Chapter 9 Flashcards
Research 9.1: Predator Avoidance by Cryptic Colouration in Crabs
a) They live and feed on the benthic substrate or bottom of marine coastal habitats, where they’re often eaten
b) Bottom habitat is a uniform sandy colour due to small shell fragments, shell-hash
c) As juveniles grow, their body colour changes to a more uniform light purple
d) Juveniles experience higher predation than adults
CRABS & PREDATOR AVOIDANCE: Hypothesis
Complex colouration is an adaptation to minimize detection by predators
CRABS & PREDATOR AVOIDANCE: Methods
a) They tethered individual juvenile crabs to ceramic tiles of different colours
b) One set of tiles had a uniform white surface, while the other had a heterogenous shell-hash surface
c) All tiles were randomly placed in the ocean for a fixed period of time and the researchers recorded the number of crabs alive at the end
CRABS & PREDATOR AVOIDANCE: Results
a) They found very different survival rates for the crabs on the two different surfaces
b) Only 30% survived on the white surface while 60% survived on the shell-hash coloured titles
c) Conclusion: juvenile crabs are indeed more cryptic when on the heterogenous shell-hash background
CRABS & PREDATOR AVOIDANCE: Continuation
a) They wanted to see whether juvenile crabs would prefer the shell-hash background if given a choice
b) They established experimental aquaria that contained ten small plastic trays
c) Half of each tray was covered in a thin layer of shell-hash and the other was left empty (white)
d) This gave crabs a choice of substrates
e) To manipulate predation risk, experimenters treated half of the trays with predator odour by pumping seawater from a tank that housed several predatory fish and the other half with seawater that contained no predator odours
f) In each aquarium, nine crabs were placed in the centre of each tray and they recorded the proportion of crabs on each substrate after three hours
g) Results: almost all of the small crabs preferred the shell-hash and that even more crabs used the shell-hash in the predator odour treatment, larger crabs showed no preference for either background in the control tanks BUT they strongly preferred the shell-hash in predator odour treatment
h) Conclusion: juvenile crabs can select an appropriate cryptic background when given a choice and that the complex colour of juvenile crabs is an adaptation to minimize detection by predators
Research 9.1: Predators & Reduced Activity in Lizards
a) All animals can reduce detection by predators by reducing overall activity level
b) Predators often use motion detection to find their prey and so are less likely to notice slow-moving prey
WHIPTAIL LIZARDS & REDUCED ACTIVITY: Methods
a) Established pens in the desert, which had tall walls to prevent lizards from entering or leaving
b) They also contained natural desert vegetation
c) Three pens were designated the “predator-present” experimental treatment and contained two large adult leopard lizards
d) The other three pens had no predators
e) Each pen had six adult whiptail lizards
WHIPTAIL LIZARDS & REDUCED ACTIVITY: Results
a) Leopard lizards did hunt the whiptail lizards, presenting a high risk of predation for whiptails
b) During the experiment, the lizards in the different pens exhibited significant differences in behaviour
c) Whiptails in the predator pens were less active, spending less time moving and moved more slowly, making them likely less noticeable to predators
Research 9.1: Startle Display in Butterflies
a) Typified by abrupt changes in behaviour, often involving sudden exposure of conspicuous colours that may be accompanied by a sound
b) Many butterflies rely on cryptic colouration to avoid detection by predators but will suddenly reveal their brightly coloured wings when a predator is nearby
BUTTERFLIES & GREAT TITS: Research Question
Is this behaviour an effective startle display that can discourage the Great Tit from attacking?
BUTTERFLIES & GREAT TITS: Methods
a) Captured wild birds and maintained them indoors in cages
b) Butterfly larvae were reared in the lab
c) At eclosion (emergence of adult from pupal case), half the butterflies were euthanized by freezing, and the others were maintained for one week in the lab
d) Experimental trials offered one live and one dead swallowtail butterfly to a single bird in an experimental room
e) Birds were trained to feed on mealworms attached to two small wooden planks, 1m apart, which were mounted on one wall of the room
BUTTERFLIES & GREAT TITS: Results
a) Of the birds that attacked at least one butterfly, significantly more (22 of 24) attacked the dead butterfly first
b) There were a total of 158 visits to the live butterfly and it responded with a startle display 75% of the time
c) In 80% of the bird visits that elicited a startle display, the Great Tit either quickly flew away or hopped back
d) Only three live butterflies were killed, suggesting an important anti-predator function of the wing-flick startle display
Research 9.2: Vigilance and Predation Risk in Elk
ELK & VIGILANCE: Research Question
What affects vigilance level of prey?
ELK & VIGILANCE: Hypothesis
Animals will trade off feeding time for vigilance based on the level of risk
ELK & VIGILANCE: Methods
a) They recorded elk behaviour and presence of wolves each winter
b) Every two weeks, they used instantaneous scan sampling to record the behaviour of all members of elk herds in different drainages
c) For each herd, they classified whether wolves were present or not
d) To determine wolf presence, they walked fixed transect routes, looking for signs like fresh kills, scat, or tracks
ELK & VIGILANCE: Results
a) Most elk herds were small and only a few contained both cows and bulls
b) Elks spent 61% of their time foraging and almost 16% of their time vigilant
c) The presence of wolves in a drainage had a strong effect on the behaviour of females
d) They spent significantly more time vigilant and less time feeding when wolves were nearby but males were unaffected
e) Two reasons: bulls are 30% larger than cows and reproductive success for males largely depends on maintaining high body mass, so males have more to lose by reducing feeding time, even if the consequence is higher predation risk
Research 9.2: Environmental Conditions and Predation Risk in Foraging Redshanks
a) Redshanks can be found feeding in a variety of habitats, like salt marshes and mudflats
b) Examined a trade-off between predation risk and foraging in a population of birds
c) They studied how weather conditions and predation risk affected daily feeding decisions
d) Main predators are sparrow hawks
REDSHANKS & PREDATION RISK TRADEOFFS: Research Question
Why do redshanks sometimes feed in the riskier salt marsh habitat instead of the safer mudflat habitat?
REDSHANKS & PREDATION RISK TRADEOFFS: Hypothesis
Energetic requirements and predation risk affect feeding behaviour
REDSHANKS & PREDATION RISK TRADEOFFS: Prediction(s)
The salt marsh habitat contains more food than the mudflat habitat and that ambient temperature affects where redshanks will feed
REDSHANKS & PREDATION RISK TRADEOFFS: Results
a) There are roughly twice as man invertebrates in each sample from the salt marsh habitat compared to the mudflat throughout the winter
b) Environmental temperature was strongly correlated with behaviour of the birds: the number of redshanks feeding in the salt marsh habitat increased significantly as temperature declined
c) On colder days, most birds fed predominantly in salt marshes, where there was more food, but at the cost of suffering higher predator attack rates
d) Conclusion: individuals trade off higher predation risk in the salt marsh for higher energy intake rates
Research 9.2: Mating and Refuge Use in Fiddler Crabs
a) They live in intertidal habitats and feed on the surface of the sand during low tide
b) Males possess a single large claw that they wave back and forth in a sexual display to attract females
c) They construct and live in burrows in the sand, which provide a safe refuge from predators
d) To feed or attract mates, crabs need to be active aboveground, but they will quickly retreat to their burrow in response to a predator attack
FIDDLER CRABS & REFUGE USE: Hypothesis
Male crabs would adjust their refuge-use behaviour based on its costs and benefits, predicting that males would emerge from their refuges more quickly after an attack if potential mating opportunities were available aboveground
FIDDLER CRABS & REFUGE USE: Methods
a) Created 30 small plots in a coastal intertidal mudflat
b) Each plot had several males and their burrows
c) In half the plots, she tethered a single, sexually receptive female by gluing a thin piece of string onto its shell
d) Waited for all males in a plot to become active aboveground and then flew an artificial model of a bird predator over the plot and recorded how long males stayed in their burrow after the “attack”
FIDDLER CRABS & REFUGE USE: Results
a) All males in the control plots retreated into their burrows and stayed underground for about 120 seconds
b) In the plots with a receptive female, 12% of males did not retreat into their burrow during attack and the males that did flee reemerged in less than 15 seconds
c) Conclusion: males adaptively adjust their refuge based on its benefits and costs
d) Males trade off the safety of the burrow for increased mating opportunities when receptive females are present
Research 9.2: Perceived Predation Risk affects Reproductive Behaviour in Sparrows
a) Song Sparrows nesting in British Columbia, Canada
b) They nest in shrubs and can lose half their offspring to predators like raccoons, crows, and hawks
SPARROWS’ REPRODUCTIVE SUCCESS & PREDATION: Methods
a) They eliminated direct predation on nests by protecting them with both electric fencing and seine netting
b) They recorded breeding activities of 24 females
c) Females were subjected to one of two treatments
d) For half the females, they played vocalizations of common predators every few minutes for four consecutive days followed by four days of silence, repeated over the breeding season
e) The other control group got nonthreatening vocalizations (seals, loons, hummingbirds)
SPARROWS’ REPRODUCTIVE SUCCESS & PREDATION: Results
a) All females produced two broods over the season but differed significantly in their reproductive activities
b) Individuals exposed to predator vocalizations nested in denser vegetation, laid fewer eggs and had fewer offspring, had a greater proportion of their nestlings die compared to control females
c) Higher perceived predation risk resulted in 40% decrease in offspring produced
Research 9.3: The Dilution Effect and Killifish
a) Dilution Effect: the probability of any one individual’s dying is diluted by the presence of others
b) There is a 1/N probability of dying when a predator makes a single kill in a group of N individuals
c) Banded killifish are small freshwater fish that live in eastern North America, they tend to move in shoals and can use chemical cues to perceive predation risk
KILLIFISH & THE DILUTION EFFECT: Methods
a) To simulate high predation risk, researchers added a diluted concentration of killifish skin extract to the tank
b) They respond to the crushed skin of conspecifics, since it indicate that a predator has made a kill nearby
c) For each trial, ten killifish acclimated to the tank overnight
d) The next day, either skin extract or water (control) was added and a 60-minute trial was recorded
e) Recorded shoal size every 30 seconds, individuals were considered to be in the same shoal if they were within four body lengths of one another
KILLIFISH & THE DILUTION EFFECT: Results
a) Median shoal size in the control was just two fish while median shoal size in the high-predation risk treatment was TEN FISH
b) Conclusion: banded killifish prefer to associate with more individuals when predation risk is high, as predicted by the Dilution Effect
Research 9.3: Group Size Effect and the Selfish Herd Hypothesis in Doves
a) Selfish Herd Hypothesis assumes that a predator is more likely to kill a member on the outside of a group because it will encounter outside individuals first
b) In contrast to the dilution effect, this hypothesis requires individuals to continually adjust their position in a group
c) Group Size Effect: the vigilance behaviour of each individual decreases as the number of individuals in its group increases
DOVES & GROUP SIZE EFFECT AND SELFISH HERD HYPOTHESIS: Research Question
Does the group size effect and selfish herd hypothesis apply to these doves?
DOVES & GROUP SIZE EFFECT AND SELFISH HERD HYPOTHESIS: Methods
a) When he found a flock of feeding birds, he recorded the group size and then selected one focal animal
b) He recorded the location of the focal bird in the flock (central or edge), its scan rate, scan durations, and the total amount of time spent feeding. He also noted any position shifts
c) Observed 150 flocks that varied in size from one to 19 individuals
DOVES & GROUP SIZE EFFECT AND SELFISH HERD HYPOTHESIS: Results
a) Individual vigilance behaviour decreased significantly as group size increased, indicating that these doves did indeed exhibit the group size effect
b) The feeding time of individuals increased as group size increased as well
c) Individuals in the centre of a flock behaved differently than the edge individuals: birds in the centre exhibited lower scan rates and higher feeding rates than edge individuals
d) When position shifts did occur, individuals more often moved toward the centre
e) Conclusion: doves exhibit a trade-off between scanning for predators and feeding
GROUND SQUIRRELS & RATTLESNAKE HARASSMENT: Research Question
How do California ground squirrels harass rattlesnakes?
GROUND SQUIRRELS & RATTLESNAKE HARASSMENT: Hypothesis
Ground squirrels use an infrared signal during rattlesnake harassment by increasing blood flow to their extremities
GROUND SQUIRRELS & RATTLESNAKE HARASSMENT: Methods
a) Conducted four types of randomly ordered trials using 12 adult female squirrels: (1) a baseline trial with no stimuli, (2) a control trial with a conspecific (squirrel) stimulus, (3) an experimental trial with a rattlesnake stimulus, and (4) an experimental trial with a gopher snake stimulus
b) Placed a squirrel’s home cage next to the opening of the test chamber
c) Trials began after the squirrel engaged the stimulus animal
d) Baseline and control trials were compared to experimental trials, ten-minute trials were spaced two days apart
e) Used infrared video to collect data on squirrel body and tail temperature
GROUND SQUIRRELS & RATTLESNAKE HARASSMENT: Results
The temperature of a ground squirrel’s tail was, on average, 2 degrees higher when the squirrel harassed a rattlesnake than when it harassed a gopher snake
GROUND SQUIRRELS & RATTLESNAKE HARASSMENT: Conclusion
Squirrels include an infrared component in their harassment of rattlesnakes, presumably by increasing blood flow to the tail, resulting in a slowing of the snake attack
Research 9.4: Tail-flagging Behaviour in Deer
a) When deer spot a predator, they lift and wag their tail, revealing the white underside as they move a short distance away
b) Pursuit-Deterrence Hypothesis: advertisement behaviour informs the predator that it has been detected and so pursuit is not likely to be successful
c) Alarm Signal Hypothesis: individuals are warning nearby conspecific of predators
d) Humans are used as potential predators
DEER & TAIL-FLAGGING BEHAVIOUR: Methods
a) They recorded deer behaviour over the course of a month in late fall
b) They acted as predators by slowly walking through the reserve
c) Once they spotted deer, they recorded the number of deer nearby and whether any were aware of their presence
d) They would select a focal animal, take note of its location, and moved slowly towards it as if stalking a prey
e) The observer would record the number of times the deer exhibited tail-flagging behaviour and the distance between the observer and deer
f) Once the deer fled, the observer would record its flight distance, flight time, and any tail-flagging
DEER & TAIL-FLAGGING BEHAVIOUR: Result
a) There was no difference in incidence of tail-flagging behaviour in solitary deer and deer in social groups, both tail-flagged 85% of the time, meaning they rejected the alarm signal hypothesis
b) Results supported the Pursuit-deterrence hypothesis
c) Found a new hypothesis, tail flagging functions to confuse a predator by providing a target that disappears when a deer drops its tail after running into dense vegetation
