Chapter 9 - Experiments

Question 1

Crabs + RQ

Answer 1

Why do juvenile crabs have a complex body colour?

Question 2

Crabs + Hypothesis + Prediction

Answer 2

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

Question 3

Crabs + Methods

Answer 3

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

Question 4

Crabs + Results + Conclusion

Answer 4

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

Question 5

Crabs (labs) + RQ

Answer 5

: Can crabs select cryptic shell-hash colour substrate?

Question 6

Crabs (labs) + Hypothesis + Prediction

Answer 6

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

Question 7

Crabs (Labs) + Methods

Answer 7

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

Question 8

Crab (Labs) + results + conclusion

Answer 8

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

Question 9

Lizards + RQ

Answer 9

How does the presence of predators affect prey behaviour? (Eifler, Eifler, & Harris 2008)

Question 10

Lizards + Hypothesis + Prediction

Answer 10

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

Question 11

Lizards + Hypothesis + Prediction

Answer 11

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

Question 12

Lizards + Methods

Answer 12

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

Question 13

Lizards + Results

Answer 13

Whiptails in predator-present pens were less active
Lizards reduce their activity level when predators are nearby

Question 14

Elk + RQ + hypothesis + Prediction

Answer 14

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

Question 15

Elk + Methods

Answer 15

Elk (Cervus elaphus)

Quantified vigilance and feeding behaviour of elk living in areas with and without wolf predators

Question 16

Elk + Results + Conclusion

Answer 16

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

Question 17

Energy Intake + RQ

Answer 17

How often should animals carry food to safety for consumption?

Question 18

Energy Intake + Hypothesis + Predictions

Answer 18

Large items should be carried to safety more often than small items
As distance to safety increases, carrying behaviour should decline

Question 19

Energy Intake + Methods

Answer 19

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

Question 20

Energy Intake + Results

Answer 20

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

Question 21

Killifish + RQ

Answer 21

How does predation risk affect shoaling behaviour in fish?

Question 22

Killifish + Hypothesis + Prediction

Answer 22

Hypothesis: Sociality reduces predation risk via the dilution effect

Prediction: Fish should prefer to associate with larger rather than smaller groups

Question 23

Killifish + Methods

Answer 23

High predation risk treatment: diluted killifish skin extract added to tank (simulates predation event)
Control: water added to tank
Recorded shoal size

Question 24

Killifish + Results + Conclusion

Answer 24

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

Question 25

Frog Eggs Hatching Early - Escape Predators

Answer 25

-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)

Question 26

Frog Eggs Hatching + Experiments

Answer 26

-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.

Question 27

Doves + RQ + Hypothesis + Prediction (1)

Answer 27

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

Question 28

Doves + RQ+ Hypothesis + Prediction (2)

Answer 28

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

Question 29

Dove + Methods

Answer 29

Recorded group size
Used focal animal sampling to record bird position in the flock, scan rate, scan duration, and feeding time

Question 30

Doves + Results + Conclusion

Answer 30

Recorded group size

Used focal animal sampling to record bird position in the flock, scan rate, scan duration, and feeding time

Question 31

Owls + RQ

Answer 31

Why do prey harass predators? (Pavey & Smyth 1998)

Question 31

Owls + Hypothesis + Prediction

Answer 31

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

Question 32

Owl + Methods

Answer 32

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

Question 33

Owl + Results + Methods

Answer 33

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