Community Ecology

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Community Ecology

• Chapter 8

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COMMUNITY STRUCTURE AND SPECIES DIVERSITY

• Biological communities differ in their structure
  or spatial distribution.

Figure 7-2
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Community Structure has 4 characteristics

• 1. Physical appearance relative size,
  stratification distribution of its populations
  and species
• 2. Species diversity or richness
• 3. Species abundance
• 4. Niche structure number of ecological
  niches, species interactions with similarities
  and differences

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Species Diversity and Niche Structure Different
Species Playing Different Roles

• Biological communities differ in the types and
  numbers of species they contain and the
  ecological roles those species play.
• Species diversity the number of different
  species it contains (species richness) combined
  with the abundance of individuals within each of
  those species (species evenness).

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Species Diversity and Niche Structure

• Niche structure how many potential ecological
  niches occur, how they resemble or differ, and
  how the species occupying different niches
  interact.
• Geographic location species diversity is highest
  in the tropics and declines as we move from the
  equator toward the poles.

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What determines species diversity ?

• Edge Effect-the boundaries between two ecosystems
  (ecotones) may have a
• different combination of species than those
  
• found in the two ecosystems.
• Forest-field ecotone and game species
• The most species rich areas
• Coral reefs
• Large tropical lakes

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Three main factors affect species diversity

• 1. Latitude decreases as moves away from
  equator

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• 2. Depth in aquatic systems increases from
  surface to 2000 m, then decreases until the sea
  bottom where diversity is usually high

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• 3. Pollution in aquatic systems

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Case StudySpecies Diversity on Islands

• MacArthur and Wilson proposed the species
  equilibrium model or theory of island
  biogeography in the 1960s.
• Model projects that at some point the rates of
  immigration and extinction should reach an
  equilibrium based on
• Island size
• Distance to nearest mainland

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TYPES OF SPECIES

• Native, nonnative, indicator, keystone, and
  foundation species play different ecological
  roles in communities.
• Native those that normally live and thrive in a
  particular community.
• Nonnative species those that migrate,
  deliberately or accidentally introduced into a
  community.

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Indicator Species Biological Smoke Alarms

• Species that serve as early warnings of damage to
  a community or an ecosystem.
• Presence or absence of trout species because they
  are sensitive to temperature and oxygen levels.
• Canary in the Coal mine they
  sang untill increase in CO
• Salmon and Stoneflies
• Amphibians

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Case Study Why are Amphibians Vanishing?

• Frogs serve as indicator species because
  different parts of their life cycles can be
  easily disturbed.

Figure 7-3
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Case Study Why are Amphibians Vanishing?

• Habitat loss and fragmentation.
• Prolonged drought.
• Pollution.
• Increases in ultraviolet radiation.
• Parasites.
• Viral and Fungal diseases.
• Overhunting.
• Natural immigration or deliberate introduction of
  nonnative predators and competitors.

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Keystone Species-

• Strong interaction with other species affect the
  health and survival of the
• other species. Significance is out of proportion
  with their biomass. In other words, a small
  biomass of these organisms have a large effect on
  the ecosystem.
• Pacific Northwest Millipede
• They process material
• out of proportion to
• their numbers or
• biomass

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• Top Predators-
• Interaction Between Species
• Intraspecific Competition-
• Territoriality-
• Interspecific Competition-
• Interference Competition-
• Exploitation Competition

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The Competitive Exclusion Principle

• Says that two species sharing the same Resource
  cannot coexist indefinitely in an ecosystem that
  does not have enough resources to meet the needs
  of both species.

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Strategies that Reduce Competition

• Resource Partitioning- share the wealth by using
  a resource at
• Different times
• In different ways
• In different places
• Fundamental verses Realized
• Niche
• Hawks and Owls
• Lions and Leopards
• Chum and Coho Salmon

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Predator-Prey Relationships

• On the population level predators are beneficial
  to prey
• because the predator
• Reduces the prey population giving remaining
• prey greater access to the available food supply
• Improve the genetic stock of the prey population
• Examples of predator adaptations that maximize
  their
• chances of getting a meal
• Cheetahs-speed
• Eagles
• Wolves and Lions-teamwork
• Snowy Owls

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PREDATION

• Some prey escape their predators or have outer
  protection
• Mimicry
• Deceptive Looks
• Deceptive Behavior
• Warning Coloration
• Camouflaged
• Chemicals warfare to repel predators.

Figure 7-8
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Symbiotic Relationships

• Parasitism- one benefits while the other is
  harmed (host) Usually draws nutrients from the
  host which weakens it, but seldom kills it.
• Some parasites live inside (tapeworm) others
  live outside (fleas and mosquitoes)

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Mutualism Win-Win Relationship

• (a) Oxpeckers (or tickbirds) feed on parasitic
  ticks that infest large, thick-skinned animals
  such as the endangered black rhinoceros.
• (b) A clownfish gains protection
  
• food by living among deadly
• stinging sea anemones and helps
• protect the anemones from some
• of their predators.
• (c) Beneficial effects of mycorrhizal fungi
  attached to roots of juniper seedlings on plant
  growth compared to
• (d) growth of such seedlings in sterilized soil
  without mycorrhizal fungi.

Figure 7-9
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Mutualism-both benefit

• Lichens are a relationship between a
• fungus and an algae. The fungus supplies
  _________ and receives___________ from the algae.
  The algae supplies ____________ and receives
  ___________ from the fungus
• Rhizobium bacteria and the roots of legumes
• Zooanthellae and coral polyps
• Clownfish and sea anemones
• Mycorrhizae fungi and the roots
• of many trees

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Commensalism Using without Harming

• Some species interact in a way that helps one
  species but has little or no effect on the other.

Figure 7-10
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Ecological Succession gradual change in species
composition in a specific area.

• 1. Primary succession establishing life on
  lifeless ground
• Begins where there is no soil in terrestrial
  ecosystems
• no bottom sediment in aquatic ecosystems
• Pioneer species start things off by getting a
  foothold on bare surfaces like rocks. Lichens and
  moss specialize at this.
• They secrete acids which begin to breakdown the
  rock and they trap wind blown soil and bits of
  organic matter.

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Primary Succession Starting from Scratch

• Primary succession begins with an essentially
  lifeless are where there is no soil in a
  terrestrial ecosystem

Figure 7-11
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• Early successional plant species follow.
  Typically these
• Grow close to the ground
• Grow quickly under harsh conditions
• Have short lives
• Ex include small perennial grasses, herbs, or
  ferns
• Mid-successional species follow these which
  include less hardy species of grasses, herbs, and
  low shrubs
• Late successional species are typically those
  that are adapted to the climate and soil type of
  the area and are typically trees

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• Secondary succession-begins in areas where an
  established natural community has been disturbed
• Abandoned farmlands
• Burned or cut forests
• Heavily polluted streams
• Land that has been dammed or flooded

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Secondary Succession Starting Over with Some
Help

• Secondary succession begins in an area where the
  natural community has been disturbed.

Figure 7-12
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Three species interactions involved in succession
1. Facilitation- one species makes an area
suitable for another species with different niche
requirements. Example lichens, legumes N 2.
Inhibition- early species hinder the
establishment and growth of other species.
Example plants that release toxins 3.
Tolerance- late successional stages are
unaffected by earlier successional stages.
Example
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Disturbances and species diversity
Intermediate disturbance hypothesis -
communities that experience fairly
frequent, moderate disturbances have the greatest
species diversity Old View of Succession Orderly
progression of successional stages building
towards a stable community of a few long lived
species known as a ______________
community. Instead, most disturbed communities
result in ever-changing mosaic of vegetation
patches at different successional stages.
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ECOLOGICAL STABILITY AND SUSTAINABILITY

• Living systems maintain some degree of stability
  through constant change in response to
  environmental conditions through
• Inertia (persistence) the ability of a living
  system to resist being disturbed or altered.
• Constancy the ability of a living system to keep
  its numbers within the limits imposed by
  available resources.
• Resilience the ability of a living system to
  bounce back and repair damage after (a not too
  drastic) disturbance.

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ECOLOGICAL STABILITY AND SUSTAINABILITY

• Having many different species appears to increase
  the sustainability of many communities.
• Human activities are disrupting ecosystem
  services that support and sustain all life and
  all economies.

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The Precautionary Principle

• When evidence indicates that our actions may harm
  the environment, even though all the cause and
  effect relationships have not been established
• between our actions and harm to the environment,
  it is better to take precautionary measures to
  prevent harm.
• It is easier to prevent pollution than it is to
  clean it up once the harm of that pollution has
  been established.
• It is easier to protect ecosystems than it is to
  recreate them once they have been destroyed.
• How much time and effort should we put into
  preventing Global Warming
• when we are not even sure of the ultimate effects
  of climate change ?