Community Ecology

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Community Ecology

• Chapter 47

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Community Concept

• A community is an assemblage of populations
  interacting with one another within the same
  environment
• Species composition is a listing of various
  species in the community
• Species diversity includes both species richness
  and species diversity
• Species richness number of species
• Species evenness number of individuals within
  each population

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Community
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Diversity and Composition Models

• Gleason - Individualistic Model
• Each population in community is there because its
  own particular abiotic requirements are met by a
  particular habitat
• Clements - Interactive Model
• Community is the highest level of organization
• Dependent on biotic interactions

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Species Richness of Communities
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Island Biogeography

• MacArthur and Wilson
• Developed a general model of island biogeography
• Explains and predicts how community diversity of
  an island is affected by
• Distance from the mainland
• Size of an island

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Model of Island Biogeography
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Community Structure

• Competition
• When two species compete for limited resources
  the abundance of both species is negatively
  impacted
• Predation (or parasitism)
• Expected to increase the abundance of the
  predator (or parasite)
• And reduce the abundance of the prey and its host

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Habitat and Ecological Niche

• Habitat
• The area an organism lives and reproduces in
• Ecological niche
• The role an organism plays in its community,
  including
• its habitat
• its interactions with other organisms
• Fundamental niche - All conditions under which
  the organism can survive
• Realized niche - Set of conditions under which it
  exists in nature

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Feeding Niches for Wading Birds
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Competition Between Populations

• Interspecific competition
• When members of different species try to utilize
  same resource
• Resource in limited supply
• Competitive Exclusion Principle
• No two species can occupy the same niche at the
  same time
• Resource Partitioning decreases competition
• Can lead to character displacement

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Competition between populations
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Character Displacement
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Niche Specialization
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Competition Between Species
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Predator-Prey Interactions

• Predation
• One living organism, the predator, feeds on
  another, the prey
• Predator is larger
• Predator has lower reproductive rate
• Prey usually entirely consumed
• Presence of predators can decrease prey
  densities, and vice-versa

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Paramecium caudatum and Didinium nasutum
interaction
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Lynx-Snowshoe Hare Interactions
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Prey Defenses

• Prey defenses are mechanisms that thwart the
  possibility of being eaten by a predator
• Spines
• Tough Epidermis
• Poisonous Chemicals
• Camouflage
• Bright Coloration
• Flocking Behavior

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Camouflage in the Anglerfish
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mperor
http//www.gotpetsonline.com/pictures-gallery/exot
ic-pictures-breeders-babies/hedgehog-pictures-bree
ders-babies/pictures/hedgehog-0009.jpg
http//animal.discovery.com/guides/reptiles/iguana
s/beardeddragon.html
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Mimicry

• Mimicry occurs when one species resembles another
  that possesses an overt antipredator defense
• Batesian - Mimic lacks defense of the organism it
  resembles
• Müllerian - Mimic shares same protective defense

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Batesian Mimicry
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Müllerian Mimicry
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Symbiotic Relationships

• Symbiosis refers to interactions in which there
  is a close relationship between members of two
  populations
• Parasitism
• Parasite derives nourishment from a host, and may
  use host as habitat and mode of transmission
• Endoparasites
• Ectoparasites

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Endoparasites
http//www.bbc.co.uk/schools/gcsebitesize/biology/
livingthingsenvironment/0habitatsandpopsrev7.shtml
www.drnatura.com/parasites.php
www.drnatura.com/parasites.php
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Ectoparasites
www.springlodgevet.co.uk/illexternal.html
www.biology.utah.edu/bionews/louse384.jpg
www.bigpawsonly.com/dog-ticks-health.htm
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Life Cycle of a Deer Tick
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Commensalism

• Commensalism is a symbiotic relationship in which
  one species is benefited and the other is neither
  benefited nor harmed
• Remoras and Sharks
• Many examples may turn out to be mutualism or
  parasitism
• Amount of harm or benefit two species do to one
  another is partially determined by the
  investigator

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Clownfish AmongSea Anemones Tentacles
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Mutualism

• Mutualism is a symbiotic relationship in which
  both members of the association benefit
• Often help organisms obtain food or avoid
  predation
• Bacteria in human intestinal tract
• Need not be equally beneficial to both species
• Cleaning Symbiosis

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Mutualism Between Bullhorn Acacia and Ants
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Cleaning Symbiosis
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Community Development

• Ecological Succession
• A change involving a series of species
  replacements in a community following a
  disturbance
• Primary Succession occurs in areas where there is
  no soil formation
• Secondary Succession begins in areas where soil
  is present
• Pioneer Species

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Secondary Succession in a Forest
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Succession Models

• Facilitation Model
• Each stage facilitates invasion and replacement
  by organisms of the next stage
• Climax Community
• Succession in a particular area will always lead
  to the same type of community

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Succession Models

• Inhibition Model
• Colonists hold onto their space and inhibit
  growth of other plants until the colonists are
  damaged or die
• Tolerance Model
• Different types of plants can colonize an area
  at the same time
• Chance determine which seeds arrive first

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Community Diversity

• Community stability can be recognized in three
  ways
• Persistence through time
• Resistance to change
• Recovery once a disturbance has occurred

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Intermediate Disturbance Hypothesis

• Moderate amounts of disturbances at moderate
  frequency are required for a high degree of
  community diversity
• If widespread disturbances occur frequently,
  diversity will be limited

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Intermediate Disturbance Hypothesis
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Predation, Competition, and Biodiversity

• In certain communities, predation by a particular
  species reduces competition and increases
  diversity
• Predators that regulate competition and maintain
  community diversity are referred to as keystone
  predators
• Introduction of exotic species into a new area
  may lead to unbridled competition and resultant
  reduction in biodiversity

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