Download Invasive Exotics

Ch. 10
Invasive Exotics
Species & geography
• May be iconic
• Ranges shift, but limited by barriers
• major or seemingly minor ~ mountains or soil pH
• short or enduring
• For a population to become distinct enough from others to be
considered a new species, there must be some type of
isolation.
Isolation
• Filters migrants out
• Keeps new alleles in
• Different environments, different selective pressures
• evolution of distinct populations or new species
• Diminishing worldwide
• humans inadvertently move other species
Terms to know
• Exotic ~ a species living outside of its native range
• Invasive ~ species that once in an ecosystem cause problems,
either ecological, economic, or in human-health
• native species can be invasive too
• Invasive exotics
People Move Species Accidently
People Move Species Purposefully
• Subsistence ~ familiar foods, timber
• feral ~ escaped domestics established in wild
• Commerce ~ boost fisheries, fur trapping
People Move Species Purposefully
• Recreation ~ fishing, hunting
• Whimsy
• acclimatization societies formed by colonists in
the late 19th century.
• Aesthetics
People Move Species Purposefully
• Science ~ breeding colonies and experimental populations
• Biological control ~ use of a species natural competitors to
control its population
• when a species is introduced to a new area its predators,
pathogens, or whatever interactions regulated its population are
often left behind -> big populations
• if an exotic is out of control, introduce it’s competitor to control it
• works occasionally, but not always
Anthropogenic Changes
Facilitate Species Movement
• Species can take advantage of changes people make to the
environment to move themselves
• canals
• deforestation
Impacts of Invasive Exotics
• May be relatively minor if ecosystem already dominated by
humans
• Affect 1/3 of listed species in the US
• Cost billions of dollars
Predators and Grazers
• Stephen Island wren, extinct because of a single cat
• Introduced brown snakes kill island birds and lizards
• 200 fish spp. extirpated after Nile perch introduced to lake
Victoria
• Agricultural pests
• Generalist herbivores ~ island plant species have no defenses
against grazers; population declines of primary producers
affect the rest of the food web
Competitors
• Invasive exotics often outcompete native species
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space
food
nesting sites
nectar and pollen
Hybridization
• Breeding between subspecies, or occasion different species
• causes decline in native species or populations
• Gene flow between domestics and their wild relatives
• Genetic swamping ~ genes of one species or subspecies
dominate the gene pool, reduces diversity
Ecosystem Effects
• New predator/competitor/pathogen
• Changes in productivity, nutrient cycling, disturbance regimes,
habitat composition and structure
What makes a successful invader?
• Number of individuals introduced
• Being introduced to an island
• more available niches
• resident species not used to competitors/predators
• Being introduced to a disturbed ecosystem
• Having evolved with humans ~ more adopted to human
disturbances
Discussion Qs
• Some exotics encouraged, others condemned. Why?
• What about exotics that support native species?
• What about exotics that fill the niche of extirpated/extinct
local species?
• What about species, like horses, that were extirpated from an
area by humans, and then reintroduced?
• What about hidden exotics, species we assume are native, but
were introduced a very long time ago?