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 predators
Predator not being able to choose the
easiest prey
Prey 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. 265:20212026
• 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):649661
• 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
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