Community Ecology

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Community Ecology

• The Affect of Invasive Species on Communities

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Vocabulary

• Introduced
• Alien
• Exotic
• Invasive Species

• Native Species
• Indigenous

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Introduced Species

• Transients founders and descendants are
  extirpated
• Casual or infrequent population becomes
  naturalized (established) but not prolific or
  widespread
• Invasive naturalized population persists and
  increases rapidly

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Definitions of Invasive Species

• Non-native (or alien) to the ecosystem under
  consideration
• Whose introduction causes or is likely to cause
  economic or environmental harm or harm to human
  health.
• Executive Order 13112

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Defining Invasive Species

• Not all introduced species become invasive
• Native species can also become invasive if
  ecosystem dynamics are sufficiently altered

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Invasive species are defined in ecological time

• Equated to the successional processes 1-500 years
• Botanical definition of native species are those
  that were present in North America in
  pre-colonial times (1-500 years ago)

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• Metasequoia (Dawn Redwood)
• Katsura tree
• China fir
• Eucommia (hardy rubber trees)
• Phellodendron (Amur cork tree)
• Japanese umbrella pine

Many of the genera now considered exotic in
North America were once part of the normal flora
of the North American continent. According to the
Flora of North America, (they) were in North
America millions of years ago and then died out.
American Nurseryman September 1996
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The author was objecting to new state regulations
that limit plantings to solely native species
The most dramatic result in such limitations
would be that hundredsif not a few
thousandnurseries would go out of business.
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Studying Invasive Species

• Predicting the course, character, and locations
  of future plant invasions
• Early detection combined with a knowledge of its
  attributes and limitations maximizes control
  efforts
• Scientists get to study contemporary
  evolutionary, ecological, and genetic processes

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Invasive Species Biology

• The Invader factors that promote invasiveness
• The Habitat characteristics of invadible
  habitats
• Invasion Dynamics how invasion takes place

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What makes a species invasive?

• Life History Traits the traits that affect an
  organisms schedule of reproduction, survival,
  and death
• Life form (herbaceous, woody, larval, mature)
• Dispersal (plants), Migration (animals)
• Reproductive regime
• Age at first reproduction
• of offspring
• Investment in parental care

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Factors that Promote Invasiveness in Plants

• Herbaceous
• Reproduce sexually and asexually (clonal)
• Rapid Reproduction growth from seedling to
  sexual maturity
• Dispersed by wind or water
• Tolerance to broad environmental conditions

Weeds
Clonal Trees
Grasses
Aquatic vegetation
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Life History Traits of Invasive Species

• Plants that invade disturbed habitats are called
  disturbance colonizers
• (ex Agricultural land)
• Reproduce sexually and asexually
• Rapid growth from seedling to sexual maturity
• Tolerance to changes in environmental conditions

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Life History Traits of Invasive Species

• Plant species that invade established communities
  are
• Primarily aquatic or semi-aquatic
• Grasses
• Nitrogen fixers (Legumes)
• Climbers (vines)
• Clonal trees (asexual reproduction)

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Eurasian Milfoil

• Aquatic plant native to Europe, Asia, Northern
  Africa
• Introduced in the 1940s
• Sexual and clonal reproduction
• Rapid time to maturity
• Ecological consequences blocks light from
  reaching other aquatic species in the shallow
  waters

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Life History Traits of Invasive Birds

• Dispersal ability
• Migratory vs. resident
• Large clutch size
• More than one clutch per season
• Compete well with native species for resources
• Repeated introductions
• Association with humans

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Invasive Fresh-water Fish

• Tolerance to broad range of environmental
  conditions
• Rapid dispersal
• Aggressive behavior
• Good competitors
• Desirability to humans

Northern Snakehead
Grass Carp
European Carp
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• At all life stages will compete for food and
  habitat with native and sport fish
• Adults are voracious predators, feed on other
  fish, crustaceans, frogs, reptiles, birds and
  small mammals
• Can survive underneath ice, northern snakeheads
  are present in Siberia and would be able to
  survive in Northern NA climates
• Can tolerate hypoxic conditions they are air
  breathers from late juvenile stage
• The use of pesticides to control or eradicate
  populations would likely be ineffective because
  of their ability to air breath and move across
  land

Northern Snakehead
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Invasive Mammals

• We know much less
• about mammals
• Introduction to an ecological vacuum
• Mammals have been very successful when introduced
  to islands
• Nutria

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Characteristics of Invadible Habitats

• Habitats with lowered biotic resistance
• Disturbed areas
• Agricultural land
• Overgrazed grassland
• New developments
• Urban areas

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• Communities of undefended prey
• Native species lose defenses against threats that
  are not present
• Islands (Hawaii)
• Habitats without an invaders specialized natural
  enemies
• Predators, pathogens, specialized herbivores
• Habitats with established invaders that
  facilitate new invasions
• Pigs and strawberry guava trees in Hawaii

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Introduced early 19th century

• Strawberry guava forms shade-casting thickets
  with dense mats of surface feeder roots that make
  it difficult for other species to coexist.
• Characteristics that promote strawberry guava's
  success as an invader include
• prolific fruiting and aggressive vegetative
  growth,
• its tolerance of shade and heavy leaf litter, and
  
• production of toxic chemicals in its leaves that
  prevent the growth of other plant species.

Introduced in 1778
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The Process of Invasion

• Introduction (can we control introductions?)
• Initial colonization (is habitat available?)
• Establishment (effect on community and ecosystem)
• Secondary spread/dispersal (becoming invasive)

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The Tens Rule

• The proportion of exotics that cause serious harm
  is estimated by the
• Tens Rule
• 10 of introduced exotics will be successful in
  becoming established
• 10 of established exotics will become invasive

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The Process of Invasion

• The process of
• invasion mimics
• logistic population
• growth
• Lag phase
• Log phase
• Stationary phase

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Kochia scoparia
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Whats Happening During the Lag Phase?

• Natural selection produces new genotypes
• Altering community relationships
• Habitat alteration fire regime, hydrology

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Ecological Consequences of Invasion

• Generalized Supercompetition
• Niche Usurpation
• Generalized Superexploitation
• Specialized Superexploitation
• Mutualisms
• Habitat modification

changes the food web
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Generalized Supercompetition

• Changes how organisms compete for resources,
  completely displacing native species in the
  process
• Alters one layer of the food web
• Supercompetition leads to ecological degradation
  and population loss
• Ex Purple Loosestrife

Native of Europe
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Natural Herbivores of Purple Loosestrife

• Foliage and root eating insects
• A root-mining weevil
• Flower feeding weevil
• Two leaf-eating beetles

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Generalized Super Competition

• The Competitive ability of purple
• loosestrife is directly related to its life
  history
• characteristics
• Very high reproductive success
• One plant can produce over 2 million seeds
  annually
• Dispersed in water and mud
• adhered to aquatic wildlife, livestock, vehicles,
  and people

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• Competitive ability of Loosestrife in non-native
  habitats
• Compared biomass of Purple Loosestrife in native
  and non-native habitats
• Purple Loosestrife biomass was greater in
  non-native habitat
• Can reallocate biomass usually used for defense
  to reproduction and growth

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Effects of Purple Loosestrife on The Food Web and
Bird Nesting Success

• Limits prey abundance
• 120 insects species in Europe
• 12 insect species in Manitoba, Canada
• Elevated predation rates of nestlings
• Change in the plant community render nests more
  susceptible to predation
• Redwing Blackbirds 6 less breeding success when
  nesting in Loosestrife vs cattails
• Nest later in Loosestrife vs cattails
• Marsh wrens never nested in Loosestrife

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Generalized Superexploitation

• Exploitation of food web, consumption of the
  primary producers, the lower end of the food web
• Superexploitation leads to extinction of species
  or groups of species
• Example Zebra mussels

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Zebra Mussels

• Native to Caspian and Black Seas (Eurasia)
• Entered Great Lakes in 1988
• Female lays 1 million eggs
• Juveniles (veligers) can disperse great distances
  by currents and boats
• Colonies of adults attain population densities of
  700,000 ind/meter

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Zebra Mussels

• Ecological impacts
• Consume large amounts of phytoplankton
• Attach to native mussels impeding their movement,
  feeding, and respiration

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Food Chain in a Fresh Water Lake
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Sea lamprey
Pacific Salmon
Lake trout
Smelt
Minnows
Alewife, smelt, ruffle, gobies
Zebra mussel
Zooplankton Spiny water flea
Phytoplankton