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APES Chapter 8


COMMUNITY ECOLOGY APES Chapter 8 8-1 COMMUNITY STRUCTURE AND SPECIES DIVERSITY Ecologist use 3 characteristics to describe a biological community. – PowerPoint PPT presentation

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Title: APES Chapter 8

Community Ecology
  • APES Chapter 8

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
  • Niche structure- the number of ecological niches,
    similarities/differences, and interaction of
    species with each other.

Species Equilibrium model (Theory of island
  • 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)

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
  • Birds are good indicators because
  • Trout and macro-invertebrates are good indicators
  • Amphibians indicate

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

ExamPles of Keystone species
Foundation Species
  • A species that shapes communities by creating
    and enhancing habitat for other species
  • Elephant tearing down tree

5 Types of Species Interactions
  • 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
    SPECIALIZATION (owls/hawks)

Warblers and resource partitioning
Niche Specialization
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)

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

  • 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

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

  • 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

  • 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

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

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

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
  • 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

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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

  • 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

Ecological Stability and Sustainability
  • 3 aspects that lead to stability of a living
  • 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.

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)
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