Chapter 9 - Experiments Flashcards
Crabs + RQ
Why do juvenile crabs have a complex body colour?
Crabs + Hypothesis + Prediction
Hypothesis: The body colouration of juvenile crabs is cryptic on a heterogeneous shell-hash substratePrediction: Juveniles on shell-hash will have higher survival than individuals on a uniform background
Crabs + Methods
Tethered individual juvenile crabs on ceramic tiles in the ocean that were either a uniform white colour or a heterogeneous shell-hash colour
Recorded survival of all individuals over time
Crabs + Results + Conclusion
Only 30% of crabs on white tiles survived
Over 60% of crabs on shell-hash tiles survived
Juvenile body colouration is cryptic on shell-hash substrate and reduces predation risk
Crabs (labs) + RQ
: Can crabs select cryptic shell-hash colour substrate?
Crabs (labs) + Hypothesis + Prediction
Hypothesis: Crabs will move to cryptic backgrounds when they are available
Prediction: Crabs prefer a shell-hash background to one that is uniform in colour, especially when predation risk is high
Crabs (Labs) + Methods
Placed small or large juvenile crabs in an aquarium with two types of tiles: one covered with shell-hash, the other a uniform white colour
Manipulated predation risk for half the crabs by adding water from a tank containing predatory fish
Recorded proportion of crabs on each tile
Crab (Labs) + results + conclusion
Results:
Small crabs always preferred the shell-hash
Large crabs showed no preference when predation risk was low but preferred shell-hash when risk was high
Conclusion:
Crabs can select an appropriate cryptic habitat to minimize detection by predators
Lizards + RQ
How does the presence of predators affect prey behaviour? (Eifler, Eifler, & Harris 2008)
Lizards + Hypothesis + Prediction
Hypothesis: Activity level of prey influences the risk of being killed by a predator
Prediction: Activity level of prey will be lower when predators are present
Lizards + Hypothesis + Prediction
Hypothesis: Activity level of prey influences the risk of being killed by a predator
Prediction: Activity level of prey will be lower when predators are present
Lizards + Methods
Whiptail lizards (Aspidoscelis uniparens) in experimental pens
Added two predator leopard lizards (Gambelia wislizenii) to half the pens
Recorded behaviour of whiptail lizards in each pen
Lizards + Results
Whiptails in predator-present pens were less active
Lizards reduce their activity level when predators are nearby
Elk + RQ + hypothesis + Prediction
Research question: What affects vigilance level of prey? (Laundré 2001)
Hypothesis: Animals will trade off feeding time for vigilance based on the level of risk
Prediction: Vigilance will be higher and feeding time will be lower when predation risk is high
Elk + Methods
Elk (Cervus elaphus)
Quantified vigilance and feeding behaviour of elk living in areas with and without wolf predators
Elk + Results + Conclusion
Females spent more time vigilant and less time feeding in areas with wolves
Male behaviour did not differ
Conclusion:
Females exhibit a vigilance-feeding trade-off due to wolves
Energy Intake + RQ
How often should animals carry food to safety for consumption?
Energy Intake + Hypothesis + Predictions
Large items should be carried to safety more often than small items
As distance to safety increases, carrying behaviour should decline
Energy Intake + Methods
Offered different sized food items (1, 2, or 3 g) at varying distances from the safety of trees (3, 6, 9, or 12 m)
Recorded the proportion of items carried to safe cover
Energy Intake + Results
The proportion of items carried increased with food size and decreased with distance to cover
Food carrying represents a behavioural trade-off between predation risk and feeding efficiency
Killifish + RQ
How does predation risk affect shoaling behaviour in fish?
Killifish + Hypothesis + Prediction
Hypothesis: Sociality reduces predation risk via the dilution effect
Prediction: Fish should prefer to associate with larger rather than smaller groups
Killifish + Methods
High predation risk treatment: diluted killifish skin extract added to tank (simulates predation event)
Control: water added to tank
Recorded shoal size
Killifish + Results + Conclusion
Median shoal size in the high predation risk treatment was ten fish (the maximum shoal size)
Median shoal size in control was two fish
Killifish prefer to associate with other fish when predation risk is high, as predicted by the dilution effect
Frog Eggs Hatching Early - Escape Predators
-50% chance of meeting a snake/wasp during the week it spends encapsulated
- Predators, pathogens, oxygen availability, bad parenting can trigger early hatching (based on environmental cues)
Frog Eggs Hatching + Experiments
-Attached accelerometers to egg clutches and recorded the vibrations when the eggs were attacked - snake vs. wind
- In the lab, they played those vibrations back
- Picked up on the pattern of vibrations over time; rain and wind batter the egg clutches more or less continuously, but snakes have to take a break to chew.
Doves + RQ + Hypothesis + Prediction (1)
Research question 1: Do doves exhibit the group size effect? (Dias 2006)
Hypothesis 1: Vigilance of an individual declines as group size increases
Prediction 1: Individual scan rates will decline as flock size increases
Doves + RQ+ Hypothesis + Prediction (2)
Research question 2: Are doves at the edge of a group exposed to higher predation risk?
Hypothesis 2: Individuals can reduce predation risk by moving to the center of a group
Prediction 2: Individuals at the edge of a flock will have higher vigilance levels than those at the center of a floc
Dove + Methods
Recorded group size
Used focal animal sampling to record bird position in the flock, scan rate, scan duration, and feeding time
Doves + Results + Conclusion
Recorded group size
Used focal animal sampling to record bird position in the flock, scan rate, scan duration, and feeding time
Owls + RQ
Why do prey harass predators? (Pavey & Smyth 1998)
Owls + Hypothesis + Prediction
Hypothesis: Harassment causes predators to move away from an area: the move-on hypothesis
Prediction: After being harassed, predators will move away from an area
Owl + Methods
Observed mobbing of this predator by birds
Noted frequency of owl predation on bird species that mobbed and those that did not mob owl predators
Recorded the response of owls to mobbing
Owl + Results + Methods
Predation on mobbing species was ten times lower than that on non-mobbing species
Mobbing may lead to owl displacement and may reduce predation risk
