Invasives II

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Transcript Invasives II

Invasive Species
• relocation of organisms across geographical
boundaries occurs naturally by various means.
• Since humans began exploring the globe, however,
the rate of new species being introduced into regions
has greatly increased.
• humans have dispersed species on purpose;
– plants transported from Europe to North America for
agricultural and ornamental purposes
• Others were transported accidentally by ship, train,
airplane - even on the shoes of hikers.
Local Examples
Asian shore crab, Hemigrapsus
Pathway: introduced from Asia
to eastern seaboard most
likely by ballast water;
reported in Long Island Sound in
Current Distribution: Maine to
North Carolina; prefers rocky
Impact: dominant rocky
intertidal crab; consumes
juvenile mussels and oysters,
green crabs, snails,
polychaetes, algae, hydroids,
Green crab, Carcinus maenas
Omnivore - consumes barnacles,
clams, hermit crabs, worms, algae,
organic debris
Pathway: introduced by end of 18th
century from Europe, probably via
ship hulls; reported in LIS in 1817.
Current Distribution: Gulf of St.
Lawrence to Delaware; lives on
rocky shores, quiet backwaters,
marshes, estuaries, brackish waters
or coastal waters
Impact: voracious predator and
scavenger; consumes juvenile
shellfish (may have caused decline
of softshell clam industry in Maine
and even Long Island Sound);
competes with native crabs.
Mute swan, Cygnus olor
Pathway: Introduced from Europe as
decorative waterfowl in late 1800s
or early 1900s
Current Distribution: southern
Ontario to North Carolina or
Florida; reported in LIS by 1920s
Impact: using long necks, the swans
graze on vegetation by ripping
important submerged aquatic
vegetation such as eelgrass out by
the roots, damaging marsh and
shallow water habitats;
overpopulated, displacing native
Invasive Species
• Some introduced species are not able to
survive in their new habitat.
• Others may find optimal conditions for
growing, reproducing, and adapting to the
new environment, and their populations soar.
– lack of predators
– ability to outcompete other species (for ex, by
surviving and growing on fewer resources)
– Alter ecosystem function and services
• "invasive", "exotic", "introduced“, “nonnative”,
• Introduced species that have profound effects
on their new ecosystems have been termed
invasive species.
• These effects include outcompeting native
species, sometimes causing their extinction,
and altering ecosystem functioning upon
which we depend!
Growth of invaders in a new range
Log phase
Lag phase
• Phases of proliferation and spread
• Lag phase makes early detection difficult
• Often no lag phase
Invasive Species –Why such a problem?
• Very hard to predict
• Difficult to identify common characteristics shared
among invasive species
• Difficult to ID characteristics among invaded
• Above problems could be partly solved if we knew
more about EARLY STAGES of invasions
• Control sometimes feasible, often costly
• Are often hard/impossible to eradicate
Community Vulnerability to Invasion
• Current hypotheses:
– Vacant niches
– Escape from biotic constraints
– Community species richness
– Disturbance before or upon immigration
Zebra Mussels
• Dressena polymorpha
• widely known example of an
aquatic invader in the U.S.
• native to southern Russia,
introduced to the Great
Lakes in 1985 or 1986 via
ballast water
• now exist in many aquatic
systems in the eastern US
and expected to invade
freshwaters throughout the
nation in about 20 years
• Progression: USGS link
Effects of Zebra Mussels
• filter feeds unusually large amounts of phytoplankton
• outcompetes other filter feeders (esp. zooplankton, an
important food for fish)
• can reach densities of up to 700,000 individuals/m2.
• smothers clams, native mussels and snails,
• clogs water intake and exit pipes for facilities such as
electric generating plants.
• annual damage for U.S. utilities at about $100 million
Why are zebra mussels succesful?
• Lack of predators and parasites
• Availability of space; attach to hard substrates with
byssal threads (pipes, boat hulls and motors, trailers,
docks, anchors, and rocky beaches)
Why are zebra mussels succesful?
• free-swimming veliger larva can disperse widely
• Females are also extremely fecund (huge release of
eggs; spawning events several times a year).
• Have a relatively long lifespan for an invertebrate (25 y)
• early sexual maturity (can be within 1 year)
• eggs and sperm viable for several or more hours
• dispersal of all life stages
• tolerance of some salinity
Figure 2A. Changes in
populations of animals that
are thought to depend on
phytoplankton for food in
response to the arrival of
zebra mussels in the
Hudson River.
(a) Macroplankton are
microscopic floating
animals that are visible to
the eye;
(b) Unionids are clams
(c) Shaeriids are clams.
The dashed line shows the
point at which the zebra
mussel became abundant.
Data are yearly averages at one
station during June-August;
Strayer, et al. 1999
Figure 2B. Changes in
concentrations of edible and
inedible particles in water in
response to the arrival of zebra
mussels in the Hudson River.
(a) phytoplankton; measurement is
concentration of the pigment
chlorophyll a
(b) biomass of microscopic
zooplankton (tiny floating
(c) solids suspended in the water,
units are milligrams per liter.
The dashed line show the point at
which the zebra mussel became
Data are yearly averages at one
station during June-August.
Unusually heavy summer rains
happened in 1996
(Strayer etal. 1999)
Figure 2C. Key variables in the
Hudson River ecosystem.
(a) freshwater discharge; units are
cubic meters per second. (b)
water temperature
(c) estimated filtration rate of zebra
mussels (grey bars) and all other
filter feeding animals (white bars)
averaged for the river.
The dashed line shows the point at
which the zebra mussel became
Data are yearly averages at one
station during June-August.
(Strayer et al. 1999)