Download How Many Invasive Species Are There in Texas?

Today: Threats to Biodiversity
Bonuses due... now.
Why are species going extinct?
Fig
55.6
data from Canada
Why are species going extinct?
"Global Biodiversity" Chapman & Hall, World Conservation Monitoring Centre, London, 1992
Why is biodiversity
important?
Areas with increasing plant biodiversity were
less affected by drought.
Fig 55.15
Why are species going extinct?
"Global Biodiversity" Chapman & Hall, World Conservation Monitoring Centre, London, 1992
CB 55.13
Not all habitats are equal
A third to a half of all
old-growth species avoid
younger (<30-year-old)
regrowth.
Ecosystem
Fragmentation
Yellowstone NP
63 mi
54 mi
•466 mi of roads
•950 mi of backcountry trails
•97 trailheads
•287 backcountry campsites
Artificial corridors allow animals to cross
fragmented areas
CB 55.16
CB 55.16
Wildlife corridors help maintain
biodiversity
Fig
55.16
Why are species going extinct?
"Global Biodiversity" Chapman & Hall, World Conservation Monitoring Centre, London, 1992
Invasive species
can disrupt an
ecosystem
CB 55.6
Nile Perch (Lates niloticus)
• Introduced to Lake Victoria in 1954 to
increase fish yield
• Caused extinction of 200+ endemic fish
species through predation, and competition
• Fish caused indirect increased erosion on
land, causing higher nutrient levels in the
lake.
Water Hyacinth (Eichhornia crassipes)
• Introduced as ornamental plant around the world
• Now in 50 countries on 5 continents including US
• In California it replaced the native pennywort
(Hydrocotyle umbellata) which occupies a similar
habitat, leading to a marked decrease in invertebrate
communities
• Limits water transport, reduces oxygen and light
levels in the water
Caulerpa Seaweed (Caulerpa taxifolia)
Slide 37
• Introduced into Mediterranean by Monaco Aquarium in
1984 by dumping aquarium waste into the sea.
• Hardier clone than the tropical species which seemed to
have developed in the aquarium.
• Smothers natural seagrass beds while being toxic to
herbivores.
• By 2000 covered 131km2 in several Mediterranean
countries.
Meinesz A, Belsher T,et al 2001 / Thibaut T, Meinesz A
Zebra mussel (Dreissena polymorpha)
• Spread from its native range in the Baltic
Sea via ballast water
• Spreads in Europe and North America
• Kills native molluscs, changes ecosystems,
and damages infrastructure
• Estimated annual damage in US $3 billion
Napela T.F., Schloesser, D.W., 1992
The brown tree snake
(Boiga irregularis)
• Its native in Australia and was introduced to Guam
accidentally in the 1950’s
• Overall responsible for the extinction of 3 out of 4
seabirds; 9 out of 13 forest birds; 3-5 out 12 reptile
species on the Island of Guam.
• This snake caused the extirpation or serious
reduction of most of the island's 25 resident bird
species on the main island of Guam.
How Many Invasive Species Are There in
Texas?
 67 terrestrial plants
 12 aquatic/wetland plants
 10 mammals
 4 birds
 7 fishes
 11 insects
 11 mollusks and crustaceans
Hydrilla verticillata
Aquatic invader covering nearly 100,000 surface
acres of water in Texas.
Spreads rapidly, in one Texas lake it covered 23 acres
in 1999 but over 200 in 2000.
Depletes water of oxygen and blocks sunlight killing
off many native plants and animal species.
Hydrilla on Longhorn dam over Town Lake
The level of Lake Austin is lowered in winter
to kill the hydrilla and other invasive plants
Why are species going extinct?
"Global Biodiversity" Chapman & Hall, World Conservation Monitoring Centre, London, 1992
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Bonuses due... now.