Natural Selection in Action:
Tadpoles vs. Crayfish
Invasive Species
• What is an invasive species?
– A species that is non-native to the ecosystem (not
originally found there)
– Presence is likely to cause environmental or
economic harm
– Can be plants, animals, microbes
– Usually introduced to an area by humans (on
purpose and accidentally)
Invasive Species
• Examples: Arundo donax – giant reed
– Found in riparian (stream) habitats
– Invasive in southern California
– Displaces native plants and provides poor habitat for
insects and wildlife
– Fire and flood hazard
Invasive Species
• Examples: Argentine Ant (Linepithema humile)
– Native to Argentina, invasive worldwide, also in southern
CA (these are the ants you see in your house)
– Displaces native ants or causes local extinctions
– In southern CA, responsible for decline of native ants
which are sole food source of CA horned lizard
Invasive Species
• Examples: Zebra mussel (Dreissena
polymorpha)
• Native to Russia, introduced worldwide
• Change natural food webs
• Huge economic impact – clog pipes, cover boats
Invader: Red swamp crayfish
(Procambarus clarkii )
• Invasive in southern California streams
• Introduced by humans worldwide for aquaculture
(eating), accidentally as bait or with fish stock
• Will eat almost anything, including amphibians (eggs,
Crayfish have invaded the
Santa Monica Mountains
Prey: Pacific treefrog tadpoles
(Pseudacris regilla)
• Native range from Mexico to British Columbia,
Pacific coast to Montana, Nevada
• Found in streams with and without crayfish in the
Santa Monica Mountains but show reduced
abundance in the presence of crayfish
Predator Escape
• What traits might help a tadpole escape
from a crayfish?
My Research
• Predation is a strong form of natural
selection
• Are crayfish causing tadpoles to
evolve?
McCollum and Leimberger 1997
My Research
• I am examining tadpoles from streams
with and without crayfish and looking at
anti-predator traits
• I will compare morphology, behavior,
and ability to survive with crayfish
My Research
• Tadpoles from streams with crayfish
may show these adaptations:
– Longer tails or bigger tail muscles
– Behavioral response of hiding and
swimming less when crayfish are present
– Increased survival in the presence of
crayfish
Credits
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Slide 1: http://www.freewebs.com/siganurme/seapea.htm and http://giraffian.com/pictionaryfiles/t/tadpole.png
Slide 3: http://thegreencuttingboard.blogspot.com/Arundo-donax.jpg and
http://members.tripod.com/~Hatch_L/arundodonaxvar.jpg
Slide 4: http://www.issg.org/database/species/ecology.asp?si=127&fr=1&sts=&lang=EN and
http://news.illinois.edu/WebsandThumbs/Suarez,Andrew/argentine_ants_b.jpg and
http://i.livescience.com/images/060914_ant_fight_02.jpg
Slide 5: http://www.issg.org/database/species/ecology.asp?si=50&fr=1&sts=&lang=EN and
http://conservationreport.files.wordpress.com/2008/11/zebra-mussel-not-wanted-poster.jpg and
http://upload.wikimedia.org/wikipedia/commons/0/0b/Zebra_mussel_GLERL_3.jpg
Slide 6: http://nas.er.usgs.gov/taxgroup/Crustaceans/maps/pr_clarkii.gif andhttp://naturaljapan.net/photos/Procambarus_clarkii_04.jpg
Slide 7: Images from Katherine Pease
Slide 8: http://www.iucnredlist.org/details/55897/0 and images from Katherine Pease
Slides 9 and 11: Images from Katherine Pease
Slide 10: Image from McCollum and Leimberger (1997) Oecologia
Slide 12: http://www.mister-toad.com/PacificTreeFrog.html