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, tadpoles)

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• Slide 1: http://www.freewebs.com/siganurme/seapea.htm and

http://giraffian.com/pictionary-files/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://natural-japan.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