Community Ecology

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Community Ecology
CHAPTER 5

• Structure
• Species Interaction
• Succession Sustainability

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Key Concepts

• Community structure

• Roles of species

• Species interactions

• Changes in ecosystems

• Stability of ecosystems

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CASE STUDY FLYING FOXES

• fruit-eating bats
• pollinate flowers from Durian trees
• ? prized fruit in SE Asia
• ? strong odor, custard-like delicious fruit
• mutualism (durian flying fox)
• referred to as keystone species
• ? pollinate plant species
• ? disperse plant seeds in dropping
  (biodiversity)

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COMMUNITY STRUCTURE
OBJ 8.1

• CHARACTERISTICS
• Physical Appearance
• - stratification, relative size, distribution
• Species Diversity
• - richness vs. eveness
• Niche Structure
• - ecological Roles of Species

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Community Structure Appearance and Species
Diversity

• Stratification

Fig. 8-2p. 144
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SPECIES DIVERSITY
Species richness different species Species
evenness abundance within each of its species
Sample A could be described as being the more
diverse as it contains three species to sample
B's two. But there is less chance in sample B
than in sample A that two randomly chosen
individuals will be of the same species.
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Three Factors Affecting Biodiversity

• Latitude(terrestial)- the closer to the equator,
  the higher the biodiversity
• Highest species diversity in tropics lowest in
  polar regions
• Depth(aquatic)- biodiversity increases with depth
  to _at_ 2000 m then begins its decrease
• Pollution- as levels increase, biodiversity
  decreases

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Figure 8-4 Page 145
Number of individuals per diatom species
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Island Biodiversity

• Theory of Island Biogeography-the number of
  species found on an island is determined by
• Species immigration
• Immigration- movement of organisms into a place
• Emigration- movement of organisms out of a place
• Species extinction

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Island Species
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General Types of Organisms
OBJ 8.2

• Native-organisms that are naturally found in an
  ecosystem
• Nonnative (Exotic/ Invasive/Alien)- any organism
  that is not found naturally in an ecosystem
  usually transported in by humans
• Indicator- organisms that serve as early warnings
  of damage to a community
• Keystone- organisms whose role in more important
  than their numbers or biomass
• Strong interactions with other species affect the
  life of others
• Process out materials out of proportion to their
  numbers or biomass

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Competition
OBJ 8.3

• CompetitionTwo organisms compete to obtain the
  same limited resource, and both are harmed to
  some extinct.
• IntraspecificMembers of same species competing
  for resources.
• InterspecificMembers of different species
  competing for resources.
• The more similar the competing species, the more
  intense the competition.

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Competition
OBJ 8.4

• Competitive Exclusion PrincipleNo two species
  can occupy the same ecological niche in the same
  place at the same time.
• Less fit species must evolve into a slightly
  different niche.

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Resource Partitioning
OBJ 8.5
Overlapping Niche of 2 species creates
competition
Over time, species evolve and become specialized
Fig. 8-7 p. 150
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Kinds of Organism Interactions

• PredationOne animal kills/eats another.
• Predator benefits from food.
• Prey adaptation is manifested in a higher
  reproduction rate.
• Prey species benefits by eliminating non-adaptive
  genes from the gene pool.
• Poorly adapted predators are less likely to
  obtain food and thus pass on non-adaptive genes.

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PREY DEFENSE MECHANISMS

• adaptation the prey uses adds to the chances of
  survival for the species
• Examples of some defense mechanisms prey use
  are? Chemical combat
• ? Camouflage
• ? Speed
• ? Trickery false features and mimicry

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Symbiotic Relationships
OBJ 8.7

• SymbiosisClose, physical relationship between
  two different species. At least one species
  derives benefit from the interaction.
• ParasitismOne organism (parasite) living in or
  on another organism (host), from which it derives
  nourishment.
• EctoparasitesLive on hosts surface.
• Fleas
• EndoparasitesLive inside host.
• Tapeworms

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Symbiotic Relationships

• CommensalismOne organism benefits, while the
  other is unaffected.
• Remoras and Sharks
• MutualismBoth species benefit. Obligatory in
  many cases as neither can exist without the
  other.
• Mycorrhizae

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WHAT IS HAPPENING?
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Succession

• SuccessionA series of regular, predictable
  changes in the structure of a community over
  time.
• Activities of organisms change their surroundings
  and make the environment suitable for other kinds
  of organisms.
• Climax communityStable, long-lasting community,
  primarily determined by climate.

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Succession
OBJ 8.8

• Primary SuccessionBegins with bare mineral
  surfaces or water and total lack of organisms.
• Secondary SuccessionBegins with disturbance of
  an existing ecosystem.
• Much more commonly observed.

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Primary Succession

• Terrestrial Primary Succession
• Pioneer Community Collection of organisms able
  to colonize bare rock
• (i.e. lichens, mosses).
• Lichens help break down rock, and accumulate
  debris helping to form a thin soil layer.
• Soil layer begins to support small life forms.

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Terrestrial Primary Succession

• Lichen community replaced by annual plants.
• Annuals replaced by perennial community.
• Perennial community replaced by shrubs.
• Shrubs replaced by shade intolerant trees.
• Shade intolerant trees replaced by shade tolerant
  trees.
• Stable, climax community often reached.
• Successional (seral) StageEach step in the
  process.

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Terrestrial Primary Succession
OBJ 8.9
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Climax Community Characteristics

• Maintain species diversity for extended period.
• Multiple specialized ecological niches.
• High level of organism interactions.
• Nutrients recycled and biomass levels remain
  constant.

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Aquatic Primary Succession

• Except for oceans, most aquatic systems are
  considered temporary.
• All aquatic systems receive inputs of soil
  particles and organic matter from surrounding
  land.
• Gradual filling of shallow bodies of water.
• Roots and stems below water accumulate more
  material.
• Wet soil established.

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Aquatic Primary Succession
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Secondary Succession

• Occurs when an existing community is disturbed or
  destroyed.
• With most disturbances, most of the soil remains,
  and many nutrients necessary for plant growth may
  be available for reestablishment of the previous
  ecosystem.
• Nearby undamaged communities can serve as sources
  of seeds and animals.
• Tends to be more rapid than primary growth.

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Terrestrial Secondary Succession
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Modern Concepts of Succession and Climax

• As settlers changed original ecosystems to
  agriculture, climax communities were destroyed.
• Many farms were abandoned, and land began to
  experience succession.
• Ecologists began to recognize there was not a
  fixed, pre-determined community.
• Only thing differentiating climax community from
  successional community is time scale.