The Evolution of Dilution

Andrew Paitsel

Allen Patton

Co-evolutionary Arms Race

• Predator/Prey Survival Adaptions– Faster prey = faster predators– Better eyesight = better camoflauge

• Other Survival Adaptations- Warning calls

- Mobbing behaviors

- Traveling in herds (Dilution Effect)

Questions to Address• What is the Dilution Effect?

• What are the advantages/disadvantages?

• What species has practiced this trait?

• What is the Selfish Herd theory?

• How does it affect the population?

• What other ways do animals behave due to predation?

Dilution Effect

the assumption that everyone has an equal chance of survival while in large groups due to the fact that no individual is being singled out by a predator.

Advantages More eyes watching out for predatorsPredator not being able to choose the

easiest preyPrey species spend more time foraging

instead of scanning for predators

The frequency of scans as a result of relative danger

Bednekoff et al, 1998.

Disadvantages

• More likely to be seen by predators

• More competition over resources

• More competition over mate selection

Examples

Stotting

Stotting

• Alarm signal hypothesis

• Social cohesion hypothesis

• Confusion effect hypothesis

• Pursuit deterrence hypothesis

Disadvantages of Stotting

• Time Cost

• Energy Cost

• Survivorship Cost

The Selfish Herd

• Competition for safer positioning within the herd. – Middle position has overall higher survival

probability that individuals on the outer parts– Increasing your overall fitness at the expense

of others

Future Research

Determine if traveling in herds is a learned or genetic trait

Look into how predators counteract the Dilution Effect

Is stotting a learned or inherited trait

Continue to evolve until someone gets the upper hand

References• Alcock J. 2005. Animal Behavior: An Evolutionary Approach. Sinauer

Associates, Inc. 8:176-199• Bednekoff P.A., Lima S.L. 1998 Re-examining safety in numbers:

interactions between risk dilution and collective detection depend upon predator targeting behaviour. The Royal Society. 265:2021- 2026

• Caro T.M. 1986. The Functions of Stotting in Thomson’s Gazelles: some tests of the predictions. Animal Behaviour. 34(3):663-684

• Caro T.M. 1985. Functions of Stotting. Animal Behaviour. 34(3):649-661

• Cresswell W., Jakobsson S., Kaby U., Lind J., Quinn J.L. 2003. Animal Behaviour. 66:643-648

• Garay J. 2008 Cooperation in defence against a predator. Journal of Theoretical Biology 257:45-51

References Cont.Pictures• http://static.howstuffworks.com/gif/gazelle-body-language-1.jpg• http://www.teameveresttravel.com/main/images/stories//InternationalVa cations/gallery-

africa/Day3/Herds_Maasai_Mara.jpg• http://images.google.com/imgres?imgurl=http://www.travelphotos.in/thumbs/lrg-106-

img_3500_cheetah_brothers.jpg&imgrefurl=http://www.serengeti.in/index.php%3Fcat%3D102&usg=__-6gpONj-zFPa-tqP3oSTLkZk2s0=&h=459&w=400&sz=76&hl=en&start=28&tbnid=ltIijJbwd6BUDM:&tbnh=128&tbnw=112&prev=/images%3Fq%3DCheetah%2Bvs.%2Bherd%26gbv%3D2%26ndsp%3D18%26hl%3Den%26sa%3DN%26start%3D18

• http://images.google.com/imgres?imgurl=http://scienceblogs.com/clock/upload/2006/06/zebra%2520lion.jpeg&imgrefurl=http://scienceblogs.com/clock/2006/06/bio101_lecture_7_physiology_co_1.php&usg=__4u3AfFA8W3wSxJwtO7X3est7kng=&h=323&w=448&sz=102&hl=en&start=2&tbnid=XCMpf2ZkAhcQLM:&tbnh=92&tbnw=127&prev=/images%3Fq%3DZebra%26gbv%3D2%26hl%3Den

• http://images.google.com/imgres?imgurl=http://lh4.ggpht.com/_ntEIaR868hs/RpwQkCU_I0I/AAAAAAAAA3w/nN0Qbe1dr3o/Africa-227.JPG&imgrefurl=http://picasaweb.google.com/lh/photo/O9qg8k9BUkfv5fxiJgZY6g&usg=__qmMBImFnwIvSowsez5V1Ayeaaig=&h=1068&w=1600&sz=11&hl=en&start=3&tbnid=CbmEpymRX0P63M:&tbnh=100&tbnw=150&prev=/images%3Fq%3DWildabeest%2Bherd%26gbv%3D2%26hl%3Den

• http://pro.corbis.com/images/CB012940.jpg?size=572&uid=%7B001FD655-525A-4DFD-8B6A-8C548047F4D5%7D