homogenizing of the world’s flora and fauna
I. Invasive species in general
A. Rule of tens
1. 10% of imported plants escape to become introduced
2. 10% of introduced organisms
(found in the wild, released, but not yet breeding successfully) species become established
(have a self-sustaining natural population)
3. 10% of those established become pests
B. Pattern of establishment and spread of exotic species
1. LAG phase, before growth occurs (small numbers, adaptation).
2. During this lag is the best opportunity for control.
3. Then there is a rapid expansion of range.
4. Expansion decreases when all of the suitable habitat is colonized, or when there are barriers to expansion.
C. Is invasion success predictable?
1. Attributes of invaders – (not universal)
(resting stages, fast reproducers, generalists, related to other
2. Community vulnerability
-‘vacant niches’/community species richness
-escape from biotic constraints
D. Theory predicts that there will be species extinction (based on species-area curves)
E. Deliberate versus accidental invasions
II. Notorious Aquatic Invaders
A. Nutria (Myocastor coypus)
1. Introduced from South America in the 1940's; fur industry
2. Relatively large herbivorous rodent that lives in marsh habitats.
3. Has increased marsh loss along the tidal, emergent marsh habitats.
C. Water Hyacinth, Eichornia
1. Pest to people in many areas of Southern U.S., S. America, and Africa
2. Clogs waterways
3. Increases evapotranspiration
4. Floats into littoral zone and decomposes -- decreases oxygen, hurts fish breeding zones;
5. Blocks light penetration
D. Eurasian watermilfoil (Myriophyllum
1. Accidentally introduced to North America from Europe
2. Can interfere with water recreation.
3. Can also crowd out important native water plants
4. Fragments clinging to boats and trailers can spread the plant from lake to lake.
E. Hydrilla (Hydrilla verticillata)
loosestrife (Lythrum salicaria),
1. Native of Eurasia first introduced into the northeastern U.S. and Canada in the early 1800's for ornamental and medicinal uses
2. Subsequently spread W and S through most of temperate North America.
3. Crowds out native wetlands and vegetation, forming extensive monospecific stands; affects some federally
endangered orchids, and reduces habitat for waterfowl.
4. Alters flow
1. Nile perch (Lates nilatica) - effects on native cichlid fish
2. 1991 study -- 44
species of fish in
the US were endangered by the introduction of non-native fishes.
3. Of the 40 fish species that have gone extinct since 1890, 27 were negatively affected by the introduction of non-native
fishes [Wilcove and Bean 1994])
B. Mysis in Flathead Lake (Spencer et al. 1991)
IV. Invasions in the Laurentian Great Lakes
A. Importance of the Great Lakes
20% of the freshwater in the world
important fishery, historically a commercial fishery, now more important sport fishery
lots of shipping
B. Historically many intentional fish introductions
C. Unintentional introductions -- Spread via canals and shipping
example – Sea Lamprey, Petromyzon marinus
1. First found in Lake Ontario in 1835, and then spread after the extension of shipping channels to the other
2. Parasite that attaches to deepwater fish, especially lake trout and chubs.
3. Lake trout, burbot and whitefish populations were devastated by lamprey predation by the early 1940s.
4. Today the lampreys are less abundant in the Great Lakes, but this is only due to expensive continued control
D. Unintentional transport by ballast water
1. European ruffe
Are we turning the Great Lake into the Caspian
1. Zebra mussel Dreissena polymorpha
a. Filter much of the algae out of the lake, leaving less food for zooplankton, and potentially for fish
b. Clear the water by reducing phytoplankton abundance, and transfer energy to the benthos
c. Have harmed many native clams and crustaceans by settling on them and covering them
d. Large cleanup costs at water intakes for industry and drinking water
2. Goby, Neogobius melanostomus,
a. Presumably introduced via ballast water
b. Spread to lakes Erie, Michigan and Superior and to many rivers including the Mississippi watershed.
c. This fish is an aggressive, voracious feeder and takes over spawning sites used by native species.
3. Spiny waterflea, Bythotrephes cederstroemi
a. Not much known in its native habitat
b. Like Mysis, but unlike most invertebrate predators, it eats large zooplankton; responsible for local extinction of two
daphnids in Lake Michigan
d. Competes with juvenile fish
e. Tailspine protects it from predation by small fish
f. Less energy going up the food web because it is more inefficient than are small fish
4. Cercopagis pengoi -- fish hook flea
Native of tropical and subtropical lakes in east Africa, east
Australia, and India was first found
in Texas in 1990
b. Aquaculture introduction? It is suspected that Daphnia lumholzi may have been transported with shipments of Nile perch or tilapia
c. Very spiny
d. Invaded many southern lakes; reached Lake Erie in 2001
7. Bacteria and viruses
a. Ballast is dispersing human pathogens
b. Vibrio cholerae – causes cholera – found in 93% of ships tested
V. Management of invasions
A. Economic costs
Loss in potential economic output
Cost of combating the invasion
Effects to human health – disease, vectors of disease (mosquitoes that carry disease), parasites
US estimate -- $138 billion/year
B. Management of Invasions
1. Preventing entry
3. Maintenance control
-Chemical control – resistance, cost, health hazards for humans and other species
C. What can be done?
Get better at predicting invaders and systems at risk
Cheaper/quicker methods for preventing and controlling invasive species
3. Ultimately a policy question
Publicize to make people aware of the problem
Evaluate the current human dispersal rate compared with historic rate
Determine costs/benefits of preventing/controlling invasions
Unexpected effects of invasions
1. some because animal not well known
2. some because no predators/enemies/disease in the new habitat
3. not coevolved with new prey/ competitors
4. propagated effects through the food web
Need for increased predictability
Importance of overlooked small invaders
Importance of preventing future introductions
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