
• Size of island (smaller has less diversity) and
  distance from mainland (closer to mainland,
  increases species richness)

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General Types of species

• Generalist
• Specialist
• Native species that normally live and thrive in
  a particular ecosystem
• Non-native species species that migrate into an
  ecosystem or are deliberately or accidentally
  introduced into an ecosystem by humans.
• Also known as Exotic/ Alien
• Problems caused by Non-native species
• the non-natives have no natural enemies so they
  can thrive in the new ecosystem and crowd out the
  native species Examples Melaleuca plants,
  Burmese pythons, iguanas

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Indicator Species

• A species that serve as early warnings that a
  community or ecosystem is being damaged or
  changed.
• Birds are good indicators because
• Trout and macro-invertebrates are good indicators
  of
• Amphibians indicate

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Keystone species

• species that play a pivotal role in the
  structure, function, and integrity of an
  ecosystem because
• Their strong interactions with other species
  affect the health and survival of these species
• They process material out of proportion to their
  numbers and biomass
• Keystone species
• Pollinate
• Scatter seeds
• Modify habitats
• Predation to control prey populations
• Help plants get nutrients
• Recycle animal waste

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ExamPles of Keystone species
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Foundation Species

• A species that shapes communities by creating
  and enhancing habitat for other species
• Elephant tearing down tree

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5 Types of Species Interactions
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• Competition Two or more animals competing for
  the same resources.
• Two Types
• Intraspecific competition between members of the
  same species (mates)
• Interspecific competition between members of two
  different species (food, space, sunlight)
• The more a species niche overlaps, then the more
  competition. This can lead to one species
  migrating, adapting new behaviors or dying out.
  Over a long time scale, adaptations lead to
  RESOURCE PARTITIONING (warblers) or NICHE
  SPECIALIZATION (owls/hawks)
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Warblers and resource partitioning
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Niche Specialization
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Species Interactions (continued)

• Predation members of one species feed directly
  on all or part of a living organism or other
  species. They do not live on or in the other
  species. One species is clearly harmed and the
  other clearly benefits.
• Benefits
• Predation can be a good thing for the population
  of prey species as predators often weed out the
  sick and dying animals, thereby reducing
  competition amongst the prey species and
  controlling population growth. Also, enhances
  the passing of successful genetic traits to the
  next generations. (Sharks)

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• Predators have characteristics that help them
  catch prey, such as
• Running fast
• Good eyesight
• Hunting in packs
• Camouflage for ambush
• Give examples!

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• Prey have characteristics that help them escape
  predators, such as
• Run fast
• Good sense of smell and eyesight to alert them to
  the presence of predators
• Protective shell
• Spines
• Camouflage
• Chemical warfare like poisonous skin
• Foul smells
• Bad tasting
• Warning coloration
• Mimicking a predator
• Examples

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Species Interactions (continued)

• 3) Symbiosis a long lasting relationship in
  which species live together in an intimate
  association. (3 major symbiotic relationship)

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• Parasitism when one species feeds on part of
  another organism (host) by living on or in the
  host. In this relationship the host is harmed and
  the parasite benefits.
• Examples

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• Mutualism symbiotic relationship in which both
  species involved benefit from the relationship.
  Ways in which this happens are pollination,
  providing food, and providing shelter.
• Examples

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• Commensalism a symbiotic relationship in which
  one species benefits and the other species is
  neither helped nor harmed.
• Example

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Ecological Succession Communities in Transition

• Ecological Succession One characteristic of all
  ecosystems is that they change over time due to
  changes in environmental conditions.
• There are 2 types of succession
• Primary succession
• Secondary succession

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Primary Succession

• Succession that starts with an essentially
  lifeless area where there is no soil or bottom
  sediment in an area.
• Examples include new lava, an abandoned parking
  lot, land exposed from retreating glaciers, etc.
  
• Succession happens in stages
• 1) Pioneer species move in and make soil Ex.
  Lichens and mosses
• 2) When enough soil is made and spread out, then
  plants that are small and close to the ground
  move in. These plants can live under harsh
  conditions and usually have short lives. They are
  called early successional species. Examples
  small annuals
• After hundreds of years, there is enough soil for
  
• Mid-successional species. Examples small
  herbs/shrubs
• 4) As the Mid-successional plants grow they
  create enough shelter for Late successional
  species such as trees.

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Secondary Succession

• Begins in an area where the natural community of
  organisms has been disturbed or destroyed, but
  the soil remains.
• For example
• abandoned farms, burned or cut forests, and
  heavily polluted streams.
• Secondary succession occurs in the same way as
  primary starting with pioneer species and ending
  with late successional species.
• Climax community- stable, self-sustaining
  community at the ending stages of ecological
  succession.

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Factors that affect the rate of succession and
how one species replaces another

• 1) Facilitation one species makes a area
  suitable for species with different niche
  requirements (Ex. Lichens, mosses gradually build
  up soil for small grasses to colonize site)
• 2) Inhibition earlier species hinder the
  growth of later species (release toxic chemicals
  to reduce competition)
• 3) Tolerance late successional species are
  unaffected by earlier successional species

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DISTURBANCES CAN AFFECT SUCCESSION

• Some disturbances can be beneficial in the long
  run like fire, because they increase
  biodiversity, clear out excess brush, renew
  nutrients and encourage other species to grow.
  Bog succession animation
• Some catastrophic disturbances can convert the
  ecosystem back to a lower level of succession.
  Its an ongoing struggle to always progress
  towards a climax community.
• Intermediate disturbance hypothesis- communities
  that experience fairly frequent disturbances have
  the greatest species diversity. (allows time to
  create openings for colonizing species but
  infrequent enough to allow some species to
  mature)

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Ecological Stability and Sustainability

• 3 aspects that lead to stability of a living
  system
• Inertia/persistence ability of a living system
  to resist being disturbed or altered
• Constancy- ability of a living system to keep its
  numbers within limits of available resources.
• Resilience- ability of a living system to repair
  damage after an external disturbance that is not
  too drastic.
• Complexity- Populations with more biodiversity
  are more stable. More biodiversity means greater
  primary productivity and more resilience.

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Everything is Connected!

• There is overwhelming evidence that human
  disturbances are disrupting important ecosystem
  services that support and sustain all life and
  economies. Taking action to prevent these
  disruptions even if they havent happened yet is
  the precautionary principle. (Better safe then
  sorry approach)