PREDATOR-PREY
I. Introduction
A. Evolution of predator-prey interactions
1. Selection favors the development of traits that enable prey to evade predators
2. Selection also favors the development of traits in predators that better enable them to find prey
3. Thus, this leads to an evolutionary arms race
B. Relationship to communication
1. Scientists tend to view interactions between predator and prey as some form of communication
2. Such interactions can actually be cooperative (think of stotting in the gazelle); but the majority are deceptive in nature.
3. We will start with adaptations in prey that better enable them to evade predators
II. PREY ADAPTATIONS
A. Cryptic Coloration
1. Description: prey escapes detection by appearing to be "invisible" to the predator. this is a form of deception
2. Four approaches to achieving invisibility (be sure to list an example)
a. _______________________________
b. color changing (matching)
c. ________________________________
d. disguise (resembling something else)
3. Proving Crypsis requires:
a. demonstrating that prey are in fact cryptic to a predator (not just humans)b. _________________________________________
c. very few examples of crypsis have been subject to these tests
4. Example: Blending in with the Background (most of the research in this area has focused on the phenomenon of blending in with the background)
a. requires at least two activities:1. finding a suitable background in which to blend in
2.__________________________
b. Experimental studies with bluejays as predators and cryptically colored moths as prey
1. creation of foraging situations using operant conditioning2. jays were shown slides of tree trunks that sometimes contained a moth.
3. Two cryptically colored moth species were used:
a. Catacola retecta, normally rests on oak in a sideways positionb. Catacola relicta, normally rests on birch in a head up position
4. The slides were constructed by taking photographs of the two species of moths under the following conditions
a. on the correct bark background in the correct orientation (cryptic)
b. on the correct bark background in the wrong orientation
c. on an incorrect bark background in the correct orientation
d. on the incorrect bark background in the wrong orientation
3. During the task, the bluejays would look at the slide and then had two options:
4. They could peck the slide 10 times (attack)
a. if correct, ___________________
b. if incorrect, __________________
5. They could hit a change key (producing the next slide)
a. if correct, ___________________
b. if incorrect,__________________
6. What happened when orientation and bark bakground were varied?
a. For retecta
b. For relicta
B. Warning Coloration
1. Description: the opposite of crypticity; the prey is brightly colored and highly visible to a predator. Bright coloration is a cue to advertise toxicity. Thus it is a form of cooperative communication between predator and prey.
2. The requirement of exposure
a. In order for this system to work, the predator must actually encounter a prey and learn about its toxicity by attempting to ingest the prey.
b. Monarch butterflies are brightly colored and are toxic to bluejay predators; after one exposure, blue jays subsequently avoid all monarch butterflies (taste aversion learning).
3. Characteristics As you might expect, warning coloration includes colors, postures, and behaviors that are exaggerated for the predator's benefit and hence easy to learn (See video clip of skunk characteristics). Most warningly colored species share some of the basic characteristics listed below.
a._________________________
b._________________________
c._________________________
d._________________________
4. Dilemma: How did warning coloration evolve as a defense against predation?
a. Being conspicuously colored should actually increase the ability of a naive predator to find the prey.
b. By the time, the predator discovers the unpalatability, the prey is already wounded or dead
c. How can we explain this in terms of natural selection if predators actually kill the prey in order to learn? Think back to the monarch butterfly
1. the monarch may live (monarch wings are extremely toxic and brief exposure with the inside of the mouth may cause bluejays to spit the monarch out without killing it).
2. the death of one monarch may benefit close relatives who are nearby
3. the death of one monarch may benefit other monarchs close by involving some kind of reciprocal altruism
b. Ideas 2 and 3 suggest that aggregation may be the answer and indeed members of a warningly colored species do seem to stick together
5. Alatalo's studies of predation by tits in a "novel world" environment
a.tits were given experience with obtaining food items wrapped in paperb. During simulations of predation, there were two types of food items:
1. unpalatable items that were warningly colored (wrapped in white with a big black square)2. palatable items that were cryptic (wrapped with an X). The latter was cryptic because both types of food items were placed on a white background consisting of Xs.
c. Unpalatable prey were presented either singly or in aggregrated groups
d. findings
1. _______________prey survived better than___________________prey
2. birds ate more _________________________prey
3. learning was best when prey were ___________________
C. Batesian Mimicry
1. definition - an organism (mimic) comes to resemble another species (model) in order to alter the response of a third species (usually a predator). This is a form of deception
2. examples
3. characteristics
a. mimic and model must be found _________________________
b. there must be _______________mimics than models (why does that have to be the case?)
c. mimic must be _______________________________than the model
d. mimic must differ from closely related species
e. imitation should be external only
VERY FEW OF THESE CHARACTERISTICS HAVE BEEN EXAMINED EXPERIMENTALLY
4. Pfennig's Study of the coral/king snake complex
a. Coral snakes are venomous, but king snakes are not.b. There are areas of the U.S. where both species occur together and other areas where the king snake is found alone.
c. Pfennig tested the prediction that:
d. He placed 3 plasticine models of snakes in the area (what were the 3 models?)
e. What did he find?
5. Mimicry of a Predator (tephritid flies and jumping spiders -see video) This example is an unusual form of mimicry in that there is no model. The prey species (tephritid flies) mimic the predator itself in order to fool the predator (jumping spider). There are two parts of the response:
a. the fly's wings have a striped coloration that partially looks like spider legs
b.______________________________________
Both elements appear to be important. How do we know that (see also text question)?
D. Diversions and Startle Responses
1. startle reactions with eyespots and underwing stripes (see video)
2. behavioral reactions (what are the two examples)
E. Group Defense
1. Mobbing Behavior (caciques)
2. Increased Vigilance
a. group size can promote vigilance in woodpigeonsb. what does the graph show on median reaction time?
c. what does the graph show on percentage of attack success?
3. Dilution Effect refers to ___________________________
4. Selfish Herd refers to _______________________________