Exam 4 Flashcards
Cryptic coloration
Reduces the ability of a predator to find it
Countershading, disruptive colors, background matching
Countershading
often aquatic, dorsal (backside) is darker, ventral side is brighter to match brightness of ocean floor and surface
Ponyfish Countershading Example
Bioluminescent organ that illuminates the bottom side of the fish’s body
Disruptive Coloration
High contrast makes it difficult to tell foreground from background or to distinguish an animal
Example: cannot tell zebras apart when they are in a pack
Background matching
pattern blends in with the environment, some can change color to camouflage. Squid can do this despite being unable to see color
Predator Avoidance in Crabs Example
Crabs on shell-hash have higher survival
Placed crabs with two types of tile, one with shell-hash and one white
Small crabs preferred the shell-hash more than the large crabs
Large crabs preferred the shell-hash when predation risk was high
Caterpillar Defensive Example
Squeezed by wasp predators
Measured parasitism
Drop and bite measures were most effective
Startle display
sudden movement that exposes conspicuous colors or a sound to reduce attack rate by predators
Great Tit & Butterfly Example
The butterfly’s movement is retrained
Resting position is usually closed
The dead butterfly is positioned with wings open
Live butterfly exhibited startle display 75% of the time
The bird attacks the dead butterfly more quickly (latency was longer for live butterfly)
Wolves and Elk Example
In Yellowstone, wolves were reintroduced to the park
Elk behavior changes with the presence of wolves
Female elk spent more time vigilant and less time feeding when the wolves were nearby
Male behavior didn’t differ
Food patch risk
Rich food patches are riskier, more prey aggregated for predators to attack
Redshank Bird Food Patch Example
Salt marsh is twice as abundant with food as the mudflat
Proportion of birds on the salt marsh is higher when the temperature is lower—birds are warm-blooded, and therefore have to eat more in order to maintain their body temperature
Fiddler Crab Food Patch Example
Hides in a burrow, but must leave in order to mate
Control: no female present
The recorded how long the males stayed in their burrow in response to (fake) bird attack
When female was present, they reemerged much more quickly
Song Sparrow Example
Do changes in perceived predation risk affect song sparrow life history?
Researchers protected the bird nests from predation
Then they played vocalizations of common predators, four days at a time
Predation treatment females laid fewer eggs, had less offspring, and nested in denser vegetation
She decides to save energy for the next breeding season in response to the predation risk
Relationship between perceived predation and reproduction
Group living: main purpose
reduce predation
Dilution effect
when swimming with many other fish, the chance of being caught is much lower than if the fish is swimming solo in open water
Confusion effect
it is easier for the predator to follow and catch one fish instead of multiple fish
Selfish herd theory
the predators are more likely to kill the members on the outside of the social group, so individuals can reduce predation risk by moving to the center of the group
Hamilton proposed this theory as an alternative explanation to the popular hypothesis—that evolution of animal aggregation is based on mutual benefits in the population
- Grouping is a result of selfish motivation, not for mutual benefits
- The group mutual benefits are merely a consequence
Group size effect
vigilance behavior of individuals declines as group size increases
Predator harassment
rapid movement around a predator, often coupled with loud vocalizations
Squirrels Harassing Snakes Example
the squirrel moves around and flaps its tail, the tail temperature of the squirrel is higher when harassing a rattlesnake to make the tail visible (rattlesnakes have pit organs), its tail doesn’t heat up when harassing gopher snakes (which can’t see infrared)
Chemical deterrence
release of a noxious repellant
Ex: Skunks
Bombardier Beetle Example
Creates a noxious hot chemical
Sprays it onto parasites / predators
Sprays quickly enough that it does not burn the beetle, creates steam
Escape Behavior
Some animals show themselves to predators by stotting or tail flagging
Stotting: jumping movements, makes itself more visible
Pursuit-deterrence hypothesis
advertisement behavior informs a predator that it has lost the element of surprise, so pursuit will not be successful
Alarm signal hypothesis
advertisement behavior is a warning signal to other members of the group
Cheetah and Gazelle Example
The cheetah can run faster than the gazelle
However, the gazelle can run for longer
Therefore, the cheetah stalks the gazelles until they gets close enough to catch them
The gazelle stotts to make itself more visible before attack attempt
Tail Flagging Deer Example
Researcher stalked a deer and measured the tail flagging based on researcher’s distance from the deer
No difference between solitary and social deer, so it doesn’t support the alarm signal hypothesis
As the distance shortens, there is less tail flagging
